Graphite surface erosion by 100 keV helium and hydrogen bombardment

Surface erosion in pyrolytic graphite by 100 keV ⁴He⁺ and 200 keV H⁺₂ ion bombardment has been observed by scanning electron microscopy. The particle fluence ranged from 1 × 10¹⁷ to 5 × 10¹⁸ particles/cm². Although the surface is eroded at 1 × 10¹⁷ particles/cm² in helium bombardment, it is not eroded so heavily even at 5 × 10¹⁷ particles/cm² in hydrogen bombardment. In helium bombardment flaking is significantly observed at 1 × 10¹⁸ particles/cm², and a cone structure appears at 5 × 10¹⁸ particles/cm², which is produced after the first cover flakes off completely. In hydrogen bombardment at 1 × 10¹⁸ particles/cm², many circular blisters are formed which are sputtered off at 5 × 10¹⁸ particles/cm². The surface roughness of the target also affects the erosion.     

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.     

Sputtering of silicon carbide coatings by low-energy hydrogen ions

Various types of silicon carbide coatings made by reactive ion-plating have been bombarded with a 3.0 keV H⁺₃ ion beam at temperatures around 500°C. The sputtering yield in stoichiometric samples (i.e. Si : C = 1 : 1) at 500°C was $\text{1.15 × 10}{}^{\mathrm{?2}}$ atoms/H⁺. As the stoichiometry deviates from this point, the sputtering yield has larger values. The temperature dependence of the sputtering yield in stoichiometric samples was negligible below 600°C. No surface topography changes occurred in stoichiometric samples even at a high fluence of $\text{2 × 10}{}^{20}\text{H}{}^{\mathrm{+}}\text{/cm}{}^2$, while severe erosion took place in non-stoichiometric samples. By Auger electron spectroscopy (AES), carbon exists on the surface in the form of carbide in stoichiometric SiC before and after bombardment, while it exists in the form of graphite in carbon rich samples, which suggests that the bound state of carbon in the form of carbide should correspond to the low sputtering yield in stoichiometric SiC coatings. The surface stoichiometry changes due to hydrogen bombardment were observed by AES, where the carbon population increases in stoichiometric SiC, while it decreases in carbon rich samples, which was supported as well by the results from electron probe X-ray microanalysis.     

Erosion yield of Ti from TiC-deposited graphite by hydrogen ion bombardment at high temperatures

Erosion yields of Ti atoms from a TiC-deposited graphite by bombardment with 1 keV hydrogen ion beam of various current densities at 900°C have been investigated by means of the Rutherford backscattering (RBS) technique. It has been observed that the sputtering yields for Ti atoms at 900°C are almost zero below a critical ion flux of 1 × 10¹⁵/cm²·s, compared with the sputtering yield of Ti atoms at room temperature which has been measured to be 1 × 10⁻²atoms/ion. No sputtering of Ti atoms observed at 900°C is explained in terms of self-sustaining coating of the TiC surface with segregated carbon layer. The condition for the self-sustaining coating is discussed.     

Blistering of niobium due to 0.5 to 9 keV helium and hydrogen bombardment

Blistering of well-annealed niobium single crystals due to 0.5 to 9 keV helium and hydrogen ion bombardment at temperatures between ?110°C and 1000°C has been investigated by Rutherford backscattering (RIBS) in double alignment and with a scanning electron microscope (SEM). For He bombardment blistering was observed by RIBS in the temperature range investigated for all energies above 1 keV. The critical dose at which blisters first appear is about 1 to 2 × 10¹⁷ incident He ions per cm². It increases slightly with increasing ion energy and with decreasing target temperature. Blisters of 500 to 5000 Å in diameter were found. The depth at which the blisters develop increases from ≈ 180 Å for 1 keV to 1100 Å for 9 keV He ions. It is a factor of ≈ 3 larger than the theoretical mean range of the ions in amorphous material. Above ≈ 600°C grain boundaries develop extending also into the unbombarded region. For hydrogen bombardment no blistering could be observed at room temperature up to doses of 2 × 10¹⁹ ions per cm².     

Ion mass effects on bombardment-induced disordering of γ'-Ni3Si

The kinetics of disordering of the ordered compound γ'-Ni₃Si during ion bombardment were investigated at a temperature of 270°C. The disordering followed first order kinetics and the rate constant was measured as a function of incident ion flux, ion energy, and ion mass. The rate constant varied approximately in direct proportion with the ion flux during bombardment with 1 MeV ⁸⁴Kr⁺-ions: from ~ 0.28 min ^?1 at ~ 70 nA/cm² to ~ 50 min ^?1 at ~ 4.4 μA/cm ². During bombardment with a flux of $\text{~ 1 μA}\text{cm}{}^2$ of ¹³²Xe⁺-ions, the rate constant was directly proportional to the calculated near-surface damage ra te. It varied from ~ 50 min ^?1 for 200 KeV ions with calculated damage rates of ~ 2.3 × 10^?1 dpa to ~ 1.8 min ^?1 for 3 MeV ions with damage rates of 2 × 10^?3dpa/s. The disordering rate was also observed to be directly proportional to the near surface damage rate for heavier mass ions (⁴⁰Ar⁺, ⁸⁴Kr⁺ and ¹³²Xe⁺); the ratio of disordering rate to damage rate was ~ 17. This ratio dropped to ~ 3 for ²⁰Ne⁺-ion bombardment, and to ~ 0.4 for bombardment with ⁴He⁺-ions. The decrease in the ratio with decreasing mass is discussed in terms of cascade size, replacement-to-displacement ratio, and random recombination.     

Corrosion Resistance Modification of AISI 304 Stainless Steel Using Argon Ion Bombardment

Ion implantation has been widely used as a surface modification technique to improve surface properties. In this work, argon ions of 30 keV energy have been implanted into AISI 304 stainless steel at different fluences ranging from 3 × 10¹⁷ to 1 × 10¹⁸ Ar⁺/cm². The surface bombardment with inert gases mainly produces structural changes and modify topography and morphology of the surface. The AFM analysis of implanted samples clearly shows significant change in surface. In order to evaluate the effect of the ion bombardment on the corrosion behavior, potentiodynamic tests were performed. The results show that the corrosion resistance of the samples strongly depends on the implantation fluences.     

The effects of gas transport properties on blister formation in He+-implanted glass

Blister formation in He⁺-implanted glasses is correlated with the measured helium gas diffusivity. A scries of glasses with diffusivities from ～3 × 10^?7 to ～5 × 10^?12cm²sec^?1 was implanted under nearly identical conditions with 150 keV He⁺ ions at a flux of 15 μA cm^?2 and a nominal sample temperature of 110°C. Glasses with D less than ～1 × 10^?9cm²sec^?1 were fully blistered, whereas those with D greater than ～3 × 10^?8cm²sec^?1 showed no surface deformation. Glasses with diffusivities between ～3 × 10^?8 and ～1 × 10^?9cm²sec^?1 had local regions with low density coverage of relatively large blisters. The critical concentration of implanted helium, estimated by comparing experimental data with results from a simple theoretical model, is ^{～1 × 1019 cm?3}, consistent with high pressure solubility measurements. Reemission data at low fluence are qualitatively in agreement with analytical calculations. Implications for CTR technology are discussed.     

Effect of CH<Subscript>4</Subscript> Ion Implantation in Pure Aluminium

In this paper, aluminium samples with 99.96% purity were exposed to ion beam, extracted from CH₄ plasma. Implantation of ions were performed for 50 keV energy and various doses ranging from 1 × 10¹⁷ to 6 × 10¹⁷ ions/cm². Morphology of surfaces, roughness and its evolution during variation of ion dose has been studied by atomic force microscopy (AFM). Microstructure of the modified surfaces after ion implantation has been obtained by X-ray diffraction technique and Raman spectroscopy. Formation of aluminium carbide (Al₄C₃) was confirmed by XRD results at implantation doses of 3 × 10¹⁷ and 6 × 10¹⁷ ions/cm². In addition, it was observed that when the ion dose is increased, orientation of aluminium planes change from (2 2 0) to (2 0 0). Corrosion test was performed and compared for implanted and un-implanted samples. The results showed that corrosion resistivity increase by accumulation of ion dose.     

Two types of MeV ion beam enhanced adhesion for Au films in SiO2

The ion beam-enhanced adhesion of thin Au films on vitreous silica sus studied for a wide range of Cl ion beam doses for beam energies between 6.5 MeV and 21.0 MeV. Since the residual adhesion of Au on SiO₂ is low, the improved adhesion can be easily seen using the Scotch Tape Test. The threshold in the enhanced adhesion corresponding to passing the tape test occurs at two different dose ranges for a given energy; one at very low dose centered around 1 × 10¹³ /cm², the other at higher doses with a threshold of around 1.5 × 10¹⁴ /cm² (depending upon the beam energy). At low doses (2 × 10¹² to 5 × 10¹³ /cm²) surface cracks occur on the SiO₂ substrates, these cracks close up at doses higher than 5 × 10¹³ /cm². A possible explanation of enhanced adhesion in the low dose range is associated with the surface crazing of the SiO₂ substrate. To make the adhesion test more quantitative, a scratch test was also used on the samples.     

Matrix effects in SIMS analysis of high-dose boron implanted silicon wafers

Secondary ion emission from ¹¹B⁺ implanted silicon wafers with dose of 1 × 10¹²−5 × 10¹⁶ cm⁻² has been investigated. Experiments were performed using O₂⁺ primary ions with an impact energy of 8.0 keV and an incident angle of 39° from the surface normal. The emission of ¹¹B⁺ is enhanced and ²⁸Si⁺ is suppressed at the peak region of boron profile for the high-dose sample, such as at doses ⩾ 5 × 10¹⁵ cm⁻² (peak concentration ∼5 × 10²⁰ cm⁻³). The secondary ion energy distribution of ¹¹B⁺ is broadened and ²⁸Si⁺ is sharpened with increasing the boron concentration. The mechanisms of these phenomena are also considered.     

Effect of fast-neutron irradiation on mechanical properties of stainless steels: AISI types 304, 316 and 347

The effect of low-temperature (< 100° C) fast-neutron irradiation on the room-temperature tensile and hardness properties of stainless steels, AISI Types 304, 316, and 347, was investigated up to a fluence of 1.43 × 10²⁰ n/cm² (E > 1 MeV). Several methods were used for analysis of results and the approach using the irradiation-induced increase in yield stress, Δσ = σ ? σ, where σ_i and σ are the yield stresses of irradiated and unirradiated specimens, respectively, proved to be the best for describing irradiation-hardening. Below saturation fluence, ≈ 4?5 X 10¹⁹n/cm² (E > 1 MeV), it was shown that $\text{Δσ ∝(øt)}\text{1}\text{2}$ in agreement with Seeger's model. Yield points were observed at a fluence of _{1.3 × 10¹⁹ n/cm²} (E > 1 MeV) and above. The results are discussed in relation to transmission electron microscopy results of irradiated materials. The relation between irradiation-induced changes in yield stress and Vickers hardness was described by ΔH = KΔσ, where K = 2.82 for AISI Type 304, and 3 for both AISI Type 316 and AISI Type 347.     

Low-energy helium implantation of aluminum

A series of 20 keV He⁺ implantations was conducted on well-annealed MARZ grade aluminum at fluxes of 6 × 10¹⁴ and 8 × 10¹³He⁺/cm² sec. Three distinct, temperature dependent He release mechanisms were found by He re-emission measurements during implantation, and by subsequent SEM and TEM investigations. At 0.08 of the melting temperature (T_m) gas re-emission rose smoothly after a critical dose of 3 × 10¹⁷He⁺/cm², with extensive blistering. The intermediate temperature range (~0.3 T_m) was characterized by repeated flake exfoliation and bursts of He after a dose of 3 × 10¹⁷He⁺/cm². Rapid He evolution, with hole formation, was found above 0.7 T_m. No significant differences in either gas re-emission or surface deformation were found between the two fluxes employed.     

Helium irradiation of Ni-(Zr or Nb) metallic glasses: Blistering,flaking and bubble formation

NiZr and NiNb are potential metallic glasses for nuclear applications. We have studied blistering, flaking and bubble formation in Ni₆₄Zr₃₆, Ni₃₃Zr₆₇ and Ni₆₀Nb₄₀ glasses under helium ion bombardment at room temperature. The effect of projectile energy (50–150 keV), total dose (0.01–10 × 10¹⁸ ions/cm²), dose rate (10–100 μA/cm²) and thermal crystallization on critical dose for blistering and/or flaking, average blister diameter and development of surface topography was examined. The surface damage effects in metallic glasses were in general similar to those for crystalline materials with the notable exception that the critical dose values are higher by about 50–100% for metallic glasses. TEM investigations revealed irradiation induced partial crystallization of Ni₃₃Zr₆₇ glass. Metallic glasses Ni₆₄Zr₃₆ and Ni₆₀Nb₄₀ were stable under helium irradiation and have also shown very high resistance against blistering and/or flaking. The possible mechanisms of helium trapping in metallic glasses are also discussed.     

Estimation de I'Influence du Mode d'Écoulement du Gaz sur le Facteur de Séparation d'une Colonne de Diffusion Thermique

The transport equation relevant to the heavier of two elements forming a gaseous mixture was derived from the following equations.

Heat balance:d ² T/dr ²+(l/r)·(dT/dr))= 0

Material balance:d ² v ₂+(l/r)·=α·(T-T _c)

Diffusion equation concerning the heavier element: σ(rJ _c)/σz+σ(rJ _DZ )σz+σ(rJ _DR)/σrσ(rJ _TD)/σr=0

Concentration of the heavier element in the radial direction: C ₁(r,z)=C₁+(R _i,Z)+(r-R i)K ₁.

The transport equation thus derived became that of Jones & Furry when the smaller terms were neglected.

The influence on the separation factor brought by the axial gas velocityv _i along the hot wire surface was then analyzed. The results were as follows:

The maximum separation factor displaces toward lower operating pressures when the gas velocity v _i is increased to a certain degree. It would appear from the present calculation that to obtain maximum separation, lower operating pressures should be combined with higher gas velocity v _i, while with increasing operating pressure, v _i should have to be gradually reduced, finally to reach zero at a certain pressure.     

Light ion bombardment sputtering,stress buildup,and enhanced surface contamination

Several effects of high fluence light ion bombardment which are relevant to fusion reactor inner wall problems are under investigation. The impurity loading and lateral stress from high fluence ion bombardments can alter sputtering yields markedly. This is demonstrated with sputtering measurements of 45 keV Kr incident upon Au. Sputtering yields for 150 keV⁴ He onto Au are presented for two different background hydrocarbon partial pressures during bombardment. It is shown that there is a polymerized hydrocarbon buildup on the surface for hydrocarbon partial pressures greater than $\text{1 × 10}{}^{\mathrm{?10}}\text{mm Hg}$ even for ion current densities ranging as high as 4 μA/cm²; true sputtering of the Au has been observed only for lower hydrocarbon partial pressures. Additional effects of oxidizing background gases on sputtering measurements of reactive metals are discussed.It is concluded that the background gas partial pressures, temperatures, and particle fluxes in a fusion device and in simulation experiments must be well defined before sputtering effects can be understood.     

Range profiles of Ar implanted into C films

⁴⁰Ar implants with energies ranging from 10–200 keV into C films were profiled using the Rutherford backscattering technique. The obtained projected range (R_p) and projected range stragglings (σ_p) are compared with recent range-energy calculations. The analysis shows that the experimental R_p and σ_p values are respectively on average 20% and 25% larger than the predicted ones.     

Sputtering and surface state evolution of Bi under oblique incidence of 120 keV Ar ions

The sputtering and surface state evolution of Bi/Si targets under oblique incidence of 120 keV Ar⁺ ions have been investigated over the range of incidence angles 0° ? θ_i ? 60°. Increasing erosion of irradiated samples (whose surface thickness reduced by ∼3% at normal incidence up to ∼8% at θ = 60°) and their surface smoothing with reducing grain sizing were pointed out using Rutherford backscattering (RBS), atomic force (AFM) and X-ray diffraction (XRD) techniques. Measured sputtering yield data versus θ_i with fixed ion fluence to ∼1.5 × 10¹⁵ cm⁻² are well described by Yamamura et al. semi-empirical formula and Monte Carlo (MC) simulation using the SRIM-2008 computer code. The observed increase in sputter yield versus incidence angle is closely correlated to Bi surface topography and crystalline structure changes under ion irradiation.     

The solid film lubrication by carbon ion implantation into α-Al2O3

Improvement in tribological performance by C⁺110 keV implantation can be achieved by having a more graphite-like carbon structure on Al₂O₃. It was shown that fracture toughness and critical peeling load increased for a fluence of 5 × 10¹⁷C⁺/cm² because of residual compression stress and amorphism of surface. The testing in a different implantation dose indicated that the friction and wear mechanism in Optimol fretting wear machine (SRV) was a combination of surface structure and its abrasive wear. Raman shift shows that the amorphous graphite with 5 × 10¹⁷–1 × 10¹⁸ C⁺/cm² implantation dose was formed on Al₂O₃ surface, so that it reduced friction coefficient and wear of Al₂O₃, also it is noticed that the failure of lubrication due to graphite-like film wear is much earlier in the implantation sample with 1 × 10¹⁷C⁺/cm² dose.     

High dose He+ bombardment of niobium at 800° tO 1400°C

In proposed fusion reactors, the first wall will be bombarded by low energy D⁺, T⁺ and He⁺ ions to very high doses. Room temperature irradiations with 9 keV He⁺ (Roth et al. 1975) showed an initial phase of blistering between 0.05 and 0.25 C/ cm², and a final state of considerable surface roughness at 8 to 112 C/cm²(7 × 10²⁰He⁺/cm²). The present irradiation experiments with 6 keV He⁺ are carried out with polycrystalline Nb foils at temperatures between 800 and 1400°C in order to study the influence of He mobility and of Nb surface diffusion during irradiation. The applied doses range from 2.5 × 10¹⁷He⁺/cm² (blistering) to 5 × 10²⁰He⁺/cm² which corresponds to at least several weeks of reactor operation. The resulting changes of the niobium surface structures are observed by scanning electron microscopy and are pictorially presented in this paper. Mainly, sponge-like open structures are seen to develop at high doses, with increasing physical dimensions at higher temperatures.