Interface Engineering of Metal Oxynitride Lateral Heterojunctions for Photocatalytic and Optoelectronic Applications

Abstract

Significant improvements of the photocatalytic and optoelectronic applications demand materials that exhibit finely tuned band gaps, band edge potentials, exciton dynamics, charged states, and crystal facets/edges that facilitate enhanced chemical reactivity. Fundamental insights into the structure–function relationships can dictate the synthesis requirements of these materials. Zinc oxynitride-based materials have demonstrated excellent photocatalytic activity, and they also present a perfect platform for tailoring the material properties of interest. We hereby investigate lateral heterojunctions of zinc oxynitrides toward photocatalytic and optoelectronic applications by computationally examining their response to composition, lattice strain, and anion vacancy defect variation. Along with tuning the band gap of the materials toward optimal optical performance, we demonstrated the site specificity of the vacancy defects. Oxygen vacancies and nitrogen vacancies were found to be favored at the bulk and at the interface, respectively. Biaxial and vertical compressive strain increased the band gap, whereas tensile strain reduced the band gap. The neutral and charged vacancies rendered either increased electronic density of states at the conduction and valence band edges or the formation of mid-gap states. These insights into electronic state variation via intrinsic material parameters are fundamental toward synthesis of future materials for enhanced photocatalysis and optoelectronic purposes.

Synthesis of Surface-Oxygen-Vacancy-Rich (GaN)0.5(ZnO)0.5 Particles with Enhanced Visible-Light Photodegradation Performance

“…However, the possibility cannot be excluded for the presence of a great deal of N vacancy (V N ) in the oxynitrides, especially for the samples of 2.5 g- and 1.0 g-ZnGaNO. The existence of V N in (GaN) 1– x (ZnO) x has been suggested in a few reports recently. − The quantitative estimation of V N , however, is still difficult because of the lack of solid experimental evidence and theoretical investigation. No XPS peak related to V N has been identified in GaN or (GaN) 1– x (ZnO) x .…”

Relationships between Compositional Heterogeneity and Electronic Spectra of (Ga1–xZnx)(N1–xOx) Nanocrystals Revealed by Valence Electron Energy Loss Spectroscopy

“…(Ga 1– x Zn x )­(N 1– x O x ) is a quaternary semiconductor with unusual optical properties: although the parent semiconductors, GaN and ZnO, have UV band gaps, (Ga 1– x Zn x )­(N 1– x O x ) absorbs in the visible, in an apparent violation of Vegard’s law, with the band gap determined by the value of x . − The absorption of visible wavelengths of sunlight and chemical stability have led to interest in using (Ga 1– x Zn x )­(N 1– x O x ) for photochemical water splitting ,,, and, more recently, Z-scheme CO 2 reduction and photobiocatalytic H 2 evolution . The origin of visible absorption in (Ga 1– x Zn x )­(N 1– x O x ) remains under debate, with leading candidates being p–d repulsion between N 2p and Zn 3d atomic orbitals that increases the valence band energy, ,− the formation of defect bands, and interfacial absorption between small domains of ZnO and GaN …”

Defect and Interface Engineering on Two‐Dimensional Nanosheets for the Photocatalytic Nitrogen Reduction Reaction

“…Performance enhancement mainly relies on the structure design of catalysts, such as defect engineering (anion and cation vacancies), or interface design (such as 0 and 2 dimensional (0D-2D) composites, 2 and 2 dimensional (2D-2D) composites, etc). [29][30][31][32][33][34][35][36] Defect and interface engineering of photocatalysts are of great importance. On one hand, surface defects engineering has enormous advantages for (1) modifying the band edges and band gap energies in semiconductor photocatalysts, (2) enhancing photo-excited electron transfer, (3) promoting the adsorption and activation of N 2 on semiconductor surfaces.…”

“…To date, several strategies have been used to fabricate different kinds of photocatalysts to explore catalytic performance. Performance enhancement mainly relies on the structure design of catalysts, such as defect engineering (anion and cation vacancies), or interface design (such as 0 and 2 dimensional (0D‐2D) composites, 2 and 2 dimensional (2D‐2D) composites, etc) [29–36] . Defect and interface engineering of photocatalysts are of great importance.…”