Characterization of microwave plasma generated in inhomogeneous magnetic field

The paper is devoted to the investigation of the electron cyclotron resonance (ECR) discharge in the decreasing magnetic field in the pressure range from 0.02 Pa to 90 Pa and the absorbed microwave power from 50 W to 400 W. For a discharge characterization we used the floating potentialU _fl and the saturated ion current densityi _sat ⁺ . The influence of the substrate holder presence on the plasma microparameters was studied. It was shown that for the substrate holder located near ECR at pressures below 0.3 Pa mainly the magnitude ofU _fl strongly depends on the pressurep, the absorbed microwave powerP _a, and the position of the substrate holder with respect to ECR. The values ofU _fl in the plasma in which the substrate holder is inserted strongly differ from those in the plasma without the substrate holder.U _fl of low pressuresp<0.05 Pa achieves high positive values of about +50 V and this results in sputtering of chamber walls.     

电子回旋共振等离子体特性及其对生长氮化镓晶膜的影响

为了解并优化在电子回旋共振等离子体辅助化学汽相沉积GaN晶膜的工艺研究中的等离子体特性,利用朗缪尔探针及法拉第筒系统地测量了离子密度(N_i)、等离子体势(V_p)、电子温度(T_e)及离子流强(J_i)等多个等离子体参量随微波功率(P_w)及沉膜室气压(p)变化的关系.给出了在P_w＝850W,p＝0.22Pa时,上述等离子体参量的轴向及径向分布.GaN晶膜的生长速率、电学及晶体学性能 关键词：     

Some properties of a-C:N films prepared by KrF laser ablation

Thin a-C:N films were prepared by pulsed laser ablation using a KrF excimer laser and a graphite target. The influence of the substrate temperatureT _s (27°C and 330°C), and the nitrogen gas ambient pressurep n (1.5 Pa, 13.3 Pa and 40 Pa) on the film properties was studied. The films were characterized by scanning electron microscopy, Rutherford backscattering, spectroscopic ellipsometry and by Raman scattering. The nitrogen content in the films was in the range from 20 to 31 at.%, and those of oxygen from 5.6 to 10.7 at.%. For lowerp n andT _s the film delamination was observed.The authors wish to thank J. Sobota from the Institute of Scientific Instruments of ASCR, Brno, for valuable discussions.This work was supported by Grant Agency of the Academy of Sciences of the Czech Republic under Grant No. 202/93/0464.     

Reactivity at the oxygen/titania interface and the related charge transfer

The present paper reports the reactivity between TiO₂ and oxygen and the related charge transfer at 298 and 1,073 K. The studies were performed using work function measurements. It was found that oxidation of TiO₂ at 1,073 K and p(O₂) = 75 kPa, initially standardized at 1,173 K and p(O₂) = 10 Pa, results in work function changes that are consistent with the theoretical model of the charge transfer during oxygen chemisorption and oxygen incorporation at the absence of structural transitions. However, oxidation of TiO₂ at 298 K, p(O₂) = 75 kPa, which has been initially standardized at 1,173 K in extremely reducing conditions at p(O₂) = ∼10⁻¹⁰ Pa, results in work function changes that are consistent with low-dimensional structural changes of the surface layer. It is shown that oxidation of strongly reduced TiO₂ at 298 K results in a decrease of work function, which cannot be explained without assuming the structural changes of the outermost surface layer.     

Microwave plasma enhanced low pressure d.c. sputtering of copper films

This paper reports on d.c. sputtering of copper films using a cylindrical magnetron (CyM) with the discharge enhanced and/or ignited by a microwave plasma produced in an external magnetic fieldB _e . The sputtering system was optimized with the aim to achieve high deposition rate of films at low argon pressures. It was achieved by enhancing the ionization degree of the discharge plasma by microwaves absorbed in the plasma and by the control of the distribution ofB _e (z) along the device axis, i.e. by controlling the transport of the plasma to within a close vicinity of the sputtered target of the CyM. The optimized sputtering system can sputter films at low argon pressures from about 0.1 Pa down to 0.005 Pa and at quite large discharge currentsI _d up to 1 A, i.e. at quite large deposition ratesa _D of about several hunderds of nanometers per minute. The sputtering system operates at pressures lower than conventional magnetrons, i.e., under conditions when fast neutrals play a significant role. It opens the possibility to produce films of new properties. As an example, the microwave enhanced sputtering discharge was used to deposit Cu films. Resistivity and preferred crystal orientation of Cu films prepared under different argon pressures and at microwave powers ranging from about 100 W to 800 W is reported.This work was supported in part by the Grant Agency of Czech Republic under Grant No. 202/93/0508.     

氧分压对Mg掺杂ZnO薄膜结晶质量和光学特性的影响

利用脉冲激光沉积技术,通过改变沉积过程中的氧气压力,在蓝宝石(0001)基片上制备了一系列ZnMgO合金.通过X射线衍射、反射和透射光谱以及室温和变温荧光光谱,对薄膜的结构和光学性能进行了系统地表征,分析了工作气压对ZnMgO合金薄膜的结晶质量及光学特性的影响.研究结果表明:随着沉积环境中氧气压力的增大,ZnMgO薄膜的结晶质量下降,富氧环境下,与蓝宝石晶格平行的ZnO晶粒的出现是导致薄膜结晶质量下降的主要原因;相对于本征ZnO,不同氧气环境下沉积的ZnMgO薄膜的紫外荧光峰均出现了不同程度的蓝移.随着工 关键词： ZnO Mg掺杂 脉冲激光沉积 薄膜生长 光学特性     

Time-resolved emission spectra of plasma produced by excimer laser ablation of Pb-Bi-Sr-Ca-Cu-O

Time-resolved emission spectroscopy was employed to detect excited species formed in the laser ablation of superconductor Pb-Bi-Sr-Ca-Cu-O by an excimer laser at various background gas pressures. A simple model has been created to explain the chemical kinetics of reactions in a plasma plume by its expansion. We explained the time dependence of plasma emission on the wavelengths of lead, strontium and their oxides. For the purpose of this paper, we determined reaction rates of lead deexcitation and the rate of recombination of Pb⁺ ion. This work was supported by the Grant Agency of Charles University (Grant No. 28/97) and Grant Agency of Academy of Sciences of the Czech Republic (Grant No. A4040708).     

Present status of thin oxide films creation in a microwave plasma

This paper summarizes present knowledge of the creation of thin films in isotropic and magnetoactive plasma. It analyses conditions under which films in the microwave plasma can be created and shows how the growth rate and properties of films depend on microparameters of plasma. On the basis of plasma floating potential measurements it is shown why the creation of thin films in microwave discharges takes place at high electron plasma densities (N 10¹² cm^–3) only. Besides this it describes properties of created films, underlies negative role of fast electrons in forming of good quality films and gives recommendation how to avoid their generation. Considerable attention is devoted also to a comparison of films creation in pulse and continuous plasma. At the end possibility of films creation at low temperatures by a deposition technique utilizing a microwave excitation of molecular gases is given.The authors gratefully acknowledge many stimulating and fruitful discussions with Dr. F. áek of Institute of Plasma Physics of Czechoslovak Academy of Sciences. We also thank Dr. V. Malina of Institute of Radioelectronics of Czechoslovak Academy of Sciences for measurements of C—V curves of SiO₂ films.     

Mass spectroscopic investigation of ionized compenents of vacuum-arc discharge plasma

Special features of the application of a mass spectroscopic method to analysis of ionized components of the plasma of a vacuum-arc discharge are discussed. The intensities of N⁺, O ₂ ⁺ , Ar⁺, TiN⁺, and TiO⁺ ions as functions of the pressure of the corresponding neutral gas and the magnitude of the magnetic-field strength on the cathode surface are measured. The average energy of the N⁺ and TiN⁺ ions as measured with an electrostatic probe is equal to ≈25 eV. The number of the N⁺, O⁺, TiN⁺, and TiO⁺ ions that emerge on the cathode and propagate in the direction of the substrate is tenths of a percent of the number of metal ions, which confirms the mechanism of reactive vacuum-arc coating forming directly on the substrate. Physico-Technical Institute Academy of Sciences of Belarus, 4, Zhodinskaya St., Minsk, 220730. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 674–678, September–October, 1997.     

Optical characterization of atmospheric‐pressure plasma needle

The atmospheric‐pressure plasma needle is a promising source that can be used efficiently for different industrial applications. A radio frequency (RF) (13.56 MHz) generator was used to generate a He–O₂/Ar mixture plasma. The ground‐state oxygen atomic density [O] was calculated as a function of discharge parameters by “actinometry”. The Ar‐I (2p₁ → 1s₂) line at 750 nm and the O‐I (³P → ³S) line at 844 nm were used to estimate the [O] atomic density. The rotational temperature T _R of He–O₂/Ar mixture was measured from the rotational levels of the “first negative system” (FNS) by using the “Boltzmann plot”. The effect of discharge parameters on the atomic oxygen density [O] and the gas temperature was monitored. These results show that [O] density increases with RF power and O₂ concentration, but decreases with the gas flow rate. Whereas the gas temperature increases with increase in the input RF power, it decreases with increase in the gas flow rate and O₂ concentration in the mixture. Since the [O] atomic density contributes to plasma‐based biomedical applications, the proposed optimum conditions for plasma‐based decontamination of heat‐sensitive materials in the present study are 0.6% oxygen, 500 sccm flow rate, and 26 W RF power.     

Radiative Transitions and Temperature Time Dependences in Pulse Excited Microwave Discharges – (N2, Ar + N2)

Quantitative spectral and microwave measurements of vibrational temperatures and electron densities were performed for 2400 MHz non-isothermic pulse excited discharges in flowing nitrogen and argon at pressures (60–2700) Pa. A detailed analysis of the N₂ vibrational states population for the N₂ C³Π_u, X¹Σ_g⁺ electronic states has been carried out. The basic difficulties encountered when comparing the spectroscopically determined values of vibrational temperatures with corresponding quantities of the ground electronics state are mentioned and the time resolved dependences of the translational gas temperature in N₂ during the microwave pulse is evaluated. The steady state in the nitrogen pulse excited microwave plasma is reached within 3 · 10^?4 s, but generally, this time depends on the gas pressure in the discharge tube. In the Ar + N₂ mixtures the excitation conditions are complicated by the metastable argon atoms (3P_2,0) creating the nonequilibrium populations of electronic, vibrational and rotational N₂ states.     

Spherical and deformed configurations of18O in the model of K-harmonics with a potential well

From the point of view of the model ofK-harmonics an estimation of the relative positions of the spherical (K=K _min) and deformed (K=K _min+2) configurations of¹⁸O is carried out, which is useful for more exact calculations. In these configurations the structure (1s)⁴ (1p)¹² of the 16 nucleons (the hypothetical nucleus¹⁶O) is separated out as determining and their binding energy is calculated. Nuclear forces are taken in the schematic form of a rectangular potential well. At first it is derived from the realistic nucleon-nucleon rectangular well and results in overbound states. It is, therefore, derived directly from the experimental data (the binding energy and the root mean square radius of¹⁶O and¹⁸O respectively). Although the energies of the hypothetical nucleus¹⁶O are close together in both configurations of¹⁸O, they differ. In Appendix a very effective expression for the logarithmic derivative of the MacDonald function is given.The work has been begun in the Nuclear Research Institute of the Czechoslovak Academy of Sciences, e.     

Electron-stimulated desorption of negative O? ions from the oxidized O/Ru surface

This paper reports on a study of the electron-stimulated desorption of negative oxygen ions from the O/Ru surface, which represents an additional factor responsible for the destruction of the protective oxide layer of the mirrors used in ultraviolet lithography. The cross section of degradation of the O/Ru layer due to the electron-stimulated desorption of the O⁺ and O⁻ ions and the O atoms has been found to be 1.6 × 10⁻¹⁹ cm². A comparison of the dependences of the electron-stimulated desorption yield of O⁺ and O⁻ ions on the incident electron energy E with the ionization cross section of the adsorbate core level σ _O2s (E) has revealed that the ionization of the O 2s level is the main channel of the electron-stimulated desorption of O⁻ ions.     

Kinetic mechanisms of initiating hydrogen-oxygen mixture combustion through the excitation of electronic degrees of freedom of molecular oxygen by laser radiation

Kinetic mechanisms resulting in the enhancement of combustion of H₂+O₂ mixtures when O₂ molecules are excited to the a ¹Δ_g and b ¹Σ _g ⁺ states with laser radiation (λ=1.268 and 0.762 μm) are analyzed. It is shown that the excitation of O₂ molecules by the laser radiation leads to the appearance of new O, H, and OH formation channels; promotes the ignition of the starting mixture; and reduces the self-ignition temperature. With initial pressures in the range P ₀=10³–10⁴ Pa, the self-ignition temperature can be reduced to 300 K even at relatively low energies of the laser radiation with λ=0.762 μm.     

Oxygen adsorption on the tungsten (110) plane. Electron impact and thermal desorption at high temperatures

When a layer of oxygen on the (110) plane of tungsten at coverages O/W≦0.5 is heated from 100 K, O⁺ evolution under electron impact becomes almost negligible at 600 K. On further heating, however, a slow, temperature-dependent evolution of O⁺ current is observed atT≳1500 K. For O/W>0.3 there is also desorption under massive bombardment. Once an equilibrium value of O⁺ current has been established, there is rapid adjustment to the appropriate equilibrium value when the temperature changes in the range 1500–1700 K. On cooling toT<1000 K, O⁺ decreases rapidly; on reheating toT>1500 K, O⁺ increases slowly again. Above 1700 K there is thermal desorption which is also reflected in the O⁺ signal. These facts indicate that there is a slow activated evolution of an electron sensitive state above 1500 K, from a reconstructed state formed by heating the low temperature layer toT≧1000 K. The latter state seems to be reformed on cooling below 1500 K.     

Vibrational non-equilibrium in the hydrogen–oxygen reaction. Comparison with experiment

A theoretical model is proposed for the chemical and vibrational kinetics of hydrogen oxidation based on consistent accounting of the vibrational non-equilibrium of the HO₂ radical that forms as a result of the bimolecular recombination H+O₂ → HO₂. In the proposed model, the chain branching H+O₂ = O+OH and inhibiting H+O₂+M = HO₂+M formal reactions are treated (in the terms of elementary processes) as a single multi-channel process of forming, intramolecular energy redistribution between modes, relaxation, and unimolecular decay of the comparatively long-lived vibrationally excited HO₂ radical, which is able to react and exchange energy with the other components of the mixture. The model takes into account the vibrational non-equilibrium of the starting (primary) H₂ and O₂ molecules, as well as the most important molecular intermediates HO₂, OH, O₂(¹Δ), and the main reaction product H₂O. It is shown that the hydrogen–oxygen reaction proceeds in the absence of vibrational equilibrium, and the vibrationally excited HO₂(v) radical acts as a key intermediate in a fundamentally important chain branching process and in the generation of electronically excited species O₂(¹Δ), O(¹D), and OH(²Σ⁺). The calculated results are compared with the shock tube experimental data for strongly diluted H₂–O₂ mixtures at 1000 < T < 2500 K, 0.5 < p < 4 atm. It is demonstrated that this approach is promising from the standpoint of reconciling the predictions of the theoretical model with experimental data obtained by different authors for various compositions and conditions using different methods. For T < 1500 K, the nature of the hydrogen–oxygen reaction is especially non-equilibrium, and the vibrational non-equilibrium of the HO₂ radical is the essence of this process. The quantitative estimation of the vibrational relaxation characteristic time of the HO₂ radical in its collisions with H₂ molecules has been obtained as a result of the comparison of different experimental data on induction time measurements with the relevant calculations.     

Electron stimulated desorption of CO from

The electron impact behavior of CO adsorbed on was investigated. The desorption products observed were neutral CO, CO⁺, and O⁺. After massive electron impact residual carbon, C/W = 0.15, but not oxygen was also found, suggesting that energetic neutral O, not detected in a mass analyzer must also have been formed. Formation of β-CO, i.e., dissociated CO with C and O on the surface was not seen. The total disappearance cross section varies only slightly with coverage, ranging from 9 × 10 ⁻¹⁸ cm² at low to 5 × 10⁻¹⁸ cm² at saturation (CO/W = 0.75). The cross section for CO⁺ formation varies from 4 × 10⁻²² cm² at satura to 2 × 10⁻²¹ cm² at low coverage. That for O⁺ formation is 1.4 × 10⁻²² cm² at saturation and 2 × 10⁻²¹ cm² Threshold energies are similar to those found previously [J.C. Lin and R. Gomer, Surf. Sci. 218 (1989) 406] for and CO/Cu₁/W(110) which suggests similar mechanisms for product formation, with the exception of β-CO on clean W(110). It is argued that the absence or presence of β-CO in ESD hinges on its formation or absence in thermal desorption, since electron impact is likely to present the surface with vibrationally and rotationally activated CO in all cases; β-CO formation only occurs on surfaces which can dissociate such CO. It was also found that ESD of CO led to a work function increase of the remaining Pd₁/W(110) surface of 500 meV, which could be annealed out only at 900 K. This is attributed to surface roughness, caused by recoil momentum of energetic desorbing entities.     

Study of the plasmas produced during the deposition of TiC/SiC thin films in a hybrid magnetron-laser system

Time- and spatially-resolved optical emission spectroscopy was performed to characterize the plasma produced in a hybrid magnetron-sputtering-laser deposition system, which is used for TiC or SiC thin films preparation. A graphite target was ablated by a KrF excimer laser (λ=248 nm,τ=20 ns) and either Ti or Si targets were used for DC magnetron sputtering in argon ambient. Spectra were measured in the range 250–850 nm. The evolution of the spectra with varying magnetron powers (0–100 W) and argon pressures (0.3–10 Pa) was studied. Spectra of the plasmas produced by a) the magnetron alone, b) the ablation laser alone, and c) the magnetron and the ablation laser together, were recorded. Spectra (a) were dominated by Ar atoms and Ar⁺ ions. Emission lines of Ti and Si were detected, when Ti target and Si target was used, respectively. Spectra (b) revealed emission of C, C⁺, C₂, Ar, Ar⁺. Spectra (c) showed presence of all previously mentioned species and further of Ti⁺ ions emission was detected. The research was supported by Grant Agency of the Czech Republic No. 202/06/02161, GA ASCR project number A1010110/01 and Institutional Research Plan AV CR No. AV0Z 10100522.     

Production of supersymmetric particles ine + e − andep collisions

A review is given of the theoretical predictions for chargino, neutralino and selectron pair production ine ⁺ e ^– annihilation and for slepton and squark production inep collisions. The energy range considered is that of LEP, SLC and HERA. The expectations for the production of SUSY particles at ane ⁺ ev ^– collider in the TeV energy range are also discussed.Invited talk at the International Symposium Hadron Interactions — Theory and Phenomenology, Bechyn, Czechoslovakia, June 26–July 1, 1988.I want to thank H. Baer, H. Fraas, D. Karatas, W. Majerotto and X. Tata for discussions and correspondence. Financial supports of the Czechoslovak Academy of Sciences and the Austrian Academy of Sciences are gratefully acknowledged.     

Energetic Characteristics of Oxygen Plasma

A low-temperature oxygen plasma is studied using the thermocouple, probe and spectral method in the range of 2–8 Torr pressure, 30–100 mA discharge currents, 0, 5, 10 m/s pumping velocity. The gas temperature, concentrations of electrons and oxygen atoms in the 3 p⁵P state, and the longitudinal electric field are measured. Radial distributions of gas temperature and electron concentration are obtained. Ranges of pressures and currents are found in which considerable increases in electric field, discharge voltage, temperatures of gas and electrons are observed at pumping switched on. An estimate of the rate constant of the steplike ionization through the O₂(a¹Δg) state is given. The concentration of atomic oxygen in the ground state and excitation constant of the triplet O(3p⁵P) by electron impact are obtained from the solution of the balance equations and our experimental data.