Vacancy driven surface disorder catalyzes anisotropic evaporation of ZnO (0001) polar surface

Abstract

The evaporation and crystal growth rates of ZnO are highly anisotropic and are fastest on the Zn-terminated ZnO (0001) polar surface. Herein, we study this behavior by direct atomic-scale observations and simulations of the dynamic processes of the ZnO (0001) polar surface during evaporation. The evaporation of the (0001) polar surface is accelerated dramatically at around 300 °C with the spontaneous formation of a few nanometer-thick quasi-liquid layer. This structurally disordered and chemically Zn-deficient quasi-liquid is derived from the formation and inward diffusion of Zn vacancies that stabilize the (0001) polar surface. The quasi-liquid controls the dissociative evaporation of ZnO with establishing steady state reactions with Zn and O2 vapors and the underlying ZnO crystal; while the quasi-liquid catalyzes the disordering of ZnO lattice by injecting Zn vacancies, it facilitates the desorption of O2 molecules. This study reveals that the polarity-driven surface disorder is the key structural feature driving the fast anisotropic evaporation and crystal growth of ZnO nanostructures along the [0001] direction.

Templated Synthesis of SiO2 Nanotubes for Lithium-Ion Battery Applications: An In Situ (Scanning) Transmission Electron Microscopy Study

“…At the experimental parameters of 900 °C and 1 bar, the amorphous porous silica layer allows the H 2 to bind to the surface of the ZnO via heterolytic chemisorption at elevated temperatures before reacting and reducing the Zn 2+ . − Within the scope of this experiment, a direct reduction process in which ZnO is reduced to metallic Zn vapor without an intermediate liquid phase in the presence of H 2 in the reducing gas mixture can be observed. , This is consistent with the literature experimental values for the vaporization point of Zn. , The constant loss of Zn from the surface through the porous SiO 2 shell exposes more ZnO for reduction, resulting in total removal of the ZnO core without damaging or altering the nanostructure of the SiO 2 coating (see Figure and Movie S1). The ZnO core is completely removed, while the silica remains intact as a result of this reaction, as evidenced by the disappearance of the Zn K α , K β , and L α peaks at 8.63, 9.57, and 1.012 keV, respectively, and retention of the Si K α peak at 1.739 keV from the simultaneously captured EDX spectra during the experiment shown in Figure C,D.…”

“…47−54 Within the scope of this experiment, a direct reduction process in which ZnO is reduced to metallic Zn vapor without an intermediate liquid phase in the presence of H 2 in the reducing gas mixture can be observed. 55,56 This is consistent with the literature experimental values for the vaporization point of Zn. 57,58 The constant loss of Zn from the surface through the porous SiO 2 shell exposes more ZnO for reduction, resulting in total removal of the ZnO core without damaging or altering the nanostructure of the SiO 2 coating (see Figure 3 and Movie S1).…”

Vacancy controlled nanoscale cation ordering leads to high thermoelectric performance

“…1a). Although there are ample examples of vacancy induced disorder in materials, 51,52 ordering of cations in the crystal lattice via the introduction of cation vacancies has not been evidenced so far. Extensive experimental investigation of low-temperature electrical transport, positron annihilation spectroscopy, and atomic resolution high resolution STEM along with the theoretical first principlebased calculations confirm the enhancement in cationic ordering in Ag 1Àx SbTe 2 (x = 1-3 mol%).…”

Effect of Strain Rate on Nano-Scale Mechanical Behavior of A-Plane (112¯0) ZnO Single Crystal by Nanoindentation

“…The zinc oxide (ZnO) single crystal is regarded as a promising third-generation semiconductor, owing to its wide band gap (~3.37 eV), high exciton binding energy (~60 meV), high thermal conductivity, high chemical stability, piezoelectricity and optical transparency [ 1 , 2 , 3 , 4 , 5 ]. Nowadays, the ZnO single crystal has broad application prospects in piezoelectric transducers, surface-acoustic-wave filters, short-wavelength photoelectric devices, gas sensors, transparent electrodes and solar cells [ 6 , 7 , 8 , 9 , 10 ].…”