Liuwen Chang

The influence of interface modifier on the performance of nanostructured ZnO/polymer hybrid solar cells

We have demonstrated an improvement of photovoltaic performance based on the nanostructured ZnO/poly(3-hexylthiophene) (P3HT) hybrid through interface molecular modification on ZnO nanorod surface. By probing the carrier dynamics at ZnO/P3HT interfaces, we have found that the interfacial molecules can play the role of assisting charge separation and suppression of back recombination at interfaces, which accounts for the observed enhanced short circuit current (Jsc) and open circuit voltage (Voc) in photovoltaic performance.

Structural relaxation and nanoindentation response in Zr–Cu–Ti amorphous thin films

Ternary Zr–Cu–Ti system, especial with a high Ti content, is normally difficult to be fully vitrified. In this paper, we demonstrate that cosputtering can produce amorphous Zr–Cu–Ti thin films with an excessive Ti content even as high as 19%. Sub-Tg annealing of the film induces the formation of medium-range-ordered clusters and to raise the nanohardness by 35% to 6.6GPa. The promising mechanical properties of the sub-Tg annealed Zr52Cu29Ti19 films offer great potential for microelectromechanical system applications.

Electrodeposition of Ni – P Alloys From a Sulfamate Electrolyte Relationship Between Bath pH and Structural Characteristics

This study describes the effects of the electrolyte pH on phosphorus content, microstructures, and internal stress of Ni-P deposits prepared from a sulfamate bath containing phosphorous acid. Decreasing the pH increases the concentration of nondissociated phosphorous acid in the electrolyte, which results in a monotonic increase of the phosphorus content in the deposits. The increase in phosphorus content decreases the grain size but increases the strength of the (111) texture. Decreasing the pH to about 1.5 can decrease the internal stress dramatically to values close to that of the pure Ni deposited at the same pH. A consistent mechanism of the internal stress evolution in both pure Ni and Ni-P deposits associated with varying the pH is proposed.

Improved quality of nonpolar m-plane GaN [101¯0] on LiAlO2 substrate using a modified chemical vapor deposition

Nonpolar GaN crystal on lattice-matched [100] γ-LiAlO2 substrate was grown by a newly designed chemical vapor deposition (CVD) reactor. Following the CVD growth, x-ray diffraction indicated that the GaN film was oriented in the nonpolar m-plane with [101¯0] orientation. Further structural characterizations and defect analysis of nonpolar GaN material was performed using transmission electron microscope. Low-temperature photoluminescence was dominated by neutral donor bound excitons and the yellow luminescence was negligible. Raman spectroscopy showed that the as-grown GaN {101¯0} epilayer on [100] γ-LiAlO2 substrate were indeed of good quality. Compared to the previous report, nonpolar GaN with an improved quality was demonstrated by modifying the inner structure of the CVD reactor.

Spectral and Spatial Luminescence Distribution of m-Plane ZnO Epitaxial Films Containing Stacking Faults: A Cathodoluminescence Study

The luminescence of stacking faults (SFs) in m-plane ZnO epilayers grown by metal organic chemical vapor deposition is analyzed using spatially resolved cathodoluminescence (CL) spectroscopy. Complementary features observed in CL images for detection energies of 3.379 (near-band-edge) and 3.324 eV confirm the latter to be a typical SF-associated luminescence. A clear blue shift of the SF-associated luminescence is observed when the electron beam approaches the SF. This experimental result proves the existence of a polarization field in the SFs along the c-axis of the ZnO film. Furthermore, we clearly identify the SF-related transition at low temperatures and at room temperature.

Microstructure of non-polar GaN on LiGaO2 grown by plasma-assisted MBE.

We have investigated the structure of non-polar GaN, both on the M - and A-plane, grown on LiGaO2 by plasma-assisted molecular beam epitaxy. The epitaxial relationship and the microstructure of the GaN films are investigated by transmission electron microscopy (TEM). The already reported epi-taxial relationship and for M -plane GaN is confirmed. The main defects are threading dislocations and stacking faults in both samples. For the M -plane sample, the density of threading dislocations is around 1 × 1011 cm-2 and the stacking fault density amounts to approximately 2 × 105 cm-1. In the A-plane sample, a threading dislocation density in the same order was found, while the stacking fault density is much lower than in the M -plane sample.

Growth of MgO doped near stoichiometric LiNbO3 single crystals by a hanging crucible Czochralski method using a ship lockage type powder feeding system assisted by numerical simulation

MgO doped near stoichiometric LiNbO3 (MgOSLN) crystals have great potential for use in periodically poled structured LiNbO3 (PPLN) for doubling frequency lasers and optical parametric oscillation infrared lasers, because of their high optical damage threshold, single domain characteristics, and very low coercive field. However, few MgOSLN crystals are commercially available in the present market because of the great difficulty in growing them. This paper describes how a hanging crucible Czochralski technique with a newly-designed ship lockage type powder feeding system assisted by numerical simulation was developed for the successful growth of high quality near stoichiometric LiNbO3 (SLN) and MgOSLN (~1 mol%) crystals. The physical properties of the crystals were assessed by measuring their crystallinity, Curie temperature, optical properties, coercive field and thermal properties. These properties, including a coercive field of 1.4 kV mm−1 and a thermal conductivity of 6.61 W (m K)−1 demonstrated that the crystals meet the demands for manufacturing periodically poled crystal devices. This growth method has great potential in the mass production of SLN and other incongruently melting crystals.

Microstructure Characterization of Cu-Alloyed GaN Grown by Plasma Assisted Molecular Beam Epitaxy

Cu-alloyed GaN epilayers were prepared by plasma assisted molecular beam epitaxy with Cu-to-Ga beam equivalent pressure ratios of 1.2 to 4.8 %. Islands enriched with Cu are found on the GaN epitaxial layers grown in a Ga-rich environment. The islands are composed of a Cu9Ga4 intermetallic phase and GaN with the orientation relationship: [111]Cu9Ga4//[1 2 10]GaN and (10 1)Cu9Ga4//(0001)GaN. X-ray spectroscopy analyses indicated that the 1.2 % and 4.8 % samples contains 0.10 ± 0.02 wt.%Cu and 0.04 ± 0.03 wt.%Cu, respectively.