Y. H. Yang

Field emission of one-dimensional micro- and nanostructures of zinc oxide

A variety of one-dimensional (1D) micro- and nanostructures of zinc oxide (ZnO) were self-assembled on amorphous carbons using thermal chemical vapor transport and condensation without any metal catalysts. The low turn-on electronic field and the higher current density were achieved on these 1D ZnO micro- and nanostructural emitters. It was found that the geometry of the micro- and nanostructural emitters plays a crucial role in the field emission of ZnO.

Field emission and photoluminescence of SnO2 nanograss

Two-dimensional SnO2 nanograsses were synthesized on single-crystal Si substrates by catalyst-assisted thermal evaporation. The photoluminescence spectra from the products revealed multipeaks consistent with previous reports, with the exception of a new peak at 574 nm. The large field emission current from SnO2 nanograss was observed at a high turn-on voltage, which is attributed to a shorter length and a wide emitter radius. The formation of SnO2 nanograsses at the low temperature was pursued on the basis of the vapor-liquid-solid mechanism.

Radial ZnO nanowire nucleation on amorphous carbons

Radial ZnO nanowire arrays were self-assembled on the amorphous carbon thin layer on silicon substrates using thermal chemical vapor transport and condensation without any metal catalysts. We experimentally performed a systematic study to clarify the mechanism of the anomalous nucleation and growth and found that the physical origin of the nucleation aggregation and the one-dimensionally radial orientation is the immiscibility in the zinc oxide-carbon system.

Nanostructures and self-catalyzed growth of SnO2

SnO2 nanostructures including one-dimensional nanowires and two-dimensional nanobelts have been grown on a gold covered single crystal silicon substrates using thermal evaporation of active carbon and SnO2 powders. Field emission scanning electron microscopy, x-ray diffraction, Raman spectra, and high-resolution transmission electron microscopy are used to identify the morphology and the structure of these resulting SnO2 nanostructures. Based on these experimental analyses, we found self-catalyzed growth of SnO2 nanocrystals on top of SnO2 nanowires, i.e., SnO2 can spontaneously nucleate on the (110) crystalline plane of SnO2 nanowires without any catalyst. The growth behavior of these synthesized SnO2 nanostructures is discussed on the basis of the vapor-liquid-solid mechanism.

Self-assembled ZnO agave-like nanowires and anomalous superhydrophobicity

Thin films of ZnO agave-like nanowires were prepared on amorphous carbon thin layers on silicon substrates using thermal chemical vapour transport and condensation without any metal catalysts. The unusual superhydrophobicity of the fabricated surface was measured; the water contact angle reaches 151.1°. On the basis of experimental and theoretical analyses, it appears likely that the biomimetic microcomposite and nanocomposite surfaces of the prepared thin films of ZnO agave-like nanowires are responsible for the excellent superhydrophobicity.

Growth mechanisms of SnO2/Sn nanocables

SnO(2)/Sn nanocables have been grown on single-crystal Si substrates by metal catalyst assisted thermal evaporation of SnO powders. The morphologies and structures of the prepared nanocables were determined on the basis of field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD), Raman and photoluminescence (PL) spectra analyses. The microstructures and compositions of the top and bottom regions of the SnO(2)/Sn nanocables were identified by HRTEM in detail, which revealed some basic physical and chemical processes involved in the formation of the nanocables. A growth model was proposed to address the formation of SnO(2)/Sn nanocables on the basis of the vapour-liquid-solid (VLS) process.

Thermodynamical predictions of nanodiamonds synthesized by pulsed-laser ablation in liquid

Based on the nanothermodynamical approach, we performed the thermodynamical predictions of nanodiamonds synthesized by pulsed-laser ablation in liquid. The nanothermodynamical analyses showed that the formation of nanodiamonds with sizes of 3–5 nm would be preferable to that of large nanodiamonds in the pressure-temperature region of 10–15 GPa and 4000–5000 K created by pulsed-laser ablation of a graphite target in water in the carbon phase diagram. Meanwhile, the probabilities of the phase transition from graphite to diamond are calculated to be rather high, up to 10−3–10−2 in the same pressure-temperature region. These theoretical results indicate that pulsed-laser ablation in liquid is expected to be an effective industrial route to synthesize ultrananocrystalline diamonds.

Growth, structure, and cathodeluminescence of Eu-doped ZnO nanowires prepared by high-temperature and high-pressure pulsed-laser deposition

Eu-doped ZnO nanowires have been prepared by the high-temperature and high-pressure pulsed-laser deposition, and the structure and cathodeluminescence (CL) of the as-prepared nanostructures were characterized. It was found that the alloying catalyst droplets are located at the top of the as-prepared Eu-doped ZnO nanowires, meaning that the Eu-doped ZnO nanowires growth is a typical vapor-liquid-solid process. X-ray photoelectron spectra of samples provided the experimental evidence of the Eu-doping in ZnO nanowires. Two peaks near 611 and 755 nm, respectively, are identified to be from the doped Eu in the CL spectra of samples.Eu-doped ZnO nanowires have been prepared by the high-temperature and high-pressure pulsed-laser deposition, and the structure and cathodeluminescence (CL) of the as-prepared nanostructures were characterized. It was found that the alloying catalyst droplets are located at the top of the as-prepared Eu-doped ZnO nanowires, meaning that the Eu-doped ZnO nanowires growth is a typical vapor-liquid-solid process. X-ray photoelectron spectra of samples provided the experimental evidence of the Eu-doping in ZnO nanowires. Two peaks near 611 and 755 nm, respectively, are identified to be from the doped Eu in the CL spectra of samples.

Electron-beam irradiation induced shape transformation of Sn?SnO2 nanocables

In situ observations of the shape transformation of Sn–SnO2 coaxial nanocables induced by electron-beam irradiation have been performed in a transmission electron microscope. First, nanocables spontaneously transform into nanopeapods with Sn peas and SnO2 pods through the melting and condensing mechanism of Sn in SnO2 nanoshells. Nanopeapods then transform into SnO2 nanotubes covered by Sn islands through the nano-jet mechanism, and Sn islands spirally enwind the nanotubes with a spiral angle of 26.56° due to the chirality of the SnO2 nanoshells. Nanostructures consisting of SnO2 trunks and Sn branches finally form through size-confinement basal growth.

Fabry–Pérot and whispering gallery modes enhanced luminescence from an individual hexagonal ZnO nanocolumn

Strongly enhanced luminescence was observed from an individual hexagonal ZnO nanocolumn using the monochromatic cathodeluminescence equipment attached at a scanning electron microscopy. The intense luminescence emissions are focused on two regions, i.e., the profile and the center of the nanocolumn, respectively. The luminescence from the center region is attributed to the Fabry–Perot (FP) mode enhanced emission, and the one from the hexagonal profile is attributed to the whispering gallery (WG) mode enhanced emission when the individual ZnO nanocolumn is regarded as an optical resonator. The FP enhanced emission is much stronger than the WG enhanced one.