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Taku Yoshimura, Hiroshi Shigeno, Rikuto Yamamura, [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), Yusuke Hoshi

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[Electrical and Optical Properties of hBN Capped MoTe<sub>2</sub> Monolayers Fabricated by Gold‐Mediated Exfoliation](https://mdr.nims.go.jp/datasets/d98e2d10-93fa-46f5-9a06-e30b3851e2ab)

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Electrical and Optical Properties of hBN Capped MoTe2 Monolayers Fabricated by Gold‐Mediated ExfoliationElectrical and Optical Properties of hBN Capped MoTe2Monolayers Fabricated by Gold-Mediated ExfoliationTaku Yoshimura, Hiroshi Shigeno, Rikuto Yamamura, Kenji Watanabe,Takashi Taniguchi, and Yusuke Hoshi*1. IntroductionTransition metal dichalcogenides (TMDCs) have attracted con-siderable research interest owing to their distinct band structuresand unique properties in ideal and atom-ically thin 2D systems. In particular,TMDCs with a monolayer (1L) thicknessare recognized as advanced materials foruse in nano- and microelectronic deviceswith various functionalities, taking advan-tage of features such as an ultrahighsurface-to-volume ratio and piezoelectricityresulting from the spatial inversion sym-metry breaking of crystal structures.[1–3]Recently, 1L-TMDCs have been employedin developing gas and chemical sensorsowing to their exceptional sensitivityto selected gases and environmentalconditions.[4–6] Among the different sens-ing technologies, semiconductor-basedfield-effect transistor (FET) sensors offerhigh potential for realizing mass productionowing to their low cost, miniaturization, andhigh compatibility with conventionalSi-based device fabrication processes. TheFET-type sensors operate by detecting thechange in the resistance of the 1L-TMDCs owing to the chargetransfer resulting from the adsorption of gas molecules on thechannel surface.[6–9] Therefore, understanding the effect of envi-ronmental conditions on the electrical properties of 1L-TMDCchannel FETs is crucial for improving sensor performance.The semiconducting molybdenum ditelluride monolayer(1L-MoTe2) exhibits outstanding ambipolar carrier transportcompared to other TMDC-based materials and an opticalbandgap of 1.1 eV, close to that of Si.[10–14] In addition, MoTe2FET sensors exhibit high sensitivity and excellent reversibilityat room temperature for various gases such as O2, NO2, andNH3 detection.[7,15,16] 1L-MoTe2 flakes are usually prepared bya mechanical tape exfoliation technique because high-qualitycrystals can be obtained. However, the resultant crystal size issmall, and the production yield is poor compared to that of otherTMDCs. Chemical vapor deposition (CVD) can be used to growlarge-area monolayer and multilayer MoTe2, but the resultantcrystal quality is inferior to that produced by mechanical tapeexfoliation.[17,18] In addition, the growth processes for producingsemiconducting MoTe2 must be sophisticated owing to the smalldifference in the formation energy between the semiconducting(2H) and metallic (1T 0) phases.[19] Recently, gold-mediated exfo-liation, a technique for peeling off the top monolayer of bulkcrystals using the strong adhesion of gold to TMDCs, hasbeen reported to enable the formation of large-area TMDCmonolayers.[20–22] The monolayer flakes are macroscopic inT. Yoshimura, H. Shigeno, R. Yamamura, Y. HoshiAdvanced Research LaboratoriesTokyo City University1-28-1 Tamazutsumi, Setagaya-ku, Tokyo 158-8557, JapanE-mail: yhoshi@tcu.ac.jpK. WatanabeResearch Center for Electronic and Optical MaterialsNational Institute for Materials ScienceTsukuba 305-0044, JapanT. TaniguchiResearch Center for Materials NanoarchitectonicsNational Institute for Materials ScienceTsukuba 305-0044, JapanThe ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/pssb.202400374.© 2024 The Author(s). physica status solidi (b) basic solid state physicspublished by Wiley-VCH GmbH. This is an open access article under theterms of the Creative Commons Attribution-NonCommercial-NoDerivsLicense, which permits use and distribution in any medium, providedthe original work is properly cited, the use is non-commercial and nomodifications or adaptations are made.DOI: 10.1002/pssb.202400374This study focuses on the electrical and optical properties of monolayerMoTe2 (1L-MoTe2) flakes fabricated via gold-mediated exfoliation, and it is demonstrated thatthis technique applies to the development of 1L-MoTe2 channel field-effect tran-sistors (FETs). The average area of the gold-exfoliated flakes is larger than that ofconventional tape exfoliation. While the samples without an hBN cap layer areeasily oxidized by atmospheric exposure for 1 day, increasing the number ofnonradiative recombination centers, the surface oxidation of 1L-MoTe2 can besuppressed by the deposition of the hBN cap layer. The transfer characteristics ofthe 1L-MoTe2 channel FETs show clear ambipolar behavior and excellent switchingproperties, with an on/off ratio of 105. It is shown that graphite/1L-MoTe2 junctionsform a Schottky barrier with an energy of 280meV, consistent with the theoreticalvalue. By lowering the vacuum level, the gate voltage at the conductivity minimumpoint shifts to a negative value and the subthreshold swing decreases, implyinga reduction in the interfacial trapped charge density due to the physisorption ofO2/H2O molecules. These results demonstrate that the electrical properties ofgold-exfoliated 1L-MoTe2 strongly depend on the environmental conditions.RESEARCH ARTICLEwww.pss-b.comPhys. Status Solidi B 2025, 262, 2400374 2400374 (1 of 6) © 2024 The Author(s). physica status solidi (b) basic solid state physicspublished by Wiley-VCH GmbHmailto:yhoshi@tcu.ac.jphttps://doi.org/10.1002/pssb.202400374http://creativecommons.org/licenses/by-nc-nd/4.0/http://www.pss-b.comhttp://crossmark.crossref.org/dialog/?doi=10.1002%2Fpssb.202400374&domain=pdf&date_stamp=2024-11-21centimeter size, and the crystal quality of the 1L-TMDCs can bedegraded during the chemical wet etching of gold films. In addi-tion, 1L-MoTe2 is easily oxidized upon exposure to air for severaldays owing to poor structural stability, leading to an increase innonradiative recombination centers.[23,24] However, reports ondevice applications of 1L-MoTe2 fabricated by gold-mediatedexfoliation remain limited. In this study, we focus on the electri-cal and optical properties of 1L-MoTe2 flakes prepared by gold-mediated exfoliation and demonstrated this technique applies tothe development of 1L-MoTe2 devices. Our device structuresinclude an hBN cap layer and graphite source/drain electrodeson the 1L-MoTe2 channels. hBN was stacked to avoid surface oxi-dation of the 1L-MoTe2 flakes under atmospheric conditions andsuppress crystal quality degradation due to the heating effectsduring device operation.[25–27] Graphite was chosen as thesource/drain electrode since it is a layered metallic material thatcan be easily integrated into a van der Waals heterostructure andexhibits the work function featuring near-midgap energy inMoTe2. The 1L-MoTe2 channel FETs exhibit clear ambipolarbehavior and switching properties, with an on/off ratio of≈105. Furthermore, the vacuum level reduction strongly affectsthe electrical properties of 1L-MoTe2 channel FETs due to thedesorption of some molecules, which causes the charge transferof electrons.2. Results and DiscussionFigure 1a shows an optical microscopy image of the MoTe2 sam-ple prepared by gold-mediated exfoliation. TheMoTe2 flakes havesome different contrast regions owing to different thicknesses ineach region. Figure 1b represents a photoluminescence (PL)intensity map around photon energies of 1.05–1.17 eV in the areasurrounded by the red dashed line in Figure 1a. The PL intensityis uniform over the area surrounded by the white dashed line,indicating the uniformity of the crystal quality in MoTe2. As pre-viously reported, the PL intensity strongly depends on the layernumber owing to the band structure modulation; thus, the areawith a large PL intensity corresponds to the thinner MoTe2.[14]We measured the PL spectrum at room temperature to identifythe number of layers in the MoTe2 region with high PL intensity.Figure 1c shows a PL spectrum at the P1 position in Figure 1b.The spectrum has an intense peak at 1.09 eV owing to the radia-tive recombination of a neutral exciton, resulting in a monolayerof the MoTe2 flake. Moreover, the spectrum also has a low-energyshoulder, which is tentatively attributed to the PL signals fromthe exciton–phonon interactions.[28,29] Figure 1d shows a repre-sentative Raman spectrum for the as-prepared 1L-MoTe2 flakes.It is characterized by two prominent peaks based on the A1g andE2g vibration modes at 165 and 230 cm�1 and by the absence of aB12g mode at ≈290 cm�1, which are typical signatures of 1L-MoTe2.[14,30,31] Figure 1e shows histograms of the areas of theMoTe2 flakes prepared by gold-mediated exfoliation and standardtape exfoliation techniques. The average area of the gold-exfoliated 1L-MoTe2 flakes is 30 times larger than that of the tapeexfoliation. The gold-mediated exfoliation technique enabled theformation of large-area 1L-MoTe2 flakes with uniform crystalquality, demonstrating its usefulness for applications in 1L-MoTe2channel devices. The monolayer areas of MoTe2 appear to besmaller than those of the other TMDCs prepared by Au-mediatedexfoliation, possibly owing to the differences in the crystal qualityand size of the initial bulk crystal before gold deposition.We measured the PL spectra of samples prepared by gold-mediated exfoliation to investigate the effect of atmosphericexposure under typical laboratory room light illumination onthe crystal quality degradation of 1L-MoTe2. Figure 2a shows thePL spectra of 1L-MoTe2 with and without the hBN cap layer. Theblack traces correspond to the as-prepared samples while the redtraces correspond to the samples exposed to air for 2 days. The PLintensity drastically reduces after atmospheric exposure for thesample without the hBN cap layer but not for the sample withthe hBN cap layer. Figure 2b shows the PL intensities normalizedto the intensity I0 obtained from the as-prepared sample, plottedas a function of the atmospheric exposure time for samples withand without the hBN cap layer. For the sample without the hBNcap layer, the normalized PL intensities are reduced to less than0.5 after 1 day. Note that the PL spectral shape, except for the PLintensity, is not changed even after the exposure time of 7 days(see Figure S2, Supporting Information). This indicates that thesurface oxidation of the 1L-MoTe2 enhances the nonradiativerecombination rates of neutral excitons, rather than throughthe formation of defect-bound excitons that emit the photonsat a lower energy than that of the neutral exciton. In contrast,the PL intensity of the samples with the hBN cap layer is almostconstant, with no reduction in the PL intensity by atmosphericFigure 1. a) Optical microscope image of the gold-exfoliated MoTe2 flake.b) PL intensity map in the area surrounded by red dashed line in (a). c) PLspectrum at the P1 position in (b). d) Raman spectrum of the 1L-MoTe2fabricated by Au-mediated exfoliation. e) Histogram of flake areas for con-ventional mechanical-exfoliated and gold-exfoliated 1L-MoTe2.www.advancedsciencenews.com www.pss-b.comPhys. Status Solidi B 2025, 262, 2400374 2400374 (2 of 6) © 2024 The Author(s). physica status solidi (b) basic solid state physicspublished by Wiley-VCH GmbH 15213951, 2025, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/pssb.202400374 by National Institute For, Wiley Online Library on [08/07/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.pss-b.comexposure even after 30 days. These results indicate that the hBNcap layer effectively suppressed crystal quality degradation basedon the surface oxidation of 1L-MoTe2 prepared by gold-mediatedexfoliation.Electrical properties were measured to verify that the gold-mediated exfoliation technique is effective for developinglarge-area 1L-MoTe2 channel devices with graphite source-draincontacts. Figure 3a shows an optical microscope image of a1L-MoTe2 channel FET. Figure 3b shows the ISD–VG character-istics as a function of temperature with VG ranging from �40 to10 V. The source-drain current increases when high positive andnegative back-gate voltages are applied, indicating ambipolartransport behavior. In addition, excellent switching propertieswith a large on/off ratio of ≈105 were observed in the n-type oper-ating regime at room temperature.The Schottky barrier height was determined from thetemperature-dependent transport characteristics using the fol-lowing equationISD ¼ A�T2exp �qΦB=kBT� �1� exp �qVSD=kBT� �� �(1)where A* is Richardson’s constant, q is the elementary charge, kBis Boltzmann’s constant, T is the temperature, VSD is the source-drain voltage of 0.5 V, and ΦB is the potential barrier height mea-sured from the Fermi level.[13,32] Notably, exp(�qVSD/kBT ) ismuch smaller than unity under the experimental conditions.Therefore, the electron injection barrier energy qΦB can be esti-mated from the slope of the ln(ISD/T2) in the positive gate voltageregion plotted as a function of 1000/T in Figure 3c according toEquation (1). Figure 3d shows the barrier height plotted as a func-tion of back-gate voltage. The electron injection is divided intotwo schemes; at their boundary, the band configuration becomesa flat band condition. At a gate voltage smaller than the flat bandvoltage (VFB), an electron injection barrier is formed at the graph-ite/1L-MoTe2 interfaces owing to the band bending of 1L-MoTe2by applying the back-gate voltage; thus, the electron injection bythe thermionic emission scheme dominates the current. A back-gate voltage larger than VFB lowers the 1L-MoTe2 band, and elec-trons accumulate in the 1L-MoTe2 channel. Under a sufficientlyhigh back-gate bias, the Schottky barrier becomes sufficientlythin to allow thermally assisted tunneling of electrons. As the bar-rier height does not change under a large back-gate bias condi-tion, the tunneling component begins to dominate the current.Considering these band configurations, the injection barrierenergy qΦB at VG=VFB corresponds to the Schottky barrierheight; the qΦB value can be estimated to be ≈0.28 eV. TheSchottky barrier height is consistent with the theoretical valuescalculated from the work functions of graphite (≈4.7 eV) andn-type MoTe2 (≈4.49 eV).[11,33]We measured the transfer characteristics of hBN/1L-MoTe2channel FETs at room temperature at different vacuum levelsto investigate the effect of environmental conditions on the elec-trical properties of 1L-MoTe2. Figure 4a shows the dependence ofthe ISD–VG properties of a 1L-MoTe2 channel FET on the vacuumlevel. The transfer curves of the device exhibit symmetrical ambi-polar characteristics. The carrier mobilities are estimated to be0.8–1.1 cm2 Vs�1 for electrons and 0.6–1.0 cm2 Vs�1 for holesindependent of the vacuum level, which are comparable to thepreviously reported values in the few-layer MoTe2 channelFETs.[10,12,34,35] Figure 4b shows the back-gate voltage at the con-ductivity minimum point (VCMP) plotted as a function of vacuumlevel. The VCMP gradually shifts to negative values due to electronFigure 2. a) PL spectra for gold-exfoliated 1L-MoTe2 with and without hBNcap layer. Black and red traces correspond to the as-prepared samples andthe samples exposed to air for 2 days, respectively. b) Normalized PL inten-sity plotted as a function of exposure time in air. Filled and opened symbolsrepresent the samples with and without hBN cap layer, respectively.Figure 3. a) Optical microscope image of the 1L-MoTe2 channel FET withgraphite S/D electrodes. b) Temperature dependence of transfer charac-teristics in 1L-MoTe2 channel FET with graphite contacts. c) ln(ISD/T2) isplotted against 1000/T at different back gate voltages. The solid lines rep-resent a guide. d) Electron injection barrier height qΦB versus VG for theFET, and extraction of Schottky barrier height (black dashed line). The insetshows the band configurations of the Schottky junction around the1L-MoTe2/graphite interfaces when the VG is lower and higher than theflat band voltage VFB.www.advancedsciencenews.com www.pss-b.comPhys. Status Solidi B 2025, 262, 2400374 2400374 (3 of 6) © 2024 The Author(s). physica status solidi (b) basic solid state physicspublished by Wiley-VCH GmbH 15213951, 2025, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/pssb.202400374 by National Institute For, Wiley Online Library on [08/07/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.pss-b.comdoping as the vacuum level decreases. The change in sheet elec-tron density by the reduced pressure can be calculated asΔn2d=ΔVCMPCg/q where ΔVCMP is the back-gate voltage shiftat the conductivity minimum point by the reduced pressure fromatmospheric pressure to 6.9� 10�4 Pa, and Cg is the gate oxidecapacitance per unit area. The increase in the sheet electrondensity by the reduced pressure is found to be 1.3� 1012 cm�2.To confirm the pressure-dependent electron density modulationin the 1L-MoTe2, we investigated the dependence of pressure on aPL spectrum (see Figure S3, Supporting Information). Radiativerecombination of neutral excitons dominates under atmosphericconditions, indicating that the 1L-MoTe2 channel is nearly intrin-sic. As the pressure is reduced, the exciton PL intensity decreasesmonotonically due to the increased trion nonradiative recombina-tion rates.[36] This result supports that the reduced pressureincreases the electron density in the 1L-MoTe2. It has beenreported that when O2/H2O molecules are adsorbed on the1L-MoTe2 channel, electrons are transferred from the valenceband of 1L-MoTe2 to the energy level of the lowest unoccupiedmolecular orbits (LUMO) of the O2/H2O molecules, that is a holedoping to 1L-MoTe2 (Figure 4d).[37–39] Therefore, the reducedpressure is believed to cause the desorption of the O2/H2O mol-ecules physically adsorbed on 1L-MoTe2 and to increase the elec-tron density. In this device structure, the hBN cap layer isdeposited on the 1L-MoTe2 channel. As the hBN/1L-MoTe2 inter-face is atomically flat, the molecules exist at the interface between1L-MoTe2 and SiO2 rather than at the hBN/1L-MoTe2 interfaceand are desorbed by lowering the vacuum level.[40,41]Assuming that all the O2/H2O molecules physically adsorbedon 1L-MoTe2 are desorbed by reducing the vacuum level, we canquantitatively estimate the molecular density from the variationof the trapped charge density between the atmospheric condi-tions and the reduced pressure. We evaluated the trapped chargedensity using a method similar to that in ref. [10]. In 2D systems,the density of the interfacial trapped charge is obtained via thesubthreshold swing (SS) as followsSS ¼ kBT=q� �lnð10Þ 1þ Cit=Cg� �(2)where kB is the Boltzmann constant, T is the temperature, and Citis the interfacial charge capacitance. The trapped charge density isgiven by Dit=Cit/q. Since the physisorbed O2/H2O moleculeslead to the electron transfer from the valence band of the1L-MoTe2, we focus on the SS variation in the p-type regimeby reducing the vacuum level (Figure 4c). Under atmospheric con-ditions, the SS is 5.5 V dec�1, corresponding to a trapped chargedensity of 6.8� 1012 cm�2, while it is reduced to 4.2 V dec�1,corresponding to 5.2� 1012 cm�2, by lowering the pressure to6.9� 10�4 Pa. Thus, the density of the molecules physicallyadsorbed on the 1L-MoTe2 is estimated to be 1.6� 1012 cm�2,which is consistent with the aforementioned sheet electron densityvariation Δn2d calculated from the VCMP shift by lowering the vac-uum level. These results demonstrate that the phenomenon ofpressure-dependent changes in the electrical properties of the1L-MoTe2 channel FETs is responsible for the electron transferbased on the adsorption and desorption of O2/H2O molecules.In fact, we have confirmed that the pressure-dependent transportbehavior in the 1L-MoTe2 channels does not occur in the N2 envi-ronment. On the other hand, in the n-type regime, SS seems toincrease under reduced pressure. Since physisorbed moleculesare removed under reduced pressure, the van der Waals gapbetween 1L-MoTe2 and SiO2 becomes small. Thus, electrons inthe conduction band of 1L-MoTe2 may be trapped by the surfacestates on SiO2.There is concern that the presence of physisorbed O2/H2Omolecules at the 1L-MoTe2/SiO2 interface promotes oxidationof the 1L-MoTe2. Kotsakidis et al. analyzed the surface oxidationof CVD-grown WS2 and found that oxidation is observed uponexcitation of an electronic transition such as light irradiation forthe WS2 areas containing more defects.[42] In 1L-MoTe2, the typ-ical laboratory room light easily excites carriers due to the smalloptical bandgap of 1.09 eV, and thus, oxidation should proceeddue to the presence of O2/H2O molecules physisorbed at the 1L-MoTe2/SiO2 interface. However, the PL signals obtained fromthe hBN/1L-MoTe2 structures are stable even after long-termexposure to air under laboratory room light illumination asshown in Figure 2c, indicating that the surface oxidation ofthe 1L-MoTe2 is sufficiently suppressed. This phenomenon isexplained as follows. The surface oxidation of the 1L-MoTe2proceeds with the formation of crystal defects in the 1L-MoTe2,rather than by chemical reactions involving redox oxidation withO2/H2O molecules. In our case, the 1L-MoTe2 channels are cov-ered by hBN multilayers, which effectively suppress the forma-tion of crystal defects such as Te vacancies in the 1L-MoTe2.[25]Therefore, it is believed that the oxidation does not proceed by thepresence of O2/H2O molecules physisorbed at the interfacebetween the 1L-MoTe2 and SiO2 although the charge transferoccurs.Figure 4. a) Transfer characteristics at different vacuum levels for the 1L-MoTe2 channel FET. b) Back gate voltage at conductivity minimum pointVCMP and c) subthreshold swing in p-type regime plotted as a function ofthe vacuum levels. d) Schematic diagram illustrating charge transferbetween 1L-MoTe2 and O2/H2O molecules.www.advancedsciencenews.com www.pss-b.comPhys. Status Solidi B 2025, 262, 2400374 2400374 (4 of 6) © 2024 The Author(s). physica status solidi (b) basic solid state physicspublished by Wiley-VCH GmbH 15213951, 2025, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/pssb.202400374 by National Institute For, Wiley Online Library on [08/07/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.pss-b.com3. ConclusionWe investigated the electrical and optical properties of 1L-MoTe2flakes prepared by the gold-mediated exfoliation. The averagearea of the fabricated 1L-MoTe2 was ≈30 times larger than thatobtained by conventional tape exfoliation. In addition, surface oxi-dation of 1L-MoTe2 after exposure to air for 1 day occurred for thesamples without the hBN cap layer, leading to an increase innonradiative recombination centers. In contrast, oxidation wassufficiently suppressed for the samples with hBN. The transfercharacteristics of the 1L-MoTe2 channel FETs with graphite con-tacts showed clear ambipolar behavior and switching propertieswith an on/off ratio of ≈105. A shift in the gate voltage at the mini-mum conductivity point to a negative value was observed by low-ering the vacuum level. In addition, it was found that the SSdecreased as the vacuum level was lowered, indicating a reductionin the interfacial trapped charge density due to the physisorptionof O2/H2O molecules. The electrical properties of the 1L-MoTe2channel FETs fabricated by gold-mediated exfoliation werestrongly affected by the environmental conditions, and thesefindings are useful for developing FET-type gas sensors.4. Experimental SectionSchematics of the fabrication process and the 1L-MoTe2 channel devicestructure are shown in Figure S1 (see Section S1, Supporting Information).1) First, bulkMoTe2 crystalsweremechanically exfoliatedusing a commonlyavailable Nitto SPV 224R tape. 2) Gold was deposited on the exfoliatedMoTe2 crystals by thermal evaporation. 3) The gold film was peeled offtogether with the top layer of theMoTe2 crystals using thermal release tape(TRT).Theexfoliationof thesingle topmostMoTe2 layerwasattributedto thestronger adhesion strength between the topmost layer of MoTe2 and theevaporated gold than the van der Waals forces in the bulk MoTe2 crystal.4)Theexfoliatedgold/1L-MoTe2structuresontheTRTwere transferredontoa highly doped Si substrate with a 290 nm-thick SiO2 film. 5) The gold filmsurface was selectively etched using amixed aqueous solution consisting ofKI (4 g), I2 (1 g), andH2O (50mL). Next, graphite and hBNmultilayers wereprepared by mechanical tape exfoliation on a polydimethylsiloxane sheet.These flakes were successively picked by a stamping technique using poly-propylene carbonatewith a lens shape.[43,44] 6) ThehBN/graphite structureswere stacked directly on the 1L-MoTe2 formed by the Au-mediated exfolia-tion.Thegraphitecrystalswereusedas thesourceanddrainelectrodes in thedevice. Finally, the FET structures were annealed at 200 °C for 15 min toremove the residues at the 2D material interfaces.[25]A standard confocal microscope with a focusing diameter of≈2 μmwasused to observe PL signals from 1L-MoTe2. Spectrally and spatiallyresolved PL measurements were performed using a continuous-wave laserwith an emission wavelength of 532 nm coupled to a 60� microscopeobjective with a long working distance. PL signals were collected in a back-scattering geometry and detected using a liquid-nitrogen-cooled InGaAsdetector with a spectrometer. For the PL measurements, the excitationpower was maintained at 100 μW to avoid the spectral shape changesdue to power-dependent behavior.[45] For electrical measurements, thedevices were placed in a cryostat equipped with an electrical feedthrough,with the measurement temperature varied in the range of 180–300 K.A gate voltage VG was applied to the highly doped Si substrate.Supporting InformationSupporting Information is available from the Wiley Online Library or fromthe author.AcknowledgementsY.H. acknowledges the support from JSPS KAKENHI (grant nos. JPJP21K04812 and JP24K08206). K.W. and T.T. acknowledge support fromJSPS KAKENHI (grant nos. 20H00354 and 23H02052) and the WorldPremier International Research Center Initiative (WPI), MEXT, Japan.Conflict of InterestThe authors declare no conflict of interest.Data Availability StatementThe data that support the findings of this study are available from thecorresponding author upon reasonable request.Keywordsexfoliations, field-effect transistors, molybdenum ditelluride, monolayersReceived: July 24, 2024Revised: October 13, 2024Published online: November 21, 2024[1] H. Zeng, J. Dai, W. Yao, D. Xiao, X. Cui,Nat. Nanotechnol. 2012, 7, 490.[2] H. Zhu, Y. Wang, J. Xiao, M. Liu, S. Xiong, Z. J. Wong, Z. Ye, Y. Ye,X. Yin, X. Zhang, Nat. Nanotechnol. 2015, 10, 151.[3] A. Castellanos-Gomez, R. van Leeuwen, M. Buscema, H. S. J. van derZant, G. A. Steele, W. J. Venstra, Adv. Mater. 2013, 25, 6719.[4] Y. Tong, Z. Lin, J. T. L. Thong, D. S. H. Chan, C. Zhu, Appl. Phys. Lett.2015, 107, 123105.[5] Y. Kim, S.-K. Kang, N.-C. 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Status Solidi B 2025, 262, 2400374 2400374 (6 of 6) © 2024 The Author(s). physica status solidi (b) basic solid state physicspublished by Wiley-VCH GmbH 15213951, 2025, 4, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/pssb.202400374 by National Institute For, Wiley Online Library on [08/07/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.pss-b.com Electrical and Optical Properties of hBN Capped MoTe2 Monolayers Fabricated by Gold-Mediated Exfoliation 1. Introduction 2. Results and Discussion 3. Conclusion 4. Experimental Section