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Quantum Theory of Electronic Double-Slit Diffraction
WU Xiang-Yao, ZHANG Bai-Jun, LI Hai-Bo, LU Jing-Bin, LIU Xiao-Jing, WANG Li, ZHANG Chun-Li, LIU Bing, FAN Xi-Hui, GUO Yi-Qing
Chin. Phys. Lett. 2007, 24 (10):
2741-2744
.
Phenomena of electron, neutron, atomic and molecular diffraction have been studied in many experiments, and these experiments have been explained by some theoretical works. We study electronic double-slit diffraction with a quantum mechanical approach and obtain the following results: (1) When the ratio of d+a/a=n (n=1, 2, 3,...), orders n, 2n, 3n,... are missing in diffraction pattern. (2) When the ratio of d+a/a≠n (n=1, 2, 3,...), there is not missing order in diffraction pattern. (3) The slit thickness c has a large affect on the electronic diffraction pattern, which is a new quantum effect. We believe that all the predictions in our work can be tested by the electronic double slit diffraction experiment.
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Duplication: a Mechanism Producing Disassortative Mixing Networks in Biology
ZHAO Dan, LIU Zeng-Rong, WANG Jia-Zeng
Chin. Phys. Lett. 2007, 24 (10):
2766-2768
.
Assortative/disassortative mixing is an important topological property of a network. A network is called assortative mixing if the nodes in the network tend to connect to their connectivity peers, or disassortative mixing if nodes with low degrees are more likely to connect with high-degree nodes. We have known that biological networks such as protein--protein interaction networks (PPI), gene regulatory networks, and metabolic networks tend to be disassortative. On the other hand, in biological evolution, duplication and divergence are two fundamental processes. In order to make the relationship between the property of disassortative mixing and the two basic biological
principles clear and to study the cause of the disassortative mixing property in biological networks, we present a random duplication model and an anti-preference duplication model. Our results show that disassortative mixing networks can be obtained by both kinds of models from uncorrelated initial networks. Moreover, with the growth of the network size, the disassortative mixing property becomes more obvious.
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Transition Temperature of Two-Degenerate-Flavour QCD in the Chiral Limit
WU Liang-Kai, LUO Xiang-Qian
Chin. Phys. Lett. 2007, 24 (10):
2769-2772
.
We present the results for the transition temperature of quantum chromodynamics (QCD) with two degenerate flavours (Nf=2) of Wilson quarks. On lattice 83×4 with 4 representing the temporal extent, by using the Ferrenberg--Swendsen reweighting method, we determine the critical β=6/g2 where the transition occurs, g is the coupling constant. On lattice 82×20×4, by using the axial vector Ward--Takahashi identity, we calculate the current quark mass amq, a is the lattice spacing. Assuming the O(4) scaling, the critical β in the chiral limit is determined. We calculate the ρ meson mass amρ at zero temperature on lattice 83×20. By using the experimental ρ meson mass to set the scale, we obtain 194(1)MeV for the transition temperature in the chiral limit.
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Analysis of Bd→ψ KS CP Asymmetry in a Flavour Changing Z' Model
WANG Shuai-Wei, SONG Tai-Ping, LU Gong-Ru, ZHONG Zhi-Guo
Chin. Phys. Lett. 2007, 24 (10):
2777-2780
.
According to the recent experimental data, the time-dependent CP asymmetry SψKS for Bd→KS decay might still be inconsistent with the standard model (SM) expectations. We try to understand the anomaly with a Z' model associated with flavour changing neutral currents (FCNCs) at the tree level. We find that (i) if neglecting the contributions from the right-handed flavour changing coupling BRsb and setting ξLL=ξLR=ξ and ξLL=ξ, ξLR=0, we may obtain 0.01< ξ <0.014, 0.0175< ξ <0.0205, 0.021< ξ <0.0255 and 0.004< ξ <0.008, 0.018< ξ <0.028, 0.042< ξ <0.048 for the Bd→ψ KS decay, respectively; (ii) if considering the contributions coming from BRsb and setting
ξLL=ξRL=ξLR=ξRR=ξ and ξLL=ξRL=ξ, ξLR=ξRR=0, we can obtain 0.005<
ξ<0.075, 0.0085< ξ<0.0105, 0.011<ξ<0.013 and 0.0125<ξ<0.0177, 0.0224< ξ<0.025. These results are consistent with the constraints and the assumptions in some literature.
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Single-Proton Pickup Reaction of the Halo Nucleus 6He on a 9Be Target at 25MeV/nucleon
PANG Dan-Yang, YE Yan-Lin, JIANG Dong-Xing, ZHENG Tao, LI Zhi-Huan, LI Xiang-Qing, GE Yu-Cheng, HUA Hui, WU Cui-E, LOU Jian-Ling, LUFei, FAN Feng-Ying, A. Ozawa, Y. Yamaguchi, R. Kanungo, D. Fang, I.Tanihata
Chin. Phys. Lett. 2007, 24 (10):
2785-2788
.
The inclusive differential cross sections of the 7Li nucleus in a reaction induced by 6He on a 9Be target are measured at an incident energy of 5MeV/nucleon. Finite-range distorted-wave Born approximation calculations suggest that these 7Li particles are formed in a direct single-proton pickup reaction 9Be(6He,7Li)8Li. The experimental data can be well reproduced by taking into account of the contributions of both the ground states and the first excited states of 7Li and 8Li.
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Neutron Generation and Kinetic Energy of Expanding Laser Plasmas
HUANG Yong-Sheng, WANG Nai-Yan, DUAN Xiao-Jiao, LAN Xiao-Fei, TAN Zhi-Xin, TANG Xiu-Zhang, HE Ye-Xi
Chin. Phys. Lett. 2007, 24 (10):
2792-2795
.
We investigate the kinetic energy of expanding plasma of a solid target heated by a ultra-short and ultra-intense laser pulse and the efficiency of energy coupling between the ultra-intense laser pulse and the solid target, in order to increase the utilization ratio of laser energy and to raise the neutron generation farther. Some new ideas about improving the energy utilization by head-on collisions between the expanding plasmas are proposed. The significance is the raise of generation of shorter duration neutron, of the order of picoseconds, which allows for an increase of energy resolution in time-of-flight experiments and also for the investigation of the dynamics of nuclear processes with high temporal resolution.
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The Average Lifetime of Giant Composite Systems Formed in Strongly Damped Collisions
TIAN Jun-Long, WU Xi-Zhen, OU Li, LI Zhu-Xia,
Chin. Phys. Lett. 2007, 24 (10):
2796-2799
.
The dynamic, adiabatic and diabatic entrance potentials in strongly damped reactions of 238U+238U, 232Th+250Cf are calculated and compared. The feature of the dynamical potential implies that it is possible for the composite systems to stick together for a period of time. By means of the improved quantum molecular dynamics model the time evolution of the density and
charge distributions of giant composite systems and their fragments for reactions 238U+238U, 232Th+250Cf are investigated, from which the lifetimes of giant composite systems at different energies are obtained. The longest average lifetime of 238U+238U is found when the incident energy is about
Ec.m=1080MeV, which is about 1200fm/c.
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Vapour-to-Liquid Nucleation in Associating Lennard-Jones Fluids with Multiple Association Sites
FU Dong, LIAO Tao
Chin. Phys. Lett. 2007, 24 (10):
2804-2807
.
The excess Helmholtz free energy functional for associating Lennard-Jones (LJ) fluid is formulated in terms of a weighted density approximation for short-ranged interactions and a Weeks--Chandler--Andersen approximation for long-range attraction. Within the framework of density functional theory, phase equilibria, vapour--liquid surface tension and vapour--liquid nucleation properties including the density profile, work of formation, excess number of
particles and critical supersaturation are investigated for associating LJ fluids with different numbers of association sites (M =1, 2, 3, 4) per particle. The influences of association energy and association sites on phase equilibria, surface tension and vapour-liquid nucleation properties are discussed.
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Additivity Rule for Electron--Molecule Total Cross Section Calculations at 50--5000eV: A Geometrical Approach
SHI De-Heng, SUN Jin-Feng, MA Heng, ZHU Zun-Lue, YANG Xiang-Dong
Chin. Phys. Lett. 2007, 24 (10):
2819-2822
.
To quantify the changes of the geometric shielding effect in a molecule as the incident electron energy varies, we present an empirical fraction, which represents the total cross section (TCS) contributions of shielded atoms in a molecule at different energies. Using this empirical fraction, a new formulation of the additivity rule is proposed. Using this new additivity rule, the TCSs for electron scattering by CO2, C2H2, C6H12 (cyclo-hexane) and C8H16 (cyclo-octane) are calculated in the range 50--5000eV. Here the atomic cross sections are derived from the experimental TCS results of simple molecules (H2, O2, CO). The quantitative TCSs are compared with those obtained by experiments and other theories, and good agreement is attained over a wide energy range.
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Fabrication of Nanoimprint Stamp Using Interference Lithography
CHEN Xian-Zhong, LI Hai-Ying
Chin. Phys. Lett. 2007, 24 (10):
2830-2832
.
Interference lithography is used to fabricate a nanoimprint stamp, which is a key step for nanoimprint lithography. A layer of chromium in thickness of about 20nm is deposited on the newly cleaned fused silica substrate by thermal evaporation, and a layer of positive resist in thickness of 150nm is spun on the chromium layer. Some patterns, including lines, holes and pillars, are observed on the photoresist film by exposing the resist to interference patterns and they are then transferred to the chromium layer by wet etching. Fused silica stamps are fabricated by reactive ion etching with CHF3/O2 as
etchants using the chromium layer as etch mask. An atomic force microscope is used to analyse the pattern transfer in each step. The results show that regular hole patterns of fused silica, with average full width 143nm at half maximum (FWHM), average hole depth of 76nm and spacing of 450nm, have been fabricated. The exposure method is fast, inexpensive and applicable for fabrication of nanoimprint stamps with large areas.
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Realization of an All-Fibre Self-Organization Intra-Cavity Coherent Erbium-Doped Fibre Laser
JIA Xiu-Jie, LIU Yan-Ge, LIU Feng-Nian, FU Sheng-Gui, LIU Bo, YUAN Shu-Zhong, KAI Gui-Yun, DONG Xiao-Yi
Chin. Phys. Lett. 2007, 24 (10):
2842-2845
.
An intra-cavity coherent coupling Michelson Er-doped fibre (EDF) laser (MCEDFL) is proposed and demonstrated. Characteristics of the MCEDFL are
investigated. It is found that the MCEDFL with a polarizer can be coherent combined effectively. By the experiment based on fibre Bragg gratings (FBGs) with different reflectivity, we find that the reflectivity of the FBG play a vital role in improving the performance of the MCEDFL. This outcome adequately shows many favourable features, such as high efficiency, easy operation, and simple all-fibre configuration.
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Transmission Properties of W3 Y-Branch Filters in Two-Dimensional Photonic Crystal Slabs
REN Cheng, REN Kun, LIU Rong-Juan, TAO Hai-Hua, FENG Shuai, XIONGZhi-Gang, LIU Ya-Zhao, TIAN Jie, LI Zhi-Yuan, CHENG Bing-Ying, ZHANG Dao-Zhong
Chin. Phys. Lett. 2007, 24 (10):
2863-2866
.
A highly efficient W3 Y-branch filter in a two-dimensional photonic crystal slab with triangular lattice of air holes is designed and fabricated, and its transmission properties are measured. By accurately adjusting the size of the resonant cavities, the minimum wavelength spacing of 7nm between two channels is realized. The corresponding resonant wavelengths of the two cavities agree well with the calculated ones. This implies that this kind of filter may be promising in integrated wavelength division multiplexing system.
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Influence of Vacuum Organic Contaminations on Laser-Induced Damage of 1064nm Anti-Reflective Coatings
CUI Yun, LIU Shi-Jie, HE Hong-Bo, ZHAO Yuan-An, SHAO Jian-Da, FAN Zheng-Xiu
Chin. Phys. Lett. 2007, 24 (10):
2873-2875
.
We investigate the influence of vacuum organic contaminations on laser-induced damage threshold (LIDT) of optical coatings. Anti-reflective (AR) coatings at 1064\,nm made by Ta2O5/SiO2 are deposited by the ion beam
sputtering method. The LIDTs of AR coatings are measured in vacuum and
in atmosphere, respectively. It is exhibited that contaminations in vacuum are easily to be absorbed onto optical surface because of lower pressure, and they become origins of damage, resulting in the decrease of LIDT from 24.5J/cm2 in air to 15.7J/cm2 in vacuum. The LIDT of coatings in vacuum has is slightly changed compared with the value in atmosphere after the organic contaminations are wiped off. These results indicate that organic contaminations are the main reason of the LIDT decrease in vacuum. Additionally, damage morphologies have distinct changes from vacuum to atmosphere because of the differences between the residual stress and thermal decomposability of filmy materials.
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Fabrication of Pure Silica Core Multimode Ultraviolet Optical Fibre Probes by Tube Etching
HUO Xin, PAN Shi, WU Shi-Fa
Chin. Phys. Lett. 2007, 24 (10):
2876-2878
.
As a light wave-guide component for transmitting ultraviolet (UV) laser pulses, pure silica core UV fibre probes have attracted a great deal of attention in the near-field optical data storage and bio-medical studies. We fabricate UV fibre probes with tips in dimension of about 2--5μm and taper angle 16°by the tube etching method, using 40% HF acid as etching solution and xylene as overlayer. Probes produced have curvy configuration with smooth surface. The yield of fine probes is rather high and etching operation greatly simplified. With higher damage threshold, pure silica core multimode UV fibre probes can be coupled into more laser power. In addition, using UV light reduces the cutoff wavelength of the fibre probes, which is in favour of increasing the
transmission efficiency of the probe. Furthermore, the larger tip dimension helps to enhance the light throughput either. The advances of fabrication technique of UV optical fibre probe may further support the studies of UV light data storage, pulsed laser biosurgery and UV photolithography.
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Birefringence of Irregular-Microstructure Fibre
LI Yan, LIU Jian-Guo, KAI Gui-Yun, LIU Yan-Ge, XUE Li-Fang, WANG Zhi, YUAN Shu-Zhong, DONG Xiao-Yi
Chin. Phys. Lett. 2007, 24 (10):
2879-2882
.
Birefringence of a microstructure fibre with irregular structures is investigated using the finite element method. The birefringence of each sample is statistically analysed, and the relation between the birefringence and the irregular structure of the microstructure fibre is derived. The results indicate that the irregular structure of the symmetrical microstructure fibre result in the birefringence which is more strongly affected by disorder of air holes than the
nonuniformity. Moreover, lower birefringence can be obtained with smaller air holes and larger pitch in the fibre structure.
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Solitary Wave Interactions in Granular Media
WEN Zhen-Ying, WANG Shun-Jin, ZHANG Xiu-Ming, LI Lei
Chin. Phys. Lett. 2007, 24 (10):
2887-2890
.
We numerically study the interactions of solitary waves in granular media, by considering a chain of beads, which repel upon contact via the Hertz-type potential, V ∝ δn, with 5/2≤n≤3 and δ≥0, δ being the bead--bead overlap. There are two collision types of solitary waves, overtaking collision and head-on collision, in the chain of beads. Our quantitative results show that after collision the large solitary wave gains energy and the small one loses energy for overtaking type while the large one loses energy, and the small one gains energy for head-on type. The scattering effects decrease with n for overtaking collision whereas increase with n for head-on collision.
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Lattice Boltzmann Simulation for the Optimized Surface Pattern in a Micro-Channel
WANG Jin-Feng, LIU Yang, XU You-Sheng, WU Feng-Min
Chin. Phys. Lett. 2007, 24 (10):
2898-2901
.
Based on the Bhatangar--Gross--Krook (BGK) models, numerical simulation
using the lattice Boltzmann model is performed to investigate the optimized surface pattern in a micro-channel. In order to simulate the practical situation correctly, a slip/no-slip boundary condition is applied with making several assumptions. To assess the validity and efficiency of the model, one benchmark problem with considering the surface patterns is studied. Numerical results show the value of rms velocity Vrms increases with the increasing ratio β and larger Reynolds number Re, higher fluctuation of the rms oscillating velocity. Furthermore, the results show that a good mixing
effect can be obtained when Re is large enough and the ratio β is about 1.618, which is the appropriate choice, i.e. the well known golden section phenomenon.
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Non-Contact to Contact Transition: Direct Measurements of Interaction Forces between a Solid Probe and a Planar Air--Water Interface
WU Di, WANG Yi-Zhen, ZHANG Jin-Xiu
Chin. Phys. Lett. 2007, 24 (10):
2914-2917
.
The interaction force between a solid probe and a planar air--water interface is measured by using an atomic force microscope. It is demonstrated that during the approach of the probe to the air--water interface, the force curves decline all the time due to the van der Waals attraction and induces a stable profile of water surface raised. When the tip approaches very close to the water surface, force curves jump suddenly, reflecting the complex behaviour of the unstable water surface. With a theoretical analysis we conclude that before the tip touches water surface, two water profiles appear, one stable and the other unstable. Then, with further approaching, the tip touches water
surface and the non-contact to contact transition occurs.
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Low-Dimensional Forest-Like and Desert-Like Fractal Patterns Formed in a DDAN Molecular System
CAI Jin-Ming, BAO Li-Hong, GUO Wei, CAI Li, HUAN Qing, LIAN Ji-Chun, GUO Hai-Ming, WANG Ke-Zhi, SHI Dong-Xia, PANG Shi-Jin, GAO Hong-Jun
Chin. Phys. Lett. 2007, 24 (10):
2918-2921
.
Two kinds of forest-like and desert-like patterns are formed by thermal
evaporation of 4-dicyanovinyl-N, N-dimethylamino-1-naphthalene (DDAN)
onto SiO2 substrates. Based on thermal kinetics of the molecules on the substrate the transformation between the forest and desert patterns is due to two factors. The first one is the diffusion length, which is related to the deposition rate, the diffusion potential energy barrier and the substrate temperature. The second one is the strong interaction between the two polarity chemical groups of the molecules, which is beneficial to the formation of branches. Totally different patterns are also found on mica substrates, and are attributed to the anisotropic diffusion and the stronger interaction between DDAN molecules and the mica surface.
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Electric Field Enhancement of Nano Gap of Silver Prisms
KENZO Yamaguchi, TOMOHIRO Inoue, MASAMITSU Fujii, MASANOBU Haraguchi, TOSHIHIRO Okamoto, MASUO Fukui, SHU Seki, SEIICHI Tagawa
Chin. Phys. Lett. 2007, 24 (10):
2934-2937
.
Using numerical calculation, we examine the effects of gap distance of a pair of nano gap silver prisms with rounded corners on the local light intensity enhancement. Two peaks due to localized surface plasmon (LSP) excitation are observed in a wavelength range from 900nm to 300nm. The results demonstrate that peaks at a longer and a shorter wavelength corresponded to dipole-like and quadrupole-like LSP resonances, respectively. It is found that a gap distance up to 20nm provides larger light intensity enhancement than that of a single silver nano prism with rounded corners. Furthermore, nano gap silver prisms are fabricated by direct focused ion beam processing, and we measure the scattering light spectrum of a pair of nano prisms by a
confocal optical system. However, the two LSP peaks are not observed in
visible range because the sizes of the nano gap and prisms are too large.
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Barrier Enhancement Effect of Postannealing in Oxygen Ambient on Ni/AlGaN Schottky Contacts
SANG Li-Wen, QIN Zhi-Xin, CEN Long-Bin, CHEN Zhi-Zhong, YANG Zhi-Jian, SHEN Bo, ZHANG Guo-Yi
Chin. Phys. Lett. 2007, 24 (10):
2938-2941
.
Al0.2Ga0.8N/GaN samples are grown by metalorganic chemical vapour deposition (MOCVD) method on (0001) sapphire substrates. A 10nm-thick Ni layer is deposited on AlGaN as the transparent Schottky contact. The effect of postannealing in oxygen ambient on the electrical properties of Ni/AlGaN is studied by current--voltage--temperature (I--V--T) measurement. The annealing at a relatively low temperature of 300°C for 90s results in a
decrease of the ideality factor from 2.03 to 1.30 and an increase of the
Schottky barrier height from 0.77eV to 0.954eV. The I--V--T analysis confirms the improvement originated from the formation of NiO, a layer with higher resistance, which could passivate the surface states of AlGaN and suppress the tunnelling current. Furthermore, the annealing also leads to an increase of the transmittance of the contacts from 57.5% to 78.2%, which would be favourable for AlGaN-based photodetectors.
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Electrical Characterization of Metal--Insulator--Metal Capacitors with Atomic-Layer-Deposited HfO2 Dielectrics for Radio Frequency Integrated Circuit Application
HUANG Yu-Jian, HUANG Yue, DING Shi-Jin, ZHANG Wei, LIU Ran
Chin. Phys. Lett. 2007, 24 (10):
2942-2944
.
Metal--insulator--metal (MIM) capacitors with atomic-layer-deposited HfO2 dielectric and TaN electrodes are investigated for rf integrated circuit applications. For 12nm HfO2, the fabricated capacitor exhibits a high capacitance density of 15.5fF/μm2 at 100kHz, a small leakage current density of 6.4×10-9A/cm2 at 1.8\,V and 125°C, a breakdown electric field of 2.6MV/cm as well as voltage coefficients of capacitance (VCCs) of 2110ppm/V2 and -824ppm/V at 100kHz. Further, it is deduced that the conduction mechanism in the high field range is dominated by the Poole--Frenkel emission, and the conduction mechanism in the low field range is possibly related to trap-assisted tunnelling. Finally, comparison of various HfO2 MIM capacitors is present, suggesting that the present MIM capacitor is a promising candidate for future rf integrated circuit application.
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Dielectric Performance of Porous Methyl Silsesquioxane/Triacetyl-β-Cyclodextrin Thin Films
HU Yi-Fan, FU Dan-Rong, ZHANG Ying, ZHANG Fan, TANG Ting
Chin. Phys. Lett. 2007, 24 (10):
2959-2962
.
Porous methyl silsesquioxane thin films with low dielectric constant are successfully synthesized by means of the sol-gel spin-coating method. The precursor solutions are prepared by properly mixing the polymer as a matrix with different contents of triacetyl-β-cyclodextrin (TABCD) as a porogen. The chemical structure, dielectric constants, optical constants and void fraction are investigated by the ellipsometric porosimetry, Fourier transform infrared (FTIR)
spectroscopy, and other methods. Influences of TABCD and methyl trimethoxysilane (MTMS) on the dielectric properties are discussed. For those samples with higher porogen loading, orientation and electronic polarizations are lower in low and high frequency regions, respectively, because of a considerably smaller number of polar molecules. The FTIR results suggest that high R value (molar ratio of H2O to MTMS) is more advantageous for formation of cage structures and the cage/network structural ratio increases with the
increasing R value.
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Influences of Annealing on Residual Stress and Structure of HfO2 Films
SHEN Yan-Ming, SHAO Shu-Ying, DENG Zhen-Xia, HE Hong-Bo, SHAOJian-Da, FAN Zheng-Xiu
Chin. Phys. Lett. 2007, 24 (10):
2963-2966
.
HfO2 films are deposited on BK7 glass substrates by electron beam evaporation. The influences of annealing between 100°C and 400°C on residual stresses and structures of HfO2 films are studied. It is found that little differences of spectra, residual stresses and structures are obtained after annealing at lower temperatures. After annealing at higher temperatures, the spectra shift to short wavelength, the residual stress increases with the increasing annealing temperature. At the same time, the crystallite size increases and interplanar distance decreases. The variations of optical spectra and residual stress correspond to the evolutions of structures induced by annealing.
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Preparation and Luminescence Characteristics of Ca3Y2(BO3)4:Eu3+ Phosphor
LI Pan-Lai, YANG Zhi-Ping, WANG Zhi-Jun, Guo Qing-Lin
Chin. Phys. Lett. 2007, 24 (10):
2977-2979
.
Ca3Y2(BO3)4:Eu3+ phosphor is synthesized by high temperature solid-state reaction method, and the luminescence characteristics are investigated. The emission spectrum exhibits two strong red emissions at 613 and 621nm corresponding to the electric dipole 5D0--7F2 transition of Eu3+ under 365nm excitation, the reason is that Eu3+ substituting for Y3+ occupies the non-centrosymmetric position in the crystal structure of Ca3Y2(BO3)4. The excitation spectrum for 613nm indicates that the phosphor can be effectively excited by ultraviolet (UV) (254nm, 365nm and 400nm) and blue (470nm) light. The effect of Eu3+ concentration on the emission intensity of Ca3Y2(BO3)4:Eu3+ phosphor is measured, the result shows that the emission intensities increase with increasing Eu3+ concentration, then decrease. The CIE colour
coordinates of Ca3Y2(BO3)4:Eu3+ phosphor is (0.639, 0.357) at 15mol% Eu3+.
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Local Surface-Plasmons in Nonspherical Metal Nanoparticles
CHEN Chun-Chong, LU Yong-Hua, WANG Pei, MING Hai
Chin. Phys. Lett. 2007, 24 (10):
2987-2990
.
When a small metallic nanoparticle is irradiated by incident light, the oscillating electric field can cause the conduction electrons to oscillate coherently, which excites the local surface plasmons (LSPs). As is well known, excited LSPs can gather the energy of incident light to the surface of metallic nanoparticle. Recently, some nonspherical particles, e.g. tetrahedron, are suggested to obtain stronger localized electric field. We employ the discrete dipole approximation method to calculate the optical response of the tetrahedron nanoparticle, including the extinction and distribution of the electric field around the particle. The influences of some parameters, including the nanoparticle size, incident direction and polarization, are investigated to analyse the response modes and to obtain stronger localized electric field.
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Surface Structure of Large Synthetic Diamonds by High Temperature and High Pressure
ZANG Chuan-Yi, HUANG Guo-Feng, MA Hong-An, JIA Xiao-Peng,
Chin. Phys. Lett. 2007, 24 (10):
2991-2993
.
With NiMnCo and FeCoNi alloys as solvent metals, large single-crystal diamonds of about 3mm across are grown by temperature gradient method
(TGM) under high temperature and high pressure (HPHT). Although both {100} and {111} surfaces are developed by a layer growth mechanism, some different characteristic patterns are seen clearly on the different surfaces, no matter whether NiMnCo or FeCoNi alloys are taken as the solvent metals. For {100} surface, it seems to have been melted or etched greatly, no dendritic patterns to be found, and only a large number of growth hillocks are dispersed net-likely; while for {111} surface, it often seems to be more smooth-faced, no etched or melted traces are present even when a lot of depressed trigonal growth layers. This distinct difference between {111} and {100} surfaces is considered to be related to the difference of surface-atom distribution of different surfaces, and {111} surfaces should be more
difficult to be etched and more steady than {100} surfaces.
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Preparation and Dielectric Properties of Nanostructured ZnO Whiskers
SHI Xiao-Ling, YUAN Jie, ZHOU Wei, RONG Ji-Li, CAO Mao-Sheng
Chin. Phys. Lett. 2007, 24 (10):
2994-2997
.
By a novel controlled combustion synthesis method, a large number of nanostructured ZnO whiskers with different morphologies, such as tetra-needles, long-leg tetra-needles and multi-needles, are prepared without any additive in open air at high temperature. The morphologies and crystalline structures of the as-prepared ZnO nanostructured whiskers are investigated by SEM and XRD. The possible growth mechanism on the nanostructured ZnO whiskers is proposed. The experimental results indicate that the dielectric constants and losses of the nanostructured ZnO whiskers are very low, demonstrating that the nanostructured ZnO whiskers are low-loss materials for microwave absorption in X-band. However, obvious microwave absorption in nanostructured ZnO whiskers is observed. The quasi-microantenna model may be attributed to the microwave absorption of the ZnO whiskers.
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83 articles
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