Yizun Wang

Photovoltaic enhancement of Si solar cells by assembled carbon nanotubes

Photovoltaic conversion was enhanced by directly assemble of a network of single-walled carbon nanotubes (SWNTs) onto the surface of n-p junction silicon solar cells. When the density of SWNTs increased from 50 to 400 tubes μm−2, an enhancement of 3.92% in energy conversion efficiency was typically obtained. The effect of the SWNTs network is proposed for trapping incident photons and assisting electronic transportation at the interface of silicon solar cells.

The vacuum ultraviolet beamline/endstations at NSRL dedicated to combustion research

An undulator-based vacuum ultraviolet (VUV) beamline (BL03U), intended for combustion chemistry studies, has been constructed at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China. The beamline is connected to the newly upgraded Hefei Light Source (HLS II), and could deliver photons in the 5-21 eV range, with a photon flux of 10(13) photons s(-1) at 10 eV when the beam current is 300 mA. The monochromator of the beamline is equipped with two gratings (200 lines mm(-1) and 400 lines mm(-1)) and its resolving power is 3900 at 7.3 eV for the 200 lines mm(-1) grating and 4200 at 14.6 eV for the 400 lines mm(-1) grating. The beamline serves three endstations which are designed for respective studies of premixed flame, fuel pyrolysis in flow reactor, and oxidation in jet-stirred reactor. Each endstation contains a reactor chamber, an ionization chamber where the molecular beam intersects with the VUV light, and a home-made reflectron time-of-flight mass spectrometer. The performance of the beamline and endstations with some preliminary results is presented here. The ability to detect reactive intermediates (e.g. H, O, OH and hydroperoxides) is advantageous in combustion chemistry research.

Local structures of nanocrystalline GaN studied by X-ray absorption fine structure

X-ray absorption fine structure (XAFS) was used to investigate the local structures around Ga atoms in the hexagonal nanocrystalline and crystalline GaN under 78 and 300 K. For the first nearest neighbor coordination shell of Ga–N, the average bond length R (0.194 nm), coordination number N (4.0), thermal disorder σT (0.0052 nm) and static disorder σS (0.0007 nm) are nearly independent of the measured temperature and the crystalline state. This indicates that the Ga–N covalent bond is much stronger, and the 4 nitrogen atoms in first nearest neighbor around Ga atoms keep the tetrahedral structure Td. For the second nearest neighbor coordination shell of Ga–Ga, their bond lengths are about 0.318 nm. However, the σS (0.0057 nm) of nanocrystalline GaN is 0.0047 nm larger than that of crystalline GaN (0.001 nm), and the σT of nanocrystalline is 0.0053 nm and 0.0085 nm at the temperature of 78 and 300 K, respectively. The result indicates that the difference of local structure around Ga atoms between nanocrysta...