Guanzhong Wang

Controllable synthesis of submillimeter single-crystal monolayer graphene domains on copper foils by suppressing nucleation

Submillimeter single-crystal monolayer and multilayer graphene domains were prepared by an atmospheric pressure chemical vapor deposition method with suppressing nucleation on copper foils through an annealing procedure. A facile oxidation visualization method was applied to study the nucleation density and morphology of graphene domains on copper foils. Scanning electron microscopy, transmission electron microscopy, atomic force microscopy, polarized optical microscopy, and Raman spectra showed that the submillimeter graphene domains were monolayer single crystals.

Synthesis and optical properties of well-aligned ZnO nanorod array on an undoped ZnO film

High-density well-aligned ZnO nanorod array was successfully synthesized on a PLD prepared undoped ZnO film by a catalyst-free method. X-ray diffraction and scanning electron microscopy show that the nanorods are well-oriented perpendicular to the substrate. The photoluminescence from free excitons and Raman spectra of the ZnO nanorods reflect the high purity and nearly defect free structure of nanorods. The well-aligned feature of the nanorod array is attributed to the nanorods’ epitaxial growth from the ZnO film.

Optical properties of ZnO/GaN heterostructure and its near-ultraviolet light-emitting diode

We report on photoluminescence in a ZnO/GaN heterostructure, which showed a donor–acceptor pair emission band at 3.270 eV and the longitudinal optical phonon replicas at 12 K. In comparison with p-type GaN, the positions of the peaks are redshifted. This may be associated with the variation of the residual strain in the GaN layer of the heterostructure. Using this heterostructure, near-ultraviolet light-emitting diodes were fabricated and their electroluminescence properties were characterized.

Synthesis and Characterization of Aligned ZnO Nanorods on Porous Aluminum Oxide Template

Aligned high-density ZnO nanorods were successfully synthesized on porous aluminum oxide (PAO) template. The growth process involves carbonthermal reduction of ZnO as a Zn vapor source and ZnO nucleation on the PAO template without metal catalysts. Field-emission scanning electron microscope images revealed that the nanorods have uniform length distributions and hexagon end planes, and the intense c-axis growth was also confirmed by X-ray diffraction. Strong ultraviolet emission at 380 nm and weak green band emission at 520 nm at room-temperature photoluminescence clearly indicated the high quality of the ZnO nanorods. A growth mechanism is proposed that the multipore surface of the PAO template plays a critical role in the nucleation of ZnO in the initial stage of growth, and nanorods grow from the nuclei due to intense ZnO c-axis orientation growth.

Ultraviolet lasing and time-resolved photoluminescence of well-aligned ZnO nanorod arrays

Well-aligned ZnO nanorod arrays were synthesized by thermal evaporation of ZnO powder on ZnO thin films. The nanorods are almost the same length of 5.5μm and well-oriented perpendicular to the substrates. The time-integrated and time-resolved photoluminescence spectra of the nanorod arrays revealed the existence of laser action with the excitation threshold of 130μJ∕cm2 and emission lifetime of less than 30 ps. At the excitation fluence a little below threshold, the decay fits well to a biexponential function with a fast component (∼80ps) and a slower component (∼360ps).

Crystal orientation-ordered ZnO nanorod bundles on hexagonal heads of ZnO microcones: epitaxial growth and self-attraction

We demonstrate a preferential nucleation, epitaxial growth, and self-attraction of crystal orientation-ordered ZnO nanorod bundles on (0001) plane of single-crystal ZnO microcones.

Fiber-integrated diamond-based magnetometer

We demonstrated a fiber-integrated diamond-based magnetometer in this paper. In the system, the fluorescence of nitrogen vacancy (NV) centers in nanodiamonds deposited on a tapered fiber was coupled to the tapered fiber effectively and detected at the output end of the fiber. By using this scheme, optically detected electron spin resonance spectra were recorded for single NV centers. The results confirmed that such a tapered fiber-nanodiamond system can act as a magnetometer. Featured with excellent portability, convenient fabrication, and potential for further integration, the constructed system has been demonstrated to be a practical magnetometer prototype.

Anisotropic Growth of One-Dimensional Silver Rod−Needle and Plate−Belt Heteronanostructures Induced by Twins and hcp Phase

In this paper, we report a one-step, high-yield synthesis of one-dimensional Ag heteronanostructures in aqueous solution. Besides the usual fcc phase of Ag, the heteronanostructures also contain a rare hcp (4H polytypic) phase, which favors asymmetrical growth. The rod-needle heteronanostructures (RNHSs) and plate-belt heteronanostructures (PBHSs) are formed through two different mechanisms. For RNHSs, the 4H and fcc phases coexist but have different densities in different segments, while for PBHSs, the fcc and 4H crystal structures exist in plate and belt segments, respectively. Condition-sensitive coexisting phase preferences can be applied as a new way of controlling the shape and thus the properties of Ag nanostructures.

Graphene aerogel prepared by thermal evaporation of graphene oxide suspension containing sodium bicarbonate

We present a facile, environment-friendly and mild method to fabricate graphene hydrogel by heating graphene oxide (GO) suspension containing sodium bicarbonate (NaHCO3). This method demonstrates a new type of in situ reduction-assembly approach to construct graphene hydrogel through simultaneous water evaporation and GO reduction. The freeze-dried graphene aerogel (G-Gel) shows excellent adsorptivity to heavy metal ions and dyes. The thermally treated G-Gel (TG-Gel) exhibits promising performance in recyclable selective absorption of oils and organic solvents.

Simple-cubic microcubes assembled by palladium nanocubes

We report a method to prepare nanocube-based super-crystals, which not only have a well-defined structure but also have a well-defined shape and size.