We study the piezoelectric behavior of metal-doped monolayer MoS2. Its three-dimensional charge density, work function (WF), and piezoresponse with various metal dopants are theoretically predicted based on density functional theory, and the real-time piezoelectric power of these samples is experimentally verified. Selected p-type metal dopants (Au, Ag, Pd, Pt, and Al) increase the WF of monolayer MoS2, affecting electron emission from the MoS2 surface. The reason is that p-type metal dopants suppress excess electrons and prevent screening effects. A nanogenerator constructed from Au-doped monolayer MoS2 has been used to explore the possibility of a practical device.
|Journal||Composites Part B: Engineering|
|Publication status||Published - 2022 Nov|
Bibliographical noteFunding Information:
This work was financially supported by Basic Science Research Programs ( 2021R1A2C2010990 ) through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT . This research was also supported by the Chung-Ang University Research Grants in 2022.
Monolayer MoS2 was synthesized by the chemical vapor deposition (CVD) method using MoO3 powder and H2S gas as precursors. The synthesis of MoS2 and the Au doping method using AuCl3 solution are described in detail in the Supporting Information. Fig. 2 shows the experimental results of the WF change of monolayer MoS2 before and after Au doping through atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), and X-ray photoelectron spectroscopy (XPS) measurements. Fig. 2a is an AFM image showing the surface topology of pristine MoS2 and Au-doped MoS2. The surface roughness of pristine MoS2 and Au-doped MoS2 at 5 ㎛ × 5 ㎛ was 0.57 nm and 0.61 nm, respectively, showing a very flat surface without any noticeable difference. In the KPFM images of Fig. 2b, the WF values of pristine MoS2 and Au-doped MoS2 were measured to be 5.13 ± 0.2 eV and 5.46 ± 0.2 eV, respectively, showing differences. The diagram in the KPFM mapping image in Fig. 2b shows the Fermi level changes of pristine MoS2 and Au-doped MoS2. After Au doping, the work function of MoS2 increases by about 0.33 eV, which means that the Fermi level is close to the intrinsic Fermi level. This result is good agreement with the calculation result in Fig. 1. XPS spectra are also an experimental result demonstrating the binding energy shift of MoS2. Fig. 2c and Fig. S4 show the Mo 3d and S 2p peaks of MoS2 before and after the Au doping process. First, the stoichiometric ratio of the synthesized MoS2 confirmed through the XPS result was found to be Mo: S = 1: 1.87, and it can be confirmed that the Mo 3d and S 2s peaks were downshifted (∼0.29 eV) after Au doping. Mo 3d3/2 shifts from 232.94 to 232.65 eV, Mo 3d5/2 shifts from 229.72 to 229.43 eV, and S 2s shifts from 226.97 to 226.68 eV. The downshift of the peaks is directly attributed to the p-doping, since it causes a Fermi level shift toward the valence band edge, and the Fermi level is where the zero energy lies . In addition to the Mo 3d and S 2s peaks, the S 2p peak of Fig. S4 does not show results such as a peak appearing at a new position after Au doping, which means that no new chemical bonds were formed due to doping. It shows the same shift in direction and value as the Mo 3d and S 2s peaks in Fig. 2c, proving the shift of the Fermi level. The WF change caused by Au doping is clearly confirmed through calculations and experimental results.This work was financially supported by Basic Science Research Programs (2021R1A2C2010990) through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT. This research was also supported by the Chung-Ang University Research Grants in 2022.
All Science Journal Classification (ASJC) codes
- Ceramics and Composites
- Mechanics of Materials
- Mechanical Engineering
- Industrial and Manufacturing Engineering