Kaixing Zhu

Graphene covered SiC powder as advanced photocatalytic material

Graphene covered SiC powder (GCSP) has been fabricated by well established method of high temperature thermal decomposition of SiC. The structural and photocatalystic characteristics of the prepared GCSP were investigated and compared with that of the pristine SiC powder. Under UV illumination, more than 100% enhancement in photocatalystic activity is achieved in degradation of Rhodamine B (Rh B) by GCSP catalyst than by pristine SiC powder. The possible mechanisms underlining the observed results are discussed. The results suggested that GCSP as a composite of graphene based material has great potential for use as a high performance photocatalyst.

Heterogeneous ZnS hollow urchin-like hierarchical nanostructures and their structure-enhanced photocatalytic properties

Hexagonal wurtzite ZnS nanowires radially arrayed on cubic zinc-blende ZnS hollow spheres have been successfully achieved for the first time, and such novel heterogeneous ZnS hollow urchin-like hierarchical nanostructures show greatly enhanced photocatalytic properties due to their two-phase enhanced light-harvesting and high surface-to-volume ratio.

Polarized micro-Raman study of the field-induced phase transition in the relaxor 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 single crystal

Polarized Raman spectroscopy has been performed to investigate the effects of the electric field on 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 (PMN–33%PT) single crystal. The electric-field-evolution of Raman spectra differed from one microarea to another. In the crossed polarization geometry, the abrupt changes in the intensities of the Raman bands at around 570 and 780 cm−1 indicated the occurrence of the field induced phase transition from the MC-type to the MA-type monoclinic structure. On the other hand, the Raman spectra for the microarea that was initially in the MA phase exhibited no obvious changes. All these results revealed the microheterogeneity in PMN–33%PT single crystal, which is useful for understanding the field-induced superior electromechanical properties.

Phase transition of Zn2SnO4 nanowires under high pressure

In situ high-pressure angle dispersive x-ray diffraction experiments using synchrotron radiation on inverse spinel structure Zn2SnO4 nanowires were carried out with a diamond anvil cell at room temperature. The crystal symmetry becomes lower at around 12.9 GPa and an intermediate phase with an orthorhombic structure occurs. At about 32.7 GPa, a phase transition occurs accompanying a high-pressure phase. In situ Raman scattering investigation was also performed to explore the phase transition. In the pressure range 15.5–32.8 GPa, the intermediate phase is also detected and a high-pressure phase is observed above 32.8 GPa. The high-pressure phase is considered to possess the ambient pressure structure of CaFe2O4.

Experimental observation of ferromagnetism evolution in nanostructured semiconductor InN

Recently, undoped semiconductors have been pushed to the frontiers of diluted magnetic semiconductors (DMSs) since no spurious ferromagnetism (FM) signal from metal segregation occurs. However, some aspects still remain untouched in undoped semiconductors nanostructures, including: 1) the evolution of spin moments during the fabrication process; 2) possible intrinsic relationship between the magnetic properties and morphological features, the latter being also dependent on formation process. In this article, we synthesized undoped InN nanostructures and observed a gradual magnetic transition from diamagnetic to FM, and an obvious morphology evolution from tube-shape to wire-shape products with the increase of nitridation time. It is speculated that increasing surface defects such as N vacancies in the morphology transition process are the intrinsic causes for the enhanced FM order with increase of nitridation time. The results provide some useful clues in understanding the true magnetic origin in nanostructured DMSs and reported properties inconsistencies in nanostructured materials.

Structural and magnetic properties of (Al, Fe)-codoped SiC

In this study, as a first attempt, we choose Al and transition metals (TMs), Fe, as codoping atoms to synthesize (Al, TM)-codoped SiC. X-ray diffraction and Raman analysis showed that a series of single-phase codoped 4H-SiC samples were obtained and no trace of any other impurity phases, such as Fe3Si and polytypes of other types of SiC, was found. Measurement of magnetic properties showed that codoping by Al and Fe elements changed the original glassy ferromagnetism (FM) features in Al-doped SiC and induced a robust room temperature FM order that gradually dominated (Al, Fe)-codoped 4H-SiC with increase in Fe content. The contribution of Al elements to the magnetic properties of (Al, Fe)-codoped 4H-SiC can be neglected and the magnetic origin should be ascribed to be induced by Fe doping. The only major role of Al is to stabilize the codoped crystal structure as 4H- single phase. As the first investigation on (Al, TM)-codoped SiC, this study opens a new pathway to obtain TM-doped SiC-based diluted magnetic semiconductors with a high Tc via the codoping strategy.

Enhanced photoluminescence from porous silicon by hydrogen-plasma etching

Porous silicon (PS) was etched by hydrogen plasma. On the surface a large number of silicon nanocone arrays and nanocrystallites were formed. It is found that the photoluminescence of the H-etched porous silicon is highly enhanced. Correspondingly, three emission centers including red, green, and blue emissions are shown to contribute to the enhanced photoluminescence of the H-etched PS, which originate from the recombination of trapped electrons with free holes due to SiO bonding at the surface of the silicon nanocrystallites, the quantum size confinement effect, and oxygen vacancy in the surface SiO2 layer, respectively. In particular, the increase of SiOx(x<2) formed on the surface of the H-etched porous silicon plays a very important role in enhancing the photoluminescence properties.

Structure and photoluminescence properties of carbon nanotip-vertical graphene nanohybrids

We report on the effective enhancement and tuning of photoluminescence (PL) by combining vertical graphene nanoflakes (VGs) and carbon nanotips (CNTPs). The VGs are grown on the vertical CNTPs by hot filament chemical vapor deposition in the methane environment, where the CNTPs are synthesized on silicon substrates by CH4-H2-N2 plasma-enhanced hot filament chemical vapor deposition. The results of field emission scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy indicate that the VGs can be grown on the CNTP and silicon substrate surfaces with the orientation perpendicular to the surfaces of CNTPs and silicon substrates. The PL properties of VG, CNTP, and CNTP-VG structures are studied using a 325 nm line of He-Cd laser as the excitation source. The PL results indicate that the PL of VGs is enhanced by the CNTPs due to the increasing density of PL emitters, while the PL properties of the nanohybrid system can be tuned. Furthermore...

Observation of stimulated emission from a single Fe-doped AlN triangular fiber at room temperature

Aluminum nitride (AlN) is a well known wide-band gap semiconductor that has been widely used in fabricating various ultraviolet photo-electronic devices. Herein, we demonstrate that a fiber laser can be achieved in Fe-doped AlN fiber where Fe is the active ion and AlN fiber is used as the gain medium. Fe-doped single crystal AlN fibers with a diameter of 20–50 μm and a length of 0.5–1 mm were preparated successfully. Stimulated emission (peak at about 607 nm and FWHM ~0.2 nm) and a long luminescence lifetime (2.5 ms) were observed in the fibers by a 532nm laser excitation at room temperature. The high quality long AlN fibers are also found to be good optical waveguides. This kind of fiber lasers may possess potential advantages over traditional fiber lasers in enhancing power output and extending laser wavelengths from infrared to visible regime.

Amorphization of C60 nanotubes under pressure

C60 nanotubes with diameters of smaller than 500 nm are fabricated by a modified liquid–liquid interfacial precipitation method. In situ angle dispersive synchrotron x ray diffraction and Raman scattering under pressures have been employed to study the structure evolution of the C60 nanotubes. The experimental results indicate that there is a pressure induced irreversible amorphization at 40.1 GPa. An isostructural phase transition occurs in the pressure range of 9.29–12.2 GPa, which is probably relative to the changes in the bonding type of C60 nanotubes.