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221.
J. Mass M. Avella J. Jiménez M. Callahan E. Grant K. Rakes D. Bliss B. Wang 《Applied Physics A: Materials Science & Processing》2007,88(1):95-98
We present a study of the visible luminescence in ZnO hydrothermal crystals. The study is carried out on oxygen polarity basal
plane (000-1) plates that are sliced through several distinct growth sectors of the crystal. The plates reveal three distinct
regions that display differences in the luminescence emission, especially in the visible range. These differences should be
related to the variation in the distribution of impurities and native defects in the various growth sectors of hydrothermal
ZnO. CL images also expose the presence of nonradiative recombination centers that are associated with point defects or complexes
of point defects. CL measurements varying the acceleration voltage of the e-beam reveal that the deep levels responsible for
the green luminescence, and in a minor extension those responsible for the yellow-orange luminescence are depleted near the
surface. A discussion about the main hypothesis accounting for such behavior is presented.
PACS 71.55.Gs; 71.55.-i; 78.55.Et; 78.60.Hk 相似文献
222.
Basic research in the chemistry of hexameric resorcin[4]arenes and pyrogallol[4]arenes during the last decade is reviewed. Applications of NMR methods to determine solution structures, host guest properties and exchange dynamics are discussed. The scientific issue is the behavior of molecules in small spaces; the challenge is to translate this information to practical applications in, say, catalysis or transport. 相似文献
223.
The closure of a three-residue loop was studied using a developed kinematic method. It was shown that there are infinite number of three-residue loops (a locus of conformations), which can connect two segments of a polypeptide. This adds to the current understanding of a finite number of conformations for three-residue loop-closure. In the developed method, some of the equations can be solved analytically to reduce the computation cost. Benefiting from the reduced computation time, we determined all the relative positions of two polypeptide segments that can be connected by a three-residue loop. 相似文献