Thermally stimulated desorption of Na<Superscript>+</Superscript> and Cs<Superscript>+</Superscript> ions from a NaAu alloy film grown on Au

The formation of Na⁺ and Cs⁺ ions on and their thermal desorption from the surface of a NaAu alloy film grown on metallic gold are studied. It is shown that thermionic emission from insulator-coated metallic substrates is governed by a sequence of processes, such as diffusion of Na and Cs adatoms into the film, ionization of these atoms at the insulator-metal interface, diffusion of the resulting ions toward the surface, and desorption of the ions. The effect of weak electric fields on ion diffusion and desorption is investigated.     

Field electron emission and field desorption of cesium from graphene

Field electron emission and field desorption of cesium ions from a monatomic graphene film on Ir and graphene clusters in amorphous carbon are investigated using field electron microscopy and continuous-mode field desorption microscopy. The deposition of cesium on amorphous carbon with graphite clusters leads to inversion of the emission (i.e., emission from the emission centers disappears against the back-ground of uniform emission from the previously nonemitting surface). In both systems, ion current pulses are observed during field desorption in a stationary electric field. During field desorption from the graphene film, current pulses of Cs⁺ ions with a duration shorter than 0.1 s appear from the plane faces of the iridium point. During desorption from graphite clusters, ion current pulses form a pattern of “collapsing rings” on the screen. Possible mechanisms of the observed processes are considered using the model of cesium intercalation by graphite and by the graphene layer and the desorption of Cs atoms under the action of the electric field, as well as the “flip” of the dipole moment during the cesium intercalation.     

Cesium ion emission from a graphene surface on iridium in a high-intensity electric field

Features of cesium ion emission from a graphene film on iridium in a 10⁷–10⁸ V cm^?1 electric field of are studied. Field electron and desorption images demonstrate that the film consists of regions (islands) 20–100 nm in size. Intercalated cesium lies under the film. There is continuous desorption of cesium ions from the defects in the graphene film and the regions of where islands abut one another. Cesium ions arrive at the desorption sites from the intercalated state.     

Ion transport mechanism in solid electrolyte films on lithium

The rate of Li⁺ ion transport in an insulating solid electrolyte film on the Li metal surface versus electric field (<10⁷ V/cm) and temperature (in the range 238–343 K) is studied. The dependences found in this work are shown to reflect structural disorder in the electrolyte film material. Disorder causes a spread in the site-to-site hopping length and time.     

Investigation of interaction between lithium and tantalum under a silicon film coating by electron-stimulated desorption technique

The electron-stimulated desorption of Li⁺ ions from lithium layers adsorbed on the tantalum surface coated with a silicon film has been investigated. The measurements are performed using a static magnetic mass spectrometer equipped with an electric field-retarding energy analyzer. The threshold of the electron-stimulated desorption of lithium ions is close to the ionization energy of the Li 1s level. The secondary thresholds are observed at energies of about 130 and 150 eV. The threshold at an energy of 130 eV is approximately 30 eV higher than the ionization energy of the Si 2p level and can be associated with the double ionization. The threshold at 150 eV can be caused by the ionization of the Si 2s level. It is demonstrated that the yield of Li⁺ ions does not correlate with the silicon amount in near-the-surface region of the tantalum ribbon and drastically increases at high annealing temperatures. The dependence of the current of Li⁺ desorption on the lithium concentration upon annealing of the tantalum ribbon at T>1800 K exhibits two maxima. The ions desorbed by electrons with energies higher than 130 and 150 eV make the largest contribution to the current of lithium ions after the annealing. The yield of lithium ions upon ionization of the Li 1s level at an energy of 55 eV is considerably lesser, but it is observed at higher concentrations of deposited lithium. The results obtained can be interpreted in the framework of the Auger-stimulated desorption model with allowance made for relaxation of the local surface field.     

Photon and electron stimulated desorption of adsorbates from W {100}

We have performed photon and electron stimulated desorption (PSD and ESD) studies of F⁺, Cl⁺ and O⁺ ions from a W {100} surface and have measured the kinetic energies for a small range of emission angles of these ions as well as the effect of different electron and photon excitation energies. We find that the PSD and ESD processes show essentially the same threshold energies and produce the same ion energy and angle distribution, and so evidently involve the same mechanism. For the case of O⁺ we also find clear evidence that substrate core-level excitation initiates the desorption process as proposed by Knotek and Feibelman for adsorbates bonded to surface atoms with a maximal valency configuration. The substrate levels are not seen to play a role in the F⁺ and Cl⁺ desorption, indicating a very different type of bonding for these species on the W surface.     

Effect of an electric field on the emission of sodium ions from the surface of NaAu alloy

We investigate how an electric field affects the desorption of sodium ions from the surface of a NaAu semiconductor film formed on a gold substrate. It is shown that an external electric field affects the equilibrium concentrations for sodium cations in the near-surface area and their dilution in a Na _x Au _y film.     

Formation of N3+ in pulsed-laser stimulated field desorption of nitrogen from metal surfaces

In pulsed-laser stimulated field desorption of nitrogen from metal surfaces, a plenty of N₃⁺ can be detected. Here we present the result of a study of the field dependence and emitter material specificity of N₃⁺ formation in pulsed-laser stimulated field desorption. These ions are formed by field ionization of N₃ molecules which are thermally desorbed from their field adsorption states by laser pulse heating of the surface.     

Electron stimulated desorption of condensed,branched alkanes

Electron stimulated desorption of H⁺, CH₃⁺, H₂⁺ and D⁺ has been measured as a function of excitation energy for condensed phase neopentane, tetramethylsilane, 2-methylpropane-1-d₁, and 2-methylpropane-2-d₁. The data show that the processes which result in both H⁺ and CH₃⁺ production are initiated by the same excitation. The excitations which produce H⁺, CH₃⁺ and H₂⁺ appear to be largely localized on the methyl groups. The results indicate that multi-electron (hole) final states are responsible for H⁺ and CH₃⁺ desorption.     

Electron induced ion desorption of oxygen adsorbed on rhenium

The behavior of low energy electron-stimulated O⁺ ions desorbing from oxygen adsorbed on polycrystalline rhenium samples has been found to be significantly different from those observed desorbing from other oxygen ad layers. Oxygen initially adsorbed at 300°K has an ionic desorption cross section below the level of detectability, (< 10⁻⁹ ions/electron) in these experiments, a result in accordance with that previously observed on other metals. On continued oxygen exposure, the O⁺ signal first increases to a maximum value and then decays to a lower level; the rate of both these processes is directly proportional to the oxygen pressure in the gas phase. If the temperature of the ad layer is raised above 300°K, the adsorbed species with high ionic desorption cross section are removed at about 500°K. At higher temperatures, O⁺ ions which can be related to the oxygen initially adsorbed are detected. The possible reasons for the observed O⁺ desorption characteristics for oxygen on rhenium are discussed.     

Study on selective adsorption of deuterium on boron nitride using photon-stimulated ion-desorption

Adsorption behavior of atomic deuterium on a hexagonal boron nitride (h-BN) thin film is studied by photon-stimulated ion desorption (PSID) of D⁺ and near edge X-ray absorption fine structure (NEXAFS) at the B and N K-edges. After the adsorption of atomic deuterium, D⁺ desorption yield η(hν) shows clear enhancement at the B K-edge and almost no enhancement at the N K-edge. NEXAFS spectra show a large change in the B K-edge and a small change in the N K-edge after the adsorption. We propose selective adsorption of atomic deuterium on the h-BN thin film based on the experimental results, and mention the effectiveness of applying the PSID method with X-ray to study hydrogen storage materials.     

Influence of the surface electric field in ion-beam-surface interaction at grazing incidence

We have measured the polarization of light emitted after ion surface scattering at small angle of incidence. The measurements are carried out with H⁺-, H ₂ ⁺ - and He⁺-ions under UHV-conditions with mono- and polycrystalline targets. We explain the typical variation of the polarization as “post collision Stark interaction” (PCSI) in the surface electric field, which can force transitions between nearly degenerate terms. The electric field is composed of two different contributions, a strong but short range surface field which is “seen” by atomsand ions and a long range but weak field due to the image charge which is “seen” to first orderonly by ions. The influence of the electric field on H-Balmer radiation is negligible at typical survival distances r_s≧0.35nm. But in contrast to H-atoms He⁺-ions feel the additional influence of the image field leading to a strong alteration of the polarization of the emitted light. The polarization of the Balmer-radiation stemming from Coulomb exploding H ₂ ⁺ -beams is observed to be modified by the electric field of the “spectator proton”.     

Study of the sputtering of adsorbates by low energy ions (O on Ni)

Sputtering or ion impact desorption of adsorbed layers has been studied by low energy ion scattering and model calculations. For adsorption of a monolayer or less (e.g. oxygen on nickel) the desorption by ions can be readily observed by He⁺ ion scattering from the development of the adsorbate and substrate signal as a function of time. Desorption cross sections for Ne⁺ and He⁺ ions in the energy range from 500 eV to 1600 eV are given. These results are compared with the model calculations and the influence of various parameters can be studied by this comparison. The contribution of different processes to the sputtering mechanism is discussed.     

Diffusionstheoretische Beschreibung der Dissoziation und des Ionenhaushaltes im schwachionisierten Säulenplasma der Wasserstoffentladung. III. Kenngrößen der positiven Säule bei verschiedenen Drücken (0,3 … 10 Torr) und Strömen (10−4 … 1 A)

Based on the solution of the electron Boltzmann equation the particle balances of different ions (H⁺, H₂⁺, H₃⁺, H₅⁺) and of the neutral components are discussed in the H/H₂, column plasma taking into account a large number of elementary processes (volume and wall processes). This results in a detailed understanding of the electric characteristic in relation to the chemical composition of the gas. In the region of low pressures and larger currents considerable high degrees of dissociation occur. Experimental investigations confirm these theoretical results. Remaining differences between the measured and calculated electric characteristic are mentioned.     

由纳米管和纳米颗粒构成的TiO2膜的制备与机理研究

采用聚苯乙烯小球修饰Ti片表面,并进行阳极氧化,制备出一种由纳米颗粒和纳米管构成的TiO₂膜．通过数值模拟,分析了氧化表面附近的局部电场分布对TiO₂膜形貌的影响．结果表明,覆盖物增强了局部电场,从而加快了O^2-与Ti的反应速率,有利于TiO₂的生长;与此同时,[TiF₆]^6-的扩散受到阻碍,使得TiO₂的溶解速率减慢．可见,覆盖物打破了TiO₂纳米管形成的平衡条件,导致纳米颗粒的生成．此外,通过X射线衍射和Raman光谱的测试分析发现,所制备的TiO₂为锐钛矿结构.     

Electric field-induced quasi-elastic inter-landau level scattering in the space-charge-limited magnetoconductivity of n+n−n+ InP structures

Magnetophonon resonance and quasi-elastic inter-Landau level scattering (QUILLS) are investigated in the transverse magnetoconductivity, σ_xx, of short (1 μm) n⁺n⁻n⁺ InP structures under conditions of space-charge-limited conduction. The damping of the magnetophonon resonance amplitudes at large E is also investigated. The electric field dependence of the QUILLS process in InP is in excellent agreement with a model that we have previously proposed to describe the process in n⁺nn⁺ GaAs layers. The observed form of the space-charge-limited current-voltage characteristics (I ∝ V²) is discussed in terms of the behaviour of electrons in short, lightly doped semiconductor layers under the influence of large, mutually perpendicular electric and magnetic fields.     

Molecular adsorbate detection using hyperthermal Cs+ surface scattering: chemisorbed water on Si(111)

Cs⁺ ion beams are scattered from an Si(111) surface chemisorbed with water. Scattering of Cs⁺ ions from the surface at the incidence energies of 10–;15 eV gives rise to reaction products CsOH⁺, CsOH⁺₂ and CsSiO⁺. We interpret that these cluster ions are formed by desorption of X (X = OH, H₂O and SiO), followed by Cs⁺X association and energy quenching near the surface. The Cs⁺ scattering method has potential advantages for adsorbate detection over desorption techniques, in particular for identification of molecular and thermally unstable species.     

CH4或CH4+Ar介质阻挡放电中的离子能量和类金刚石膜制备

实验上，利用纯CH₄及CH₄+Ar在几百帕量级气压下的介质阻挡放电 制备类金刚石膜，研究了气压p与放电间隙d乘积(pd值)以及Ar的体积百分比R_Ar 对膜硬度的影响.理论上，从离子与气体分子的双体碰撞出发，利用较高折合电场强度E/n( 电场强度与粒子数密度之比)下离子及中性粒子速度分布的双温模型、离子在其他气体中运 动时遵守的朗之万方程及离子在混合气体中运动时遵守的布兰克法则，对CH⁺4和Ar⁺离子能量进行了分析.结果表明：1)CH₄介质阻挡 放电中，pd值由1.862×10³Pa mm降低至2.66×10²Pa mm时，CH+₄能量由5.4eV增加到163eV，类金刚石膜硬度由2.1GPa提高到17.6GPa ; 2) 保持总气压p=100Pa,放电间距d=5mm不变，在CH₄中加入Ar气，当R_Ar 由20％增加至83%时，CH⁺₄的能量由69eV增加到92eV,而Ar＋能量由93eV降低至72eV.虽然CH⁺₄能量增加有助于提高 沉积膜硬度，但当R_Ar大于67%，高强度Ar⁺轰击会导致膜表面石墨 化，膜硬度降低.为了验证离子能量理论模型的正确性，实验测量了H₂介质阻挡 放电中离子能量，测量结果与理论计算之间最大相对误差为16%. 关键词： 离子能量 介质阻挡放电 类金刚石膜     

Silver sulphide growth on Ag(111): A medium energy ion scattering study

The interaction of S₂ with Ag(111) under ultra-high vacuum conditions has been investigated by medium energy ion scattering (MEIS). 100 keV He⁺ MEIS measurements provide a direct confirmation of a previous report, based on thermal desorption, that the growth of multilayer films of Ag₂S occurs through a continuous corrosion process. These films show a commensurate (√7 × √7)R19° unit mesh in low energy electron diffraction, consistent with the epitaxial growth of (111) layers of the high-temperature F-cubic phase of Ag₂S. The substantial range of co-existing film thicknesses found indicates that the growth must be in the form of variable-thickness islands. The use of 100 keV H⁺ incident ions leads to a very rapid decrease in the sulphide film thickness with increasing exposure that we attribute to an unusual chemical leaching, with implanted H atoms interacting with S atoms and desorption of H₂S from the surface.     

Crystal electric field next to a hydrogen-like interstitial— µ+ in PrNi5

Muon spin rotation measurements of the temperature dependence and the anisotropy of the μ⁺ Knight shift in single crystals of the crystal electric field singlet ground state system PrNi₅ reveal pronounced deviations from a linear scaling of the Knight shift with the bulk magnetic susceptibility atT≤50 K. They are explained by a μ⁺ induced modification of the atomic susceptibility of neighboring Pr³⁺ ions. From the Knight shift anisotropy atT> 50 K it is determined that the implanted μ⁺ occupy a single intersitial site, namely the 6i site (0.5, 0, 0.21±0.02). Using this site information, good model fits to the measured data are obtained assuming a μ⁺ induced perturbation of the crystal electric field at the Pr³⁺ ions next to the μ⁺. Apparently, the presence of the μ⁺ leads to a lowering of the local symmetry, causing a lifting of the degeneracy and a pronounced rearrangement of the low lying crystal electric field levels for these ions.