Wei Zhu

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.

Enhancement in Three-Phase Boundary of SOFC Electrodes by an Ion Impregnation Method: A Modeling Comparison

Solid oxide fuel cells SOFCs are promising to be the nextgeneration energy-conversion devices due to their high efficiency and ultralow pollution emission. 1 Many efforts have been made recently to lower their operating temperatures from conventional 1000°C to 600–800°C, in order to significantly reduce the manufacturing cost and improve the stability of the SOFC system. At a reduced operating temperature, the electrode performance becomes the most important determinant of the overall cell output, especially when a thin-film electrolyte i.e., 5–20 m is applied. The electrode performance is believed to be determined by the sum of various polarizations typically associated with the length of the socalled three-phase boundary TPB where the electronic conductor, ionic conductor, and gases are in contact with each other so that the electrochemical reaction can take place. Therefore, a large TPB length is generally essential for high electrode performance. Several experimental studies demonstrated the inverse proportionality of activation overpotential with respect to the TPB length in standard composite electrodes such as Ni–yttria-stabilized zirconia YSZ anodes 2,3 and La,SrMnO3 LSM–YSZ cathodes. 4,5 A composite electrode is usually composed of an electronic conducting phase, an oxygen-ion conducting phase, and pores for gas transportation. Typical examples of the electronic phases are Ni and LSM, which also serve as the electrocatalyst in the anode and cathode, respectively. The ionic phase is generally an electrolyte material such as YSZ and doped ceria DCO. The TPB length of such a composite electrode is dominantly affected by its microstructure characteristics including particle size, porosity, and distribution state of the electronic and ionic conducting phases. Various electrode models have been established to predict and improve the performance of the composite electrode with regards to its microstructure parameters.

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.

LuVO4:Ln3+ (Ln = Sm, Eu, Dy, Er and Tm) with high uniform size and morphology: Controlled synthesis, growth mechanism and optical properties

Uniform nanoerythrocyte-like, dodecahedron and spindle-like LuVO4 had been successfully synthesized on a large scale by a simple complex agent assisted hydrothermal method. The nanoerythrocyte-like LuVO4 was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence and cathodoluminescence. The possible formation mechanism of the LuVO4 with different morphologies were proposed. The LuVO4:Ln3+ (Ln = Sm, Eu, Dy, Er and Tm) phosphors show strong light emissions with different colors due to the different activator ions under ultraviolet light excitation or low-voltage electron beam excitation and the LuVO4:Sm3+ samples with different complex agents exhibit interesting morphology-dependent optical properties. The complex-agents-assisted hydrothermal synthesis provides us one method to explore the special morphology of nano/micromaterials and the new optical materials.

Shape-Controlled Synthesis of Palladium Nanoparticles and Their SPR/SERS Properties

Morphological evolution of Pd nanoparticles was studied in a solution-phase synthesis using cetyltrimethylammonium bromide (CTAB) and CTAB/sodium citrate mixture as capping agents, respectively. The morphological diversity of Pd nanoparticles is the combined effect of different Pd twinned seeds formed in the nucleation stage and selectively enlarging one set of crystallographic facets in the growth stage, both of which can be affected by the concentrations of CTAB. Through changing the concentrations of CTAB and sodium ascorbate, Pd nanoparticles with different shapes were obtained. When citrate ions were introduced to manipulate the nucleation and growth process, star-shaped icosahedra and nanorods with pentagram cross-sections were obtained. Pd nanoparticles with different shapes have quite different surface plasmon resonance and surface-enhanced Raman scattering properties.

Energy transfer from a single nitrogen-vacancy center in nanodiamond to a graphene monolayer

In this work, we experimentally demonstrate energy transfer from a single negatively charged nitrogen-vacancy (NV) center in nanodiamond to a graphene monolayer. The mode values of lifetime and intensity of the fluorescence from the single NV center in nanodiamond on monolayer graphene are shorter and weaker than that on bare quartz substrate. The energy transfer efficiency is measured about 40%, consistent with our theoretical estimation.

Generation of nitrogen-vacancy color center in nanodiamonds by high temperature annealing

We make use of inherent vacancies and nitrogen substitutions in nanodiamonds to generate nitrogen-vacancy (NV) centers by high temperature annealing. After 800 °C annealing, low temperature photoluminescence intensity of nanodiamonds shows more than eight times improvement compared with that of unannealed samples. Confocal microscope images of well dispersed nanodiamonds indicate a dramatically increased proportion of nanodiamonds containing NV centers after annealing. Optically detected magnetic resonance spectrum of single NV center demonstrates that the resultant nanodiamonds are suitable for further application as magnetic field sensor. The annealing-oxidation method could be an attractive option for NV center generation in nanodiamonds.