ZnO, as a low-cost yet significant semiconductor, has been widely used in solar energy conversion and optoelectronic devices. In addition, Cu/ZnO-based catalysts can convert syngas (H2, CO, and CO2) into methanol. However, the main concern about the intrinsic connection between the physical and chemical properties and the structure of ZnO still remains. In this work, efforts are made to decipher the physical and chemical information encoded into the structure. Through using NMR–IR techniques, we, for the first time, report a new ZnO model with three H+ cations incorporated into one Zn vacancy. 1H magic-angle spinning NMR and IR spectra demonstrate that Ga3+ cations are introduced into the Zn vacancies of the ZnO lattice, which replace the H+ cation, and thus further confirm the feasibility of our proposed model. The exchange between the H+ cation in Zn vacancies and the D2 gas phase shows that ZnO can activate H2 because of the quantized three H+ cations in the defect site.

Tungsten selenide (WSe2) as a van der Waals layered crystal has anisotropic light absorption and light scattering on its out-of-plane surface. However, the Raman tensor of WSe2, which determines the anisotropy of inelastic light scattering, is still unknown without being carefully studied. Here, via establishing angle-resolved polarized Raman spectroscopy measurement, we obtained the experimental Raman tensor of WSe2. Additionally, theoretical Raman tensors under different incident laser line excitations from ultraviolet to infrared were calculated via the first-principles density functional approach, coinciding fairly well with the experimental ones. The first-principles results also reveal that WSe2 has different Raman tensor forms under different laser line excitations, especially the phase difference between Raman tensor elements of the A1g mode. It is suggested that the photon-energy dependent phase differences are determined by the dispersion and absorption of WSe2 on different pump lights.

Black phosphorus has a strong Raman anisotropy on the basal and cross planes due to its orthorhombic crystal structure. However, almost all the studies on black phosphorus' anisotropy focus on basal plane with the cross plane neglected. Here, we performed a systematic angle-resolved polarized Raman scattering on both the basal and cross planes of black phosphorus and obtained its integral Raman tensors. It is discovered that when the polarization direction of excitation light is along different crystal axes, the Raman intensity ratio (I xx : I yy : I zz) of A 1 g mode is 256:1:5. Besides, via calculation, it is confirmed that the strong Raman anisotropy mainly comes from different differential polarizability alone different directions. This phenomenon is also observed when it comes to the A 2 g mode.

Due to the similar atom arrangement with black phosphorus, black arsenic also has obvious Raman anisotropy at both the base and cross planes. However, the polarization characteristics of black arsenic have been rarely reported so far with most relevant studies devoted to the base plane. Here, to compensate for the blank of the anisotropy in cross plane, we implemented a systematical angle‐resolved polarized Raman measurement on both planes of layered black arsenic and observed that the Raman intensity ratios (Ixx : Iyy : Izz) of optical phonons and modes along different axes are 1:4.8:2.76 and 6.9:1:5.7, respectively. Based on the definition of Raman intensity, we abstracted integral Raman tensors of black arsenic. In addition, according to density functional theory, it can be affirmed that the Raman anisotropy of Ag mode is sourced from the anisotropy of differential polarizability along different crystal axes.

Molybdenum selenide (MoSe2) is a van der Waals layered crystal with both the anisotropic light absorption and light scattering outside its surface. At present, the study of the Raman tensor of MoSe2, which affects and even determines the inelastic light scattering’s anisotropy, is not sufficient. In this research, with the aim of studying the out-of-plane anisotropy, we performed systematic angle-resolved polarized Raman (APR) spectroscopy and abstracted complete Raman tensors both experimentally and theoretically. In addition, according to first-principles calculations, in different conditions of laser excitation, MoSe2 has various Raman tensor forms, of which the phase difference between Raman tensor elements of the A 1g mode is a particular one. By studying the anisotropic optical absorption properties, we confirmed that it is the dispersion and absorption of MoSe2 under different pump light that lead to the photon-energy-dependent phase differences.