Applied Physics Express

LETTER • OPEN ACCESS

You may also like

Time-resolved force microscopy using the delaytime modulation method- A step-by-step simulation code for
estimating yields of water radiolysis
species based on electron track-structuremode in the PHITS code
Yusuke Matsuya, Yuji Yoshii, Tamon
Kusumoto et al.

To cite this article: Hiroyuki Mogi et al 2024 Appl. Phys. Express 17 015003- Electric-field effect on magnetic anisotropy
in Pt/Co/Pd/MgO structures deposited on
GaAs and Si substrates
Yohei Hayashi, Yuki Hibino, Fumihiro
Matsukura et al.

View the article online for updates and enhancements.

- Observation of depolarized guided
acoustic-wave Brillouin scattering inpartially uncoated optical fibers
Neisei Hayashi, Sze Yun Set and Shinji
Yamashita

This content was downloaded from IP address 133.51.188.51 on 11/01/2024 at 00:18

LETTER

Applied Physics Express 17, 015003 (2024)
https://doi.org/10.35848/1882-0786/ad0c04

Time-resolved force microscopy using the delay-time modulation method
Hiroyuki Mogi1, Rin Wakabayashi1, Shoji Yoshida1, Yusuke Arashida1, Atsushi Taninaka1,2, Katsuya Iwaya3,
Takeshi Miura3, Osamu Takeuchi1, and Hidemi Shigekawa1*
1Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
TAKANO Co., Ltd, Miyada-mura, Kamiina-gun, Nagano 399-4301, Japan
3
UNISOKU Co., Ltd, Hirakata, Osaka 573-0131, Japan2*

E-mail: hidemi@ims.tsukuba.ac.jp

Received October 29, 2023; accepted November 12, 2023; published online January 9, 2024
We developed a time-resolved force microscopy technique by integrating atomic force microscopy using a tuning-fork-type cantilever with the delay
time modulation method for optical pump-probe light. We successfully measured the dynamics of surface recombination and diffusion ofphotoexcited carriers in bulk WSe2, which is challenging owing to the effect of the tunneling current in time-resolved scanning tunnelingmicroscopy. The obtained results were comprehensively explained with the model based on the dipole-dipole interaction induced by photo
illumination. © 2024 The Author(s). Published on behalf of The Japan Society of Applied Physics by IOP Publishing Ltd
Supplementary material for this article is available onlineResearch and development aiming to develop new
functionalities by rapidly controlling quantum processes in materials and devices is ﬂourishing, becoming one of the critical challenges. In fundamental properties such as phase transitions, the ﬂuctuations in the dynamics
of non-equilibrium systems at the nanoscale deﬁne theircharacteristics. Efforts are also being made in semiconductors
to control regions to be as small as ∼1 nm. To achieve theseobjectives, it is essential to properly understand and utilize
the elementary processes in non-equilibrium states. For
instance, it is indispensable to elucidate the ultrafast dynamics of carriers and phase changes induced by externalﬁelds with high temporal and spatial resolution.
The scanning tunneling microscopy (STM) system canobtain a range of information in real space with atomic-levelspatial resolution, but its time resolution is constrained byfactors such as circuitry. On the other hand, with theadvancement in quantum optical techniques, pump-probe
methods using ultrashort pulse lasers have achieved timeresolved measurements using pulse widths in the femtosecond and attosecond domains. However, typically, there arelimitations in spatial resolution. Therefore, over the past
decade, efforts have been made to combine these cuttingedge technologies, enabling the development of measurement
and control techniques for local spectroscopy with opticaltime resolution while observing atomic structures and electronic states with atomic-level spatial resolution. Several
time-resolved microscopy methods have been realized1–10)(see Note 1 in the supplementary information for more details
concerning time-resolved STM).
Time-resolved STM is a highly promising method, but
owing to the use of tunneling current in STM, the samples arelimited to those with conductivity. Therefore, as a complementary measurement method, the development of timeresolved atomic force microscopy (AFM), which is one of theprobe microscopy methods and measures the force between
the probe tip and the sample, has been attempted.11–16) For
example, interactions based on surface photovoltage (SPV)11)
and dipole induced in a probe tip by light (PiFM),17,18) havebeen used as a time-resolved force probe.11–14) Initially,methods synchronizing the cantilever vibration with pulse
light excitation were used; however, they had limited time
resolution.14) Subsequently, picosecond-range time resolution was achieved, but the S/N ratio was not particularlyhigh.15) Other innovations include techniques that use thedifference in modulation frequency between pump light andpulse light to remove noise effects12) and a self-detection
tuning-fork-type cantilever driven by a quartz oscillator toeliminate the effects of light irradiation used for force
measurement.19) However, these methods all relied on theintensity modulation of the excitation light, similar to themacroscopic optical pump-probe method.
Here, we demonstrate a time-resolved force microscopy
technique developed by integrating a tuning-fork-type frequency modulation (FM)-AFM with the delay time modulation method. We successfully measured the dynamics ofsurface recombination and diffusion of photoexcited carriersin bulk WSe2, which are challenging in time-resolved STM
owing to the effect of the tunneling current.
Figure 1(a) shows an overview of the system developed. In
this study, we used an optical system with the delay time
modulation of two pulse lasers (532 nm, 45 ps pulse width,
500 kHz) that can be driven by an external voltage pulse
generator.20,21) The delay time modulation shown in Fig. 1(b)is a method by which the delay time between the pump lightand pulse light periodically changes (in this case at 20 Hz)
between the measurement time td and the sufﬁciently
separated time td,ref, and the corresponding signal is detectedby lock-in detection. With the delay time modulation method,
it is possible to not only eliminate the effects of thermal
expansion but also extract only the force component thatreﬂects the dynamics of the sample excited by the pumplight.1,4,20–22)
As shown in Fig. 1, a tuning-fork-type cantilever was used,eliminating the need for an optical system for probe vibration
detection. This choice makes the method implementable even
within complex devices inside a UHV chamber. The spring
constant can be high, allowing for a reduced vibration
amplitude. The probe tip was attached at an angle to allow
for light irradiation directly from the direction of the sample

Content from this work may be used under the terms of the Creative Commons Attribution 4.0 license. Any further distribution of thiswork must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
© 2024 The Author(s). Published on behalf of015003-1
The Japan Society of Applied Physics by IOP Publishing Ltd

Appl. Phys. Express 17, 015003 (2024)

H. Mogi et al.
(c)

(a)

(b)

(d)

(e)

Fig. 1. (a) Schematic of the time-resolved FM-AFM system developed. H.M.: Half mirror, JK F. F.: JK ﬂip ﬂop, SP ﬁlter: short-pass ﬁlter. Delay time
modulation of the two pulse lasers can be driven by an external voltage pulse generator. Inside a UHV chamber (5 × 10−8 Pa), a tuning fork (fundamental
frequency of ∼32.768 kHz) was mounted on an XYZ piezo scanner. The probe tip was positioned at an angle of about 45° to the sample surface. A thin goldplated W wire was used to electrically connect the probe tip holder and the W tip to measure the current ﬂowing through the probe. (b) Delay time modulation
scheme. By adjusting the timing of H/L voltage sequence from JK F.F., the delay time modulation between (H, delay time = td) and (L, delay time = td, ref), as
shown in the ﬁgure, occurs. (c) Resonance characteristics measured to determine the Q-factor (∼10,000). The excitation was achieved by applying an A.C.
voltage to the electrodes of the tuning fork, and the vibration signal was detected by a charge ampliﬁer. (d) CCD image of measurement setup. The WSe2 ﬂakeon the left side was used to adjust the spotlight position. (e) Atomically resolved STM image of a bulk WSe2 sample.

surface. By choosing the probe tip type, both STM and AFM
measurements are possible. A tungsten (W) probe, electropolished to a length of ∼1 mm, was attached to the cantileverusing silver epoxy paste [the frequency resonance Q-factor∼10000 was conﬁrmed in Fig. 1(c)]. Laser light was
introduced through an objective lens (N.A. ∼0.4) positioned
right at the top (below) of the probe tip, allowing for lightirradiation with a spot diameter of several μm without
interference with the probe structure [Fig. 1(d)]. With a
550 nm short-pass ﬁlter, the laser light and the light from thelamp for illumination were combined. The position of the
spot was observed with a CCD camera placed on theobjective lens. For time-resolved force measurement, theamplitude of the frequency shift Δf responding to the delay
time modulation was determined as a time-resolved signal
using a lock-in ampliﬁer.
As the sample, we used WSe2, one of the layered materials[Fig. 1(e)]. In a previous study using time-resolved STM,
photoexcited carrier dynamics, including photoinduced SPV,
recombination, and diffusion, were investigated.21,22)
Considering that the results of our time-resolved AFM canbe compared with the ﬁndings of the previous study, we
conducted experiments on multilayered WSe2.
First, to investigate the band alignment and photoexcited
carriers near the surface of the bulk WSe2 sample, we
conducted force spectroscopy (Δf-Vs curves, Vs: samplebias)23) under both dark and illuminated conditions[Fig. 2(a)]. We selected three representative conditions: (i)dark state, (ii) weak excitation: only illuminating with thecontinuous LED lamp used for microscopy (28 μW; spot

diameter, 200 μm; wavelength, 550 ∼ 750 nm; namely,
excitation density of ∼90 pW μm−2), and (iii) strong excitation. In addition to (ii), we illuminated with a pulse laser(1 mW; spot diameter, ∼5 μm; central wavelength, 532 nm;
implying excitation density of ∼50 μW μm−2). The averaged
results from 20 curves obtained for each condition are shownin Fig. 2(a). The feedback was conducted in the repulsive
regime.
By ﬁtting the obtained Δf-Vs curves with a quadratic
function for each, we derived the contact potential difference(Vcpd), under the three conditions: (i) −0.13 ± 0.02 V, (ii)0.37 ± 0.01 V, and (iii) 0.92 ± 0.02 V, indicating theexistence of SPV. SPV is the difference in Vcpd with andwithout illumination, producing the force between the probe
tip and the sample. The quadratic curvature became pronounced as the light intensity increased, and Δf at the peaktended to increase. The curvature depends on the distance
between the probe tip and the sample.23) These results
suggest that, owing to the attractive interaction produced
upon illumination, the probe tip-sample distance decreased tocounteract this attraction owing to the feedback (Vs = −3 V
and Δf = +1 Hz), increasing the repulsive force at the peak.
The I-V curve obtained by simultaneously capturing thecurrent between the probe tip and the sample It whilemeasuring the Δf-Vs curve is shown in Fig. 2(b). In the (i)dark and (ii) weak excitation states, almost no current ﬂowed.
In contrast, in the (iii) strong excitation state, we detected acurrent on the order of several hundred fA. This result
corresponds to the observation on Vcpd, where the distance
between the probe tip and the sample decreased, thinning the© 2024 The Author(s). Published on behalf of015003-2

The Japan Society of Applied Physics by IOP Publishing Ltd

Appl. Phys. Express 17, 015003 (2024)

H. Mogi et al.

Fig. 2. (a) Force spectroscopy results obtained under three representative conditions. Δf is the shift of the resonance frequency of cantilever sensitive to theinteraction between the probe tip and the sample. After setting the tip position with a repulsive force condition (Vs = −3 V and Δf = +1 Hz), we turned off the
feedback control and swept Vs from −3 V to +3 V to measure the Δf −Vs curves. (b) I-V curves obtained by simultaneously capturing the current between theprobe tip and the sample while measuring the Δf-Vs curve. (c) Band alignment of the sample and probe tip considered in the dark state. (d) SPV-induced bylight irradiation under the condition of Vs = VCPD.

tunneling barrier. The minor current observed within the
bandgap region was not noted in previously recorded resultsof time-resolved STM.22) Namely, for the present sample, it
is considered that defects or impurities, which can inducestates within the gap, exist at the surface.24)
From the results above, the band structure of the sample
and probe tip, as considered in the dark state, is shown in
Fig. 2(c). Bulk WSe2 exhibits p-type behavior internally,
with an electron afﬁnity of ∼4.1 eV and a bandgap of∼1.3 eV.22,25) Near the surface, theoretical calculations andresults of photoelectron spectroscopy have shown the presence of inherent surface band bending.26) Furthermore, Se
vacancy defects on the surface have also been reported togenerate donor-like states.27) Consequently, as shown in
Fig. 2(d), a very large SPV is generated, which is the originof the Vcpd variation shown in Fig. 2(a).
Next, we present the results of time-resolved measurements conducted at three different light intensities in
Figs. 3(a)–3(c). The measurements were conducted understable feedback conditions in the repulsive regime(Δf = +1 Hz, corresponding tip-sample force ∼10 nN in
this setup), with an amplitude of 4 nm, the Vs of approximately 0 V, and the It of less than 10 fA. The mid-lightintensity corresponds to that used for the Vcpd = 0.92 V
condition in Fig. 2(a). We successfully obtained a timeresolved signal with a very high S/N ratio as shown in
Fig. 3(a). Fitting the data with a two-component exponentialfunction (Afast exp (-t/τfast)+ Aslow exp (-t/τslow)) yieldedτfast ∼ 30 ns and τslow ∼ 150 ns [Fig. 3(b)].
A schematic model explaining the observed results isshown in Figs. 3(d)–3(g). Previously, when measured bytime-resolved STM, both fast and slow components wereidentiﬁed.22) On one hand, the slow component on the 100 ns
scale was considered to correspond to carrier diffusion in thebulk, because the carrier lifetime inside the crystal isextremely long on the μs scale. On the other hand, the fastcomponent was considered to correspond to the process of
extracting electrons that accumulated on the surface as thetunneling current (not shown here). Indeed, for a current of
500 pA, a lifetime of τfast ∼ 4 ns was observed. As thecurrent decreases (i.e., increasing the distance between theprobe and the sample, thus extracting fewer electrons), thelifetime increases (250 pA leads to τfast ∼ 8 ns), providing agood explanation for the experimental ﬁndings.
The slow component in this study roughly matches theresults obtained from STM measurements, and this component can be attributed to the diffusion process within the bulk
[Fig. 3(g)]. The fast component is related to the relaxation ofphotoexcited carriers on the surface [initial relaxation of
SPV, Fig. 3(f)], similar to the case with time-resolved STM.
However, the fast component in this experiment is about∼30 ns, slightly longer than that in STM measurements. We
conducted experiments using the AFM system as a probe to
exploit the force interactions under conditions where almost

015003-3© 2024 The Author(s). Published on behalf of
The Japan Society of Applied Physics by IOP Publishing Ltd

Appl. Phys. Express 17, 015003 (2024)

H. Mogi et al.

Fig. 3. (a) Time-resolved force signals obtained for three different excitation light intensities. Decay time (b) and Δf amplitude (c) obtained from ﬁtting theresults shown in (a). (d)-(g) Model explaining the results obtained by time-resolved force microscopy.

no tunneling current ﬂows (Vs ∼ 0 V, It < 10 fA). Therefore,
the relaxation of about ∼30 ns after photoexcitation can be
attributed to the recombination or capture of surface electrons
via the gap states suggested by the I-V curve measurements.
This process is considered the reason why the lifetime
appears slightly longer than in the STM experiment.
For the data obtained at the three excitation intensities, theresults of ﬁtting analysis using a two-component exponentialfunction are shown in Figs. 3(b) and 3(c). These results arederived by averaging the ﬁtting outcomes on both thepositive and negative sides of the delay time. As shown in

Fig. 3(b), the time constant did not change signiﬁcantly withintensity, but the signal strength shown in Fig. 3(c) changed.
Concerning the signal strength, when the light intensity was
reduced (0.6 mW), the intensity ratio of the fast component tothe slow one became particularly large (Afast/Aslow ∼ 2.14
(0.6 mW), ∼0.89 (1.1 mW), and ∼1.13 (2.3 mW)). This trend
also matches the results of time-resolved STM measurement.
In the case of STM, under the weak excitation condition, asmall amount of photoexcited carriers were easily pulled out
from the surface as tunneling current; therefore, a lessdiffusion component from the bulk was observed.
© 2024 The Author(s). Published on behalf of015003-4

The Japan Society of Applied Physics by IOP Publishing Ltd

Appl. Phys. Express 17, 015003 (2024)

However, as the excitation became stronger, a slow component became evident owing to the bulk-side carriers diffusing
in the direction perpendicular to the surface after the fasterrecombination processes of photoexcited carriers via tunneling. The observation that the time constant did not changewith light intensity in this study also supports the idea that therecombination processes via the surface states determine thedecay rate. The time-resolved signals obtained in this study
are consistent with the results obtained by time-resolved
STM, indicating the successful measurement of the dynamics
of photoexcited carriers using the system developed.
Owing to the use of delay time modulation, the typicalforces that the probe experiences when light is irradiated onto
a semiconductor sample is the force induced by SPV[Fig. 4(a)] and the image dipole force discussed for PiFM
[Fig. 4(b)]. The SPV-induced force is a coulomb force acting
between the probe tip and the sample due to the photoexcited
carriers that accumulate under the probe after photoexcitation[electrons in this case, Fig. 2(d)]. Under the experimental
conditions where the distance between the probe tip and thesample does not change with light irradiation (slow feedback
condition), the change in SPV due to light irradiation
corresponds to the change in VCPD, producing the force
between the probe tip and the sample. As long as SPV exists
under the probe tip, the force due to it will persist, and its
time integral becomes the measured force signal.

(a)H. Mogi et al.

On the other hand, according to the discussion on PiFM,
the gradient and scattering forces operate owing to theinteraction with the optical ﬁeld.28) When a dipole is inducedon the probe tip side by the optical ﬁeld, an image dipole isinduced below the probe tip by assuming a semi-inﬁnite
sample shape as the experiments in Figs. 3(a)–3(c). As aresult, an attractive force Fimage µ Re {a*t as} | E0 |2 operates
between these dipoles.19,28) Here, αt and αs are the complex
effective polarizabilities of the tip and sample, respectively,
within the point dipole approximation. E0 is the incident lightelectric ﬁeld vectors. When using pulsed light, a dipole ismomentarily induced within the pulse width, and this force
operates while plasmons exist on the probe tip side. The
lifetime of plasmons in metals is very short on the fs scalecompared with that within the laser pulse width (45 ps) usedin this study,29) so it can be approximated that the force
which reﬂects instantaneous as only operates while the laser
pulse is being applied.
Figures 4(c) and 4(d) show how the SPV-induced or image
dipole force is detected in time-resolved measurement,
respectively. Considering the ultrafast time domain, as shownin Figs. 3(d) to 3(e), there is a certain delay from when the
carriers are excited until they accumulate on the surface,leading to corresponding change in generating attractive
interactions (rising time shown in Figs. 4(c) and 4(d), seeNote 2 in the supplementary information for more details).

(b)

(c)

(d)

Fig. 4. Schematics explaining the observed attractive forces through (a), (c) formation of SPV and (b), (d) dipole-dipole interaction mechanisms. αt and αs
are the complex effective polarizabilities of the tip and sample, respectively, within the point dipole approximation. E0 is the incident light electric ﬁeld vectors.
〈FSPV〉 and 〈Fimage〉 represent time-averaged force owing to surface photovoltage and image dipole forces, respectively. Trep is the repetition period of thepump-probe laser pulses. In ﬁgure (d), the instantaneous image dipole forces are shown as a height of orange and red bars, and differences from the largest
delay time condition (left ﬁgure) are indicated as red.
© 2024 The Author(s). Published on behalf of015003-5
The Japan Society of Applied Physics by IOP Publishing Ltd

Appl. Phys. Express 17, 015003 (2024)

H. Mogi et al.

When the delay time td is sufﬁciently long, the responses tothe pump and probe light excitations are induced equally. Let
us consider the case of irradiating the probe pulse while
photoexcited carriers by the pump pulse are present by
reducing td. For simplicity, assuming the ﬂat band condition(where the amount of photoexcited carriers on the surface issaturated, therefore SPV and αs also saturate for each lightirradiation), the change induced by the probe light will
increase to the same peak height as that caused by thepump light.
For the case of the force induced by SPV, as previously
mentioned, since the force induced by SPV appears as a time
integral (green area in Fig. 4(c)), the shorter the delay time,
the weaker the measured attractive force becomes. This trend
is similar to the signal detection principle of time-resolved
STM when optical absorption bleaching is present.1,20,21)
On the other hand, for the image dipole force shown in
Fig. 4(b), when contemplating the force transient response in
the high-speed regime, the force is only measured during
light irradiation that is sufﬁciently shorter than the rising timeof αs due to the carrier accumulation on the surface, as shownby the orange and red bars in Fig. 4(d). Furthermore, whenusing delay time modulation, since the value at longer delay
times serves as a reference, the change in the magnitude of
the force induced by the pump light indicated by the red bars
in Fig. 4(d) is probed at td, ΔFimage = Fimage(td)—Fimage(td, ref). Therefore, a larger attractive force is detected forshorter delay times. That is, the observed signal with thedelay time modulation shows opposite polarity in case of theforce derived from SPV shown in Fig. 4(c) and image dipole
shown in Fig. 4(d).
Here, the latter mechanism corresponds well to theexperimental results. To clarify this point, we measured Δf
responsive to the delay time modulation and the time
variation of the phase (Fig. S1). The attractive force wasstronger when the delay was shorter, indicating that we
captured the time-resolved signal through the image dipole
force. By utilizing the dipole that forms momentarily when
the probe light is irradiated, we successfully measured thecarrier dynamics of the sample excited by the pump light,
such as recombination through intragap states and diffusion.
Using a tuning fork and setting the measurement conditions
to the repulsive region with a small amplitude of 4 nm, it isconsidered that the measurement of the near-ﬁeld forces by
PiFM became straightforward.
In conclusion, we developed a time-resolved force microscopy technique by integrating AFM using a tuning fork-type
cantilever with the delay time modulation method for opticalpump-probe light. We successfully measured the dynamics ofsurface recombination and diffusion of photoexcited carriersin bulk WSe2, which is challenging owing to the effect of thetunneling current in time-resolved STM. By combining withmultiprobe systems and using even shorter-pulse laser
light,4,30) we anticipate new developments such as timeresolved measurements of light-induced ultrafast non-equilibrium dynamics, including measurements in the operation conditions of nanostructures and device structures.
Acknowledgments We acknowledge the ﬁnancial support of a Grant-inAid for Scientiﬁc Research (20H00341, 22H00289, 22K14597 and 23H00264,)
from the Japan Society for the Promotion of Science, Japan Core Research
Evolutional Science and Technology (CREST) (JPMJCR1875), and JST
PRESTO (JPMJPR22AA).
Supporting Information The supporting information is available on the
publication’s website at DOI 10.35848/1882-0786/ad0c04.
Notes

The authors declare no competing interests.

1) Y. Terada, S. Yoshida, O. Takeuchi, and H. Shigekawa, Nat. Photonics 4,869 (2010).
2) S. Yoshida, Y. Aizawa, Z.-H. Wang, R. Oshima, Y. Mera, E. Matsuyama,
H. Oigawa, O. Takeuchi, and H. Shigekawa, Nat. Nanotechnol. 9, 588 (2014).
3) S. Yoshida, Y. Arashida, H. Hirori, T. Tachizaki, A. Taninaka, H. Ueno,
O. Takeuchi, and H. Shigekawa, ACS Photonics 8, 315 (2021).
4) H. Mogi et al., NPJ 2D Mater. Appl. 6, 72 (2022).
5) Y. Arashida, H. Mogi, M. Ishikawa, I. Igarashi, A. Hatanaka, N. Umeda,
J. Peng, S. Yoshida, O. Takeuchi, and H. Shigekawa, ACS Photonics 9,3156 (2022).
6) L. Wang, Y. Xia, and W. Ho, Science 376, 401 (2022).
7) M. Plankl et al., Nat. Photonics 15, 594 (2021).
8) V. Jelic, K. Iwaszczuk, P. H. Nguyen, C. Rathje, G. J. Hornig, H. M. Sharum,
J. R. Hoffman, M. R. Freeman, and F. A. Hegmann, Nat. Phys. 13, 591(2017).
9) K. Yoshioka, I. Katayama, Y. Minami, M. Kitajima, S. Yoshida,
H. Shigekawa, and J. Takeda, Nat. Photonics 10, 762 (2016).
10) M. Abdo, S. Sheng, S. Rolf-Pissarczyk, L. Arnhold, J. A. J. Burgess,M. Isobe, L. Malavolti, and S. Loth, ACS Photonics 8, 702 (2021).
11) R. J. Hamers and D. G. Cahill, Appl. Phys. Lett. 57, 2031 (1990).
12) J. Jahng, J. Brocious, D. A. Fishman, S. Yampolsky, D. Nowak, F. Huang,
V. A. Apkarian, H. K. Wickramasinghe, and E. O. Potma, Appl. Phys. Lett.
106, 083113 (2015).
13) Z. Schumacher, R. Rejali, R. Pachlatko, A. Spielhofer, P. Nagler,Y. Miyahara, D. G. Cooke, and P. Grütter, Proc. Natl. Acad. Sci. U. S. A.
117, 19773 (2020).
14) K. Araki, Y. Ie, Y. Aso, H. Ohoyama, and T. Matsumoto, Commun. Phys. 2,
10 (2019).
15) Z. Schumacher, A. Spielhofer, Y. Miyahara, and P. Grutter, Appl. Phys.
Lett. 110, 053111 (2017).
16) T. Kuroiwa and T. Takahashi, Jpn. J. Appl. Phys. 61, SL1004 (2022).
17) I. Rajapaksa, K. Uenal, and H. K. Wickramasinghe, Appl. Phys. Lett. 97,
073121 (2010).
18) J. Yamanishi, H. Yamane, Y. Naitoh, Y. J. Li, N. Yokoshi, T. Kameyama,
S. Koyama, T. Torimoto, H. Ishihara, and Y. Sugawara, Nat. Commun. 12,3865 (2021).
19) J. Jahng, H. Kwon, and E. Lee, Sensors 19, 1530 (2019).
20) K. Iwaya, M. Yokota, H. Hanada, H. Mogi, S. Yoshida, O. Takeuchi,
Y. Miyatake, and H. Shigekawa, Sci Rep. 13, 818 (2023).
21) H. Mogi, Z. Wang, R. Kikuchi, C. Hyun Yoon, S. Yoshida, O. Takeuchi,
and H. Shigekawa, Appl. Phys. Express 12, 025005 (2019).
22) S. Yoshida, Y. Terada, M. Yokota, O. Takeuchi, Y. Mera, and
H. Shigekawa, Appl. Phys. Express 6, 016601 (2013).
23) T. Arai and M. Tomitori, Phys. Rev. Lett. 93, 256101 (2004).
24) R. Addou and R. M. Wallace, ACS Appl. Mater. Interfaces 8, 26400 (2016).
25) C. M. Smyth, R. Addou, S. McDonnell, C. L. Hinkle, and R. M. Wallace,
2D Mater. 4, 025084 (2017).
26) R. Liu et al., Appl. Phys. Lett. 112, 211603 (2018).
27) J. Kim, H. Park, S. Yoo, Y. Im, K. Kang, and J. Kim, Adv. Mater. Interfaces
8, 2100718 (2021).
28) J. Jahng, J. Brocious, D. A. Fishman, F. Huang, X. Li, V. A. Tamma,
H. K. Wickramasinghe, and E. O. Potma, Phys. Rev. B 90, 155417 (2014).
29) M. L. Brongersma, N. J. Halas, and P. Nordlander, Nat. Nanotechnol. 10, 25(2015).
30) H. Mogi et al., Appl. Phys. Express 12, 045002 (2019).

015003-6© 2024 The Author(s). Published on behalf of
The Japan Society of Applied Physics by IOP Publishing Ltd