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.     

Submonolayer films on a Si(111) surface under low-energy ion bombardment

The kinetics of deposition for monomolecular submonolayer films on a Si(111) surface is studied via low-energy electron diffraction with measurements of the intensities of diffraction reflection and the elastic background. The degree of structural perfection in growing films is estimated for alkali-metal silicides and silicon from low-energy beams. The optimum energy and dose intervals of silicide film formation are determined.     

Effect of low-energy ion bombardment on the crystal structure and superconductivity of niobium films

The effect of ion bombardment on the growth of Nb films and their crystal structure is investigated. Epitaxial niobium films with the (001) orientation are grown on (01i2) Al₂O₃ substrates heated to 600°C and biased at ?20 V. Niobium films with pronounced axial texture in the [110] direction are grown on water-cooled Sitall (devitrified glass such as Pyroceram) substrates. In Nb films biased at ?50 V, which are in the superconducting state, the motion of individual magnetic vortices is observed with a magnetooptic indicator.     

Raman scattering characterization of a carbon coating after low-energy argon ion bombardment

The characteristic of Raman scattering spectra of a carbon coating, which was modified by radio frequency argon plasma, has been investigated. The argon ion bombardment causes changes in the microstructure and amount of stress in the coating. Raman scattering spectra are discussed in terms of intensity, bandwidth and wavenumber. The evolvement of Raman spectra shows the following behavior with increasing bombardment time: the intensity changes of the disordered D band, amorphous D″ band and graphite G band could be separated into several stages; low-energy argon ion bombardment over a short period can reduce the number of defects in the carbon coating, while a larger bombardment period can increase the number of defects; the widths of the D and G bands both increase, while that of the D″ band decreases; the wavenumbers of all the three bands fluctuate according to the changes in electronic configuration and amount of stress in the carbon coating.     

Mechanisms of oxidation-reduction processes on metal and oxide surfaces under ion bombardment

Surface oxidation occurs if metals are bombarded with low-energy (1–5 keV) ions of a chemically active gas (oxygen) in vacuum. It is ascertained that ion bombardment leads to the generation of lower, intermediate, and higher oxides. The composition and thickness of an oxidized layer depend on the metal reactivity and the dose and energy of oxygen ions. The mechanism underlying the ion-beam oxidation of metal surfaces is proposed. Surface reduction is observed if higher oxides are bombarded with low-energy (1–5 keV) ions of inert gases (argon and helium) in vacuum. It is revealed that ion bombardment not only generates intermediate and higher oxides but sometimes gives rise to surface metallization. The composition and thickness of the reduced layer are determined by the oxide type, the kind of inert gases, and the dose and energy of bombardment. The mechanism describing the ion-beam reduction of higher metal oxide surfaces is proposed.     

Influence of ion bombardment on residual stresses in diamond-like carbon films

The dependence of internal residual stresses in thin diamond-like carbon films grown by the PECVD technique on the most important growth parameters such as the power of the exciting RF discharge and the substrate bias potential is considered. The results have shown that the mechanical stresses in films reach the uppermost value of 1.9 GPa at the smallest values of power and potential. The stress decreases with the growth of both parameters and has only a slight dependence on the film thickness in the range 0.1–1 μm. The bombardment of the obtained films by argon ions with energy of 300 keV and phosphorus ions with energy of 200 keV has resulted in the reduction of compressive stress with the ion dose growth down to its inversion. AFM study of the bombarded films has revealed significant changes in their surface morphology.     

The effect of low-energy ion bombardment on the density and crystal structure of thin films

The effect of low-energy ion bombardment on the growth and properties of thin films deposited by rf plasma sputtering at low substrate temperatures is studied. The dependences of the film thickness, density, crystal structure, and conductivity on the bias voltage applied to the substrate are obtained. At biases ranging from 0 to −30 V, nickel films are polycrystalline; at higher biases, they exhibit axial (111) texture. At the bias −60 V, the density of the Ni films is close to that of the bulk metal and the crystal structure of the films is the most ordered. With a further increase in the bias, the density of the films drops because of gas (argon and residual gases) atoms incorporated into the films. The same bias dependence of the density is observed for amorphous films of binary alloys of d and f metals. In this case, the films deposited at the substrate bias −40 V have the highest density.     

Accommodation coefficients for low-energy ions on metal surfaces

The interaction of low-energy ions (E = 3 to 100 eV) with the surface of a solid cannot be treated in terms of gas dynamics. The scattering of particles at an energy of E _o > 20 eV may be explained in terms of binary collisions with the atoms of the target. The validity of the single collision model with free surface atoms for medium energies from 10 to 100 eV and even down to 1 eV was confirmed on the basis of both experimental and computational data. This paper describes experimental studies of the secondary ion emission from the (100) and (110) faces of a Mo single crystal and both experimental and theoretical studies of alkaline ion accommodation coefficient on polycrystalline Mo within the energy range E = 3 to 50 eV with a varying direction of the primary ion beam from normal to the glancing angle of incidence (ρ = 0 to 75°). On the basis of the retarding potential method using a spherical condenser whose central electrode was the target, we measured the energy distribution of secondary ions. Calculations have been performed for the energy of scattered ions and the high energy portion of accommodation coefficient on the basis of single and double binary collisions using the Born-Mayer potential and taking into consideration the influence of adsorption forces at the surface of the target.     

Electronic properties of silicon-nitride films deposited by low-energy ion-beam bombardment

Ultrathin silicon-nitride films have been synthesized on silicon substrates by low-energy nitrogen-ionbeam bombardment. The thicknesses of the obtained films are found to increase slightly with the duration of bombardment. Capacitance-voltage and current-voltage characteristics of silicon-nitride films prepared at different bombarding times show that the density of damages, charges in the films and interface states, the capacitance of the obtained ultrathin silicon-nitride films, the flat-band capacitance and the flat-band voltage increase with the duration of the bombarding process. The results of these analyses suggest a short bombarding processing for such a silicon-nitridation technique proposed here.     

Effect of ion bombardment on the phase composition and mechanical properties of diamond-like carbon films

It is established that the addition of hydrogen to methane in the reaction mixture upon the fabrication of diamond-like carbon films via the plasma-enhanced chemical vapor deposition method decreases residual stresses in the obtained films and significantly reduces their growth rate. The films were investigated via atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Irradiation of the prepared films with P⁺ and PF ₄ ⁺ ions results in strong sample swelling with increasing dose, as well as in a decrease in the compressive stress up to transition to tensile one reaching saturation. Moreover, the fraction of sp ³ bonds increases with increasing ion dose while the fraction of sp ² bonds decreases symmetrically with the processes proceeding faster upon irradiation with molecular ions. Qualitative mechanisms explaining the experimental results are proposed.     

Investigation of oxygen adsorption on Cu(110) by low-energy ion bombardment

The interaction of molecular oxygen with a Cu(110) surface is investigated by means of low energy ion scattering (LEIS) and secondary ion emission. The position of chemisorbed oxygen relative to the matrix atoms of the Cu(110) surface could be determined using a shadow cone model, from measurements of Ne⁺ ions scattered by adsorbed oxygen atoms. The adsorbed oxygen atoms are situated 0.6 ± 0.1 Å below the midpoint between two adjacent atoms in a 〈100〉 surface row. The results of the measurements of the ion impact desorption of adsorbed oxygen suggest a dominating contribution of sputtering processes. Ion focussing effects also contributes to the oxygen desorption. The ion induced and the spontaneous oxygen adsorption processes are studied using different experimental methods. Sticking probability values obtained during ion bombardment show a strong increase due to the ion bombardment.     

Synthesis and structure of nitrogenated tetrahedral amorphous carbon films prepared by nitrogen ion bombardment

The tetrahedral amorphous carbon (ta-C) films with more than 80% sp³ fraction firstly were deposited by filtered cathode vacuum arc (FCVA) technique. Then the energetic nitrogen (N) ion was used to bombard the ta-C films to fabricate nitrogenated tetrahedral amorphous carbon (ta-C:N) films. The composition and structure of the films were analyzed by visible Raman spectrum and X-ray photoelectron spectroscopy (XPS). The result shows that the bombardment of energetic nitrogen ions can induce the formation of CN bonds, the conversion of C-C bonds to CC bonds, and the increase of size of sp² cluster. The CN bonds are made of CN bonds and C-N bonds. The content of CN bonds increases with the increment of N ion bombardment energy, but the content of C-N bonds is inversely proportional to the increment of nitrogen ion energy. In addition, C≡N bonds are not existed in the films. By the investigation of AFM (atom force microscopy), the RMS (root mean square) of surface roughness of the ta-C film is about 0.21 nm. When the bombarding energy of N ion is 1000 eV, the RMS of surface roughness of the ta-C:N film decreases from 0.21 to 0.18 nm. But along with the increment of the N ion energy ranging from 1400 to 2200 eV again, the RMS of surface roughness of the ta-C:N film increases from 0.19 to 0.33 nm.     

Near-edge X-ray absorption fine-structure studies of GaN under low-energy nitrogen ion bombardment

The electronic structure of p-type GaN layers exposed to low-energy nitrogen ion bombardment was studied by near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy. It was found that ion bombardment lead to the creation of states lying below the nitrogen absorption edge which posses p-symmetry. These states are attributed to nitrogen interstitials with different local topologies created during ion bombardment. Furthermore, the NEXAFS spectra also shows the development of a strong -resonance above the absorption edge with increasing incident nitrogen ion energy. This peak is attributed to the formation of molecular nitrogen at interstitial positions, arising from a build up of nitrogen ions on these sites.     

Molecular dynamics simulation of bipartite bimetallic clusters under low-energy argon ion bombardment

The evolution of bipartite bimetallic atomic clusters within 5 ps under bombardment with monoenergetic argon ions at the initial energy ranging from 1 eV to 1.4 keV has been simulated by the classical molecular dynamics method with a target obtained from Ni?Al and Cu?Au clusters consisting of 78 and 390 atoms, equally divided between the corresponding monometallic parts, the simulated pairs of which have different heats of intermixing. The changes in the potential energy and temperature, the sputtering yields, and the intensity of the ion-stimulated movement of atoms at the interface of the monometallic parts of clusters of both sizes have been determined as functions of the energy of the bombardment.     

Investigation of the local atomic arrangement on surfaces using low-energy ion scattering

Ions with energies around 1 keV are well suited for detecting atoms on solid surfaces and for investigating their relative arrangement. This is due to the large scattering cross-sections which are of the order of 10^–2Ų/sr. The conceptually simple method is limited by the fact that interaction potentials and, more so, charge exchange processes are only approximately known. Progress in low-energy ion scattering has recently been made by applying special scattering geometries and by using alkali ions, in addition to noble gas ions.Among the successful applications there are studies of the arrangement of atomic layers on supported catalysts, ordered adsorption systems on metal surfaces, surface reconstruction, and surface disordering due to defects and thermal motion. Energy spectra of recoil atoms and ions convey additional information. The fundamental physical features of low-energy ion scattering are discussed on the basis of examples of recent results.     

Resistance changes in thin metallic films under ion bombardment

Resistance changes in thin films of copper, aluminium and bismuth have been studied under the bombardment of nitrogen, carbon and argon ions. Variations in resistance with implantation dose have been observed upto doses of ∼ 3 × 10¹⁷ ions/cm² for ion energies in the range 40 to 120 keV. The results are discussed in terms of desorption of gases from the film and a composite action of sputter removal of the film and its structural changes upon ion bombardment. A simple theoretical model is discussed which can qualitatively explain the experimental observations.