Field-ion microscope observations of helium ion bombardment damage in tungsten

The field-ion microscope has been used in a pilot investigation of the damage caused to tungsten surfaces following bombardment with low-energy helium ions. Such effects could be important because the first wall of a fusion reactor will have to withstand high doses of these particles. The damage observed following bombardment with total doses in the range 10¹³ to 5 × 10¹⁸ ions cm^?2 has been found to be dose dependent. These results have then been related to those derived from studies using more conventional techniques and this has led to the conclusion that the origin of the observed damage lies in the formation of near-surface gas bubbles and surface blisters.     

Evolution,migration and clustering of helium-vacancy complexes in RAFM steel- depth resolved positron annihilation Doppler broadening study

Indian Reduced Activation Ferritic Martensitic steel is implanted with 130 keV helium ions to a fluence of 5 × 10¹⁴ and 1 × 10¹⁶ ions/cm² and investigated using positron annihilation spectroscopy. The samples were characterised by defect sensitive S and W-parameters using depth resolved slow positron beam. A dose dependency is observed in the nucleation and growth of helium bubbles with annealing temperature. An experimental evidence for the migration of smaller helium-vacancy complexes is observed via the variation in thickness/width of irradiated layer with temperature. The S–W plot clearly shows the regions corresponding to defect annealing, bubble nucleation and growth.     

On the mechanism of cluster emission in sputtering

The intensity and the energy distribution of Si⁺_n cluster ions emitted from clean silicon have been measured for different target orientations as a function of the primary ion energy (3–30 keV) and the projectile mass (noble gas ion bombardment). The results favour the idea that clusters are emitted as such rather than being produced by vacuum recombination of individually emitted atoms and ions.     

High-fluence he-implantation in Ni trapping,re-emission,and surface modification

Simultaneous measurements have been made of blister formation and gas re-emission during bombardment of Ni with 8–40 keV ³He⁺ at room temperature. It is shown that re-emission and blister formation start at the same critical fluence. An initial peak in the re-emission rate is correlated to a step in the total number of blisters. A more detailed analysis of the experimental data shows that the area contributing to gas re-emission is much larger than the blister area. This suggests the formation of an interconnected layer below the surface in which cracks at blister sites provide gas emission channels to the surface.     

Photoluminescence and structural defects in silicon layers implanted by iron ions

The photoluminescence spectra of silicon samples implanted by ⁵⁶Fe⁺ ions [energy, 170 keV; dose, 1×10¹⁶, (2–4)×10¹⁷ cm^?2] and annealed at temperatures of 800, 900, and 1000°C are measured. The structure of the samples at each stage of treatment is investigated using transmission electron microscopy (TEM). It is found that the phase formation and morphology of crystalline iron disilicide precipitates depend on the dose of iron ions and the annealing temperature. A comparison of the dependences of the intensity and spectral distribution of the photoluminescence on the measurement temperature, annealing temperature, and morphology of the FeSi₂ phase revealed the dislocation nature of photoluminescence.     

Some studies of BF2 and B+F implanted Silicon

Ion-implanted shallow junctions have been investigated using BE₂ (molecular ions) by the anodic oxidation method coupled with a four-point probe technique. BF₂ ions were implanted through screen oxide at doses of 3–5 × 10¹⁵ ions/cm² and energies of 25 and 45 keV which is equivalent to 5.6 keV and 10 keV of boron ions. The effect of energy, dose and annealing temperature on shallow junctions is presented in this paper. The shallow junctions in the range of 0.19 μm to 0.47 μm were fabricated.

The effect of fluorine on sheet resistivity of boron implanted silicon at various doses, treated with two-step and three-step annealing, is also presented for comparison in the paper.     

Influence of irradiation damage on formation of iron nitrides in α-Fe

Pure iron foils were implanted with nitrogen ions at energy of 10 keV and with 1×10¹⁷N ions/cm². Doses of pre-self-implantation were 5×10¹⁶ and 3.7×10^{16 17}Fe ions/cm² respectively, and the iron ion energy was 27 keV. A comparison of iron nitrides formed on surfaces with and without pre-self-implantation has been obtained. The results show that radiation damage apparently influences the formation of iron nitrides. The formation and transformation of nitrides after N implantation or after annealing can be explained by a model of implantation-induced transformation.     

Characteristic photon emission from ion bombarded silicon and silica surfaces

Ion bombardment with 50 keV inert gas and reactive gas ions has been used to study the photon emission from excited radiating atoms and ions in the immediate vicinity of the surface of both silicon and silica glass targets (SiO₂).     

Light Emission and Scanning Electron Microscopic Characterization of Porous Silicon

Optical emission resulting from sputtered species during ion bombardment of porous and oxidized porous silicon targets has been studied. Samples were bombarded with 5‐keV Kr⁺ ions at an incidence angle of 70 degrees, and the light emitted was analyzed over the wavelength range 200–300 nm. The surface morphology was investigated, and the micrographs revealed grooves parallel to the plane of incidence when the porosity was surprisingly observed in the grooves under each pore. The results are discussed as a function of the incidence angle and the porosity of the silicon targets.     

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.     

Selective X-ray generation by heavy ions (Part 2) measurement of the concentration distribution of ion-implanted antimony in silicon by the use of selective heavy ion X-ray excitation

This investigation demonstrates how the total, concentration distribution of antimony, previously implanted into silicon at 100 keV, may be elucidated without recourse to the usual radioactive isotope techniques. It uses the fact that 100 keV Kr⁺ ions can preferentially excite characteristic X-rays from antimony, even in the presence of a huge excess of silicon. The resultant high sensitivity for the detection of antimony in silicon is accompanied by the fact that the X-rays arise predominantly from less than one hundred Angstroms below the surface of the specimen. Thus bombardment by 100 keV Kr⁺ íons is used ín conjunction with an anodic stripping technique (which removes 169±20 Å at a time) to obtain the antimony distribution profile in silicon. Consideration is also given to the possibility of obtaining the implanted antimony range distribution by using 100 keV Kr⁺ ions to detect the antimony and simultaneously remove silicon by sputtering.     

Lattice disorder in germanium by boron ion bombardment

Abstract

The lattice disorder produced in germanium by 56keV boron-ion bombardment has been measured using the channeling-effect technique. The dependence on dose (10¹⁴-10¹⁶ ions/cm²) and implantation temperature (?90 °C to +130°C) has been studied. It is found that at room-temperature, each incident boron ion creates ?10 times more disorder in germanium than in silicon. It is remarked that, contrary to the present results, previously established anneal stages generally occur at significantly lower temperatures in germanium than in silicon.     

Luminescent collisions of He+ and He++ ions with H2 molecules at energies below 2 keV

Spectroscopic studies of collisions between He⁺ and He⁺⁺ ions with H₂ gas target have been performed in the 200–600 nm wavelength range. Atomic lines of hydrogen Balmer series and several helium lines were identified and their excitation functions between 50 eV and 1 keV (2 keV for He⁺⁺) were determined.     

Accumulation of deuterium in radiation-damaged tungsten

Experimental studies have been performed to determine the effect of high-level radiation damage on the accumulation of deuterium and erosion of tungsten samples exposed to deuterium plasma. Tungsten samples were exposed first to fast helium ions having an energy of 3–4 MeV (providing from one to ten displacements per atom) and then to deuterium plasma up to a dose of 10²⁵ ion/m². The effects of deformation and modification of the surface microstructure have been observed. The concentrations of helium and deuterium have been measured by the methods of elastic nuclear proton backscattering and nuclear recoil detection of helium ions. A high concentration of deuterium in the damaged layer of a tungsten sample has been measured, and helium has been detected in a layer ～5 μm thick. The proposed method shows promise for determining the lifetime of materials used in fusion reactors and measuring the concentration of tritium accumulated in these materials.     

Secondary-ion emission from silicon bombarded with atomic and molecular noble-gas ions

The emission of Si⁺ from a clean silicon surface has been studied for bombardment with various atomic and molecular noble gas ions at energies between 1.5 and 30 keV. It was found that the degree of ionization of Si⁺ depends strongly (l?inearly) on the projectile energy but only weakly on the projectile mass. These results suggest that the degree of ionization is heavily affected by the (dynamic) perturbation of the bulk properties of the bombarded area which increases with increasing nuclear energy deposition.     

Effect of inelastic and elastic energy losses of Xe ions on the evolution of hydrogen blisters in silicon

We analyze the effect of irradiation by heavy ions on the formation of blisters on the silicon surface preliminarily ion-doped with hydrogen. An attempt is made at differentiating inelastic and elastic processes of interaction between ions and Si atoms using bombardment of the sample with high-energy charged particles through a bent absorbing filter by varying the radiation doses and the energy of bombarding Xe ions. It is found that irrespective of specific ionization energy losses of heavy ions, the blister formation is completely suppressed in the zone of the inelastic interaction during postradiation annealing. Conversely, stimulated development of hydrogen porosity takes place at the same time in the zone of elastic interaction, which is manifested in the form of blisters and flaking.     

On the creation of ordered nuclei by ion bombardment for obtaining nanoscale si structures on the surface of CaF<Subscript>2</Subscript> films

The effect of preliminary low-energy (~1 keV) and low-dose (~10¹²–10¹⁴ cm^–2) ion bombardment on the initial stages of growth of Si films on a CaF₂/Si surface is investigated. Ordered nanocrystal phases (thickness less than 5–6 monolayers) and homogeneous epitaxial nanofilms (thickness more than 8–10 monolayers) of silicon are shown to be formed after annealing.     

Possibilities of the formation of carbides and borides by ion implantation

In the system of boron and carbon, the formation of boron carbide was investigated after ion implantation of 25 keV B ions into carbon or of 25 keV C ions into boron and subsequent annealing. TEM and electron diffraction studies showed that the crystallization of boron carbide begins only at temperatures above 1050°C. By implantation of 20 keV C ions into iron (ion dose 10¹⁷ C ions/cm²) only the metastable ε-Fe₂O will be generated, which at above 220°C transforms into the stable cementite Fe₃C. After implantation of 20 keV B ions into iron, no formation of iron boride could be found. These experimental facts can be understood qualitatively with the help of the thermal-spike model. The energy density or the temperature in the thermal spikes is not sufficient for the generation of cementite iron boride or boron carbide.     

The effects of Xe irradiation on He and H co-implanted Si

A combination of X-ray diffraction, cross-sectional transmission electron microscopy (XTEM), and Raman spectroscopy was used to study the effects of irradiation with swift heavy ions on helium and hydrogen co-implanted silicon.<100>-oriented silicon wafers were co-implanted with 30 keV helium to a dose of 3×10¹⁶He⁺/cm² and 24 keV protons to a dose of 2×10¹⁶ H⁺/cm². Moreover, selected helium and hydrogen co-implanted Si wafers were irradiated with 94 MeV xenon. After He and H co-implantation and Xe-irradiation, the wafers were annealed at a temperature of 673 K for 30 min. The damage region of the wafers was examined by the XTEM analysis. The results reveal that most of the platelets are aligned parallel to the (100) plane in the He and H co-implanted Si. However, majority of the platelets lie in<texlscub>111</texlscub>planes after Xe irradiation. Blisters do not occur on the sample surface after Xe irradiation. Raman results reveal that the intensities of both SiH₂ and V₂H₆ modes increase with the increase in the dose of Xe. A possible explanation is that strong electronic excitation during Xe irradiation produces annealing effect, which reduces both lattice damage and the out-of-plane tensile strain.     

Effect of simultaneous helium implantation on the microstructure evolution of Inconel X-750 superalloy during dual-beam irradiation

This study focuses on investigation into the effect of helium implantation on microstructure evolution in Inconel X-750 superalloy during dual-beam (Ni⁺/He⁺) irradiation. The 1 MeV Ni⁺ ions with the damage rate of 10^?3 dpa/s as well as 15 keV He⁺ ions using rate of 200 appm/dpa were simultaneously employed to irradiate specimens at 400 °C to different doses. Microstructure characterization has been conducted using high-resolution analytical transmission electron microscopy (TEM). The TEM results show that simultaneous helium injection has significant influence on irradiation-induced microstructural changes. The disordering of γ′ (Ni₃ (Al, Ti)) precipitates shows noticeable delay in dose level compared to mono heavy ion irradiation, which is attributed to the effect of helium on promoting the dynamic reordering process. In contrast to previous studies on single-beam ion irradiation, in which no cavities were reported even at high doses, very small (2–5 nm) cavities were detected after irradiation to 5 dpa, which proved that helium plays crucial role in cavity formation. TEM characterization also indicates that the helium implantation affects the development of dislocation loops during irradiation. Large 1/3 〈1?1?1〉 Frank loops in the size of 10–20 nm developed during irradiation at 400 °C, whereas similar big loops detected at higher irradiation temperature (500 °C) during sole ion irradiation. This implies that the effect of helium on trapping the vacancies can help to develop the interstitial Frank loops at lower irradiation temperatures.