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1.
A series of PdxNi1 − x nanoparticles in a diameter of 6-7 nm were prepared by wet chemical reduction. They were then modified with two surfactants, stearic acid (SA) and polyethylene glycol (PEG). Desorption of the surfactant was studied using a temperature programmed desorption technique, and the sintering behavior of surface-modified PdxNi1 − x nanoparticles was examined. Since surface energy of the nanoparticles depends on the alloy composition, it can be correlated with the desorption temperature of surfactant from the nanoparticle surface. Because Ni has a higher surface energy, the surfactant desorption temperature increases as the Ni content increases. With the same stoichiometry, the desorption temperature of SA is always higher than that of PEG. The SA-modified nanoparticles have higher thermal stability and are less sintered than PEG-modified nanoparticles. The sintering and growth behavior of the nanoparticles can be correlated with variation of surface energy due to different surface modification. 相似文献
2.
Tianqing Jia Motoyoshi Baba Fuli Zhao Xiaojun Wu Masayuki Suzuki Zhizhan Xu 《Solid State Communications》2007,141(11):635-638
We present a simple route for ZnSe nanowire growth in the ablation crater on a ZnSe crystal surface. The crystal wafer, which was horizontally dipped in pure water, was irradiated by femtosecond laser pulses. No furnace, vacuum chamber or any metal catalyst were used in this experiment. The size of the nanowires is about 1-3 μm long and 50-150 nm in diameter. The growth rate is 1-3 μm/s, which is much higher than that achieved with molecular-beam epitaxy and chemical vapor deposition methods. Our discovery reveals a rapid and simple way to grow nanowires on designed micro-patterns, which may have potential applications in microscopic optoelectronics. 相似文献
3.
Chemical-vapor-deposited (CVD) nanostructured thin films have been recently developed to overcome the limitations of thin
films from one material class. In particular polymer/SiO2 nanocomposite thin films have been developed to reduce power consumption, cross-talk, and RC delay in the next generation
of ultralarge-scale integrated devices. Since polymers mainly possess electronic polarization they inherently have a low dielectric
constant. However, they often suffer from poor dielectric anisotropy, low elastic and shear moduli, and have poor resistance
to metallic diffusion. As a proof of concept, poly(chloro-p-xylylene)/SiO2 thermal CVD nanocomposites have been developed to overcome such material deficiencies. Additionally, the CVD process allows
for high manufacturing throughput and compositional control in situ, both potentially advantageous for IC fabrication. The
study here focuses on the polymeric phase of the nanocomposite, which as a homopolymer can possess ≈60% crystallinity and
a positive optical birefringence of 0.034, both post-deposition-annealed just before the polymer’s melting point. With increasing
volume percent of SiO2, the percent crystallinity is reduced, the thin film becomes more isotropic and the index of refraction can be varied depending
on the volume percent SiO2.
Received: 15 December 1999 / Accepted: 7 January 2000 / Published online: 5 April 2000 相似文献
4.
We present a new way to demodulate complicated fringe patterns containing closed fringes using a genetic algorithm (GA). The entire fringe pattern is divided into a set of partially overlapping smaller sub-image windows. Each of these has a lower dimensionality and as a consequence is faster and can be demodulated more reliably. The demodulation process proceeds row-by-row way passing from one sub-image in a neighborhood until the whole interferogram is processed. The modulating phase of each sub-image is modeled as a parametric analytic function whose parameters are optimized using a GA. The technique is demonstrated demodulating some normalized fringe patterns that have two main difficulties: closed fringes within the interferogram and regions of under-sampled fringes. These fringe images cannot be demodulated by techniques such as the regularized phase tracker (RPT). 相似文献
5.
Zhengping Fu Beifang Yang Zhen Wang Hongwei Yan Jian Zuo Xianming Liu 《Solid State Communications》2006,138(4):179-183
By glycine-nitrate combustion route and followed by 900 °C annealing in air, ZnO-MgO nanocomposite with heterojunction-like structures between ZnO and MgO phase was successfully produced. The ultraviolet photoluminescence band from ZnO is enhanced by the incorporation of MgO, as compared to the pure ZnO synthesized via the similar route. The charge transfer required by electronic equilibrium across the junction creates an electron depletion region in ZnO phase, which greatly changes the electron states of visible emission-related defects, as a result, the band-edge emission is enhanced while the visible emission in ZnO is suppressed. This mechanism may provide an effective way to modify the emission property of nanomaterials. 相似文献
6.
M. Merschdorf W. Pfeiffer A. Thon S. Voll G. Gerber 《Applied Physics A: Materials Science & Processing》2000,71(5):547-552
Two-photon photoemission spectroscopy using femtosecond laser pulses is used to investigate the excitation and decay mechanisms
of the surface plasmon resonance in Ag nanoparticles grown on graphite. The resonant excitation of this collective excitation
leads to a two-orders-of-magnitude-enhanced two-photon photoemission yield from a graphite surface with Ag nanoparticles compared
to the yield from pure graphite. From the shape of the photoemission spectra, the polarization dependence of the photoemission
yield and the excitation probabilities for different excitation pathways we conclude that excitation with 400-nm femtosecond
laser pulses leads to the coherent multiple excitation of the surface plasmon in the Ag nanoparticles. This multiply excited
plasmon mode can decay via the coupling to a single-particle excitation leading to the emission of an electron if its final
state is located in the continuum. The surface plasmon in metallic nanoparticles is a model system to investigate collective
excitations in multiphoton processes.
Received: 26 June 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000 相似文献
7.
T. Bergmann M. DeKieviet T. Gasenzer O. Nachtmann M.-I. Trappe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(3):551-574
We discuss the propagation of hydrogen atoms in static electric and magnetic fields in a longitudinal atomic beam spin echo
(lABSE) apparatus. There the atoms acquire geometric (Berry) phases that exhibit a new manifestation of parity-(P-)violation
in atomic physics. We provide analytical as well as numerical calculations of the behaviour of the metastable 2S states of
hydrogen. The conditions for electromagnetic field configurations that allow for adiabatic evolution of the relevant atomic
states are investigated. Our results provide the theoretical basis for the discussion of possible measurements of P-violating
geometric phases in lABSE experiments. 相似文献
8.
This paper reports the photoluminescence (PL) properties of nanocrystalline YVO4: Tm phosphor synthesized by the polymerizable complex method based on the Pechini-type reaction. The powder was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), absorption spectroscopy and PL. The results of XRD and TEM show that, high-quality nanopowders with controlled morphology and microstructure were prepared at a relatively low temperature about 700 °C. Upon ultra violet excitation the vanadate host transferred energy to thulium ions efficiently and strong blue emission (475 nm) assigned to 1G4→3H6 transmission is observed. By analyzing excitation and emission spectra of thulium doped yttrium vanadate, we deduced the mechanism of the energy transfer between vanadate host and thulium ions. 相似文献
9.
Yongjun He 《Applied Surface Science》2006,252(6):2115-2118
One-dimensional polyaniline nanostructures were synthesized by interfacial polymerization in a solids-stabilized oil/water emulsion for the first time. The products were characterized with TEM, FTIR and UV-vis. FTIR analyses proved the polyaniline synthesized were of emeraldine salt form; the results of TEM showed that when MgCO3 and CaCO3 particles were used as emulsifiers, polyaniline nanofibers with an average diameter of 33 nm and nanotubes with an average outer diameter of 28 nm were obtained, respectively. Comparing to ordinary interfacial polymerization approach, our new route needed much less amount of oil phase and shorter polymerization time. A possible mechanism for the formation of one-dimensional polyaniline nanostructures was suggested. 相似文献
10.
V. Turco Liveri M. Rossi G. D’Arrigo D. Manno G. Micocci 《Applied Physics A: Materials Science & Processing》1999,69(4):369-373
ZnS nanoparticles were synthetized using water-containing AOT reversed micelles as nanoreactors and characterized by UV-Vis
spectrophotometry, HRTEM (high-resolution transmission electron microscopy), SAED (selected-area electron diffraction), and
digital image processing. The experimental data evidence a slow growing process of fractal-like ZnS nanoparticles’ coupled
with a change of their photophysical properties. Both these processes are well described by power laws. The nanoparticles
size is mainly controlled by the micellar size. After evaporation of the organic solvent, it has been found that the deposit
is constituted by smaller and more stable ZnS nanoparticles bathed in a surfactant matrix.
Received: 20 April 1999 / Accepted: 23 April 1999 / Published online: 8 September 1999 相似文献