Production of Kr2+ in collisions of rare gas ions with Kr

Total and differential cross sections for the production of fast Kr²⁺ ions in collisions of He⁺, Ne⁺ and Ar⁺ with Kr were measured at primary energies below 500 eV. In the system Ar⁺+Kr most of these reactions occur in close collisions and are accompanied by a large momentum transfer. For Ne⁺+ Kr collisions the angular distribution in the centre of mass system is approximately isotropic over a wide angular range. The cross section values for the Kr²⁺ production amount to 1% of the total charge transfer cross section in the investigated energy range.     

3s vacancy production in Ar+-Ar and Ar+-He collisions

The 3s vacancy production in Ar⁺-He and Ar⁺-Ar collisions has been studied at impact energies of 100 keV to 550 keV. A comparison is made for the Ar⁺-He system with theoretical calculations based on the quasi-molecular model.     

Preferential sputtering of TIC under keV Ar+ ion bombardment: Simultaneous sputtering-ISS measurement with He+ and Ar+ ions

The composition change of the outermost atom layer of TiC(110) under ion bombardment with 1.5–3 keV He⁺ and He⁺ + Ar⁺ ions has been measured by ion scattering spectroscopy with He⁺ ions at different sample temperatures. It has been found that the preferential sputtering of C atoms takes place for both the He⁺ and Ar⁺ ion bombardment, however the preferred sputtering is more pronounced for Ar⁺ ions than for He⁺ ions. The ion bombardment with He⁺ ions at elevated sample temperatures hardly results in any change in surface composition below ～800°C, while Ar⁺ ion bombardment results in C enrichment for elevated temperatures as reported so far.     

Linewidth studies on the Ar+ 476.5 nm and 480.6 nm lines excited in a helium-agron hollow cathode discharge

The spectral line shapes of the Ar⁺ 476.5 nm and 480.6 nm lines, excited in a He-Ar hollow cathode (HC) discharge, were measured using the Fabry-Perot technique. The collisional and Doppler linewidths were determined for the two lines. The collisional broadening constants are estimated to be (5±3) MHz/mbar and (6±3) MHz/mbar, respectively. The temperature obtained from the two Ar ion transitions was found to be 260 K higher than that expected for the rest of the gas mixture from earlier measurements. The possibility is discussed, that this excess temperature is caused by Ar ions partially created in the HC discharge by charge transfer collisions with He ₂ ⁺ molecules.     

Ar+离子与原子碰撞中真空紫外辐射

对Ar⁺离子与He,Ne,Xe原子碰撞中的真空紫外辐射进行绝对测量,观察到入射离子的电离激发过程和靶原子电离激发过程,并以Fano和Lichten的电子提升分子轨道模型和非绝热分子轨道相关图对此进行定性解释。 关键词：     

Metastable Decomposition of Ar3+ Cluster Ions Into Ar2+ and Ar+

In this note we present the first account of a study of metastable (unimolecular decay) and collision-induced dissociation of Ar₃+ cluster ions using an experimental setup consisting of a molecular beam-electron impact ion source and a double focussing (reversed Nier Johnson geometry) mass spectrometer. The existence of the following metastable decay processes (accessible by our sampling time window) could be demonstrated: Ar₃⁺* → Ar₂+ and Ar₃⁺* → Ar⁺. The processes were studied as a function of electron impact energy. The present results are of importance in order to provide some guidance for the development of appropriate theoretical models for the dissociation of cluster ions.     

Study of the heavy products from84Kr+238U collisions at 522 MeV

Angular distributions and integral cross sections for heavy reaction products from⁸⁴Kr +²³⁸U collisions at 522 MeV were measured using catcher foil techniques and off-line X-ray identification of individual reaction product isotopes. There is no evidence for a fission-fusion mechanism being responsible for the formation of the “gold finger”. The data show that usual deep inelastic collisions account for the formation of all products with 70≦Z≦86. Compared to existing data atE≦605 MeV, the deduced mass distribution indicates reduced fission probabilities forZ≧80 fragments at 522 MeV. This is consistent with the expected dependence of fission probability on excitation energy and especially on angular momentum.     

Absolute auger yields in Ar+ Al collisions: experiments and computer simulations

Experiments and computer simulations of absolute Auger yields in Ar⁺ Al collisions were performed. Dependence of the experimental Auger yields on the ionic energy and on the incidence angle are in reasonable agreement with the calculated variation laws. For this, a convenient set of model parameters were determined.     

L α emission from Ar++H2 collisions in the threshold energy region

In the energy range 2.4 to 33.3 eV_CM, relative cross sections have been measured forL _α emission from impact of Ar⁺ ions in a beam on a H₂ gas target. Absolute cross sections, obtained by normalization to literature data, are 1–10×10^?16cm² for metastable Ar⁺ and 1–20×10^?18cm² for ground state Ar⁺. In the former case, the dominant mechanism is probably dissociative electronic energy transfer, while in the latter case dissociative charge transfer is the most likely process. In addition, at the lowest energiesL _α resulting from a chemiluminescent rearrangement Ar⁺+H₂→ArH⁺+H(2p) has been observed.     

Secondary ion and Auger electron emissions from Ar+-ion-sputtered FeAl alloys

Some FeAl alloys, and pure Al and Fe samples, are sputtered in ultrahigh vacuum with Ar⁺ ions between 4 and 15 keV. As previously observed with CuAl alloys, the intensity of the principal Al Auger peak at 63.5 eV is a parabolic function of the Al concentration. Symmetric collisions Al → Al are thus much more efficient for Auger emission from pure aluminium than asymmetric collisions Ar → Al, the proportion of which among effective collisions hardly reaches 20% at 15 keV. Whatever the initial ion energy, the intensities of singly charged atomic secondary ions Al⁺ and Fe⁺, normalized to pure metals, are equal to the atomic concentration of the corresponding elements, whereas the normalized intensities of the multiply charged ions Al²⁺ and Al³⁺ are roughly equal to the square of Al concentration. These results agree with the occurence of two mechanisms in intrinsic ion emission: an electronic excitation process during the separation of the outgoing particle from the target (singly charged ions) and a collisional process from the symmetric collisions Al → Al only, with multiple Auger de-excitation outside the target (multicharged ions of light elements).     

X-ray productions in symmetric heavy ion-atom collisions

X-ray measurements for 50–200 keV impact Ne⁺ → Ne, Ar⁺ → Ar and Kr⁺ → Kr show an increase of a factor of 10 in the flourescence yield for Ar-L₂₃, a similar increase may occur for Kr-M₂₃, but for Ne-K the yield does not vary much.     

Momentum transfer theory of ion transport under the influence of resonant charge transfer collisions: the case of argon and neon ions in parent gases

Transport properties of ion swarms in presence of Resonant Charge Transfer (RCT) collisions are studied using Momentum Transfer Theory (MTT). It was shown that, not surprisingly, RCT collisions may be represented as a special case of elastic scattering. Using the developed MTT we tested a previously available anisotropic set of cross-sections for Ar+Ar ⁺ collisions by making the comparisons with the available data for the transverse diffusion coefficient. We also developed an anisotropic set of Ne+Ne ⁺ integral cross-sections based on the available data for mobility, longitudinal and transverse diffusion. Anisotropic sets of cross-sections are needed for Monte Carlo simulations of ion transport and plasma models. Received 16 June 2002 / Received in final form 2nd August 2002 Published online 24 September 2002 RID="a" ID="a"e-mail: vrhovac@phy.bg.ac.yu RID="b" ID="b"e-mail: zoran@phy.bg.ac.yu     

X-ray photoelectron spectroscopic studies of PbO surfaces bombarded with He+, Ne+, Ar+, Xe+ and Kr+

The surface composition of PbO has been studied with X-ray photoelectron spectroscopy after bombardment with several inert gas ions of 400 eV. The results show reduction of PbO to metallic Pb with the degree of damage following the order He⁺ > Ne⁺ >Ar⁺. Both Kr⁺ and Xe⁺ did not reduce the oxide. The depth of damage varied from ≈9 Å for He⁺ to ≈1 Å for Ar⁺ bombardment. The results were compared to a collisional and a thermal model of the sputtering process.     

Mixing of Au in Si induced by secondary and high-order recoil implantation

The mixing of Au in Si induced by secondary and high-order recoil implantation was investigated using 350 keV Ar⁺ and 350 keV Kr⁺ ions to fluences from 1?×?10¹⁶ to 3?×?10¹⁶ ions/cm² at room temperature. The thickness of the Au layer evaporated on Si substrate was ～2400 Å.The ranges of the Ar and Kr ions were chosen to be lower than the thickness of the Au layer in order to avoid the ballistic mixing produced by the primary knock-on atoms. Rutherford backscattering spectrometry (RBS) experiments were carried out to study the effects induced by Ar and Kr irradiation at the interface of Au–Si system. We observed that in the case of the irradiation with Ar⁺ ions, a broadening of the Au–Si interface occurred only at the fluence of 3?×?10¹⁶ Ar⁺/cm² and it is attributed to the surface roughening induced by ion bombardment. In contrast, the RBS analysis of a sample irradiated with 2?×?10¹⁶ Kr⁺/cm² clearly showed, in addition to the broadening effect, the formation of a mixed zone of Au and Si atoms at the interface. The mixing of Au in Si atoms can be explained by the secondary and high-order recoil implantation followed by subsequent collision cascades.     

ISS measurement of surface composition of AuCu alloys by simultaneous ion bombardments with Ar+ and He + ions

Surface composition of Au-Cu(43 at%) alloy under 1.5–5 keV argon ion bombardment has been investigated by ion scattering spectroscopy (ISS). In this experiment, we adopted a specific technique to use mixed He⁺ and Ar⁺ ions as primary beam in order to perform sputtering (Ar⁺) and ISS measurement (He⁺) simultaneously. The outermost atom layer of Au-Cu alloys under Ar⁺ ion bombardment is Au-rich leading to the conclusion that Ar⁺ ion bombardment of AuCu alloys causes the preferential sputtering of Cu atoms, resulting in a Au-rich outermost atom layer and a depletion layer of Au atoms beneath the outermost atom layer due to ion-beam-enhanced surface segregation. This result explains the experimental results obtained by AES as well.     

Subthreshold K+ production in proton-nucleus collisions

Double differential K⁺ cross sections have been measured in p+C collisions at 1.2, 1.5 and 2.5 GeV beam energy and in p+Pb collisions at 1.2 and 1.5 GeV. The K⁺ spectrum taken at 2.5 GeV can be reproduced quantitatively by a model calculation which takes into account first chance proton-nucleon collisions and internal momentum with energy distribution of nucleons according to the spectral function. At 1.2 and 1.5 GeV beam energy the K⁺ data excess significantly the model predictions for first chance collisions. When taking secondary processes into account the results of the calculations are in much better agreement with the data.     

Subthreshold K+ production in proton-nucleus collisions

Double differential K⁺cross sections have been measured in p+C collisions at 1.2, 1.5 and 2.5 GeV beam energy and in p+Pb collisions at 1.2 and 1.5 GeV. The K⁺ spectrum taken at 2.5 GeV can be reproduced quantitatively by a model calculation which takes into account first chance proton-nucleon collisions and internal momentum with energy distribution of nucleons according to the spectral function. At 1.2 and 1.5 GeV beam energy the K⁺ data excess significantly the model predictions for first chance collisions. When taking secondary processes into account the results of the calculations are in much better agreement with the data.     

Pion-production in heavy-ion collisions at SIS energies

We investigate the production of pions in heavyion collisions in the energy range of 1–2 GeV/A. The dynamics of the nucleus-nucleus collisions is described by a set of coupled transport equations of the Boltzmann-Uehling-Uhlenbeck type for baryons and mesons. Besides theN(938) and theΔ(1232) we also take into account nucleon resonances up to masses of 1.95 GeV/c² as well asπ-,η- andρ-mesons. We study in detail the influence of the higher baryonic resonances and the 2π-production channels (NN→NNππ) on the pion spectra in comparison toπ ^? data fromAr+KCl collisions at 1.8 GeV/A andπ ⁰-data forAu+Au at 1.0GeV/A. We, furthermore, present a detailed comparison of differential pion angular distributions with the BEVALAC data forAr+KCl at 1.8 GeV/A. The general agreement obtained indicates that the overall reaction dynamics is well described by our novel transport approach.     

Electron multiplicity in slow collisions of Ar ions with C

Electron capture by Ar⁸⁺ in collisions with C₆₀ fullerene has been investigated using coincident measurements of the number n of ejected electrons, the mass and charge of multicharged Cr+ ₆₀ recoil ions and their fragments Ci+ m and the final charge state of outgoing projectiles Ar(8-s)+ (). The number of captured electrons r is the sum of the numbers of stabilized and emitted electrons: r = n + s. The ratio n / s decreases by a factor three with s increasing from 1 to 7 showing that the multiply excited states populated by capture of a large number of electrons are rather stable against auto-ionisation. Each kinetic energy spectrum of Ar⁺ and Ar²⁺ projectiles is composed of two peaks which we attribute to collisions “inside” and “outside” the C₆₀ cage. The measured energy shift of the projectile keV is consistent with the corresponding energy loss keV in a carbon foil with an equivalent thickness. Inside collisions are characterized by a strong dissociation of recoil ions into light monocharged fragments and by a high multiplicity of ejected electrons. Received: 25 March 1998 / Received in final form and Accepted: 9 June 1998     

Ar+, He+，S+离子轰击n-InP单晶表面的机理研究

通过X射线光电子能谱和低能电子衍射实验研究了10～180 eV的Ar⁺、 He⁺、S⁺离子轰击n-InP(100)表面, 发现S⁺离子轰击可以产生In-S组分,减轻离子轰击对表面的物理损伤.对于Ar⁺离子轰击后的表面,经过S⁺离子处理和加热过程以后,表面损伤得到了修复,最终得到了2×2的InP表面,进一步验证了S⁺离子对InP表面的修复作用.