Sputtering of Cu and Zn atoms from elemental and alloy targets

The energy distributions of Cu and Zn atoms sputtered from elements and Cu_xZn_1-x alloys (x=0.80, 0.24) with a 6 keV Ar⁺ beam have been measured. It was found that the collision-cascade theory properly described the flux of sputtered atoms. From the spectra the binding energies of Cu and Zn atoms in the elemental and alloy surfaces were determined. The collision-cascade theory and the experimentally adjusted values of the binding energies allowed for calculation of the total and partial sputtering yields, and the equilibrium surface composition of the ion bombarded alloys. This work was carried out as a part of Research Project M.R. I/5.     

Sputtering of SiC with low energy He and Ar ions under grazing incidence

The effect of low energy sputtering under grazing incidence upon the surface composition of SiC was investigated by Auger electron spectroscopy. The energy of the sputtering projectiles (He, Ar) varied from 200 to 1500?eV. Peak shifts to the higher energies with increasing argon ion energy were observed for all silicon and carbon Auger transitions. These shifts were explained by enhanced damage of the surface region within the sampling depth of the Auger electrons. The insensitivity of the Auger peak position to the energy of helium ions indicates that the damage state in the surface region does not change with the increasing energy of helium ions. An increase of the carbon concentration with the decrease of the argon energy was observed. The experiments were accompanied by dynamic Monte Carlo simulations by the TRIDYN code.     

Multielectron processes in collisions of Xe23+ ions with Ar atoms

We report the measurements of relative cross sections for multielectron processes in collisions of Xe²³⁺ ions with argon atoms in the velocity range of 0.65–1.32 a.u. By means of the coincidence time-of-flight (TOF) technique, the final charge states of both the projectile and target ions for each collision event are determined. The present experimental data are compared with the scaling law by Selberg et al. [Phys. Rev. A 54, 4127 (1996)] and the extended classical over-barrier (ECB) model.     

Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys by keV Ar+ ion bombardment

Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys under 3 keV AR⁺ ion bombardment were measured to understand the preferential sputtering. The surface composition of sputter-deposited Au-Cu films on substrates mounted at different ejection angles was analyzed by Auger electron spectroscopy and electron probe microanalysis. Although the result indicated that the proportion of sputtered Cu atoms to the Au atoms in the Au-Cu alloy depends on the ejection angle, marked enhancement of the lighter component in the direction normal to the surface has not been observed in spite of the larger mass ratio of the constituent atoms of the Au-Cu alloy.     

Sputtering of AlxGa1−x As semiconductor targets by Ar+ ions with energies of 2–14 keV

Investigations of the sputtering of Al_xGa_1−x As semiconductor solid solutions by Ar⁺ ions with energies of 2–14 keV are performed. The dependence of the sputtering yield on the energy and angle of incidence of the ions are determined and the character of the surface relief formed during the sputtering is investigated. A comparison with theory shows that the best agreement between theory and experiment is achieved when the Haff-Switkowski formula is used together with Yudin’s stopping cross section. It is shown that the surface binding energies obtained differ from the atomization energies by an amount approximately equal to the amorphization energy. Zh. Tekh. Fiz. 67, 113–117 (June 1997)     

Sputtering of condensed noble gases by keV ions

Layers of Kr and Xe condensed at ～ 15 K and 35 K have been bombarded by 3-6 keV Ar+, Kr+ and Xe+ ions.

The sputtered neutrals were detected after a 1.43 m flight path by means of a mass spectrometer. Among the sputtered particles are considerable numbers of Van der Waals molecules, like Kr₂, Kr₃, Xe₂ XeKr and XeKr₂. The energy distribution of the sputtered particles give clues to the sputtering mechanisms involved.     

Experiments on the sputtering of neutral Cu2 dimers from Cu by Ar+ ions (60–300 eV)

A planar polycrystalline copper target was bombarded normally by Ar⁺ ions with energies ranging from 60 to 300 eV. in the source of a mass spectrometer. The neutral particles sputtered normally from the target were post-ionized and analyzed in the mass spectrometer. A thermionically sustained, magnetically confined low pressure arc plasma was used to supply the bombarding ions, and for post-ionization of the neutral sputtered species. It was found that the relative yields of the sputtered neutral post-ionized Cu₂ dimers are linearly proportional to S², where S is the total sputtering yield for Ar⁺ -Cu. The results support the recombination model for the formation of neutral dimers in sputtering.     

Sputtering of solicon and germanium by middle-energy heavy ions

The angular and energy dependences of the sputtering ratios of silicon and germanium targets under bombardment by argon ions of ten-keV energy are studied.     

Total cross section measurements for charge exchange of He++ ions with He and Ar atoms

Total charge exchange cross sections were measured for He⁺⁺ in He and Ar gas in the energy range from 50 to 540 eV using a single beam apparatus. For He⁺⁺ in He the measured cross section is in agreement with calculations for symmetric resonant charge exchange. For He⁺⁺ in Ar the cross section for charge exchange decreases with decreasing energy below 300 eV. The measured cross section suggests the formation of Ar⁺ ions to be more important at lower energies and the production of Ar⁺⁺ to be dominant at higher energies.     

Ar离子溅射生成碳纳米管

用扫描电子显微镜(SEM)和透射电子显微镜(TE),研究了离子溅射石墨表面的形貌特征和结构,证实了碳纳米管可通过溅射原子在表面形貌突起部位沉积生长.     

Sputtering and electron excitation of gold by hydrogen atoms of thermal energies

The effect of gold sputtering by atomic hydrogen is discovered. It is established that the sputtering mechanism is related to the electron excitation of the metal via the heterogeneous reaction H + H → H₂.     

Ionization of atoms and ions by intense laser radiation

The ionization of negative ions by ultrashort electromagnetic pulses, the multiphoton ionization of atoms beyond the perturbation theory taking into account the Coulomb interaction, and the relativistic theory of tunneling in application to the ionization problems have been analyzed. The main results have been obtained using the imaginary time method.     

K-shell ionization of atoms and ions by relativistic projectiles

We evaluate the total cross section for the single K-shell ionization of atoms and ions by the impact of relativistic electrons. The study is performed to leading orders of the QED perturbation theory with respect to the parameters αZ and 1/Z. The results obtained are in good agreement with experimental data for different atomic targets. In the case of moderate values of the nuclear charge Z, the total cross section is described by a simple analytic formula. The K-shell ionization by relativistic heavy particles is also considered.     

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.     

Structural features of aluminium alloy 1441 irradiated by Ar+ ions

Using electron microscopy it was found that irradiation of clad cold-worked specimens made of commercial aluminium-lithium alloy 1441 by the Ar ⁺ ions of energy 40 keV at low doses of irradiation (10¹⁵ cm⁻², irradiation time 1 s, T < 70 °C) and ion-current density of about 100 μA/cm² results in the transformation of the cellular structure formed in the alloy under deformation. As the dose of irradiation is increased up to 10¹⁶ cm⁻², a transition from a cellular to a subgrain structure close to a polygonal one is observed. The efficiency of the process is increased with ion-current density. Furthermore, under ion irradiation at increased ion-current densities, the β′(Al ₃ Zr) and Al ₈ Fe ₂ Si particles present in the deformed alloy dissolve, and disperse particles of a new Al ₂ LiMg phase of platelet shape are formed. The changes in the dislocation structure and phase composition in alloy 1441 are observed several seconds after irradiation not only in the surface layer adjacent to the ion incorporation band but also through the thickness of the specimen tens of thousands times greater than ion projective ranges. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 73–81, February, 2007.     

Multiphoton ionization of atoms and ions by high-intensity X-ray lasers

Coulomb corrections to the action function and rate of multiphoton ionization of atoms and ions in a strong linearly polarized electromagnetic field are calculated for high values of the Keldysh adiabaticity parameter. The Coulomb corrections significantly increase the ionization rate for atoms (by several orders of magnitude). An interpolation formula proposed for ionization rate is valid for arbitrary values of the adiabaticity parameter. The high accuracy of the formula is confirmed by comparison with the results of numerical calculations. The general case of elliptic polarization of laser radiation is also considered.     

Quenching cross-sections of metastable Ar,Kr and Xe atoms by halogen molecules

Summary The quenching of metastable Ar, Kr and Xe atoms by halogen molecules via an electron jump mechanism is examined by using the multiple curve-crossing formalism of Bauer, Fisher and Gilmore. Cross-sections for the quenching process are calculated which are found in good agreement with experiment. Finally, the model presented here is compared with other quenching mechanisms.

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Riassunto Si esamina la tempra di atomi metastabili di Ar, Kr, e Xe mediante molecole di alogeni attraverso un meccanismo di salto di elettroni, usando il meccanismo d'incrocio multiplo di curve di Bauer, Fisher e Gilmore. Si calcolano le sezioni d'urto per il processo di tempra che appaiono in buon accordo coi dati sperimentali. Infine il modello qui presentato è confrontato con altri meccanismi di tempra.

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Резюме Используя формализм Бауэра, Фишера и Джилмора, исследуется гашение метастабильности атомов Ar, Kr и Xe молекулами галогенов через механизм электронного перескока. Вычисляются поперечные сечения для процесса гашения, которые согласуются с экспериментом. В заключение предложенная модель сравнивается с другими механизмами гашения.

     

Carrier-envelope-phase effect in nonsequential double ionization of Ar atoms by few-cycle laser pulses

A classical ensemble method is used to investigate nonsequential double ionization(NSDI) of Ar atoms irradiated by linearly polarized few-cycle laser pulses. The correlated-electron momentum distribution(CMD) exhibits a strong dependence on the carrier-envelope phase(CEP). When the pulse duration is four cycles, the CMD shows a cross-like structure, which is consistent with experimental results. The CEP dependence is more notable when the laser pulse duration is decreased to two cycles and a special L-shaped structure appears in CMD. Recollision time of returning electrons greatly depends on CEP, which plays a significant role in accounting for the appearance of this structure.