Photon emission from rare gas ion bombardment of metal surfaces

Metal surfaces (Mg, Cu, Zr, Mo) are bombarded with He⁺, Ne⁺ and Ar⁺ in the energy range of 400 eV to 8 keV. Radiation from scattered projectiles and sputtered target particles is observed between 200 and 700 nm. It is shown that most of the radiating particles originate from surface collisions. Auger neutralization, resonance tunneling and direct electron transitions are the important electronic processes involved.     

Spectres auger et sections efficaces d'ionisation de la couche L23 du magnésium et de l'aluminium sous impact de protons et d'ions lourds (10–100 keV)

A comparison of Auger structures observed on the energy distributions of secondary electrons emitted from Mg and A1 solid targets bombarded by either light particles (H⁺ and He⁺) or heavy ions (Ne⁺, Ar⁺, …) is presented. With incident protons, it essentially appears a broad peak corresponding to a L₂₃VV transition and a weak shoulder due to the surface and bulk plasmon excitation. The Auger structures obtained with heavy ions are richer and the peaks which compose it are sharper. Such atomic-like structures correspond to Auger transitions from excited (with one or two L₂₃ holes) moving recoiling atoms. The experimental L₂₃ Mg and A1 ionization cross sections were determined from Auger spectra. In H⁺?Mg (or A1) collisions our results are in good agreement with the theoretical values calculated in a PWBA model. In the case of heavy ion-target interactions, we compared the experimental measurements with ionization cross section calculations obtained in a Landau-Zener model.     

An AES and ESCA study of GCr15 steel coated with Ti,Cr and bombarded by N+ and Ar+

GCr15 steel specimens coated with Ti, Cr and bombarded with N⁺, Ar⁺ were analyzed by AES and ESCA (PHI-550). The results show that (1) the specimens bombarded with N⁺ have improved surface mechanical properties compared to those bombarded with Ar⁺; (2) the changes in the surface properties are related to the composition of the surface layer, mainly to TiO₂, TiN, Cr₂O₃, and other compounds. Also, the presence of carbon is found to be advantageous in modifying GCr15 bearing steel.     

Atomic excitations in sputtering studied with group two element targets

Solid targets of Be, Mg, Zn, and Cd have been bombarded with 50 keV Ar⁺ ions. The relative excitation of the lowest-lying excited levels in sputtered neutrals and singly-charged ions have been measured using optical spectrometry. It is found that singly-charged ions are excited much more efficiently than neutral atoms. This is discussed, and it is concluded that atomic excitation in sputtering results from electron pick-up to excited states in initially ionized atoms rather than from inelastic atom-atom or electron-atom collisions.     

Studies of the bombarded surface of solids by methods of secondary ion-electron emission

Energy distributions of secondary electrons emitted from the (100) surface of a copper single crystal bombarded with 3 keV N₂⁺ and Ar⁺ ions were obtained by the method of electric differentiation and the homodyne technique. In the high-energy part of the spectrum there is a peak whose position in the energy scale depends on the type of bombarding ions (25 eV for Ar⁺ and 45 eV for N₂⁺). The high-energy electrons are the outcome of autoionization of adsorbed and implanted bombarding ions. It is shown that the high-energy peak may be a good indication of the state of saturation of the surface with bombarding ions.     

4He-stopping power measurements by using ion implantation and backscattering techniques

Experimental results on changes in conductivity of N₂+ and Ar⁺ bombarded thin copper, aluminium and bismuth films are given along with the preliminary observations on photoconductivity of N₂+ bombarded Bi₂O₃ thin films. The performance of a low cost, medium resolution 200 keV ion implantation system, used in the above experiments is also discussed.     

Distribution d'énergie des électrons secondaires émis par InP et GaP soumis à un bombardement d'ions Ar de 40 keV

The energy distributions N(E) of secondary electrons emitted from GaP and InP samples bombarded with 40 keV Ar⁺ ions have been studied by a retarding potential method and an electronic derivation. The spectra show beyond an intensive peak developed at 2 eV, a detailed spectrum between 80 and 140 eV. The analysis of this spectrum reveales Auger electrons corresponding to L₂₃(P) VV and L₂₃M_IV–V(Ga) V [or L₂₃(P) N_IV-V(In) V] transitions; moreover, peaks due to plasmon excitations and d band excitations can be distinguished.     

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.     

Infrared studies on ion irradiated quartz

Damage produced inα- and fused quartz bombarded with low energy (∼ 100 keV) D⁺, He⁺ and Ar⁺ ions, has been studied by observing the changes in their spectrum. Besides bulk reflectivity, the attenuated total reflection spectrum has also been studied, the latter with a view to obtaining the surface polariton frequencies. It is observed that for the same fluence, the changes following D⁺ irradiation are much higher compared to that for Ar⁺ irradiation. The variation of the surface polariton frequency inα-quartz with the damage energy deposited has the same trend as observed earlier for refractive index. Some annealing studies have also been performed in argon-irradiated samples. These studies indicate that whereas in fused quartz the damaged layer recovers completely, inα-quartz there is a residual amorphization even after annealing. A two-layer model is proposed which gives a reasonable simulation of the observedir properties.     

Ion-beam reduction of the surface of tantalum higher oxide

The process of reduction of the surface of higher oxide Ta₂O₅ under irradiation by inert gas (Ar⁺) and chemically active gas (O₂⁺) ions with an energy of 3 keV in high vacuum is investigated by X-ray photoelectron spectroscopy at room temperature. It is found that intermediate oxide TaO₂, lower oxide TaO, and metallic Ta form in the surface layers of Ta₂O₅ under Ar⁺ ion bombardment. An insignificant amount of intermediate oxide TaO₂ forms in the surface layers of Ta₂O₅ under O₂⁺ ion bombardment. Ion-beam-induced reduction of the Ta₂O₅ surface is shown to depend on the type of ion and irradiation dose.     

On the energy spectra of secondary ions emitted from silicon and graphite single crystals

Secondary ion emission from silicon and graphite single crystals bombarded by argon ions with energies E ₀ varied from 1 to 10 keV at various angles of incidence α has been studied. The evolution of the energy spectra of C⁺ and Si⁺ secondary ions has been traced in which the positions of maxima (E _max) shift toward higher secondary-ion energies E ₁ with increasing polar emission angle θ (measured from the normal to the sample surface). The opposite trend has been observed for ions emitted from single crystals heated to several hundred degrees Centigrade; the E _max values initially remain unchanged and then shift toward lower energies E ₁ with increasing angle θ. It is established that the magnitude and position of a peak in the energy spectrum of secondary C⁺ ions is virtually independent of E ₀, angle α, and the surface relief of the sample (in the E ₀ and α intervals studied). Unusual oscillating energy distributions are discussed, which have been observed for secondary ions emitted from silicon (111) and layered graphite (0001) faces. Numerical simulations of secondary ion sputtering and charge exchange have been performed. A comparison of the measured and calculated data for graphite crystals has shown that C⁺ ions are formed as a result of charge exchange between secondary ions and bombarding Ar⁺ ions, which takes place both outside and inside the target. This substantially differs from the ion sputtering process in metals and must be taken into account when analyzing secondary ion emission mechanisms and in practical applications of secondary-ion mass spectrometry.     

Effect of oxide surface metallization under ion-beam irradiation

Changes in the surface chemical composition of WO₃, Ta₂O₅, MoO₃, and Nb₂O₅ oxides after Ar⁺ ion irradiation and those of the WO₃ surface after He⁺ ion irradiation under high vacuum were investigated by X-ray photoelectron spectroscopy. Upon Ar⁺ ion irradiation with an energy of 3 keV, the pronounced effect of ion-beam metallization was observed on the WO₃ oxide surface; a moderate effect was found for the Ta₂O₅ oxide surface; a weak one for the MoO₃ oxide surface; and no effect was discovered for the Nb₂O₅ oxide surface. At the saturation dose, 44 at % W, 12 at % Ta, and 2 at % Mo form on the oxide surfaces. Irradiation by light He⁺ ions with energies of 1 and 3 keV results in WO₃ surface metallization. At the saturation dose, 2 and 10 at % W (at 1 and 3 keV, respectively) forms on the oxide surface. The nature, mechanisms, and features of the oxide surface metallization effect induced by ion-beam irradiation are discussed.     

Secondary ion emission from Si bombarded with large Ar cluster ions under UHV conditions

Si was bombarded with size-selected 40 keV Ar cluster ions and positive secondary ions were measured using the time-of-flight technique under high and ultra-high vacuum (HV and UHV respectively) conditions. Si⁺ ions were main species detected under the incidence of 40 keV Ar cluster ions, and the yields of Si cluster ions such as Si₄⁺ were also extremely high under both conditions. On the other hand, oxidized secondary ions such as SiO⁺ were detected with high intensity only under the HV condition. The yield ratios of oxidized ions decreased in UHV to less than 1% of their values in HV. The effect of residual gas pressure on Si cluster ion yields is relatively low compared to oxidized ions, and the UHV condition is required to obtain accurate secondary ion yields.     

kinetic energy reflection from polycrystals bombarded with Ar+, Kr+, and Xe+ ions

When the surface of a solid is bombarded with ions a fraction of the primary energy is reemitted by ion reflection and sputtering. The contribution of ion reflection or sputtering to energy reflection is determined by the mass ratio of the bombarding ions to the target atoms.^1,2 In the case of light ions the contribution of reflected ions is dominant. Results for He⁺ and Ne⁺ bombardment were described in a previous paper.³ The present paper deals with results for Ar⁺, Kr⁺, and Xe⁺ bombardment of the same targets as investigated before.³ The energies of the mass selected bombarding ions range from 9 to 16 keV. The measurements were carried out by means of the thermic detector described in a separate paper.⁴ For the given mass ratios most of the reemitted energy is related to sputtering.     

On the velocity distribution of excited Fe-atoms by sputtering of iron

From the velocity distribution of excited sputtered particles detailed information on the excitation process can be obtained. In the present paper the first direct measurement of velocity distribution of excited atoms sputtered from a metal target is presented. The irradiation of the Fe-target was performed with 10keV Ar⁺-ions. The sputtered atoms were detected using pulsed laser induced fluorescence (LIF). The sputtered Fe atoms in the metastable statea ⁵ F ₅ at 0.86 eV shows a much broader distribution, than found for the ground-state atoms, but no energy threshold, implied in the statistical excitation models, was found.     

Die Zerstäubung von Kupfer durch Ne+-, Ar+-, Kr+- und Xe+-Ionen im Energiebereich von 75keV bis 1MeV

Using a 1,3 MeV Van de Graaff-accelerator the sputtering ratioS of polycristalline copper bombarded by normally incident Ne⁺-, Ar⁺-, Kr⁺-, and Xe⁺-ions was measured in the energy range from 75 keV to 1 MeV. In the case of Kr⁺-ions a broad, plateau-like maximum of the sputtering-curveS=f(E) was found at about 100 keV, for Xe⁺-ions a more pronounced maximum at about 125 keV. The results are discussed applying the theories ofGoldman-Simon, Pease, andMartynenko.     

X-ray spectra induced by slow highly charged Ar q + ions in collision with Nb surface

The X-ray spectra of Nb surface induced by Ar ^q+ (q = 16,17) ions with the energy range from 10 to 20 keV/q were studied by the optical spectrum technology. The experimental results indicate that the multi-electron excitation occurred as a highly charged Ar¹⁶⁺ ion was neutralized below the metal surface. The K shell electron of Ar¹⁶⁺ was excited and then de-excited cascadly to emit K X-ray. The intensity of the X-ray emitted from K shell of the hollow Ar atom decreased with the increase of projectile kinetic energy. The intensity of the X-ray emitted from L shell of the target atom Nb increased with the increase of projectile kinetic energy. The X-ray yield of Ar¹⁷⁺ is three magnitude orders larger than that of Ar¹⁶⁺. Supported by the National Natural Science Foundation of China (Grant Nos.10774149 and 10405025)     

Absolute measurement of sputtered ion fractions using matrix isolation spectroscopy

Sputtering yields for neutrals and ions have been measured by collecting the sputtered species in a noble gas matrix and determining their amounts from optical absorption spectroscopy. The atomic ion fractions for Ti and Zr bombarded by O₂⁺ at 2 keV are 0.8 and 0.4, respectively, whereas TiO and ZrO are sputtered largely as neutrals. Neutral sputtering yields from Ar⁺ bombardment arc consistent with previous measurements. The experimental results are compared with various theoretical models for the sputtering process.     

Energy distributions and emission coefficients of secondary ions ejected from AIIIBV group semiconductors

The energy distributions of Ga⁺ and Ga₂ ⁺ secondary ions sputtered from the surface of single crystals of GaAs and GaP by Ar⁺ (E = 18 keV, j = 1·10^–6 A/cm²) ions were studied. Integral emission coefficients for secondary ions from four semiconductors (GaAs, GaP, InAs, and A1_0.35Ga_0.65As) bombarded by Ar⁺ ions (E = 2 keV, j₀ = 1·10^–6 A/cm²) were also measured. It is shown that the energy distribution of the Ga⁺ secondary ions are broad and qualitatively similar to distributions of secondary ions sputtered from metal oxide surfaces. Very high integral emission coefficients (up to 20–30%) for secondary ions are also observed, exceeding analogous coefficients for clean metal surfaces. These facts (the significant number of low energy secondary electrons and high secondary ion emission coefficients) are due to the lower density of free electrons in comparison with metals, which ensures a high degree of survival of sputtered ions, and the partially ionic character of the bonds in the semiconductors under study.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 88–92, November, 1990.     

Ion bombardment of ordered Zr3Al

The behaviour of the ordered alloy Zr₃Al was investigated by transmission electron microscopy following ion bombardments at temperatures ranging from 30 to 850 K. Utilizing high energy(0.5–2.0 MeV) C⁺, N⁺ and Ar⁺ ion bombardments, observations were made of the irradiation-induced transformation from the ordered → disordered → amorphous states. Information about individual damage cascades was also obtained using both high energy (C⁺. N⁺ and Ar⁺) and low energy (15–120 keV Cu⁺) ion bombardments.