Epitaxial growth of wafer-scale 2D superconductor single crystals by metal-organic chemical vapor deposition

Domain: physics
Published: 2025-12-21
Editorial outcome: major_revision

Abstract
Metallic two-dimensional (2D) transition metal dichalcogenides (TMDCs) are garnering significant attention for their ability to enhance device performance when used as 2D contacts with semiconducting 2D materials, as well as for their intriguing low-temperature properties, including superconductivity, magnetism, and charge density waves (CDWs). However, the advancement of both fundamental studies and practical applications has been hindered by challenges in synthesizing high-quality, large-area materials. In this work, we report the epitaxial growth of wafer-scale 2D superconducting TMDC single-crystal multilayers by metal–organic chemical vapor deposition (MOCVD). Our NbS2 multilayer films achieve high wafer-scale uniformity and single crystallinity of 2H phase, as confirmed by AFM, Raman spectroscopy, SHG mapping, LEED and STEM measurements. This is enabled by a dual-precursor strategy that drives self-templated concurrent epitaxy on lattice-matched sapphire, which is further supported by a kinetic growth model. Devices fabricated from the NbS2 film demonstrate superconductivity below a transition temperature of 3 K, consistent with a Berezinskii-Kosterlitz-Thouless (BKT) type superconducting phase transition, with an impressive yield of 95.1% and a resistance variation of only 12%. Additionally, we demonstrate the wafer-scale growth of superconducting NbSe2 films (Tc = 5 K) via MOCVD. Our work underscores a versatile and scalable approach for synthesizing wafer-scale 2D superconductor single crystals, which is essential for their integration into next-generation TMDC-based electronic devices.

Introduction
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been attracting great attention due to their broad range of properties, including their use as semiconducting materials (e.g., MoS2, WS2) and metallic compounds (e.g., NbS2, NbSe2). With the rapid advancement of semiconducting TMDC-based electronic devices, there is an escalating demand for higher performance. However, achieving this is often constrained by the poor interface between 2D materials and conventional 3D contacts, which hinders efficient charge transfer and overall device efficiency. In this context, metallic TMDCs are considered ideal candidates for 2D metal electrodes due to their van der Waals (vdW) interactions and minimal lattice mismatch with other TMDCs. These 2D metal-semiconductor junctions are effective in reducing contact resistance by mitigating Fermi level pinning, thereby improving electrical performance compared to conventional 3D metal electrodes. Furthermore, metallic TMDCs exhibit intriguing low-temperature phenomena such as superconductivity, magnetism, and charge density waves (CDWs), showing potential applications in quantum computing, spintronics, and nanoscale sensors due to their unique electronic properties and ability to maintain coherence at low temperatures. These interesting electronic properties and prospective applications highlight the importance of developing efficient synthesis methods for 2D metallic and superconducting TMDCs.

In recent years, various approaches have been developed to grow metallic TMDCs, with chemical vapor deposition (CVD) emerging as a particularly promising method. Compared to other techniques, CVD offers precise control over layer thickness, the ability to grow large areas with high crystallinity, and the capability to produce heterostructures. However, the size of the grown flakes remains constrained, generally within the several to hundred micrometer range, which not only limits the scalability of these materials but also hinders their integration into practical devices that require larger, more uniform films. Additionally, due to the lack of a well-established mechanism for controlling the growth of specific crystalline phases, such as the metallic 3R or superconducting 2H phases, achieving the desired electronic properties remains challenging. As a result, the grown samples typically exhibit metallic behavior but rarely demonstrate superconductivity. Addressing these challenges is essential for advancing the field and fully harnessing the potential of 2D superconducting TMDCs in next-generation technologies.

Here we demonstrate the epitaxial MOCVD growth of wafer-scale 2D superconducting NbS2 single-crystal multilayers on c-plane sapphire. By combining a dual-precursor strategy with a selected sapphire substrate, we achieve wafer-scale multilayer single crystallinity and uniform 2H-phase composition, as verified by atomic force microscopy (AFM), Raman spectroscopy, second-harmonic generation (SHG) mapping, low-energy electron diffraction (LEED), and scanning transmission electron microscopy (STEM). This growth is driven by self-templated concurrent epitaxy, in which lateral expansion and vertical layer addition proceed simultaneously, as supported by our kinetic model. Furthermore, devices fabricated from the NbS2 film exhibit superconductivity below a transition temperature of 3 K, consistent with a Berezinskii-Kosterlitz-Thouless (BKT) type superconducting phase transition, achieving an impressive yield of 95.1% and a variation of only 12%. Additionally, we demonstrate the MOCVD growth of wafer-scale superconducting NbSe2 films (Tc = 5 K), highlighting the versatility and potential of our approach for synthesizing 2D superconductors.

Results
Epitaxial growth of 2D NbS2 multilayer films by MOCVD
We performed the epitaxial growth of 2D NbS2 using a home-built metal-organic chemical vapor deposition (MOCVD) system, schematically shown in Supplementary Fig. 1. A 2-inch c-plane sapphire wafer was used as the substrate and pre-annealed in air at 1000 °C for 6 h to generate atomically smooth step terraces (Supplementary Fig. 3), which is essential for epitaxial TMDC growth. Prior to growth, a mixed solution of niobium chloride (NbCl5) and sodium chloride (NaCl) was spin-coated onto the substrate. NbCl5 acted as the initial Nb source, while NaCl facilitated growth by lowering the energy barrier and reducing nucleation density. However, we found that relying solely on NbCl5 is insufficient to achieve continuous wafer-scale single crystals. At the spin-coating concentration employed (0.00125 mol/L), the NbCl5 precursor fails to supply an adequate Nb flux to support full wafer coverage. Conversely, increasing the NbCl5 concentration significantly raises the nucleation density, which disrupts epitaxial alignment and impedes the formation of large-area single-crystal domains. To address this trade-off, we implemented a dual-precursor strategy that decouples nucleation and growth dynamics. The spin-coated NbCl5 locally promotes nucleation with a controlled density, enabling unidirectional alignment of initial domains. Meanwhile, the gaseous Nb(OC2H5)5 provides a continuous and spatially uniform Nb supply during the prolonged growth stage, facilitating the lateral propagation of aligned domains toward full wafer coverage. This combination of a spatially enriched solid precursor and a steady gas-phase feed naturally establishes local chemical-potential gradients that favor subsequent self-templated concurrent epitaxy, as discussed below. Detailed growth conditions are provided in the Methods section and Supplementary Fig. 2.

The growth process consists of four sequential stages, as illustrated in Fig. 1a: initial crystallization at terrace step edges, self-templated epitaxial concurrent growth, inter-domain stitching and grain merging, and finally, the formation of a continuous epitaxial multilayer film across the entire wafer. In the first stage (Fig. 1a(i)), NbS2 nuclei preferentially form along the terrace step edges of the c-plane sapphire substrate, where the local energy environment favors heterogeneous nucleation, as shown in Fig. 1b. Most nuclei align along the same epitaxial orientation, which can be attributed to the underlying sapphire substrate. These nuclei act as a crystalline template, so that subsequent adatom incorporation occurs preferentially on the existing NbS2 lattice rather than by random secondary nucleation. As growth continues, the small crystals expand laterally along the substrate terraces, forming single-crystal domains from micrometer to millimeter scale (Fig. 1a(ii) and Fig. 1c). At the same time, the well-aligned domains serve as a structural template that directs vertical layer incorporation, allowing the film to thicken while preserving the established in-plane registry, illustrated in Fig. 1f. The multilayer domains exhibit unidirectional alignment, while their lateral expansion is confined by the atomic step edges, leading to the formation of trapezoidal or rectangular shapes (evidenced by AFM image in Fig. 1g). With continued precursor supply, neighboring domains grow and begin to merge (Fig. 1a(iii) and Fig. 1d). In the final stage, domain coalescence proceeds with minimal formation of grain boundaries due to their pre-aligned orientation, eventually yielding a wafer-scale, epitaxially aligned multilayer NbS2 film (as shown in Fig. 1a(iv) and Fig. 1e).

To gain quantitative insight into the self-templated concurrent epitaxy, we developed a minimal kinetic model that quantitatively couples the lateral domain expansion and vertical layer accumulation. The total arrival rate of reactive Nb species at the growth front is expressed as Feff(t) = Fseed e−t/τ + Fgas, where Fseed represents the initial Nb flux released from the spin-coated NbCl5 layer, Fgas is the continuous gaseous precursor supply during MOCVD, and τ is the decay time of the seed-layer contribution. The lateral growth rate RL is governed by the adatom diffusion length ℓ and domain size L, approximately following RL ∝ ke Feff ℓ / (L + ℓ), where ke is the kinetic coefficient for edge-limited incorporation. The vertical growth rate RV scales with the terrace capture probability and is given by RV ∝ kt Feff ℓ / (L + ℓ), where kt is the kinetic coefficient for surface-limited incorporation. Thus, the competition between RL and RV is controlled by two key physical parameters: (i) the flux ratio, Γ = Fseed / (Fgas + Fseed), which quantifies the relative contribution of seed-layer versus gas-phase supply, and (ii) the normalized diffusion length, Λ = ℓ / L0, representing the balance between adatom mobility and initial nucleus size. As summarized in the kinetic regime map (Fig. 1h), the film growth transitions from lateral-dominated to vertical-dominated, with an intermediate concurrent epitaxy region. Our experimental dual-precursor conditions fall within this balanced regime, consistent with the observed wafer-scale few-layer single crystallinity. Detailed model parameters and derivations are provided in the Supplementary Information.

Wafer-scale NbS2 single crystals
We next investigated the single crystalline and wafer-scale uniformity of the continuous NbS2 films. Figure 2a displays a typical photograph of wafer-scale NbS2 single crystals on a 2-inch c-plane sapphire substrate. AFM images obtained from various regions of the 2-inch wafer reveal a smooth surface with a low roughness of less than 100 pm, as illustrated in Fig. 2b(i) and the Supplementary Fig. 6. The absence of grain boundaries in all the AFM images indicates the uniform single-crystalline nature of NbS2 across the entire wafer, which is further corroborated by additional characterizations discussed below. By intentionally creating a scratch, a clear contrast between the continuous NbS2 film and the bare sapphire substrate is observed in Fig. 2b(ii). A height profile in Fig. 2b(iii) confirm that the thickness of the as-grown NbS2 film is approximately 6 nm. Figure 2c illustrates Raman line scans across a 2-inch NbS2 film on a sapphire wafer, comprising 11 spectra taken at 5 mm steps. The presence of two characteristic peaks, E12g at 340 cm−1 and A1g at 379 cm−1, confirms the 2H phase of NbS2. While additional modes such as Eg and E12g exist in the 2H-NbS2 phonon dispersion, they are either symmetry-forbidden or Raman-inactive in standard backscattering configurations. Consequently, only the E12g and A1g modes are consistently observed with appreciable intensity, which is consistent with prior studies of TMDC single crystals. Additionally, we performed Raman mapping in several regions of the same wafer (Supplementary Fig. 7). No obvious variations in peak position and intensity were observed in both line scans and 2D mappings, demonstrating the high uniformity of our NbS2 films. Given that NbS2 is more prone to oxidation compared to other transition metal dichalcogenides (TMDCs), which could impede further characterization and application, we examined the film post-transfer (Methods). Raman line scans were first performed on the transferred film on a Si/SiO2 substrate (a typical photograph in Supplementary Fig. 8), with representative spectra shown in Supplementary Fig. 9. The spectra exhibit uniform peak positions and intensities with no detectable shifts, demonstrating that the film remains well preserved after transfer. Complementary XPS analysis was carried out to assess the Nb oxidation state. As shown in Supplementary Fig. 10, the Nb 3d spectrum displays the characteristic Nb4+ doublet with no discernible Nb5+ components, confirming the absence of significant oxidation after transfer.

To further verify the wafer-scale single crystallinity of the NbS2 films, we performed SHG mapping and LEED measurements. The Fig. 2d(ii), (i) present the SHG mapping and corresponding polarization patterns measured at multiple locations across merging NbS2 domains. The mapping reveals a strong and spatially uniform SHG response, and the polarization maxima are identical within experimental uncertainty, confirming the absence of rotational domains or grain boundaries. The Fig. 2d(iii) and Supplementary Fig. 11 further show large-area SHG mapping on continuous NbS2 film with high intensity uniformity, providing compelling evidence of wafer-scale single crystallinity. Furthermore, LEED measurements were carried out at multiple positions across the 2-inch wafer (Fig. 2e). All probed regions display identical threefold-symmetric diffraction patterns with the same in-plane orientation, confirming the wafer-scale single crystallinity and epitaxial alignment of the NbS2 film. The Fig. 2f(i) presents a high-resolution high-angle annular dark-field (HAADF)-STEM image of the NbS2 film, with the corresponding fast Fourier transform (FFT) image shown in Fig. 2f(ii). A large contamination-free region is visible, displaying a clear lattice arrangement. Upon zooming into the region marked by the yellow square, the lattice structure of 2H NbS2 features Nb atoms in a trigonal prismatic coordination with S atoms (lattice parameter: a = b = 0.332 nm, c = 1.197 nm), indicative of a 2H-polytype stacking, which corroborates the Raman spectroscopy results. In addition, the same lattice structure was observed in STEM images from various areas of the NbS2 film, shown in Supplementary Fig. 12. Additionally, we verify the single-crystal nature of our NbS2 film and the absence of grain boundaries by conducting selected area electron diffraction (SAED) on the several positions across the 2-inch NbS2 film (top-left panel in Supplementary Fig. 13). In total, 20 areas were examined across the entire TEM grid, and the corresponding SAED patterns are shown in Supplementary Fig. 13. All the SAED patterns show the single crystalline structure with the same lattice orientation, meaning that lattice of all the TEM-probed area is part of one single crystal lattice of NbS2.

Substrate-guided growth mechanism of 2H-NbS2
Although NbS2 can crystallize in both 2H and 3R polytypes, our structural characterizations (see previous section) confirm the exclusive formation of the 2H phase in our MOCVD-grown films. Understanding the underlying mechanisms governing this selective phase formation is essential for the controlled synthesis of desired crystal structures.

To investigate the substrate-guided selective growth of different crystal phases, we compared the epitaxial behaviors of 2H and 3R polytypes of NbS2 on our growth substrate, c-plane sapphire. As shown in Fig. 3a, both phases consist of stacked 1H layers in which Nb atoms are coordinated in trigonal prismatic sites with surrounding sulfur atoms, and the interlayer spacing is approximately 0.7 nm. The key structural distinction lies in the relative stacking between adjacent layers: 2H-NbS2 features antiparallel Nb atom alignment across layers, while 3R-NbS2 exhibits a slight lateral displacement without rotational offset. This subtle difference leads to markedly different interactions with the substrate. C-plane sapphire (α-Al2O3) presents a stable hexagonal lattice with close lattice match to the 2H-NbS2 basal plane, facilitating coherent epitaxial nucleation and lateral propagation. In contrast, the rhombohedral symmetry of the 3R phase introduces lattice mismatch and suppresses ordered growth on this substrate. These differences are further clarified by first-principles calculations (See Supplementary Information).

As illustrated in Fig. 3b, the nucleation process at step edges was modeled by placing initial NbS2 clusters on a stepped Al2O3 surface. The binding energy at nucleation sites (ΔE1) was found to be significantly lower for 2H-NbS2 (−0.0216 eV) than for 3R-NbS2 (−0.0115 eV), indicating that the 2H phase experiences a stronger interfacial interaction and is thermodynamically favored for initial nucleation. This suggests that the hexagonal symmetry and oxygen-terminated surface of the sapphire promote better lattice registry and orbital overlap with the 2H stacking, stabilizing its early formation. However, the actual nucleation behavior may also be influenced by additional factors, such as local strain accumulation or kinetic limitations during precursor adsorption and diffusion, which could lead to the thickness-dependent phase evolution observed in our previous study. Beyond nucleation, the lateral growth stage was analyzed by evaluating the climbing binding energy (ΔE2), which reflects the energy cost for edge atoms to incorporate into the advancing crystal front. The 2H phase exhibited a more favorable ΔE2 (−0.1051 eV) compared to 3R (−0.0792 eV), implying that adatoms diffusing along the step edge can more easily integrate into the 2H lattice. This points to lower kinetic barriers for 2H expansion, which supports continuous lateral growth once nucleation is established.

Additionally, we calculated the total formation energies for the two stacking configurations at a thickness of 6 nm on sapphire steps, as shown in Fig. 3c. The formation energy of 2H-NbS2 was −0.0835 eV, markedly lower than that of the 3R phase (−0.0676 eV), confirming that the 2H phase (for a thickness of 6 nm) is more stable under growth conditions. This energy difference is attributed to better lattice matching and reduced interfacial strain in the 2H configuration, which aligns with the experimental observation of single-phase 2H-NbS2. Although phase formation may also be influenced by kinetic factors and other growth conditions, the calculated energy difference (~16 meV per formula unit) is consistent in magnitude with values reported in prior studies for stacking-dependent stability in layered TMDCs and represents an important contributing factor to the observed 2H phase selectivity.

Electrical transport in 2D wafer-scale NbS2
To characterize the electrical transport properties of the MOCVD-grown 2-inch NbS2 film (thickness = 6 nm), an array of multiterminal devices was fabricated after transferring the samples onto a Si/SiO2 substrate, as shown in Fig. 4a. The inset of Fig. 4a provides a zoomed view of a multiterminal device, where a stack of Ti/Au was deposited on top of NbS2 to serve as drain and source electrodes, as well as probes. The detailed fabrication process is described in the Methods section. By performing a typical four-terminal V–I measurement illustrated in the inset of Fig. 4b, the resistance of NbS2 between probe 1 and 2 (R12) can be calculated as a value of around 20 Ω at room temperature, indicating its metallic behavior. Figure 4c shows the resistance distribution of 144 NbS2 devices within a 1.2 × 0.9 cm2 area depicted in Fig. 4a. Due to the high uniformity of our NbS2 film, we achieved a device yield of 95.1% (137 functional devices out of 144) and a resistance variation of 12%, defined as the ratio of the standard deviation (σ = 2.7 Ω) to the mean of the resistance values (μ = 22.6 Ω), across a centimeter range. These results are comparable with values reported for CVD-grown 2D materials, suggesting that the observed spread mainly originates from polymer contamination or local fabrication-related defects rather than intrinsic film non-uniformity.

Since our NbS2 exhibits the 2H phase, as confirmed by Raman and STEM measurements in Fig. 2, and 2H phase NbS2 is known to behave as a superconductor at low temperatures, we further investigated its superconducting properties by measuring its resistance (R12) as a function of temperature in zero magnetic field. As shown in Fig. 4d, the resistance decreases linearly with decreasing temperature down to 3.5 K due to its metallic nature. Upon further cooling from around 3.5 K, the resistance sharply drops to zero, indicating the superconducting transition. A residual resistance ratio (RRR) of around 8, defined as the ratio between the resistance at T = 300 K and the normal-state resistance above the superconducting transition temperature, can be calculated. This high RRR value indicates the high crystalline quality of our NbS2 superconductor in terms of its electrical behavior.

Figure 4e presents the resistance of 16 NbS2 devices as they are cooled from 6 K in the absence of a magnetic field (red and gray curves), together with the distribution of their critical temperatures (Tc), defined as the temperature where the resistance reaches half of the normal-state resistance (RN), i.e., R(T) = 0.5 RN. All devices display nearly identical superconducting transitions, with Tc = 3.0 ± 0.1 K, highlighting the high uniformity of superconductivity across the NbS2 film. When a magnetic field of 1 T is applied (blue curve), the NbS2 devices exhibit metallic behavior without a resistance drop, indicating that the superconductivity is entirely suppressed by the magnetic field. Furthermore, we evaluated the environmental stability of the NbS2 devices by monitoring their temperature-dependent resistance over time (see Supplementary Fig. 15). The superconducting properties remain unchanged after 30 days in a high-purity helium environment, indicating high long-term stability under cryogenic and oxygen-free conditions. In contrast, when exposed to ambient air, the superconducting transition gradually degrades and disappears entirely after 10 days, highlighting the strong sensitivity of NbS2 to oxidation.

Figure 4f depicts the four-probe I–V characterization of the NbS2 device across various temperatures without a magnetic field applied. At 3.5 K, the device shows linear Ohmic behavior with a resistance of around 2.7 Ω, consistent with the metallic normal-state resistance. As the temperature decreases further, the I–V curve becomes non-linear near the critical current gap, revealing varying resistance values. A critical current gap of around ±145 μA can be estimated by plotting dV/dI as a function of Ids for the curves at various temperatures, as shown in Supplementary Fig. 16. The curve exhibits a sharp peak at the critical current, signifying the transition from the normal resistive state to the superconducting zero-resistance state. Furthermore, the logarithmic scale inset of the V–I curves illustrates a transition from a linear V–I relationship to a power-law dependence (V ∝ Iα), consistent with a BKT type superconducting phase transition. The BKT transition temperature (TBKT) can be estimated to be 3.0 K, corresponding to an α value of 3 for our NbS2 crystal, which aligns well with the R–T results presented in Fig. 4e. These findings emphasize that our MOCVD-grown 2-inch NbS2 film exhibits the characteristics expected of a 2D superconductor.

Other than NbS2, we further demonstrate the generalizability of our growth strategy by achieving the epitaxial synthesis of 2H-NbSe2 single crystals on sapphire substrates (Supplementary Fig. 17). Structural and morphological characterizations, including optical microscopy, AFM, TEM and Raman spectroscopy, confirm the high crystallinity, phase purity, and large-area uniformity of the as-grown NbSe2 films. Low-temperature transport measurements (Supplementary Fig. 17f) reveal a sharp superconducting transition at Tc ≈ 5 K, which is entirely suppressed under an external magnetic field of 1.5 T, confirming the intrinsic superconducting nature of the 2H-NbSe2.

Methods
Materials synthesis
Our NbS2 single crystal films were synthesized using a home-built MOCVD system, as illustrated in Supplementary Fig. 1. A 2-inch c-plane sapphire wafer was used as growth substrate and annealed in air at 1000 °C for 6 h. A mixed solution was prepared by dissolving niobium chloride (NbCl5, 0.00125 mol/L) and sodium chloride (NaCl, 0.1 mol/L) in isopropanol (IPA). The mixture was ultrasonicated for 15 min to ensure high dispersion quality and then spin-coated onto the sapphire substrate before loading it into the growth chamber. The reactor tube was purged with argon to remove any residual oxygen and humidity before growth. The furnace was first heated to 850 °C and maintained for 10 min while H2S was introduced into the chamber with argon as the carrier gas, allowing the pre-coated NbCl5 to react with H2S and form initial NbS2 seeds. The temperature then increased to 950 °C and held for 20 min, during which the NbS2 domains expanded with continuous H2S supply. Finally, the furnace was heated to 980 °C, and niobium ethoxide (Nb(OC2H5)5) was introduced as a gaseous precursor, carried by 10 sccm of argon, further promoting the lateral growth of NbS2. A 4 sccm flow of hydrogen (H2) was used to reduce carbon contamination. Throughout the process, argon and H2S were supplied at a flow rate of 200 sccm and 30 sccm, respectively, with the growth conducted at 800 mbar. After the growth was completed, the chamber was allowed to cool naturally, with the H2S flow reduced to 5 sccm until the furnace temperature reached 150 °C to minimize sulfur vacancies.

Our NbSe2 single crystal films were synthesized using the same MOCVD system and substrate preparation procedures as those employed for NbS2. The main differences in growth conditions lie in the growth temperature and the choice of gaseous precursors, as described below. The furnace was first heated to 900 °C and maintained for 10 min while H2Se was introduced into the chamber, allowing the pre-coated NbCl5 to react with H2Se and form initial NbSe2 seeds. The temperature was then increased to 950 °C and held for 20 min, during which the NbSe2 domains expanded under continuous H2Se supply. Finally, the furnace was heated to 990 °C, and niobium ethoxide (Nb(OC2H5)5) was introduced as a gaseous precursor, carried by 8 sccm of argon, to further promote lateral domain growth. A 6 sccm flow of hydrogen (H2) was used to reduce carbon contamination. Throughout the process, argon and H2Se were supplied at flow rates of 200 sccm and 25 sccm, respectively. The growth was conducted at a pressure of 800 mbar. After the growth was completed, the chamber was allowed to cool naturally.

Optical characterization
Raman spectra and mapping were obtained using a Renishaw inVia Confocal Raman Microscope. The spectra were collected with a 532 nm laser and a 3000 g/mm grating at room temperature. The excitation spot size was approximately 1 μm with a laser power of 1 mW.
LEED measurements were performed using an OCI MCP-LEED system at room temperature in an ultrahigh vacuum of 10−10 torr. The electron acceleration voltage was 240 eV for LEED.
SHG mapping was performed in a Spectra-Physics InSight system under excitation from a femtosecond laser centred at 820 nm with an average power of 800 μW.
AFM measurements were performed using an Asylum Research system to evaluate the surface morphology and roughness of the films. The root-mean-square (RMS) roughness was computed on representative areas of the wafer from a 5 µm × 5 µm flattened window using the Asylum Research analysis software.

Scanning transmission electron microscopy measurements
The as-grown samples were first transferred onto a silicon nitride TEM grid by using the following approach: The samples were first spin-coated with PMMA (poly(methyl methacrylate)) A4 at 2000 rpm for 60 s and then heated on a hot plate at 180 °C for 5 min to dry. After immersing in water for 5 min, the PMMA film with the samples was detached by water tension and transferred using a silicon nitride TEM grid. The samples were then baked on a hot plate at 65 °C for 10 min to dry and enhance adhesion. Finally, the PMMA film was removed by immersing in acetone overnight, followed by annealing in high vacuum at 250 °C for 6 h.
High-resolution high-angle annular dark field (HAADF) STEM imaging was conducted using a double aberration-corrected FEI Titan Themis microscope. The beam convergence half-angle was set to 20 mrad, corresponding to a HAADF detector collection angle of 49.5–198 mrad. The microscope operated at an accelerating voltage of 80 kV, below the threshold for electron-beam induced knock-on damage of the samples. The electron probe current was set to around 20 pA. To prevent sample drift, images were acquired at various locations using a faster scan with 512 × 512 pixels and 8 µs dwell times.

Wafer-scale sample transfer
To transfer the wafer-scale NbS2 film from the sapphire substrate, the sample was spin-coated with PMMA (poly(methyl methacrylate)) A4 at 2000 rpm for 1 min and then baked on a hot plate at 180 °C for 10 min for drying. The edges of the PMMA layer were carefully scratched with a sharp tweezer, and the sample was then covered with thermal-release tape to provide additional mechanical support and immersed in water for 15 min. The PMMA layer, along with the NbS2 film, detached from the sapphire substrate and adhered to the thermal-release tape. To minimize film wrinkling and mechanical damage during transfer, the sample was gently dried with a nitrogen gun and visually inspected to avoid large bubbles or delamination. It was then attached to the target Si/SiO2 substrate, using a tweezer to remove any bubbles between the sample and the substrate. To promote adhesion, the sample was baked again on a hot plate at 55 °C for 1 h. The thermal-release tape was then removed by increasing the baking temperature to 135 °C. Finally, the sample was immersed in acetone overnight and annealed in high vacuum at 250 °C for 6 h to remove PMMA residue and eliminate trapped interfacial bubbles.

Device fabrication
The samples were first transferred onto a 4-inch Si/SiO2 substrate before undergoing fabrication. The samples were then etched into the desired geometry using laser writer photolithography (utilizing LOR 5A and AZ1512 HS as photoresist layers) and a XeF2 chemical etcher. The photoresist layers were cleaned by immersing them in dimethyl sulfoxide (DMSO) overnight. Laser writer photolithography was used again to pattern the electrodes. Finally, a stack of 2 nm/80 nm thick Ti/Au was deposited by e-beam evaporation to form the electrodes, followed by a lift-off process in DMSO to remove the photoresist layer. Between fabrication steps, the samples were kept in an inert Ar environment inside a glovebox to prevent degradation from exposure to air.

Transport measurements
Cryogenic electrical transport measurements were conducted using an ICE Oxford liquid helium continuous flow system, achieving a base temperature of approximately 1.4 K. V–I characteristics were obtained by applying a constant DC current via a Keithley 2636b source meter, while simultaneously measuring the DC voltage with a Keithley 2182a nanovoltmeter.

First-principles modeling
Density functional theory (DFT) calculations were conducted using the VASP package to investigate the thermodynamic preference between 2H and 3R phases of NbS2 on c-plane sapphire. Stepped sapphire surfaces were modeled to simulate nucleation and lateral growth processes. Binding energies, climbing energies, and formation energies were computed by comparing the total energies of combined and isolated systems.
To complement the first-principles calculations, we developed a minimal kinetic model to capture the coupled lateral and vertical growth dynamics. Numerical integration of the rate equations was performed using Python with the NumPy and SciPy libraries, while parameter sweeps and regime-map generation were carried out with custom scripts. All simulations and figure generation were implemented in Python/Matplotlib, and full details of the equations and parameters are provided in Supplementary Information.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This study reports a significant advance in wafer-scale epitaxial growth of 2D superconducting NbS2 and NbSe2 single crystals via MOCVD, achieving impressive uniformity and superconducting properties. However, concerns regarding the insufficient validation of wafer-scale single crystallinity, the inadequate depth in mechanistic explanations, and the lack of clarity in some details lead to a recommendation for major revision.\n1. The dual-precursor approach (starting with NbCl5 + NaCl, then switching to Nb2(OC2H5)10) needs better explanation. The manuscript doesn't clarify why this switch occurs, and in Supplementary Information Figure S2 only shows how the process works not the underlying mechanism behind changing precursors.\n2. While this work emphasizes the technological breakthrough in wafer-scale single-crystal growth, the evidence supporting single crystallinity remains insufficient. Although the Raman line scans in Figure 2c (with 5 mm spacing) demonstrate good uniformity across the wafer diameter (~50 mm), Raman spectroscopy's limited spatial resolution (~1 μm) cannot reliably detect grain boundaries unless they exhibit significant compositional/stress variations. Furthermore, the selected-area electron diffraction (SAED) patterns in Figure 2f present only 20 sampled regions across a 2-inch wafer. This sparse sampling provides inconclusive evidence for wafer-scale single crystallinity, as undetected grain boundaries likely exist in unprobed areas. To conclusively validate single crystallinity, additional characterization such as second-harmonic generation (SHG) mapping or large-area SAED mapping demonstrating boundary-free continuity and uniform crystallographic orientation is essential (e.g., following the methodology in Li et al., Nat. Nanotechnol. 16, 1201, 2021).\n3. In 2021 work (ACS Nano 2021, 15, 11, 18403–18410), the authors reported that thin-layer NbS₂ (<4 nm) favors the 3R phase, while thicker layers (>6 nm) transition to the 2H phase, attributing this to substrate stress relaxation (indicating interface strain dominates the phase transition). However, this study attributes the dominance of the 2H phase in their DFT calculations (Figure 3) to interactions with sapphire and fails to reconcile this attribution with their previous findings.\n4. Transferring large-area 2D materials from growth substrates is crucial for device integration. While traditional wet methods face significant challenges in preserving large-area, continuous, high-quality layers, optimizations exist (e.g., Nat. Commun. 15, 6795, 2024; Nat. Commun. 13, 4409, 2022).However, the description of the material transfer method (Page 14) is brief and does not mention how to avoid damage to the superconducting properties (such as cracks or doping) during the transfer process.\nFurthermore, the paper states, ''Given that NbS2 is more prone to oxidation compared to other transition metal dichalcogenides (TMDCs)...'' However, the claim that the material remains unoxidized after transfer lacks verification by XPS/EDS analysis (only Raman data in Figure S7 is provided).\n5. The 12% resistance variation (σ/μ) suggests moderate variability (±2.4 Ω). However, the full 0–40 Ω distribution range (Figure 4c) indicates pronounced local nonuniformity, demonstrating that σ/μ is insufficient to characterize spatial homogeneity.\n6. The data for NbSe2 provided in Figure S12 is very limited (only optical microscopy, AFM, Raman, and a single R-T curve). In the manuscript's Results and Discussion section, add a dedicated paragraph describing the growth, characterization, and superconducting results of NbSe2, rather than just briefly mentioning it in the Supplementary Information and Conclusions. Emphasize the similarities and differences in growth conditions and properties between NbSe2 and NbS2.\n7. Some cited references are outdated (e.g., Ref. 16 from 1965). We recommend reviewing and prioritizing recent advances (particularly in MOCVD-grown 2D TMDCs) from the last 3-5 years to enable a more thorough comparative discussion of the field's current state.\n8. Page 13: \"Nb2(OC2H5)10\" needs to be consistent in the manuscript and Figure S1/S2. (Figure S1/S2 have it written as Nb2(OC2H2)10).\n9. Figure S3: The scale bar and step width labels in the AFM image need to be clearer.\nI appreciate your consideration of these suggestions. With rigorous revision, this work has the potential to establish a foundational platform for wafer-scale 2D superconductor integration.\n10. The paper mentions that NbS2 is prone to oxidation. So how stable are the devices of the samples?\n11. How was the device yield of 95.1% and resistance variation of 12% calculated? Please provide specific data.", "reviewer_2": "This manuscript reports on the MOCVD synthesis of a wafer-size single-crystalline 2H NbS2. However, after review, it is not recommended for publication in Nature Communications at current version. The reason and suggestions are provided follow for further improvement:\n1. The growth mechanism. It has been reported that the epitaxy machenism of sapphire substrate plays a significant role in the growth of monolayer (Nat. Nano. 2021, 16, 1201), bilayer (Nature 2022, 605, 69) and few-layer (Nat. Mater. 2025, 24, 1195) MoS2. However, to control the uniformity of the final film, the nucleation process is normally quite slow. By using the spin coating and MOCVD process, the author claims that they can achieve uniform multilayer growth, which is hard to believe. Since not only the MOCVD reaction rate is too fast to control, even for the spin-coated precursor, there should be so many nucleation centers in the sapphire surface. And we don’t see any control, then the author claimed the film is finally not only uniform multilayer (not achieved before), but also single crystalline (also not achieved for few-layer film). So here comes the question: what is the mechanism of the few-layer growth and how to control? Since the few-layer mechanism is different from the monolayer and bilayer, we can’t just believe the data via a static simulation in Fig. 3a&3b and more dynamic simulations are required. Is the growth a layer-by-layer mode or a multilayer nucleation mode?\n2. Also, in Fig 1b&1c, the data shows different modes of nucleation processes and they just look like two materials. And at same time, we can see the samples in some areas are multilayered. It is hard to believe the author can control them into uniform and single crystalline few-layer film. The author needs to provide more data to prove it.\n3. Simulation. For the energy barrier calculation, the author should give more details about the calculation, instead of only showing the results.\n4. The author claims this method can also be applied in the synthesis of NbSe2. However, the data can only be found in Fig. S12. And no more discussion about the data in the manuscript. More details about the synthesis should be provided, such as the precursors, as it is not provided in the method part. Also, Why does the author place it in the SI?\n5. Data presentation and illustration. The author is recommended to show more analyses about the data in the figure. For example, in Fig 2e&2f, the calculated crystal lattice parameters should be provided. In Fig 4c, the mean value and standard deviation should be provided. As shown in the Figure, the deviation should be quite high, which is not consistent with what the author claims. This also happens in Fig. 4f, the power law fitting of the data, what the power value is should be provided.\n6. The Raman data. Since the samples are claimed to be single crystalline, the Raman signal should be much better and more peaks should be able to label out, such as E1g and E2g.\n7. AFM data. There are so many particles that it is hard to believe the roughness is only 100 pm. Can the author show how they calculate the roughness? And also the height profile, the data have a clear base line, which should be deducted to get a more reliable thickness value.", "reviewer_3": "General Comment: This work reports the epitaxial growth of wafer-scale 2D superconducting transition metal dichalcogenide (TMDC) single crystals via metal‒organic chemical vapor deposition (MOCVD), achieving high-quality, uniform 2H-phase NbS₂ films with a BKT-type superconducting transition below 3 K and a 95.1% device yield. Similar wafer-scale growth is also demonstrated for NbSe₂ films with Tc = 5 K, which provides a scalable strategy for next- generation TMDC-based electronics. While these results show potential in the controlled synthesis of large-area 2D superconducting TMDCs, several critical scientific issues and experimental data need to be clarified and improved before the manuscript can be considered for publication in Nature Communications.\n1. The authors claim the growth of wafer-scale NbS₂ single crystals but have not yet provided compelling evidence for such large-area single crystallinity. For verifying large-area single crystals, low-energy electron diffraction (LEED) or second harmonic generation (SHG) mapping across a large area are more reliable than selected area electron diffraction (SAED), as commonly adopted in analogous single-crystal reports (Nat. Nanotechnol. 16, 1201–1207 (2021); Nat. Nanotechnol. 17, 33–38 (2022)). Supporting data from these characterizations are needed to confirm the single-crystalline nature over the entire wafer scale.\n2. The epitaxial growth of layered materials typically follows a layer-by-layer growth model, which is crucial for ensuring film uniformity and single crystallinity. However, the 6-nm-thick NbS₂ single crystal reported here does not exhibit this typical growth behavior. The authors must clarify the correlation between their observed growth and the layer-by-layer model, or explicitly explain why this system deviates from the established growth mode for layered materials.\n3. The methods section describes the precursor as a mixed solution of NbCl₅ and NaCl but omits the solvent used. Notably, NbCl₅ is insoluble in water (and prone to hydrolysis), whereas NaCl has low solubility in organic solvents (e.g., ethanol and acetone), creating ambiguity about how these two compounds can coexist in a single solution.\n4. The AFM images in Figure 2b and the supplementary materials all show surfaces with numerous white particles. How are these particles formed? It is necessary to clarify the impact of these particles on both the film quality and flatness.\n5. The 2H and 3R phases of NbS₂ significantly affect its properties, and the manuscript devotes substantial text to discussing the growth mechanism. However, the hexagonal Al₂O₃ substrate—with its lattice matching and hexagonal symmetry— intrinsically favors the growth of 2H-NbS₂. Under this scenario, the calculated differences in binding energy (ΔE₁) and climbing binding energy (ΔE₂) at the nucleation sites are relatively small, and their magnitude is insufficient to form a persuasive argumentative support.\n6. Figure 3 focuses on substrate-guided selective growth of 2H-NbS₂, but the analysis overemphasizes the formation energies of 2H- and 3R-NbS₂ on sapphire steps, diverting attention from the core issue: epitaxial growth of single-crystalline NbS₂. Since 3R-NbS₂ is not the focus of this work, the authors should reframe the analysis to highlight key evidence for single-crystal epitaxy (e.g., orientation relationships, interface structure) rather than noncore phase comparisons.\n7. Figure 4c shows the resistance distribution across 144 NbS₂ devices to demonstrate film uniformity, but the resistance variation is relatively large, weakening the argument. For superconductors, the superconducting transition temperature (Tc) is a more intrinsic property, and the Tc distribution provides a more robust proof of uniformity. Supplementary data on the spatial distribution of Tc are strongly recommended to strengthen this claim.\n8. The thickness of NbS₂ during these electrical and superconductivity measurements must be explicitly provided to ensure the completeness and comparability of the performance analysis."}, "author_response": "POINT-TO-POINT RESPONSE TO REVIEWER COMMENTS\nReviewer #1 (Remarks to the Author):\nThis study reports a significant advance in wafer-scale epitaxial growth of 2D\nsuperconducting NbS2 and NbSe2 single crystals via MOCVD, achieving impressive\nuniformity and superconducting properties. However, concerns regarding the\ninsufficient validation of wafer-scale single crystallinity, the inadequate depth in\nmechanistic explanations, and the lack of clarity in some details lead to a\nrecommendation for major revision.\nWe sincerely thank Reviewer #1 for the time and effort devoted to carefully evaluating\nour manuscript, and we greatly appreciate the recognition of our work in advancing the\nwafer-scale epitaxial growth of 2D superconducting single crystals.\nIn response to your constructive comments, we have thoroughly revised the\nmanuscript to address the concerns raised, with corresponding changes clearly\nmarked in the revised version. Detailed point-by-point responses to each of the\nreviewer’s comments are provided below.\nWe respectfully hope that, with the current improvements, the manuscript will be\nconsidered suitable for publication in Nature Communications.\n1. The dual-precursor approach (starting with NbCl5 + NaCl, then switching to\nNb2(OC2H5)10) needs better explanation. The manuscript doesn't clarify why this\nswitch occurs, and in Supplementary Information Figure S2 only shows how the\nprocess works not the underlying mechanism behind changing precursors.\nWe sincerely thank Reviewer #1 for raising this important point. We apologize for not\nproviding a sufficient mechanistic explanation in the original manuscript. The dual-\nprecursor strategy we employed combines a spin-coated NbCl + NaCl solid source\n5\nwith a gaseous Nb (OC H ) precursor and is designed to overcome the limitations of\n2 2 5 10\nusing a single Nb source for wafer-scale NbS single-crystal growth.\nfacilitate nucleation at the early stage and to locally enrich the precursor concentration\nnear the substrate surface. In our previous study (ACS Nano 2021, 15, 11, 18403–\n18410), we demonstrated that NbCl alone is sufficient to grow large single crystals of\n2 5\nfeasible for achieving continuous, wafer-scale monolayer single crystals. This is\ndue to two key limitations:\n1. Precursor insufficiency: At the concentration currently used for spin-coating\n(0.00125 mol/L, which is a very low concentration and amount), the NbCl\n5\nsource does not provide sufficient Nb to achieve full wafer coverage.\n2. Excessive nucleation with high concentration: Increasing the amount of\nNbCl leads to a higher nucleation density, which hinders control over crystal\n5\norientation and prevents the formation of epitaxial single-crystal domains\nacross the wafer.\nOn the other hand, using only the gaseous Nb (OC H ) precursor results in very\n2 2 5 10\npoor nucleation. In fact, in our experiments, we observed no crystal growth when this\nprecursor was used in isolation.\nTherefore, the dual-precursor approach allows us to finely balance nucleation\nand growth dynamics: the spin-coated NbCl promotes controlled nucleation at an\n5\nappropriate density to enable epitaxial alignment, while the gaseous Nb (OC H )\n2 2 5 10\nensures sufficient and continuous Nb feedstock during the extended growth period,\nsupporting the lateral expansion of single-crystal domains toward full wafer coverage.\nWe have revised the manuscript to clarify this rationale, as detailed in the\nResults section (pages 5–6; revisions highlighted in red).\n2. While this work emphasizes the technological breakthrough in wafer-scale single-\ncrystal growth, the evidence supporting single crystallinity remains insufficient.\nAlthough the Raman line scans in Figure 2c (with 5 mm spacing) demonstrate good\nuniformity across the wafer diameter (~50 mm), Raman spectroscopy's limited spatial\nresolution (~1 μm) cannot reliably detect grain boundaries unless they exhibit\nsignificant compositional/stress variations. Furthermore, the selected-area electron\ndiffraction (SAED) patterns in Figure 2f present only 20 sampled regions across a 2-\ninch wafer. This sparse sampling provides inconclusive evidence for wafer-scale single\ncrystallinity, as undetected grain boundaries likely exist in unprobed areas. To\nconclusively validate single crystallinity, additional characterization such as second-\nharmonic generation (SHG) mapping or large-area SAED mapping demonstrating\nboundary-free continuity and uniform crystallographic orientation is essential (e.g.,\nfollowing the methodology in Li et al., Nat. Nanotechnol. 16, 1201, 2021).\nWe thank Reviewer #1 for this insightful comment. We fully agree that while Raman\nand SAED provide valuable information, they may not be sufficient to conclusively\nvalidate wafer-scale single crystallinity.\nTo address this critical concern, we have performed second-harmonic generation\n(SHG) mapping and low-energy electron diffraction (LEED) measurements. The top-\nright and left panels of Figure R1a present the SHG mapping and corresponding\npolarization patterns measured at multiple locations across merging NbS domains.\npolarization maxima are identical within experimental uncertainty, confirming the\nabsence of rotational domains or grain boundaries. The bottom-right panel of Figure\nR1a further shows large-area SHG mapping on continuous NbS film with excellent\n2\nintensity uniformity, providing compelling evidence of wafer-scale single crystallinity.\nFurthermore, LEED measurements were carried out at multiple positions across the 2-\ninch wafer (Figure R1b, following the method in Nat. Nanotechnol. 17, 33–38 (2022)).\nAll probed regions display identical threefold-symmetric diffraction patterns with the\nsame in-plane orientation, confirming the wafer-scale single crystallinity and epitaxial\nalignment of the NbS film.\ncrystallinity of our NbS films. A detailed discussion has been incorporated into the\n2\nrevised manuscript (Results section, page 9-10), and the corresponding SHG\nand LEED image is now included as Figure 2d&e.\nWe appreciate the reviewer’s recommendation, which helped us significantly\nstrengthen the validation of our main claim.\nFigure R1: (a): Top-right and bottom-right panels: Polarization-resolved second-harmonic generation\n(SHG) mapping on merging NbS2 domains (Scale bar: 5 μm) and continuous NbS2 film (Scale bar: 10\nμm), respectively. Left panel: Polar plot (°) of the SHG intensity from three areas shown in the right-top\npanel. (b): Typical LEED patterns collected from several positions across the 2-inch NbS2 film.\n3. In 2021 work (ACS Nano 2021, 15, 11, 18403–18410), the authors reported that\nthin-layer NbS (<4 nm) favors the 3R phase, while thicker layers (>6 nm) transition to\nthe 2H phase, attributing this to substrate stress relaxation (indicating interface strain\n₂\ndominates the phase transition). However, this study attributes the dominance of the\n2H phase in their DFT calculations (Figure 3) to interactions with sapphire and fails to\nreconcile this attribution with their previous findings.\nWe thank the reviewer for raising this thoughtful question regarding the consistency\nbetween our current DFT results and our earlier experimental findings.\nIn the present work, the DFT results shown in Figure 3 correspond to the relaxed\nregime at a thickness of approximately 6 nm, where the 2H phase becomes\nthermodynamically favored through interaction with the sapphire substrate. This\ncalculation intentionally excludes the influence of interfacial effects dominant at\nlower thicknesses, such as strong substrate-induced strain or kinetic limitations\nduring precursor adsorption and diffusion, which could account for the thickness-\ndependent phase evolution reported in our previous study. The experimental results in\nthis work are consistent with this interpretation.\nIn response to the reviewer’s concern and to clarify the full phase formation mechanism,\nwe have now included additional discussion in the revised manuscript (Results\nsection, pages 12, revisions highlighted in red) and added clarification of the\nmodeled thickness in the caption.\n4. Transferring large-area 2D materials from growth substrates is crucial for device\nintegration. While traditional wet methods face significant challenges in preserving\nlarge-area, continuous, high-quality layers, optimizations exist (e.g., Nat. Commun. 15,\n6795, 2024; Nat. Commun. 13, 4409, 2022). However, the description of the material\ntransfer method (Page 14) is brief and does not mention how to avoid damage to the\nsuperconducting properties (such as cracks or doping) during the transfer process.\nFurthermore, the paper states, “Given that NbS2 is more prone to oxidation compared\nto other transition metal dichalcogenides (TMDCs)...” However, the claim that the\nmaterial remains unoxidized after transfer lacks verification by XPS/EDS analysis (only\nRaman data in Figure S7 is provided).\nWe thank Reviewer #1 for highlighting the importance of reliable transfer techniques\nfor preserving the structural and functional integrity of large-area NbS films.\n(1) Regarding transfer method, we have added a more detailed des ₂ cription of the\ntransfer process in the Methods section of the revised manuscript (Page 20,\nrevisions highlighted in red). Specifically, we employed thermal-release tape to\nprovide mechanical support to the PMMA/NbS stack during detachment and\n2\nalignment, which helps reduce film wrinkling and cracking. To address the\nchallenge of bubble formation, we performed a post-transfer vacuum annealing\nstep at 250 °C, which effectively eliminates interfacial bubbles and polymer\nresidues. These optimizations enable reliable transfer for wafer-scale device\nintegration and are in line with recent advances in large-area 2D material transfer\n(e.g., Nat. Nanotechnol. 16, 1201 (2021); Nat. Commun. 15, 6795 (2024); Nat.\nCommun. 13, 4409 (2022)).\nDespite these efforts, we acknowledge that microscale imperfections such as\nisolated cracks or wrinkles may still occur during manual transfer, especially for\nlarge-area ultrathin superconductors. Nonetheless, the superconducting properties\nof transferred films were well preserved and a high device yield of 95.1% was\nachieved, as evidenced by the transport measurements shown in Figure 4.\n(2) Regarding oxidation: In our study, the post-transfer Raman spectra\n(Supplementary Fig. S8) exhibit sharp and unshifted modes, with no additional\npeaks or significant background increase, which indicates that the 2H-NbS\nstructure remains intact and that no substantial oxidation has occurred. In addition,\n₂\nthe robust superconducting behavior observed in the transferred devices serves\nas indirect but strong evidence that oxidation is minimal. It is well known that\noxidation of NbS into Nb O or related oxides introduces insulating phases, which\n2 2 5\nwould significantly increase sheet resistance and suppress superconductivity.\nNevertheless, to further confirm the chemical integrity of the transferred film,\nwe\nhave performed complementary XPS analysis to assess the Nb oxidation\nstate and added corresponding discussion in the revised manuscript (Page\n9, highlighted in red). As shown in Figure R2 (also updated in Supplementary\nFigure S9), the Nb 3d spectrum exhibits characteristic doublet peaks\ncorresponding to Nb4+, with no discernible Nb5+ components, indicating the\nabsence of significant oxidation after transfer.\nWe appreciate the reviewer’s suggestion and believe that these clarifications\nstrengthen the discussion on material integrity during transfer.\nFigure R2 | XPS spectra of NbS2 film post-transfer. (a) Wide-scan XPS spectrum showing\ncharacteristic peaks of Nb 3d, S 2p, and additional elements. (b) High-resolution XPS spectrum of the Nb\n3d region, with deconvolution showing contributions from Nb4+ states. No discernible Nb5+ components\nwere observed, indicating the absence of significant oxidation after transfer.\n5. The 12% resistance variation (σ/μ) suggests moderate variability (±2.4 Ω). However,\nthe full 0–40 Ω distribution range (Figure 4c) indicates pronounced local nonuniformity,\ndemonstrating that σ/μ is insufficient to characterize spatial homogeneity.\nWe thank the reviewer for this comment and the opportunity to clarify the purpose and\ninterpretation of Figure 4c.\nOur intention in presenting the resistance distribution in Figure 4c was not solely to\ncharacterize the spatial uniformity of the NbS film, but rather to demonstrate the\n2\noverall device yield and performance consistency after full fabrication and transfer\nprocesses over the wafer scale. In large-area 2D material systems, a certain degree\nof device loss or electrical failure is generally expected due to processing-related\nissues such as polymer residues, metal contact variability, or microscopic cracks\nintroduced during transfer—especially in brittle metallic TMDCs like NbS .\nwith wafer-scale MoS single crystals, variations in mobility (15%), subthreshold swing\n(11%), and current levels (~16%) were observed across a small 1 × 0.6 cm² region.\n₂\nLikewise, we have included a discussion comparing our performance metrics with\nprevious reports on CVD-grown 2D materials (Li et al., Nat. Nanotechnol. 2021; He et\nal., Nat. Mater. 2025), showing that our resistance variation and device yield are within\nthe same order of magnitude as established high-quality systems, as shown in the\nrevised manuscript (Results section, pages 13, revisions highlighted in red).\nWe hope this clarification aligns with the reviewer’s expectation and strengthens the\ninterpretation of the device performance statistics.\n6. The data for NbSe2 provided in Figure S12 is very limited (only optical microscopy,\nAFM, Raman, and a single R-T curve). In the manuscript's Results and Discussion\nsection, add a dedicated paragraph describing the growth, characterization, and\nsuperconducting results of NbSe2, rather than just briefly mentioning it in the\nSupplementary Information and Conclusions. Emphasize the similarities and\ndifferences in growth conditions and properties between NbSe2 and NbS2.\nWe thank the reviewer for this valuable suggestion.\nIn the original version of the manuscript, we placed the NbSe data in the\nstrategy, growth mechanism, and characterization techniques for NbSe are largely\n2\nanalogous to those of NbS . Our aim was to maintain focus on the wafer-scale growth\n2\nand superconductivity of NbS while demonstrating the generalizability of our approach.\nthe growth of MoSe was reported in the Supplementary Information, with the main\n2\nmanuscript focused on MoS .\nthe synthesis and superconducting properties of NbSe . In response, we have now\n2\nadded a paragraph in the revised Results and Discussion section (Page 15-16,\nhighlighted in red) briefly discussing the characterization and superconductivity of\nMOCVD-grown 2H-NbSe films. In addition, we have included the detailed\n2\nsynthesis procedure of NbSe in the revised Methods section（Page 18）to\n2\nemphasize the similarities and differences in growth conditions with NbS .\n2\n7. Some cited references are outdated (e.g., Ref. 16 from 1965). We recommend\nreviewing and prioritizing recent advances (particularly in MOCVD-grown 2D TMDCs)\nfrom the last 3-5 years to enable a more thorough comparative discussion of the field's\ncurrent state.\nWe thank the reviewer for this valuable suggestion. In response, we have carefully\nreviewed the recent literature and updated our citations to reflect the latest progress in\nthe field, particularly in MOCVD-grown 2D TMDC materials and their large-area\nepitaxial growth.\nNewly added references include:\n1) Dual-coupling-guided epitaxial growth of wafer-scale single-crystal WS2\nmonolayer on vicinal a-plane sapphire. Wang, J. et al. Nat. Nanotechnol. 17, 33–\n38, 2022.\n2) Step engineering for nucleation and domain orientation control in WSe2 epitaxy\non c-plane sapphire. Zhu, H. et al. Nat. Nanotechnol. 18, 1295–1302, 2023.\n3) Two-dimensional Czochralski growth of single-crystal MoS2. Jiang, H. et al. Nat.\nMater. 24, 188–196, 2025.\n4) Homoepitaxial growth of large-area rhombohedral-stacked MoS2. Liu, L. et al. Nat.\nMater. 24, 1195–1202, 2025.\n5) Channel and contact length scaling of two-dimensional transistors using\ncomposite metal electrodes. Chen, S. et al. Nat. Electron. 8, 394–402, 2025.\nThese citations have been incorporated into both the Introduction and Discussion\nsections where relevant, and we have revised the surrounding text accordingly to\nprovide improved comparative context.\nWe appreciate the reviewer’s recommendation, which helped us strengthen the\nmanuscript's relevance and scholarly completeness.\n8. Page 13: \"Nb2(OC2H5)10\" needs to be consistent in the manuscript and Figure\nS1/S2. (Figure S1/S2 have it written as Nb2(OC2H2)10).\nWe thank the reviewer for pointing out this inconsistency. We apologize for the\ntypographical error in the chemical formula. The correct precursor used in our study is\nNb (OC H ) (niobium(V) ethoxide), and we have corrected the formula in all\n2 2 5 10\ninstances, including Figures S1 and S2, to ensure consistency throughout the\nmanuscript and supplementary information.\n9. Figure S3: The scale bar and step width labels in the AFM image need to be clearer.\nWe thank the reviewer for pointing this out. We have revised Supplementary Figure\nS3 to enhance the clarity of both the scale bar and step height annotations in the AFM\nimage.\n10. The paper mentions that NbS2 is prone to oxidation. So how stable are the devices\nof the samples?\nWe thank the reviewer for raising this important question regarding device stability.\n(1) Stability under cryogenic conditions:\nTo assess long-term stability, we stored a batch of NbS devices in high-purity liquid\n2\nhelium (the measurement environment) and conducted periodic transport\nmeasurements over a one-month period. As shown in Figure R3(a), the\nsuperconducting properties remained stable throughout, with negligible change in R–\nT characteristics observed on days 0, 5, 10, and 30. This indicates that the\nsuperconducting performance of NbS is well preserved in inert cryogenic\nenvironments.\n₂\n(2) Stability under ambient air exposure:\nIn contrast, devices stored under ambient conditions exhibited progressive\ndegradation. As shown in Figure R3(b), devices exposed to air for 1, 3, 5, and 10 days\nshow increased normal-state resistance and broadening of the superconducting\ntransition. By day 10, the zero-resistance state disappears entirely, indicating a loss of\nsuperconductivity likely due to the formation of surface oxides such as Nb O .\n2 5\nThese two sets of experiments provide a comprehensive understanding of the\nenvironmental sensitivity of NbS -based devices. Further studies on device\n2\nencapsulation are expected to be beneficial for improving long-term ambient stability.\nWe have included these stability data and the corresponding figures in\nSupplementary Figure S13 and updated the relevant discussion in the Results\nsection (Page 14-15, highlighted in red).\nWe once again thank the reviewer for emphasizing this important consideration, which\nhas helped us improve the clarity and rigor of the manuscript.\nFigure R3 | Stability of NbS2 devices under different storage environments. a, R–T characteristics\nof NbS2 devices stored in high-purity liquid helium for 0, 5, 10, and 30 days, showing negligible variation\nin superconducting behavior and confirming excellent cryogenic stability. b, R–T characteristics of devices\nexposed to ambient air for 0, 1, 3, 5, and 10 days, exhibiting progressive degradation of superconductivity\nand indicating surface oxidation and the formation of insulating species such as Nb2O5\n.\n11. How was the device yield of 95.1% and resistance variation of 12% calculated?\nPlease provide specific data.\nWe thank the reviewer for the thoughtful question regarding the calculation of device\nyield and resistance variation in Figure 4c.\nAs shown in Figure 4c, we fabricated and measured a total of 144 NbS devices within\na 1.2 × 0.9 cm2 area. Among them, 137 devices exhibited functional and consistent\n₂\ntwo-probe resistance (R ) values, while 7 devices were non-functional (e.g., due to\n12\nfabrication defects or broken contacts). Accordingly, the device yield was calculated as:\nTo quantify the uniformity of the resistance values, we computed the relative standard\ndeviation (RSD) across the 137 working devices, defined as:\nwhere μ is the mean resistance and σ is the standard deviation. Based on the\nmeasured dataset, we obtained an average resistance of approximately 22.6 Ω, with\na standard deviation of 2.7 Ω, leading to:\nWe have now included additional data in the revised manuscript to clarify this\npoint, as shown in the Results section (pages 13; revisions highlighted in red).\nI appreciate your consideration of these suggestions. With rigorous revision, this work\nhas the potential to establish a foundational platform for wafer-scale 2D\nsuperconductor integration.\nWe sincerely appreciate the reviewer’s encouraging remarks and thoughtful\nsuggestions. We have carefully addressed all the comments and performed substantial\nrevisions to improve the clarity, depth, and completeness of the manuscript. We are\ngrateful for the reviewer’s recognition of the potential impact of our work in establishing\na foundational platform for wafer-scale integration of 2D superconductors.\nWe respectfully hope that, with the current improvements, the manuscript will be\nconsidered suitable for publication in Nature Communications.\nReviewer #2 (Remarks to the Author):\nThis manuscript reports on the MOCVD synthesis of a wafer-size single-crystalline 2H\nNbS2. However, after review, it is not recommended for publication in Nature\nCommunications at current version. The reason and suggestions are provided follow\nfor further improvement:\nWe sincerely thank the reviewer for the careful evaluation of our manuscript and for\nthe constructive comments and suggestions. We fully understand the concerns raised\nand appreciate the opportunity to improve our work.\nIn response, we have thoroughly revised the manuscript and addressed all\ncomments point by point. We have added new experimental data, clarified key\nmechanistic explanations, and improved the overall clarity and completeness of the\ndiscussion.\nWe believe these revisions have significantly strengthened the manuscript and clarified\nthe novelty and validity of our findings. We respectfully hope that the revised version\nmay now be considered suitable for publication in Nature Communications.\n1. The growth mechanism. It has been reported that the epitaxy mechanism of\nsapphire substrate plays a significant role in the growth of monolayer (Nat. Nano. 2021,\n16, 1201), bilayer (Nature 2022, 605, 69) and few-layer (Nat. Mater. 2025, 24, 1195)\nMoS2. However, to control the uniformity of the final film, the nucleation process is\nnormally quite slow. By using the spin coating and MOCVD process, the author claims\nthat they can achieve uniform multilayer growth, which is hard to believe. Since not\nonly the MOCVD reaction rate is too fast to control, even for the spin-coated precursor,\nthere should be so many nucleation centers in the sapphire surface. And we don’t see\nany control, then the author claimed the film is finally not only uniform multilayer (not\nachieved before), but also single crystalline (also not achieved for few-layer film). So\nhere comes the question: what is the mechanism of the few-layer growth and how to\ncontrol? Since the few-layer mechanism is different from the monolayer and bilayer,\nwe can’t just believe the data via a static simulation in Fig. 3a&3b and more dynamic\nsimulations are required. Is the growth a layer-by-layer mode or a multilayer nucleation\nmode?\nWe thank the reviewer for this careful and important critique. In the revised manuscript\nwe have substantially expanded our mechanistic discussion and added both new\nfigures and quantitative analysis to address these concerns.\n1. Distinct from classical layer-by-layer epitaxy\nWe now clarify (Results & Discussion, Dual-precursor self-templated epitaxial\ngrowth of 2D NbS film, Figure 1) that our films grow through a self-templated\nconcurrent epitaxy mechanism, which differs from the monolayer/bilayer\n₂\nmechanisms previously reported for MoS on sapphire (Nat. Nanotechnol. 16,\n1201 (2021); Nature 605, 69 (2022); Nat. Mater. 24, 1195 (2025)). Spin-coated\n₂\nNbCl (a low concentration of 0.00125mol/L) creates a controlled density of\n5\nseeds along the sapphire terrace steps. During the subsequent high-\ntemperature MOCVD stage, gaseous Nb (OC H ) (precisely controlled by\nMFC) continuously feeds Nb species that are incorporated both at the lateral\n₂ ₂ ₅ ₁₀\nedges and onto the surface of NbS domains, enabling simultaneous\n2\nlateral domain expansion and vertical layer addition.\n2. Dynamic modelling\nWe have therefore introduced a minimal kinetic model (Page 7-8; full\nderivation in Supplementary Information), which couples lateral growth rate\nand vertical growth rate . The competition between and is\n𝑅𝑅𝐿𝐿\ncontrolled by two key physical parameters: (i) the precursor flux ratio,\n𝑅𝑅𝑉𝑉 𝑅𝑅𝐿𝐿 𝑅𝑅𝑉𝑉\n, which quantifies the relative contribution of seed-layer\nseed gas seed 𝛤𝛤 =\nversus gas-phase supply, and (ii) the normalized diffusion length, ,\n𝐹𝐹 /(𝐹𝐹 +𝐹𝐹 )\nrepresenting the balance between adatom mobility and initial nucleus size. We\n𝛬𝛬 = ℓ/𝐿𝐿0\nobtain a regime map (new Figure 1h) that delineates lateral-dominated,\nvertical-dominated, and simultaneous-growth regions. The experimental dual-\nprecursor, high-temperature window falls squarely inside the simultaneous-\ngrowth regime, quantitatively supporting the self-templated mechanism. We\nhave also revised the text in the Results and Discussion section to reflect this\nclearer separation of purpose: Figure 1 for epitaxy, and Figure 3 for phase-\nselectivity rationale.\n3. Experimental verification of wafer-scale single crystallinity\nTo substantiate the proposed growth mechanism, we emphasize the\ncomprehensive structural characterizations presented in the revised\nmanuscript—including SHG mapping and LEED (new added in Figure 2d&e),\nlarge-area SAED, Raman mapping, and AFM—which collectively demonstrate\nthe wafer-scale single-crystalline nature of the few-layer NbS film. As the\n2\nreviewer correctly noted, achieving multilayer uniformity is indeed challenging.\nWe acknowledge that in some zoomed-in regions of the large-area optical\nmicrographs (Supplementary Figure S4), areas with slightly higher\nthickness can be observed, which likely arise from minor variations in the\nlateral and vertical growth rates, and we have added a note in the revised SI\nto avoid overclaiming. Nevertheless, these local fluctuations do not affect the\noverall epitaxial alignment or the uniform 2H-phase crystallinity across the\nwafer.\nWith these additions and clarifications, we believe the growth mechanism of the few-\nlayer NbS film is now clearly explained and fully supported by both experimental\n2\nevidence and kinetic modelling. We hope that these revisions substantially improve the\nclarity and completeness of the manuscript and that they satisfactorily address the\nreviewer’s concerns.\nFigure R4 | Growth mode of wafer-scale NbS2 films via MOCVD. a, Schematic illustration of the four-\nstage epitaxial growth process of NbS on a 2-inch c-plane sapphire wafer: (i) preferential crystallization\nat terrace step edges; (ii) Self-templ₂ated epitaxial multilayer growth; (iii) domain merging and grain\nstitching; and (iv) formation of a continuous epitaxial film. b, Schematic of self-templated concurrent\nepitaxial growth of NbS2. Adatoms incorporate both along the basal-plane edges (horizontal arrows) and\nonto existing terraces (vertical arrows), enabling simultaneous lateral expansion and vertical stacking. c,\nCalculated phase diagram showing the growth regimes as a function of the precursor flux ratio Γ =\nFseed/Fgas+Fseed and the normalized surface diffusion length Λ = ℓ/L0.\n2. Also, in Fig 1b&1c, the data shows different modes of nucleation processes and they\njust look like two materials. And at same time, we can see the samples in some areas\nare multilayered. It is hard to believe the author can control them into uniform and\nsingle crystalline few-layer film. The author needs to provide more data to prove it.\nWe thank the reviewer for the thoughtful comment. We acknowledge that the original\nFigure 1b may not have been sufficiently representative of the typical early-stage\nmorphology of our growth process, and could potentially cause confusion regarding\nmaterial identity. To address this, we have replaced Figure 1b with a more\nrepresentative AFM image that clearly shows the early-stage NbS nuclei and the\n2\nunderlying sapphire terrace steps, ensuring that the figure accurately reflects the initial\ngrowth morphology.\nThe presence of multilayer regions in Figure 1c and 1d is not a structural defect but\nrather a manifestation of the ongoing self-templated epitaxial process that leads to the\ndesired multilayer growth. And we acknowledge that these areas with slightly higher\nthickness can be observed in our as-grown films, which likely arise from minor\nvariations in the lateral and vertical growth rates. Nevertheless, these local fluctuations\ndo not affect the overall epitaxial alignment or the uniform 2H-phase crystallinity across\nthe wafer, as further supported by the following evidence:\n• SHG mapping and LEED across the NbS films (see below Figure R5), which\n2\nwe have added as new experimental data in the revised manuscript (Figure\n2d&e), confirming the wafer-scale single crystallinity and epitaxial alignment of\nthe NbS film. This technique has also been successfully used in prior studies—\n2\nsuch as Nat. Nanotechnol. 16, 1201 (2021), Nat. Nanotechnol. 17, 33–38\n(2022)—to validate wafer-scale single crystallinity in 2D TMDC films.\n• Selected-area electron diffraction (SAED) patterns from multiple regions\nacross the wafer (Supplementary Figure S11), which consistently exhibit a\nsingle-zone axis diffraction pattern, confirming the uniform single-crystalline\nnature of the film in all sampled locations.\n• Reproducible superconducting behavior (Figure 4) across a large number\nof devices on the wafer, with sharp transitions and low resistance variation,\nindirectly supporting the uniformity and high quality of the material.\nWe thank the reviewer for encouraging us to provide additional clarification and\nstronger supporting data, which have been incorporated in the revised manuscript.\nFigure R5: (a): Top-right and bottom-right panels: Polarization-resolved second-harmonic generation\n(SHG) mapping on merging NbS2 domains (Scale bar: 5 μm) and continuous NbS2 film (Scale bar: 10\nμm), respectively. Left panel: Polar plot (°) of the SHG intensity from three areas shown in the right-top\npanel. (b): Typical LEED patterns collected from several positions across the 2-inch NbS2 film.\n3. Simulation. For the energy barrier calculation, the author should give more details\nabout the calculation, instead of only showing the results.\nWe thank the reviewer for pointing out the need for additional information on the\nenergy barrier calculations. In the revised manuscript we have clarified the\ncomputational workflow and provided full numerical details in the Supplementary\n-\nInformation (highlighted in red).\n DFT calculations were performed with the VASP package using the PBE\nexchange–correlation functional, a plane-wave cutoff of 500 eV, and a Γ-centered\n6 × 6 × 1 k-point mesh.\n The stepped α-Al O (0001) substrate was modeled with a four-layer slab\nseparated by a 20 Å vacuum gap, and the bottom two layers were fixed during\n₂ ₃\nrelaxation.\n Total energies of the combined NbS /sapphire systems and the isolated\ncomponents were calculated after full ionic relaxation until forces were below 0.01\n₂\neV Å ¹.\n4. The au⁻thor claims this method can also be applied in the synthesis of NbSe2.\nHowever, the data can only be found in Fig. S12. And no more discussion about the\ndata in the manuscript. More details about the synthesis should be provided, such as\nthe precursors, as it is not provided in the method part. Also, Why does the author\nplace it in the SI?\nWe thank the reviewer for this valuable suggestion.\nIn the original version of the manuscript, we placed the NbSe data in the\nstrategy, growth mechanism, and characterization techniques for NbSe are largely\n2\nanalogous to those of NbS . Our aim was to maintain focus on the wafer-scale growth\n2\nand superconductivity of NbS while demonstrating the generalizability of our approach.\nthe growth of MoSe was reported in the Supplementary Information, with the main\n2\nmanuscript focused on MoS .\nthe synthesis and superconducting properties of NbSe . In response, we have now\n2\nadded a paragraph in the revised Results and Discussion section (Page 15-16,\nhighlighted in red) briefly discussing the characterization and superconductivity of\nMOCVD-grown 2H-NbSe films. In addition, we have included the detailed\n2\nsynthesis procedure of NbSe in the revised Methods section (Page 18).\n2\n5. Data presentation and illustration. The author is recommended to show more\nanalyses about the data in the figure. For example, in Fig 2e&2f, the calculated crystal\nlattice parameters should be provided. In Fig 4c, the mean value and standard\ndeviation should be provided. As shown in the Figure, the deviation should be quite\nhigh, which is not consistent with what the author claims. This also happens in Fig. 4f,\nthe power law fitting of the data, what the power value is should be provided.\nWe thank the reviewer for the constructive suggestion.\nIn response, we have added the relevant quantitative analyses to the revised\nmanuscript. Specifically, the calculated lattice parameters (a = b = 0.332 nm, c = 1.197\nnm) have been provided for Figures 2e and 2f; the mean value (22.6 Ω) and standard\ndeviation (2.7 Ω) of the resistance distribution in Figure 4c are now included and\ndiscussed; and the extracted power-law exponent from the fitting has also been added\nin Figure 4f. All corresponding values are now presented in the figure captions or the\nmain text (highlighted in red).\n6. The Raman data. Since the samples are claimed to be single crystalline, the Raman\nsignal should be much better and more peaks should be able to label out, such as E1g\nand E2g.\nWe thank the reviewer for the observation.\nWe would like to clarify that for 2H-NbS , the E g and E g² modes are symmetry-\nforbidden or extremely weak in standard backscattering Raman configurations due to\n₂ ₁ ₂\nRaman selection rules. As a result, only the E g¹ (in-plane) and A g (out-of-plane)\nmodes are typically observed with appreciable intensity in such measurements, as\n₂ ₁\nshown in our Raman data. This is consistent with prior reports on other TMDC single\ncrystals (Nat. Mater. 24, 188–196, 2025; Nat. Nanotechnol. 17, 33–38, 2022; Nat.\nNanotechnol. 16, 1201, 2021), where only these two modes are clearly resolved. In\nour own previous work on single-crystalline NbS (ACS Nano 2021, 15, 11, 18403–\n18410), we also observed only the E g¹ and A g peaks, despite extensive structural\n₂\ncharacterizations confirming the single-crystalline nature of the film.\n₂ ₁\nWe have added a clarifying note in the revised manuscript (Page 8, highlighted\nin red) to address this point, and we appreciate the reviewer’s suggestion for\nprompting us to elaborate on the Raman interpretation.\n7. AFM data. There are so many particles that it is hard to believe the roughness is\nonly 100 pm. Can the author show how they calculate the roughness? And also the\nheight profile, the data have a clear base line, which should be deducted to get a more\nreliable thickness value.\nWe thank the reviewer for the valuable observation.\n(1) On surface particles and roughness calculation:\nThe white particles observed in the AFM images may originate from residual\nadsorbates, PMMA residue, or environmental contamination, which are commonly\nencountered in 2D material synthesis and device processing (Zhu, H. et al. Nat.\nNanotechnol. 18, 1295–1302, 2023; Fu, J. et al. Nat. Nanotechnol. 18, 1289–1294,\n2023). However, the root-mean-square (RMS) roughness value of ~100 pm was\nnot calculated over the entire scan area, but rather over a selected clean region\nof a representative single-crystal domain, where no visible particles are present. This\napproach is commonly adopted in AFM-based roughness evaluation of 2D materials\nto isolate intrinsic topographic variation from processing-related extrinsic noise.\nIn the revised manuscript, we have:\n• Replaced the AFM images in Figure 2b and Supplementary Figure S5 with\nhigher-clarity data to enhance clarity and prevent potential confusion.\n• Provided the exact region (marked box) where roughness was evaluated, and\nclarified that particles were excluded from the roughness window. Software\nparameters used for RMS calculation: Asylum Research, with a 3.5 µm × 3.5\nµm flattened window;\n(2) On thickness and baseline correction:\nWe agree with the reviewer that baseline tilt can affect the accuracy of step height\nmeasurements. We confirm that a first-order flattening and baseline subtraction were\napplied to the raw AFM data before extracting the height profile. The thickness values\nreported in the manuscript reflect this corrected profile. In the revised manuscript, we\nhave added the note in the caption of Figure 2b for clarity.\nWe appreciate the reviewer’s attention to detail and have revised the manuscript and\nSI accordingly to ensure transparency and reproducibility.\nReviewer #3 (Remarks to the Author):\nGeneral Comment: This work reports the epitaxial growth of wafer-scale 2D\nsuperconducting transition metal dichalcogenide (TMDC) single crystals via metal‒\norganic chemical vapor deposition (MOCVD), achieving high-quality, uniform 2H-\nphase NbS films with a BKT-type superconducting transition below 3 K and a 95.1%\ndevice yield. Similar wafer-scale growth is also demonstrated for NbSe films with Tc\n₂\n= 5 K, which provides a scalable strategy for next-generation TMDC-based electronics.\n₂\nWhile these results show potential in the controlled synthesis of large-area 2D\nsuperconducting TMDCs, several critical scientific issues and experimental data need\nto be clarified and improved before the manuscript can be considered for publication\nin Nature Communications.\nWe sincerely thank Reviewer #3 for the thoughtful evaluation and constructive\nfeedback. We greatly appreciate the recognition of our work on the epitaxial growth of\nwafer-scale 2D superconducting TMDC single crystals, and the potential it offers for\nenabling scalable superconducting electronics.\nWe have carefully addressed all your comments and suggestions point by point in the\nrevised manuscript. We believe these revisions have substantially improved the clarity,\nscientific rigor, and completeness of the manuscript, and respectfully hope that the\nrevised version will now be considered suitable for publication in Nature\nCommunications.\n1. The authors claim the growth of wafer-scale NbS single crystals but have not yet\nprovided compelling evidence for such large-area single crystallinity. For verifying\n₂\nlarge-area single crystals, low-energy electron diffraction (LEED) or second harmonic\ngeneration (SHG) mapping across a large area are more reliable than selected area\nelectron diffraction (SAED), as commonly adopted in analogous single-crystal reports\n(Nat. Nanotechnol. 16, 1201–1207 (2021); Nat. Nanotechnol. 17, 33–38 (2022)).\nSupporting data from these characterizations are needed to confirm the single-\ncrystalline nature over the entire wafer scale.\nWe thank Reviewer #3 for this insightful comment. We fully agree that while Raman\nand SAED provide valuable information, they may not be sufficient to conclusively\nvalidate wafer-scale single crystallinity.\nTo address this critical concern, we have performed second-harmonic generation\n(SHG) mapping and low-energy electron diffraction (LEED) measurements. The top-\nright and left panels of Figure R6a present the SHG mapping and corresponding\npolarization patterns measured at multiple locations across merging NbS domains.\npolarization maxima are identical within experimental uncertainty, confirming the\nabsence of rotational domains or grain boundaries. The bottom-right panel of Figure\nR1a further shows large-area SHG mapping on continuous NbS film with excellent\n2\nintensity uniformity, providing compelling evidence of wafer-scale single crystallinity.\nFurthermore, LEED measurements were carried out at multiple positions across the 2-\ninch wafer. All probed regions display identical threefold-symmetric diffraction patterns\nwith the same in-plane orientation, confirming the wafer-scale single crystallinity and\nepitaxial alignment of the NbS film.\ncrystallinity of our NbS films. A detailed discussion has been incorporated into the\n2\nrevised manuscript (Results section, page 9-10), and the corresponding SHG\nand LEED image is now included as Figure 2d&e.\nWe appreciate the reviewer’s recommendation, which helped us significantly\nstrengthen the validation of our main claim.\nFigure R6: (a): Top-right and bottom-right panels: Polarization-resolved second-harmonic generation\n(SHG) mapping on merging NbS2 domains (Scale bar: 5 μm) and continuous NbS2 film (Scale bar: 10\nμm), respectively. Left panel: Polar plot (°) of the SHG intensity from three areas shown in the right-top\npanel. (b): Typical LEED patterns collected from several positions across the 2-inch NbS2 film.\n2. The epitaxial growth of layered materials typically follows a layer-by-layer growth\nmodel, which is crucial for ensuring film uniformity and single crystallinity. However, the\n6-nm-thick NbS single crystal reported here does not exhibit this typical growth\nbehavior. The authors must clarify the correlation between their observed growth and\nthe layer-by-layer model, or explicitly explain why this system deviates from the\nestablished growth mode for layered materials.\nWe thank the reviewer for this careful and important critique. In the revised manuscript\nwe have substantially expanded our mechanistic discussion and added both new\nfigures and quantitative analysis to address these concerns.\n1. Distinct from classical layer-by-layer epitaxy\nWe now clarify (Results & Discussion, Dual-precursor self-templated epitaxial\ngrowth of 2D NbS film, Figure 1) that our films grow through a self-templated\nconcurrent epitaxy mechanism, which differs from the monolayer/bilayer\n₂\nmechanisms previously reported for MoS on sapphire (Nat. Nanotechnol. 16,\n1201 (2021); Nature 605, 69 (2022); Nat. Mater. 24, 1195 (2025)). Spin-coated\n₂\nNbCl (a low concentration of 0.00125mol/L) creates a controlled density of\n5\nseeds along the sapphire terrace steps. During the subsequent high-\ntemperature MOCVD stage, gaseous Nb (OC H ) (precisely controlled by\nMFC) continuously feeds Nb species that are incorporated both at the lateral\n₂ ₂ ₅ ₁₀\nedges and onto the surfaces of NbS domains, enabling simultaneous\n2\nlateral domain expansion and vertical layer addition.\n2. Dynamic modelling\nWe have therefore introduced a minimal kinetic model (Page 7-8; full\nderivation in Supplementary Information), which couples lateral growth rate\nand vertical growth rate . The competition between and is\n𝑅𝑅𝐿𝐿\ncontrolled by two key physical parameters: (i) the precursor flux ratio,\n𝑅𝑅𝑉𝑉 𝑅𝑅𝐿𝐿 𝑅𝑅𝑉𝑉\n, which quantifies the relative contribution of seed-layer\nseed gas seed 𝛤𝛤 =\nversus gas-phase supply, and (ii) the normalized diffusion length, ,\n𝐹𝐹 /(𝐹𝐹 +𝐹𝐹 )\nrepresenting the balance between adatom mobility and initial nucleus size. We\n𝛬𝛬 = ℓ/𝐿𝐿0\nobtain a regime map (new Figure 1h) that delineates lateral-dominated,\nvertical-dominated, and simultaneous-growth regions. The experimental dual-\nprecursor, high-temperature window falls squarely inside the simultaneous-\ngrowth regime, quantitatively supporting the self-templated mechanism. We\nhave also revised the text in the Results and Discussion sections to reflect this\nclearer separation of purpose: Figure 1 for epitaxy, and Figure 3 for phase-\nselectivity rationale.\n3. Experimental verification of wafer-scale single crystallinity\nTo substantiate the proposed growth mechanism, we emphasize the\ncomprehensive structural characterizations presented in the revised\nmanuscript—including SHG mapping and LEED, large-area SAED, Raman\nmapping, and AFM—which collectively demonstrate the wafer-scale single-\ncrystalline nature of the few-layer NbS film.\nlayer NbS film is now clearly explained and fully supported by both experimental\n2\nevidence and kinetic modelling. We hope that these revisions substantially improve the\nclarity and completeness of the manuscript and that they satisfactorily address the\nreviewer’s concerns.\nFigure R7 | Growth mode of wafer-scale NbS2 films via MOCVD. a, Schematic illustration of the four-\nstage epitaxial growth process of NbS on a 2-inch c-plane sapphire wafer: (i) preferential crystallization\nat terrace step edges; (ii) Self-templ₂ated epitaxial multilayer growth; (iii) domain merging and grain\nstitching; and (iv) formation of a continuous epitaxial film. b, Schematic of self-templated concurrent\nepitaxial growth of NbS2. Adatoms incorporate both along the basal-plane edges (horizontal arrows) and\nonto existing terraces (vertical arrows), enabling simultaneous lateral expansion and vertical stacking. c,\nCalculated phase diagram showing the growth regimes as a function of the precursor flux ratio Γ =\nFseed/Fgas+Fseed and the normalized surface diffusion length Λ = ℓ/L0.\n3. The methods section describes the precursor as a mixed solution of NbCl and NaCl\nbut omits the solvent used. Notably, NbCl is insoluble in water (and prone to\n₅\nhydrolysis), whereas NaCl has low solubility in organic solvents (e.g., ethanol and\n₅\nacetone), creating ambiguity about how these two compounds can coexist in a single\nsolution.\nWe thank the reviewer for this detailed and chemically insightful comment. In our\nexperiments, we prepared the precursor solution using isopropanol (IPA) as the\nsolvent, with concentrations of 0.00125 mol/L for NbCl and 0.1 mol/L for NaCl.\nWe selected IPA because: ₅\n• NbCl is prone to hydrolysis in water, whereas it remains stable and soluble at\nlow concentrations in IPA;\n₅\n• Although NaCl has low solubility in IPA, it exists in our system as a finely\ndispersed phase, likely functioning as a nucleation modulator rather than as a\nfully dissolved species;\n• To ensure uniformity, the precursor solution is ultrasonicated prior to each spin-\ncoating process to maintain high dispersion quality.\nThe mixed solution remains homogeneous and reproducible throughout the\ndeposition process, enabling consistent coating over the wafer. We have updated the\nMethods section in the revised manuscript to include the solvent type,\nconcentrations, and dispersion procedure (as highlighted in red on Page 17). We\nappreciate the reviewer’s suggestion, which helped improve the clarity of our\nexperimental methodology.\n4. The AFM images in Figure 2b and the supplementary materials all show surfaces\nwith numerous white particles. How are these particles formed? It is necessary to\nclarify the impact of these particles on both the film quality and flatness.\nWe thank the reviewer for this important observation. The white particles observed in\nthe AFM images may originate from residual adsorbates, PMMA residue, or\nenvironmental contamination, which are commonly encountered in 2D material\nsynthesis and device processing (Zhu, H. et al. Nat. Nanotechnol. 18, 1295–1302,\n2023; Fu, J. et al. Nat. Nanotechnol. 18, 1289–1294, 2023). These particles are non-\ncrystalline surface residues rather than intrinsic structural defects. To evaluate their\nimpact on film quality:\n• We confirm that key structural measurements were performed in clean,\nparticle-free regions;\n• The RMS surface roughness (~100 pm) reported in the manuscript was\ncalculated from a selected flat region excluding particles, as clarified in the\nrevised caption of Figure 2b;\n• In addition, we have replaced the AFM images in Figure 2b and\nSupplementary Figure S5 with higher-clarity data to enhance clarity and\nprevent potential confusion.\nWe sincerely thank the reviewer for raising this point. We hope that the additional\nclarifications and updated data adequately address the concern.\n5. The 2H and 3R phases of NbS significantly affect its properties, and the manuscript\ndevotes substantial text to discussing the growth mechanism. However, the hexagonal\n₂\nAl O substrate—with its lattice matching and hexagonal symmetry—intrinsically\nfavors the growth of 2H-NbS . Under this scenario, the calculated differences in\n₂ ₃\nbinding energy (ΔE ) and climbing binding energy (ΔE ) at the nucleation sites are\n₂\nrelatively small, and their magnitude is insufficient to form a persuasive argumentative\n₁ ₂\nsupport.\nWe thank the reviewer for raising this important point. Indeed, the hexagonal symmetry\nof the Al O (0001) substrate provides a lattice and symmetry environment that\n2 3\nsupports van der Waals epitaxy of 2H-phase NbS . However, symmetry alone does\nnot determine phase selectivity—interfacial binding energy, nucleation barrier, and\n₂\nthermodynamic stability also play significant roles.\nWhile the computed difference in binding energy between 2H and 3R NbS on sapphire\nis ΔE ≈ 0.02 eV per formula unit, we respectfully note that in 2D materials epitaxy,\n₂\nenergy differences in this range are considered meaningful and phase-selective.\n₁\nFor example, prior studies have shown that energy differences as small as ~5 meV/U.C.\n(He, et al., Phys. Rev. B, 89, 075409 (2014)) or 13.8 meV/U.C. (Winkle, et al., Nature\nCommunications, 14, 2989 (2023)) can govern stacking preference and guide\nexperimental phase stabilization.\nIn our case, the consistent experimental observation of 2H-phase formation across the\nentire wafer, confirmed by Raman, SHG mapping, LEED, and SAED. We also agree\nthat DFT alone may not fully account for the complexity of the growth process, and we\ndo not claim it as a definitive explanation. Rather, we provide the DFT results to offer\na complementary energetic perspective that aligns with our experimental findings\nand helps rationalize why the 2H phase is consistently favored over 3R under our\nconditions.\nWe have clarified this point in the revised manuscript (see Page 12-13,\nhighlighted in red), and we thank the reviewer for prompting this important\nclarification.\n6. Figure 3 focuses on substrate-guided selective growth of 2H-NbS , but the analysis\noveremphasizes the formation energies of 2H- and 3R-NbS on sapphire steps,\n₂\ndiverting attention from the core issue: epitaxial growth of single-crystalline NbS .\n₂\nSince 3R-NbS is not the focus of this work, the authors should reframe the analysis\n₂\nto highlight key evidence for single-crystal epitaxy (e.g., orientation relationships,\n₂\ninterface structure) rather than noncore phase comparisons.\nWe thank the reviewer for this valuable comment and fully agree that epitaxial\nalignment and single crystallinity are central to the main claim of our work. To better\naddress this, we have restructured the logic of the manuscript and clarified the\ndistinct roles of Figures 1 and 3.\n• Figure 1 has been revised to include a new schematic model (Figure 1f&h),\nwhich collectively illustrate the epitaxial growth mechanism of few-layer\nNbS .\n2\n• Figure 3, by contrast, is retained to address a complementary but critical\naspect—the energetic favorability of the 2H phase on Al O . The DFT\ncalculations in Figure 3 support the experimental observation that the 2H phase\n₂ ₃\nis more stable and preferentially formed, providing a structural basis for the\nsuperconducting properties observed in Figure 4.\nWe have revised the text in the Results and Discussion sections to reflect this clearer\nseparation of purpose: Figure 1 for epitaxy, and Figure 3 for phase-selectivity\nrationale. We appreciate the reviewer’s feedback, which helped us improve the\nmanuscript structure and better highlight the core contributions.\n7. Figure 4c shows the resistance distribution across 144 NbS devices to demonstrate\nfilm uniformity, but the resistance variation is relatively large, weakening the argument.\n₂\nFor superconductors, the superconducting transition temperature (Tc) is a more\nintrinsic property, and the Tc distribution provides a more robust proof of uniformity.\nSupplementary data on the spatial distribution of Tc are strongly recommended to\nstrengthen this claim.\nWe thank the reviewer for this insightful suggestion.\nWe agree that the resistance variation observed in Figure 4c is relatively broad, but\nthis is a common characteristic of large-scale 2D device arrays, often arising from\nextrinsic factors such as transfer-related polymer residues, contact interface\ndifferences, and local fabrication-induced defects. Similar degrees of variation have\nbeen reported in high-quality 2D systems—for example, Li et al. (Nat. Nanotechnol.\n16, 1201, 2021) reported ~16% variation in on-state current across a wafer-scale MoS\nsingle-crystal array. We have added a note in the revised manuscript to compare\n₂\nour results with such previously reported values (Page 13, highlighted in red).\nWe fully agree with the reviewer that superconducting transition temperature (T ) is a\nc\nmore intrinsic and relevant indicator of uniformity for superconducting films. In\nresponse, we have extracted T values from the R–T curves of 16 devices presented\nc\nin Figure 4e, and summarized their spatial distribution in the newly added Inset of\nFigure 4e (also see below Figure R8). The results show that the T values are highly\nc\nuniform across the sampled devices, with a narrow variation of only ± 0.1 K. This\nstrongly supports the conclusion that the NbS film exhibits excellent superconducting\n2\nuniformity and consistent phase purity.\nWe appreciate this suggestion, which has significantly improved the strength and\nclarity of our argument.\nFigure R8. The resistance of 16 NbS2 devices as they are cooled from 6 K to 1.3 K in the absence of a\nmagnetic field (red and grey curves) and in a magnetic field of 1 T (blue curve). Inset: Spatial distribution\nof the superconducting transition temperature (Tc) across 16 NbS2 devices, exhibiting a narrow variation\nrange of ± 0.1 K.\n8. The thickness of NbS during these electrical and superconductivity measurements\nmust be explicitly provided to ensure the completeness and comparability of the\n₂\nperformance analysis.\nWe thank the reviewer for pointing out this important detail. All electrical and\nsuperconducting measurements reported in this work were performed on few-layer\n2H-NbS films with a uniform thickness of ~6 nm, as determined by AFM (see\nFigure 2b and Supplementary Figure S5).\n₂\nWe have now explicitly added this thickness information in the main text (Page 13,\nhighlighted in red), to ensure clarity and enable direct comparison with other reported\n2D superconducting systems.\nWe appreciate the reviewer’s suggestion, which has helped improve the completeness\nand reproducibility of the device performance analysis."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have now addressed all my previous concerns, and I now support publication of the manuscript.", "reviewer_2": "The authors have made a great effort to clarify the underlying mechanisms, and many of my earlier concerns have been addressed. However, for acceptance in Nature Communications, I believe the manuscript must demonstrate deeper understanding in the growth mechanism and better scientific illustration. There are still several problems need to be modified before the manuscript can be considered for publication.\n1.In order to more clearly represent the sample morphology at different stages of the growth process, could the substrate be marked? A morphological comparison can be conducted from the beginning to the end of the reaction, allowing for an intuitive observation of the reaction results.\n2.In Figure 1b, the nucleation points are actually randomly arranged. The authors claim that they are arranged directionally along the steps is not credible, and the authors need to explain how they conducted the experiment and how they achieved only NbS2 nucleation without growth.\n3.In the optical image of Figure 1c, the sample does not exactly follow the direction indicated by the white dotted line. This raises doubts about the influence of the terrace step edges and the resulting directional growth that ultimately leads to the formation of a single crystal.\n4.For Supplementary Figures S10 and S11, the authors need to specify the exact collection positions of the high-resolution images and the corresponding selected area electron diffraction patterns.\n5.The effect of NbCl5 and Nb2(OC2H5)10 is still unclear, the authors need to provide experimental separately and conduct corresponding analysis.\n6.The collected area of second-harmonic generation mapping on NbS2 film is small. Providing a larger collection area would be more solid evidence of single crystal.", "reviewer_3": "My concerns were well responsed by the author. I think this article is publishable."}, "author_response": "Response To Reviewers’ Comments\nReviewer #1 (Remarks to the Author):\nThe authors have now addressed all my previous concerns, and I now support publication\nof the manuscript.\nWe sincerely thank the reviewer for the positive evaluation and support for the publication\nof our manuscript. Your valuable comments have greatly helped us improve the quality and\nclarity of the work. We truly appreciate your time and effort.\nReviewer #2 (Remarks to the Author):\nThe authors have made a great effort to clarify the underlying mechanisms, and many of\nmy earlier concerns have been addressed. However, for acceptance in Nature\nCommunications, I believe the manuscript must demonstrate deeper understanding in the\ngrowth mechanism and better scientific illustration. There are still several problems need\nto be modified before the manuscript can be considered for publication.\nWe sincerely thank Reviewer #2 for your valuable and constructive comments, which are\nvery helpful for improving the quality and clarity of our manuscript. We also appreciate your\nrecognition of our efforts in the first-round revision, where we strengthened the\nexperimental validation and mechanistic explanation of wafer-scale single-crystal NbS2\ngrowth. We acknowledge, however, that certain aspects of the growth mechanism and\nscientific illustration were not yet fully clarified. In this revision, we have carefully refined\nthe mechanistic discussion and improved the scientific visualization to address all\nremaining concerns. We sincerely hope that the revised manuscript will meet your\nexpectations and be recommended for publication.\n1. In order to more clearly represent the sample morphology at different stages of the\ngrowth process, could the substrate be marked? A morphological comparison can be\nconducted from the beginning to the end of the reaction, allowing for an intuitive\nobservation of the reaction results.\nWe thank the reviewer for the helpful suggestion. The morphological evolution from the\nbeginning to the end of the reaction has already been presented in Figure 1 (also shown\nas Figure R1 below). Specifically, Figure R1a schematically illustrates the four sequential\nstages of the epitaxial growth process (in chronological order from left to right): (i)\npreferential crystallization at terrace step edges; (ii) self-templated epitaxial multilayer\ngrowth; (iii) domain merging and grain stitching; and (iv) formation of a continuous epitaxial\nfilm. These schematic stages correspond directly to the experimental images shown in\nFigures R1b-e.\nWe acknowledge that, due to the limited optical contrast between the 2D NbS2 film and the\nsapphire substrate, the morphologies were not very clear in the optical micrographs.\nFollowing the reviewer’s suggestion, we have now marked the sapphire substrate and\nNbS2 regions, and labeled the corresponding growth stages in each image of the revised\nFigure 1b-e to further improve visual clarity and readability.\nFigure R1. a, Schematic illustration of the four-stage epitaxial growth process of NbS2 on a 2-inch c-plane\nsapphire wafer: (i) preferential crystallization at terrace step edges; (ii) Self-templated epitaxial multilayer\ngrowth; (iii) domain merging and grain stitching; and (iv) formation of a continuous epitaxial film. b-e, AFM\nand optical images corresponding to the sequential growth stages illustrated in a. Scale bar of c-e: 30 μm.\n2.In Figure 1b, the nucleation points are actually randomly arranged. The authors claim\nthat they are arranged directionally along the steps is not credible, and the authors need\nto explain how they conducted the experiment and how they achieved only NbS2\nnucleation without growth.\nWe thank the reviewer for this valuable suggestion. We acknowledge that the previous\nFigure 1b, due to its limited magnification, was not sufficiently clear to support the claim of\nstep-edge nucleation. To address this, we have replaced Figure 1b with a more highly\nmagnified AFM image (as shown as Figure R2 below), in which the sapphire terrace steps\ncan be clearly observed, and the NbS2 nuclei are shown to align directionally along these\nsteps with a consistent orientation.\nRegarding the experimental control of NbS2 nucleation without subsequent growth, we\nnote that the epitaxial process involves a distinct nucleation stage followed by lateral\ngrowth (as shown in Supplementary Figure S2). By precisely tuning the temperature and\ngrowth duration, we can halt the reaction immediately after the nucleation stage, i.e., by\ncooling down the system once the nucleation temperature is reached, thus obtaining NbS2\nnuclei without further domain expansion.\nUsing the same approach, Figures 1b-e were obtained by intentionally interrupting the\nreaction at different growth times, thereby capturing the characteristic morphologies\ncorresponding to four sequential stages: nucleation, domain growth, domain merging, and\ncontinuous film formation.\nFigure R2. A typical AFM image showing the initial nucleation stage of NbS2 on sapphire substrate. The\nsapphire terrace steps can be clearly observed, and the NbS2 nuclei are shown to align directionally along\nthese steps with a consistent orientation.\n3.In the optical image of Figure 1c, the sample does not exactly follow the direction\nindicated by the white dotted line. This raises doubts about the influence of the terrace step\nedges and the resulting directional growth that ultimately leads to the formation of a single\ncrystal.\nWe thank the reviewer for this insightful comment. We agree that in the optical image of\nFigure 1c, the growth direction does not perfectly coincide with the white dashed line. This\napparent deviation arises because, while the initial nucleation and early-stage growth are\nindeed guided by the sapphire terrace steps, the subsequent lateral expansion involves\ndomain coalescence and step over events, where growing NbS2 domains merge or extend\nacross terrace steps. These processes naturally reduce the apparent long range\n-\ndirectional contrast in optical images.\n-\nTo provide clearer evidence of the terrace-guided epitaxial behavior, we have provided\nadditional optical microscope images (see Figure R3 below, also added in\nSupplementary Figure S4) showing the directional growth of NbS2 domains along the\nterrace steps prior to the formation of the continuous film.\nFigure R3. Optical microscope images showing the directional growth of NbS2 domains along the terrace\nsteps prior to the formation of the continuous film.\n4.For Supplementary Figures S10 and S11, the authors need to specify the exact collection\npositions of the high-resolution images and the corresponding selected area electron\ndiffraction patterns.\nWe thank the reviewer for this constructive comment. We acknowledge that the original\nSupplementary Figures S10 and S11 did not indicate the exact collection positions of the\nhigh-resolution STEM images and the corresponding SAED patterns. To address this, we\nhave now annotated the optical image in Supplementary Figure S11 (now Figure S13) with\nthe specific hole numbers of the TEM grid used for measurement. The corresponding\nSTEM and SAED data (see below Figure R4 and R5, also updated in Supplementary\nInformation) are labeled with the same numbers, indicating that they were acquired from\nthe respective holes shown in the optical image. These measurements collectively cover\nregions across a centimeter-scale area, providing statistically representative structural\ninformation.\nFigure R4. Large-scale STEM images showing single crystalline NbS2 across various regions of a TEM\ngrid, covering a total area on the millimeter scale. Each panel is collected from the corresponding region\nmarked in the top-right panel of Figure R5.\nFigure R5. Optical microscope image of a TEM grid covered by a transferred NbS2 film, along with\nselected area electron diffraction (SAED) patterns taken from various holes across the film, demonstrating\nthe single crystalline structure with consistent lattice orientation. Each panel is collected from the\ncorresponding region marked in the top-right panel.\n5.The effect of NbCl5 and Nb2(OC2H5)10 is still unclear, the authors need to provide\nexperimental separately and conduct corresponding analysis.\nWe thank the reviewer for this valuable comment and the opportunity to clarify the distinct\nroles of the two niobium precursors, NbCl5 and Nb2(OC2H5)10.\nNbCl5 serves as a solid precursor that is pre-deposited on the sapphire substrate by spin-\ncoating at a low concentration (0.00125 mol/L). However, as described in the manuscript\n(Page 5), relying solely on NbCl5 is insufficient to achieve continuous wafer-scale single\ncrystals. The limited Nb flux from the spin-coated layer cannot sustain film growth over the\nfull wafer, while increasing the NbCl5 concentration significantly raises the nucleation\ndensity and disrupts epitaxial alignment.\nTo overcome this limitation, we introduced Nb2(OC2H5)10 as a gaseous precursor, whose\nsupply is precisely tuned by mass flow controller during the MOCVD process. As noted in\nthe text (Pages 5-6), the gaseous Nb2(OC2H5)10 provides a continuous and spatially\nuniform Nb feed during the prolonged growth stage, promoting lateral propagation of\naligned domains and ensuring full wafer coverage.\nIn addition, the ratio between NbCl5 and Nb2(OC2H5)10 critically influences the balance\nbetween vertical and lateral growth. As illustrated in Figure 1h, this relationship is\nrepresented by the precursor flux ratio: Γ = Fseed/Fgas+Fseed. A higher proportion of NbCl5\n(Fseed-dominant) favors vertical growth, producing thicker multilayer domains but with\nreduced surface coverage (see below Figure R6a), whereas a higher proportion of\nNb2(OC2H5)10 (Fgas-dominant) promotes excessive lateral expansion, often leading to\ndendritic-like crystal morphologies (Figure R6b). The following figures have also been\nadded in Supplementary Information.\nFigure R6. Optical microscope images of as-grown NbS2 crystals under different growth conditions. A\nhigher proportion of NbCl5 favors vertical growth, producing thicker multilayer domains but with reduced\nsurface coverage (a), whereas a higher proportion of Nb2(OC2H5)10 promotes excessive lateral expansion,\noften leading to dendritic-like crystal morphologies (b).\n6.The collected area of second-harmonic generation mapping on NbS2 film is small.\nProviding a larger collection area would be more solid evidence of single crystal.\nWe thank the reviewer for this valuable suggestion. We agree that extending the mapping\narea would further strengthen the validation of wafer-scale single crystallinity. Following\nthis comment, we have performed additional SHG mapping on multiple regions across\nthe NbS2 wafer. As shown in Figure R7 (also added in Supplementary Figure S11), the\nlarge-area SHG mapping exhibits excellent intensity uniformity over a continuous NbS2 film,\ncovering an area on the millimeter scale, thus providing compelling evidence for the\nwafer-scale single-crystalline nature of the film.\nWe also acknowledge that SHG measurements are inherently limited by their optical\nprobing area. Therefore, to further confirm the uniform crystallographic orientation on a\nlarger scale, we refer the reviewer to the low-energy electron diffraction (LEED) results\nin Figure 1e, which extend the structural verification to the centimeter scale. Together,\nthese complementary techniques provide consistent and convincing evidence for the\nwafer-scale single crystallinity of our NbS2 films.\nFigure R7. Polarization-resolved second-harmonic generation (SHG) mapping collected from six regions\non continuous NbS2 film. Scale bar: 20 μm.\nReviewer #3 (Remarks to the Author):\nMy concerns were well responsed by the author. I think this article is publishable."}]

Decision letter