甚高频电容耦合氢等离子体特性研究

采用高H₂稀释的SiH₄等离子体放电, 特别是甚高频等离子体增强化学气相沉积技术是当前高速制备优质微晶硅薄膜的主流方法. 尽管在实验上取得了很大的突破, 但其沉积机理一直是研究的热点和难点. 本文通过建立二维时变的轴对称模型,在75 MHz放电频率下, 对与微晶硅沉积非常相关的甚高频电容耦合氢等离子体放电进行了数值模拟, 研究了沉积参数对等离子体特性的影响, 并与光发射谱(OES)在线监测结果进行了比较. 结果表明: 电子浓度 n_e在等离子体体层中间区域最大, 而电子温度 T_e及H_α与H_β的数密度在体层和鞘层界面附近取极大值; 当气压从1 Torr (1 Torr=133.322 Pa)增大至5 Torr时, 等离子体电势单调降低, 在体层中间区域 n_e先快速增大然后逐渐减小, T_e先下降后趋于稳定; 随着放电功率从30 W增大到70 W, 电子浓度 n_e及H_α与H_β的数密度均线性增大, 而电子温度 T_e基本保持不变; OES在线分析结果与模拟结果符合得很好.     

双温度氩-氮等离子体热力学和输运性质计算

获得覆盖较宽温度和压力范围内的等离子体热力学和输运性质是开展等离子体传热和流动过程数值模拟的必要条件.本文通过联立Saha方程、道尔顿分压定律以及电荷准中性条件求解等离子体组分;采用理想气体动力学理论计算等离子体热力学性质;基于Chapman-Enskog方法求解等离子体输运性质.利用上述方法计算了压力为0.1, 1.0和10.0 atm (1 atm=101325 Pa),电子温度在300—30000 K范围内,非局域热力学平衡(电子温度不等于重粒子温度)条件下氩-氮等离子体的热力学和输运性质.结果表明压力和非平衡度会影响等离子体中各化学反应过程,从而对氩-氮等离子体的热力学及输运性质有较大的影响.在局域热力学平衡条件下,计算获得的氩-氮等离子体输运性质和文献报道的数据符合良好.     

7Li2(X1Σ+g)分子的振动能级、转动惯量及离心畸变常数

使用密度泛函理论B3LYP和B3P86，以及组态相互作用方法CCSD(T)和QCISD, 利用多个基组对⁷Li₂(X¹Σ⁺_g)分子的平衡核间距(R_e)、谐振频率(ω_e)和离解能(D_e)进行了计算, 发现在CCSD(T)/cc-PVQZ理论水平下得到的结果(R_{e相似文献}   

燃料电池系统最大热力学电效率及对氢气、甲烷和丙烷的应用结果

燃料电池系统的最大电效率（η_e^max）对理解和发展燃料电池技术至关重要.本文通过对燃料电池系统的热力学分析,在考虑加热燃料与空气至燃料电池工作温度的热量需求的基础上,建立了燃料电池运行过程的能量平衡关系,进而推导出了η_e^max的显式理论表达式.结果表明,与卡诺效率不同,η_e^max与燃料有关.由于除氢燃料外,计算η_e^max需要进行化学平衡计算,本文推导了烷烃燃料化学平衡态的解析解.所得理论模型被用于分析温度（T）与燃料水含量及废热回收率对η_e^max的影响.结果表明,甲烷和丙烷燃料的η_e^max随温度的升高而显著降低.此外,对中等废热回收率且运行于700 ℃≤T≤900 ℃的燃料电池系统,氢气燃料的η_e^max要高于甲烷和丙烷燃料的η_e^max.     

PH, PD和PT分子常数理论研究

采用内收缩多参考组态相互作用(MRCI)方法和包含Davidson修正(+Q) 的MRCI方法结合相关一致基aug-cc-pV5Z研究了PH (X³Σ^-, a¹Δ和A³∏)分子的势能曲线. 在同位素质量识别的基础上对势能曲线进行拟合, 得到PH, PD和PT分子各个电子态的光谱常数(T_e, R_e, ω_e, ω_ex_e, α_e和 B_e). 通过与已有实验数据的比较发现, 本文的结果与实验结果非常一致. 对于PH, PD和PT分子的Σ^-电子态, 计算得到了J = 0时的前12个振动态. 对于每一个振动态, 还分别计算了它的振动能级、惯性转动常数和离心畸变常数. 与其他理论结果和实验数据进行比较可知, 本文的结果更精确、更完整. 文中PD和PT分子的光谱常数和分子常数均属首次报导.     

Eu掺杂TbMnO3多晶材料的介电性质

采用固相反应法制备了Tb_0.8Eu_0.2MnO₃多晶材料.对样品的X射线衍射（XRD）分析表明Eu³⁺固溶于TbMnO₃中.测量了样品在低温(100 K ≤T≤ 300 K)和低频下(200 Hz≤f≤100 kHz)的复介电性质.在此温度区间内发现了两个介电弛豫峰.经分析认为低温峰（T≈170 K）起源于局域载流子漂移引起的偶极子极化效应,而高温峰（T≈290 K）则是由离子电导产生的边界和界面层的电容效应引起的.电阻率的测量显示在低温下（T≈230 K）存在明显的导电机制转变.     

YH,YD,YT分子基态的结构与势能函数

在Y的有效核势近似下, 对H分别选6-311++G(3df,2pd), AUG-cc-PVTZ, AUG-cc-PVQZ基组, 应用密度泛函理论的B3LYP方法, 优化计算了YH(D,T)分子基态的能量, 平衡结构, 和谐振频率.根据原子分子反应静力学原理, 导出了YH(D,T)分子基态的合理离解极限. 通过优化计算结果和已有的实验和理论数据对比, 得出LANL2TZ/AUG-cc-PVQZ混合基组为对体系进行计算的最优基组. 基于此, 在B3LYP/LANL2TZ/AUG-cc-PVQZ水平对YH(D,T)分子基态的势能面进行了单点能扫描. 并采用最小二乘法拟合得到了相应的Murrell-Sorbie势能函数. 计算出了这些分子的力常数(f₂, f₃, f₄)和光谱常数(B_e, α_e, ω_e, ω_eχ_e, D_e).结果与已有的实验数据符合得很好.     

金属玻璃温度依赖的拉压屈服不对称研究

通过引入静水应力对自由体积演化的影响, 研究了金属玻璃在不同温度下的拉压屈服行为. 结果表明, 在拉伸和压缩载荷下, 屈服强度均满足(T/T_g)^1/2的温度依赖关系; 同时, 在不同温度下, 材料的压力敏感系数保持为常值0.1. 随着温度的升高, 压力对自由体积的影响逐渐降低, 从而导致材料的拉压屈服不对称性逐渐趋于不显著. 在高温下, 显著的结构弛豫减缓了自由体积增长速率从而抑制材料迅速屈服. 这些结果将有助于更深入的认识金属玻璃屈服及其拉压不对称性的内在机理.     

氙等离子体输运性质计算

采用基于将Chapman-Enskog方法扩展到高阶近似的方法计算获得了温度范围在300—40000 K,不同压力条件下氙等离子体的黏性、热导率和电导率.热力学平衡条件下的计算结果与文献报道的实验和计算结果符合良好,验证了计算方法和结果的合理性与准确性.在此基础上,计算获得了电子温度(T e)不等于重粒子温度(T h)的热力学非平衡和化学平衡条件下氙等离子体的输运性质,并分析了输运性质随压力和热力学非平衡程度变化的原因.     

正交LiMnO2中的重入自旋玻璃行为

用水热技术合成了单相正交LiMnO₂(o-LiMnO₂)粉末，X射线衍射表明其空间群为Pmnm.X射线衍射精修结果指出该材料存在少量的阳离子无序，但这种无序对材料的磁性没有表现出明显的影响.静态和动态的磁性研究结果表明o-LiMnO₂中存在重入自旋玻璃行为，即在T≤T_C≈118K，反铁磁态转向铁磁态，在T≤T_f≈50K，铁磁态又转向自旋倾斜玻璃态.     

Non-LTE Argon-plasma Composition

In this paper theory of calculation of non-LTE plasma composition is presented. The calculations are conducted for argon plasma for temperature ranges from 500 K to 30, 000 K and T _e/T _h ratios from 1 to 10. The effect of different versions of the Saha equation, Debye length, lowering of ionisation energy and pressure correction on the argon-plasma composition is evaluated. It was concluded that the modified Saha equation could not be used for calculation of non-LTE plasma composition. Application of various Debye lengths can change the electron number density by 8%. The lowering of the ionisation energy decreases the electron number density by 18%. For LTE-plasma pressure correction has a negligible effect on the electron number density.     

Electron Temperature Measurement in a Premixed Flat Flame Using the Double Probe Method

The electron temperatures T_e were measured using a double probe in a premixed methane flame produced by a calibration burner according to Hartung et al. The experiment was performed at atmospheric pressure. In contrast to other authors, we have managed to find typical nonlinearities corresponding to the retarding electron current region and to calculate electron temperatures using a suitable fit on the basis of the measured characteristics. A Pt‐Rh thermocouple was used to measure temperatures T_h corresponding to “heavy” species. Our results indicate that the flame plasma can be considered to be weakly non‐isothermic — T_e = (2400–4000) K, T_h = (1400–1600) K. On the basis of measurement of the saturated ion current, the number density of the charged particles was estimated at (0.3–3.8) · 10¹⁷ m^‐3. The trends in T_e and T_h in dependence on the positions of the probes and thermocouple in the flame differ substantially; this fact has not yet been explained (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hot-wire measurements of the electron thermal conductivity in a potassium plasma

The electron thermal conductivity λ_e of a potassium plasma is found by measuring the electron heat flux in a hot-wire device placed in a magnetic field. In the range 2300–3000 K, λ_e (W/mK) = 0.906 X 10¹⁰ T^-2_e exp(-3.2 X 10⁴/T_e) at a plasma pressure of 800 Pa and a gas temperature T_a = T_e/1.3.     

Bestimmung von Transportkoeffizienten des Stickstoffs bis 13000 °K

In a cascade arc chamber a stationary nitrogen plasma was produced at a pressure of 1 atm. In this plasma the integral material function, the E-I-characteristic, could be measured very exactly. From this characteristic the transport coefficients of nitrogen — the electrical conductivity σ and the heat flux potentialS — were evaluated in dependence on the arc radiusr with the arc currentI as parameter. With these and by the help of the temperature distributions measured by Schade the transport coefficients dependent on temperatureT only were obtained. The thermal conductivity κ was found by differentiation of theS(T)-curve. The evaluation was only performed up to 13,000 °K because the radiation has been neglected in the calculation what is no longer allowed above 13,000 °K. At low currents the influence of the high field strength causes non-LTE increasing with rising field strength. This effect of non-LTE could be regarded qualitatively and quantitatively. As result the thermal and electrical conductivity ofN ₂ from 5,000 °K to 13,000 °K were obtained. The consistence with former measurements and with theoretical calculations is very satisfying.     

Zur Mikrowellendiagnostik stromstarker Entladungen mit Skineffekt. Teil II: Bestimmung der Plasmaparameter eines angeströmten Stickstoffbogens bei Atmosphärendruck

Microwave diagnostics of an inhomogeneous, dense, cylindrical plasma column may be used to determine the complex impedance and a mean noise temperature in the range of strong skin effect (theory see part I). This case is realized if the specific d.c. impedance E/I falls below a critical value, e.g. 20 Ω/cm for ω = 10¹⁰. It is shown, that for any radial conductivity profile the complex impedance is a function of E/I only. A formula is derived for calculating the noise temperature of the column as a weighted mean value due to the local plasma temperature and conductivity. In the case of strong skin effect this mean value equals the electron temperature of plasma regions near the boundary of the conducting diameter. These results in connection with spectroscopical diagnostics are use to determine some plasma parameters of an arc discharge in a streaming nitrogen atmosphere at 760 Torr. The temperature profil was obtained from the intensity of the 3371 Å molecular band and then the conductivity profile was calculated using an energy balance equation. The results show that even in the 10 A-case the arc plasma is not in thermal equilibrium, the difference T_e—T_g being about 1,500 ºK. This large difference is due to the flow of neutral gas streaming downward the discharge chamber. The length of the discharge (1·3 cm) is not sufficient for the neutral atoms to reach their equilibrium temperature.     

A Power Interruption Technique for Investigation of Temperature Difference in Stabilized Low Direct-Current Arc Burning in Pure Argon on Atmospheric Pressure

Plasma of argon stabilized arc column, in a current range 3-11 A, is investigated using emission spectrometric diagnostic techniques. Temperatures are evaluated using several methods： argon line to adjacent recombinational continuum intensity ratio, absolute emissivity of argon line, measurement of electron number density, and power interruption. Electron number density is evaluated from absolute emissivity of recombinational continuum. The difference between electron Te and heavy particle Th temperature ranged from 4500 K for 3 A to 2300 K for 11A arc current. By comparing the present with the previously obtained results, using the same arc device but with the introduction of water aerosol, it is concluded that water aerosol reduces the difference Te - Th and brings plasma closer to the partial thermodynamic equilibrium state.     

Thermal conductivity of nitrogen in the temperature range 350–2500 K

The thermal conductivity of nitrogen is determined in a conductivity column instrument in the temperature range of 338 to 2518 K with an estimated uncertainty of about ± 1·5 per cent. The experimental data points are correlated by a cubic polynomial in temperature, viz. k(T)/(mW m^-1 K^-1) = 12·18 + 0·05224(T/K) - 0·6482 × 10^-6(T/K)² - 0·2765 × 10^-9(T/K)³. These conductivity values determined from heat transfer data taken in the continuum regime are found to be in fair agreement with the values obtained from similar data referring to low pressure range.

The present results are compared with the conductivity determinations of other workers and with the predictions of various theories developed for polyatomic gases. It is pointed out that a reliable calculation of thermal conductivity over an extended temperature range is impossible at the present time due to the absence of a large variety of experimental molecular data needed for such an effort. Average values of the vibrational energy diffusion coefficient, D _vib, are computed from the present k(T) data.     

Transport properties of high temperature air in local thermodynamic equilibrium

In the paper new calculated transport coefficients of air in the temperature range 50-100 000 K are presented. The results have been obtained by means of the perturbative Chapman-Enskog method, assuming that the plasma is in local thermodynamic equilibrium (LTE). The calculations include viscosity, thermal conductivity, electric conductivity and multicomponent diffusion coefficients. For the calculation, a recent compilation of collision integrals obtained by Capitelli et al. [1] has been utilized. Analytical expression for all transport coefficients and thermodynamic parameters of the air plasma are also reported. Received 17 November 1999     

Measurement of hydrogen transport functions by means of precision arc experiments

Motivated by discrepancies of measured and calculated hydrogen transport coefficients, pure hydrogen arc plasmas have been investigated again in the wide temperature range from 5000 to 27,000 K. The plasmas are generated in cascaded arc chambers with 2, 3, and 5 mm channel diam. Temperature diagnostics are performed by side-on spectroscopy in the Balmer region, using an automatic data acquisition system and computer processing. The immediate results are in excellent agreement with precision measurements by other authors. The electricalE—I characteristics are recorded using cascade plates as probes. These characteristics and the temperature measurements together yield the transport coefficients as a function ofT. The present results for the electrical conductivity are in very good agreement with theory. As for the heat conductivity, some improvements could be achieved in the relative dependence, but the experimental values are still above the theoretical ones. In the region of low ionization this discrepancy is explained by deviations from LTE in the arc plasma. Here, a rigid PLTE analysis is presented.     

Plasma parameters in the upgraded Trimyx-M Galathea

Results are presented from measurements of the plasma parameters in the upgraded Trimyx-M Galathea. After the barrier magnetic field and the energy of the injected hydrogen plasma bunch were increased to B _bar ∼ 0.1 T and W ₀ ≈ 200 J, respectively, the following plasma parameters were achieved: the density n ∼ 5 × 10¹³ cm⁻³, the plasma confinement time τ* = 800–900 μs, the elergy of the confined plasma W ₁ ∼ 100 J, the ratio of the plasma pressure to the barrier magnetic pressure β ₀ ∼ 0.2, the electron temperature T _e ∼ 20 eV, and the ion temperature T _i ∼ 2T _e . The maximum time during which the plasma density decreased e-fold, τ _p , was found to be 300 μs at B _bar = 0.1 T, which agrees with the classical transport model.