Thermal stability of ZnO thin film prepared by RF-magnetron sputtering evaluated by thermal desorption spectroscopy

Thermal stability of sputter deposited ZnO thin films was evaluated by thermal desorption spectroscopy (TDS). Desorption of Zn was mainly observed from the films deposited at low O₂/Ar gas ratio and low RF power. In contrast, O₂ desorption was mainly observed from the films deposited at high O₂/Ar gas ratio and high RF power. The amount of desorbed O₂ from the film increased with increasing the O₂/Ar gas flow ratio and the RF power. Furthermore, the desorption temperature of O₂ increased with increasing the RF power during the deposition. Thermal stability of the ZnO films was controlled not only by the O₂/Ar gas flow ratio, but also applied RF power to the target.     

Defect-related relaxation processes in irradiated rare gas solids

Electronic and atomic relaxation processes in preirradiated solid Ar doped with N 2 were studied with a focus on the role of radiative electronic transitions in relaxation cascades. Combining methods of activation spectroscopy - thermally stimulated and photon-stimulated exoelectron emission, a new channel of relaxation induced by photon emission from metastable N atoms was detected. It was shown that in insulating materials with a wide conduction band photons of visible range can release electrons from both kinds of traps - shallow (lattice defects) and deep thermally disconnected ones. Correlation in the charge recombination reaction yield and the yield of low temperature desorption - important relaxation channel in a preirradiated solid - clearly demonstrates interconnection between atomic and electronic processes of relaxation.     

Prominent higher-order contributions to electronic recombination

Intershell higher-order (HO) electronic recombination is reported for highly charged Ar, Fe, and Kr ions, where simultaneous excitation of one K-shell electron and one or two additional L-shell electrons occurs upon resonant capture of a free electron. For the mid-Z region, HO resonance strengths grow unexpectedly strong with decreasing atomic number Z (∝Z(-4)), such that, for Ar ions the 2nd-order overwhelms the 1st-order resonant recombination considerably. The experimental findings are confirmed by multiconfiguration Dirac-Fock calculations including hitherto neglected excitation pathways.     

Evaluation of the rate constants of dissociative and ternary recombination reactions of argon ions on the basis of the results of ballistic experiments

AbstractExperimental data on the change in the electron density in the wake of a ballistic object traveling at velocities V _∞=3.4–4.9 km/s in argon at pressures p _∞=30–100 Torr are processed and analyzed. A reaction scheme is proposed which takes into account the recombination of charged particles, processes of ionic conversion, and the excited states of the atom. The solution of the equations of a nonequilibrium boundary layer for flow in the wake is used to formulate the inverse problem of determining the rate constants for dissociative recombination Ar ₂ ⁺ +e→Ar+Ar and ternary recombination Ar⁺+e+Ar→Ar+Ar. The “nearest-neighbor” approximation is used to obtain theoretically an expression for the ternary recombination coefficient as a function of temperature and pressure. Numerous solutions of inverse problems and a comparison with experiments demonstrates the validity of the expression obtained for the ternary recombination coefficient. It is shown that this expression is valid for moderate pressures and complements the Pitaevskii result for low pressures and the Langevin result for high pressures. Zh. Tekh. Fiz. 67, 12–18 (May 1997)     

“Bottleneck” calculation of ion-electron recombination coefficients for lithium-like ions

Collisional-radiative recombination coefficients, including pure radiative and three-body recombination contributions, are computed for C(IV), O(VI), Ne(VIII), Si(XII), and Ar(XVI) by the “bottleneck” method of Byron et al. A convenient expression is developed for electron collisional excitation of ions and is used in the calculation.     

Isotope effects in the kinetics of simultaneous H and D thermal desorption from Pd

The kinetics of simultaneous hydrogen and deuterium thermal desorption from PdH_xD_y has been investigated. A novel experimental approach for the study of the transition state (TS) characteristics of the surface recombination reaction is proposed based on the analysis of the H and D partitioning into H₂, HD and D₂ molecules. It has been found that the hydrogen molecular isotopes distribution is determined by the energy differences of the corresponding TS of the atom-atom recombination reactions. On the other hand, the mechanisms and activation energies of the desorption process have been obtained. At 420 K, the desorption reaction changes from a surface recombination limiting mechanism during desorption from β-PdH_xD_y to a reaction limited by the rate of β to α phase transformation during the two phase coexistence. Surface recombination reaction becomes again rate limiting above 480 K, due to a change in the catalytic properties of the Pd surface. TS energies obtained from the kinetic analysis of the thermal desorption spectra are in good accordance with those obtained from the analysis of the H₂, HD and D₂ distributions. Anomalous TS energies have been observed for the H-D recombination reaction, which may be related to the heteronuclear character of this molecule.     

磁压缩系统中热脱附杂质粒子研究

磁压缩系统为俄罗斯实验物理研究院提出的核聚变方案。磁压缩系统腔室中杂质粒子可能来源于热脱附、等离子体刮削器壁等途径。利用ANSYS工具模拟5 MA脉冲电流流过腔室,并给出电极温度的二维分布图,结合研究小尺寸铜样品上杂质的解吸附来分析磁压缩系统腔室中热脱附过程产生的杂质粒子。通过测量3 keV的Ar+离子入射到Cu(110),Cu(111)样品表面的飞行时间谱,分析样品表面吸附的杂质种类,以及样品表面杂质含量随温度的变化关系。研究表明杂质粒子含量跟电极温度有关联性,且跟电极材料表面结构相关。     

Strong Enhancement of Electron–Ion Recombination Owing to Free–Bound and Bound–Bound Resonance Transitions

The effect of free–bound and bound–bound resonance nonadiabatic transitions of an electron on electron–ion recombination rates in the plasma of a Ne/Xe and Ar/Xe inert gas mixture has been studied. A kinetic model of recombination has been proposed including energy relaxation in collisions with electrons, resonant electron capture to Rydberg states through three-body collisions of Xe⁺ ions with Ne or Ar atoms and dissociative recombination of NeXe⁺ or ArXe⁺ ions, and n → n' resonance transitions. It has been shown that effective resonance processes occurring in quasimolecular systems sharply increase both the recombination coefficient and the effect of collisions with neutral particles even at quite high degrees of ionization of the plasma.     

Nonwetting and sticking of the heavy rare gases on potassium surfaces

We have investigated the adsorption, growth, and desorption of Ar, Kr, and Xe on K mono- and multilayers on Ru(001) at 6.5 K. In all cases, three-dimensional growth from very low rare gas (RG) coverages on, clearly indicates nonwetting, and the desorption energies for low RG coverages are much lower than the RG sublimation energies, and lower on K multi- than on K monolayers. Nevertheless, initial sticking coefficients of the RG on both types of K layers are well defined and not dominated by nucleation or by impurities or defects. Their values and dependence on type of substrate can be understood qualitatively, and quantitatively for Ar in terms of a recently developed quantum mechanical model, extending adsorption dynamics studies to nonwetting systems.     

Temperature Dependence of the Rate of the Reaction N + H + Ar → NH + Ar

The rate constant for the 3 body atom recombination N + H + M with M = Ar has been measured over the temperature range 550 to 750 K in an Ar ? N₂ ? H₂ microwave flowing discharge. A temperature dependence for the rate constant is reported.     

Adsorption of D(H) atoms on Ar ion bombarded (0 0 0 1) graphite surfaces

Adsorption of thermal (2000 K) D (H) atoms on HOPG surfaces prior to and after bombardment with 500 eV Ar ions was studied with thermal desorption and vibrational spectroscopies. Ion bombardment of HOPG generates vacancy (VD, displaced surface C atoms) and interstitial (ID, Ar captured between 1st and 2nd C plane) defects. These defects remove the ability of the surface to adsorb D like on virgin HOPG surfaces and to form C_gr–D bonds. After a dose of 0.1 Ar per C surface atom, D adsorption is markedly suppressed. Annealing of bombarded surfaces at 1350 K, connected with desorption of trapped Ar and removal of ID, recovers a large fraction of the adsorption capacity for D. Therefore, the long range stress in the surface plane introduced by ID must be responsible for a significant fraction of D adsorption blocking. It is suggested that ID prevent reconstruction of the C surface which is required for the formation of C_gr–D bonds. For ion doses above 0.5 Ar/C, adsorption of D on the surface is negligible. After annealing at 1350 K, D can be adsorbed in quantities comparable to the virgin HOPG surface, however forming C–D bonds which are similar to those observed in hydrogenated amorphous carbon instead of those which are normally formed on HOPG. Instationary etching via release of deuterocarbon species occurs primarily in the C₁ and C₂ channels. It is only observed at bombarded HOPG prior to annealing and probably due to the presence of isolated C₁ and C₂ species on the surface generated upon VD formation.     

Electronic excitation and dynamic promotion of a surface reaction

The mechanism of recombinative desorption of hydrogen from a Ru(0001) surface induced by femtosecond-laser excitation has been investigated and compared to thermally initiated desorption. For the laser-driven process, it is shown that hot substrate electrons mediate the reaction within a few hundred femtoseconds resulting in a huge isotope effect between H2 and D2 in the desorption yield. In mixed saturation coverages, this ratio crucially depends on the proportions of H and D. Deviations from second order desorption kinetics demonstrate that the recombination is dynamically promoted by excitation of neighboring, but nonreacting adatoms. A concentration dependent rate constant which accounts for the faster excitation of H versus D is proposed.     

Impact of electron–hole pair excitation on the kinetics of exoergic processes at metal surfaces

The effect of energy disposal to metal surfaces, via electron–hole (e–h) pair excitation, on the rate of exoergic processes such as adsorption and adatom recombination, has been investigated. The modeling is based on the mean field rate equations and allows one to couple e–h pair excitation with either recombination or stimulated-desorption processes within a unique kinetic scheme. The energy distribution function of the metal electrons and the number of electrons available for detection as “chemicurrent” have been computed and compared to experimental results on chemicurrent yield for the H–Cu system. The kinetic model can also be applied to interpret experimental data on H(D)-adatom abstraction and recombination and on adsorption stimulated desorption of CO from metal surfaces. Rate coefficients of these desorption processes are proper for non-equilibrium energy distribution functions of the adlayer, which depend on the flux of adsorbing species and correlate to the surface electron density as modified by the adsorbate.     

Image theory of lateral interactions applied to desorption rate of Xe from W and Ag

The image theory of lateral interactions between rare gas atoms given by Mahanty and March [J. Phys. C9 (1976) 2905] is shown to be consistent with the mean features of desorption rate measurements for Xe on W(111) and W(110). Some results are also presented for both Xe and Ar on Ag(111).     

Enhancement of electron–ion recombination rates at low energy range in the heavy ion storage ring CSRm

Recombination of Ar¹⁴⁺, Ar¹⁵⁺, Ca¹⁶⁺, and Ni¹⁹⁺ ions with electrons has been investigated at low energy range based on the merged-beam method at the main cooler storage ring CSRm in the Institute of Modern Physics, Lanzhou,China. For each ion, the absolute recombination rate coefficients have been measured with electron–ion collision energies from 0 meV to 1000 meV which include the radiative recombination(RR) and also dielectronic recombination(DR)processes. In order to interpret the measured results, RR cross sections were obtained from a modified version of the semiclassical Bethe and Salpeter formula for hydrogenic ions. DR cross sections were calculated by a relativistic configuration interaction method using the flexible atomic code(FAC) and AUTOSTRUCTURE code in this energy range. The calculated RR + DR rate coefficients show a good agreement with the measured value at the collision energy above 100 meV.However, large discrepancies have been found at low energy range especially below 10 meV, and the experimental results show a strong enhancement relative to the theoretical RR rate coefficients. For the electron–ion collision energy below 1 meV, it was found that the experimentally observed recombination rates are higher than the theoretically predicted and fitted rates by a factor of 1.5 to 3.9. The strong dependence of RR rate coefficient enhancement on the charge state of the ions has been found with the scaling rule of q^3.0, reproducing the low-energy recombination enhancement effects found in other previous experiments.     

New model of electron stimulated desorption from physisorbed monolayers application to Ar and N2O on Ru(001)

A new model of electron stimulated desorption from monolayers physisorbed on metal surfaces is proposed in which the excited surface state potential is due to a chemical rather than an image force acting on the adsorbed particle after the initial electronic excitation is completed. The equilibrium positions of the excited and the ground state potentials may nearly coincide and desorption is a purely quantum mechanical effect. It is demonstrated that, unlike for the commonly accepted Antoniewicz model, both, the kinetic energy distributions of desorbing neutral particles and the total desorption yields calculated in the model proposed here are consistent with the existing experimental data for Ar and N₂O physisorbed on Ru(001).     

Population processes in high-pressure inert-gas-mixture lasers

Working-level-population processes are analyzed on the basis of detailed investigations of the amplitude-time structure of the laser and spontaneous emission following a pulsed electric discharge in the mixtures He + R (R = Ar, Kr, Xe), Ar + Xe. Account is taken in the analysis of excitation by electrons (direct and stepwise) and of population as a result of relaxation processes (collisions of second kind with electrons; radiative cascades, recombination processes; collisions with the atoms of the working and buffer gases; excitation transfer from helium molecules). It is concluded that under optimum efficiency conditions inversion is produced in the lasers considered as a result of direct electron collision with the working atoms (Ar, Kr, Xe), which are in the ground state.Translated from Lazernye Sistemy, pp. 15–34, 1982.     

Hot oxygen atom ballistics on Pt(111): collisional desorption of noble gases

Hot oxygen atoms formed by ultraviolet photofragmentation of chemisorbed O₂ on Pt(111) at T_s=20 K induced collisional desorption of coadsorbed noble gases. Angular distributions of desorbing Ar, Kr, and Xe were sharply peaked at 35° from the surface normal. Mean translational energies of the noble gases were in the 0.12 eV (1400 K) range. The O atom photofragments were found to chatter between the surface and the noble gases during the desorption process. The fastest O atom photofragments produced at 250 nm had an energy of at least 0.73 eV.     

用Monte Carlo模拟方法研究ICP－AES中的电离和激发过程──Ⅱ．有关电离激发机理的讨论

本文应用ＭｏｎｔｅＣａｒｌｏ模拟所得到的结果，定量地评价ＩＣＰ中各种可能发生的反应过程对电离激发的贡献，详细讨论了不同条件下ＩＣＰ中分析元素电离激发机理。结果表明ＩＣＰ中存在的电离激发机理很大程度上取决于电子密度，温度以及氢等粒子的密度。