Microgravity-activated high-performance van der Waals InSe ferroelectric semiconductor

Domain: physics
Published: 2026-03-12
Editorial outcome: major_revision

Abstract
The space microgravity environment, scarcely attainable on Earth, is considered to have
a positive effect on crystal growth, especially the van der Waals layered materials with
low interlayer sliding energy barriers. Here, we investigate the structure and
optical/electrical properties of van der Waals InSe semiconductor cultivated in
microgravity environment on China space station. Atomic-level microstructure analyses
reveal that this unique environment can successfully annihilate the naturally-existing
stacking faults in flexible InSe, directly activating the intrinsic sliding ferroelectricity with
excellent retention stability. The corresponding ferroelectric semiconductor field-effect
transistors present obviously large non-volatile memory window, high on/off ratio and
excellent mobility. More essentially, they can also give superior amplified spontaneous
emission with exceptionally low excitation thresholds of photons for near infrared
nonlinear light sources. These findings not only present an unconventional strategy for
achieving high-quality van der Waals layered single crystals like InSe but also highlight
their potential for next-generation emitter-integrated computing architectures combining
memory and sensor functions.

Introduction
Advancements in space technology have brought new opportunities for the development
of material science. The material growth experiments conducted in outer space since the
late 1970s heralded the birth of a new discipline—microgravity material science1-4. The
microgravity environment in space provides new degrees of freedom for material growth
and processing, while also significantly enhances our understanding of fundamental
issues related to material’s structure and property optimization5. The objectives of
microgravity material science mainly encompass three aspects6: i) preparing high-
performance materials that are unobtainable on the earth by suppressing gravitational
effects; ii) understanding physical phenomena obscured by terrestrial gravitational effects;
and iii) improving terrestrial crystal growth processes. From the improvement in one or
more indicators, the benefits of crystal growth in microgravity are confirmed with over 80%
of experiments, specifically the dislocation density in materials which has been drastically
reduced in InSb, Ge, GaAs, and CdZnTe crystals7-10 (see Supplementary Table 1).

Indium selenide (InSe), as a typical van der Waals (vdW) layered semiconductor
possessing advantages such as non-toxicity, suitable bandgap and high mobility, and in
particular sliding ferroelectricity, has attracted considerable attention11-15. As a flexible
material, InSe exhibits excellent optical properties that are effectively tunable by both
applied stress and material thickness16-19. Through optical studies, its hydrogenation and
oxidation properties have also been widely investigated20,21. When combined with other
vdW semiconductors such as GaSe, graphene or transition metal dichalcogenides, it can
generate unique interlayer excitons or form efficient type-II heterostructures22-27. Very
recently, it shows a promising potential for surpassing silicon electronics since the ~5-
centimeter wafer-level InSe single crystalline films have been successfully achieved28.
However, numerous dislocation defects29 or stacking faults naturally exist in routinely-
grown InSe crystal due to the extremely low sliding energy barrier12,30,31, limiting its
application in optoelectronic, thermoelectric and novel sliding ferroelectric nanodevices32-
35. Therefore, it is imperative to address the critical challenge of synthesizing high-quality
vdW-layered InSe single crystals. To overcome this issue, several approaches have been
successfully implemented, e.g., the post-annealing treatment31,36 or intentional doping
with the yttrium element32,33. Although they can annihilate the interlayer stacking faults
and simultaneously optimize the optical/electrical properties in γ-InSe, new questions are
unavoidably introduced31-33 including the undesirable extrinsic dopants or impurity levels
that should influence the carrier mobility, and the tuned microstructure and bandedge
electronic structure by the complicated post-annealing procedure that may reduce the
lifetime of interlayer exciton and quenching its emission.

Here, we prepare the vdW-layered γ-InSe single crystal under microgravity condition
(marked as s-InSe) on China space station. A series of physical property characterizations
demonstrates that this special strategy remarkably enhances the quality of InSe single
crystals and fully activates its intrinsic performance in electrical/optical nanodevices. The
atomic-level imaging analysis from the state-of-the-art spherical aberration-corrected
transmission electron microscopy (Cs-TEM) reveals that the microgravity condition can
effectively annihilate interlayer dislocations or stacking faults that can be frequently
observed in vdW-layered materials. It advantages the direct observation of sliding
ferroelectric hysteresis loops and the domain writing and erasing with stable retention by
piezoresponse force microscopy (PFM). The obviously large memory window and
enhanced on/off ratio in InSe-based ferroelectric semiconductor field effect transistors
(FeSFETs) as well as the superior superlinear photoluminescence with approximately one
order of magnitude lower thresholds compared to that grown on the earth (marked as e-
InSe) indicate promising applications of s-InSe in photon-integrated in-memory and in-
sensor computing chips.

Results
Crystal growth and characterization

Fig. 1a schematically demonstrates the growth process of s-InSe and e-InSe. The ingot
growth employs the Bridgman method with a furnace temperature controlled at 715°C
and a crystal growth temperature gradient of approximately 30°C/cm (see Experimental
section). For comparison, both crystals are grown under identical parameters except for
the microgravity condition. Fig. 1b shows a macroscopic comparison between the as-
grown e-InSe and s-InSe crystal ingots. X-ray diffraction (XRD) characterizations are
performed on the upper and lower parts of the samples (Supplementary Fig. 1). The upper
part of them is the polycrystalline/mixed phase region, and the lower part is a dense single
crystal region, also consistent with the design prediction of growth conditions
(Supplementary Note 1). Notice that the polycrystalline/mixed phase region in s-InSe
features large and aggregated bubbles, sharply contrast to the multiple small bubbles in
e-InSe, because the air expelled after the solidification of the bottom region was collected
by the central rapid-cooling zone. Under microgravity conditions, this air spontaneously
coalesced into large bubbles due to liquid surface tension (Supplementary Fig. 2 and
Supplementary Note 2). Flakes cleaved from both crystal ingots present single crystalline
two-dimensional (2D) layered feature (Fig. 1c,d). XRD patterns of both crystals exhibit
similar {00l} diffraction peaks37, as shown in Fig. 1e, indicating that the single crystalline
structure of s-InSe remains unchanged in the microgravity environment. Raman results
(Fig. 1f) suggest that both InSe point to the R3m (C5 ) space group38. Notice that the
3V
A (LO) mode can be observed in both e-InSe and s-InSe, but becomes less pronounced
1g
with the flake thickness increase (Supplementary Figs. 3 and 4). Scanning electron
microscopy (SEM) images (Fig. 1g) demonstrate that the two crystals exhibit clear vdW-
layered morphology with cleavage angles of 60°/120°, consistent with their hexagonal
lattices and previous reports33. Notably, the layer structure of s-InSe appears straighter
and more uniform, which may be related to the suppression of stacking faults and the
improvements of crystal quality under microgravity. Room temperature optical
transmission spectra (Fig. 1h) show that both InSe crystal flakes (with thickness ranging
from 8 μm to 124 μm) have direct optical bandgaps with a close value of ~1.21 eV. It is
interesting to mention that they both exhibit similar thickness-dependent bandgaps even
in the micrometer scale, far beyond the routinely-accepted atomic-level thickness for 2D
vdW-layered materials. These results represent that both crystals retain various
macroscopic properties and structures of InSe with single crystal quality, except for the
potential reduction of interlayer defects or stacking faults due to the microgravity growth
condition.

Atomic-level characterization of stacking faults

The interlayer sliding barrier has been theoretically predicted to be extremely low in vdW-
layered InSe30, which can result in abundant naturally-formed stacking faults in as-
prepared crystals grown by the Bridgman method or other techniques (e.g., chemical
transport deposition) due to the factors such as the gravity, the contact stress from the
ampoule bottles and the substrate-induced non-uniformity2, as also partially
demonstrated in our previous work33. This will strongly influence the uniformity of
optical/electrical properties32,39, and may compromise the intrinsic performance of InSe
crystals. As known, the γ-InSe with a rhombohedral structure belongs to the non-
centrosymmetric space group R3m with ABCABC-stacking (Fig. 2a). It features three
armchair and three zigzag directions, and has the lattice parameters of a=b=4.00 Å and
c=25.32 Å. However, as frequently observed31, the earth-grown InSe crystals hold
amounts of stacking faults with different stacking sequences, e.g., the ABAC- ABCB-, and
ACAC-types, as schematically shown in Fig. 2b-d separately. To explore the influence of
the microgravity condition on stacking faults modulation, we perform comprehensive high
angle annular dark field- scanning transmission electron microscopy (HAADF-STEM)
analyses to investigate the atomic configurations of both crystals. For e-InSe, the high-
resolution TEM (HRTEM) image (Fig. 2e, with the selected area electron diffraction/SAED
pattern as the inset) together with the HAADF image (Fig. 2f) can be indexed as γ-InSe
projected along [100] zone axis with layered structures but with various stacking faults
(as similarly shown in the ref.31). The staggered arrangement between layers and straight
line-type SAED patterns can be clearly observed. While for s-InSe (Fig. 2g), the stacking
faults are obviously reduced by referring to the clear SAED diffraction spots and the
uniform HRTEM contrast32,40. The HAADF image in Fig. 2h shows the atomic
arrangement of the microgravity-grown InSe, which manifests that the s-InSe crystal
presents the better stacking-style with ABCABC sequences. More characterizations are
presented in Supplementary Figs. 5 and 6. It can be then inferred that without the effect
of gravity in a single direction, the atomic arrangement becomes more regular and the
dislocations decrease remarkably, which may significantly improve the intrinsic physical
properties of InSe crystals.

Direct observation of intrinsic sliding ferroelectricity

As reported experimentally and theoretically31,41,42, the non-centrosymmetric bulk γ-InSe
with ABCABC-stacking type may intrinsically exhibit out-of-plane (OOP) sliding
ferroelectricity, yet its observation is often obscured by the high density of stacking faults
with low sliding energy barriers. As depicted above, the microgravity condition can
effectively reduce the defects and improve the quality of InSe crystal, which may play
positive effects on the sliding ferroelectricity detection. We then perform PFM
measurements to characterize the electromechanical response of s-InSe flakes. During
PFM measurements, we have calibrated the vertical spring constant (k) and the inverse
optical lever sensitivity (InvOLS) of the probe to reduce the electrostatic contribution in
PFM measurements43. Specially, as representatively shown in Fig. 3a, stable PFM
hysteresis loops are obtained at individual points of a ~6.2 nm (~7 layers) flake with the
direct voltage (V ) sweeping from −9 V to +9 V and an alternating voltage (V ) of 0.8 V
dc ac
with a resonant frequency of ~0.5 Hz at the needle tip. The vertical electric field applied
between the probe (as the top electrode) and the bottom electrode under the sample
causes the ferroelectric-like amplitude response to show a butterfly-shape loop with an
opening of ~12 V (Fig. 3b), and the phase switches 180° at the same turning point (Fig.
3c). After cycling the tests, the amplitude hysteresis loops remain butterfly-shaped and
the phase transition remains at 180°. To exclude the possible artifacts in PFM
measurements31,33,44 and evidence the intrinsic ferroelectricity of s-InSe, we reduce the
applied DC biases gradually and repeat the tests correspondingly (Fig. 3d). As expected,
when the DC biases are lower than the coercive field, the phase hysteresis loops
completely disappear, verifying the ferroelectric feature of s-InSe. Additionally, the
polarization switching by domain writing technique can successfully manipulate the
reverse polarity domains on s-InSe flake using opposite voltages applied on the tip (as
the polarization electrode) (Fig. 3d). We also perform additional V -dependent PFM
dc
measurements on a 25 nm-thick s-InSe flake (Supplementary Fig. 7), and repeat the PFM
measurements on s-InSe flakes with different thicknesses (Supplementary Fig. 8). Notice
that the piezo magnitude by the effective d seemingly presents an increase to saturation
33
with the increase of layer number (from about 3 to 10 unit cells) in s-InSe (Supplementary
Fig. 9). These results on the one hand confirm the intrinsic sliding ferroelectricity in vdW
γ-InSe, and on the other hand indicate the avoidance of harsh prerequisites, such as
intentional-doping or post-annealing procedures31-33, for its observation.

Enhanced electric properties of s-InSe based FeSFETs

We further investigate the electrical properties of s-InSe-based FeSFETs for potential
applications in low-consumptive high-speed in-memory computing. Fig. 4a schematically
shows the structure of the devices using the highly-doped silicon as the back-gate
followed by a 50 nm SiO plus 22 nm h-BN, above which is the 15 nm s-InSe flake as the
2
channel material; see the practical optical image (Fig. 4b). Notice that the additional h-
BN as the vdW insulator without dangling bonds can effectively eliminate the possible
hysteresis windows caused by charge trapping in SiO 45. For better understanding, the
2
band diagrams of the metal-oxide-InSe heterostructure in polarization (P) down and up
states are schematically presented in Fig. 4c, where both mobile charges and polarization
bound charges appear in the channel because of the semiconducting and ferroelectric
properties of s-InSe semiconductor. When a negative gate voltage is applied, the
polarization is aligned toward the h-BN/InSe interface, and the energy band is bend down
due to the polarization bound charges. As a result, the charge carriers (electrons)
accumulate and the channel is in the low resistance state (LRS). When a positive gate
voltage is applied, the polarization is aligned against the h-BN/InSe interface, and the
polarization bound charges bend up the energy band. Thus, the electrons deplete and
the channel is in high resistance state (HRS).

We then validate the transfer characteristics of the device on a vacuumed probe station
combining with a 4200-semiconductor parameter analyzer at room temperature. The
output curves indicate a good Ohmic contact between the metal electrodes (5 nm Cr/35
nm Au) and the channel material (Fig. 4d). Fig. 4e shows the back-gate transfer curves
of a typical s-InSe FeSFET. The difference between V -write and V -erase represents
th th
the memory window of the device, corresponding to the two opposite OOP ferroelectric
polarization states (HRS and LRS) in s-InSe channel (Fig. 4c), which increases as the
gate scanning voltages increase. At a maximum gate voltage of 20 V, the maximum
memory window of the s-InSe FeSFET is ~11.4 V. The clockwise hysteresis memory
windows demonstrate that the s-InSe FeSFET exhibits n-type semiconductor
characteristics (on/off ratio of 10-6)41. Fig. 4f presents the carrier mobility (μ ) of the device,
0
which gives a max value of ~195.3 cm2v-1s-1, significantly higher than limited reports of
as-grown e-InSe FeSFETs46, as well as that of e-InSe devices fabricated using the same
procedure (Supplementary Fig. 10 and Supplementary Table 2).

High-efficient superlinear emission of s-InSe with lower thresholds

Next, we compare the room temperature emission property of e-InSe and s-InSe samples
(Fig. 5a-d). As shown by photoluminescence (PL) spectra obtained at different positions
of single e-InSe flake (Fig. 5a), multiple emission peaks or bands can be observed with
evident position-dependence. For simplicity, we roughly divide the emission into three
bands marked by A, B and C. By referring to the theoretical and experimental reports31,
the A-band peaking at ~1.23 eV can be attributed to the intralayer bandedge exciton
emission (also referring to the intrinsic absorption spectra in Fig. 1h), and the B-band
peaking at ~1.17 eV is related to the interlayer bandedge exciton emission in InSe47. The
weak C-band, which approximately involves two separate peaks at ~0.96 eV and ~0.81
eV, is rather broad that should be (deep) defects related emissions including the
contribution from interlayer dislocations. It can be seen that the defect-related peaks are
much distinct for different positions of e-InSe, implying that there are randomly distributed
defects (Fig. 2e,f) in e-InSe. In sharp contrast, the s-InSe presents a rather simple PL
spectral shape (Fig. 5b), notably the position-independent uniformity and the narrowly-
distributed B-band relevant to the interlayer exciton emission. This may correspond to the
optimization of the interlayer stacking sequences, as evidenced in Fig. 2g,h. Fig. 5c,d
demonstrates the excitation power (density) dependent PL spectra of e-InSe and s-InSe
(in semi-logarithm scale). It is clear that the defect-related C-band in e-InSe increases
remarkably, even approaching to the level of the main A-band, with excitation power
increase. However, for s-InSe, this band is extremely weak with an ignorable increase
when the A-/B-bands increase evidently with the increase of excitation power. More
importantly, the main PL peak intensity in s-InSe is stronger by over one order of
magnitude than that in e-InSe within the similar excitation power range. These physically
reflect that the crystal quality of InSe grown under microgravity has been highly improved,
subsequently resulting in a remarkable enhancement of emission in s-InSe.

To further disclose the advantages of the microgravity, we plot the excitation power
dependent integral intensity of the emission bands (Fig. 5e,f). The integral intensity of the
defect-related C-band in e-InSe (Fig. 5e) is almost by orders of magnitude higher than
that of A-band (coupling with B-band) at low excitation powers, and then both show a
slightly superlinear increase after the threshold of ~0.8 W/cm2. We should point out that
the defect-related C-band is always stronger by one order of magnitude than the intralayer
exciton-related A-band (also the interlayer exciton-related B-band). However, the A-band
(also B-band) in s-InSe (Fig. 5f) behaves a perfect superlinear evolution with a tripled
slope (S≈3 in double-logarithmic scale) during the entire excitation power range, while the
C-band almost shows an independence of excitation power and has a lower intensity than
A-band at the high excitation power side. To exclude the influence of high excitation power,
we record excitation power-dependent PL spectra of s-InSe flakes (Supplementary Fig.
11). It can be observed that some of them exhibit a decrease in slope (or from sub-linearity
to saturation in intensity) at the high power side. However, the slope of the curve in Fig.
5f remains unchanged in the entire excitation power range, indicating that the extrinsic
factors such as the excitation power induced thermal effect can be ignorable. Fig. 5g
shows the excitation-dependent intensity ratio between A- and C-bands in both samples,
which can unveil the competition of carrier recombination between them. At the extremely
low excitation level of ~0.2 W/cm2, the main emission peak A predominates in s-InSe,
while for e-InSe the critical point is ~2 W/cm2, suggesting the much higher emission
efficient of the main peak A in s-InSe. Simultaneously, this subfigure also demonstrates
that with excitation power increase, the main A-band of s-InSe can be enhanced by one
order of magnitude than that of e-InSe, which is due to the annihilation of defects and is
much better than reports48. More essentially, the threshold for the superlinear emission in
s-InSe is reduced by almost one order of magnitude (from ~0.8 W/cm2 to <0.1 W/cm2).
This indicates that as compared to the e-InSe, the s-InSe has a higher emission efficiency
with a lower threshold that are beneficial for amplified spontaneous emission or even
lasing. Li et al.16 also displayed room-temperature in-plane lasing of vdW InSe microflake
via mechanical exfoliation. Notice that recently similar optical results have been obtained
in post-annealed InSe as-grown under gravity31, where the reason was ascribed to the
annealing-resulted elimination of stacking faults and crystal quality improvement
(Supplementary Fig. 12 and Supplementary Note 3). In view of the above results, both
post-annealing and microgravity strategies can reach the goal for improving the physical
properties of the single crystalline InSe, however, the current one is more superior by
considering the more excellent thresholds and slopes of intralayer exciton emission
accompanied with uniform interlayer exciton emission (i.e., the B-band in Fig. 5).
Furthermore, time-resolved PL (TR-PL) results in another way support this argument by
referring to the slightly shorter lifetime of carriers for spontaneous emission in e-InSe
(Supplementary Fig. 13), because the existence of more defects such as the interlayer
stacking-faults in it can trap the carriers for defect emission or non-radiation
recombination.

Methods
Sample Preparation: Raw materials of In and Se elements (6N purity) with a mole ratio of
0.52 : 0.48 were weighted as start materials. After melting and soaking for 3 hours, the
growth of InSe crystal was started by ascending the furnace at a rate of 1.0 mm/hour and
with a temperature gradient of ~30°C/cm on the China space station and on the earth,
respectively. The specific growth process is shown in Supplementary Fig. 14. For optical
(e.g., Raman, optical transmission, PL), PFM and electrical characterizations, InSe flakes
with different thicknesses were prepared from bulk InSe single crystal via mechanical
exfoliation.

Structural Characterizations: XRD patterns of the InSe crystals were acquired on a Bruker
D8 Advance X-ray diffractometer (with a Cu target tube at 40 kV and 40 mA) with a
scanning step of 0.02o per second. SEM analyses were performed on a Zeiss Gemini 450
microscope equipped with a windowless EDS detector (Ultim Extreme, Oxford, UK).
Cross-section TEM specimens were prepared on a dual-beam focus ion beam (FIB)
system (Helios G4 UAX, FEI, USA) using Ga-ion accelerating voltages. Atomic-resolution
imaging measurements were performed on a Cs-TEM (JEOL Grand ARM300, Japan).

PFM Measurement. PFM measurements at the dual amplitude resonance tracking (DART)
mode were performed on a commercial scanning probe microscopy (SPM) system
(Asylum Research Cypher, Oxford, UK) with conductive Pt-coated silicon cantilevers. The
LithoPFM mode of the Asylum Research software was used for permanent domain writing
with the PFM tip carrying reverse DC biases (V = ±8 V).
dc

Device Preparation and Electrical Characterizations: Mechanically exfoliated 2D h-BN
and InSe flakes were transferred onto the heavily-doped Si wafer covered by 50 nm SiO
2
substrate by a PDMS stamping method. The source and drain electrode regions were
defined by photolithography and then formed by depositing Cr/Au (5 nm/35 nm) via
thermal evaporation. Electrical characterizations of FeSFETs were performed on a
Keithley 4200A-SCS semiconductor parameter analyzer matched with a vacuumed probe
station.

Optical Characterizations: Raman spectra were recorded from a μ-Raman system with a
backscattering configuration (Renishaw inVia Reflex, UK) using a 532 nm excitation
source. To avoid possible damage to the samples, the laser power was set below 1 mW
(diameter ~5 µm; fast scan in 10 seconds per curve). A Fourier transform infrared
spectrometer (Vertex 80v, Bruker) covering a wavelength range of ~0.4−15 µm was
employed for optical transmission and PL measurements. For PL measurements, the
excitation wavelengths including 405 nm and 532 nm were employed with reflectance
geometric configuration. The laser power density is set below 3 W/cm2 without excitation-
induced thermal effect on samples (Supplementary Fig. 11).

Data Availability
The data supporting the finding of this work are included within the paper. Extra data are
available from the corresponding authors upon reasonable request.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Jin, Sui et al. report on the growth of InSe single crystals on the China space station, and thus under different microgravity conditions to those present on Earth. The properties of the InSe crystals are compared to those of InSe grown on Earth (e-InSe), and higher quality is overall demonstrated for the space-InSe (s-InSe).\nThe growth of van der Waals crystals under different microgravity conditions is indeed little explored due to the technical difficulties that are implied. From this point of view, the growth on a space station reported in this work is noteworthy.\nThe work presented here, however, holds moderate significance to the field of 2D materials, as such a growth is difficult to be done and the proposed approach can hardly become a standard growth approach.\nAs for the quality comparison between e- and s-InSe, the results of Figs. 2, 3 and 5 would require a larger statistical analysis, and thus repeating the same measurements on different pieces/flakes of the crystals to ensure the general validity of the results.\nThe PL results are rather strange and controversial. Upon increase of the laser power, defect states typically saturate and free exciton states tend to dominate. In turn, defect states typically feature a sublinear behavior with power. Here, the authors are showing an opposite behavior, which is in contrast with what typically observed for van der Waals crystals. Furthermore, the laser powers used in this work seem to be huge. The authors are claiming that they are keeping the power below 1 mW with a spot size of 5 microns to avoid damages, but are the author sure that this power does not damage InSe? I am wondering if the strange power dependence observed in this work is actually due to the fact that the crystal is being destroyed while measuring it.\nThe experimental section of this manuscript is not detailed enough, especially the section related to the growth. The growth process should be discussed in detail.\nThe figures are not always clear. First, all figure should contain a label on top of the e-InSe and s-InSe plots to immediately distinguish them.\nFig. 1: the text in the top panels is big, while that in the bottom panels is very small and sometimes difficult to read. The Raman results are not discussed well as it is not motivated why the s-InSe shows the A1g(LO) mode while the e-InSe does not.\nFig. 5: The excitation power range in panels c-d should be specified. In panel g, the meaning of intensity ratio should be made explicit.\nFrom the point of view of the text, the language should be checked.\nFrom the point of view of the references, the number of works cited here is extremely low. InSe has attracted interest for a variety of reasons, including its excellent transport properties, its tunable bandgap with layer number, ferroelectricity, and so on. Techniques to modify its properties have been developed, such as strain or ion bombardments. It has also gained interest for the creation of novel heterostructures, if coupled to graphene or other 2D semiconductors such as GaSe and transition metal dichalcogenides, leading to the formation of twist-independent interlayer excitons or to efficient type-I heterostructures. The oxidation properties of InSe have also been widely investigated through optical studies, clarifying the presence of defects. All these studies show the potential interest of this material and motivate future studies. However, none of these topics and related works are cited in the manuscript. Here are some related references (and even more could be found by searching a bit).\nhttps://iopscience.iop.org/article/10.1088/1361-6528/aa749e\nhttps://pmc.ncbi.nlm.nih.gov/articles/PMC4065344/\nhttps://www.nature.com/articles/srep39619\nhttps://pmc.ncbi.nlm.nih.gov/articles/PMC4768130/\nhttps://pubs.acs.org/doi/10.1021/acsnano.1c09844\nhttps://doi.org/10.1021/acsami.7b17247\nhttps://advanced.onlinelibrary.wiley.com/doi/full/10.1002/adom.202000828\nhttps://www.mdpi.com/1420-3049/25/11/2526\nhttps://doi.org/10.1021/acsnano.2c07394\nhttps://www.nature.com/articles/s41563-019-0601-3\nhttps://www.nature.com/articles/s41467-022-31605-9\nhttps://pubs.acs.org/doi/full/10.1021/acs.nanolett.4c04252\nhttps://iopscience.iop.org/article/10.1088/2053-1583/aa61e0/meta\nOverall, while this manuscript reports interesting results on the improvement of the InSe properties upon growth in different microgravity conditions. Its applicability is however restricted. Furthermore, the quality improvement on the properties of the material lacks some statistics and has not been demonstrated for exfoliated few layers of InSe, while InSe has attracted interest especially in its 2D form. The results here reported would thus be more suitable for a more specialized journal.", "reviewer_2": "This manuscript presents a compelling study on the growth of high-quality γ-InSe single crystals under microgravity conditions aboard the China Space Station, demonstrating that the absence of gravitational forces significantly reduces stacking faults and activates intrinsic sliding ferroelectricity. Through atomic-resolution imaging and piezoresponse force microscopy, the authors confirm improved crystal uniformity and robust ferroelectric behavior without the need for doping or annealing. Devices fabricated from microgravity-grown InSe exhibit enhanced electrical performance, including high carrier mobility and large memory windows, while photoluminescence measurements reveal superlinear emission with lower excitation thresholds, indicating superior optoelectronic properties. These findings suggest that microgravity offers a promising route for synthesizing defect-free van der Waals semiconductors with potential applications in next-generation in-memory and in-sensor computing technologies. However following comments should be considered for revision before any consideration for publication:\n1. How does the microgravity-grown InSe compare to other defect-reduction strategies (e.g., annealing, doping) in terms of scalability and reproducibility?\n2. Can the authors clarify the broader implications of this work for space-based materials synthesis beyond InSe?\n3. Were there any control experiments to isolate the effect of microgravity from other variables (e.g., ampoule design, thermal gradients)?\n4. How many samples were grown in space vs. on Earth, and was there statistical analysis to support the claims of defect reduction and performance enhancement?\n5. PFM measurements show ferroelectricity—how do the authors rule out electrostatic or electrochemical artifacts, especially in such thin flakes?\n6. Authors must clearly differentiate background response from the piezo/ferroelectricity from the samples. Refer to recent publications: https://pubs.rsc.org/en/content/articlelanding/2025/nh/d4nh00580e\n7. PFM hysteresis graph appears very noisy and is taken at high applied voltage. It would be helpful to discuss possible non-piezoelectric effects in PFM signal with references.\n8. How does the piezo magnitude vary with layer number of InSe? Is there any difference between e-InSe and s-InSe?\n9. Authors should depict piezo response from multiple layers including bulk samples than just showing one particular layer, to confirm that s-InSe retain piezoelectricity although out.\n10. The PL enhancement is attributed to defect reduction—could strain or other microgravity-induced effects also play a role?\n11. Authors should consider time resolved PL and/or Pump-probe measurements to to confirm exciton lifetimes and recombination pathways in addition to providing more insights into the origin of PL dynamics.\n12. The manuscript notes larger bubbles in s-InSe. Could these bubbles introduce local strain or affect electronic properties?\n13. Is the observed mobility enhancement solely due to defect reduction, or could contact engineering or dielectric environment also contribute?\n14. Some figures (e.g., PL spectra and band diagrams) could benefit from clearer labelling and quantitative annotations. Figure 1c-d should be labelled to improve reader understanding. All acronyms (e.g., FeSFET, PFM) should defined clearly at first use for a broad readership", "reviewer_3": "The authors investigated how the microgravity growth environment affects the growth of the vdWs InSe single crystals. They discovered that this unique condition could eliminate interlayer stacking faults in the materials, which promotes the inherent sliding ferroelectricity. As a result, high performance FeSFETs with high carrier mobility and clear memory window were demonstrated. Moreover, superlinear emission from the microgravity-grown InSe was observed with low excitation thresholds of photons. The topic is interesting and the experimental results are of good quality, which could support their conclusion very well. I would recommend the article for publication after minor changes or explained:\n1. On page 5, line 2, it is inappropriate to claim a single-crystal or polycrystalline region without conducting any characterization first.\n2. For Figure 1b, the authors declared that the microgravity have significant differences influence on the morphology of the InSe crystals from those grown under gravity. Please explained why the microgravity could bring the large bubbles on the InSe crystal?\n3. For Figure 1c, the manuscript shows “… both crystal ingots present single crystalline…”, how could you determine that they are single crystals just from the optical images?\n4. Figure 1f presents the Raman spectra of InSe crystals at different positions. The manuscript does not mention the variation of Raman spectra to the positions. As show in the figure, the intensity of Raman peaks from s-InSe is varied for different measured positions. Please comment the possible reason.\n5. In Figure 1h, the authors compared the transmission spectra of e-InSe and s-InSe with different thickness. What is the exact thickness/layer number of these InSe nanosheets?\n6. Did the authors conduct comparative experiments for the e-InSe and s-InSe in characterization of the sliding ferroelectricity and FeSFET device tests?\n7. For the organization of this article, why the photoluminescence spectra measurement is arranged after the ferroelectricity and FeSFET characterization? The emission test is also a characterization for the optical properties of the InSe crystals, which has a closer connection with the structural and optical properties discussed earlier in Figure 2.\n8. What is the main mechanism by which microgravity growth environment reduces the interlayer stacking faults?"}, "author_response": "Responseletter Jinetal.,#NCOMMS-25-72542\nResponse Letter to the Reviewers\nWe would like to thank you very much for the high evaluation on our manuscript\ntitled “Microgravity-activated high-performance van der Waals InSe ferroelectric\nsemiconductor (#NCOMMS-25-72542)”.The comments are invaluable for improving\nthe quality of our manuscript. In the light of your comments and suggestions, we have\nchecked and revised our manuscript carefully, including additional experimental\nresults and language improvement. We are convinced that the modifications fully\naddress your comments and agree with all the suggestions made. For your\nconvenience, all changes to our manuscript (including the main text and\nsupplementary materials) have been marked in red for your convenience. Below we\naddress each ofyour concerns point-by-point.\nReviewer#1(Remarks totheAuthor)\nJin, Sui et al. report on the growth of InSe single crystals on the China space station,\nand thus under different microgravity conditions to those present on Earth. The\nproperties of the InSe crystals are compared to those of InSe grown on Earth (e-InSe),\nand higher qualityis overall demonstrated for thespace-InSe (s-InSe).\nThe growth of van der Waals crystals under different microgravity conditions is\nindeed little explored due to the technical difficulties that are implied. From this point\nofview,thegrowth ona space station reported inthis work is noteworthy.\nThe work presented here, however, holds moderate significance to the field of 2D\nmaterials, as such a growth is difficult to be done and the proposed approach can\nhardly become astandard growth approach.\nWe thank you very much for your affirmation on the performance comparison of the\ngrown van derWaals InSe crystals under different microgravity conditions.\nIndeed, the growth on a space station is difficult but noteworthy, since it is becoming\na competitive strategy for developing new materials or exploring novel fundamental\nphysics of materials.As summarized in our manuscript, the growth of materials under\nmicrogravity originated from thelate 1970s, and many typical semiconductors such as\nSi, Ge, indium antimony (InSb) and gallium arsenide (GaAs) have been successfully\ngrown; details see Table R1-1 from Cryst. Res. Technol. 2018, 53, 1700265 (DOI:\n10.1002/crat.201700265). The corresponding comprehensive analyses have confirmed\nthe significantly improved quality of materials under the microgravity growth\ncondition. Furthermore, the International Space Station (ISS) National Laboratory has\nbuilt a website to introduce the significance and progress of crystal growth in space\n(https://issnationallab.org/research-and-science/space-research-overview/research-are\nas/in-space-production-applications/crystal-growth/), significantly accelerated the\nrapid development ofspace material growth and research.\nSpecially, the growth of van der Waals (vdW) layered materials should present much\nmore special advantages, since the weak interlayer vdW forces should be more easily\nmanipulated by microgravity, e.g., to avoid the disordering of the layer stacking\nsequences and even to modulate the lattice parameters. As far as we know, the vdW\nlayered semiconductors including InSe, GeSe and SnSe have (or will be) grown in\nspace, e.g., Adv.Mater.,2025,37,2506506(DOI: 10.1002/adma.202506506).\nWe should emphasize that the vdW-layered InSe semiconductor possesses high\nmobility, suitable bandgap, out-of-plane sliding ferroelectricity and\ntheoretically-predicted fractional quantum ferroelectricity (or in-plane ferroelectricity),\nwhich is benefit for high-performance, low-consumptive photodetectors, in-sensing,\nin-memory computing and even lasing nanodevices. However, the native\nstacking-faults in superplastic and ultra-flexible InSe make it challenging in practical\napplications. Besides the post-annealing process or extrinsic doping techniques, the\nmicrogravity circumstance can provide another strategy for improving the quality of\nvdW-layered InSe crystals.\nWecan alsoinfer that theextensive and systematic research results of materials grown\nin space can provide critical foundation experience and reference for material growth\nwithmanually-established microgravity condition onEarth.\nTab.R1-1\nQ1: As for the quality comparison between e- and s-InSe, the results of Figs. 2, 3 and\n5 would require a larger statistical analysis, and thus repeating the same\nmeasurements on different pieces/flakes of the crystals to ensure the general validity\noftheresults.\nAnswer-1: We appreciate you so much for your key suggestions. Indeed, we have\nperformed extensive comparisons of e- and s-InSe in structure by HRTEM and\nHAADF imaging, electrical property by PFM loops, and optical property by PL\nspectra.All these results point to the statistical conclusion that the quality of s-InSe is\nbetter that that of e-InSe. For your convenience, we list the representative statistical\nanalysis results in thefollowing.\nAdditionalatomic-level characterization ofstacking-faults ine-InSeand s-InSe.\nWe have prepared samples from other four additional bulk crystals, and their\ncorresponding high-resolution transmission electron microscope (HRTEM) and\nhigh-angleannular dark-field (HAADF)images are shown inFig.R1-1andFig.R1-2,\nwhere the S1 and S3 are e-InSe and the S3 and S4 are s-InSe. For e-InSe, the HRTEM\nimage (Fig. R1-1a and Fig. R1-2a; with the selected area electron diffraction/SAED\npattern as the inset) together with the HAADF image (Fig. R1-1b and Fig. R1-2b)\nshow various stacking-faults (as similarly shown in Fig. 2 in the main text). The\nstaggered arrangement between layers and straight line-type SAED patterns can be\nclearly observed. However, for s-InSe (Fig. R1-1c and Fig. R1-2c), the\nstacking-faults are obviously reduced by referring to the clear SAED diffraction spots\nand theuniform HRTEM contrast.The HAADF images in Fig. R1-1d and Fig. R1-2d\nshow the atomic arrangement of the microgravity-grown InSe, from which we can\ninfer that the s-InSe crystal statistically presents the better stacking-style with\nABCABC sequences with less stacking-faults.\nAdditionalevidences fortheintrinsicslidingferroelectricity.\nWe have performed PFM measurements for other s-InSe flakes with different\nthicknesses, i.e., 7.5 nm (Fig. R1-3a), 10.0 nm (Fig. R1-3b), 20.2 nm (Fig. R1-3c),\nand 25.8 nm (Fig. R1-3d), all of which present repeatable hysteresis butterfly-shaped\namplitudeloopsand reversiblephaseloops, evidencing robust ferroelectricity.\nHigh-efficientsuperlinearemission ofs-InSewith lowerthresholds.\nAs shown in Fig. R1-4a, the s-InSe samples present a rather similar and simple PL\nspectral shape, which demonstrates the position-independent uniformity and the\nnarrowly-distributed B-band relevant to the interlayer exciton emission. The\nexcitation power dependent PL spectra of other two s-InSe samples (Fig. R1-4b,c)\nclearly demonstrateidentical findings presented in Fig. 5d.\nFig. R1-1.Additional structure characterizations of e-InSe and s-InSe samples. a,\nb, HRTEM image (a; with SAED pattern as the inset) of e-InSe (S1) and\ncorresponding HAADF image (b). c, d, HRTEM image (c; with SAED pattern as the\ninset)of s-InSe (S2)and corresponding HAADF image (d).The red lines in b,d show\nthe stacking abnormal sequences. The green rectangles in b, d mark the “A”-layers of\ntheABC-stacking style.\nFig. R1-2.Additional structure characterizations of e-InSe and s-InSe samples. a,\nb, HRTEM image (a; with SAED pattern as the inset) of e-InSe (S3) and\ncorresponding HAADF image (b). c, d, HRTEM image (c; with SAED pattern as the\ninset) of s-InSe (S4) and corresponding HAADF image (d). The red lines in b show\nthe stacking abnormal sequences. The green rectangles in b, d mark the A-layers of\ntheABC-stacking style.\nFig. R1-3. Additional PFM characterization of s-InSe flakes with different\nthicknesses. a, 7.5 nm (~3 unit cells/u.c.). b, 10.0 nm (~4 u.c.). c,20.2 nm (~8 u.c.). d,\n25.8 nm (~10 u.c.). i - AFM images, ii - thickness profiles, and iii - corresponding\nPFM amplitudeand phase loops.\nFig. R1-4. The excitation power dependent PL spectra of s-InSe crystals. a, PL\nspectra of different s-InSe flakes. b, c, PL spectra of s-InSe flakes at different\nexcitationpowers from 1mWto 80mWwith alaser spotarea of~0.03 cm2.\nQ2: The PL results are rather strange and controversial. Upon increase of the laser\npower,defect states typically saturate and free exciton states tend todominate. In turn,\ndefect states typically feature a sublinear behavior with power. Here, the authors are\nshowing an opposite behavior, which is in contrast with what typically observed for\nvan der Waals crystals. Furthermore, the laser powers used in this work seem to be\nhuge. The authors are claiming that they are keeping the power below 1 mW with a\nspot size of 5 microns to avoid damages, but are the author sure that this power does\nnot damage InSe? I am wondering if the strange power dependence observed in this\nwork is actually due to thefact that the crystal is being destroyed whilemeasuring it.\nAnswer-2: We totally agree with you that defect emissions generally feature a\nsaturation or sub-linear behavior with power increase. From the results shown in Fig.\n5, we can see that the defect-related C-band seems to have a slightly superlinear\nbehavior at the high excitation power side in e-InSe, but without evident excitation\ndependence in s-InSe. This may suggest a much higher density of defects in e-InSe\nfor efficient emission than in s-InSe. Simultaneously, it needs to point out that in\ne-InSe the C-band is rather broad and even gives an evident sharp peak at ~0.95 eV\n(Fig. 5a) that cannot be observed in s-InSe (Fig. 5b,d), which may suggest that the\ncontribution for C-band is not only from the conventional defect states but also\nprobably from thestacking faults-induced interlayer excitons.\nRegarding the laser power, actually, we only used the power of around 1 mW with a\nspot size of 5 µm for µ-Raman measurements at fast scanning mode. This power\ndensity is on the order of 1 kW/cm². We should point out that the testing time of\nRaman spectra we employed was relatively short, only 10 seconds per curve, and the\ntesting conditions for both bulk e-InSe and s-InSe were consistent. No significant\nchanges between their Raman spectra are observed. Additionally, we repeatedly\nrecord the Raman spectra of e-InSe and s-InSe bulk (Fig. R1-5a,c) and flakes (Fig.\nR1-5b,d) under the same intensity level, and the signals remain stable. Notice that the\nspectra of the flakes show a worse signal-to-noise ratio (SNR) than that of the\ncorresponding bulk states. The A (LO) mode can become more visible in the thin\n1g\nflakes (Fig. R1-5b,d). Considering the stronger (better SNR) Raman signal of s-InSe,\nhalf of the laser power was used for Raman measurements (Fig. R1-5d), where\nsimilar A (LO) mode can be observed as that in e-InSe flakes with a doubled\n1g\nexcitationpower.\nNotice that for excitation-dependent PL measurements, the laser power used is much\nlower, ranging from 1 to 100 mW with a spot area of ~0.03 cm2 (corresponding to\nabout 0.03 – 3 W/cm²). Our results demonstrated that no significant damage was\nobserved on bulk samples under this power range. In response to your concerns, we\nselect another sample and measure its room-temperature PL spectra, as shown in Fig.\nR1-6a. Obviously, the superlinear emission persists within the range of 1 – 80 mW,\nbutthe deviation from super-linearity occurs from 80mW(Fig.R1-6b). Consequently,\nPL tests were performed repeatedly at around 100 mW (Fig. R1-6c), demonstrating a\nslight decrease in PL intensity after 100 mW. This in another way confirms that the\nexcitation power corresponding to the superlinear emission region of the samples is\nreliable. Back to Fig. 5 in the text, the slope of the integrated intensity shows no\nchange in the entire excitation power range, indicating that the laser intensity used in\nthemeasurement has not yet reached thedamage threshold ofthesamples.\nFig.R1-5.Raman spectra of e-InSeands-InSeundervaryinglaserpower.a,b,\nshowtheRamanspectra ofe-InSe bulk and e-InSe thinflakes,respectively.c,d,show\ntheRaman spectra of s-InSebulk and s-InSe thinflakes,respectively.All spectra were\nacquired from different sampleregions, with a laser spotareaof ~3 μm2.\nFig. R1-6. Excitation-dependent PL of s-InSe. a, PL spectra at different excitation\npowers. b, The intensity ratio of A-peak/C-band. c, PL spectra of s-InSe before and\nafter theexcitation powerof100mWwith alaser spotarea of0.03cm2.\nQ3: The experimental section of this manuscript is not detailed enough, especially the\nsection related tothegrowth.Thegrowth process should bediscussed indetail.\nAnswer-3: Thank you so much for this precious suggestion. We have added the\ngrowth process of InSe on the space station in details in the Supplementary\nInformation, which has also been referred to in the main text. For your convenience,\nweprovide thegrowth process as below.\nThegrowth ofInSe onthespace stationincludes two parts.\nI) The pre-synthesis of the polycrstalline InSe ingot on Earth. 6N high-purity In and\nSe elements as raw materials were mixed in a stoichiometric ratio of 0.52 : 0.48.\nThese mixtures were sealed into a Φ20 mm highly cleaned quartz ampoule,\nvacuumed to ~10−3 Pa and then sintered adequately in a rocking furnace under 800°C\nat a rate of 30 r/min for half an hour. After the mixed alloy was naturally cooled to\nroom temperature, InSe polycrystals were obtained, as shownin Fig.R1-7a.\nII) Space growth of InSe crystal.The synthesized InSe polycrystal ingot was cut into\na segment with a length of ~120 mm and resealed into another brand-new quartz\nampoule (Fig. R1-7b). It was worth noting that the ingot must be fastened and\nimmovable to ensure the safety of space launch transportation of samples. Then, the\nquartz ampoule containing the InSe polycrystal ingot was fixed into a standardAl O\n2 3\ntube (Fig. R1-7c). The schematic diagram of InSe growth on the space station is\nshown in Fig. R1-8a. The furnace holds a narrow high temperature zone ~10 mm in\nheight. The temperature profile along the vertical direction is illustrated in Fig.\nR1-8b. During space growth, the Al O tube was moved into the high-temperature\n2 3\nmaterials science experimental apparatus (furnace) and fixed to one of the working\npositions by an astronaut. The furnace was controlled at 715°C and the temperature\ngradient for crystal growth was ~30°C/cm. After the polycrystals were melted and\nsoaked for 3 hours among the high temperature region, the re-crystallization of InSe\ncrystal took place at the low temperature zone with the furnace moving up at a speed\nof 1.0 mm/hour. After the space growth of InSe finished, the furnace was cooled to\nroom temperature in 2hours.\nFig. R1-7. Pre-synthesis of InSe polycrystals grown on Earth. a, The photo of\nsynthesized InSe polycrystalline ingot in the quartz ampoule. b, Dissected InSe\npolycrystalline ingot resealed into a new quartz ampoule. c, A standard Al O tube\n2 3\ncontaining thequartz ampoulewith polycrystallineInSe ingot for growth ofs-InSe.\nFig. R1-8. Schematic of s-InSe grown on the space sation under microgravity\ncondition using the Bridgman method (a). Right panel is the temperature\ngradientprofile(b).\nQ4: The figures are not always clear. First, all figure should contain a label on top of\nthee-InSe and s-InSe plotsto immediately distinguish them.\nAnswer-4:Wesincerely appreciate you for thisnicesuggestion.\nWe have updated all figures with mandatory revisions in the revised version of our\nmanuscript.\nQ5: Fig. 1: the text in the top panels is big, while that in the bottom panels is very\nsmalland sometimes difficultto read.\nAnswer-5:Thank you very much foryour helpful suggestion.\nWe have optimized this figure, as shown in the revised manuscript. Simultaneously,\nwealso added thecurve of thetemperature gradient as asub-panelin Fig. 1a.\nQ6: The Raman results are not discussed well as it is not motivated why the s-InSe\nshows theA (LO) modewhilethe e-InSe does not.\n1g\nAnswer-6:Thank you very much forthis comment.\nInterestingly, the A (LO) mode can only be observed in thinned InSe including\n1g\ns-InSe and e-InSe flakes, but it gradually disappears in bulk InSe. As a confirmation,\nfive more flakes with different thicknesses are exfoliated from both e-InSe and s-InSe\ncrystals. The detailed Raman spectra (Fig. R1-9 and Fig. R1-10) demonstrate that the\nA (LO) mode can be clearly observed in both e-InSe and s-InSe thinner flakes, but it\n1g\nbecomes less pronounced as thethickness increases.\nThis interpretation has also been added into the revised manuscript; please see line\n22-24,page 5.\nFig. R1-9. Raman results of e-InSe flakes (F1, F2, F3 and F4) with different\nthicknesses. a, 30.6 nm. b, 20.7 nm. c, 11.4 nm. d, 8.6 nm. i - AFM topography, ii -\nthickness plot,and iii- corresponding Raman spectrum.\nFig. R1-10. Raman results of s-InSe flakes (F1, F2, F3 and F4) with different\nthicknesses. a, 98.0 nm. b, 72.9 nm. c, 11.7 nm. d, 9.5 nm. i - AFM topography, ii -\nthickness plot,and iii- corresponding Raman spectrum.\nQ7: Fig. 5: The excitation power range in panels c-d should be specified. In panel g,\nthemeaning of intensityratio should bemade explicit.\nAnswer-7:Thank you very much foryour valuablecomments and suggestions.\nWehave addedexcitationpower information together with corresponding descriptions\\inthe revised manuscript.\nRegarding the intensity ratio of the main peakAand the defect-related C-band in Fig.\n5g, we think it can unveil the competition of carrier recombination between these two\ntotally different emission origins, and more effectively reflects the behavior of peakA\nwhen comparing the results between s-InSe and e-InSe. For instance, the main\nemission peakApredominates in s-InSe at the extremely low excitation level of ~0.2\nW/cm2, while the critical point is ~2W/cm2 for e-InSe.This suggests the much higher\nemission efficient of the main peak A in s-InSe. Simultaneously, it can demonstrate\nthat with excitation power increase, the main peak A of s-InSe can be enhanced by\none order of magnitude than that of e-InSe possibly due to the annihilation of defects\nins-InSe, which is much better than reports (Nano Lett.2016,16,3221−3229).\nQ8: From the pointof viewofthetext, thelanguage shouldbechecked.\nAnswer-8:Weare truly grateful to you forthis comment.\nWe have carefully revised our text and try our best to polish the language. We think\ntherevised version should havea remarkable improvement and a betterreadability.\nQ9: From the point of view of the references, the number of works cited here is\nextremely low. InSe has attracted interest for a variety of reasons, including its\nexcellent transport properties, its tunable bandgap with layer number, ferroelectricity,\nand so on. Techniques to modify its properties have been developed, such as strain or\nion bombardments. It has also gained interest for the creation of novel\nheterostructures, if coupled to graphene or other 2Dsemiconductors such as GaSe and\ntransition metal dichalcogenides, leading to the formation of twist-independent\ninterlayer excitons or to efficient type-I heterostructures. The oxidation properties of\nInSe have also been widely investigated through optical studies, clarifying the\npresence of defects. All these studies show the potential interest of this material and\nmotivate future studies. However, none of these topics and related works are cited in\nthe manuscript. Here are some related references (and even more could be found by\nsearching abit).\nhttps: //iopscience.iop.org/article/10.1088/1361-6528/aa749e\n(Fast, multicolor photodetection with graphene-contacted p-GaSe/n-InSe van der\nWaals heterostructures)\nhttps: //pmc.ncbi.nlm.nih.gov/articles/PMC4065344/\n(Tuningthebandgap ofexfoliated InSe nanosheets byquantum confinement)\nhttps: //www.nature.com/articles/srep39619\n(The direct-to-indirect band gap crossover in two-dimensional van der Waals Indium\nSelenidecrystals)\nhttps: //pmc.ncbi.nlm.nih.gov/articles/PMC4768130/\n(High broad‐band photoresponsivity of mechanically formed InSe–graphene van der\nWaals heterostructures)\nhttps: //pubs.acs.org/doi/10.1021/acsnano.1c09844\n(Room-temperature near-infrared excitonic lasing from mechanically exfoliated InSe\nmicroflake)\nhttps: //doi.org/10.1021/acsami.7b17247\n(Largely tunable band structures offew-layer InSebyuniaxial strain)\nhttps: //advanced.onlinelibrary.wiley.com/doi/full/10.1002/adom.202000828\n(Enhanced optical emission from 2DInSe bent onto Si-pillars)\nhttps: //www.mdpi.com/1420-3049/25/11/2526\n(The interaction of hydrogen with thevan derWaals crystal γ-InSe)\nhttps: //doi.org/10.1021/acsnano.2c07394\n(Thickness- and twist-angle-dependent interlayer excitons in metal monochalcogenide\nheterostructures)\nhttps: //www.nature.com/articles/s41563-019-0601-3\n(Design of van derWaals interfaces for broad-spectrum optoelectronics)\nhttps: //www.nature.com/articles/s41467-022-31605-9\n(Light sources withbias tunable spectrum based onvan derWaals interface transistors)\nhttps: //pubs.acs.org/doi/full/10.1021/acs.nanolett.4c04252\n(Giant light emission enhancement in strain-engineered InSe/MS (M = Mo orW) van\n2\nderWaalsHeterostructures)\nhttps: //iopscience.iop.org/article/10.1088/2053-1583/aa61e0/meta\n(Engineering p–n junctions and bandgap tuning of InSe nanolayers by controlled\noxidation)\nAnswer-9: We would like to thank you very much for these helpful references. We\nhave carefully studied them. They are focusing on either the excellent transport\nproperties, tunable bandgap with layer number, emission properties, ferroelectricity or\nheterostructures of InSe, which can improve the width and depth of our manuscript.\nThus, we have cited them in the introduction and result parts together with\ncorresponding descriptions and discussions, e.g., see Refs. 15-27 in line 19-25, page 3\nand in line5-6, page 12in therevised manuscript.\nOverall, while this manuscript reports interesting results on the improvement of the\nInSe properties upon growth in different microgravity conditions. Its applicability is\nhowever restricted. Furthermore, the quality improvement on the properties of the\nmaterial lacks some statistics and has not been demonstrated for exfoliated few layers\nof InSe, while InSe has attracted interest especially in its 2D form. The results here\nreported would thus bemore suitablefor a morespecialized journal.\nAnswer: Based on the detailed point-by-point reply to your comments by providing\ncomprehensive statistic results, including structural, optical and electrical ones\ntogether with the corresponding interpretations and discussions, we think we have\nfully addressed all the issues or concerns raised by you. Considering the high-quality\nvdW InSe crystal and its high performance of resulted devices, which may popularize\nthegrowth strategy in space oronEarth with simulated microgravity environment and,\nmore importantly, push the applications of InSe-based devices in photon-integrated\nin-memory computing nanodevices, we think the revised manuscript presents\nimportant advances of significance to specialists within material, physic, applied, and\nengineering sciences that are complied with the aims and scope of Nature\nCommunications,and thus deserves publication in it.\nPlease note that all major revisions have been marked in red in our revised manuscript\nin an additional PDF version. Simultaneously a supplementary information file has\nalso been provided.\nReviewer#2(Remarks totheAuthor)\nThis manuscript presents a compelling study on the growth of high-quality γ-InSe\nsingle crystals under microgravity conditions aboard the China Space Station,\ndemonstrating that the absence of gravitational forces significantly reduces stacking\nfaults and activates intrinsic sliding ferroelectricity. Through atomic-resolution\nimaging and piezoresponse force microscopy, the authors confirm improved crystal\nuniformity and robust ferroelectric behavior without the need for doping or annealing.\nDevices fabricated from microgravity-grown InSe exhibit enhanced electrical\nperformance, including high carrier mobility and large memory windows, while\nphotoluminescence measurements reveal superlinear emission with lower excitation\nthresholds, indicating superior optoelectronic properties. These findings suggest that\nmicrogravity offers a promising route for synthesizing defect-free van der Waals\nsemiconductors with potential applications in next-generation in-memory and\nin-sensor computing technologies. However following comments should be\nconsidered for revision before any consideration for publication.\nWe appreciate you very much for your highly evaluating our manuscript. Below we\nwillreply your comments orconcerns point-by-point.\nQ1: How does the microgravity-grown InSe compare to other defect-reduction\nstrategies (e.g., annealing, doping) interms ofscalability and reproducibility?\nAnswer-1:Thank you somuch for your comments.\nWith the advancement of space station technology, the process of microgravity-grown\ntwo-dimensional (2D) materials including van der Waals (vdW) layered\nsemiconductors becomes increasingly mature, and more and more variety of 2D\nmaterials have been grown in space station, greatly promoting the development of\nspace material growth and the material growth under microgravity (actual or\nsimulated ones). For instance, our research group mainly focuses on the space-growth\nof (doped) InSe and GeSe vdW-layered materials. As far as we know, other research\ngroups are successively conducting studies on space-grown GaSe, and the\nthermoelectric SnSe is being considered to grow in space from the project list of the\nChinaspace station.\nTaking InSe as an example, we find that the optimized post-annealing process, the\nspecial elemental doping strategy (e.g., yttrium/Y and dysprosium/Dy) and the\nmicrogravity-growth condition can reach the goal of defect-reduction. However, there\nare someessential differences among thesestrategies.\nVia post-annealing process, we have obtained high-quality InSe samples, based on\nwhich the intrinsic sliding ferroelectricity can be evidenced from the hysteresis loops\nby piezoresponse force microscope (PFM), and the intrinsic superlinear emission can\nalso be presented. However, to obtain cracked-free flat and large area samples by this\nprocedure isdifficult, although thereproducibilitycan beguaranteed.\nThe elemental doping (e.g., Y-doping) strategy can enhance the quality, especially the\nlayer rigidity of InSe with flat and straight surface, demonstrating good scalability,\nalthough the growth process is more complicated. This product benefits for the\nmeasurements of sliding ferroelectricity, and is also helpful for the fabrication of\nhigh-density nanodevice arrays. However, due to the low interlayer sliding barrier, the\ntiny interlayer pre-sliding naturally exists with a long layer periodicity in Y-doped\nInSe, which may influence the transport performance of nanodevices, e.g., the\nmobility.\nFor microgravity-grown InSe involved in this work, existing results demonstrate the\noutstanding scalability and reproducibility, except for the special growth condition.\nBy now, our group have successfully grown two batches of InSe single-crystalline\ningots in China space station. Both show great reproducibility in the crystal quality\nand the fundamental properties. With rapidly development of the space science\nresearch and the in-depth understanding of the crystal growth under microgravity\ncondition, the scalability of space growth or microgravity-growth of crystals will be\nguaranteed a lot.\nIt is interesting to point out that there are essential differences regarding the emission\nproperty among the annealed, Y-doped, microgravity-grown InSe, as shown in Fig.\nR2-1. In order to amplify the weak defect-related signals at low energy side, the\nspectra are shown in a single (vertical) logarithm scale. The s-InSe involved in our\ncurrent work can showsuperlinear emissions ofboth intralayer and interlayer excitons.\nThe annealed InSe (green curve) shows excellent (superlinear) emission of intralayer\nexcitons (peak A) but with relatively low interlayer excitonic emission (peak B). The\nY-doped InSe(red curve) shows interlayer and interlayer excitonicemissions (peaksA\nand B), but they both are rather weak as compared to that of annealed and\nmicrogravity-grown InSe, and even weakerthan the defect-related C-band.\nFig. R2-1. Room temperature PL spectra of s-InSe (blue), annealed InSe (green)\nandY-doped InSe(red).Theexcitationwavelength is 405nm.\nQ2: Can the authors clarify the broader implications of this work for space-based\nmaterials synthesis beyond InSe?\nAnswer-2:Thanks alot foryour constructivecomment.\nConsidering the facts that high-quality vdW InSe crystal and resulted high\nperformance devices are obtained, we think our work may not only popularize the\ngrowth strategy in space or on Earth with simulated microgravity environment, but\nalso pave up the way of in-depth understanding the fundamental physics of InSe\ncrystals with high-quality, push its broad applications in electric- and\nphoton-integrated in-memory computing chips.\nWe should point out that prior to this, various alloys and semiconductors such as Si,\nGe, InSb and GaAs have been successfully grown in space; see Table R2-1 from\nCryst. Res. Technol. 2018, 53, 1700265 (DOI: 10.1002/crat.201700265), and the\ncorresponding analyses have confirmed the significant improvement of material\nquality under microgravity.The International Space Station (ISS) National Laboratory\nalso specifically introduce the significance and progress of crystal growth in space\n(https://issnationallab.org/research-and-science/space-research-overview/research-are\nas/in-space-production-applications/crystal-growth/), significantly accelerated the\nrapid development ofspace material growth and research.\nHowever, no documented researches are accessible for 2D vdW-layered\nsemiconductors in this realm. Generally, vdW-layered materials should have more\nspecial advantages for growing in space, since the weak interlayer vdW forces can be\nmore easily manipulated by microgravity condition, e.g., to avoid the disordering of\nthe layer stacking sequences and even to modulate the lattice parameters.As far as we\nknow,besides InSe (Adv.Mater., 2025, 37, 2506506; DOI: 10.1002/adma.202506506),\nother vdW semiconductors such as GeSe and SnSe are being considered to grow on\nChina space station. We should emphasize that the vdW InSe semiconductor\npossesses high mobility, suitable bandgap, out-of-plane sliding ferroelectricity and\ntheoretically-predicted fractional quantum ferroelectricity (or in-plane ferroelectricity),\nwhich is benefit for high-performance, low-consumptive photodetectors, in-sensing,\nin-memory computing and even lasing nanodevices. However, the native\nstacking-faults in superplastic and ultra-flexible InSe limit its practical application.\nBesides the post-annealing or extrinsic doping techniques, the microgravity growth\ncan provideadditional strategy for improving thequality ofInSecrystals.\nThus, our work can offer a valuable reference regarding the feasibility and potential\napplications of growing other vdW materials in space. In addition, the extensive and\nsystematic research results of space-grown InSe can provide experience and reference\nformaterial growth under manually-established microgravity condition onEarth.\nTab.R2-1\nQ3: Were there any control experiments to isolate the effect of microgravity from\nothervariables (e.g., ampouledesign, thermal gradients)?\nAnswer-3:Thank you very much foryour professional comments.\nWe should point out that the growth conditions including growth parameters are fully\nthe same but for the microgravity in space. This can absolutely exclude the other\npotential factors. For your convenience, we provide the growth process in details\nbelow.\nI) The pre-synthesis of the polycrstalline InSe ingot on Earth. 6N high-purity In and\nSe elements as raw materials were mixed in a stoichiometric ratio of 0.52 : 0.48.\nThese mixtureswere sealed into aΦ20mmhighly cleaned quartz ampoule,vacuumed\nto ~10−3 Pa and then sintered adequately in a rocking furnace under 800°C at a rate of\n30 r/min for half an hour. After the mixed alloy was naturally cooled to room\ntemperature, InSepolycrystals were obtained, as shown in Fig.R2-2a.\nII) Space growth of InSe crystals. The synthesized InSe polycrystalline ingot was cut\ninto a segment with a length of ~120 mm and resealed into another brand-new quartz\nampoule (Fig. R2-2b). It was worth noting that the ingot must be fastened and\nimmovable to ensure the safety of space launch transportation of samples. Then, the\nquartz ampoule containing the InSe polycrystal ingot was fixed into a standard Al O\n2 3\ntube (Fig. R2-2c). The schematic diagram of InSe crystal growth on the space station\nis shownin Fig.R2-3a.The furnace holdsa narrow high temperature zoneof ~10mm\nin height. The temperature profile along the vertical direction is illustrated in Fig.\nR2-3b. During the space growth, theAl O tube was moved into the high-temperature\n2 3\nmaterials science experimental apparatus (furnace) and fixed to one of the working\npositions by an astronaut. The furnace was controlled at 715°C and the temperature\ngradient for crystal growth was ~30°C/cm. After the polycrystals were melted and\nsoaked for 3 hours among the high temperature region, the re-crystallization of InSe\ncrystal took place at the low temperature zone with the furnace moving up at a speed\nof 1.0 mm/hour. After the space growth of InSe finished, the furnace was cooled to\nroom temperature in 2hours.\nFig. R2-2. Pre-synthesis of polycrystalline InSe ingot on Earth. a, The photo of\nsynthesized polycrystalline InSe ingot inside the quartz ampoule. b, Dissected\npolycrystalline InSe ingot resealed into a new one. c, A standard Al O tube\n2 3\ncontaining the quartz ampoule with polycrystalline InSe ingot for space growth of\nsingle crystallineInSe.\nFig. R2-3. Schematic of s-InSe grown on the space station under microgravity\ncondition using the Bridgman method (a). Right panel is the temperature\ngradientprofile(b).\nQ4: How many samples were grown in space vs. on Earth, and was there statistical\nanalysis to support theclaims ofdefect reduction and performance enhancement?\nAnswer-4:Thank you very much forthis question.\nThe growth on a space station is difficult but noteworthy, since it is becoming a\ncompetitive strategy for developing new materials or exploring novel fundamental\nphysics of materials. The growth of materials under microgravity originated from the\nlate 1970s, and many typical semiconductors such as Si, Ge, indium antimony (InSb),\ngallium arsenide (GaAs), etc have been successfully grown. The corresponding\ncomprehensive analyses have confirmed the significantly improved quality of\nmaterials under the microgravity growth condition (Cryst. Res. Technol. 2018, 53,\n1700265;DOI: 10.1002/crat.201700265).\nBy now,we have obtained two batches of s-InSe samples including undoped (intrinsic)\nand specifically Bi-doped s-InSe, together with at least five matching batches of\nintrinsic and Bi-doped e-InSe. Currently, we have already finished the matching\nexperiments of Dy- and Er-doped InSe growth on Earth, which will be grown inspace\nin the near future. The reason of doping is to manipulate the carrier mobility,\nthermoelectric property, or special emission wavelengths of s-InSe. As discussed\npreviously in Q1, different growth strategies can obtain InSe with distinct physical\nproperties. Our systematical results on lots of intrinsic s-InSe flakes via\nmicrostructure analysis, optical andelectrical characterizations support ourconclusion\nthat the microgravity can effectively optimize the native stacking-faults and enhance\nthe crystal quality of InSe. For your convenience, we summarize the PL spectra of\nintrinsic s-InSe measured at different conditions, as shown in Fig. R2-4.As shown in\nFig. R2-4a, different s-InSe flakes present a rather similar and simple PL spectral\nshape, especially the position-independent uniform and narrowly-distributed B-band\nrelevant to theinterlayer exciton emission.The excitationpower dependent PLspectra\nof different s-InSe flakes (Fig. R2-4b and Fig. R2-4c) show similar results, also\naligning with that (superlinear emissionsofpeaksAand B) in Fig. 5inourmanuscript.\nAdditional statistical analyses to support the improvement come from a comparative\nstudy ofthree devices based one-InSe ands-InSe viatheidentical fabricating process,\nofwhich the key electrical parameters are summarized inTable R2-2.\nFig. R2-4. Excitation power dependent PL spectra of s-InSe. a, PL spectra of\ndifferent s-InSe flakes. b, c, PL spectra of s-InSe flakes at different excitation powers\nfrom 1mWto80mWwith a laser spot area of~0.03 cm2.\nTab.R2-2.Electrical properties of s-InSeande-InSe nanodevices.\nSample On/offratio Mobility(cm2v-1s-1)\n1 106 195.3\ns-InSe 2 106 187.4\n3 105 160.8\n1 105 103.9\ne-InSe 2 105 81.8\n3 105 49.4\nQ5: PFM measurements show ferroelectricity—how do the authors rule out\nelectrostaticorelectrochemical artifacts, especially in such thinflakes?\nAnswer-5:Weare grateful to you for thisprofessional comment.\nIn our work, dual amplitude resonance tracking (DART)-PFM mode on a commercial\nscanning probe microscopy (SPM) system (Asylum Research Cypher, Oxford, UK)\nwas used to ensure strong signal-to-noise ratio. During PFM measurements, we have\ncalibrated the vertical spring constant (k) and the inverse optical lever sensitivity\n(InvOLS) of the probe to reduce the electrostatic contribution in PFM measurements.\nTo exclude the possible artifacts in PFM measurements and evidence the intrinsic\nferroelectricity of s-InSe , different testing conditions are adopted, including changing\nthe V (Fig. 3b and Fig. R2-5) and repeating the PFM measurements on flakes with\ndc\ndifferent thicknesses (Fig. R2-6). Besides Fig. 3, Fig. R2-5 shows the additional\nV -dependent PFM results of the s-InSe flake with thickness of ~25.4 nm, which\ndc\ndemonstrates clear, repeatable amplitude and phase loops with sweeping V above 6\ndc\nV, while no ferroelectric hysteresis loops at low voltage (below the coercive field),\nverifying the ferroelectric feature of s-InSe. It is a critical way to rule out the\nelectrostatic effect. These results have been added to the Supplementary Information\nof our revised manuscript. Further, domain writing at the LithoPFM mode of the\nAsylum Research software with reverse DC biases (V = ±8 V) in Fig. 2d also rules\ndc\nout the electrostatic or electrochemical artifacts and proofs the ferroelectricity in\ns-InSe.\nFig. R2-5. PFM results of s-InSe. a, AFM image. b, The thickness plot giving a\nthickness of ~25.4 nm (~30 layers). c, d, A series of local PFM amplitude (c) and\nphase(d) loopsat different V .\ndc\nFig. R2-6. Additional PFM characterization of s-InSe flakes with different\nthicknesses. a, 7.5 nm. b, 10.0 nm. c, 20.2 nm. d, 25.8 nm. i - AFM topography\nimages, ii - thickness profiles, and iii - corresponding PFM amplitude and phase\nloops.\nQ6: Authors must clearly differentiate background response from the\npiezo/ferroelectricity from the samples. Refer to recent publications: https:\n//pubs.rsc.org/en/content/articlelanding/2025/nh/d4nh00580e\nAnswer-6:Weappreciate you very much forthis important comment.\nWe have added relevant discussion to the revised version of our manuscript; please\nsee the last paragraph, page 7. At the same time, we have also cited relevant\nreferences including Nanoscale Horiz. 2025, 10, 987-999 (Doi:10.1039/d4nh00580e),\nwhere it indicated that employing a cantilever with higher stiffness and greater length\ncan further reduce the electrostatic contribution in PFM measurements. This is\nbecause the electrostatic contribution is inversely proportional to the stiffness of the\ncantilever, and it is known that a larger tip length can attenuate the capacitive\ncoupling between the tip and the sample surface. This is a highly significant issue.\nMeanwhile, we note that the PFM measurements were done using SCM-PIT-V2\n(Bruker). When we use an Oxford Instruments Asylum Research Cypher system, the\nsame type of calibration is essential. This includes calibrating the vertical spring\nconstant (k) and the inverse optical lever sensitivity (InvOLS) of the probe. During\nour testing, we have calibrated the true deflection of the cantilever and the force\naccording to theinstrument's manual, thereby eliminatingthepotential interferences.\nQ7: PFM hysteresis graph appears very noisy and is taken at high applied voltage. It\nwould be helpful to discuss possible non-piezoelectric effects in PFM signal with\nreferences.\nAnswer-7: Thank you very much for this insightful and absolutely correct\nobservation.\nWe totally agree with you that under high DC biases, non-intrinsic piezoelectric\nsignals may be introduced, e.g., originating from effects such as electrostatic\ninteractions, electrostriction, and ion migration. Regarding your concerns, we have\nsupplemented relevant discussions on page 8 in the revised manuscript and cited\nsupportable literatures (Refs. 31, 33, 44) to analyze the potential non-piezoelectric\ncontributions under high electric fields and their impact on hysteresis loop shape and\nnoise.\nFurthermore, as you highlighted the importance of experimental validation, we would\nlike to clarify that our experimental section has already included systematical PFM\nmeasurements on samples with different thicknesses (Fig. R2-6) under different DC\nvoltages (Fig. R2-5), which rules out the non-intrinsic piezoelectric signals. Further,\ndomain writing at the LithoPFM mode of the Asylum Research software with reverse\nDC biases (V = ±8 V) in Fig. 2d can also rule out the electrostatic or electrochemical\ndc\nartifacts and proofs theferroelectricity in s-InSe.\nThis relevant explanation and corresponding figure captions have been\nadded/emphasized in line 16-18, page 8 in the revised main text and Supplementary\nInformation.\nQ8: How does the piezo magnitude vary with layer number of InSe? Is there any\ndifferencebetween e-InSe and s-InSe?\nAnswer-8:Thank you very much forthis important comment.\nYes, the piezo magnitude varies with the layer number of InSe. However, it is\ninteresting to mention that the value represented by the effective d seemingly\n33\nincreases to a saturation with the increase of layer number (from about 3 to 10 unit\ncells) in s-InSe, but it is opposite in rare earth yttrium (Y)-doped InSe (from about 4\nto48unit cells), as shown in Fig. R2-7.\nNotice that to directly detect the intrinsic ferroelectricity in e-InSe is often a challenge\ndue to the high density of natural stacking-faults in this material. These native defects\ncan mask or disrupt the long-range order necessary for observing clear ferroelectric\nsignatures. Therefore, we only compared the layer number dependence of the piezo\nmagnitude in Y-doped InSe (Fig. R2-7a) and s-InSe (Fig. R2-7b), whose\nferroelectricity was explicitly demonstrated.\nFig. R2-7.The piezo magnitude results ofY-doped InSe and s-InSe with different\nthicknesses.a,ForY-doped InSe. b,For s-InSe.\nQ9: Authors should depict piezo response from multiple layers including bulk\nsamples than just showing one particular layer, to confirm that s-InSe retain\npiezoelectricity although out.\nAnswer-9:Weappreciate you for thiscomment.\nFollowing your suggestions, we carried out additional PFM measurements on s-InSe\nwith different thicknesses. As shown in Fig. R2-6, clear hysteresis loops can be\nobserved in four other s-InSe flakes with different thicknesses of 7.5nm (Fig. R2-6a),\n10.0nm(Fig.R2-6b), 20.2nm (Fig.R2-6c), and 25.8nm (Fig.R2-6d).\nQ10: The PL enhancement is attributed to defect reduction—could strain or other\nmicrogravity-induced effects also play arole?\nAnswer-10:Thank you forthis concern.\nAs known, the interlayer sliding barrier is extremely low in InSe, so there will be\nabundant randomly distributed stacking-faults in the as-prepared crystals by the\nBridgman method, due to the contact stress from the ampoule bottles and buoyancy\nconvection-induced crystal non-uniformity, which will strongly influence the\nuniformity of the optical and electrical properties of InSe. In contrast, the primary\nmechanism through which the microgravity operates is \"detachment growth\" (a\nprocess where crystal growth occurs detached from the container walls), which is\ncritical for the enhancement of the crystal quality. Under such conditions, no stress is\nintroduced between the container and the material. In addition, the buoyancy\nconvection-induced crystal non-uniformity will be greatly reduced in space under the\nmicrogravity condition, which will also result in better crystal quality (defect\nreduction).\nIn our work, the e-InSe used for optical property comparison are synchronously\ngrown on Earth following the same operation procedure under the normal gravity\ncondition. Thus, we can infer that the PL enhancement in s-InSe can be attributed to\ntheroleof microgravity.\nCurrently, there is a lack of comprehensive studies on 2D vdW materials. Therefore,\nthis work specifically explores how microgravity leads to alterations in the crystal\nstructure of 2D vdW materials, in turn leading to changes in their ferroelectric and\nemissionproperties.\nQ11: Authors should consider time resolved PL and/or Pump-probe measurements to\nto confirm exciton lifetimes and recombination pathways in addition to providing\nmoreinsights into theorigin ofPLdynamics.\nAnswer-11:Thank you very muchfor this suggestion.\nFollowing your suggestions, we have performed time-resolved PL (TR-PL)\nmeasurements on e-InSe and s-InSe flakes with pulsed 405 nm as the excitation\nsource. Fig. R2-8 shows the four PL decay curves for peaks A (intralayer) and B\n(interlayer) of e-InSe and s-InSe (in a semi-logarithm scale). We can see that all\ncurves are similar and consist of at least two distinguishable decay processes. The fit\nprocedure by a double-exponential decay function gives two time constants for each\ncurve. As reported previously (e.g., see Nat. Commun. 2023, 14, 36; DOI:\n10.1038/s41467-022-35490-0), the slow component of about 2~3 ns is related to the\ncarrier lifetime of spontaneous emission in InSe, including the intralayer and\ninterlayer excitons. However,we shouldemphasizethat our InSeincluding e-InSe and\ns-InSe can give superlinear emission at a rather low excitation power density of ~1\nW/cm2, less than that of TR-PL measurements. Considering the fact that the fast time\nconstant is almost the same for all curves, i.e., ~0.33 ns, and is by almost one order of\nmagnitude shorter than the slow one, we can attribute the fast process to the\nsuperlinear (or amplified spontaneous and even lasing) emission of both intralayer\nand interlayer excitons,as observed inthe steady-state PLresults.\nThen, we focus on the slow time component, which is related to the spontaneous\nemission process of interlayer and intralayer excitons. It is clear to see that the slow\ncomponent of both peaks A and B in e-InSe (~2.4 ns and ~2.3 ns, respectively) is\nslightly shorter than that of s-InSe (~3.2 ns and ~2.9 ns, respectively). The short\nlifetime of carriers for spontaneous emission in e-InSe may due to the existence of\nmore defects including the interlayer stacking-faults, which can trap the carrier for\ndefect emission or non-radiation recombination, compared to that of s-InSe. This in\nanother way can support thehigher-quality ofs-InSethan e-InSe.\nFig. R2-8. TR-PL decay curves corresponding to the intralayer (A at ~1.23 eV)\nand interlayer (B at ~1.17 eV) exciton emission positions in e-InSe and s-InSe.\nThe green curves are the fit results of a double-exponential decay function, which\ngives thefast and slowtimeconstants, as separately shown onthepanel.\nQ12: The manuscript notes larger bubbles in s-InSe. Could these bubbles introduce\nlocal strain or affect electronic properties?\nAnswer-12: Thank you very much for this concern. Your observation regarding the\nlarge bubbleissueis both timely and highly meaningful.\nThe large bubble may represent the typical characteristic of crystal growth under\nmicrogravity condition. As we have described in details in the response to Q4, the\nschematic diagram of crystal growth process in the zone melting furnace on the China\nspace station are shown in Fig. 1a and Fig. R2-9a. The furnace heater comprises high\ntemperature zone and low temperature zone. During InSe growth in space, the\npre-synthesized InSe polycrystals is first melted in the high temperature zone for 3\nhours. Then, the heater will be moved up at a very slow speed (1.0 mm/h) to ensure\nthe InSe single crystal growth at the low temperature zone.The specific parameters of\nthe resulting crystalline InSe ingot are shown in Fig. R2-9b. A total length of ~95.7\nmmcan bedivided into three parts (A, B, C in Fig. R2-9)as below,\nA) InSe single crystal. The controllable growth procedure ensures the good quality\nof the InSe crystal in part A. In this process, the previously existed pores trapped\nat the boundary of polycrystals in part A will be released and migrated upwards\n(B).\nB) InSe polycrystals formed during the cooling process.At this part, the raw InSe\npolycrystals are heated to melt but without controllable recrystallization. So,\nduring the cooling process, InSe liquid in part B will transform to polycrystalline\nstate during naturally cooling to the ambient temperature of the space station.\nUnder microgravity conditions, the air rising from the bottom zone, combined\nwith the inherently present air in this region, spontaneously coalesces into large\nbubbles due toliquidsurface tension.\nC) Raw InSe polycrystals. The section from 72 mm to 95.7 mm is the region that\nis not heated due to the limited travel distance of the space-based furnace.\nTherefore, inthisregion, gas cannot migrateor accumulate.\nIn contrast, for crystals melted on the ground, gravity causes most of the gas to be\nexpelled to the very top of the quartz tube, so no formed large bubbles are observed.\nTherefore, we can infer that the formation of the big bubble is indeed caused due to\nthe microgravity.Weshould emphasize that this large bubble does not introduce stress\ninto the single-crystal region, but it can serve as the strong evidence of the\nmicrogravity growth process.\nFig. R2-9. Schematic of s-InSe grown in the microgravity condition using the\nBridgman method. a, The high temperature scientific experiment cabinet for\nmicrogravity-growing InSe crystals. b, The specific parameters of the as-grown\ncrystal ingot. c,Thephotooftheas-grown s-InSe ingot.\nQ13: Is the observed mobility enhancement solely due to defect reduction, or could\ncontact engineering or dielectric environment also contribute?\nAnswer-13:Thank you very much foryour professional comments.\nDuring device fabrication, we employ highly insulating 2D h-BN flake as the contact\nlayer between the InSe channel and the highly-doped Si substrate. The dielectric\nconstant of h-BN is as high as 4, which helps to avoid introducing a hysteresis\nwindow due to the surface effects of the dielectric. However, this material does not\nprovide charge carriers for the channel. In existing reports (Adv. Mater., 2018, 30,\n1803690; DOI:10.1002/adma.201803690), the mobility could be enhanced through\nsurface doping processes on the transistor channel or coating techniques. In this work,\nsuch processes were not employed. The channel and electrodes form a pure\nmetal-semiconductor contact, and no additional materials (such as In coating) were\ndeposited on the surface. For precise comparison, the e-InSe based ferroelectric\nsemiconductor field effect transistors (FeSFETs) are also prepared following the same\nfabrication procedures. Fig. R2-10a shows the typical back-gate transfer curves of\ne-InSe and s-InSe based FeSFETs. Clearly, the s-InSe FeSFETs has a larger on/off\nratio by about one order of magnitude (Fig. R2-10b).The mobility of s-InSe FeSFETs\ncan be calculated to be ~195.30 cm2v-1s-1, approximately doubling that of e-InSe\nFeSFETs (~103.86 cm2v-1s-1) (Fig. R2-10c).All three devices electrical properties are\nsummarizedin Table R2-2.\nFig. R2-10. Electrical properties of e-InSe and s-InSe based devices. a, Transfer\ncurves of the transistors under bidirectional V sweeping of s-InSe and e-InSe based\nbg\ndevices. b, On/off ratio curves of the transistors. c, Mobility of corresponding\nback-gated s-InSe ande-InSe FeSFETs.\nQ14: Some figures (e.g., PL spectra and band diagrams) could benefit from clearer\nlabelling and quantitative annotations. Figure 1c-d should be labelled to improve\nreader understanding. All acronyms (e.g., FeSFET, PFM) should defined clearly at\nfirst usefor abroad readership\nAnswer-14:Thank you very much forthese nicesuggestions.\nWe have updated the figures and some descriptions including acronyms in the revised\nmanuscript accordingly.\nPlease note that all major revisions have been marked in red in our revised manuscript\nin an additional PDF version. Simultaneously a supplementary information file has\nalso been provided.\nReviewer#3(Remarks totheAuthor)\nThe authors investigated how the microgravity growth environment affects the growth\nof the vdWs InSe single crystals. They discovered that this unique condition could\neliminate interlayer stacking faults in the materials, which promotes the inherent\nsliding ferroelectricity. As a result, high performance FeSFETs with high carrier\nmobility and clear memory window were demonstrated. Moreover, superlinear\nemission from the microgravity-grown InSe was observed with low excitation\nthresholds of photons.Thetopicis interesting and the experimental results are of good\nquality, which could support their conclusion very well. I would recommend the\narticle forpublication after minorchanges orexplained.\nWe appreciate you very much for your highly evaluating our manuscript. Below we\nwillreply your comments point-by-point.\nQ1: On page 5, line 2, it is inappropriate to claim a single-crystal or polycrystalline\nregion without conducting any characterization first.\nAnswer-1:Thank you very much foryour timelyand critical comments.\nTo address this question, XRD characterizations were performed for the samples\ntaken from thetop and thebottom zonesof space grown InSe ingots.As shown in Fig.\nR3-1, it can be seen that the sample taken at the top zone exhibit polycrystalline\nfeature with all the diffraction peaks corresponding to those of the standard InSe.\nWhile the sample at the bottom zone demonstrates the excellent single crystalline\nfeature along {00l} planes. This result has been added as Fig. S1 in the\nSupplementary Information ofour revised manuscript.\nFig. R3-1. XRD patterns of InSe samples at the top zone and the bottom zone,\nexhibiting polycrystalline (red curve) and single crystalline (blue curve) features,\nrespectively.Thestandard powdered PDF card forInSe isalso shown.\nQ2: For Figure 1b, the authors declared that the microgravity have significant\ndifferences influence on the morphology of the InSe crystals from those grown under\ngravity. Please explained why the microgravity could bring the large bubbles on the\nInSecrystal?\nAnswer-2: Thank you very much for this concern. Your observation regarding the\nlarge bubbleissueis both timely and highly meaningful.\nThe large bubble may represent the typical characteristic of crystal growth under\nmicrogravity condition. As we have described in details in the response to Q4, the\nschematic diagram of crystal growth process in the zone melting furnace on the China\nspace station are shown in Fig. 1a and Fig. R3-2a. The furnace heater comprises high\ntemperature zone and low temperature zone. During InSe growth in space, the\npre-synthesized InSe polycrystals is first melted in the high temperature zone for 3\nhours. Then, the heater will be moved up at a very slow speed (1.0 mm/h) to ensure\nthe InSe single crystal growth at the low temperature zone.The specific parameters of\nthe resulting crystalline InSe ingot are shown in Fig. R3-2b. A total length of ~95.7\nmmcan bedivided into three parts (A, B, C in Fig. R3-2)as below,\nA) InSe single crystal. The controllable growth procedure ensures good quality of\nthe InSe crystal in part A. In this process, the previously existed pores trapped at\ntheboundary ofpolycrystals in partAwillbe released and migrated upwards (B).\nB) InSe polycrystals formed during the cooling process.At this part, the raw InSe\npolycrystals are heated to melt but without controllable recrystallization. So,\nduring the cooling process, InSe liquid in part B will transform to polycrystalline\nstate during naturally cooling to the ambient temperature of the space station.\nUnder microgravity conditions, the air rising from the bottom zone, combined\nwith the inherently present air in this region, spontaneously coalesces into large\nbubbles due toliquidsurface tension.\nC) Raw InSe polycrystals. The section from 72 mm to 95.7 mm is the region that\nis not heated due to the limited travel distance of the space-based furnace.\nTherefore, inthisregion, gas cannot migrateor accumulate.\nIn contrast, for crystals melted on the ground, gravity causes most of the gas to be\nexpelled to the very top of the quartz tube, so no formed large bubbles are observed.\nTherefore, we can infer that the formation of the big bubble is indeed caused due to\nthe microgravity.Weshould emphasize that this large bubble does not introduce stress\ninto the single-crystal region, but it can serve as the strong evidence of the\nmicrogravity growth process.\nFig. R3-2. Schematic of s-InSe grown in the microgravity condition using the\nBridgman method. a, The high temperature scientific experiment cabinet for\nmicrogravity-growing InSe crystals. b, The specific parameters of the as-grown\ncrystal ingot. c,Thephotooftheas-grown s-InSe ingot.\nQ3: For Figure 1c, the manuscript shows “… both crystal ingots present single\ncrystalline…”, how could you determine that they are single crystals just from the\noptical images?\nAnswer-3:Thank you very much forthis critical comment.\nWe are sorry for this irrigorous description, which may be misleading. This\nconclusion is based on our growth method. As shown in Fig. 1a and Fig. R3-2,\nduring space-growth of InSe, we melt the raw InSe polycrystals in the high\ntemperature zone, and then the InSe single crystals will controllable grow in the\nbelow low temperature zone.As a result, InSe crystals can only form at the bottom of\ntheampoule,whilethe upperpart consistsof incompletely melted polycrystals.\nAs confirmation, we have supplemented the XRD results as Fig. S1 in the\nSupplementary Information and revised thetextaccordingly inline9-10, page 5in the\nrevised manuscript.\nQ4: Figure 1f presents the Raman spectra of InSe crystals at different positions. The\nmanuscript does not mention the variation of Raman spectra to the positions.As show\nin the figure, the intensity of Raman peaks from s-InSe is varied for different\nmeasured positions.Please comment thepossiblereason.\nAnswer-4:Thank you very much forthis professional comment.\nWewould liketo point out that intheoriginal manuscript, theRaman spectra were not\nsubjected to uniform baseline processing. After baseline calibration, the observed\ndifferences are primarily located at the position of theA (LO) mode. The appearance\n1g\nor intensity changes of this Raman mode are related to the thicknesses of the flakes.\nTo confirm this argument, we have prepared five more flakes with different\nthicknesses from e-InSe and s-InSe crystals, as shown in Fig. R3-3 and Fig. R3-4,\nrespectively. We can see that the A (LO) mode can be observed in both e-InSe and\n1g\ns-InSeflakes,andthe signal became morepronounced as theirthicknesses decrease.\nThese results have been added into the Supplementary Information (see Fig. S2 and\nFig. S3), and the interpretation has also been added accordingly in the revised\nmanuscript (see line24-26,page 5).\nFig. R3-3. Raman results of e-InSe flakes (F1, F2, F3 and F4) with different\nthicknesses. a, 30.6 nm. b, 20.7 nm. c, 11.4 nm. d, 8.6 nm. i - AFM topography, ii -\nthickness plot,and iii- corresponding Raman spectrum.\nFig. R3-4. Raman results of s-InSe flakes (F1, F2, F3 and F4) with different\nthicknesses. a, 98.0 nm. b, 72.9 nm. c, 11.7 nm. d, 9.5 nm. i - AFM images, ii -\nthickness profiles,and iii-corresponding Raman spectra.\nQ5: In Figure 1h, the authors compared the transmission spectra of e-InSe and s-InSe\nwith different thickness. What is the exact thickness/layer number of these InSe\nnanosheets?\nAnswer-5:Thank you forthis suggestion.\nWe have added the thickness information on the corresponding curve in Fig. 1h,\nwhere the values are mainly calculated based on the interference fringes at the low\nenergy side.\nQ6: Did the authors conduct comparative experiments for the e-InSe and s-InSe in\ncharacterizationof theslidingferroelectricity and FeSFETdevice tests?\nAnswer-6: Yes, for precise comparison, we have prepared the e-InSe based FeSFETs\nby following the same fabrication procedures. Fig. R3-5a shows the typical back-gate\ntransfer curves of e-InSe and s-InSe based FeSFETs. It indicates that the s-InSe\nFeSFETs has a larger on/off ratio by about one order of magnitude (Fig. R3-5b). The\nmobility of s-InSe FeSFETs can be calculated to be ~195.3 cm2v-1s-1, approximately\ndoubling that of e-InSe FeSFETs (~103.86 cm2v-1s-1) (Fig. R3-5c). All electrical\nproperties of devices are summarized in Table R3-1, which is also added to the\nSupplementary Information ofour revised manuscript.\nFig. R3-5. Electrical properties of e-InSe and s-InSe based devices. a, Transfer\ncurves of the transistors under bidirectional V sweeping of s-InSe and e-InSe based\nbg\ndevices. b, On/off ratio curves of the transistors. c, Mobility of corresponding\nback-gated s-InSe (blue)and e-InSe (red) FeSFETs.\nTab.R3-1.Electrical properties of s-InSeande-InSe nanodevices.\nSample On/offratio Mobility (cm2v-1s-1)\n1 106 195.3\ns-InSe 2 106 187.4\n3 105 160.8\n1 105 103.9\ne-InSe 2 105 81.8\n3 105 49.4\nQ7: For the organization of this article, why the photoluminescence spectra\nmeasurement is arranged after the ferroelectricity and FeSFET characterization? The\nemission test is also a characterization for the optical properties of the InSe crystals,\nwhich has a closer connection with the structural and optical properties discussed\nearlierinFigure 2.\nAnswer-7:Thanks alot foryour comment.\nWe totally agree with you that it is better to display all PL results in the optical\ncharacterization part. The reason why we use the current organization is based on the\nsignificance of the systematic photoluminescence (PL) results of s-InSe.Wethink that\nwhile PL can serve as a fundamental characterization method for the optical property\nof the crystals, the interesting results including the superlinear emission in\ndefect-reduced s-InSe also represent a promising application as a near infrared source\nor even lasing device. Therefore, we specifically present and discuss the important PL\nresults after the intrinsic sliding ferroelectricity of s-InSe. We expect this will\ndefinitely broaden the application of s-InSe as a milestone in the ferroelectric\nInSe-based photon-integrated nanodevices.\nQ8: What is the main mechanism bywhich microgravity growth environment reduces\ntheinterlayer stacking faults?\nAnswer-8:Thank you very much forthis comment.\nAs known, the interlayer sliding barrier is extremely low in InSe, so there will be\nabundant randomly distributed stacking faults in the as-prepared crystals, due to the\ncontact stress from the ampoule bottles and buoyancy convection-induced crystal\nnon-uniformity, which will strongly influence the uniformity of the optical and\nelectrical properties of InSe. In contrast, the primary mechanism through which the\nmicrogravity operates is \"detachment growth\" (a process where crystal growth occurs\ndetached from the container walls), which is critical for the enhancement of the\ncrystal quality. Under such condition, no stress is introduced between the container\nand thematerial. In addition, the buoyancy convection-induced crystal non-uniformity\nwill be greatly reduced in space under the microgravity condition, which will also\nresult in bettercrystal quality (stacking defect reduction).\nIn our work, the e-InSe used for optical properties comparison are synchronously\ngrown on Earth following the same operation procedure under the normal gravity\ncondition. Thus, we can infer that the optimized layer stacking-order and resulted\nenhancement of superlinear PL signal in s-InSe can be attributed to the role of\nmicrogravity.\nCurrently, there is a lack of comprehensive studies on 2D vdW materials. Therefore,\nthis work specifically explores how microgravity leads to alterations in the crystal\nstructure of 2D vdW materials, in turn leading to changes in their ferroelectric and\nemissionproperties.\nPlease note that all major revisions have been marked in red in our revised manuscript\nin an additional PDF version. Simultaneously a supplementary information file has\nalso been provided.\nResponse Letter to the Reviewers\nWewould like to thank our reviewers to agree the publication of our manuscript titled\n“Microgravity-activated high-performance van der Waals InSe ferroelectric\nsemiconductor (#NCOMMS-25-72542A)”. In the light of the comments and\nsuggestions from our reviewer #2, we have added some figures and notes in the main\ntext and supplementary materials. For convenience, all changes to our manuscript\n(including themain textand supplementary materials) have beenmarked in red.\nReviewer#2(Remarks totheAuthor)\nThe authors have extensively addressed the concerns. However the following minor\ncomments shouldbe addressed before publication:\n1. Fig R2-1 to Fig R2-10 should be added to SI in appropriate place and reference to\nthese figures must be made in the main text.Authors can add in SI note to add in the\nexplanationfor thefigures. Samegoes forTab. R2-1.\nThanks a lotfor your constructive comments.\nWe have added figures and notes in the main text and supplementary materials. The\ndescriptions or interpretations have been accordingly added into the revised\nmanuscript; e.g., see line20,page5; line20-23, page8; line14-24, page12.\nPlease note that all major revisions have been marked in red in our revised manuscript\nand supplementary information filein additional PDF version.\nResponse Letter to the Reviewers\nWe would like to thank you very much for the high evaluation on our manuscript\ntitled “Microgravity-activated high-performance van der Waals InSe ferroelectric\nsemiconductor (#NCOMMS-25-72542)”.The comments are invaluable for improving\nthe quality of our manuscript. In the light of your comments and suggestions, we have\nchecked and revised our manuscript carefully, including additional experimental\nresults and language improvement. We are convinced that the modifications fully\naddress your comments and agree with all the suggestions made. For your\nconvenience, all changes to our manuscript (including the main text and\nsupplementary materials) have been marked in red for your convenience. Below we\naddress each ofyour concerns point-by-point.\nReviewer#1(Remarks totheAuthor)\nJin, Sui et al. report on the growth of InSe single crystals on the China space station,\nand thus under different microgravity conditions to those present on Earth. The\nproperties of the InSe crystals are compared to those of InSe grown on Earth (e-InSe),\nand higher qualityis overall demonstrated for thespace-InSe (s-InSe).\nThe growth of van der Waals crystals under different microgravity conditions is\nindeed little explored due to the technical difficulties that are implied. From this point\nofview,thegrowth ona space station reported inthis work is noteworthy.\nThe work presented here, however, holds moderate significance to the field of 2D\nmaterials, as such a growth is difficult to be done and the proposed approach can\nhardly become astandard growth approach.\nWe thank you very much for your affirmation on the performance comparison of the\ngrown van derWaals InSe crystals under different microgravity conditions.\nIndeed, the growth on a space station is difficult but noteworthy, since it is becoming\na competitive strategy for developing new materials or exploring novel fundamental\nphysics of materials.As summarized in our manuscript, the growth of materials under\nmicrogravity originated from thelate 1970s, and many typical semiconductors such as\nSi, Ge, indium antimony (InSb) and gallium arsenide (GaAs) have been successfully\ngrown; details see Table R1-1 from Cryst. Res. Technol. 2018, 53, 1700265 (DOI:\n10.1002/crat.201700265). The corresponding comprehensive analyses have confirmed\nthe significantly improved quality of materials under the microgravity growth\ncondition. Furthermore, the International Space Station (ISS) National Laboratory has\nbuilt a website to introduce the significance and progress of crystal growth in space\n(https://issnationallab.org/research-and-science/space-research-overview/research-are\nas/in-space-production-applications/crystal-growth/), significantly accelerated the\nrapid development ofspace material growth and research.\nSpecially, the growth of van der Waals (vdW) layered materials should present much\nmore special advantages, since the weak interlayer vdW forces should be more easily\nmanipulated by microgravity, e.g., to avoid the disordering of the layer stacking\nsequences and even to modulate the lattice parameters. As far as we know, the vdW\nlayered semiconductors including InSe, GeSe and SnSe have (or will be) grown in\nspace, e.g., Adv.Mater.,2025,37,2506506(DOI: 10.1002/adma.202506506).\nWe should emphasize that the vdW-layered InSe semiconductor possesses high\nmobility, suitable bandgap, out-of-plane sliding ferroelectricity and\ntheoretically-predicted fractional quantum ferroelectricity (or in-plane ferroelectricity),\nwhich is benefit for high-performance, low-consumptive photodetectors, in-sensing,\nin-memory computing and even lasing nanodevices. However, the native\nstacking-faults in superplastic and ultra-flexible InSe make it challenging in practical\napplications. Besides the post-annealing process or extrinsic doping techniques, the\nmicrogravity circumstance can provide another strategy for improving the quality of\nvdW-layered InSe crystals.\nWecan alsoinfer that theextensive and systematic research results of materials grown\nin space can provide critical foundation experience and reference for material growth\nwithmanually-established microgravity condition onEarth.\nTab.R1-1\nQ1: As for the quality comparison between e- and s-InSe, the results of Figs. 2, 3 and\n5 would require a larger statistical analysis, and thus repeating the same\nmeasurements on different pieces/flakes of the crystals to ensure the general validity\noftheresults.\nAnswer-1: We appreciate you so much for your key suggestions. Indeed, we have\nperformed extensive comparisons of e- and s-InSe in structure by HRTEM and\nHAADF imaging, electrical property by PFM loops, and optical property by PL\nspectra.All these results point to the statistical conclusion that the quality of s-InSe is\nbetter that that of e-InSe. For your convenience, we list the representative statistical\nanalysis results in thefollowing.\nAdditionalatomic-level characterization ofstacking-faults ine-InSeand s-InSe.\nWe have prepared samples from other four additional bulk crystals, and their\ncorresponding high-resolution transmission electron microscope (HRTEM) and\nhigh-angleannular dark-field (HAADF)images are shown inFig.R1-1andFig.R1-2,\nwhere the S1 and S3 are e-InSe and the S3 and S4 are s-InSe. For e-InSe, the HRTEM\nimage (Fig. R1-1a and Fig. R1-2a; with the selected area electron diffraction/SAED\npattern as the inset) together with the HAADF image (Fig. R1-1b and Fig. R1-2b)\nshow various stacking-faults (as similarly shown in Fig. 2 in the main text). The\nstaggered arrangement between layers and straight line-type SAED patterns can be\nclearly observed. However, for s-InSe (Fig. R1-1c and Fig. R1-2c), the\nstacking-faults are obviously reduced by referring to the clear SAED diffraction spots\nand theuniform HRTEM contrast.The HAADF images in Fig. R1-1d and Fig. R1-2d\nshow the atomic arrangement of the microgravity-grown InSe, from which we can\ninfer that the s-InSe crystal statistically presents the better stacking-style with\nABCABC sequences with less stacking-faults.\nAdditionalevidences fortheintrinsicslidingferroelectricity.\nWe have performed PFM measurements for other s-InSe flakes with different\nthicknesses, i.e., 7.5 nm (Fig. R1-3a), 10.0 nm (Fig. R1-3b), 20.2 nm (Fig. R1-3c),\nand 25.8 nm (Fig. R1-3d), all of which present repeatable hysteresis butterfly-shaped\namplitudeloopsand reversiblephaseloops, evidencing robust ferroelectricity.\nHigh-efficientsuperlinearemission ofs-InSewith lowerthresholds.\nAs shown in Fig. R1-4a, the s-InSe samples present a rather similar and simple PL\nspectral shape, which demonstrates the position-independent uniformity and the\nnarrowly-distributed B-band relevant to the interlayer exciton emission. The\nexcitation power dependent PL spectra of other two s-InSe samples (Fig. R1-4b,c)\nclearly demonstrateidentical findings presented in Fig. 5d.\nFig. R1-1.Additional structure characterizations of e-InSe and s-InSe samples. a,\nb, HRTEM image (a; with SAED pattern as the inset) of e-InSe (S1) and\ncorresponding HAADF image (b). c, d, HRTEM image (c; with SAED pattern as the\ninset)of s-InSe (S2)and corresponding HAADF image (d).The red lines in b,d show\nthe stacking abnormal sequences. The green rectangles in b, d mark the “A”-layers of\ntheABC-stacking style.\nFig. R1-2.Additional structure characterizations of e-InSe and s-InSe samples. a,\nb, HRTEM image (a; with SAED pattern as the inset) of e-InSe (S3) and\ncorresponding HAADF image (b). c, d, HRTEM image (c; with SAED pattern as the\ninset) of s-InSe (S4) and corresponding HAADF image (d). The red lines in b show\nthe stacking abnormal sequences. The green rectangles in b, d mark the A-layers of\ntheABC-stacking style.\nFig. R1-3. Additional PFM characterization of s-InSe flakes with different\nthicknesses. a, 7.5 nm (~3 unit cells/u.c.). b, 10.0 nm (~4 u.c.). c,20.2 nm (~8 u.c.). d,\n25.8 nm (~10 u.c.). i - AFM images, ii - thickness profiles, and iii - corresponding\nPFM amplitudeand phase loops.\nFig. R1-4. The excitation power dependent PL spectra of s-InSe crystals. a, PL\nspectra of different s-InSe flakes. b, c, PL spectra of s-InSe flakes at different\nexcitationpowers from 1mWto 80mWwith alaser spotarea of~0.03 cm2.\nQ2: The PL results are rather strange and controversial. Upon increase of the laser\npower,defect states typically saturate and free exciton states tend todominate. In turn,\ndefect states typically feature a sublinear behavior with power. Here, the authors are\nshowing an opposite behavior, which is in contrast with what typically observed for\nvan der Waals crystals. Furthermore, the laser powers used in this work seem to be\nhuge. The authors are claiming that they are keeping the power below 1 mW with a\nspot size of 5 microns to avoid damages, but are the author sure that this power does\nnot damage InSe? I am wondering if the strange power dependence observed in this\nwork is actually due to thefact that the crystal is being destroyed whilemeasuring it.\nAnswer-2: We totally agree with you that defect emissions generally feature a\nsaturation or sub-linear behavior with power increase. From the results shown in Fig.\n5, we can see that the defect-related C-band seems to have a slightly superlinear\nbehavior at the high excitation power side in e-InSe, but without evident excitation\ndependence in s-InSe. This may suggest a much higher density of defects in e-InSe\nfor efficient emission than in s-InSe. Simultaneously, it needs to point out that in\ne-InSe the C-band is rather broad and even gives an evident sharp peak at ~0.95 eV\n(Fig. 5a) that cannot be observed in s-InSe (Fig. 5b,d), which may suggest that the\ncontribution for C-band is not only from the conventional defect states but also\nprobably from thestacking faults-induced interlayer excitons.\nRegarding the laser power, actually, we only used the power of around 1 mW with a\nspot size of 5 µm for µ-Raman measurements at fast scanning mode. This power\ndensity is on the order of 1 kW/cm². We should point out that the testing time of\nRaman spectra we employed was relatively short, only 10 seconds per curve, and the\ntesting conditions for both bulk e-InSe and s-InSe were consistent. No significant\nchanges between their Raman spectra are observed. Additionally, we repeatedly\nrecord the Raman spectra of e-InSe and s-InSe bulk (Fig. R1-5a,c) and flakes (Fig.\nR1-5b,d) under the same intensity level, and the signals remain stable. Notice that the\nspectra of the flakes show a worse signal-to-noise ratio (SNR) than that of the\ncorresponding bulk states. The A (LO) mode can become more visible in the thin\n1g\nflakes (Fig. R1-5b,d). Considering the stronger (better SNR) Raman signal of s-InSe,\nhalf of the laser power was used for Raman measurements (Fig. R1-5d), where\nsimilar A (LO) mode can be observed as that in e-InSe flakes with a doubled\n1g\nexcitationpower.\nNotice that for excitation-dependent PL measurements, the laser power used is much\nlower, ranging from 1 to 100 mW with a spot area of ~0.03 cm2 (corresponding to\nabout 0.03 – 3 W/cm²). Our results demonstrated that no significant damage was\nobserved on bulk samples under this power range. In response to your concerns, we\nselect another sample and measure its room-temperature PL spectra, as shown in Fig.\nR1-6a. Obviously, the superlinear emission persists within the range of 1 – 80 mW,\nbutthe deviation from super-linearity occurs from 80mW(Fig.R1-6b). Consequently,\nPL tests were performed repeatedly at around 100 mW (Fig. R1-6c), demonstrating a\nslight decrease in PL intensity after 100 mW. This in another way confirms that the\nexcitation power corresponding to the superlinear emission region of the samples is\nreliable. Back to Fig. 5 in the text, the slope of the integrated intensity shows no\nchange in the entire excitation power range, indicating that the laser intensity used in\nthemeasurement has not yet reached thedamage threshold ofthesamples.\nFig.R1-5.Raman spectra of e-InSeands-InSeundervaryinglaserpower.a,b,\nshowtheRamanspectra ofe-InSe bulk and e-InSe thinflakes,respectively.c,d,show\ntheRaman spectra of s-InSebulk and s-InSe thinflakes,respectively.All spectra were\nacquired from different sampleregions, with a laser spotareaof ~3 μm2.\nFig. R1-6. Excitation-dependent PL of s-InSe. a, PL spectra at different excitation\npowers. b, The intensity ratio of A-peak/C-band. c, PL spectra of s-InSe before and\nafter theexcitation powerof100mWwith alaser spotarea of0.03cm2.\nQ3: The experimental section of this manuscript is not detailed enough, especially the\nsection related tothegrowth.Thegrowth process should bediscussed indetail.\nAnswer-3: Thank you so much for this precious suggestion. We have added the\ngrowth process of InSe on the space station in details in the Supplementary\nInformation, which has also been referred to in the main text. For your convenience,\nweprovide thegrowth process as below.\nThegrowth ofInSe onthespace stationincludes two parts.\nI) The pre-synthesis of the polycrstalline InSe ingot on Earth. 6N high-purity In and\nSe elements as raw materials were mixed in a stoichiometric ratio of 0.52 : 0.48.\nThese mixtures were sealed into a Φ20 mm highly cleaned quartz ampoule,\nvacuumed to ~10−3 Pa and then sintered adequately in a rocking furnace under 800°C\nat a rate of 30 r/min for half an hour. After the mixed alloy was naturally cooled to\nroom temperature, InSe polycrystals were obtained, as shownin Fig.R1-7a.\nII) Space growth of InSe crystal.The synthesized InSe polycrystal ingot was cut into\na segment with a length of ~120 mm and resealed into another brand-new quartz\nampoule (Fig. R1-7b). It was worth noting that the ingot must be fastened and\nimmovable to ensure the safety of space launch transportation of samples. Then, the\nquartz ampoule containing the InSe polycrystal ingot was fixed into a standardAl O\n2 3\ntube (Fig. R1-7c). The schematic diagram of InSe growth on the space station is\nshown in Fig. R1-8a. The furnace holds a narrow high temperature zone ~10 mm in\nheight. The temperature profile along the vertical direction is illustrated in Fig.\nR1-8b. During space growth, the Al O tube was moved into the high-temperature\n2 3\nmaterials science experimental apparatus (furnace) and fixed to one of the working\npositions by an astronaut. The furnace was controlled at 715°C and the temperature\ngradient for crystal growth was ~30°C/cm. After the polycrystals were melted and\nsoaked for 3 hours among the high temperature region, the re-crystallization of InSe\ncrystal took place at the low temperature zone with the furnace moving up at a speed\nof 1.0 mm/hour. After the space growth of InSe finished, the furnace was cooled to\nroom temperature in 2hours.\nFig. R1-7. Pre-synthesis of InSe polycrystals grown on Earth. a, The photo of\nsynthesized InSe polycrystalline ingot in the quartz ampoule. b, Dissected InSe\npolycrystalline ingot resealed into a new quartz ampoule. c, A standard Al O tube\n2 3\ncontaining thequartz ampoulewith polycrystallineInSe ingot for growth ofs-InSe.\nFig. R1-8. Schematic of s-InSe grown on the space sation under microgravity\ncondition using the Bridgman method (a). Right panel is the temperature\ngradientprofile(b).\nQ4: The figures are not always clear. First, all figure should contain a label on top of\nthee-InSe and s-InSe plotsto immediately distinguish them.\nAnswer-4:Wesincerely appreciate you for thisnicesuggestion.\nWe have updated all figures with mandatory revisions in the revised version of our\nmanuscript.\nQ5: Fig. 1: the text in the top panels is big, while that in the bottom panels is very\nsmalland sometimes difficultto read.\nAnswer-5:Thank you very much foryour helpful suggestion.\nWe have optimized this figure, as shown in the revised manuscript. Simultaneously,\nwealso added thecurve of thetemperature gradient as asub-panelin Fig. 1a.\nQ6: The Raman results are not discussed well as it is not motivated why the s-InSe\nshows theA (LO) modewhilethe e-InSe does not.\n1g\nAnswer-6:Thank you very much forthis comment.\nInterestingly, the A (LO) mode can only be observed in thinned InSe including\n1g\ns-InSe and e-InSe flakes, but it gradually disappears in bulk InSe. As a confirmation,\nfive more flakes with different thicknesses are exfoliated from both e-InSe and s-InSe\ncrystals. The detailed Raman spectra (Fig. R1-9 and Fig. R1-10) demonstrate that the\nA (LO) mode can be clearly observed in both e-InSe and s-InSe thinner flakes, but it\n1g\nbecomes less pronounced as thethickness increases.\nThis interpretation has also been added into the revised manuscript; please see line\n22-24,page 5.\nFig. R1-9. Raman results of e-InSe flakes (F1, F2, F3 and F4) with different\nthicknesses. a, 30.6 nm. b, 20.7 nm. c, 11.4 nm. d, 8.6 nm. i - AFM topography, ii -\nthickness plot,and iii- corresponding Raman spectrum.\nFig. R1-10. Raman results of s-InSe flakes (F1, F2, F3 and F4) with different\nthicknesses. a, 98.0 nm. b, 72.9 nm. c, 11.7 nm. d, 9.5 nm. i - AFM topography, ii -\nthickness plot,and iii- corresponding Raman spectrum.\nQ7: Fig. 5: The excitation power range in panels c-d should be specified. In panel g,\nthemeaning of intensityratio should bemade explicit.\nAnswer-7:Thank you very much foryour valuablecomments and suggestions.\nWehave addedexcitationpower information together with corresponding descriptions\\inthe revised manuscript.\nRegarding the intensity ratio of the main peakAand the defect-related C-band in Fig.\n5g, we think it can unveil the competition of carrier recombination between these two\ntotally different emission origins, and more effectively reflects the behavior of peakA\nwhen comparing the results between s-InSe and e-InSe. For instance, the main\nemission peakApredominates in s-InSe at the extremely low excitation level of ~0.2\nW/cm2, while the critical point is ~2W/cm2 for e-InSe.This suggests the much higher\nemission efficient of the main peak A in s-InSe. Simultaneously, it can demonstrate\nthat with excitation power increase, the main peak A of s-InSe can be enhanced by\none order of magnitude than that of e-InSe possibly due to the annihilation of defects\nins-InSe, which is much better than reports (Nano Lett.2016,16,3221−3229).\nQ8: From the pointof viewofthetext, thelanguage shouldbechecked.\nAnswer-8:Weare truly grateful to you forthis comment.\nWe have carefully revised our text and try our best to polish the language. We think\ntherevised version should havea remarkable improvement and a betterreadability.\nQ9: From the point of view of the references, the number of works cited here is\nextremely low. InSe has attracted interest for a variety of reasons, including its\nexcellent transport properties, its tunable bandgap with layer number, ferroelectricity,\nand so on. Techniques to modify its properties have been developed, such as strain or\nion bombardments. It has also gained interest for the creation of novel\nheterostructures, if coupled to graphene or other 2Dsemiconductors such as GaSe and\ntransition metal dichalcogenides, leading to the formation of twist-independent\ninterlayer excitons or to efficient type-I heterostructures. The oxidation properties of\nInSe have also been widely investigated through optical studies, clarifying the\npresence of defects. All these studies show the potential interest of this material and\nmotivate future studies. However, none of these topics and related works are cited in\nthe manuscript. Here are some related references (and even more could be found by\nsearching abit).\nhttps: //iopscience.iop.org/article/10.1088/1361-6528/aa749e\n(Fast, multicolor photodetection with graphene-contacted p-GaSe/n-InSe van der\nWaals heterostructures)\nhttps: //pmc.ncbi.nlm.nih.gov/articles/PMC4065344/\n(Tuningthebandgap ofexfoliated InSe nanosheets byquantum confinement)\nhttps: //www.nature.com/articles/srep39619\n(The direct-to-indirect band gap crossover in two-dimensional van der Waals Indium\nSelenidecrystals)\nhttps: //pmc.ncbi.nlm.nih.gov/articles/PMC4768130/\n(High broad‐band photoresponsivity of mechanically formed InSe–graphene van der\nWaals heterostructures)\nhttps: //pubs.acs.org/doi/10.1021/acsnano.1c09844\n(Room-temperature near-infrared excitonic lasing from mechanically exfoliated InSe\nmicroflake)\nhttps: //doi.org/10.1021/acsami.7b17247\n(Largely tunable band structures offew-layer InSebyuniaxial strain)\nhttps: //advanced.onlinelibrary.wiley.com/doi/full/10.1002/adom.202000828\n(Enhanced optical emission from 2DInSe bent onto Si-pillars)\nhttps: //www.mdpi.com/1420-3049/25/11/2526\n(The interaction of hydrogen with thevan derWaals crystal γ-InSe)\nhttps: //doi.org/10.1021/acsnano.2c07394\n(Thickness- and twist-angle-dependent interlayer excitons in metal monochalcogenide\nheterostructures)\nhttps: //www.nature.com/articles/s41563-019-0601-3\n(Design of van derWaals interfaces for broad-spectrum optoelectronics)\nhttps: //www.nature.com/articles/s41467-022-31605-9\n(Light sources withbias tunable spectrum based onvan derWaals interface transistors)\nhttps: //pubs.acs.org/doi/full/10.1021/acs.nanolett.4c04252\n(Giant light emission enhancement in strain-engineered InSe/MS (M = Mo orW) van\n2\nderWaalsHeterostructures)\nhttps: //iopscience.iop.org/article/10.1088/2053-1583/aa61e0/meta\n(Engineering p–n junctions and bandgap tuning of InSe nanolayers by controlled\noxidation)\nAnswer-9: We would like to thank you very much for these helpful references. We\nhave carefully studied them. They are focusing on either the excellent transport\nproperties, tunable bandgap with layer number, emission properties, ferroelectricity or\nheterostructures of InSe, which can improve the width and depth of our manuscript.\nThus, we have cited them in the introduction and result parts together with\ncorresponding descriptions and discussions, e.g., see Refs. 15-27 in line 19-25, page 3\nand in line5-6, page 12in therevised manuscript.\nOverall, while this manuscript reports interesting results on the improvement of the\nInSe properties upon growth in different microgravity conditions. Its applicability is\nhowever restricted. Furthermore, the quality improvement on the properties of the\nmaterial lacks some statistics and has not been demonstrated for exfoliated few layers\nof InSe, while InSe has attracted interest especially in its 2D form. The results here\nreported would thus bemore suitablefor a morespecialized journal.\nAnswer: Based on the detailed point-by-point reply to your comments by providing\ncomprehensive statistic results, including structural, optical and electrical ones\ntogether with the corresponding interpretations and discussions, we think we have\nfully addressed all the issues or concerns raised by you. Considering the high-quality\nvdW InSe crystal and its high performance of resulted devices, which may popularize\nthegrowth strategy in space oronEarth with simulated microgravity environment and,\nmore importantly, push the applications of InSe-based devices in photon-integrated\nin-memory computing nanodevices, we think the revised manuscript presents\nimportant advances of significance to specialists within material, physic, applied, and\nengineering sciences that are complied with the aims and scope of Nature\nCommunications,and thus deserves publication in it.\nPlease note that all major revisions have been marked in red in our revised manuscript\nin an additional PDF version. Simultaneously a supplementary information file has\nalso been provided.\nReviewer#2(Remarks totheAuthor)\nThis manuscript presents a compelling study on the growth of high-quality γ-InSe\nsingle crystals under microgravity conditions aboard the China Space Station,\ndemonstrating that the absence of gravitational forces significantly reduces stacking\nfaults and activates intrinsic sliding ferroelectricity. Through atomic-resolution\nimaging and piezoresponse force microscopy, the authors confirm improved crystal\nuniformity and robust ferroelectric behavior without the need for doping or annealing.\nDevices fabricated from microgravity-grown InSe exhibit enhanced electrical\nperformance, including high carrier mobility and large memory windows, while\nphotoluminescence measurements reveal superlinear emission with lower excitation\nthresholds, indicating superior optoelectronic properties. These findings suggest that\nmicrogravity offers a promising route for synthesizing defect-free van der Waals\nsemiconductors with potential applications in next-generation in-memory and\nin-sensor computing technologies. However following comments should be\nconsidered for revision before any consideration for publication.\nWe appreciate you very much for your highly evaluating our manuscript. Below we\nwillreply your comments orconcerns point-by-point.\nQ1: How does the microgravity-grown InSe compare to other defect-reduction\nstrategies (e.g., annealing, doping) interms ofscalability and reproducibility?\nAnswer-1:Thank you somuch for your comments.\nWith the advancement of space station technology, the process of microgravity-grown\ntwo-dimensional (2D) materials including van der Waals (vdW) layered\nsemiconductors becomes increasingly mature, and more and more variety of 2D\nmaterials have been grown in space station, greatly promoting the development of\nspace material growth and the material growth under microgravity (actual or\nsimulated ones). For instance, our research group mainly focuses on the space-growth\nof (doped) InSe and GeSe vdW-layered materials. As far as we know, other research\ngroups are successively conducting studies on space-grown GaSe, and the\nthermoelectric SnSe is being considered to grow in space from the project list of the\nChinaspace station.\nTaking InSe as an example, we find that the optimized post-annealing process, the\nspecial elemental doping strategy (e.g., yttrium/Y and dysprosium/Dy) and the\nmicrogravity-growth condition can reach the goal of defect-reduction. However, there\nare someessential differences among thesestrategies.\nVia post-annealing process, we have obtained high-quality InSe samples, based on\nwhich the intrinsic sliding ferroelectricity can be evidenced from the hysteresis loops\nby piezoresponse force microscope (PFM), and the intrinsic superlinear emission can\nalso be presented. However, to obtain cracked-free flat and large area samples by this\nprocedure isdifficult, although thereproducibilitycan beguaranteed.\nThe elemental doping (e.g., Y-doping) strategy can enhance the quality, especially the\nlayer rigidity of InSe with flat and straight surface, demonstrating good scalability,\nalthough the growth process is more complicated. This product benefits for the\nmeasurements of sliding ferroelectricity, and is also helpful for the fabrication of\nhigh-density nanodevice arrays. However, due to the low interlayer sliding barrier, the\ntiny interlayer pre-sliding naturally exists with a long layer periodicity in Y-doped\nInSe, which may influence the transport performance of nanodevices, e.g., the\nmobility.\nFor microgravity-grown InSe involved in this work, existing results demonstrate the\noutstanding scalability and reproducibility, except for the special growth condition.\nBy now, our group have successfully grown two batches of InSe single-crystalline\ningots in China space station. Both show great reproducibility in the crystal quality\nand the fundamental properties. With rapidly development of the space science\nresearch and the in-depth understanding of the crystal growth under microgravity\ncondition, the scalability of space growth or microgravity-growth of crystals will be\nguaranteed a lot.\nIt is interesting to point out that there are essential differences regarding the emission\nproperty among the annealed, Y-doped, microgravity-grown InSe, as shown in Fig.\nR2-1. In order to amplify the weak defect-related signals at low energy side, the\nspectra are shown in a single (vertical) logarithm scale. The s-InSe involved in our\ncurrent work can showsuperlinear emissions ofboth intralayer and interlayer excitons.\nThe annealed InSe (green curve) shows excellent (superlinear) emission of intralayer\nexcitons (peak A) but with relatively low interlayer excitonic emission (peak B). The\nY-doped InSe(red curve) shows interlayer and interlayer excitonicemissions (peaksA\nand B), but they both are rather weak as compared to that of annealed and\nmicrogravity-grown InSe, and even weakerthan the defect-related C-band.\nFig. R2-1. Room temperature PL spectra of s-InSe (blue), annealed InSe (green)\nandY-doped InSe(red).Theexcitationwavelength is 405nm.\nQ2: Can the authors clarify the broader implications of this work for space-based\nmaterials synthesis beyond InSe?\nAnswer-2:Thanks alot foryour constructivecomment.\nConsidering the facts that high-quality vdW InSe crystal and resulted high\nperformance devices are obtained, we think our work may not only popularize the\ngrowth strategy in space or on Earth with simulated microgravity environment, but\nalso pave up the way of in-depth understanding the fundamental physics of InSe\ncrystals with high-quality, push its broad applications in electric- and\nphoton-integrated in-memory computing chips.\nWe should point out that prior to this, various alloys and semiconductors such as Si,\nGe, InSb and GaAs have been successfully grown in space; see Table R2-1 from\nCryst. Res. Technol. 2018, 53, 1700265 (DOI: 10.1002/crat.201700265), and the\ncorresponding analyses have confirmed the significant improvement of material\nquality under microgravity.The International Space Station (ISS) National Laboratory\nalso specifically introduce the significance and progress of crystal growth in space\n(https://issnationallab.org/research-and-science/space-research-overview/research-are\nas/in-space-production-applications/crystal-growth/), significantly accelerated the\nrapid development ofspace material growth and research.\nHowever, no documented researches are accessible for 2D vdW-layered\nsemiconductors in this realm. Generally, vdW-layered materials should have more\nspecial advantages for growing in space, since the weak interlayer vdW forces can be\nmore easily manipulated by microgravity condition, e.g., to avoid the disordering of\nthe layer stacking sequences and even to modulate the lattice parameters.As far as we\nknow,besides InSe (Adv.Mater., 2025, 37, 2506506; DOI: 10.1002/adma.202506506),\nother vdW semiconductors such as GeSe and SnSe are being considered to grow on\nChina space station. We should emphasize that the vdW InSe semiconductor\npossesses high mobility, suitable bandgap, out-of-plane sliding ferroelectricity and\ntheoretically-predicted fractional quantum ferroelectricity (or in-plane ferroelectricity),\nwhich is benefit for high-performance, low-consumptive photodetectors, in-sensing,\nin-memory computing and even lasing nanodevices. However, the native\nstacking-faults in superplastic and ultra-flexible InSe limit its practical application.\nBesides the post-annealing or extrinsic doping techniques, the microgravity growth\ncan provideadditional strategy for improving thequality ofInSecrystals.\nThus, our work can offer a valuable reference regarding the feasibility and potential\napplications of growing other vdW materials in space. In addition, the extensive and\nsystematic research results of space-grown InSe can provide experience and reference\nformaterial growth under manually-established microgravity condition onEarth.\nTab.R2-1\nQ3: Were there any control experiments to isolate the effect of microgravity from\nothervariables (e.g., ampouledesign, thermal gradients)?\nAnswer-3:Thank you very much foryour professional comments.\nWe should point out that the growth conditions including growth parameters are fully\nthe same but for the microgravity in space. This can absolutely exclude the other\npotential factors. For your convenience, we provide the growth process in details\nbelow.\nI) The pre-synthesis of the polycrstalline InSe ingot on Earth. 6N high-purity In and\nSe elements as raw materials were mixed in a stoichiometric ratio of 0.52 : 0.48.\nThese mixtureswere sealed into aΦ20mmhighly cleaned quartz ampoule,vacuumed\nto ~10−3 Pa and then sintered adequately in a rocking furnace under 800°C at a rate of\n30 r/min for half an hour. After the mixed alloy was naturally cooled to room\ntemperature, InSepolycrystals were obtained, as shown in Fig.R2-2a.\nII) Space growth of InSe crystals. The synthesized InSe polycrystalline ingot was cut\ninto a segment with a length of ~120 mm and resealed into another brand-new quartz\nampoule (Fig. R2-2b). It was worth noting that the ingot must be fastened and\nimmovable to ensure the safety of space launch transportation of samples. Then, the\nquartz ampoule containing the InSe polycrystal ingot was fixed into a standard Al O\n2 3\ntube (Fig. R2-2c). The schematic diagram of InSe crystal growth on the space station\nis shownin Fig.R2-3a.The furnace holdsa narrow high temperature zoneof ~10mm\nin height. The temperature profile along the vertical direction is illustrated in Fig.\nR2-3b. During the space growth, theAl O tube was moved into the high-temperature\n2 3\nmaterials science experimental apparatus (furnace) and fixed to one of the working\npositions by an astronaut. The furnace was controlled at 715°C and the temperature\ngradient for crystal growth was ~30°C/cm. After the polycrystals were melted and\nsoaked for 3 hours among the high temperature region, the re-crystallization of InSe\ncrystal took place at the low temperature zone with the furnace moving up at a speed\nof 1.0 mm/hour. After the space growth of InSe finished, the furnace was cooled to\nroom temperature in 2hours.\nFig. R2-2. Pre-synthesis of polycrystalline InSe ingot on Earth. a, The photo of\nsynthesized polycrystalline InSe ingot inside the quartz ampoule. b, Dissected\npolycrystalline InSe ingot resealed into a new one. c, A standard Al O tube\n2 3\ncontaining the quartz ampoule with polycrystalline InSe ingot for space growth of\nsingle crystallineInSe.\nFig. R2-3. Schematic of s-InSe grown on the space station under microgravity\ncondition using the Bridgman method (a). Right panel is the temperature\ngradientprofile(b).\nQ4: How many samples were grown in space vs. on Earth, and was there statistical\nanalysis to support theclaims ofdefect reduction and performance enhancement?\nAnswer-4:Thank you very much forthis question.\nThe growth on a space station is difficult but noteworthy, since it is becoming a\ncompetitive strategy for developing new materials or exploring novel fundamental\nphysics of materials. The growth of materials under microgravity originated from the\nlate 1970s, and many typical semiconductors such as Si, Ge, indium antimony (InSb),\ngallium arsenide (GaAs), etc have been successfully grown. The corresponding\ncomprehensive analyses have confirmed the significantly improved quality of\nmaterials under the microgravity growth condition (Cryst. Res. Technol. 2018, 53,\n1700265;DOI: 10.1002/crat.201700265).\nBy now,we have obtained two batches of s-InSe samples including undoped (intrinsic)\nand specifically Bi-doped s-InSe, together with at least five matching batches of\nintrinsic and Bi-doped e-InSe. Currently, we have already finished the matching\nexperiments of Dy- and Er-doped InSe growth on Earth, which will be grown inspace\nin the near future. The reason of doping is to manipulate the carrier mobility,\nthermoelectric property, or special emission wavelengths of s-InSe. As discussed\npreviously in Q1, different growth strategies can obtain InSe with distinct physical\nproperties. Our systematical results on lots of intrinsic s-InSe flakes via\nmicrostructure analysis, optical andelectrical characterizations support ourconclusion\nthat the microgravity can effectively optimize the native stacking-faults and enhance\nthe crystal quality of InSe. For your convenience, we summarize the PL spectra of\nintrinsic s-InSe measured at different conditions, as shown in Fig. R2-4.As shown in\nFig. R2-4a, different s-InSe flakes present a rather similar and simple PL spectral\nshape, especially the position-independent uniform and narrowly-distributed B-band\nrelevant to theinterlayer exciton emission.The excitationpower dependent PLspectra\nof different s-InSe flakes (Fig. R2-4b and Fig. R2-4c) show similar results, also\naligning with that (superlinear emissionsofpeaksAand B) in Fig. 5inourmanuscript.\nAdditional statistical analyses to support the improvement come from a comparative\nstudy ofthree devices based one-InSe ands-InSe viatheidentical fabricating process,\nofwhich the key electrical parameters are summarized inTable R2-2.\nFig. R2-4. Excitation power dependent PL spectra of s-InSe. a, PL spectra of\ndifferent s-InSe flakes. b, c, PL spectra of s-InSe flakes at different excitation powers\nfrom 1mWto80mWwith a laser spot area of~0.03 cm2.\nTab.R2-2.Electrical properties of s-InSeande-InSe nanodevices.\nSample On/offratio Mobility(cm2v-1s-1)\n1 106 195.3\ns-InSe 2 106 187.4\n3 105 160.8\n1 105 103.9\ne-InSe 2 105 81.8\n3 105 49.4\nQ5: PFM measurements show ferroelectricity—how do the authors rule out\nelectrostaticorelectrochemical artifacts, especially in such thinflakes?\nAnswer-5:Weare grateful to you for thisprofessional comment.\nIn our work, dual amplitude resonance tracking (DART)-PFM mode on a commercial\nscanning probe microscopy (SPM) system (Asylum Research Cypher, Oxford, UK)\nwas used to ensure strong signal-to-noise ratio. During PFM measurements, we have\ncalibrated the vertical spring constant (k) and the inverse optical lever sensitivity\n(InvOLS) of the probe to reduce the electrostatic contribution in PFM measurements.\nTo exclude the possible artifacts in PFM measurements and evidence the intrinsic\nferroelectricity of s-InSe , different testing conditions are adopted, including changing\nthe V (Fig. 3b and Fig. R2-5) and repeating the PFM measurements on flakes with\ndc\ndifferent thicknesses (Fig. R2-6). Besides Fig. 3, Fig. R2-5 shows the additional\nV -dependent PFM results of the s-InSe flake with thickness of ~25.4 nm, which\ndc\ndemonstrates clear, repeatable amplitude and phase loops with sweeping V above 6\ndc\nV, while no ferroelectric hysteresis loops at low voltage (below the coercive field),\nverifying the ferroelectric feature of s-InSe. It is a critical way to rule out the\nelectrostatic effect. These results have been added to the Supplementary Information\nof our revised manuscript. Further, domain writing at the LithoPFM mode of the\nAsylum Research software with reverse DC biases (V = ±8 V) in Fig. 2d also rules\ndc\nout the electrostatic or electrochemical artifacts and proofs the ferroelectricity in\ns-InSe.\nFig. R2-5. PFM results of s-InSe. a, AFM image. b, The thickness plot giving a\nthickness of ~25.4 nm (~30 layers). c, d, A series of local PFM amplitude (c) and\nphase(d) loopsat different V .\ndc\nFig. R2-6. Additional PFM characterization of s-InSe flakes with different\nthicknesses. a, 7.5 nm. b, 10.0 nm. c, 20.2 nm. d, 25.8 nm. i - AFM topography\nimages, ii - thickness profiles, and iii - corresponding PFM amplitude and phase\nloops.\nQ6: Authors must clearly differentiate background response from the\npiezo/ferroelectricity from the samples. Refer to recent publications: https:\n//pubs.rsc.org/en/content/articlelanding/2025/nh/d4nh00580e\nAnswer-6:Weappreciate you very much forthis important comment.\nWe have added relevant discussion to the revised version of our manuscript; please\nsee the last paragraph, page 7. At the same time, we have also cited relevant\nreferences including Nanoscale Horiz. 2025, 10, 987-999 (Doi:10.1039/d4nh00580e),\nwhere it indicated that employing a cantilever with higher stiffness and greater length\ncan further reduce the electrostatic contribution in PFM measurements. This is\nbecause the electrostatic contribution is inversely proportional to the stiffness of the\ncantilever, and it is known that a larger tip length can attenuate the capacitive\ncoupling between the tip and the sample surface. This is a highly significant issue.\nMeanwhile, we note that the PFM measurements were done using SCM-PIT-V2\n(Bruker). When we use an Oxford Instruments Asylum Research Cypher system, the\nsame type of calibration is essential. This includes calibrating the vertical spring\nconstant (k) and the inverse optical lever sensitivity (InvOLS) of the probe. During\nour testing, we have calibrated the true deflection of the cantilever and the force\naccording to theinstrument's manual, thereby eliminatingthepotential interferences.\nQ7: PFM hysteresis graph appears very noisy and is taken at high applied voltage. It\nwould be helpful to discuss possible non-piezoelectric effects in PFM signal with\nreferences.\nAnswer-7: Thank you very much for this insightful and absolutely correct\nobservation.\nWe totally agree with you that under high DC biases, non-intrinsic piezoelectric\nsignals may be introduced, e.g., originating from effects such as electrostatic\ninteractions, electrostriction, and ion migration. Regarding your concerns, we have\nsupplemented relevant discussions on page 8 in the revised manuscript and cited\nsupportable literatures (Refs. 31, 33, 44) to analyze the potential non-piezoelectric\ncontributions under high electric fields and their impact on hysteresis loop shape and\nnoise.\nFurthermore, as you highlighted the importance of experimental validation, we would\nlike to clarify that our experimental section has already included systematical PFM\nmeasurements on samples with different thicknesses (Fig. R2-6) under different DC\nvoltages (Fig. R2-5), which rules out the non-intrinsic piezoelectric signals. Further,\ndomain writing at the LithoPFM mode of the Asylum Research software with reverse\nDC biases (V = ±8 V) in Fig. 2d can also rule out the electrostatic or electrochemical\ndc\nartifacts and proofs theferroelectricity in s-InSe.\nThis relevant explanation and corresponding figure captions have been\nadded/emphasized in line 16-18, page 8 in the revised main text and Supplementary\nInformation.\nQ8: How does the piezo magnitude vary with layer number of InSe? Is there any\ndifferencebetween e-InSe and s-InSe?\nAnswer-8:Thank you very much forthis important comment.\nYes, the piezo magnitude varies with the layer number of InSe. However, it is\ninteresting to mention that the value represented by the effective d seemingly\n33\nincreases to a saturation with the increase of layer number (from about 3 to 10 unit\ncells) in s-InSe, but it is opposite in rare earth yttrium (Y)-doped InSe (from about 4\nto48unit cells), as shown in Fig. R2-7.\nNotice that to directly detect the intrinsic ferroelectricity in e-InSe is often a challenge\ndue to the high density of natural stacking-faults in this material. These native defects\ncan mask or disrupt the long-range order necessary for observing clear ferroelectric\nsignatures. Therefore, we only compared the layer number dependence of the piezo\nmagnitude in Y-doped InSe (Fig. R2-7a) and s-InSe (Fig. R2-7b), whose\nferroelectricity was explicitly demonstrated.\nFig. R2-7.The piezo magnitude results ofY-doped InSe and s-InSe with different\nthicknesses.a,ForY-doped InSe. b,For s-InSe.\nQ9: Authors should depict piezo response from multiple layers including bulk\nsamples than just showing one particular layer, to confirm that s-InSe retain\npiezoelectricity although out.\nAnswer-9:Weappreciate you for thiscomment.\nFollowing your suggestions, we carried out additional PFM measurements on s-InSe\nwith different thicknesses. As shown in Fig. R2-6, clear hysteresis loops can be\nobserved in four other s-InSe flakes with different thicknesses of 7.5nm (Fig. R2-6a),\n10.0nm(Fig.R2-6b), 20.2nm (Fig.R2-6c), and 25.8nm (Fig.R2-6d).\nQ10: The PL enhancement is attributed to defect reduction—could strain or other\nmicrogravity-induced effects also play arole?\nAnswer-10:Thank you forthis concern.\nAs known, the interlayer sliding barrier is extremely low in InSe, so there will be\nabundant randomly distributed stacking-faults in the as-prepared crystals by the\nBridgman method, due to the contact stress from the ampoule bottles and buoyancy\nconvection-induced crystal non-uniformity, which will strongly influence the\nuniformity of the optical and electrical properties of InSe. In contrast, the primary\nmechanism through which the microgravity operates is \"detachment growth\" (a\nprocess where crystal growth occurs detached from the container walls), which is\ncritical for the enhancement of the crystal quality. Under such conditions, no stress is\nintroduced between the container and the material. In addition, the buoyancy\nconvection-induced crystal non-uniformity will be greatly reduced in space under the\nmicrogravity condition, which will also result in better crystal quality (defect\nreduction).\nIn our work, the e-InSe used for optical property comparison are synchronously\ngrown on Earth following the same operation procedure under the normal gravity\ncondition. Thus, we can infer that the PL enhancement in s-InSe can be attributed to\ntheroleof microgravity.\nCurrently, there is a lack of comprehensive studies on 2D vdW materials. Therefore,\nthis work specifically explores how microgravity leads to alterations in the crystal\nstructure of 2D vdW materials, in turn leading to changes in their ferroelectric and\nemissionproperties.\nQ11: Authors should consider time resolved PL and/or Pump-probe measurements to\nto confirm exciton lifetimes and recombination pathways in addition to providing\nmoreinsights into theorigin ofPLdynamics.\nAnswer-11:Thank you very muchfor this suggestion.\nFollowing your suggestions, we have performed time-resolved PL (TR-PL)\nmeasurements on e-InSe and s-InSe flakes with pulsed 405 nm as the excitation\nsource. Fig. R2-8 shows the four PL decay curves for peaks A (intralayer) and B\n(interlayer) of e-InSe and s-InSe (in a semi-logarithm scale). We can see that all\ncurves are similar and consist of at least two distinguishable decay processes. The fit\nprocedure by a double-exponential decay function gives two time constants for each\ncurve. As reported previously (e.g., see Nat. Commun. 2023, 14, 36; DOI:\n10.1038/s41467-022-35490-0), the slow component of about 2~3 ns is related to the\ncarrier lifetime of spontaneous emission in InSe, including the intralayer and\ninterlayer excitons. However,we shouldemphasizethat our InSeincluding e-InSe and\ns-InSe can give superlinear emission at a rather low excitation power density of ~1\nW/cm2, less than that of TR-PL measurements. Considering the fact that the fast time\nconstant is almost the same for all curves, i.e., ~0.33 ns, and is by almost one order of\nmagnitude shorter than the slow one, we can attribute the fast process to the\nsuperlinear (or amplified spontaneous and even lasing) emission of both intralayer\nand interlayer excitons,as observed inthe steady-state PLresults.\nThen, we focus on the slow time component, which is related to the spontaneous\nemission process of interlayer and intralayer excitons. It is clear to see that the slow\ncomponent of both peaks A and B in e-InSe (~2.4 ns and ~2.3 ns, respectively) is\nslightly shorter than that of s-InSe (~3.2 ns and ~2.9 ns, respectively). The short\nlifetime of carriers for spontaneous emission in e-InSe may due to the existence of\nmore defects including the interlayer stacking-faults, which can trap the carrier for\ndefect emission or non-radiation recombination, compared to that of s-InSe. This in\nanother way can support thehigher-quality ofs-InSethan e-InSe.\nFig. R2-8. TR-PL decay curves corresponding to the intralayer (A at ~1.23 eV)\nand interlayer (B at ~1.17 eV) exciton emission positions in e-InSe and s-InSe.\nThe green curves are the fit results of a double-exponential decay function, which\ngives thefast and slowtimeconstants, as separately shown onthepanel.\nQ12: The manuscript notes larger bubbles in s-InSe. Could these bubbles introduce\nlocal strain or affect electronic properties?\nAnswer-12: Thank you very much for this concern. Your observation regarding the\nlarge bubbleissueis both timely and highly meaningful.\nThe large bubble may represent the typical characteristic of crystal growth under\nmicrogravity condition. As we have described in details in the response to Q4, the\nschematic diagram of crystal growth process in the zone melting furnace on the China\nspace station are shown in Fig. 1a and Fig. R2-9a. The furnace heater comprises high\ntemperature zone and low temperature zone. During InSe growth in space, the\npre-synthesized InSe polycrystals is first melted in the high temperature zone for 3\nhours. Then, the heater will be moved up at a very slow speed (1.0 mm/h) to ensure\nthe InSe single crystal growth at the low temperature zone.The specific parameters of\nthe resulting crystalline InSe ingot are shown in Fig. R2-9b. A total length of ~95.7\nmmcan bedivided into three parts (A, B, C in Fig. R2-9)as below,\nA) InSe single crystal. The controllable growth procedure ensures the good quality\nof the InSe crystal in part A. In this process, the previously existed pores trapped\nat the boundary of polycrystals in part A will be released and migrated upwards\n(B).\nB) InSe polycrystals formed during the cooling process.At this part, the raw InSe\npolycrystals are heated to melt but without controllable recrystallization. So,\nduring the cooling process, InSe liquid in part B will transform to polycrystalline\nstate during naturally cooling to the ambient temperature of the space station.\nUnder microgravity conditions, the air rising from the bottom zone, combined\nwith the inherently present air in this region, spontaneously coalesces into large\nbubbles due toliquidsurface tension.\nC) Raw InSe polycrystals. The section from 72 mm to 95.7 mm is the region that\nis not heated due to the limited travel distance of the space-based furnace.\nTherefore, inthisregion, gas cannot migrateor accumulate.\nIn contrast, for crystals melted on the ground, gravity causes most of the gas to be\nexpelled to the very top of the quartz tube, so no formed large bubbles are observed.\nTherefore, we can infer that the formation of the big bubble is indeed caused due to\nthe microgravity.Weshould emphasize that this large bubble does not introduce stress\ninto the single-crystal region, but it can serve as the strong evidence of the\nmicrogravity growth process.\nFig. R2-9. Schematic of s-InSe grown in the microgravity condition using the\nBridgman method. a, The high temperature scientific experiment cabinet for\nmicrogravity-growing InSe crystals. b, The specific parameters of the as-grown\ncrystal ingot. c,Thephotooftheas-grown s-InSe ingot.\nQ13: Is the observed mobility enhancement solely due to defect reduction, or could\ncontact engineering or dielectric environment also contribute?\nAnswer-13:Thank you very much foryour professional comments.\nDuring device fabrication, we employ highly insulating 2D h-BN flake as the contact\nlayer between the InSe channel and the highly-doped Si substrate. The dielectric\nconstant of h-BN is as high as 4, which helps to avoid introducing a hysteresis\nwindow due to the surface effects of the dielectric. However, this material does not\nprovide charge carriers for the channel. In existing reports (Adv. Mater., 2018, 30,\n1803690; DOI:10.1002/adma.201803690), the mobility could be enhanced through\nsurface doping processes on the transistor channel or coating techniques. In this work,\nsuch processes were not employed. The channel and electrodes form a pure\nmetal-semiconductor contact, and no additional materials (such as In coating) were\ndeposited on the surface. For precise comparison, the e-InSe based ferroelectric\nsemiconductor field effect transistors (FeSFETs) are also prepared following the same\nfabrication procedures. Fig. R2-10a shows the typical back-gate transfer curves of\ne-InSe and s-InSe based FeSFETs. Clearly, the s-InSe FeSFETs has a larger on/off\nratio by about one order of magnitude (Fig. R2-10b).The mobility of s-InSe FeSFETs\ncan be calculated to be ~195.30 cm2v-1s-1, approximately doubling that of e-InSe\nFeSFETs (~103.86 cm2v-1s-1) (Fig. R2-10c).All three devices electrical properties are\nsummarizedin Table R2-2.\nFig. R2-10. Electrical properties of e-InSe and s-InSe based devices. a, Transfer\ncurves of the transistors under bidirectional V sweeping of s-InSe and e-InSe based\nbg\ndevices. b, On/off ratio curves of the transistors. c, Mobility of corresponding\nback-gated s-InSe ande-InSe FeSFETs.\nQ14: Some figures (e.g., PL spectra and band diagrams) could benefit from clearer\nlabelling and quantitative annotations. Figure 1c-d should be labelled to improve\nreader understanding. All acronyms (e.g., FeSFET, PFM) should defined clearly at\nfirst usefor abroad readership\nAnswer-14:Thank you very much forthese nicesuggestions.\nWe have updated the figures and some descriptions including acronyms in the revised\nmanuscript accordingly.\nPlease note that all major revisions have been marked in red in our revised manuscript\nin an additional PDF version. Simultaneously a supplementary information file has\nalso been provided.\nReviewer#3(Remarks totheAuthor)\nThe authors investigated how the microgravity growth environment affects the growth\nof the vdWs InSe single crystals. They discovered that this unique condition could\neliminate interlayer stacking faults in the materials, which promotes the inherent\nsliding ferroelectricity. As a result, high performance FeSFETs with high carrier\nmobility and clear memory window were demonstrated. Moreover, superlinear\nemission from the microgravity-grown InSe was observed with low excitation\nthresholds of photons.Thetopicis interesting and the experimental results are of good\nquality, which could support their conclusion very well. I would recommend the\narticle forpublication after minorchanges orexplained.\nWe appreciate you very much for your highly evaluating our manuscript. Below we\nwillreply your comments point-by-point.\nQ1: On page 5, line 2, it is inappropriate to claim a single-crystal or polycrystalline\nregion without conducting any characterization first.\nAnswer-1:Thank you very much foryour timelyand critical comments.\nTo address this question, XRD characterizations were performed for the samples\ntaken from thetop and thebottom zonesof space grown InSe ingots.As shown in Fig.\nR3-1, it can be seen that the sample taken at the top zone exhibit polycrystalline\nfeature with all the diffraction peaks corresponding to those of the standard InSe.\nWhile the sample at the bottom zone demonstrates the excellent single crystalline\nfeature along {00l} planes. This result has been added as Fig. S1 in the\nSupplementary Information ofour revised manuscript.\nFig. R3-1. XRD patterns of InSe samples at the top zone and the bottom zone,\nexhibiting polycrystalline (red curve) and single crystalline (blue curve) features,\nrespectively.Thestandard powdered PDF card forInSe isalso shown.\nQ2: For Figure 1b, the authors declared that the microgravity have significant\ndifferences influence on the morphology of the InSe crystals from those grown under\ngravity. Please explained why the microgravity could bring the large bubbles on the\nInSecrystal?\nAnswer-2: Thank you very much for this concern. Your observation regarding the\nlarge bubbleissueis both timely and highly meaningful.\nThe large bubble may represent the typical characteristic of crystal growth under\nmicrogravity condition. As we have described in details in the response to Q4, the\nschematic diagram of crystal growth process in the zone melting furnace on the China\nspace station are shown in Fig. 1a and Fig. R3-2a. The furnace heater comprises high\ntemperature zone and low temperature zone. During InSe growth in space, the\npre-synthesized InSe polycrystals is first melted in the high temperature zone for 3\nhours. Then, the heater will be moved up at a very slow speed (1.0 mm/h) to ensure\nthe InSe single crystal growth at the low temperature zone.The specific parameters of\nthe resulting crystalline InSe ingot are shown in Fig. R3-2b. A total length of ~95.7\nmmcan bedivided into three parts (A, B, C in Fig. R3-2)as below,\nA) InSe single crystal. The controllable growth procedure ensures good quality of\nthe InSe crystal in part A. In this process, the previously existed pores trapped at\ntheboundary ofpolycrystals in partAwillbe released and migrated upwards (B).\nB) InSe polycrystals formed during the cooling process.At this part, the raw InSe\npolycrystals are heated to melt but without controllable recrystallization. So,\nduring the cooling process, InSe liquid in part B will transform to polycrystalline\nstate during naturally cooling to the ambient temperature of the space station.\nUnder microgravity conditions, the air rising from the bottom zone, combined\nwith the inherently present air in this region, spontaneously coalesces into large\nbubbles due toliquidsurface tension.\nC) Raw InSe polycrystals. The section from 72 mm to 95.7 mm is the region that\nis not heated due to the limited travel distance of the space-based furnace.\nTherefore, inthisregion, gas cannot migrateor accumulate.\nIn contrast, for crystals melted on the ground, gravity causes most of the gas to be\nexpelled to the very top of the quartz tube, so no formed large bubbles are observed.\nTherefore, we can infer that the formation of the big bubble is indeed caused due to\nthe microgravity.Weshould emphasize that this large bubble does not introduce stress\ninto the single-crystal region, but it can serve as the strong evidence of the\nmicrogravity growth process.\nFig. R3-2. Schematic of s-InSe grown in the microgravity condition using the\nBridgman method. a, The high temperature scientific experiment cabinet for\nmicrogravity-growing InSe crystals. b, The specific parameters of the as-grown\ncrystal ingot. c,Thephotooftheas-grown s-InSe ingot.\nQ3: For Figure 1c, the manuscript shows “… both crystal ingots present single\ncrystalline…”, how could you determine that they are single crystals just from the\noptical images?\nAnswer-3:Thank you very much forthis critical comment.\nWe are sorry for this irrigorous description, which may be misleading. This\nconclusion is based on our growth method. As shown in Fig. 1a and Fig. R3-2,\nduring space-growth of InSe, we melt the raw InSe polycrystals in the high\ntemperature zone, and then the InSe single crystals will controllable grow in the\nbelow low temperature zone.As a result, InSe crystals can only form at the bottom of\ntheampoule,whilethe upperpart consistsof incompletely melted polycrystals.\nAs confirmation, we have supplemented the XRD results as Fig. S1 in the\nSupplementary Information and revised thetextaccordingly inline9-10, page 5in the\nrevised manuscript.\nQ4: Figure 1f presents the Raman spectra of InSe crystals at different positions. The\nmanuscript does not mention the variation of Raman spectra to the positions.As show\nin the figure, the intensity of Raman peaks from s-InSe is varied for different\nmeasured positions.Please comment thepossiblereason.\nAnswer-4:Thank you very much forthis professional comment.\nWewould liketo point out that intheoriginal manuscript, theRaman spectra were not\nsubjected to uniform baseline processing. After baseline calibration, the observed\ndifferences are primarily located at the position of theA (LO) mode. The appearance\n1g\nor intensity changes of this Raman mode are related to the thicknesses of the flakes.\nTo confirm this argument, we have prepared five more flakes with different\nthicknesses from e-InSe and s-InSe crystals, as shown in Fig. R3-3 and Fig. R3-4,\nrespectively. We can see that the A (LO) mode can be observed in both e-InSe and\n1g\ns-InSeflakes,andthe signal became morepronounced as theirthicknesses decrease.\nThese results have been added into the Supplementary Information (see Fig. S2 and\nFig. S3), and the interpretation has also been added accordingly in the revised\nmanuscript (see line24-26,page 5).\nFig. R3-3. Raman results of e-InSe flakes (F1, F2, F3 and F4) with different\nthicknesses. a, 30.6 nm. b, 20.7 nm. c, 11.4 nm. d, 8.6 nm. i - AFM topography, ii -\nthickness plot,and iii- corresponding Raman spectrum.\nFig. R3-4. Raman results of s-InSe flakes (F1, F2, F3 and F4) with different\nthicknesses. a, 98.0 nm. b, 72.9 nm. c, 11.7 nm. d, 9.5 nm. i - AFM images, ii -\nthickness profiles,and iii-corresponding Raman spectra.\nQ5: In Figure 1h, the authors compared the transmission spectra of e-InSe and s-InSe\nwith different thickness. What is the exact thickness/layer number of these InSe\nnanosheets?\nAnswer-5:Thank you forthis suggestion.\nWe have added the thickness information on the corresponding curve in Fig. 1h,\nwhere the values are mainly calculated based on the interference fringes at the low\nenergy side.\nQ6: Did the authors conduct comparative experiments for the e-InSe and s-InSe in\ncharacterizationof theslidingferroelectricity and FeSFETdevice tests?\nAnswer-6: Yes, for precise comparison, we have prepared the e-InSe based FeSFETs\nby following the same fabrication procedures. Fig. R3-5a shows the typical back-gate\ntransfer curves of e-InSe and s-InSe based FeSFETs. It indicates that the s-InSe\nFeSFETs has a larger on/off ratio by about one order of magnitude (Fig. R3-5b). The\nmobility of s-InSe FeSFETs can be calculated to be ~195.3 cm2v-1s-1, approximately\ndoubling that of e-InSe FeSFETs (~103.86 cm2v-1s-1) (Fig. R3-5c). All electrical\nproperties of devices are summarized in Table R3-1, which is also added to the\nSupplementary Information ofour revised manuscript.\nFig. R3-5. Electrical properties of e-InSe and s-InSe based devices. a, Transfer\ncurves of the transistors under bidirectional V sweeping of s-InSe and e-InSe based\nbg\ndevices. b, On/off ratio curves of the transistors. c, Mobility of corresponding\nback-gated s-InSe (blue)and e-InSe (red) FeSFETs.\nTab.R3-1.Electrical properties of s-InSeande-InSe nanodevices.\nSample On/offratio Mobility (cm2v-1s-1)\n1 106 195.3\ns-InSe 2 106 187.4\n3 105 160.8\n1 105 103.9\ne-InSe 2 105 81.8\n3 105 49.4\nQ7: For the organization of this article, why the photoluminescence spectra\nmeasurement is arranged after the ferroelectricity and FeSFET characterization? The\nemission test is also a characterization for the optical properties of the InSe crystals,\nwhich has a closer connection with the structural and optical properties discussed\nearlierinFigure 2.\nAnswer-7:Thanks alot foryour comment.\nWe totally agree with you that it is better to display all PL results in the optical\ncharacterization part. The reason why we use the current organization is based on the\nsignificance of the systematic photoluminescence (PL) results of s-InSe.Wethink that\nwhile PL can serve as a fundamental characterization method for the optical property\nof the crystals, the interesting results including the superlinear emission in\ndefect-reduced s-InSe also represent a promising application as a near infrared source\nor even lasing device. Therefore, we specifically present and discuss the important PL\nresults after the intrinsic sliding ferroelectricity of s-InSe. We expect this will\ndefinitely broaden the application of s-InSe as a milestone in the ferroelectric\nInSe-based photon-integrated nanodevices.\nQ8: What is the main mechanism bywhich microgravity growth environment reduces\ntheinterlayer stacking faults?\nAnswer-8:Thank you very much forthis comment.\nAs known, the interlayer sliding barrier is extremely low in InSe, so there will be\nabundant randomly distributed stacking faults in the as-prepared crystals, due to the\ncontact stress from the ampoule bottles and buoyancy convection-induced crystal\nnon-uniformity, which will strongly influence the uniformity of the optical and\nelectrical properties of InSe. In contrast, the primary mechanism through which the\nmicrogravity operates is \"detachment growth\" (a process where crystal growth occurs\ndetached from the container walls), which is critical for the enhancement of the\ncrystal quality. Under such condition, no stress is introduced between the container\nand thematerial. In addition, the buoyancy convection-induced crystal non-uniformity\nwill be greatly reduced in space under the microgravity condition, which will also\nresult in bettercrystal quality (stacking defect reduction).\nIn our work, the e-InSe used for optical properties comparison are synchronously\ngrown on Earth following the same operation procedure under the normal gravity\ncondition. Thus, we can infer that the optimized layer stacking-order and resulted\nenhancement of superlinear PL signal in s-InSe can be attributed to the role of\nmicrogravity.\nCurrently, there is a lack of comprehensive studies on 2D vdW materials. Therefore,\nthis work specifically explores how microgravity leads to alterations in the crystal\nstructure of 2D vdW materials, in turn leading to changes in their ferroelectric and\nemissionproperties.\nPlease note that all major revisions have been marked in red in our revised manuscript\nin an additional PDF version. Simultaneously a supplementary information file has\nalso been provided.\nResponse Letter to the Reviewers\nWewould like to thank our reviewers to agree the publication of our manuscript titled\n“Microgravity-activated high-performance van der Waals InSe ferroelectric\nsemiconductor (#NCOMMS-25-72542A)”. In the light of the comments and\nsuggestions from our reviewer #2, we have added some figures and notes in the main\ntext and supplementary materials. For convenience, all changes to our manuscript\n(including themain textand supplementary materials) have beenmarked in red.\nReviewer#2(Remarks totheAuthor)\nThe authors have extensively addressed the concerns. However the following minor\ncomments shouldbe addressed before publication:\n1. Fig R2-1 to Fig R2-10 should be added to SI in appropriate place and reference to\nthese figures must be made in the main text.Authors can add in SI note to add in the\nexplanationfor thefigures. Samegoes forTab. R2-1.\nThanks a lotfor your constructive comments.\nWe have added figures and notes in the main text and supplementary materials. The\ndescriptions or interpretations have been accordingly added into the revised\nmanuscript; e.g., see line20,page5; line20-23, page8; line14-24, page12.\nPlease note that all major revisions have been marked in red in our revised manuscript\nand supplementary information filein additional PDF version."}, {"round": 2, "reviewer_comments": {"reviewer_2": "The authors have extensively addressed the concerns. However the following minor comments should be addressed before publication:\n1. Fig R2-1 to Fig R2-10 should be added to SI in appropriate place and reference to these figures must be made in the main text. Authors can add in SI note to add in the explanation for the figures. Same goes for Tab. R2-1.", "reviewer_3": "The revised manuscript has adequately addressed all of my concerns and suggestions. I recommend its acceptance in its current form."}, "author_response": "Responseletter Jinetal.,#NCOMMS-25-72542A\nResponse Letter to the Reviewers\nWewould like to thank our reviewers to agree the publication of our manuscript titled\n“Microgravity-activated high-performance van der Waals InSe ferroelectric\nsemiconductor (#NCOMMS-25-72542A)”. In the light of the comments and\nsuggestions from our reviewer #2, we have added some figures and notes in the main\ntext and supplementary materials. For convenience, all changes to our manuscript\n(including themain textand supplementary materials) have beenmarked in red.\nReviewer#2(Remarks totheAuthor)\nThe authors have extensively addressed the concerns. However the following minor\ncomments shouldbe addressed before publication:\n1. Fig R2-1 to Fig R2-10 should be added to SI in appropriate place and reference to\nthese figures must be made in the main text.Authors can add in SI note to add in the\nexplanationfor thefigures. Samegoes forTab. R2-1.\nThanks a lotfor your constructive comments.\nWe have added figures and notes in the main text and supplementary materials. The\ndescriptions or interpretations have been accordingly added into the revised\nmanuscript; e.g., see line20,page5; line20-23, page8; line14-24, page12.\nPlease note that all major revisions have been marked in red in our revised manuscript\nand supplementary information filein additional PDF version.\n1"}, {"round": 3, "reviewer_comments": {"reviewer_3": "The revised manuscript has adequately addressed all of my concerns and suggestions. I recommend its acceptance in its current form."}, "author_response": ""}]

Decision letter