Power Consideration for Pulsed Discharges in Potassium Seeded Argon

Minimization of energy consumed in plasma generation is critical for applications, in which a large volume of plasmas is needed. We suggest that a high electron density atmospheric pressure plasmas can be generated by pulsed discharges in potassium seeded argon at an elevated temperature with a very small power input. The ionization efficiency and power budget of pulsed discharges in such plasmas are analytically studied. The results show that ionization efficiency of argon, especially at small reduced electric field E/N （the ratio of the electric field to the gas number density）, is improved effectively in the presence of small amount of potassium additives. Power input of pulsed discharge to sustain a prescribed average level of ionization in potassium seeded argon is three orders of magnitude lower than that in pure argon. Further, unlike in pure argon, it is found that very short high-voltage pulses with very high repetition rates are unnecessary in potassium seeded argon. A pulse with lOOns of pulse duration, 5kHz of repetition rate, and 2Td （1 Td = 1 × 10^-21 Vm^2） of E/N is enough to sustain an electron density of 10^19 m^-3 in 1 arm 1500K Ar＋0.1% K mixture, with a very small power input of about 0.08 × 10^4 W/m^3.     

Observation of E×B Flow Velocity Profile Change Using Doppler Reflectometry in HL-2A

A broadband, O-mode sweeping Doppler reflectometry designed for measuring plasma E×B flow velocity profiles is operated in HL-2A. The main feature of the Doppler reflectometry is its capability to be tuned to any selected frequency in total waveband from 26-40 GHz. This property enables us to probe several plasma layers within a short time interval during a discharge, permitting the characterization of the radial distribution of plasma fluctuations. The system allows us to extract important information about the velocity change layer, namely its spatial localization. In purely Ohmic discharge a change of the E×B flow velocity profiles has been observed in the region for 28 〈 r 〈 30cm if only the line average density exceeds 2.2×10^19 m^-3. The density gradient change is measured in the same region, too.     

Multilayer Au/TiO2Composite Films with Ultrafast Third-Order Nonlinear Optical Properties

We report on the ultrafast third-order optical nonlinearity in multilayer Au/TiO2 composite films fabricated on quartz substrates by pulsed laser deposition technique. The linear optical properties of the films are determined and optical absorption peaks due to surface plasmon resonance of Au particles are observed at about 590hm. The third-order optical nonlinearities of the films are investigated by z-scan method using a femtosecond laser （50 fs） at the wavelength of 800 nm. The sample showed fast nonlinear optical responses with nonlinear absorption coefficient and nonlinear refractive index being -3.66 × 10^-10 m/W and -2.95 × 10^-17 m^2/W, respectively. The results also show that the nonlinear optical effects increase with the increasing Au concentration in the composite films.     

凝聚炸药中超压爆轰的实验研究

 采用飞片碰撞技术，在TNT/RDX（40/60）炸药中获得了2.5倍于正常爆轰的最大超压值，得到了超压爆轰下爆轰产物物态方程p=Aρ^{k+A₁(p-p_J)}（p－爆压，单位GPa，ρ－密度，单位kg/m³，A=ρ_J/ρ^k_J，p_J=27.06 GPa，ρ_J=2.3×10³ kg/m³，k=2.77，A₁=2.7×10^-3 GPa^-1，下表J代表正常爆轰状态）。该方程还可以较好地描述超压爆轰产物的二次冲击状态。     

Measurement of Density Inhomogeneity for Glass Pendulum

The density inhomogeneity of a glass pendulum is determined by an optical interference method. The relative variations of the densities over a volume with sizes of 5 × 5×5 mm^3 are （0.64 ± 0.97） × 10^-5 and （0.99 ± 0.92） × 10^-5 for the K9 glass and silica glass pendulum, respectively. These variations of densities contributing to the relative uncertainties of the Newtonian gravitational constant G are 0.20 ppm and 0.21 ppm in our experiment on measurement of G.     

石油醚在流体静高压下的超声声速、衰减、密度和绝热压缩系数

 专门设计了用脉冲-回波-重合法在不同静水压下测量液体声速的装置，并对石油醚在0.1~650 MPa流体静压力范围内测量了其超声声速和衰减系数。还通过测量体积压缩量和质量得到石油醚密度ρ随流体静压力的变化。最后，给出了石油醚的绝热压缩系数β与流体静压力的关系。     

Large Storage Window in a-SiNx/nc-Si/a-SiNx Sandwiched Structure for Nanocrystalline Silicon Floating Gate Memory Application

An a-SiNx/nanocrystalline silicon [（nc-Si）/a-SiNx] sandwiched structure is fabricated in a plasma enhanced chemical vapour deposition （PECVD） system at low temperature （250℃）. The nc-Si layer is fabricated from a hydrogen-diluted silane mixture gas by using a layer-by-layer deposition technique. Atom force microscopy measurement shows that the density of nc-Si is about 2 ×10^11 cm^-2. By the pretreatment of plasma nitridation, low density of interface states and high-quality interface between the Si substrate and a-SiNs insulator layer are obtained. The density of interface state at the midgap is calculated to be 1 ×10^10 cm^-2eV^-1 from the quasistatic and high frequency C - V data. The charging and discharging property of nc-Si quantum dots is studied by capacitance-voltage （C- V） measurement at room temperature. An ultra-large hysteresis is observed in the C - V characteristics, which is attributed to storage of the electrons and holes into the nc-Si dots. The long-term charge-loss process is studied and ascribed to low density of interface states at SiNx/Si substrate.     

Controlled Evolution of Silicon Nanocone Arrays Induced by Ar+ Sputtering at Room Temperature

Controlled evolution of silicon nanocone arrays induced by Ar^＋ sputtering at room temperature, using the coating carbon as a mask, is demonstrated. The investigation of scanning electron microscopy indicates that the morphology of silicon nanostructures can be controlled by adjusting the thickness of the coating carbon film. Increasing the thickness of the coating carbon film from 50-60 nm, 250-300 nm and 750-800 nm to 1500 nm, the morphologies of silicon nanostructures are transformed from smooth surface ripple, coarse surface ripple and surface ripple with densely distributed nanocones to nanocone arrays with a high density of about 1 × 10^9- 2 × 10^9 cm^-2.     

氧化镍（绿镍矿）等温压缩及高压相变研究

 本文采用DAC（金刚石压砧高压腔）装置，对氧化镍进行了静水压、非静水压、电导率测量等系统高压实验，获取了氧化镍等温压缩、高压相变及电导率压力效应的新结果，并在实验数据的基础上，对其高压相变与电性及磁性变化关系及体弹性模量作了分析讨论。     

Plasma shielding of a XeCl-laser-irradiated YBCO target

Plasma shielding during the laser ablation process of YBCO high-T_c superconductor is demonstrated by observing the transmissivity of a probe beam. A plasma electron density of 1.2×10²² cm^-3 at the end of the laser pulse is estimated. Received: 7 February 2000 / Accepted: 20 April 2000 / Published online: 2 August 2000     

High-Density Stacked Ru Nanocrystals for Nonvolatile Memory Application

Stacked ruthenium （Ru） nanocrystals （NCs） are formed by rapid thermal annealing for the whole gate stacks and embedded in memory structure, which is compatible with conventional CMOS technology. Ru NCs with high density （3 × 10^12 cm-2）, small size （2 4nm） and good uniformity both in aerial distribution and morphology are formed. Attributed to the higher surface trap density, a memory window of 5.2 V is obtained with stacked Ru NCs in comparison to that of 3.5 V with single-layer samples. The stacked Ru NCs device also exhibits much better retention performance because of Coulomb blockade and vertical uniformity between stacked Ru NCs.     

The surface relaxation of Al as determined by electron energy loss spectroscopy on plasmons

Electron energy loss spectroscopy (EELS) on plasmons has been applied to determine the thermal expansion coefficient on the surface and to estimate the density of conduction electrons in the surface layer of aluminium. Using the data on the temperature dependence of the surface plasmon energy shift, the value of thermal expansion coefficient on the surface was calculated to be α_s=1.3 × 10^?4K^?1 that is about two times higher than the bulk value. A simple model is proposed which takes account of the influence of electron density non-uniformity in the surface layer on the dispersion of plasma oscillations. An estimation of the density of conduction electrons in the surface layer based on the observed dependence of the surface plasmon energy on the energy of primary electrons gave a value about 5% lower than the bulk value. The thickness of altered surface layer is about 10 Å.     

Radiative transition of hydrogen-like ions in quantum plasma

At fusion plasma electron temperature and number density regimes of 1?×?10³–1?×?10⁷?K and 1?×?10²⁸–1?×?10³¹/m³, respectively, the excited states and radiative transition of hydrogen-like ions in fusion plasmas are studied. The results show that quantum plasma model is more suitable to describe the fusion plasma than the Debye screening model. Relativistic correction to bound-state energies of the low-Z hydrogen-like ions is so small that it can be ignored. The transition probability decreases with plasma density, but the transition probabilities have the same order of magnitude in the same number density regime.     

Charge Transport and Magnetotransport Properties of Polyimide Irradiated by 80keV Co Ions

Charge transport properties of polyimide films implanted with 80 keV Co ions at two different fluences （series I： 1.25 × 10^17 ions/cm^2, series Ⅱ： 1.75 × 10^17 ions/cm^2） are studied in detail. For series I, the temperature dependence of surface resistivity fits Mott＇s equation very well. It is on the insulating side of the insulator-metal transition （IMT）. However, for series Ⅱ, the temperature dependence of surface resistivity is not in agreement with Mott＇s equation. It is on the metallic side of lMT. The magnetotransport properties of these two series are also studied. No significant magnetoresistive effect is observed for series I at both 5 K and 300 K. For series Ⅱ, an obvious magnetoresistive effect is observed at 5 K, while there is no magnetoresistive effect at 300 K. Rutherford backscattering spectrometry （RBS） is applied to confirm the actual fluence for these two series.     

Determination of the Surface Tension of Liquid Fe77.5Cu13Mo9.5 Ternary Monotectic Alloy

Thermophysical properties of undercooled liquid monotectic alloys are usually difficult to be determined because of the great dittlculty in achieving large undercoolings. We measure the surface tension of liquid Fe77.5 Cu13Mo9.5 monotectic alloy by an electromagnetic oscillating drop method over a wide temperature range from 1577 to 1784 K, including both superheated and undercooled states. A good linear relationship exists between the surface tension and temperature. The surface tension value is 1.588 N/m at the monotectic temperature of 1703K, and its temperature coefficient is -3.7 × 10^-4 Nm^-1 K^-1. Based on the Butler equation, the surface tension is also calculated theoretically. The experimental and calculated results indicate that the effect of the enriched element on droplet surface is much more conspicuous than the other elements to decrease the surface tension.     

High-Temperature Characteristics of Ti/Al/Ni/Au Ohmic Contacts to n-GaN

We present the high-temperature characteristics of Ti/Al/Ni/Au（15 nm/220 nm/40 nm/50 nm） multiplayer contacts to n-type GaN （Nd = 3.7 × 10^17 cm^-3, Nd = 3.0 × 10^18 cm^-3）. The contact resistivity increases with the measurement temperature. Furthermore, the increasing tendency is related to doping concentration. The higher the doped, the slower the contact resistivity with decreasing measurement temperature. Ti/Al/Ni/Au ohmic contact to heavy doping n-GaN takes on better high temperature reliability. According to the analyses of XRD and AES for the n-GaN/Ti/Al/Ni/Au, the Au atoms permeate through the Ni layer which is not thick enough into the AI layer even the Ti layer.     

Measurement of the KLL Dielectronic Recombination Resonances in He-like to C-like Kr Ions

The KLL dielectronic recombination processes of highly charged He-like to C-like Kr ions have been studied experimentally. The measurement was performed on the newly developed Shanghai electron beam ion trap （Shanghai-EBIT） facility. Characteristic x-rays from both dielectronic recombination and radiative recombination are detected as the electron beam energy is scanned through the resonances. The KLL resonant strengths obtained are 5.41×10^-19, 4.33×10^-19, 3.59×10^-19, 2.05×10^-19 and 0.98×10^-19 cm^2 eV for He-like to C-like Kr ions, respectively.     

Three-Step Growth Optimization of AlN Epilayers by MOCVD

A three-step growth process is developed for depositing high-quality aluminium-nitride （AlN） epilayers on （001） sapphire by low pressure metalorganic chemical vapour deposition （LP-MOCVD）. We adopt a low temperature （LT） A1N nucleation layer （NL）, and two high temperature （HT） A1N layers with different V/Ⅲ ratios. Our results reveal that the optimal NL temperature is 840-880℃, and there exists a proper growth switching from low to high V/Ⅲ ratio for further reducing threading dislocations （TDs）. The screw-type TD density of the optimized AIN film is just 7.86×10^6 cm^-2, about three orders lower than its edge-type one of 2×10^9 cm^-2 estimated by high-resolution x-ray diffraction （HRXRD） and cross-sectional transmission electron microscopy （TEM）.     

In-Situ High Pressure Raman Spectrum and Electrical Property of PbMoO4

In-situ high pressure Raman spectra and electrical conductivity measurements of scheelite-structure compound PbMoO4 are presented. The Raman spectrum of PbMoO4 is determined up to 26.5 GPa on a powdered sample in a diamond anvil cell （DAC） under nonhydrostatic conditions. The PbMoO4 gradully experiences the trans- formation from the crystal to amorphous between 9.2 and 12.5 GPa. The crystal to amorphous transition may be due to the mechanical deformation and the crystalographic transformation. Furthermore, the electrical conductivity of PbMoO4 is in situ measured accurately using a microcircuit fabricated on a DAC based on the van der Pauw method. The results show that the electrical conductivity of PbMoO4 increases with increases of pressure and temperature. At 26.5 GPa, the electrical conductivity value of PbMoO4 at 295K is 1.93 - 10-4 S/cm, while it raises by one order of magnitude at 430K and reached 3.33 - 10-3 S/cm. However, at 430K, compared with the electrical conductivity value of PbMoO4 at 26.5 GPa, it drops by about two order magnitude at 7.4 GPa and achieves 2.81 × 10^-5 S/cm. This indicates that the effect of pressure on the electrical conductivity of PbMoO4 is more obvious than that of temperature.     

Density Modulation Experiments on HT-7 Tokamak

Density modulation experiments are successfully conducted on HT-7 ohmic discharge to investigate particle transport coefficients: diffusion coefficients D and convection velocity V. The particle transport is studied at low (1.5×10¹⁹m^-3) and high (3×10¹⁹ m^-3) density regimes. The clear differences are observed that D is 0.42m²/s and 0.17m²/s, V is 4.7m/s (outward) and 1.6 m/s (inward) for low and high density plasmas respectively, where spatially constant D and V(r) = (r/a)V₀ were assumed for the analysis.