Structure and Electronic Property Correlation of 2D Platinum-Diselenide

Platinum diselenide (PtSe₂) is a two-dimensional (2D) layered noble metal dichalcogenide (NMDC), a subgroup of the transition-metal dichalcogenides (TMDCs). Its high negative piezoresistive gauge factor (GF) ^[1] and high charge carrier mobilities of up to 210 cm²/Vs. with stability in the air for many months ^[2], mechanical flexibility ^[3], and broadband optical absorption, ^[4] make it an interesting sensing, electronic and optoelectronic material.<br/><br/>PtSe₂ can be grown at CMOS-compatible temperatures below 400°C by thermally assisted conversion (TAC) ^[5]. In addition, it can be converted from a semiconductor to a semimetal by varying the number of layers ^[6–8]. Different device applications of PtS₂ have been demonstrated, both as piezoresistive nanoelectromechanical sensors (NMES) ^[1] and as isolated and waveguide-integrated photodetectors ^[4,9]. However, the experimental data shows significant variability that cannot simply be explained by the material thickness. Here, I will discuss how the nanocrystalline structure of TAC-grown PtSe₂ layers is related to the electronic properties of PtSe₂-based devices.<br/><br/>PtSe₂ layers grown with various parameters, thicknesses and methods were analyzed by Raman, X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). Large differences in Raman spectra could not be correlated with XPS and EDX data, which showed no significant differences between the chemical composition of the different films. canning tunneling electron microscopy images of two samples showed nanocrystalline films with similar thicknesses but different sizes and arrangements of the nanocrystals. Also, while one sample had well-aligned crystals in a rather homogeneous film, another sample showed slightly tilted and randomly rotated crystals.<br/><br/>The different PtSe₂ films were then transferred onto oxidized silicon substrates and electrically characterized. Sheet and contact resistance (<i>R_sh</i> and <i>R</i>_c), four-point probe field effect, and AC Hall measurements were performed to determine the material’s mobilities (µ). In addition, the PtSe₂ films were transferred onto flexible polyimide substrates to extract their piezoresistive GF using a bending beam configuration as described in ^[1].<br/><br/>We found large variations in <i>R_sh</i>, <i>R</i>_c, <i>µ</i>, and GF between the samples and clear correlations between the extracted quantities. The correlation between <i>µ</i> and GF was particularly evident. We also found both negative and positive GFs in our samples, depending on the material structures ^[10]. The electronic properties of the PtSe₂-based devices correlate with the nanocrystalline structure of the 2D films. On the other hand, the electronic properties of the PtSe₂ films vary over several orders of magnitude despite similar film thicknesses and chemical composition.<br/><br/>This work was financially supported by the German Ministry of Education and Research (BMBF) through the project NobleNEMS (16ES1121) and the German Research Foundation (DFG) through the project 2D-NEMS (LE 2440/11-1).<br/><br/>[1] S. Wagner et al., Nano Lett. <b>2018</b>, 18, 3738.<br/>[2] Y. Zhao et al., Adv. Mater. <b>2017</b>, 29, 1604230.<br/>[3] D. Kireev et al., ACS Nano <b>2021</b>, 15, 2800.<br/>[4] C. Yim et al., Nano Lett. <b>2018</b>, 18, 1794.<br/>[5] C. Yim et al., ACS Nano <b>2016</b>, 10, 9550.<br/>[6] Y. Wang et al., Nano Lett. <b>2015</b>, 15, 4013.<br/>[7] S. S. Han et al., Nano Lett. <b>2024</b>, 24, 1891.<br/>[8] C. Yim et al., npj 2D Mater. Appl. <b>2018</b>, 2, 5.<br/>[9] S. Parhizkar et al., ACS Photonics <b>2022</b>, 9, 859.<br/>[10] S. Lukas et al., Adv. Funct. Mater. <b>2021</b>, 2102929.