Calculations of the thermophysical properties of low-temperature Pb plasma at low densities

The pressure, internal energy, and electronic transport coefficients of low-temperature Pb plasma were calculated at the temperatures 10–100 kK by means of an earlier developed model (E. M. Apfelbaum, Contrib. Plasma Phys. 2019 , 59, e201800148). The plasma composition and thermodynamics were obtained using a chemical approach. The electronic transport coefficients were calculated within the relaxation time approximation with the new accurate momentum transfer cross-section electron-atom. The results of the present calculations have been compared with the new measurement data, obtained at relatively low densities, reaching 0.125 of the value in solid state, which corresponds to the area, where the model can be applied correctly. The good agreement between the calculations and measurements was obtained for both the pressure and the electrical conductivity.     

Measurement of C2 and CH temperatures in argon‐acetylene low‐pressure microwave‐induced plasma

The emission spectra of C₂(d³Π_g–a³Π_u), CH(A²Δ–X²Π), and CH(B²Σ–X²Π) bands are analysed to measure rotational T_rot, vibrational T_vib, and gas temperature T_g from Ar/C₂H₂ (5–20% C₂H₂) microwave‐induced plasma (MIP). In case when helium and hydrogen are used in the gas mixture instead of argon, no significant change in T_rot is noticed. Both studied temperatures are insensitive in terms of the C₂H₂ percentage. From CH(0–0, A²Δ–X²Π) band R₂ branch lines, two T_rot (T_rot ～ 520–580 K for J′ = 3–9 and T_rot ～ 1,700–1,800 K for J′ = 10–17) are determined. The lower T_rot equals the T_g (500–700 K) measured from C₂ bands in this study. The H₂ Fulcher‐α diagonal bands are recorded as well in the H₂/C₂H₂ mixtures and T_rot～750–900 K of the H₂ ground state measured. T_vib ～ 6,000 K in Ar/C₂H₂ MIP is calculated from the integral intensity ratio of C₂(2,1) and C₂(3,2) bands.     

热退火对等离子体增强化学气相沉积SiCOH薄膜结构与性能的影响

热退火是多孔低介电常数薄膜制备过程中的重要一环, 对薄膜结构及性能具有重要影响. 本文以四乙氧基硅烷和双戊烯为前驱体, 采用等离子体增强化学气相沉积方法制备了SiCOH薄膜, 对其进行了氮气氛围下的热退火处理, 分析了热退火对薄膜结构与性能的影响, 探究了退火过程中薄膜结构变化的可能的反应机理. 傅里叶变换红外光谱和固体核磁共振谱结果表明, 沉积薄膜是一种有机无机杂化薄膜. 退火过程中, 薄膜中的-CH₂, -CH₃等有机组分被分解除去, 形成了以稳定的Si-O-Si等无机组分为骨架的多孔结构, 并通过氮气吸附/脱附等温线测试得到了验证. 在此期间, 薄膜骨架微结构亦发生一系列调整, C=C, Si-C含量增加, Si、O、C等元素间发生进一步键合. C=C 含量的提高, 使得薄膜的消光系数和漏电流密度增大. 实验证明, 退火后薄膜具有低折射率、低介电常数特性, 是一类具有优异的介电性能和力学性能的材料, 作为芯片后端互连层间介质具有极大的应用潜力.     

High‐temperature thermoelectric properties of Cu2In4Te7

Cu₂Ga₄Te₇ has recently been reported to have a relatively high thermoelectric (TE) figure of merit (ZT). However, the TE properties of Cu₂In₄Te₇, which has the same defect zinc‐blende structure as Cu₂Ga₄Te₇, have been hardly investigated. Here, we demonstrate that Cu₂In₄Te₇ has relatively high ZT values that are similar to those of Cu₂Ga₄Te₇. High‐density polycrystalline bulk samples of Cu₂In₄Te₇ were prepared and their electrical resistivity (?), Seebeck coefficient (S), and thermal conductivity (κ) were measured. Cu₂In₄Te₇ has a maximum ZT of 0.3 at 700 K, with ?, S, and κ values of 62.1 × 10^–5 Ω m, 394 μV K^–1, and 0.61 W m^–1 K^–1, respectively. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Different effects of grain boundary scattering on chargeand heat transport in polycrystalline platinum and goldnanofilms

The in-plane electrical and thermal conductivities of several polycrystalline platinum and gold nanofilms with different thicknesses are measured in a temperature range between the boiling point of liquid nitrogen (77K) and room temperature by using the direct current heating method. The result shows that both the electrical and thermal conductivities of the nanofilms reduce greatly compared with their corresponding bulk values. However, the electrical conductivity drop is considerably greater than the thermal conductivity drop, which indicates that the influence of the internal grain boundary on heat transport is different from that of charge transport, hence leading to the violation of the Wiedemann--Franz law. We build an electron relaxation model based on Matthiessen's rule to analyse the thermal conductivity and employ the Mayadas & Shatzkes theory to analyse the electrical conductivity. Moreover, a modified Wiedemann--Franz law is provided in this paper, the obtained results from which are in good agreement with the experimental data.     

闪电首次回击过程中通道温度与电导率的演化特征

利用以高速摄像机为记录系统组装的无狭缝摄谱仪,在青海地区获得了多次云对地闪电首次回击过程400-900 nm波长范围的时间分辨光谱,分别计算了闪电电流核心通道和外围发光通道的温度;结合空气等离子体的传输理论,获得了闪电通道的电导率,探讨了回击过程中通道温度及电导率的演化特征.结果表明,闪电电流核心通道的温度比外围通道高约5000-7000 K,并且,与以往关于通道峰值温度持续时间的观点不同,回击过程中,通道保持高温的时间远远大于峰值放电电流存在的时间,在回击电流缓慢减小的数百微秒内,核心电流通道维持20000 K以上高温,这一特性是热效应导致雷电灾害的主要根源.     

闪电首次回击过程中通道温度与电导率的演化特征

利用以高速摄像机为记录系统组装的无狭缝摄谱仪,在青海地区获得了多次云对地闪电首次回击过程400-900 nm波长范围的时间分辨光谱,分别计算了闪电电流核心通道和外围发光通道的温度;结合空气等离子体的传输理论,获得了闪电通道的电导率,探讨了回击过程中通道温度及电导率的演化特征.结果表明,闪电电流核心通道的温度比外围通道高约5000-7000K,并且,与以往关于通道峰值温度持续时间的观点不同,回击过程中,通道保持高温的时间远远大于峰值放电电流存在的时间,在回击电流缓慢减小的数百微秒内,核心电流通道维持20000K以上高温,这一特性是热效应导致雷电灾害的主要根源.     

Temporal gas temperature of atmospheric pressure air plasma

In this paper, temporal gas temperature in plasma was measured by Rayleigh scattering in a passive way since synchronization was difficult due to the randomness of current pulses. The plasma was generated between a 10 mm pin-to-plane gap connected to a H.V DC voltage through a 130 MΩ resistor and a skin sample was placed on a grounded plate. Even the plasma can be touched by a human hand without any feeling of warmth, the peak temperature could be 337 K then decrease to 295 K over 60 μs at 1 mm. Moreover, the applied voltage dramatically affects peak current and the peak temperature. Therefore, the transient “high” temperature cannot be touched and the so-called “cold” plasma might not be “cold”.     

Comparison of two cold atmospheric pressure plasma jet configurations in argon

The present study compares the operation of two cold atmospheric plasma jet (CAPJ) configurations: needle-to-cylinder electrode configuration (CAPJ I) and single high-voltage cylinder electrode around the quartz tube (CAPJ II). The CAPJs were operated in argon flowing through a quartz capillary with 0.5-mm inner diameter into the ambient air, and the plasma was generated by sinusoidal kHz frequency AC power supplies. The main emphasis of the study was on the mechanism of the initiation of ionization waves for these two configurations. For both CAPJs, there appeared several ionization waves during one half-period of the applied voltage waveform, and the number of ionization waves increased at higher voltage amplitudes. However, we discovered marked differences in the initiation of the ionization waves for two different CAPJ configuration. The applied voltage controlled the initiation of consecutive ionization waves, which propagated from the grounded electrode towards the tube orifice in CAPJ I. In the case of CAPJ II, certain time had to pass for the initiation of a new ionization wave, and subsequent ionization waves within the same half-period started at the tube orifice. In addition to the differences in the initiation of the ionization waves, we observed that the CAPJ I was ignited and sustained at lower voltages, while CAPJ II produced a longer plasma jet. The observed advantages and deficiencies of investigated CAPJ configurations point out their potential in different applications.     

Mineralization of flexible mesoporous TiO2 photoanodes using two low‐temperature dielectric barrier discharges in ambient air

Two types of dielectric barrier discharges (DBDs), volume DBD (called Industrial Corona) and coplanar DBD, were used for low temperature (70 °C) atmospheric pressure plasma mineralization of mesoporous methyl‐silica/titanium dioxide nanocomposite photoanodes. The photoanodes with a thickness of approx. 300 nm were inkjet‐printed on flexible polyethylene terephthalate (PET) foils. Plasma treatments of both DBDs led to changes in the chemical stoichiometry and morphology of the mesoporous photoanodes, resulting in a significant increase of the work function from approx. 4.0 to 4.3 eV and 4.8 eV, after plasma mineralization with volume DBD and coplanar DBD, respectively. We also studied the effect of plasma mineralization on the photoelectrochemical properties of the flexible mesoporous TiO₂ photoanodes. Plasma mineralization with volume DBD and coplanar DBD showed different effects on the generated photocurrent in the photoanodes. Although the plasma mineralization with volume DBD showed only a minor effect on the photocurrent, plasma mineralization with coplanar DBD led to significantly higher photocurrents. We found that the enhancement of the photoelectrochemical properties was related to the homogeneity of the plasma‐treated surfaces—arising from different spatial properties of the plasma between volume and coplanar DBDs. Furthermore, the results showed that plasma mineralization using coplanar DBD can effectively change the energy levels of the surface. This resulted in the enhancement of the work function and the photoelectrochemical properties of the mesoporous TiO₂ photoanodes. This contribution shows that coplanar arrangement of electrodes in DBDs generates plasma of higher efficacy compared with standard volume DBD that is currently often used in industrial processes.     

Recent advances in the development of discharge‐pumped oxygen‐iodine lasers

Chemical oxygen‐iodine lasers are unique in their ability to generate high‐power beams with near diffraction limited beam quality. The operating wavelength, 1.315 µm is readily transmitted by the atmosphere and compatible with fiber optics beam delivery systems. However, applications of the laser are severely limited by logistical problems associated with the complex chemistry used to power the device. Electrical or microwave discharge excitation of oxygen‐iodine lasers offers an attractive alternative that eliminates the chemical power generation problems and has the possibility of closed‐cycle operation. A discharge oxygen‐iodine laser was first demonstrated in 2005. Since that time the power of the device has been improved by a factor of 400 and much has been learned concerning the physics and chemistry of the discharge driven system. Although our current understanding of the chemical kinetics is incomplete, parametric studies of laser performance show considerable promise for further scaling. This article reviews the basic principles of the discharge oxygen iodine laser, summarizes the most recent advances, and outlines some of the unresolved questions regarding the production and removal of excited species in the gas flow.     

激光诱导Ca等离子体温度的实验研究

 等离子体温度是激光诱导击穿光谱测量中一个重要的因素。采用Nd:YAG脉冲激光器作为光源击穿样品形成等离子体,其发射光谱由中阶梯光栅光谱仪和ICCD进行分光和光电转换。通过实验得出了300~450 nm波段的光谱图,定性分析出了Ca Ⅱ 315.9, 317.9, 393.4, 396.9 nm和Ca Ⅰ 422.7 nm等发射谱线。根据激光诱导击穿光谱定量公式,等离子体温度的变化对谱线强度有影响。先假设实验中等离子体处于局部热平衡状态,选用Ca的4条一价离子谱线,根据Boltzmann斜线法计算出了等离子体温度,并得到了等离子体温度与Ca质量分数的关系。随着Ca质量分数的增加,等离子体温度也相应增加。但当Ca质量分数小于0.50%时等离子体温度增加的幅度较小,而质量分数大于0.50%时等离子体温度的上升幅度相对较大。最后经过验证,实验中等离子体处于局部热平衡状态的假设成立。     

Differences between chloro‐carbon and hydro‐carbon precursors in low‐temperature epitaxial growth of 4H‐SiC

The advantages of using the chlorinated carbon precursor chloromethane instead of the hydrocarbon precursor propane in low‐temperature (1300 °C) epitaxial growth of 4H‐SiC were investigated. Chloromethane was found to provide a much wider process window for variation of the C/Si ratio between the lower boundary corresponding to the formation of condensed silicon face and the upper boundary corresponding to polytype inclusions and polycrystalline degradation, which is critical for achieving high growth rates without epilayer quality degradation. Use of a high Cl/Si ratio provided by HCl addition in the propane‐based epitaxial growth did not eliminate the critical differences between chloro‐carbon and hydro‐carbon precursors. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A One‐Dimensional Particle‐in‐Cell Model of Plasma Build‐Up in Vacuum Arcs

Understanding the mechanism of plasma build‐up in vacuum arcs is essential in many fields of physics. A one‐dimensional particle‐in‐cell computer simulation model is presented, which models the plasma developing from a field emitter tip under electrical breakdown conditions, taking into account the relevant physical phenomena. As a starting point, only an external electric field and an initial enhancement factor of the tip are assumed. General requirements for plasma formation have been identified and formulated in terms of the initial local field and a critical neutral density. The dependence of plasma build‐up on tip melting current, the evaporation rate of neutrals and external circuit time constant has been investigated for copper and simulations imply that arcing involves melting currents around 0.5–1 A/μm², evaporation of neutrals to electron field emission ratios in the regime 0.01 – 0.05, plasma build‐up timescales in the order of ～ 1 – 10 ns and two different regimes depending on initial conditions, one producing an arc plasma, the other one not. Also the influence of the initial field enhancement factor and the external electric field required for ignition has been explored, and results are consistent with the experimentally measured local field value of ～ 10 GV/m for copper (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tuning of near‐ and far‐field properties of all‐dielectric dimer nanoantennas via ultrafast electron‐hole plasma photoexcitation

All‐optical ultrafast signal modulation and routing by low‐loss nanodevices is a crucial step towards an ultracompact optical chip with high performance. Here, we propose a specifically designed silicon dimer nanoantenna, which is tunable via photoexcitation of dense electron‐hole plasma with ultrafast relaxation rate. On the basis of this concept, we demonstrate the effect of beam steering by up to 20 degrees through simple variation of the intensity of incident light. The effect, which is suitable for ultrafast light routing in an optical chip, is demonstrated both in the visible and near‐IR spectral regions for silicon‐ and germanium‐based nanoantennas. We also reveal the effect of electron‐hole plasma photoexcitation on the local density of states (LDOS) in the dimer gap and find that the orientation averaged LDOS can be altered by 50%, whereas modification of the projected LDOS can be even more dramatic, almost five‐fold for transverse dipole orientation. Moreover, our analytical model sheds light on the transient dynamics of the studied nonlinear nanoantennas, yielding all temporal characteristics of the suggested ultrafast nanodevice. The proposed concept paves the way to the creation of low‐loss, ultrafast, and compact devices for optical signal modulation and routing.

     

表面放电等离子体产生冲击波特性

采用压力传感器,分析XeF(CA)激光器高电压表面放电光泵浦方式不同位置、不同放电电压条件下冲击波特性。研究结果表明,表面放电等离子体膨胀产生的冲击波持续时间为ms量级,在冲击波过后伴随有相对较弱的压力波。随着充电电压增加,放电过程释放能量增多,冲击波峰值压强也变大,最大压强可达1 MPa,同时冲击波峰值延后,冲击波持续时间变长。     

硼硫协同掺杂金刚石的高压合成与电学性能研究

FeNiMnCo-C体系中,在压力6.5 GPa、温度1280—1300℃的极端物理条件下,采用温度梯度法成功合成了硼(B)、硫(S)协同掺杂金刚石大单晶.通过傅里叶红外光谱测试对高温高压所制备金刚石中的杂质进行了表征.借助霍尔效应对典型金刚石样品的电输运性能进行了测试,测试结果表明:硼硫协同掺杂有利于提高p型金刚石的电导率,而且硼硫在合成体系中的添加比例可以决定金刚石的p, n特性.此外,第一性原理计算结果表明,合成体系中不同比例的硼硫协同掺杂对金刚石的p, n特性以及电导率有着直接的影响,计算结果与实验测试结果相吻合.     

激光诱导Ca等离子体温度的实验研究

等离子体温度是激光诱导击穿光谱测量中一个重要的因素。采用Nd:YAG脉冲激光器作为光源击穿样品形成等离子体,其发射光谱由中阶梯光栅光谱仪和ICCD进行分光和光电转换。通过实验得出了300~450 nm波段的光谱图,定性分析出了Ca Ⅱ 315.9, 317.9, 393.4, 396.9 nm和Ca Ⅰ 422.7 nm等发射谱线。根据激光诱导击穿光谱定量公式,等离子体温度的变化对谱线强度有影响。先假设实验中等离子体处于局部热平衡状态,选用Ca的4条一价离子谱线,根据Boltzmann斜线法计算出了等离子体温度,并得到了等离子体温度与Ca质量分数的关系。随着Ca质量分数的增加,等离子体温度也相应增加。但当Ca质量分数小于0.50%时等离子体温度增加的幅度较小,而质量分数大于0.50%时等离子体温度的上升幅度相对较大。最后经过验证,实验中等离子体处于局部热平衡状态的假设成立。     

Ab initio potential energy curve for the neon atom pair and thermophysical properties for the dilute neon gas. II. Thermophysical properties for low-density neon

A neon–neon interatomic potential energy curve determined from quantum-mechanical ab initio calculations and described with an analytical representation (R. Hellmann, E. Bich, and E. Vogel, Molec. Phys. 106, 133 (2008)) was used in the framework of the quantum-statistical mechanics and of the corresponding kinetic theory to calculate the most important thermophysical properties of neon governed by two-body and three-body interactions. The second and third pressure virial coefficients as well as the viscosity and thermal conductivity coefficients, the last two in the so-called limit of zero density, were calculated for natural Ne from 25 to 10,000 K. Comparison of the calculated viscosity and thermal conductivity with the most accurate experimental data at ambient temperature shows that these values are accurate enough to be applied as standard values for the complete temperature range of the calculations characterized by an uncertainty of about ±0.1% except at the lowest temperatures.     

Structural characterization and low‐temperature properties of Ru/C multilayer monochromators with different periodic thicknesses

Ru/C multilayer monochromators with different periodic thicknesses were investigated using X‐ray grazing‐incidence reflectivity, diffuse scattering, Bragg imaging, morphology testing, etc. before and after cryogenic cooling. Quantitative analyses enabled the determination of the key multilayer structural parameters for samples with different periodic thicknesses, especially the influence from the ruthenium crystallization. The results also reveal that the basic structures and reflection performance keep stable after cryogenic cooling. The low‐temperature treatment smoothed the surfaces and interfaces and changed the growth characteristic to a low‐frequency surface figure. This study helps with the understanding of the structure evolution of multilayer monochromators during cryogenic cooling and presents sufficient experimental proof for using cryogenically cooled multilayer monochromators in a high‐thermal‐load undulator beamline.