N. N. Andrianova

Erosion of Carbon-Based Materials Under High-Fluence Heavy-Ion Irradiation

Carbon-based materials are widely used in aerospace industry due to their strength, heat shielding properties, and a number of other specific characteristics [1]. To trace the radiation damage influence on the erosion regularities the sputtering yields Y of highly-oriented pyrolytic graphite (HOPG), polycrystalline graphites and one-dimensional composite material under high-fluence (10 – 10 ion/cm) 30 keV N2 and Ar ions at the incidence angles from θ = 0 (normal incidence) to θ = 80, developed morphology and crystalline phase state from low temperatures (T ~ −180C) till elevated ones (T ~ 400C) have been studied. At normal and near normal ion incidence Reflection High Energy Electron Diffraction has shown that diffraction patterns correspond to a high degree of disorder (diffuse halo) at the temperatures less the defect annealing temperature Ta. At elevated temperatures (T > Ta) the patterns have been found similar to those for the non-irradiated surfaces. It has been found that Ta is easy determined by a step-like behavior of a temperature dependence of ion-electron emission yield γ. This γ-jump has been explained by the dependence of secondary electron path length λ on changes in lattice structure (transition from strongly disordered surface layer under ion irradiation at T Ta) [2]. The Y(θ) dependences measured at T Ta, due to the ion-induced diffusion processes, causing three-fold suppression of sputtering in comparison with irradiation at T < Ta. The Ar irradiation at the room temperature results to strong sputtering suppressing in comparison with the isotropic polycrystalline graphites at the same conditions.

Sputtering of highly oriented pyrolytic graphite with 30 keV Argon ions

The influence of the incidence angle of 30 keV Ar+ ions, ion fluence and target temperature on the sputtering yield and surface microgeometry of highly oriented pyrolytic graphite (UPV-1T) samples was experimentally studied. It was found that at fluences more than 5 × 1019 ion cm−2 the sputtering yield at room temperature in the range of the ion incidence angle from 0° to 80° is twice as small as the corresponding experimental data for both polycrystalline graphite and glassy carbon. The analysis of ion-induced relief permits us to suppose the topographical suppression mechanism of highly oriented pyrolytic graphite sputtering.

Regularities of Ion-Electron Emission of One-Dimensional Carbon-Based Composite Material

The temperature dependences of the ion-electron emission yield γ(T), the crystal structure, and morphology of a surface layer of a carbon-based KUP-VM composite material under high-dose irradiation with N2+ 30 keV ions have been investigated. The complex two-stage nature of the dependence γ(T) is caused by the processes of dynamic annealing of radiation damage in structural components of a composite material.

High-fluence ion-beam modification of a diamond surface at high temperature

The results of experimental investigation into modification of the (111) face of a synthetic diamond crystal under high-fluence 30-keV Ar+ irradiation are presented. It is found that irradiation at a temperature of 400°C leads to the formation of a conductive surface layer, which is detected in the Raman spectra as a broad band with a maximum close to the position characteristic of the G peak of graphite at 1580 cm−1. In addition, the intensity of the narrow peak of diamond at 1332 cm−1 decreases by an order of magnitude. Ion irradiation is accompanied by the suppression of the initial photoluminescence and gives rise to weak photoluminescence with a spectrum characteristic of gem diamonds.

Graphitization of a diamond surface upon high-dose ion bombardment

Results from structural and morphological studies, measurements of the sheet electrical resistance, and estimating resistivity ρm of a graphite-like conducting surface layer formed upon high-dose irradiation of the (111) face of a synthetic diamond with Ar+ ions at an energy of 30 keV and a target temperature of 400°C are presented. It is found that the orienting effect of the diamond lattice is visible in the suppression of the formation of graphite crystallites with axis c perpendicular to the surface. The thickness of the modified layer is 40–50 nm, and its sheet resistance is 0.5 kΩ/sq. Resistivity ρm = 20–25 μΩ m of the modified layer lies within the range of ρ values of graphite and glassy carbon materials.

Study of the radiation resistance of a carbon fiber based on viscose in carbon-carbon and carbon-ceramic composites

The results of the experimental study of the crystalline structure and morphology of carbon fibers based on viscose in a FEBUS carbon-ceramic composite and its preform as functions of temperature ranging from room values to ∼400°C under irradiation with Ar+ ions with an energy of 10–30 keV are obtained. The average level of radiation damage corresponding to the initial fiber graphitization (〈νgr> ∼ 80 dpa) is determined based on an analysis of the energy dependences of the ion-electron emission coefficient at different irradiation temperatures. It is shown that carbon fibers based on viscose are immune (in contrast to polyacrylonitrile fibers) to ion-induced destruction in the form of crimping. This is indicative of their enhanced radiation resistance.

Ion-beam erosion of carbon fibers of the composites

The results of experimental studies of the structural and morphological changes of the surface of carbon PAN fibers of a carbon-carbon KUP-VM (1D) composite as a result of high-dose irradiation (1018–1019 ion/cm2) with Ne+ and Ar+ ions with an energy of 10–30 keV are presented. The threshold values of radiation damage, resulting in an amorphization of the PAN carbon fibers at room temperature and ion-induced crimping at temperatures greater than the annealing temperature of the radiation damage, are determined.

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 (1018–1019 ion/cm2) with the purpose of studying fiber crimping. The results are compared with data obtained previously for N2+ 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 Ta reflects the highly ordered structure of the fiber’s surface shell. The results obtained are discussed within the Bradley-Harper theory.

Effect of high-fluence ion irradiation on Raman scattering in glassy carbon

The results of an experimental study of the structural and morphological changes in the surface layer of SU-2500 glassy carbon due to high-dose 30 keV Ar+ ion irradiation in the temperature range of 60–400°C are presented and discussed. The given study is performed via the Raman scattering (RS) of laser radiation with the wavelengths 514 and 244 nm. Data analysis makes it possible to identify the nanocrystalline state of the surface layer at irradiation temperatures of 140–250°C and its amorphisized and polycrystalline states at room and elevated temperatures, respectively. The D peak of RS spectra is not observed at λL = 244 nm. It is demonstrated that ion bombardment leads to appreciable suppression of the G peak and can be used to reveal ion-induced states in carbon materials.

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 Tt ≈ 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 < Tt.