# Multi-Layer Palladium Diselenide as a Contact Material for Two-Dimensional Tungsten Diselenide Field-Effect Transistors

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1.${\mathit{PdSe}}_{2}$ Crystal Growth

#### 2.2. Device Fabrication

#### 2.3. Electrical Characterization

#### 2.4. FET Figures of Merit (FOM) Extraction and Device Modelling

#### 2.5. Laser Treatment of ${\mathit{WSe}}_{2}$

#### 2.6. AFM and In Operando KPFM Measurements

#### 2.7. Raman Spectroscopy

## 3. Results and Discussions

#### 3.1. Electrical Characteristics of ${\mathit{WSe}}_{2}$ FETs with Graphite and ${\mathit{PdSe}}_{2}$ Electrodes

#### 3.2. Contact Resistance of the ${\mathit{PdSe}}_{2}$${\mathit{/WSe}}_{2}$ Interface

#### 3.3. Optimizing Contact Interface via Laser-Driven Oxidation of ${\mathit{WSe}}_{2}$

#### 3.4. Electrical Characteristics of ${\mathit{WSe}}_{2}$ FETs with ${\mathit{WSe}}_{2}$${\mathit{/WSe}}_{y}$${O}_{x}$${\mathit{/PdSe}}_{2}$ Electrode Interface

## 4. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

- Cao, W.; Bu, H.; Vinet, M.; Cao, M.; Takagi, S.; Hwang, S.; Ghani, T.; Banerjee, K. The future transistors. Nature
**2023**, 620, 501–515. [Google Scholar] [CrossRef] - Zhu, K.; Wen, C.; Aljarb, A.A.; Xue, F.; Xu, X.; Tung, V.; Zhang, X.; Alshareef, H.N.; Lanza, M. The development of integrated circuits based on two-dimensional materials. Nat. Electron.
**2021**, 11, 775–785. [Google Scholar] [CrossRef] - Ahmad, W.; Gong, Y.; Abbas, G.; Khan, K.; Khan, M.; Ali, G.; Shuja, A.; Tareen, A.K.; Khan, Q.; Li, D. Evolution of low-dimensional material-based field-effect transistors. Nanoscale
**2021**, 10, 5162–5186. [Google Scholar] [CrossRef] [PubMed] - Rawat, A.; Gupta, A.K.; Rawat, B. Performance projection of 2D material-based CMO inverters for sub-10-nm channel length. IEEE Trans. Electron. Devices
**2021**, 68, 3622–3629. [Google Scholar] [CrossRef] - Fiori, G.; Bonaccorso, F.; Iannaccone, G.; Palacios, T.; Neumaier, D.; Seabaugh, A.; Banerjee, S.K.; Colombo, L. Electronics based on two-dimensional materials. Nat. Nanotechnol.
**2014**, 9, 768–779. [Google Scholar] [CrossRef] - Li, J.; Chen, X.; Zhang, D.W.; Zhou, P. Van-der-Waals heterostructure based field effect transistor application. Crystals
**2017**, 8, 8. [Google Scholar] [CrossRef] - Illarionov, Y.Y.; Knobloch, T.; Jech, M.; Lanza, M.; Akinwande, D.; Vexler, M.I.; Mueller, T.; Lemme, M.C.; Fiori, G.; Schwierz, F.; et al. Insulators for 2D nanoelectronics: The gap to bridge. Nat. Commun.
**2020**, 118, 3385. [Google Scholar] [CrossRef] - Arora, A.; Ganapathi, K.L.; Dixit, T.; Miryala, M.; Masato, M.; Rao, M.S.R.; Krishnan, A. Thickness-Dependent Nonlinear Electrical Conductivity of Few-Layer Muscovite Mica. Phys. Rev. Appl.
**2022**, 17, 064042. [Google Scholar] [CrossRef] - Zhou, J.; Lin, J.; Huang, X.; Zhou, Y.; Chen, Y.; Xia, J.; Wang, H.; Xie, Y.; Yu, H.; Lei, J.; et al. A library of atomically thin metal chalcogenides. Nature
**2018**, 556, 355–359. [Google Scholar] [CrossRef] - Di Bartolomeo, A. Emerging 2D materials and their van der Waals heterostructures. Nanomaterials
**2020**, 10, 579. [Google Scholar] [CrossRef] - Cheng, Q.; Pang, J.; Sun, D.; Wang, J.; Zhang, S.; Liu, F.; Chen, Y.; Yang, R.; Liang, N.; Lu, X.; et al. WSe
_{2}2D p-type semiconductor-based electronic devices for information technology: Design, preparation, and applications. InfoMat**2020**, 102, 656–697. [Google Scholar] [CrossRef] - Kumar, R.; Goel, N.; Hojamberdiev, M.; Kumar, M. Transition metal dichalcogenides-based flexible gas sensors. Sens. Actuator A Phys.
**2020**, 303, 111875. [Google Scholar] [CrossRef] - Sumesh, C.K.; Peter, S.C. Two-dimensional semiconductor transition metal based chalcogenide based heterostructures for water splitting applications. Dalton Trans.
**2019**, 48, 12772–12802. [Google Scholar] [CrossRef] - Maniyar, A.; Choudhary, S. Visible region absorption in TMDs/phosphorene heterostructures for use in solar energy conversion applications. RSC Adv.
**2020**, 10, 31730–31739. [Google Scholar] [CrossRef] - Wang, C.; Yang, F.; Gao, Y. The highly-efficient light-emitting diodes based on transition metal dichalcogenides: From architecture to performance. Nanoscale Adv.
**2020**, 2, 4323–4340. [Google Scholar] [CrossRef] - Aslam, M.A.; Tran, T.H.; Supina, A.; Siri, O.; Meunier, V.; Watanabe, K.; Taniguchi, T.; Kralj, M.; Teichert, C.; Sheremet, E.; et al. Single-crystalline nanoribbon network field effect transistors from arbitrary two-dimensional materials. npj 2D Mater. Appl.
**2022**, 6, 76. [Google Scholar] [CrossRef] - Murastov, G.; Aslam, M.A.; Tran, T.H.; Lassnig, A.; Watanabe, K.; Taniguchi, T.; Wurster, S.; Nachtnebel, M.; Teichert, C.; Sheremet, E.; et al. Photoinduced edge-specific nanoparticle decoration of two-dimensional tungsten diselenide nanoribbons. Commun. Chem.
**2023**, 6, 166. [Google Scholar] [CrossRef] - Pudasaini, P.R.; Oyedele, A.; Zhang, C.; Stanford, M.G.; Cross, N.; Wong, A.T.; Hoffman, A.N.; Xiao, K.; Duscher, G.; Mandrus, D.G.; et al. High-performance multilayer WSe
_{2}field-effect transistors with carrier type control. Nano Res.**2018**, 11, 722–730. [Google Scholar] [CrossRef] - Nan, H.; Zhou, R.; Gu, X.; Xiao, S.; Ostrikov, K.K. Recent advances in plasma modification of 2D transition metal dichalcogenides. Nanoscale
**2019**, 11, 19202–19213. [Google Scholar] [CrossRef] [PubMed] - Kozhakhmetov, A.; Stolz, S.; Tan, A.M.Z.; Pendurthi, R.; Bachu, S.; Turker, F.; Alem, N.; Kachian, J.; Das, S.; Hennig, R.G.; et al. Controllable p-type doping of 2D WSe
_{2}via vanadium substitution. Adv. Funct. Mater.**2021**, 31, 2105252. [Google Scholar] [CrossRef] - Grützmacher, S.; Heyl, M.; Nardi, M.V.; Koch, N.; List-Kratochvil, E.J.W.; Ligorio, G. Local Manipulation of the Energy Levels of 2D TMDCs on the Microscale Level via Microprinted Self-Assembled Monolayers. Adv. Mater. Interf.
**2023**, 10, 2300276. [Google Scholar] [CrossRef] - Pang, Y.-D.; Wu, E.-X.; Xu, Z.-H.; Hu, X.-D.; Wu, S.; Xu, L.-Y.; Liu, J. Effect of electrical contact on performance of WSe
_{2}field effect transistors. Chin. Phys. B**2021**, 30, 068501. [Google Scholar] [CrossRef] - Liu, Y.; Duan, X.; Shin, H.-J.; Park, S.; Huang, Y.; Duan, X. Promises and prospects of two-dimensional transistors. Chin. Phys. B
**2021**, 519, 43–53. [Google Scholar] [CrossRef] [PubMed] - Liao, W.; Zhao, S.; Li, F.; Wang, C.; Ge, Y.; Wang, H.; Wang, S.; Zhang, H. Interface engineering of two-dimensional transition metal dichalcogenides towards next-generation electronic devices: Recent advances and challenges. Nanoscale Horiz.
**2020**, 5, 787–807. [Google Scholar] [CrossRef] [PubMed] - Rai, A.; Movva, H.C.P.; Roy, A.; Taneja, D.; Chowdhury, S.; Banerjee, S.K. Progress in contact, doping and mobility engineering of MoS2: An atomically thin 2D semiconductor. Crystals
**2018**, 8, 316. [Google Scholar] [CrossRef] - Poljak, M.; Matić, M. Metallization-induced quantum limits of contact resistance in graphene nanoribbons with one-dimensional contacts. Materials
**2021**, 14, 3670. [Google Scholar] [CrossRef] [PubMed] - Jain, A.; Szabó, Á.; Parzefall, M.; Bonvin, E.; Taniguchi, T.; Watanabe, K.; Bharadwaj, P.; Luisier, M.; Novotny, L. One-dimensional edge contacts to a monolayer semiconductor. Nano Lett.
**2019**, 19, 6914–6923. [Google Scholar] [CrossRef] - Cheng, Z.; Yu, Y.; Singh, S.; Price, K.; Noyce, S.G.; Lin, Y.-C.; Cao, L.; Franklin, A.D. Immunity to contact scaling in MoS
_{2}transistors using in situ edge contacts. Nano Lett.**2019**, 19, 5077–5085. [Google Scholar] [CrossRef] [PubMed] - Das, S.; Chen, H.-Y.; Penumatcha, A.V.; Appenzeller, J. High performance multilayer MoS
_{2}transistors with scandium contacts. Nano Lett.**2013**, 13, 100–105. [Google Scholar] [CrossRef] [PubMed] - English, C.D.; Shine, G.; Dorgan, V.E.; Saraswat, K.C.; Pop, E. Improved contacts to MoS
_{2}transistors by ultra-high vacuum metal deposition. Nano Lett.**2016**, 16, 3824–3830. [Google Scholar] [CrossRef] - Kwon, G.; Choi, Y.; Lee, H.; Kim, H.; Jeong, J.; Jeong, K.; Baik, M.; Kwon, H.; Ahn, J.; Lee, E.; et al. Interaction-and defect-free van der Waals contacts between metals and two-dimensional semiconductors. Nat. Electron.
**2022**, 5, 241–247. [Google Scholar] [CrossRef] - Matković, A.; Petritz, A.; Schider, G.; Krammer, M.; Kratzer, M.; Karner-Petritz, E.; Fian, A.; Gold, H.; Gärtner, M.; Terfort, A.; et al. Interfacial band engineering of MoS
_{2}/gold interfaces using pyrimidine-containing self-assembled monolayers: Toward contact-resistance-free bottom-contacts. Adv. Electron. Matter.**2020**, 6, 2000110. [Google Scholar] [CrossRef] - Liu, Y.; Guo, J.; Zhu, E.; Liao, L.; Lee, S.-J.; Ding, M.; Shakir, I.; Gambin, V.; Huang, Y.; Duan, X. Approaching the Schottky–Mott limit in van der Waals metal–semiconductor junctions. Nature
**2018**, 557, 696–700. [Google Scholar] [CrossRef] [PubMed] - Liu, G.; Tian, Z.; Yang, Z.; Xue, Z.; Zhang, M.; Hu, X.; Wang, Y.; Yang, Y.; Chu, P.K.; Mei, Y.; et al. Graphene-assisted metal transfer printing for wafer-scale integration of metal electrodes and two-dimensional materials. Nat. Electron.
**2022**, 5, 275–280. [Google Scholar] [CrossRef] - Poljak, M.; Matić, M.; Župančić, T.; Zeljko, A. Lower limits of contact resistance in phosphorene nanodevices with edge contacts. Nanomaterials
**2022**, 12, 656. [Google Scholar] [CrossRef] [PubMed] - Poljak, M.; Matić, M. Optimum Contact Configurations for Quasi-One-Dimensional Phosphorene Nanodevices. Nanomaterials
**2023**, 13, 1759. [Google Scholar] [CrossRef] [PubMed] - Shen; Su, P.C.; Lin, C.; Chou, Y.; Cheng, A.S.; Park, C.C.; Chiu, J.H.; Lu, M.H.; Tang, A.Y.; Tavakoli, H.L.; et al. Ultralow contact resistance between semimetal and monolayer semiconductors. Nature
**2021**, 593, 211–217. [Google Scholar] [CrossRef] [PubMed] - Mootheri, V.; Arutchelvan, G.; Banerjee, S.; Sutar, S.; Leonhardt, A.; Boulon, M.; Huyghebaert, C.; Houssa, M.; Asselberghs, I.; Radu, I.; et al. Graphene based Van der Waals contacts on MoS
_{2}field effect transistors. 2D Mater.**2020**, 8, 015003. [Google Scholar] [CrossRef] - Ryu, H.; Kim, D.; Kwon, J.; Park, S.K.; Lee, W.; Seo, H.; Watanabe, K.; Taniguchi, T.; Kim, S.; van der Zande, A.M.; et al. Fluorinated Graphene Contacts and Passivation Layer for MoS
_{2}Field Effect Transistors. Adv. Electron. Matter.**2022**, 8, 2101370. [Google Scholar] [CrossRef] - Li, Z.; Wang, Y.; Jiang, J.; Liang, Y.; Zhong, B.; Zhang, H.; Yu, K.; Kan, G.; Zou, M. Temperature-dependent Raman spectroscopy studies of 1–5-layer WSe
_{2}. Nano Res.**2020**, 13, 591–595. [Google Scholar] [CrossRef] - Liu; Tan, Y.; Chou, C.; Nayak, H.; Wu, A.; Ghosh, D.; Chang, R.; Hao, H.Y.; Wang, Y.; Kim, X.; et al. Thermal oxidation of WSe
_{2}nanosheets adhered on SiO_{2}/Si substrates. Nano Lett.**2015**, 15, 4979–4984. [Google Scholar] [CrossRef] - Illarionov, Y.Y.; Waltl, M.; Rzepa, G.; Knobloch, T.; Kim, J.-S.; Akinwande, D.; Grasser, T. Highly-stable black phosphorus field-effect transistors with low density of oxide traps. npj 2D Mater. Appl.
**2017**, 1, 23. [Google Scholar] [CrossRef] - Wang, J.-B.; Ren, Z.; Hou, Y.; Yan, X.-L.; Liu, P.-Z.; Zhang, H.; Zhang, H.-X.; Guo, J.-J. A review of graphene synthesis at low temperatures by CVD methods. New Carbon Mater.
**2020**, 35, 193–208. [Google Scholar] [CrossRef] - Liu, W.; Kang, J.; Sarkar, D.; Khatami, Y.; Jena, D.; Banerjee, K. Role of metal contacts in designing high-performance monolayer n-type WSe
_{2}field effect transistors. Nano Lett.**2013**, 13, 1983–1990. [Google Scholar] [CrossRef] [PubMed] - Zhang, L.; Zhang, Y.; Sun, X.; Jia, K.; Zhang, Q.; Wu, Z.; Yin, H. High-performance multilayer WSe
_{2}p-type field effect transistors with Pd contacts for circuit applications. J. Mater. Sci. Mater. Electron.**2021**, 32, 17427–17435. [Google Scholar] [CrossRef] - Oyedele, A.D.; Yang, S.; Feng, T.; Haglund, A.V.; Gu, Y.; Puretzky, A.A.; Briggs, D.; Rouleau, C.M.; Chisholm, M.F.; Unocic, R.R.; et al. Defect-mediated phase transformation in anisotropic two-dimensional PdSe
_{2}crystals for seamless electrical contacts. J. Am. Chem. Soc.**2019**, 141, 8928–8936. [Google Scholar] [CrossRef] [PubMed] - Seo, J.-E.; Park, E.; Das, T.; Kwak, J.Y.; Chang, J. Demonstration of PdSe
_{2}CMOS Using Same Metal Contact in PdSe_{2}n-/p-MOSFETs through Thickness-Dependent Phase Transition. Adv. Electron. Mater.**2022**, 8, 2200485. [Google Scholar] [CrossRef] - Long, M.; Wang, Y.; Wang, P.; Zhou, X.; Xia, H.; Luo, C.; Huang, S.; Zhang, G.; Yan, H.; Fan, Z.; et al. Palladium diselenide long-wavelength infrared photodetector with high sensitivity and stability. Adv. Electron. Mater.
**2019**, 13, 2511–2519. [Google Scholar] [CrossRef] [PubMed] - Gu, Y.; Cai, H.; Dong, J.; Yu, Y.; Hoffman, A.N.; Liu, C.; Oyedele, A.D.; Lin, Y.C.; Ge, Z.; Puretzky, A.A.; et al. Two-dimensional palladium diselenide with strong in-plane optical anisotropy and high mobility grown by chemical vapor deposition. Adv. Mater.
**2020**, 32, 1906238. [Google Scholar] [CrossRef] - Sun, J.; Shi, H.; Siegrist, T.; Singh, D.J. Electronic, transport, and optical properties of bulk and mono-layer PdSe
_{2}. Appl. Phys. Lett.**2015**, 107, 153902. [Google Scholar] [CrossRef] - Liang, Q.; Wang, Q.; Zhang, Q.; Wei, J.; Lim, S.X.; Zhu, R.; Hu, J.; Wei, W.; Lee, C.; Sow, C.; et al. High-performance, room temperature, ultra-broadband photodetectors based on air-stable PdSe
_{2}. Adv. Mater.**2019**, 31, 1807609. [Google Scholar] [CrossRef] - Wang, Y.; Pang, J.; Cheng, Q.; Han, L.; Li, Y.; Meng, X.; Ibarlucea, B.; Zhao, H.; Yang, F.; Liu, H.; et al. Applications of 2D-layered palladium diselenide and its van der Waals heterostructures in electronics and optoelectronics. Nano–Micro Lett.
**2021**, 13, 143. [Google Scholar] [CrossRef] - Liang, Q.; Chen, Z.; Zhang, Q.; Wee, A.T.S. Pentagonal 2D transition metal dichalcogenides: PdSe
_{2}and beyond. Adv. Funct. Mater.**2022**, 32, 2203555. [Google Scholar] [CrossRef] - Oyedele, A.D.; Yang, S.; Liang, L.; Puretzky, A.A.; Wang, K.; Zhang, J.; Yu, P.; Pudasaini, P.R.; Ghosh, A.W.; Liu, Z.; et al. PdSe2: Pentagonal two-dimensional layers with high air stability for electronics. J. Am. Chem. Soc.
**2017**, 139, 14090–14097. [Google Scholar] [CrossRef] [PubMed] - Withanage, S.S.; Khondaker, S.I. Low pressure CVD growth of 2D PdSe
_{2}thin film and its application in PdSe_{2}-MoSe_{2}vertical heterostructure. 2D Mater.**2022**, 9, 025025. [Google Scholar] [CrossRef] - Sata, Y.; Moriya, R.; Masubuchi, S.; Watanabe, K.; Taniguchi, T.; Machida, T. n-and p-type carrier injections into WSe
_{2}with van der Waals contacts of two-dimensional materials. Jpn. J. Appl. Phys.**2017**, 56, 04CK09. [Google Scholar] [CrossRef] - Laturia, A.; Van de Put, M.L.; Vandenberghe, W.G. Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: From monolayer to bulk. npj 2D Mater. Appl.
**2018**, 2, 6. [Google Scholar] [CrossRef] - Nečas, D.; Klapetek, P. Gwyddion: An open-source software for SPM data analysis. Open Phys.
**2012**, 10, 181–188. [Google Scholar] [CrossRef] - Zhou, L.; Ge, C.; Yang, H.; Sun, Y.; Zhang, J. A high-pressure enhanced coupling effect between graphene electrical contacts and two-dimensional materials thereby improving the performance of their constituent FET devices. J. Mater. Chem. C
**2019**, 7, 15171–15178. [Google Scholar] [CrossRef] - Watson, A.J.; Lu, W.; Guimarães, M.H.D.; Stöhr, M. Transfer of large-scale two-dimensional semiconductors: Challenges and developments. 2D Mater.
**2021**, 8, 032001. [Google Scholar] [CrossRef] - Pan, Y.; Rahaman, M.; He, L.; Milekhin, I.; Manoharan, G.; Aslam, M.A.; Blaudeck, T.; Willert, A.; Matković, A.; Madeira, T.I.; et al. Exciton tuning in monolayer WSe
_{2}via substrate induced electron doping. Nanoscale Adv.**2022**, 4, 5102–5108. [Google Scholar] [CrossRef] - Allain, A.; Kang, J.; Banerjee, K.; Kis, A. Electrical contacts to two-dimensional semiconductors. Nat. Mater.
**2015**, 14, 1195–1205. [Google Scholar] [CrossRef] - Wang, Y.; Chhowalla, M. Making clean electrical contacts on 2D transition metal dichalcogenides. Nat. Rev. Phys.
**2022**, 4, 101–112. [Google Scholar] [CrossRef] - Lee, K.; Ngo, T.D.; Lee, S.; Shin, H.; Choi, M.S.; Hone, J.; Yoo, W.J. Effects of Oxygen Plasma Treatment on Fermi-Level Pinning and Tunneling at the Metal–Semiconductor Interface of WSe
_{2}FETs. Adv. Electron. Mater.**2023**, 9, 2200955. [Google Scholar] [CrossRef] - Ngo, T.D.; Choi, M.S.; Lee, M.; Ali, F.; Hassan, Y.; Ali, N.; Liu, S.; Lee, C.; Hone, J.; Yoo, W.J. Selective Electron Beam Patterning of Oxygen-Doped WSe
_{2}for Seamless Lateral Junction Transistors. Adv. Sci.**2022**, 9, 2202465. [Google Scholar] [CrossRef] [PubMed] - Moon, I.; Lee, S.; Lee, M.; Kim, C.; Seol, D.; Kim, Y.; Kim, K.H.; Yeom, G.Y.; Teherani, J.T.; Hone, J.; et al. The device level modulation of carrier transport in a 2D WSe
_{2}field effect transistor via a plasma treatment. Nanoscale**2019**, 11, 17368–17375. [Google Scholar] [CrossRef] - Kang, W.–M.; Lee, S.T.; Cho, I.–T.; Park, T.H.; Shin, H.; Hwang, C.S.; Lee, C.; Hao, H.Y.; Park, B.-G.; Lee, J.-H.; et al. Multi-layer WSe
_{2}field effect transistor with improved carrier-injection contact by using oxygen plasma treatment. Solid-State Electron.**2018**, 140, 2–7. [Google Scholar] - Li, Q.; Song, J.; Besenbacher, F.; Dong, M. Two-dimensional material confined water. Acc. Chem. Res.
**2015**, 48, 119–127. [Google Scholar] [CrossRef] [PubMed] - Jain, A.; Bharadwaj, P.; Heeg, S.; Parzefall, M.; Taniguchi, T.; Watanabe, K.; Novotny, L. Minimizing residues and strain in 2D materials transferred from PDMS. Nanotechnology
**2018**, 29, 265203. [Google Scholar] [CrossRef] - Wang, W.; Clark, N.; Hamer, M.; Carl, A.; Tovari, E.; Sullivan-Allsop, S.; Tillotson, E.; Gao, Y.; de Latour, H.; Selles, F.; et al. Clean assembly of van der Waals heterostructures using silicon nitride membranes. Nat. Electron.
**2023**, 6, 981–990. [Google Scholar] [CrossRef] - Purdie, D.G.; Pugno, N.M.; Taniguchi, T.; Watanabe, K.; Ferrari, A.C.; Lombardo, A. Cleaning interfaces in layered materials heterostructures. Nat. Commun.
**2018**, 9, 5387. [Google Scholar] [CrossRef] [PubMed] - Jeon, D.; Kim, H.; Gu, M.; Kim, T. Imaging Fermi-level hysteresis in nanoscale bubbles of few-layer MoS
_{2}. Commun. Mater.**2023**, 4, 62. [Google Scholar] [CrossRef] - Zhang, R.; Drysdale, D.; Koutsos, V.; Cheung, R. Controlled layer thinning and p-type doping of WSe
_{2}by vapor XeF_{2}. Adv. Funct. Mater.**2017**, 27, 1702455. [Google Scholar] [CrossRef] - Park, W.; Pak, Y.; Jang, H.Y.; Nam, J.H.; Kim, T.H.; Oh, S.; Choi, S.M.; Kim, Y.; Cho, B. Improvement of the bias stress stability in 2D MoS
_{2}and WS_{2}transistors with a TiO_{2}interfacial layer. Nanomaterials**2019**, 9, 1155. [Google Scholar] [CrossRef] [PubMed] - Ye, M.; Zhang, D.; Yap, Y.K. Recent advances in electronic and optoelectronic devices based on two-dimensional transition metal dichalcogenides. Electronics
**2017**, 6, 43. [Google Scholar] [CrossRef] - Fei, W.; Trommer, J.; Lemme, M.C.; Mikolajick, T.; Heinzig, A. Emerging reconfigurable electronic devices based on two-dimensional materials: A review. InfoMat
**2022**, 4, e12355. [Google Scholar] [CrossRef] - Feng, C.; Wu, W.; Liu, H.; Wang, J.; Wan, H.; Ma, G.; Wang, H. Emerging Opportunities for 2D Materials in Neuromorphic Computing. Nanomaterials
**2023**, 13, 2720. [Google Scholar] [CrossRef]

**Figure 1.**Electrical characteristics of graphite- and ${\mathrm{PdSe}}_{2}$-contacted ${\mathrm{WSe}}_{2}$ FETs: (

**a**) Schematic representation of device configuration with optical images of ${\mathrm{WSe}}_{2}$ FETs (scale bar: 10 µm). (

**b**,

**c**) Semi-log electrical transfer curves of devices with graphite (Gr) and ${\mathrm{PdSe}}_{2}$ contacts, respectively. The ${I}_{\mathrm{D}}$ in (

**b**,

**c**) is scaled by the mean width of the channels to allow for better comparison of the current values between the different devices. The horizontal dashed lines that interconnect (

**b**,

**c**) serve as a guide to see the reached on- and off-state current levels. The red arrow in (

**c**) indicates over an order of magnitude larger current of the hole branch in the case of ${\mathrm{PdSe}}_{2}$ contacts. (

**d**) Comparison of the device width-scaled electrical transfer curves (${\mathrm{PdSe}}_{2}$ contacted device) measured at 300 K (orange) and 78 K (purple), presented in linear scale. The arrows indicate the direction of the ${V}_{\mathrm{G}}$ sweep, highlighting an increase in the hysteresis observed at 300 K. (

**e**) Output curves for the hole and electron branches at 78 K (2 × ${10}^{-2}$ mbar) of a device with ${\mathrm{PdSe}}_{2}$ contacts. Note that the current values for the n-branch are approximately one order of magnitude lower than for the p-branch. The different colored lines in (

**e**) represent the curves at the different values of ${V}_{\mathrm{G}}$, as indicated in the figure.

**Figure 2.**Contact resistance of the ${\mathrm{PdSe}}_{2}$${\mathrm{/WSe}}_{2}$ interface: (

**a**) Equivalent electrical scheme used for the self-consistent modelling of the output curves. (

**b**,

**c**) Electrical output curves of a${\mathrm{PdSe}}_{2}$${\mathrm{/WSe}}_{2}$${\mathrm{/PdSe}}_{2}$ device measured at 300 K for the hole and electron branches, respectively. Different colored circles represent the measured ${I}_{\mathrm{D}}$ values at set different ${V}_{\mathrm{G}}$ as indicated in the right corner of the sub-panels (

**b**,

**c**). The dashed lines are a model for the entire data set. Red arrows in (

**c**) indicate a severe downward bending of the output curves at lower ${V}_{\mathrm{D}}$. Contact resistance values ($W{R}_{\mathrm{C}}$) extracted by modelling the curves from (

**b**,

**c**) are indicated in each sub-panel. (

**d**–

**f**) In operando KPFM potential profiles recorded as single lines across the channel, measured under ambient conditions. Solid lines present the work function difference corrected potential drops, and the dashed lines are linear fits to the experimental curves. (

**d**) A sequence of the potential drops with varied ${V}_{\mathrm{D}}$. (

**e**) Alternating the source and drain contacts, which demonstrates that the steep potential drop is related to the grounded electrode. (

**f**) Comparison of the potential drops at ${V}_{\mathrm{D}}$ = 1.5 V, with ${V}_{\mathrm{G}}$ setting the device in an on state of the hole and electron branches, labelled with (1) and (2), respectively. Insets in (

**f**) provide the operation points and the extracted $W{R}_{\mathrm{C}}$ values from the KPFM measurements.

**Figure 3.**Laser treatment of ${\mathrm{WSe}}_{2}$: ((

**a**) i–$iii$) Schematic cross-section of the laser-treated devices (not to scale), presenting the laser treatment process of the electrode interface step by step. ((

**b**) i–$iii$) Optical micrographs (scale 5 µm) of a representative device corresponding to each fabrication step in ((

**a**) i–$iii$). ((

**a**,

**b**) i) The heterostack of ${\mathrm{WSe}}_{2}$/hBN on a local gate electrode prior to the laser treatment, and ((

**a**,

**b**) $ii$) after the top part of the ${\mathrm{WSe}}_{2}$ flake was scanned by the laser (exposed part of the ${\mathrm{WSe}}_{2}$ flake is indicated by the dashed lines). ((

**a**,

**b**) $iii$) The same device after stamping of ${\mathrm{PdSe}}_{2}$ contacts. In the presented case, only one side of the channel–electrode interface was laser-treated. (

**c**) A zoom in on the schematic in ((

**a**) $iii$) highlighting the part of the ablated ${\mathrm{WSe}}_{2}$ layer, part of the oxidised ${\mathrm{WSe}}_{y}$${O}_{x}$ layer, and the unmodified part of the ${\mathrm{WSe}}_{2}$ layer.

**Figure 4.**Topography changes and Raman investigation of laser-treated ${\mathrm{WSe}}_{2}$: (

**a**) Atomic force microscopy (AFM) image of a ${\mathrm{WSe}}_{2}$ flake on hBN before laser exposure with the corresponding line profile (height) of the flake. The predominant morphological features are water/air bubbles trapped at the${\mathrm{WSe}}_{2}$/hBN and ${\mathrm{hBN/SiO}}_{2}$ interfaces. (

**b**) The same area as in (

**a**) treated with a 50 mW 532 nm laser beam. The exposed region is marked with a dashed rectangle, and the laser scanning direction is indicated with an arrow. The corresponding height profiles are presented at the bottom of the topography images. (

**a**,

**b**) Lateral scale bar 2 µm, z-scale 25 nm. (

**c**) Raman spectrum before and after laser irradiation, recorded with 5 mW, 532 nm, and 5 × 10 s acquisition parameters. The main ${\mathrm{WSe}}_{2}$ peaks are preserved and enhanced in intensity after the laser treatment. Inset (

**b**) presents a zoomed-in region of the main ${{\mathrm{E}}^{1}}_{\mathrm{2g}}$ and ${A}_{1\mathrm{g}}$ modes.

**Figure 5.**Electrical response of ${\mathrm{WSe}}_{2}$${\mathrm{/WSe}}_{y}$${O}_{x}$${\mathrm{/PdSe}}_{2}$ electrode interface: (

**a**) Semi-log scale electrical transfer curves of a ${\mathrm{WSe}}_{2}$ device with both source and drain electrode interfaces treated by a laser prior to stamping ${\mathrm{PdSe}}_{2}$ contacts measured at 298 K, 2 × ${\mathrm{10}}^{-2}$ mbar. (

**b**) ${V}_{\mathrm{H}}$ plot as a function of a scan speed (measured at 298 K, 2 × ${10}^{-2}$ mbar). (

**c**) Position of the ${V}_{\mathrm{th}}$ for both forward and backward ${V}_{\mathrm{G}}$ sweeping with varied ${V}_{\mathrm{D}}$. The difference indicates the hysteresis (${V}_{\mathrm{H}}$) is independent of ${V}_{\mathrm{D}}$. (

**d**) Semi-log scale electrical transfer curves for an asymmetric ${\mathrm{WSe}}_{2}$ FET with only one contact pad treated by the laser. The dotted lines represent the drain electrode connected to the non-treated ${\mathrm{PdSe}}_{2}$ contact side, while source and drain were swapped for the solid black line. The arrows indicate the ${V}_{\mathrm{G}}$ sweeping direction.

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## Share and Cite

**MDPI and ACS Style**

Murastov, G.; Aslam, M.A.; Leitner, S.; Tkachuk, V.; Plutnarová, I.; Pavlica, E.; Rodriguez, R.D.; Sofer, Z.; Matković, A.
Multi-Layer Palladium Diselenide as a Contact Material for Two-Dimensional Tungsten Diselenide Field-Effect Transistors. *Nanomaterials* **2024**, *14*, 481.
https://doi.org/10.3390/nano14050481

**AMA Style**

Murastov G, Aslam MA, Leitner S, Tkachuk V, Plutnarová I, Pavlica E, Rodriguez RD, Sofer Z, Matković A.
Multi-Layer Palladium Diselenide as a Contact Material for Two-Dimensional Tungsten Diselenide Field-Effect Transistors. *Nanomaterials*. 2024; 14(5):481.
https://doi.org/10.3390/nano14050481

**Chicago/Turabian Style**

Murastov, Gennadiy, Muhammad Awais Aslam, Simon Leitner, Vadym Tkachuk, Iva Plutnarová, Egon Pavlica, Raul D. Rodriguez, Zdenek Sofer, and Aleksandar Matković.
2024. "Multi-Layer Palladium Diselenide as a Contact Material for Two-Dimensional Tungsten Diselenide Field-Effect Transistors" *Nanomaterials* 14, no. 5: 481.
https://doi.org/10.3390/nano14050481