Effect of temperature on the physical sputtering of highly oriented pyrolytic graphite

The results of experimentally investigating the sputtering and erosion of the basal plane of highly oriented pyrographite UPV-1T under irradiation with 30-keV Ar⁺ in the range from room temperature to 400°C are presented. It has been found that ion-induced surface-relief evolution at higher temperatures results in a two-fold increase in the sputtering yield (Y = 2) in comparison with sputtering of a surface with a nanosized relief at temperatures less than that of the texture transition T _t ≈ 150°C. Sputtering simulation using the OKSANA code for a surface with a sinusoidal nanorelief, which reflects the instability of the basal plane of UPV-1T under ion irradiation, permits to estimate the ratio of the amplitude to the relief period at T < T _t.     

Study of ion-induced crimping of carbon composite fibers

The crystal structure and morphology of the KUP-VM (1D) carbon-carbon fiber composite are investigated upon irradiation with 15- and 30-keV Ne⁺ ions with high fluences (10¹⁸?C10¹⁹ ion/cm²) with the purpose of studying fiber crimping. The results are compared with data obtained previously for N ₂ ⁺ and Ar⁺ ion irradiation. It is assumed that the formation of regular prismatic topographic elements (crimps) at temperatures near and above the dynamic annealing temperature T _a reflects the highly ordered structure of the fiber??s surface shell. The results obtained are discussed within the Bradley-Harper theory.     

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.     

Several features of the Ar<Superscript>+</Superscript>-ion irradiation of vanadium and its alloys

Changes in the surface properties of vanadium and its alloys irradiated by Ar⁺ ions with the energy 20 keV, to a dose of 10²² m⁻² at T _irr ≈ 700K have been studied. The radiation effect consists of material surface hardening, increasing the lattice parameters of the irradiated samples, and radiation erosion of the surface layers in the form of flaking. Features of radiation damage to the material’s surface irradiated by gas ions with high sputtering coefficients are discussed.     

Study of carbon material surface layers modified by nitrogen and argon ion irradiation

We present the results of the study of the elemental composition and defects of the electronic structure of the surface layer modified by high-dose irradiation (10¹⁸–10¹⁹ ion/cm²) of highly oriented pyrolytic graphite (UPV-1T) by 30-keV N ₂ ⁺ and Ar⁺ ions in the temperature range from 180 to 400°C. The EPR spectra observed during irradiation with argon ions at high temperatures and with nitrogen ions at temperatures near the liquid-nitrogen temperature T = 77 K exhibit anomalously narrow lines which probably result from the exchange interaction inside paramagnetic clusters of displaced carbon atoms. During nitrogen ion irradiation at room and higher temperatures, paramagnetic defects typical of many carbon materials (single EPR lines with g = 2.0027–2.0029) and belonging to carbon atoms bound to one or three nitrogen atoms were detected.     

Temperature dependences of the ion-electron emission of glassy carbons under 30-keV argon ion irradiation

The temperature dependences (?200°C < T ≤ 350°C) of the ion-induced electron emission yield γ and the structures of modified surface layers have been studied experimentally for SU-850, SU-1000, SU-1300, SU-2000, and SU-2500 glassy carbons under high-dose 30-keV Ar⁺ and N ₂ ⁺ ion irradiation. Glassy carbons manufactured using a relatively high heat-treatment temperature T _ht exhibit a stepwise increase in the electron yield at certain annealing temperatures T _a. The same behavior is observed for graphitized carbon materials. For low-temperature glassy carbons, the electron yield exhibits a monotonic increase with increasing irradiation temperature. The observed differences are related to the occurrence of different structural types of fullerene-like nanoparticles in the low-and high-temperature glassy carbons.     

Field ion and scanning tunnel microscopy studies of surface and bulk defects in carbon and silicon

Complex study of surface and bulk defects was performed by field ion and scanning tunnel microscopy. Specimens were irradiated by 20-to 50-keV He⁺, Ar⁺, and Bi⁺ ions at room temperature. The irradiation fluences were between 10¹⁸ and 10²⁰ ion m⁻². Calculated parameters of depletion zones and atomic displacement cascades were compared with theoretical estimates. It was shown that controlled ion bombardment of material surface is an effective tool for fabricating field-emission cathodes for vacuum microelectronics.     

Effect of the dose and energy of Ar+ ions on the surface properties of vanadium and its alloys

The features of processes occurring on the surface of vanadium and its alloys irradiated using the ILU ion-beam accelerator with Ar⁺ ions at an energy of 20 and 40 keV up to doses of 5.0 × 10²¹ m^?2 and 1.0 × 10²² m^?2 at T _irr ≈ 700 K are studied. The effect of the dose and energy of implanted ions on the surface hardness is obtained. The thickness of the hardened layer is more than two orders of magnitude higher than the theoretical and experimental projected range of Ar⁺ ions at an energy of 20 and 40 keV in vanadium. Structural changes in the surface layers, which are expressed in a change in the intensity of reflections from a number of planes and an increase in the crystal-lattice parameter of the irradiated materials, are also observed.     

Influence of some additional elements on the surface tension of copper at intermediate and high temperatures

The influence of some additional elements on the surface tension of copper at intermediate and high temperatures was measured. In the intermediate temperature range (~0.4 T_m) the voids annealing technique was used with thoroughly outgassed copper samples, implanted with He, O₂, S and Kr before irradiation with 500 keV Cu⁺ ions, in the swelling peak temperature region. In the high temperature range (~0.9 T_m) the zero creep rate technique was used to check the influence of environmental He and Si on the surface tension of bamboo-structure wires. These experiments were made with a versatile and original device which allows the strain variations to be followed through those of the electrical resistance at constant volume.     

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.     

Low energy Ar-ion bombardment effects on the CeO2 surface

The structure and electronic properties of epitaxial grown CeO₂(1 1 1) thin films before and after Ar⁺ bombardment have been comprehensively studied with synchrotron radiation photoemission spectroscopy (SRPES). Ar⁺ bombardment of the surface causes a new emission appearing at 1.6 eV above the Fermi edge which is related to the localized Ce 4f¹ orbital in the reduced oxidation state Ce³⁺. Under the condition of the energy of Ar ions being 1 keV and a constant current density of 0.5 μA/cm², the intensity of the reduced state Ce³⁺ increases with increasing time of sputtering and reaches a constant value after 15 min sputtering, which corresponds to the surface being exposed to 2.8 × 10¹⁵ ions/cm². The reduction of CeO₂ is attributed to a preferential sputtering of oxygen from the surface. As a result, Ar⁺ bombardment leads to a gradual buildup of an, approximately 0.69 nm thick, sputtering altered layer. Our studies have demonstrated that Ar⁺ bombardment is an effective method for reducing CeO₂ to CeO_2−x and the degree of the reduction is related to the energy and amount of Ar ions been exposed to the CeO₂ surface.     

Graphitization of a Polycrystalline Diamond under High-Fluence Irradiation with Noble Gas and Nitrogen Ions

To analyze the process of the ion-induced graphitization of a polycrystalline diamond, the surfacelayer conductivity and microstructure are studied experimentally after high-fluence irradiation with Ne⁺, Ar⁺, N⁺, and ions with energies of 20–30 keV at irradiation and heat-treatment temperatures ranging from 30 to 720°R in vacuum. After irradiation with argon ions at room temperature and subsequent heat treatment, the resistivity ? of a modified layer decreases exponentially with increasing treatment temperature T _ht and reaches the graphite value ? at Tht = 700°R. Such a temperature T _ht is insufficient for surface-layer graphitization by nitrogen ions. The increase in the diamond temperature under irradiation leads to a decrease in the ion-induced thermal graphitization temperature T _g by several hundred degrees. It is found that the temperature T _g is almost coincident with the corresponding temperature T_a of the dynamic annealing of radiation-induced damage in graphite. Analysis of the irradiated layer using Raman spectroscopy reveals the heterogeneous structure of the modified layer containing graphite and amorphous phases, the ratio between which correlates with the layer resistivity. Under argon-ion irradiation at diamond temperatures of 500°R or more, an increase in ? of the irradiated layer is observed, which is related to the formation of nanocrystalline graphite. This effect is not observed under nitrogen-ion irradiation.     

Spectroscopic study of plasmons in ion-irradiated single-walled carbon nanotubes

The electronic structure of single-walled carbon nanotubes was experimentally investigated using x-ray photoelectron spectroscopy, reflection electron energy-loss spectroscopy, and Auger electron spectroscopy. A shake-up satellite structure observed near the C 1s core-level lines in the x-ray photoelectron spectra at high binding energies in the range 284–330 eV due to excitation of π and π + σ plasmons was studied. The effect of irradiation by 1-keV argon ions on the shape of the spectra was analyzed. The shape of the C 1s satellite spectra was found to be sensitive to Ar⁺ irradiation in the electron energy loss range 10–40 eV corresponding to excitation of π + σ plasmons. Auger spectroscopy revealed the presence of argon on the surface of ion-irradiated samples. The argon content increased to ～4 at. % with increasing irradiation dose. An analysis of the results obtained and their comparison with the data available in the literature led to a qualitative conclusion that the bond angles of the carbon atoms making up the walls of single-walled carbon nanotubes are distorted at sites exposed to Ar⁺ irradiation.     

A new technique for the measurement of sputtering yields

We have measured the yields of 90 keV ⁴⁰Ar⁺ and V⁴He⁺ sputtering of Mo and V samples by the use of a new radio-tracer technique. This technique involves activating the samples by high-energy charged-particle irradiation before sputtering, and using conventional γ-ray counting methods to analyze the material subsequently sputtered onto collector foils. We have also measured angular distributions of the sputtered material, and compared these results and our total sputtering yields with the predictions of Sigmund's sputtering theory. Further comparisons between our radiotracer results and those obtained for ⁴⁰Ar⁺ sputtering of unactivated Mo and V samples, determined from elastic backscattering measurements using 12 MeV ¹⁶O ions, show that the techniques give consistent results.     

On the chemical sputtering of oxygen-exposed molybdenum

The sputtering of oxygen-exposed molybdenum was studied by means of mass analysis of emitted neutral and charged particles. The irradiation was performed with 8 keV Ar⁺ ions at temperatures of 25° and 485°C. It was found that the enhanced sputtering yield at elevated temperature during oxygen exposure is due to beam-induced desorption of MoO₂ and cascade sputtering of MoO. At this temperature considerable oxygen incorporation also takes place owing to recoil mixing and diffusion.EURATOM Association     

Variation of the ion dynamics parameter in stark-broadened helium lines

Stark broadening of quasidegenerate He lines at λ = 447 nm and 492 nm hasbeen investigated at low electron densities (N_e = 10²¹ and 3 x 10²¹ m^-3). The perturber mass was varied by using H⁺, He⁺ and Ar⁺ ions. Variation of the parameter (T₀/μ)^1/2 by a factor of 3 is accompanied by marked ion-dynamical effects in the forbidden component. The results are compared with calculations according to the unified theory and the model microfield method. Characteristic deviations are observed and critically discussed.     

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.     

Anisotropy of secondary ion emission from a Ni4Mo single crystal

The azimuthal and polar angle distribution of Ni⁺ and Mo⁺ ions emitted from an ordered Ni⁴ Mo single crystal irradiated with 10-keV Ar⁺ ions was studied. Different azimuthal distributions for Ni⁺ and Mo⁺ ions emitted from the (001) Ni₄Mo face were detected; emission maxima were observed in 〈 011 〉 and 〈 001 〉 directions for Ni⁺ and Mo⁺ ions, respectively. It was shown that polar distributions of nickel’s secondary ions vary with its energy. The observed systematic features were explained by correlated collisions in the upper layers of a Ni₄Mo single crystal.     

Sputtering characteristics of fullerene C60 films under bombardment with 0.1–1-keV argon ions and atoms

The sputtering of fullerene C₆₀ films under bombardment with Ar⁺ ions was studied. In thin films, blistering effects related to diffusion of the implanted argon ions along the layer and substrate interface have been found to occur. A threshold behavior was observed for sputtering at ion energies around 0.2 keV, which is much higher than in graphites. It has been shown that dependence of the work function on ion energy can be described in the framework of Zigmund-Falcone’s approximation, which takes into account anisotropic effects in cascade collisions, and with Yudin’s approximation for the sputtering of elemental materials. The obtained surface binding energy for fullerenes is U _s?6.7 eV, which is less than the value for graphites, U _{s graph}=7.7 eV.     

Origin of grey spots on the surface of metallic glasses under Ar ion irradiation: The surface and volume properties

The nature of grey spots on the surface of amorphous Fe₆₇Cr₁₈B₁₅ metglass ribbons irradiated by 30 keV Ar⁺ ions is investigated. Changes in the surface and volume properties of samples are analyzed bearing in mind the presence of competitive processes of ordering and disordering in the structure under irradiation at initial stage of crystallization (T = 500 °C). Changes in the volume properties of the samples become apparent in their structure, electrical and magnetic properties and are caused by radiation-enhanced diffusion at high gradients in the concentration of defects generated by Ar⁺ irradiation. It is established that grey spots are shown by decrease in the reflection coefficient in a visible range. They emerge as a result of reorganization in the electronic structure of irradiated ribbons due to damage in the short-range order and formation of non-uniformly scaled atomic structure during transition from the medium-range to the long-range atomic order. Experimental data are in accord with the calculations in the framework of the free electrons model.