Qinghua Fan

Field emission from single-crystalline CeB6 nanowires

Abstract We presented a field electron emission measurement of single crystalline CeB 6 nanowires. The nanowires exhibited a low turn-on electric field (7.6 V/μm at 10 μA/cm 2 ), and the deviation of Fowler-Nordheim (F-N) plots from straight line was observed in field electron emission measurements. The field enhancement factors were obtained by separate straight line fitting. The nonlinearity in the F-N plots may be attributed to the non-uniform field electron emission of CeB 6 nanowires. The field emission properties of the CeB 6 nanowires indicated a competitive candidate for field-emission-based application.

Synthesis of single-crystalline NdB6 submicroawls via a simple flux-controlled self-catalyzed method

Neodymium hexaboride (NdB6) submicroawls have been fabricated via a simple flux-controlled self-catalyzed method using neodymium (Nd) powders and boron trichloride (BCl3) as starting materials at 1000 °C. Scanning electron microscopy (SEM) reveals that the submicroawls are tapered, with a length of 2–5 μm and a diameter ranging from approximately 0.1–0.3 μm at the roots and 5–50 nm at the tips. Transmission electron microscopy (TEM) shows that the submicroawls are single crystalline with the preferred growth direction along [001]. For systematic research, we have discussed the morphological change of NdB6 submicron structures by varying reaction temperatures, catalysts and duration. Moreover, a multistage growth model of the NdB6 submicroawls is proposed.

Cheese-like bulk carbon with nanoholes prepared from egg white as an anode material for lithium and sodium ion batteries

Cheese-like bulk carbon with nanoholes has been successfully fabricated from egg white via a simple annealing method by using distilled water as a green clean “corrosive agent”. X-ray diffractions and SEM images show the decomposition product of boiled egg white after annealing is bulk carbon, containing NaCl and KCl with a trace amount of nitrogen doping. After ultrasonic washing and centrifugation, the distilled water removed the NaCl and KCl nanocrystals from the bulk carbon completely and retained empty spaces, which eventually leads to the formation of a cheese-like structured bulk carbon with nanoholes. Our electrochemical tests show this cheese-like bulk carbon with nanoholes has a high specific capacity and good cycling performance and rate stability when evaluated as an anode material for lithium-ion batteries. Meanwhile, the electrochemical performances as an anode material for a sodium-ion battery are also displayed for comparison.

Low-temperature synthesis and electronic transport of topological insulator SmB6 nanowires

We report a novel solid state method to prepare samarium hexaboride (SmB6) nanowires at low temperatures of 220–240 °C. Scanning electron microscopy (SEM) images show that the SmB6 nanowires have diameters from 50 to 120 nm and lengths from 1 to 8 μm. Transmission electron microscopy (TEM) images reveal that the SmB6 nanowires are single crystalline with a preferred [001] growth direction. Electronic transport shows that a SmB6 nanowire has a high saturation temperature of 6 K and an enhanced surface conduction.

Single-crystalline LaxNd1−xB6 nanowires: synthesis, characterization and field emission performance

We report the catalyst-free synthesis of uniform distributed single-crystalline LaxNd1−xB6 nanowires by simply heating mixed La and Nd powders to the required temperature in an inlet flux of mixed gases (H2, Ar and BCl3). FE-SEM, HRTEM, SAED, EDS, element mapping, XRD and Raman scattering results show that the LaxNd1−xB6 nanowires are structurally uniform and well-doped single crystals. Based on our experimental results, a dominant VLS-like mechanism with a self-catalytic growth mechanism was proposed and depicted conceptually. The nanowires display an excellent field emission performance with a low turn-on field value of ∼4.12 V μm−1 when evaluated as an electron emitter. Attempts were also made to understand the morphological influence of reaction time, reaction temperature and the proportion of the La and Nd powders.

Field emission from one-dimensional single-crystalline NdB6 nanowires

Abstract A facile catalysis-free method was utilized to synthesize functional neodymium hexaboride (NdB6) nanowires of single crystal using Nd powders and BCl3 as starting materials. The XRD pattern confirmed that a single phase NdB6 could be obtained. Raman-spectra elucidated the active vibrational modes of the hexaborides. The TEM images clearly showed that the hexaborides were submicron in size with a cubic morphology. The field emission of these one-dimensional NdB6 nanowires showed a low field emission turn-on (5.55 V/μm at a current density of 10 μA/cm2), and high current density with a field enhancement factor of 1037. The emission current density and the electric field followed the Fowler-Nordheim (F-N) relationship. The good performance for field emission was attributed to the single-crystalline structure and the nanowire geometry.

Preparation and growth mechanism of one-dimensional NdB6 nanostructures: nanobelts, nanoawls, and nanotubes

Three kinds of one-dimensional (1D) neodymium hexaboride (NdB6) nanostructures, including nanobelts, nanoawls, and nanotubes, have been synthesized through a chemical vapor deposition (CVD) process with a self-catalyzed mechanism. For the first time, we report the preparation of NdB6 nanotubes. The morphology and crystalline structure are characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Transmission electron microscopy images show that they have different growth directions: [111], [001], and [110], respectively. In addition, detailed growth mechanisms of the nanobelts, nanoawls, and nanotubes are presented. A droplet induced self-catalyzed mechanism, self-catalyzed with a vapor–solid mechanism, and diffusion limited self-catalyzed mechanism are proposed to explain the growth of nanobelts, nanoawls, and nanotubes, respectively.

Superstructure ZrV2O7 nanofibres: thermal expansion, electronic and lithium storage properties

ZrV2O7 has attracted much attention as a negative thermal expansion (NTE) material due to its isotropic negative structure. However, rarely has investigation of the lithium storage behaviors been carried out except our first report on it. Meanwhile, the electrochemical behaviors and energy storage characteristics have not been studied in depth and will be explored in this article. Herein, we report on the synthesis, characterization and lithium intercalation mechanism of superstructure ZrV2O7 nanofibres that were prepared through a facile solution-based method with a subsequent annealing process. The thermal in situ XRD technique combined with the Rietveld refinement method is adopted to analyze the change in the temperature-dependent crystal structure. Benefiting from the nanostructured morphology and relatively high electronic conductivity, it presents acceptable cyclic stability and rate capability. According to the operando evolution of the XRD patterns obtained from electrochemical in situ measurements, the Li intercalation mechanism of the solid solution process with a subsequent conversion reaction can be concluded. Finally, the amorphous state of the electrodes after the initial fully discharged state can effectively enhance the electrochemical performances.

A one-step chemical vapor deposition approach for solid solution PrxNd1−xB6 nanowire growth

Dual-rare earth hexaborides PrxNd1−xB6 nanowires have been successfully synthesized on silicon substrates by a one-step CVD method at a temperature of 1030 °C. The quasi-aligned nanowires are shown to be structurally uniform and well-doped single crystals based on comprehensive analysis. The present preparation technique is an effective and invaluable method to develop and optimize dual-REB6 nanostructured emitters.