G. W. Yang

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.

Structure evolution and ferroelectric and dielectric properties of Bi3.5Nd0.5Ti3O12 thin films under a moderate temperature annealing

Bi3.5Nd0.5Ti3O12 (BNT) ferroelectric thin films were fabricated on Pt∕Ti∕SiO2∕Si(100) substrates by chemical solution deposition. Structure evolution and ferroelectric and dielectric properties of the as-prepared thin films under a moderate temperature (600–750°C) annealing were studied in detail. The experimental results showed that the BNT thin films annealed at 700°C exhibit preferred (00l) orientation, and the remnant polarization (2Pr) and dielectric constant (er) are higher (the values of 2Pr and er at 100kHz are 54μC∕cm2 and 448, respectively) than those of the deposited films annealed at other temperatures. Additionally, the mechanism concerning the dependence of electrical properties of the BNT ferroelectric thin films on the annealing temperature was discussed.

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.

Resistive switching properties and physical mechanism of cobalt ferrite thin films

We report reproducible resistive switching performance and relevant physical mechanism of sandwiched Pt/CoFe2O4/Pt structures in which the CoFe2O4 thin films were fabricated by a chemical solution deposition method. Uniform switching voltages, good endurance, and long retention have been demonstrated in the Pt/CoFe2O4/Pt memory cells. On the basis of the analysis of current-voltage characteristic and its temperature dependence, we suggest that the carriers transport through the conducting filaments in low resistance state with Ohmic conduction behavior, and the Schottky emission and Poole-Frenkel emission dominate the conduction mechanism in high resistance state. From resistance-temperature dependence of resistance states, we believe that the physical origin of the resistive switching refers to the formation and rupture of the oxygen vacancies related filaments. The nanostructured CoFe2O4 thin films can find applications in resistive random access memory.

Size-dependent interface energy

A universal and analytic thermodynamic model without any adjustable parameters was established to elucidate the interface energy of multilayers at the nanometer scale by taken the size effect, the interfacial orientation, and the interfacial mismatch into account. Theoretical predictions were consistent with the calculations of the modified analytical embedded atom method and the experimental data, implying that the proposed thermodynamic model could be expected to be a general approach on nanoscale to understand interface energy in binary systems.

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.

On the physical understanding of quantum rings self-assembly upon droplet epitaxy

A quantitatively kinetic model has been established to address the quantum rings (QRs) self-assembly upon the droplet epitaxy. Taking the GaAs system as an example, we found that the diffusion of Ga atoms away from the droplet and the trapping of As atoms play crucial roles in the final shape formation of GaAs nanostructures. By calculating the amounts of the produced GaAs in each point, we performed the shape evolution of GaAs nanostructures during the crystallization process. The proposed kinetic theory nicely elucidates the physical mechanisms of the self-assembly of GaAs nanostructures including the single and double QRs and the holed nanostructure upon the droplet epitaxy.

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.

W-doping induced antiferroelectric to ferroelectric phase transition in PbZrO3 thin films prepared by chemical solution deposition

We reported on W-doping induced antiferroelectric to ferroelectric phase transition in PbZrO3 (PZO) thin films prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. The phase transition has been studied through polarization-electric field hysteresis loop, capacitance-voltage characteristic, and Raman scattering measurements. Suitable amount W-doping increased the saturated polarization of antiferroelectric W-doped PZO thin films, whereas the ferroelectric W-doped PZO thin films exhibited higher dielectric constant with a high dielectric-bias voltage tunability of about 70%. With increasing W-doping content, the orientation of the thin films changed from preferred (111)Cubic to complete (100)Cubic, due to W-doping-induced lattice distortion, meanwhile the Curie temperature dropped, and dielectric maximum broadened. Our study demonstrates that W-doping is an effective way to tailor the electrical properties of PZO thin films through the induced antiferroelectric-ferroelectric phase ...

Thermodynamic theory of shape evolution induced by Si capping in Ge quantum dot self-assembly

A quantitative thermodynamic theory has been established to investigate the shape evolution mechanisms induced by Si capping in Ge quantum dot self-assembly. It was found that the decrease in Ge concentration of the quantum dot induced by Si absorption breaks the original balance of composition between the quantum dot and wetting layer. In order to create a new balance, the wetting layer is required to increase its thickness through the Ge diffusion from the quantum dot to the wetting layer, which leads to the shape evolution of the growing quantum dot. The Ge diffusion can suppress the expansion of quantum dots and promote their shrinkage. The theoretical results not only are in well agreement with the experimental observations but also reveal physical mechanisms involved in the Ge quantum dot self-assembly induced by Si capping, which implies that the established thermodynamic theory could be expected to be applicable to address the capping-assisted self-assembly of quantum dots.