Ultrathin Transition Metal Nitrides: Synthesis, Electrocatalytic Application and Device Fabrication

Abstract

Synthesis of nitrogen-rich transition metal nitrides is of great importance for the study of novel properties of nanomaterials and the exploration of their applications. Nevertheless, it is difficult to obtain nitrogen-rich transition metal nitrides under atmospheric pressure because the incorporation of nitrogen atoms into the crystalline lattices of transition metals, e.g., Mo, W, is thermodynamically unstable under air pressure. In order to solve this issue, the aim of my thesis is to prepare nitrogen-rich transition metal nitride nanomaterials under atmospheric pressure and study their applications in catalytic reactions. In this thesis, I demonstrated my research findings in two chapters.

First, I reported a nitrogen-rich transition metal nitrides synthesis of WN₂ under atmospheric pressure. I performed nitridation experiments on CVD-grown WSe₂ nanosheets to successfully obtain nitrogen-rich tungsten nitrides, WN₂. The nitrogen-rich features were characterized by X-ray photoelectron spectroscopy (XPS), Auger electron spectrum (AES) and energy-dispersive X-ray spectroscopy (EDS). I studied the SERS properties of as-fabricated WN₂ nanosheets. In the end, electrochemical property for hydrogen evolution reaction was performed on the basal plane and edge of WSe₂ and WN₂ nanosheets.

Second, I explored the low-contact property of WN₂ by constructing a two-dimensional (2D) in-plane heterostructure. 2D WN₂-WSe₂-WN₂ heterostructure was developed via mask-assisted atomic substitution for low-contact device. I studied the intrinsic property of this 2D heterostructure and tested the transfer characteristics of bottom-gated device and output characteristics of devices. Because of 2D edge contact, it shows a smaller Schottky barrier and linear behavior for the WN₂ metallic electrodes. The low contact resistance with 2D WN₂-WSe₂-WN₂ heterostructure leads to good mobility values, outstanding on/off ratios and high output current.

Date of Award	17 Aug 2023
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Hua ZHANG (Supervisor)