A universal but simple procedure for identifying the α, β and γ phases in PVDF using FTIR is proposed and validated. An integrated quantification methodology for individual β and γ phase in mixed systems is also proposed.

Xiamen Municipal Science & Technology Bureau [2006AA03Z110]In(x)Ga(1-x)N p-i-n homojunction solar cells with different In content are studied. The measured open circuit voltages (V(oc)) are 2.24, 1.34, and 0.96 V, for x=0.02, 0.12, and 0.15, respectively. By comparing the x-ray rocking curves, the I-V characteristics and the external quantum efficiencies, it's demonstrated that the deterioration of InGaN crystal quality for larger In contents causes the decrease of V(oc). The result demonstrates that reduction of defect is a key factor in the fabrication of nitride solar cell. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3254215

Effective transformation from paraelectric to a high fraction of ferroelectric phase is crucial to produce piezoelectric materials with a high piezoelectric constant for broad applications. In polyvinylidene fluoride (PVDF) thin films, both mechanical stretching and electric poling processes have been found to be critical in the a / b phase transformation. However, in PVDF fibers fabricated by the electrospinning process, the roles of mechanical stretching and electric poling have not been well explored. Here, the properties of PVDF fibers from electrospinning and forcespinning, a mechanical spinning process without electric poling, have been characterized and analyzed by FTIR and XRD spectroscopic techniques. The results show that pure mechanical stretching in the forcespun fibers can result in a high fraction of the all-trans b-phase, at 95%. Electrospun fibers from the same material system, on the other hand, can also reach a high fraction of b-phase, at approximately 99%. These results preliminarily demonstrate that mechanical stretching is the main reason for b-phase induction in PVDF fibers. Further experiments performed in this work show that higher wt% of PVDF, lower polymer solution supply rate, and more uniformly mixed solvent systems facilitate achieving a higher level of ferroelectric b-phase in electrospun PVDF fibers.

No abstract

Gap electrospinning is a facile technique to produce aligned nanofibers useful for many applications, but its potential has not yet been fully exploited in nature, leading to the fiber length still limited to several tens of centimeters at present. In this work, we report a breakthrough in the production of well-aligned nanofibers with record length and efficiency. Using a suitable poly(vinylidene fluoride) solution and a pair of parallel plates that are substrate-free and negatively connected, we demonstrate the ease of this technique to prepare length-controllable aligned fibers in a wide range (≤125 cm). Because of the crucial roles of both the jet whipping instability that continuously drives the jet to span across the static plates and the negative voltage on the plates that effectively attracts the positively charged jet, the jet can be made to move back and forth over the superlarge gap to form ultralong aligned nanofibers. By introducing a projection method, we also redefine fiber alignment in a broader sense. This work is believed to provide a new insight into the nature of gap electrospinning, which will greatly expand the versatility of this technique to create devices for a myriad of applications.

No abstract

Influence of barrier thickness on the structural and optical properties of InGaN/GaN multiple quantum wells *Liang Ming-Ming(梁明明) a)b) , Weng Guo-En(翁国恩) a)b) , Zhang Jiang-Yong(张江勇) c) † , Cai Xiao-Mei(蔡晓梅) a)b) , Lü Xue-Qin(吕雪芹) b) , Ying Lei-Ying(应磊莹) c) , and Zhang Bao-Ping(张保平) a)c) ‡

No abstract