Electron-forbidden energy gap of hydrogen in a wide pressure interval

A simple model is used for estimating the bottom energy of the electron conduction band and the electron-forbidden gap energy. It is shown that electrons in liquid hydrogen are localized not in electron bubbles, as was considered previously, but in molecular negative ions surrounded by voids about 0.5 nm in radius. The conductivity of fluid hydrogen at not very high pressures is connected to transfer of positively charged clusters and negatively charged bubbles. As the pressure and density increase, molecular dissociation occurs and electron localization on atoms becomes more favorable, also with the creation of a void around atomic negative ions. At a sufficiently high concentration of atoms, the probability of tunnel transition of an electron from one atom to another becomes close to unity, the energy level of the negative ion degenerates in the band, and the conductivity is caused by the transfer of these quasifree electrons. It is supposed that this charge transfer mechanism may play an important role in the region of fluid hydrogen metallization.     

Effects of hydrogen and impurities on void nucleation in copper: simulation point of view

The mechanisms of hydrogen influence on vacancy cluster formation in copper are studied using numerical simulations. Vacancy agglomeration in clusters larger than divacancies is found to be energetically favourable, but in pure copper the cluster creation is prevented by the lack of binding between single vacancies. Hydrogen dissolved in the lattice readily accumulates in vacancy-type defects, changing their properties. A single vacancy can accommodate up to six hydrogen atoms. Hydrogen stabilizes divacancies and promotes vacancy cluster nucleation. In larger vacancy clusters, accumulated hydrogen prevents cluster collapse into stacking fault tetrahedra. In small voids, hydrogen prefers to remain in atomic form at the void surface, but when voids become sufficiently large, hydrogen molecules in the void interior can also be formed. Some common impurities in copper (O, S, P and Ag) contribute to void formation by capturing vacancies in their vicinity. In contrast, substitutional Ni has little effect on vacancy clustering but tends to capture interstitial hydrogen.     

Physics of coal methane: decisive role of iron compounds

The role of iron in formation of the coal methane is clarified based on the studies performed on the coal samples taken from different mines in Donetsk coal basin. Using Mössbauer spectroscopy, a correlation is found between the iron content and methane capacity of coal seams. By means of electron paramagnetic resonance, it is found that iron increases the concentration of non-compensated electron spins, i.e. dangled bonds at the carbon atoms. These bonds can be occupied by hydrogen atoms as a prerequisite of methane formation. The two-valence iron is shown to be the most effective in the increase of spin concentration. By using the ion mass spectrometry, the modelling of methane formation is carried out on the mechanical mixture of the iron-free reactor graphite, iron compounds and diluted sulphuric acid as a source of hydrogen atoms. The proposed mechanism is also confirmed by methane formation in the mixture of iron compounds and the coal from the mine where the iron and methane are practically absent.     

Numerical Simulation of Dust Void Evolution in Complex Plasmas with Ionization Effect

We develop the nonlinear theory of dust voids [Phys. Rev. Lett. 90 （2003） 075001], focusing particularly on effects of the ionization, to investigate numerically the void evolution under cylindrical coordinates [Phys. Plasmas 13 （2006） 064502]. The ion velocity profile is solved by a more accurate ion motion equation with the ion convection and ionization terms. It is shown that the differences between the previous result and the one obtained with ionizations are significant for the distributions of the ion and dust velocities, the dust density, and etc., in the void formation process. Furthermore, the ionization can slow down the void formation process effectively.     

The role of photoionization in streamer discharge formation invoids

The crucial role of photoionization in the three-dimensional (3-D) formation of a streamer discharge in a void, filled with air, in an insulator, is demonstrated by performing calculations both with and without a 3-D treatment of photoionization. Secondary electron emission from the walls due to ion impact is found to be too slow to affect the initial streamer formation     

Modulation of Void Motion Behavior in a Magnetized Dusty Plasma

Based on fluid equations,we show a time-dependent self-consistent nonlinear model for void formation in magnetized dusty plasmas.The cylindrical configuration is applied to better illustrate the effects of the static magnetic field,considering the azimuthal motion of the dusts.The nonlinear evolution of the dust void and the rotation of the dust particles are then investigated numerically.The results show that,similar to the unmagnetized one-dimensional model,the radial ion drag plays a crucial role in the evolution of the void.Moreover,the dust rotation is driven by the azimuthal ion drag force exerting on the dust.As the azimuthal component of ion velocity increases linearly with the strength of the magnetic field,the azimuthal component of dust velocity increases synchronously.Moreover,the angular velocity gradients of the dust rotation show a sheared dust flow around the void.     

Effects of ion atmosphere on hydrogen-bond dynamics in aqueous electrolyte solutions

We have performed a series of molecular dynamics simulations of aqueous NaCl and KCl solutions at different concentrations to investigate the effects of ion atmosphere on the dynamics of water-water hydrogen bonds at room temperature. The average number of hydrogen bonds per water molecule decreases with increase of ion concentration. The dynamics of hydrogen-bond breaking is found to accelerate somewhat and that of hydrogen-bond structural relaxation, which occurs at a longer time scale, is found to slow down with increasing ion concentration for both NaCl and KCl solutions.     

Effect of helium ion irradiation on the structure and electrical resistivity of nanocrystalline Cr–N and V–N coatings

The structural stability and electrical resistivity of nanocrystalline Cr–N and V–N coatings prepared by ion beam-assisted deposition were studied. The results showed that under helium ion irradiation up to doses of 1.0^.10¹⁷ ion/cm² the fine-crystalline objects successively increase their resistance without apparent structural changes. The subsequent dose increase leads to gas-vacancy void formation and chromium nitride structure destruction. The presence of the initial closed porosity in vanadium nitride favors its structural stability at investigated maximum damage doses.     

Highly regular nanometer-sized hexagonal pipes in 6H-SiC(0001)

An array of troughs was prepared on a 6H-SiC(0001) surface using focused ion beam (FIB) patterning. Troughs were etched with various ion doses and close-to-circular voids of increasing depths for larger ion doses were obtained. The samples were then etched in a hot-wall reactor at a hydrogen partial pressure of 13 mbar at 1800 °C. The resulting morphological reorganizations have been studied by scanning electron and atomic force microscopy. Very regular hexagonal voids with facets oriented perpendicular to the surface were obtained after hydrogen etching. The voids were surrounded by regular secondary facets of lower inclination. Whereas the depth of the voids increases with ion dose, the void diameter and facet sizes stay constant. This effect is explained by surface diffusion during hydrogen etching. The FIB technique in combination with hydrogen etching allows the preparation of very regular surface patterns and highly ordered wells and tubes for nanometer-sized sieves and photonic crystals. PACS 47.70.Fw; 68.37.-d; 68.37.Hk; 68.37.Ps; 81.65.Cf     

Behavior of hydrogen and defects in zirconium under irradiation

The accumulation of hydrogen and defects in the E-125 zirconium alloy (Zr-2.5% Nb) is investigated. The hydrogen concentration is maximum on the surface of zirconium alloy samples after electrolytic hydrogenation. The hydrogen concentration decreases at a depth of about 0.5 μm and then gradually grows with increasing depth. The surface of the zirconium alloy is strengthened and becomes more fragile after hydrogenation. A plastic deformation of the zirconium alloy gives rise to traps with different binding energies of hydrogen. The primary type of traps, the binding energy, and the amount of hydrogen captured by traps depend on the deformation magnitude and the sequence of deformation and hydrogenation processes. High mobility of hydrogen in plastically deformed samples is observed under bombardment of the surface of the zirconium alloy by a helium ion beam with an energy of 2.34 MeV. The variation of the hydrogen concentration in the near-surface region of zirconium under ion bombardment depends on the extent of deformation: upon bombardment by helium ions, the hydrogen concentration in the near-surface region of the metal increases for deformations from 1 to 3% and decreases for deformations of 4 and 5%.     

Atomic simulations to evaluate effects of stacking fault energy on interactions between edge dislocation and spherical void in face-centred cubic metals

In this study, molecular dynamics simulations were performed to elucidate the effects of stacking fault energy (SFE) on the physical interactions between an edge dislocation and a spherical void in the crystal structure of face-centred cubic metals at various temperatures and for different void sizes. Four different types of interaction morphologies were observed, in which (1) two partial dislocations detached from the void separately, and the maximum stress corresponded to the detachment of the trailing partial; (2) two partial dislocations detached from the void separately, and the maximum stress corresponded to the detachment of the leading partial; (3) the partial dislocations detached from the void almost simultaneously without jog formation; and (4) the partial dislocations detached from the void almost simultaneously with jog formation. With an increase in void size or SFE, the interaction morphology changed in the above-mentioned order. It was observed that the magnitude of the critical resolved shear stress (CRSS) and its dependence on the SFE were determined by these interaction morphologies. The value of the CRSS in the case of interaction morphology (1) is almost equal to an analytical one based on the linear elasticity by employing the Burgers vector of a single partial dislocation. The maximum value of the CRSS is also obtained by the analytical model with the Burgers vector of the two partial dislocations.     

Surface properties of diamond-like carbon films prepared by CVD and PVD methods

Diamond-like carbon (DLC) films have been deposited using three different techniques: (a) electron cyclotron resonance---plasma source ion implantation, (b) low-pressure dielectric barrier discharge, (c) filtered---pulsed cathodic arc discharge. The surface and mechanical properties of these films are compared using atomic force microscope-based tests. The experimental results show that hydrogenated DLC films are covered with soft surface layers enriched with hydrogen and sp$^{3}$ hybridized carbon while the soft surface layers of tetrahedral amorphous carbon (ta-C) films have graphite-like structure. The formation of soft surface layers can be associated with the surface diffusion and growth induced by the low-energy deposition process. For typical CVD methods, the atomic hydrogen in the plasmas can contribute to the formation of hydrogen and sp$^{3}$ hybridized carbon enriched surface layers. The high-energy ion implantation causes the rearrangement of atoms beneath the surface layer and leads to an increase in film density. The ta-C films can be deposited using the medium energy carbon ions in the highly-ionized plasma.     

Size of dust voids as a function of the power input in dusty plasma

A dust void is a dust-free region in dusty plasma. Theory demonstrates that the void results from the balance of the electrostatic and plasma (such as the ion drag) forces acting on a dust particle. In dusty plasma experiments, physical properties of the void show clear dependence on the power input into the plasma (in particular, its size increases with the increase of the applied power). Here, the theory and numerical results are presented for such a dependence. The text was submitted by the authors in English.     

Near-surface modification of optical properties of fused silica by low-temperature hydrogenous atmospheric pressure plasma

In this Letter, we report on the near-surface modification of fused silica by applying a hydrogenous atmospheric pressure plasma jet at ambient temperature. A significant decrease in UV-transmission due to this plasma treatment was observed. By the use of secondary ion mass spectroscopy, the composition of the plasma-modified glass surface was investigated. It was found that the plasma treatment led to a reduction of a 100 nm thick SiO2 layer to SiOx of gradual depth-dependent composition. For this plasma-induced layer, depth-resolved characteristic optical parameters, such as index of refraction and dispersion, were determined. Further, a significant plasma-induced increase of the concentration of hydrogen in the bulk material was measured. The decrease in transmission is explained by the plasma-induced near-surface formation of SiOx on the one hand and the diffusion of hydrogen into the bulk material on the other hand.     

Defect structure of alumina-rich nonstoichiometric magnesium aluminate spinel

In order to clarify the relation between the dissolution mechanism of hydrogen and the defect structure in alumina-rich nonstoichiometric magnesium aluminate spinels, several compositions of single crystals were grown by the flame fusion method and their compositional dependence of the solubility of hydrogen and that of the mass density were studied by the IR absorption and Archimedes methods, respectively. The solubility of hydrogen increased in proportion to the square root of the water partial pressure and with the increase in the excess amount of alumina. The densities of the single crystals were slightly less than the value calculated based on the reported defect structure. The compositional dependence of the solubility of hydrogen and that of the density can be explained by the model in which the concentration of the oxide ion vacancy increases with the alumina content due to the decrease in the capability of the Mg site to accept the excess Al ion.     

锥形纳米孔内的电压整流及流体流动

文章以生物纳米通道及纳米孔中的离子传输及化学反应为背景,以离子流整流、电渗流整流、离子积累耗散模型为理论基础,使用有限元数值计算方法研究压力及电场交互作用下的锥形纳米孔孔内离子浓度分布及速度场分布现象.分析了不同电压下压力和电场的交互作用对锥形纳米孔中速度场、流场及浓度分布的影响.结果表明纳米孔孔内氢离子运动方向主要受电场方向影响.由于静电吸附效应,沿着孔壁流动的电渗流中的氢离子浓度会高于体溶液中的氢离子浓度.当电压较小时,流场方向主要受压力流的影响,当电压较大时,流场流动方向由电渗流带动的流体流动和压力驱动的流体流动共同决定.      

应用分子动力学模拟和拉曼光谱对钙、镁、氯离子 水化现象的研究

应用分子动力学方法,模拟了298 K下,密度为1.0 g/cm~3的水溶液中Ca²⁺,Mg²⁺,Cl~-的水化现象,得到了相应离子周围水分子的微观分布情况.发现在钙离子周围,水分子以其氧离子去靠近中心离子;而在氯离子周围,水分子则以其中的一个氢原子去靠近中心离子.通过分析三种离子的径向分布函数、配位数曲线、水化数、水化半径,发现Ca²⁺的水化数和水化半径均大于Mg²⁺,即Ca²⁺的水合能力比Mg²⁺强.与以往研究结果相比,本文计算所得的自扩散系数更接近实验所得结果.为了使模型更好的代表真实水溶液体系,本文还应用分子动力学和拉曼光谱法研究了不同浓度的CaCl₂水溶液.分子动力学研究发现随着浓度的升高,CaCl₂溶液中Ca²⁺,Cl~-的配位数分别呈降低趋势.同时,随着浓度的升高,Ca²⁺,Cl~-的自扩散系数也呈现降低的趋势.作者推断这是由于浓度的升高,加剧了离子的微观反...     

紫外-可见光谱法研究二茂铁衍生物与血红素的相互作用

采用紫外-可见光谱法(UV-Vis)研究三种二茂铁衍生物[Fc(COOH)₂(λ_max=286 nm), Fc(OBt)₂(λ_max=305 nm), Fc(Cys)(λ_max=289 nm)]与血红素(heme, λ_max=386 nm)的相互作用。实验结果表明：当固定heme浓度时,heme的吸光度随着Fc(COOH)₂和Fc(Cys)浓度的增加而增大,而heme的吸光度随着Fc(OBt)₂的浓度的增加几乎没有增大;当分别固定Fc(COOH)₂, Fc(Cys)和Fc(OBt)₂的浓度时,Fc(COOH)₂和Fc(Cys)的吸光度随着heme浓度的增加而增大,而Fc(OBt)₂的吸光度随着heme浓度的增加没有变化,说明Fc(COOH)₂和Fc(Cys)与heme存在分子间的相互作用,主要是由于Fc(COOH)₂和 Fc(Cys)与heme能形成氢键,分子链增长,吸收的能量增加,导致吸光度增大;而Fc(OBt)₂与heme没有分子间的相互作用,是由于Fc(OBt)₂没有自由的氢,不能与heme形成分子间的氢键。同时考察了三种二茂铁衍生物与heme 的吸光度随时间的变化,Fc(COOH)₂和 Fc(Cys)与heme的吸光度随着时间的增加而减少,而Fc(OBt)₂与heme的吸光度随时间的变化几乎没有变化。Fc(COOH)₂与Fc(Cys)和heme的反应时间为0.5,18和48 h,当固定Fc(COOH)₂浓度时,在λ_max=384 nm处的吸光度由2.64分别变为2.53和2.51;当固定heme的浓度时,在λ_max=384 nm处的吸光度由1.76分别变为1.72和1.68;当固定Fc(Cys)浓度时,在λ_max=397 nm处的吸光度由2.74分别变为2.63和2.55;当固定heme的浓度时,在λ_max=397 nm处的吸光度由1.82分别变为1.58和1.49。     

热丝辅助双偏压氢等离子体制造金刚石锥状表面研究

利用热丝辅助双偏压氢等离子体对化学气相沉积金刚石薄膜进行了纳米尺度上的表面改装,制造出锥状金刚石列阵.金刚石薄膜内在的柱状结构使氢离子在刻蚀薄膜时产生非均匀的刻蚀速率,对锥状表面的形成起着重要作用.另一方面,溅射出的含碳粒子会发生二次沉积,最终的特征表面形貌取决于刻蚀与含碳基团再沉积之间的相互竞争.栅极的使用影响基底区域放电的伏安特性,改变栅极电流可以对形成的金刚石特征表面结构进行有效调节.在处理过程中少量掺入甲烷,提高了金刚石表面附近的含碳基团浓度,促进二次成核,进而诱发均匀分布的锥状列阵. 关键词： 等离子体 表面 金刚石薄膜     

Theory of dust voids in plasmas

Dusty plasmas in a gas discharge often feature a stable void, i.e., a dust-free region inside the dust cloud. This occurs under conditions relevant to both plasma processing discharges and plasma crystal experiments. The void results from a balance of the electrostatic and ion drag forces on a dust particle. The ion drag force is driven by a flow of ions outward from an ionization source and toward the surrounding dust cloud, which has a negative space charge. In equilibrium the force balance for dust particles requires that the boundary with the dust cloud be sharp, provided that the particles are cold and monodispersive. Numerical solutions of the one-dimensional nonlinear fluid equations are carried out including dust charging and dust-neutral collisions, but not ion-neutral collisions. The regions of parameter space that allow stable void equilibria are identified. There is a minimum ionization rate that can sustain a void. Spatial profiles of plasma parameters in the void are reported. In the absence of ion-neutral collisions, the ion flow enters the dust cloud's edge at Mach number M=1. Phase diagrams for expanding or contracting voids reveal a stationary point corresponding to a single stable equilibrium void size, provided the ionization rate is constant. Large voids contract and small voids expand until they attain this stationary void size. On the other hand, if the ionization rate is not constant, the void size can oscillate. Results are compared to recent laboratory and microgravity experiments.