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991.
Defects in ZnO nanorods prepared by a hydrothermal method 总被引:5,自引:0,他引:5
Tam KH Cheung CK Leung YH Djurisić AB Ling CC Beling CD Fung S Kwok WM Chan WK Phillips DL Ding L Ge WK 《The journal of physical chemistry. B》2006,110(42):20865-20871
ZnO nanorod arrays were fabricated using a hydrothermal method. The nanorods were studied by scanning electron microscopy, photoluminescence (PL), time-resolved PL, X-ray photoelectron spectroscopy, and positron annihilation spectroscopy before and after annealing in different environments and at different temperatures. Annealing atmosphere and temperature had significant effects on the PL spectrum, while in all cases the positron diffusion length and PL decay times were increased. We found that, while the defect emission can be significantly reduced by annealing at 200 degrees C, the rods still have large defect concentrations as confirmed by their low positron diffusion length and short PL decay time constants. 相似文献
992.
Lopez-Salido I Lim DC Dietsche R Bertram N Kim YD 《The journal of physical chemistry. B》2006,110(3):1128-1136
Au nanoparticles grown on mildly sputtered Highly Ordered Pyrolytic Graphite (HOPG) surfaces were studied using Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS). The results were compared with those of Ag nanoparticles on the same substrate. By varying the defect densities of HOPG and the Au coverages, one can create Au nanoparticles in various sizes. At high Au coverages, the structures of the Au films significantly deviate from the ideal truncated octahedral form: the existence of many steps between different Au atomic layers can be observed, most likely due to a high activation barrier of the diffusion of Au atoms across the step edges. This implies that the particle growth at room temperature is strongly limited by kinetic factors. Hexagonal shapes of Au structures could be identified, indicating preferential growth of Au nanostructures along the (111) direction normal to the surface. In the case of Au, XPS studies reveal a weaker core level shift with decreasing particle size compared to the 3d level in similarly sized Ag particles. Also taking into account the Auger analysis of the Ag particles, the core level shifts of the metal nanoparticles on HOPG can be understood in terms of the metal/substrate charge transfer. Ag is (partially) positively charged, whereas Au negatively charged on HOPG. It is demonstrated that XPS can be a useful tool to study metal-support interactions, which plays an important role for heterogeneous catalysis, for example. 相似文献
993.
Yang SY Shin K Kim SH Jeon H Kang JH Yang H Park CE 《The journal of physical chemistry. B》2006,110(41):20302-20307
The role of lateral interconnections between three-dimensional pentacene islands on low surface energy polyimide gate dielectrics was investigated by the measurement of the surface coverage dependence of the charge mobility and the use of conducting-probe atomic force microscopy (CP-AFM). From the correlation between the electrical characteristics and the morphological evolution of the three-dimensionally grown pentacene films-based field-effect transistors, we found that during film growth, the formation of interconnections between the three-dimensional pentacene islands that are isolated at the early stage contributes significantly to the enhancement process of charge mobility. The CP-AFM current mapping images of the pentacene films also indicate that the lateral interconnections play an important role in the formation of good electrical percolation pathways between the three-dimensional pentacene islands. 相似文献
994.
A critical advance in the technique of low-energy electron diffraction is presented and shown to enable determining detailed structures of nanomaterials, based on experimental methods that already exist or have been proposed. Our new cluster approach speeds up the computation to scale as n logn, rather than the current n3 or n2, with n the number of atoms, for example. Applications are illustrated for C60 molecules adsorbed on a Cu(111) surface, with and without coadsorbed metal atoms, exhibiting sensitivity to important structural features such as buckyball size and deformation. 相似文献
995.
We present new capacitance measurements of critical Casimir force-induced thinning of 4He films near the superfluid transition, focused on the region below Tlambda where the effect is the greatest. 4He films of 238, 285, and 340 A thickness are adsorbed on atomically smooth, N-doped silicon substrates. The Casimir force scaling function theta, deduced from the thinning of these three films, collapses onto a single universal curve, attaining a minimum theta=-1.30+/-0.03 at x=td1/nu=-9.7+/-0.8 A1/nu. The collapse confirms the finite-size scaling origin of the dip in the film thickness. Separately, we also confirm the presence down to 2.13 K of the Goldstone or surface fluctuation force, which makes the superfluid film approximately 2 A thinner than the normal film. 相似文献
996.
In this Letter, we introduce a simple metal waveguide array for realizing all-angle wide frequency bandwidth negative refraction from the visible to infrared frequencies. Theoretical analysis from the rigorous coupled-wave theory reveals that the negative coupling constant resulting from the anomalous coupling of guided surface plasmon polariton modes contributes to the negative refraction. The analytical results are confirmed by finite-difference time-domain numerical simulations. Our result provides an alternative way to construct robust all-angle negative refractive materials operating in a wide range of frequency from the near-infrared to the visible range. 相似文献
997.
Ablikim M Bai JZ Ban Y Bian JG Cai X Chang JF Chen HF Chen HS Chen HX Chen JC Chen J Chen J Chen ML Chen YB Chi SP Chu YP Cui XZ Dai HL Dai YS Deng ZY Dong LY Du SX Du ZZ Fang J Fang SS Fu CD Fu HY Gao CS Gao YN Gong MY Gong WX Gu SD Guo YN Guo YQ Guo ZJ Harris FA He KL He M He X Heng YK Hu HM Hu T Huang GS Huang L Huang XP Ji XB Jia QY Jiang CH Jiang XS Jin DP Jin S Jin Y Lai YF Li F Li G Li HB Li HH Li J Li JC Li QJ Li RB Li RY Li SM Li WG Li XL Li XQ Li XS Liang YF Liao HB Liu CX Liu F Liu F 《Physical review letters》2006,97(6):062001
The decay J/psi-->NNpi provides an effective isospin 1/2 filter for the piN system due to isospin conservation. Using 58x10(6) J/psi decays collected with the Beijing Electromagnetic Spectrometer at the Beijing Electron Positron Collider, more than 100 thousand J/psi-->ppi-n+c.c. events are obtained. Besides the two well-known N* peaks at around 1500 MeV/c2 and 1670 MeV/c2, there are two new, clear N* peaks in the ppi invariant mass spectrum around 1360 MeV/c2 and 2030 MeV/c2 with statistical significance of 11sigma and 13sigma, respectively. We identify these as the first direct observation of the N*(1440) peak and a long-sought missing N* peak above 2 GeV/c2 in the piN invariant mass spectrum. 相似文献
998.
We have measured the pressure dependence of the supersolid fraction by a torsional oscillator technique. Superflow is found from 25.6 bar up to 136.9 bar. The supersolid fraction in the low temperature limit increases from 0.6% at 25.6 bar near the melting boundary up to a maximum of 1.5% near 55 bar before showing a monotonic decrease with pressure extrapolating to zero near 170 bar. 相似文献
999.
Combinatorial library screening offers a rapid process for identifying potential therapies to toxins. Hinge peptide libraries,
which rely on conformational diversity rather than traditional molecular diversity, reduce the need for huge numbers of syntheses
and screening steps and greatly expedite the discovery process of active molecules. Hinge peptide libraries having the structures:
Acetyl-X1–X2–hinge–X3–X4–NH2 (capped) and X1–hinge–X2–X3 (uncapped), where X1 through X4 are near-equimolar mixtures of twelve L-amino acids and hinge = 4-aminobutyric acid, were screened for inhibitory activity in bioassays for botulinum neurotoxins
A and B (BoNT/A, BoNT/B) and saxitoxin. The zinc protease activity of the reduced light chains of BoNT/A and /B was assayed
by measuring the cleavage of synthetic substrates. Saxitoxin activity was measured by the restoration of the viability of
neuroblastoma cells treated with ouabain and veratridine. Deconvolution of libraries was accomplished by fixing one position
at a time beginning with the C-terminus. Primary library subsets in which position 4 was fixed showed moderate levels of inhibition
for BoNT/A. Secondary library subsets showed stronger inhibition in the bioassays. In each of the bioassays, inhibitory potency
was stronger when the second position to be fixed was on the opposite side of the hinge, rather than on the same side with
respect to the C-terminus, suggesting that the hinge facilitates the interaction of side chains. Inhibitors for all three
of the toxins studied were discovered within library subsets, although not necessarily in primary subsets. These studies demonstrate
that (1) the best strategy for deconvoluting hinge peptide libraries is by fixing residues alternately on each side of the
hinge moiety, and (2) it is essential to investigate secondary subsets even when primary subsets are inactive. The present
findings support the concept that the increased flexibility imposed by the inclusion of a central hinge residue in small peptides
increases the opportunity for side chain interactions, providing a distinct advantage for hinge peptide libraries over conventional
peptide libraries. Hinge peptide libraries are a rich source of novel ligands for modulation of biomechanisms. The library
subsets uncovered in this study may possess peptides that will lead to effective therapies to neurotoxin poisoning. 相似文献
1000.
Modification of Newton’s method with higher-order convergence is presented. The modification of Newton’s method is based on King’s fourth-order method. The new method requires three-step per iteration. Analysis of convergence demonstrates that the order of convergence is 16. Some numerical examples illustrate that the algorithm is more efficient and performs better than classical Newton’s method and other methods. 相似文献