Bombardment Dose Research Articles

Time decay of ion bombardment induced photon emission

Abstract Spectral line emission from sodium ion bombardment of aluminum polycrystalline targets has been observed to be dependent upon the target ion bombardment dose. Al and Na emission levels from an unbombarded target decay with ion dose to a saturation level. Qualitative calculations show that the photon emission decay time is consistent with implanted ion saturation times. Cesium ion bombardment, because of its shorter range and smaller saturation time did not yield any transient results.

Radiation damage, annealing and thermal desorption in tungsten induced by low energy A+ion bombardment

Abstract Prethinned foils of polycrystalline tungsten (over 70 per cent of transparent grains had (100) orientation or very near to it; other grains had (113) and (111) orientations) have been bombarded with 4 keV A+ ions. The ion doses varied from 2.1015 to 5.1017 ions/cm2. Electron microscope observations have shown that the intensity of damage in the form of large defect clusters, dislocations, complex dislocation tangles and networks increased with ion dose, but a 'saturation' effect was found at doses of 1 to 2.1017 ions/cm2. The concentration of damage depends on the crystallographic orientation of the grains. The maximum damage density was found in grains with (100) orientation at all bombardment doses. In (100) oriented grains a tendency for alignment of irradiation-induced dislocation loops was found. These row formations were parallel to the (110) direction. The development of such alignment depends on ion energy, flux and dose, and it is closely connected with surface and crystal structure. For annealing studies temperatures of 650°C, 900°C, 1200°C, 1500°C and 2000°C were used. These temperatures have been shown, by us and some other authors, to represent the desorption peak temperatures for tungsten, obtained under similar bombardment conditions as used in the present study. While the annealing of damage at 650°C (one hour in a vacuum better than 10−7 torr) produced some effect only at the highest doses, heating one hour at 900°C had a remarkable effect even for ion doses lower than 1.1017 ions/cm2. The main maximum in thermal desorption spectra at temperatures around 1200°C agrees very well with the most intense annealing of damage in tungsten. Correlation of the annealing process in ion bombardment tungsten with thermal desorption spectra helps to explain the processes occurring in tungsten connected with low energy ion bombardment, namely damage formation, thermal desorption and annealing of damage. Evidence of high damage density in tungsten at different ion doses and low ion energies suggests that the radiation damage model for desorption and the analysis of our results given earlier were correct. Our results agree with the annealing studies of damage in other bcc metals.

Ion bombardment induced phase transformations and inert gas mobility in the semiconductors Ge, Si, and GaAs

Abstract The present study contributes some new aspects to the general understanding of the ion implantation behaviour of 3 common semiconductor materials, and of diffusion processes in these materials. Single crystals of Si, Ge, and GaAs were bombarded with Kr- or Xe-ions at energies of 40 or 500 keV and doses between 1011 and 2 × 1016 ions/cm2. Gas release measurements and Rutherford scattering of 1 MeV He+-ions combined with channeling were used to study bombardment damage (amorphization) and inert gas diffusion. At low bombardment doses (1011 ions/cm2) and energy (40 keV), no damage was observed and the gas release was compatible with volume diffusion resembling Group I and VIII behaviour. Hence, the pre-exponential terms, D 0, were low (range 10-5±1 cm2 sec−1) and the activation enthalpies, Δ H, were much lower than those of self-diffusion or of diffusion of Group III and V elements. The Δ H's for gas diffusion followed the relation Δ H = (1.05±0.1) × 10−3 Tm eV with the melting point, Tm , in °K. The mechanism of gas mobility might be the Turnbull dissociative mechanism. Rutherford scattering and channeling data indicated that part of the gas occupied lattice sites. At higher doses, the bombarded layers turned amorphous. Channeling experiments showed a coincidence in temperatures for a gas release process different from the above one of volume diffusion, and recrystallization of the disordered layer to the single crystalline state. Both processes occurred in the temperature range 0.60 to 0.65 Tm . The gas release indicated a (partial) single jump character with implied Δ H's following the relation Δ H = (2.1±0.1) × 10−3 Tm eV. Contrary to previous results on oxides, this new gas release occurred at temperatures near to those or even above those of volume diffusion of the gas. Due to the easy formation of an amorphous layer it was difficult to observe the retarded release (trapping of gas) that has been found in many materials at high gas and damage concentrations. However, in a separate series of experiments with 500 keV Kr-ions, a release retarded with respect to volume diffusion of the gas was observed in Si and Ge.

On the mechanisms of diffusion in inert-gas bombarded solids. Diffusion theory for discrete media, part V

Diffusion in inert-gas bombarded solids can be described in terms of five basic processes. Stage IA, provided it is correctly attributed to gas fortuitously located in high-mobility sites, would be treated using diffusion theory with a trapping term. The total fraction of gas escaping, Fia, should be given by the relation FIA−1 = I + R̄/L, where R̄ is the 1/e range and L is the appropriate diffusion length for trapping. Stage IB, due to gas being swept out by the annealing of bombardment-induced disorder, should occur in an amount FIB given by the relation (1—FIB)−1 ≈ 1 + 1.7 Bt(V(d)43)/R̄2, where Bt is the bombardment dose and Vd is the volume disordered per ion impact. Stage IIA, which is probably due to gas in sites similar to normal substitutional sites, can be safely assumed to be described by the usual diffusion equation. It shows a marked correlation with selfdiffusion such that the following is true: TIIA = (0.86 ± 0.10)Tself-diffusion, where T stands for absolute temperature. Stage IIB is similar to IIA except that it appears to involve transient gas-gas or gasdamage interactions. The predicted amount, FIIB, should be given by the relation (1-FIIB)−1 = 1 + R̄/L, where L is now the diffusion trapping length' appropriate to gas-gas or gas-damage encounters. Stage III is generally accepted to reflect the motion of stable, gas-filled bubbles, and should, if this is so, be adequately described by the usual diffusion equation, though with-Duubbie substituted for D.

The implantation profiles of 10, 20 and 40 keV 85Kr in gallium arsenide

The possibility of making semiconductor devices by implantation of impurity atoms requires a knowledge of their depth distribution or implantation profile. The use of a micromechanical sectioning technique has made such measurements possible over depths of as small as 30 A. These measurements have been made as a function of incident energy, crystallographic direction and bombardment dose of radioactive krypton in single crystals of GaAs. It is concluded that the ion implantation of GaAs is a viable process, that GaAs suffers ion bombardment induced damage at a relatively low dose and that the energy and orientation dependence are similar to those seen previously in face-centred cubic materials.

The effect of bombardment temperature on the trapping of xenon in some oxides and halides

This investigation was concerned with the effect of ion bombardment temperature on the subsequent release of xenon during post-irradiation annealing. For materials resistant to irradiation damage, increasing the bombardment temperature had little effect if the temperature was still low enough to avoid appreciable diffusion of the free gas atoms ( T ⩽ 0.4 Tmelting). An effect was observed with bombardment doses high enough to cause trapping of xenon, if the bombardment temperature was above that required for migration of the free gas but below that required for escape of the temporarily trapped gas. The retained gas in such samples will be primarily trapped gas, while a similar sample bombarded to the same dose at room temperature will contain both free and trapped xenon. A third effect was noted with MgO, which is subject to gross structural damage during irradiation. Samples bombarded at room temperature to an appreciable dose exhibited a large release of gas at low temperature coincident with the annealing of the damage, while samples bombarded to the same dose above the annealing temperature for damage exhibited normal diffusional release.

Thermal release of rare gases implanted in metal targets by high-energy ion bombardment

Results of thermal gas release from copper, silver, and gold targets bombarded with krypton and xenon ions of energies between 20 and 450 keV will be presented. The influence of bombardment doses is shown. The desorption carried out under high-vacuum conditions was examined with the tracer technique, and the fractional release was determined as a function of temperature, energy, and dose. Depth distributions were studied using a corrosion film technique, and the correlation between such distributions and the gas release was investigated. The results are compared with earlier work, and an attempt to elucidate inert-gas diffusion in copper is described.

Inert gas diffusion and radiation damage in ionic crystals and sinters following ion bombardment

A review is given of radiation damage and diffusion phenomena in a large variety of ionic crystals (oxides and halides) and two metals following ion bombardment. Ion beams of both light and heavy nuclides between mass number 3 (tritium) and 222 (emanation) were employed. The ion doses varied between 104 and 1017 ions/cm2. Four different experimental techniques were used to detect gross structural radiation damage following bombardment: reflection electron diffraction, measurement of ranges or penetration profiles, electron microscopy in transmission or using replica techniques, and gas release measurements at low temperatures. In general, materials having cubic lattice structures were shown to be more stable than anisotropic substances.Minor local damage (such as point defects, defect clusters or voids, dislocations and loops) was studied by its interaction with rare gases or other volatile elements (Br, Rb, Cs). For the heavy rare gases (Kr, Xe, Em) and low bombardment doses, volume diffusion was observed starting between 0.4 and 0.5 of the melting point, Tm, on the absolute temperature scale. The activation enthalpies ΔH were about 80 ± 10% of those for the self-diffusion of the less mobile lattice ions and were related to Tm via ΔH = (1.4 ± 0.2) × 10−3Tm eV = (32 ± 4) Tm kcal/mole. For the diffusion mechanism, a relation with self-diffusion is suggested, the gas most probably migrating in small vacancy clusters.

Range Measurements in Oriented Tungsten Single Crystals (0.1-1.0 MeV). II. A Detailed Study of the Channeling ofK42Ions

In this paper the mechanism of channeling of ${\mathrm{K}}^{42}$ ions in monocrystalline tungsten is investigated. The influence of various parameters---ion energy, crystal direction, surface oxide thickness, misorientation, lattice temperature, and bombardment dose---has been studied. It is found that: (i) the over-all range distribution is rather sensitive to all these parameters; (ii) the maximum range ${R}_{max}$ depends only on the ion energy and crystal direction; (iii) planar channeling exists down to the lowest energy studied (70 keV); (iv) the critical angle for channeling is about 3\ifmmode^\circ\else\textdegree\fi{} at 500 keV and decreases slowly with increasing energy. In all cases, the crystals have been oriented with respect to the ion beam to \ifmmode\pm\else\textpm\fi{}0.1\ifmmode^\circ\else\textdegree\fi{}, by means of wide-angle scattering of protons. An attempt is made to correlate the results for these fairly slow heavy ions with Lindhard's theoretical treatment of the motion of charged particles in a crystal lattice, and with the experimental studies on fast light ions.

The release of some non-gaseous fission products from CaF 2, UO 2 and ThO 2

The release of certain non-gaseous fission products (Br, Rb, Cs from ion-bombarded UO 2 and ThO 2 sinters; I, Te, Ba/La from fission-recoil labelled CaF 2 single crystals) from materials with the fluorite structure was studied. The concentration of Br, Rb, and Cs was varied by using two ion doses. In most experiments, several mass transport processes contributed to the release. Release compatible with volume diffusion was found for Rb and Cs in ThO 2 at the lower bombardment dose of 3 × 10 13 ions/cm 2; release occurred at temperatures similar to those for fission gas diffusion and yielded activation enthalpies of about 100 ± 7 kcal/mole, similar to those for fission gas diffusion or uranium self-diffusion. All other releases were complex. In contrast to gas release work, no trapping was found at the high bombardment dose of 1.5 to 2 × 10 16 ions/cm 2: Release of bromine was not affected and release of Rb and Cs occurred at lower temperatures than the release at lower dose. If most of the Br or Rb was near the surface of ThO 2 sinters, an enhanced release at low temperatures was observed. Release of Br from ThO 2 was faster when the samples were annealed in hydrogen than when annealed in air. All this indicates that various factors can influence the release of these non-gaseous fission products including surface reactions (e.g. vaporization), the location of the diffusing ion with respect to the surface, the concentration of the diffusing species and the presence of radiation damage.

Xenon migration and trapping in doped ThO 2

The effect of small amounts of additives of different valence (Y 2O 3 or Nb 2O 5) on xenon migration and on radiation-induced trapping in ThO 2 has been studied to improve the understanding of the mechanism of rare gas diffusion in UO 2 and ThO 2. ThO 2 was chosen as it has the same lattice structure as UO 2 and the valence of Th 4+ is unlikely to change to compensate for the different valence of the impurity. The diffusion of 233U was measured at 1400° C and 1550° C in both doped and undoped ThO 2. More rapid diffusion in Nb 2O 5-doped ThO 2 and less rapid diffusion in Y 2O 3-doped ThO 2 were found. This indicated that doping was effective in producing extrinsic behaviour. Xenon was introduced into the specimens by ion bombardment. At low bombardment dose, doping did not appreciably affect the release indicating that xenon does not diffuse via single vacancies on either sublattice. As alternatives, diffusion via interstitial sites or in small vacancy clusters of constant size remained. Temporary trapping (retarded gas release) was observed at higher doses. Additions of Nb 2O 5 decreased and additions of Y 2O 3 increased this retardation, thus showing that impurities can affect trapping phenomena.

Decrease of Built-in Voltage in Tunnel Diodes Caused by Irradiation

When a germanium tunnel diode is irradiated by 7.2 MeV electrons with a total flux of ∼4.6 × 1017 electrons/cm2, the capacitance built-in voltage vb decreases with the increase in bombardment dose. The variation of the Fermi level obtained from the change in vb is about 0.040 eV for the total flux. Considering that the carrier concentration of a heavily doped n-type germanium decreases with the electron irradiation, the Fermi level changes only in the n-side of the tunnel diodes. This calculated variation of the Fermi level in the n-side caused by the carrier removal is in good agreement with the above result.

THE EFFECT OF CRYSTALLINITY AND BOMBARDMENT DOSE ON THE PENETRATION OF 40-keV XENON IONS IN IONIC CRYSTALS AND CERAMICS

The range and depth distributions of 40-keV xenon ions in single crystals of NaCl, KBr, MgO, SiO2 (α quartz), in sintered UO2 and in fused silica, have been measured by the sectioning techniques of vibratory polishing and chemical dissolution. Channeling is observed in the single crystals when the [Formula: see text] is oriented parallel to the incident beam of the ions. This effect is similar to that previously reported for some metal single crystals. High bombardment doses produce a factor of 2–5 decrease in penetration depth in MgO and SiO2, materials which are known to be damaged by ion bombardment. This decrease is smaller in materials that do not show gross ion bombardment damage, such as NaCl, KBr, and UO2. Thus, the study of ranges is shown to be another means of detecting gross radiation damage.

Radiation damage and xenon release in quartz and fused silica following ion bombardment

AbstractSingle‐crystalline quartz and fused silica were bombarded with 40 keV xenon ions to give integrated ion doses of up to 2 × 1016 ions/cm2. At low dose (8 × 1010 ions/cm2) diffusional release processes dominated with activation enthalpies of 58 and 61 kcal/mol for quartz (diffusion along and perpendicular to the c‐axis respectively) and 72 kcal/mol for fused silica. Diffusion in the amorphous phase was markedly slower than diffusion in the crystalline phase. At doses ≧ 4 × 1013 ions/cm2 radiation damage in the form of a phase change to a quasi‐amorphous state occurred in quartz, as revealed by reflection electron diffraction. The annealing of this structural damage coincided with enhanced thermally activated gas release at temperatures below those of volume diffusion. Fused silica showed a similar enhanced release at high bombardment dose. Thus, the quasi‐amorphous phase produced by ion bombardment is different from that of fused silica. The present results indicate further, in agreement with the literature on neutron irradiated quartz and fused silica, that both materials approach a common state at a high level of radiation damage.

Study of Ion-Bombardment Damage on a Ge (111) Surface by Low-Energy Electron Diffraction

An atomically clean and highly ordered Ge (111) surface was bombarded with Ar+ ions and the bombardment effects were studied by low-energy electron diffraction. Degradation characteristics of the (10) beam were most extensively investigated over an ion energy range from 10 eV to 1 keV with ion dosage ranging from 1012 to 1016 ions/cm2. The degradation characteristics determine the mean area of damage per incident ion. This area is 7×10−14 cm2 for a 1-keV Ar+ ion and 1×10−15 cm2 for a 40-eV ion. At low ion energies, some retention of (10) intensity is noted even for large dosages, indicating in this case that some short-range order is retained. The minimum ion energy for damage is ∼20 eV. This value is close to the sputtering threshold energy and the reported displacement energy of Ge. A bombardment damage model is proposed to explain the low-energy ion-bombardment characteristics. Thermal recovery of the bombarded surface shows a dependence on ion energy and also on total bombardment dose.

Electron Bombardment Damage in Silicon Esaki Diodes

The excess current in silicon Esaki diodes has been shown to be a sensitive indicator of the density and distribution of states intorduced into the forbidden gap by electron bombardment. Both the effects of bombardment and the annealing properties of the radiation damage have been found to depend upon the specific donor in the n-type region of the diode. The average bombardment dose of 1-Mev electron/cm2 needed to increase the excess current density by 1 amp/cm2 at a bias of 0.3 v is 1.2×1016 for P-doped diodes and 0.8×1016 for Sb- or As-doped diodes. Upon annealing in an inert atmosphere, at temperature in the range 300°–400°C, the bombarded diode is restored to its original characteristics. While the annealing studies reveal novel interactions, they show considerable similarity with other work where the radiation damage was monitored by carrier lifetime or conductivity measurements. Structures observed in the I–V characteristics during the annealing indicate that the bombardment-induced levels at Ev+0.27 and Ev+0.06 are due to pairing of a primary defect (probably a vacancy) with an arsenic and a phosphorus impurity atom, respectively.