2D wide bandgap transition metal oxides: synthesis and photoelectron spectroscopic studies

Abstract

Wide bandgap (WBG) semiconductors (Eg >2.0 eV) in two-dimensional (2D) form have demonstrated great potential in 2D electronics, optoelectronics, and power industries. However, as an essential group of WBG semiconductors, 2D transition metal oxides (TMOs) remain largely understudied in terms of physical properties and applications in 2D electronic devices due to the lack of sufficiently large 2D crystals. Here, we accomplish the synthesis of WBG 2D nickel oxide (NiO) (Eg > 2.7 eV) thermally converted from 2D nickel hydroxide (Ni(OH)2) with the largest ever reported lateral domain size (>20 µm). Besides, the process is studied via various X-ray techniques and provides significant insights on the morphology, structure and electronic band structure variation. Moreover, temperature associated defects are monitored by in-situ X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) and low energy inverse photoemission spectroscopy (LEIPS) are demonstrated to characterize band structure of materials, to establish a relation between structural defects and electronic properties.