Optical properties of Al mirrors under impact of deuterium plasma ions in experiments simulating ITER conditions

The ion-induced modification of aluminum alloy mirrors, under bombardment by deuterium plasma ions has been investigated as a simulation of the environment effects on in-vessel mirrors in ITER. Ellipsometry and reflectrometry have been used to characterize the mirror surface, along with several surface diagnostic techniques (XPS, Auger, SIMS). The results of multiangular- and spectro-ellipsometry were analyzed using both a bare surface model, and effective medium model; the medium was composed of Al, Al₂O₃ (Al(OD)₃ or AlOOD), and voids. It was found that the reflectance decreases following exposure to keV-range ions, but can be restored by subsequent exposing the mirror to low-energy ions (∼60 eV). Chemical processes related to an increased oxide layer are thought to be responsible for the decrease in reflectance, while the reduction of the oxide layer following low-energy D⁺ exposure may lead to the return of high reflectance. By comparing the measurements with the results of modeling, a mechanism is suggested to explain the experimental data. The mechanism is based on: (1) chemical processes in a surface layer and (2) сhanges in the thickness and roughness of the surface layer.     

Molecular dynamics simulations of CH ions interaction with silicon carbide

In this study, we have simulated the CH⁺ ions bombardment on a Si-terminated 3C-SiC (0 0 1) surface using molecular dynamic simulations with a Tersoff-Brenner potentials. The results show that the sputtering yields of Si atoms is more than that of C atoms. With increasing incident energy the uptake of H atoms increases, while the uptake of C atoms decreases. In amorphous layer, a carbon-rich region is observed. In the films, the CH group and SiH group are dominant. Their fractions increase with increasing incident energy, and then decrease.     

Reactive sputtering of simple condensed gases by kev ions III: Kinetic energy distributions

Condensed gas layers of H₂O, NH₃ and CO at 15–20 K have been bombarded by 6 keV H⁺₂ and 3 keV He⁺ and Ar⁺ ions. Mass spectra of the neutral species sputtered from these layers have been measured. There is a substantial yield of products which originally were not in the target material, and which have thus been formed in chemical reactions induced by the ion bombardment. The relative yields of some of the products have been found to increase with decreasing incident ion mass. This is mainly attributed to the larger amount of energy deposited by electronic stopping in such situations. From CO a nonvolatile residue is left after ion irradiation. From a layer of H₂O frozen on top of the CO-residue H₂CO was detected.     

Angular distributions of Ni and Ti atoms sputtered from a NiTi alloy under He and Ar ion bombardment

The angular distributions of sputtered components were measured for NiTi polycrystalline alloy under 9 keV Ar⁺ and He⁺ ions bombardments with various fluences in ultrahigh vacuum. Combination of Rutherford Backscattering Spectrometry (RBS) and Auger Electron Spectrometry (AES) techniques allowed us to observe enhanced concentration of Ni over a layer with thickness comparable to a primary He⁺ ions penetration depth due to selective sputtering of Ti atoms and radiation-induced diffusion processes. A preferential emission of Ni atoms towards the surface normal was observed during bombardment by both He⁺ and Ar⁺ ions. More forward-peaked “over-cosine” angular distributions of sputtered Ni in comparison with those for Ti atoms have been measured. Nonstoichiometric sputtering of NiTi alloy dependent on emission angle was observed for bombardment fluence of He⁺ well below that needed for the steady-state altered layer formation. To explain the peculiarities of NiTi sputtering, an interpretation is discussed in terms of sputtering due to backscattered He⁺ ions.     

Reactive sputtering of simple condensed gases by keV ions II: Mass spectra

Condensed gas layers of H₂O, NH₃ and CO at 15–20 K have been bombarded by 6 keV H⁺₂ and 3 keV He⁺ and Ar⁺ ions. Mass spectra of the neutral species sputtered from these layers have been measured. There is a substantial yield of products which originally were not in the target material, and which have thus been formed in chemical reactions induced by the ion bombardment. The relative yields of some of the products have been found to increase with decreasing incident ion mass. This is mainly attributed to the larger amount of energy deposited by electronic stopping in such situations. From CO a nonvolatile residue is left after ion irradiation. From a layer of H₂O frozen on top of the CO-residue H₂CO was detected.     

Mechanism of swift chemical sputtering: Comparison of Be/C/W dimer bond breaking

Current and future tokamak-like fusion reactors include the three elements Be, C, and W as the plasma-facing materials. During reactor operation, also mixtures of all these elements will form. Hence it is important to understand the atom-level mechanisms of physical and chemical sputtering in these materials. We have previously shown that athermal low-energy sputtering of pure C and Be can be understood by the swift chemical sputtering mechanism, where an incoming H (or D or T) ion enters between two atoms and pushes them apart. In the current article, we examine the model system of D impacting on a single dimer to determine the detailed mechanism of bond breaking and its probability for the Be₂, C₂, W₂, WC, BeW, and BeC dimers. The results are found to correlate well with recent experiments and simulations of sputtering of the corresponding bulk materials during prolonged H isotope bombardment.     

Effect of Incident Energy and Foil Thickness on Foil Stripping and Scattering Efficiency in Charge Exchange Analyzer Detector

Compact neutral particle analyzer (CNPA) is used to measure ion temperature in tokamaks. Calculating of stripping efficiency and scattering efficiency are most important parameters affecting on CNPA performance. We studied the dependent of these parameters with the thickness of carbon foil and incident energy of neutral hydrogen atoms. In low carbon foil thickness variation of the carbon foil stripping efficiency (η_i) and scattering efficiency of the ions (η_sc) with incident energy is very salient. For foil thickness between 200 and 600 angestrom, scattering efficiency of the chamber will be smaller than 0.11.     

Study of surface activation of PET by low energy (keV) Ni and N ion implantation

Polyethyleneterephthalate (PET) has been modified by 100 keV Ni⁺ and N⁺ ions using metal ion from volatile compound (MIVOC) ion source to fluence ranging from 1 × 10¹⁴ to 1 × 10¹⁶ ions/cm². The increasing application of polymeric material in technological and scientific field has motivated the use of surface treatment to modify the physical and chemical properties of polymer surfaces. When a material is exposed to ionization radiation, it suffers damage leading to surface activation depending on the type. The surface morphology was observed by atomic force microscopy (AFM). That show the roughness increases with fluence in both the cases. The Ni particles as precipitation in PET were observed by cross-section transmission electron microscopy (XTEM). The optical band gap (E_g) deduced from absorption spectra; was calculated by Tau’c relation. Raman spectroscopy shows quantitatively the chemical nature at the damage caused by the Ni⁺ and N⁺ bombardment. The ration of I_D/I_G shows graphite-like structure is formed on the surface. A layer of hydrogenated amorphous carbon is formed on the surface, which has confirmed by XPS results also.     

Suppression of sputtering of nickel by coverage with self-sustaining thin segregated carbon layers

Sputtering of two-layered films composed of nickel (~5000 Å) and nickel carbide (~1500 Å) at 600° C by 5 keV Ar⁺ bombardment on the nickel side has been studied using Rutherford backscattering of 1.3 MeV H⁺ ions. It is found that the removal rate of nickel atoms from specimens is dependent on ion current density and that the removal rate of nickel atoms is very much smaller than that of carbon atoms when the ion current density is low. During ion bombardments at a low current density carbon segregation by a thickness of nearly two monolayers is observed at the nickel surface. Thus suppression of the removal rate of nickel atoms is ascribed to coverage of the nickel surface with segregated carbon atoms which are continuously supplied by diffusion through the nickel film from the carbide layer.     

The broadening of energy spectra of atoms scattered by a solid surface under molecular ion bombardment

The broadening of energy spectra of atoms scattered by a metal surface under molecular ion bombardment are calculated taking into account the molecular ions to suffer dissociative neutralization on the initial part of their scattering trajectory. The results of the calculations explain the experimental data for scattering of hydrogen atoms from aluminum, palladium and palladium covered by potassium surfaces under bombardment with H₂⁺.     

Atomic simulation of energetic fluorine interacting with Si(0 0 1)

In this study, Molecular dynamics simulations were performed to investigate F continuously bombarding silicon surfaces at normal incidence and room temperature. The simulated results show that with increasing incident energy and temperature, the etch yield of Si atoms increases, which is in good qualitative agreement with experiments. Accompanying reaching the steady-state F uptake and Si etching, a steady-state SiF_x (x = 1-4) reactive layer is formed whose thickness increases with increasing incident energy. In the reaction layer, SiF species are dominant and SiF₃ species decrease with increasing incident energy.     

Sputtering of GaAs under oblique Cs bombardment: A simulation study

Sputtering of GaAs under oblique 2–10 keV Cs ion bombardment is studied by means of computer simulation as applied to the experimental data by Verdeil et al. published recently. Special attention is given to the angular distribution of sputtered atoms in the steady-state limit and to the relevant concentrations of surface Ga and As atoms, S_Ga and S_As, respectively. The best-fit values of S_Ga and S_As found in simulations favor segregation of As. A very pronounced effect of resputtering of atoms deposited on a collector of sputtered matter is noted. For forecasting purposes, the sputtering of GaAs under oblique bombardment with 0.1–1 keV Cs ions is also shortly considered.     

关于Cu-Au合金溅射机制的研究

本文报道了用热中子活化法测量Cu-Au合金在80keV Ar~+离子不同剂量轰击下的部分溅射产额比S_Cu/S_Au,并用卢瑟福背散射(RBS)技术分析样品中元素的反冲以及表面层成分的相对变化,从而研究了元素择优溅射对表面层变化所起的作用。     

Sputtering of hydrocarbons by ion-induced breaking of chemical bonds

While the physical sputtering of atoms caused by keV and MeV ions has been studied extensively both by molecular dynamics (MD) simulation and experiments, the mechanisms leading to atom and molecule erosion at energies 1–100 eV are not very well understood. We now describe how low-energy hydrogen ions can cause erosion of carbon atoms and hydrocarbon molecules by entering the region of a carbon–carbon chemical bond and hence breaking it, a process we call ‘swift chemical sputtering'. In the particular case of hydrogen bombardment of carbon-based materials, we further show that this can lead to erosion yields far exceeding those expected for a physical sputtering process.     

Raman scattering and SEM studies of graphite and silicon carbide surfaces bombarded with energetic protons,deuterons and helium ions

Experimental investigations on the chemical and physical effects of 10–15 keV H₁⁺, D₁⁺ and He⁺ ion bombardments to fluences up to 10¹⁹ ions/cm² on graphite and SiC have been conducted using the techniques of Raman scattering and scanning electron microscopy (SEM). Raman scattering data for ion bombarded graphite reveal the formation of an amorphous surface layer as indicated by the appearance of a broad band in the spectrum centered at 1525 cm which replaces the bands due to microcrystalline carbon at 1585 cm^?1 and 1360 cm^?1. The microcrystalline structure could be partially restored upon vacuum annealing at 1040°C for several hours. A weak, broad band centered at 2150 cm also appears after bombardment which is indicative of the formation of ?C = C? bonds. Surfaces of “KT” SiC were also amorphized on ion bombardment as indicated by changes in the Raman spectra. Chemical trapping of the incident h₁⁺ and D₁⁺ ions to form bulk C-H, C-D and Si-H species was observed. Preferential sputtering of Si leaving a carbon rich surface region also occurred. Blister formation was observed in the SEM studies.     

Application of the thin layer activation technique to study surface erosion under high voltage electrical spark discharges

The thin layer activation technique using a heavy ion beam has been applied to measure the erosion loss of materials by electrical spark discharges with a discharge current in the mA range. Since the range of heavy ions such as ¹⁴N, ¹⁶O and ²⁰Ne, is about one order less than that of light ions such as p, d and α, the total activity can be generated within a narrow layer by activation with heavy ions. In the present work, a narrow layer of activity of ∼27 μm thickness was produced in copper-based materials by heavy ion induced nuclear reactions using 110 MeV ¹⁶O ions to measure the surface erosion in the range of hundreds of nanometers to few microns. The sensitivity can be enhanced to tens of nanometers using suitable heavy ions.     

Sputtering process of a silicon carbide surface with energetic ions by means of an AES-SIMS-FDS combined system

Surface phenomena on silicon carbide following interaction with energetic hydrogen ions and argon ions have been studied by means of simultaneous, in situ measurements with a combined system of AES-SIMS-FDS (Flash Desorption Spectroscopy). Bombardment by 0.7 and 1.5 keV argon ions was observed to sputter the surface atoms, both silicon and carbon, with the same sputtering yields. In the case of bombardment by hydrogen ions, on the other hand, silicon atoms were sputtered out preferentially through chemical sputtering to form silicon hydrides at room temperature. In-depth composition profiles of silicon carbide irradiated by 100-keV D⁺ ions were also examined by the combined system.     

Formation of complex Al–N–C layer in aluminium by successive carbon and nitrogen implantation

The results of Auger electron spectroscopy and transmission electron microscopy of the surface layer of aluminium after successive implantation by carbon and nitrogen ions are presented in this work. The energy of implanted ions is 40 keV. The implantation dose varies in the range (3.3–6.5) × 10¹⁷ ions/cm². The findings show that successive implantation leads to the formation of two main layers in aluminium. The first layer is AlNC_x (0 < x < 0.5) layer with violated hcp. AlN structure, where carbon atoms form bonds with nitrogen atoms. The second layer contains disoriented Al₄C₃ precipitates and carbon atoms migrated from the first layer. The mechanism of migration is discussed.     

Nano-scale modification of 2D surface structures exposed to 6 keV carbon ions: Experiment and modeling

In this work, a Si pitch grating with typical lateral dimensions of 200-250 nm was exposed to 6 keV C⁺ ions at normal incidence and at an angle of 42° both parallel and perpendicular to the grating structure. In contrast to volatile and recycling ions (like Ar⁺ or H⁺), non-recycling ions are able to modify the surface not only due to sputtering, but also due to implantation of incident ions and the re-deposition of projectile atoms following sputtering or reflection. The target-projectile combination used in this work is an example of such a system forming a mixed Si-C surface. The interaction between the ion beam and the surface has been studied both experimentally and numerically with the focus on validation of the numerical model of the newly developed SDTrimSP-2D code. SDTrimSP-2D is capable of following the evolution of the Si-C system including ion-surface interactions with 2D micro- and nano-structured surfaces. The SDTrimSP-2D code takes the interdependency of surface morphology, sputtering and implantation into account. The simulated surface morphology has been compared to cross-sections of bombarded Si pitch grating obtained by SEM, revealing good agreement between experiment and simulation. The calculations also provide improved insight into the mechanisms of surface modification by sputtering, implantation and material transport by redeposition.     

Oxygen depth profiling in Kr-implanted polycrystalline alpha titanium by means of O(α,α)O resonance scattering

The ¹⁶O(α,α)¹⁶O resonance scattering was applied to study the effects of ion implantation on the oxygen distribution in the near surface region of polycrystalline titanium implanted with 180 keV krypton ions at fluences, ranging between 1 × 10¹⁴ and 5 × 10¹⁵ Kr⁺/cm². Two sample sets were chosen: as-received polycrystalline titanium discs rolled and annealed in half-hard condition which had a thick oxygen layer and similar samples in which this surface layer was removed by polishing. An increase of the mean oxygen concentration observed in both unpolished and polished samples at low fluence suggests a knock-on implantation of surface oxygen atoms. At high fluence, an overall decrease in the mean oxygen concentration and mean oxygen depth suggests an out-diffusion of near-surface oxygen atoms.