Structural and elastic properties of Ge after Kr-ion irradiation at room temperature

Changes in the elastic properties of Ge induced by room-temperature irradiation with 3.5-MeV Kr ions have been determined and correlated with changes in the microstructure determined by transmission electron microscopy. Elastic-shear-moduli changes were measured by Brillouin scattering, and changes in local atomic arrangement were determined by Raman scattering. Amorphization decreased the elastic shear modulus of Ge by 17%. The fractional decrease was correlated with the amorphous volume fraction with a cross section of 4.5±0.5 nm2/ion. No change was observed in the shear modulus during void formation and growth. The elastic properties of the voided material are described by the Voigt averaging. However, as the voids evolved into a fibrous spongelike microstructure, a second dramatic elastic softening occurs which we attribute to the inability of the fibrous structure to support shear stresses. Raman scattering showed that, once formed, there was no change in the structure of the amorphous material at the atomic scale during void formation and subsequent void coalescence

The effect of ion irradiation on inert gas bubble mobility

The effect of Al ion irradiation on the mobility of Xe gas bubbles in Al thin films was investigated. Transmission electron microscopy was used to determine bubble diffusivities in films irradiated and/or annealed at 673K, 723K and 773K. Irradiation increased bubble diffusivity by a factor of 2--9 over that due to thermal annealing alone. The Arrhenius behavior and dose rate dependence of bubble diffusivity are consistent with a radiation enhanced diffusion phenomenon affecting a volume diffusion mechanism of bubble transport. 9 refs., 3 figs., 2 tabs

Precipitation of Kr after implantation into Al

Transmission electron microscopy (TEM) was used to perform a systematic study of the microstructural evolution in Al as a function of the fluence received during 65 keV Kr/sup +/ ion implantation at room temperature. At the lower fluences (2 x 10/sup 16/ to 2 x 10/sup 19/ Kr/sup +/m/sup -2/), isolated dislocation loops and the evolution of a dislocation network was observed by TEM. Above fluences of 10/sup 19/ Kr/sup +/m/sup -2/, the microstructure is dominated by a high density of Kr bubbles whose average size increases with dose. The appearance of additional electron diffraction reflections indicates that the majority of the bubbles contain solid fcc Kr that is epitaxially aligned with the fcc Al matrix. Above fluences of 2 x 10/sup 20/ Kr/sup +/m/sup -2/ an increasing fraction of the Kr is in a liquid or gas-like phase. The thermal stability of the microstructure, characteristic of the different fluence regimes, was investigated up to 640/sup 0/C by in situ TEM annealing experiments

Plastic flow produced by single ion impacts on metals

Single ion impacts have been observed using in situ transmission electron microscopy and video recording with a time resolution of 33 ms. Gold was irradiated at 50 K and room temperature. Single ion impacts produce holes, modify existing holes, and extrude material into the initial specimen hole and holes formed by other ion impacts. The same behavior is observed at both temperatures. At both temperatures, ion impacts result in craters and ejected material. Ion impacts produce more small craters than large ones for all ion masses, while heavier mass ions produce more and larger craters than lighter mass ions. This comparison is affected by the ion energy. As the energy of an ion is increased, the probability for deposition near the surface decreases and fewer craters are formed. For a given ion mass, crater production depends on the probability for displacement cascade production in the near surface region. Craters and holes are stable at room temperature, however, ion impacts near an existing crater may cause flow of material into the crater either reshaping or annihilating it. Holes and craters result from the explosive outflow of material from the molten zone of near-surface cascades. The outflow may take the form of molten material, a solid lid or an ejected particle. The surface is a major perturbation on displacement cascades resulting from ion impacts

Amorphisation and Recrystallisation of Nanometre Sized Zones in Silicon

In this paper we present a detailed study in which the formation, by heavy ion impact, and thermal recrystallisation of individual amorphous zones have been studied using in-situ transmission electron microscopy. In agreement with previous work, we observe a reduction in the total volume of amorphous material contained within the amorphous zones following thermal annealing over a wide range of temperatures. When the evolution of the individual amorphous zones is followed, those with similar starting sizes are observed to recrystallise over a range of temperatures from 70 ºC to 500 ºC. The temperature at which an amorphous zone fully recrystallises does not appear to be correlated with initial size. In addition, zones are occasionally observed to increase in size temporarily on some isochronal annealing steps. Furthermore, observations during a ramp anneal show that many zones recrystallise in a stepwise manner separated by periods of stability. These phenomenon are discussed in terms of the I-V pair

Plastic flow in FCC metals induced by single-ion impacts

Irradiation of Au and Pb foils with Xe ions at temperatures between 30 and 450 K has been monitored using in situ transmission electron microscopy. Single ion impacts give rise to surface craters on the irradiated surface with sizes as large as 12 nm. Approximately 2%–5% of impinging ions produce craters on Au while only about 0.6% produce craters on Pb. Larger craters on Au frequently have expelled material associated with them. Temporal details of crater formation and annihilation has been recorded on video with a time-resolution of 33 ms. Craters annihilate in discrete steps due to subsequent ion impacts or anneal in a continuous manner due to surface diffusion. Craters production (those persisting for one or more video-frames) as a function of temperature indicates that the surface diffusion process responsible for thermal annealing of craters has an activation energy of 0.76 eV in Au. Crater creation results from plastic flow associated with near surface cascades. Crater annihilation in discrete steps results from plastic flow induced by subsequent ion impacts, including those that do not themselves produce a crater

Nanoparticle ejection from gold during ion irradiation

We have used in situ transmission electron microscopy to study the sputtering of gold by inert-gas ions and, in particular, nanoparticles ejected by individual ion impacts. Irradiations were performed at room temperature in transmission geometry with Ne, Ar, Kr and Xe ions at energies between 100 and 600 keV. Nanoparticles result from situations in which ion impacts also give rise to nanometer size craters on the surface. The number of nanoparticles increased linearly with increasing ion dose. The rate of nanoparticle ejection scales with the probability, calculated with standard Monte Carlo techniques, for high-energy deposition events by individual ions in the near-surface region regardless of the irradiation. The percentage of near-surface, high-energy recoils that eject a nanoparticle is high. The rate of nanoparticle ejection depends on energy transfer to the Au lattice and not on the ion that makes the impact or its energy. Ejected nanoparticles account for the nonlinear component of sputtering. Monte Carlo calculations offer a general technique for predicting situations in which nanoparticles can be ejected and thus when the nonlinear contribution to the sputtering yield is likely to be significant

Nanocluster formation during ion irradiation of SiO2/Ag/SiO2 multilayers

Nanocluster formation during heavy ion bombardment of a thin contiguous Ag layer sandwiched between two continuous SiO2 layers has been observed using in situ transmission electron microscopy (TEM). During ion bombardment, irradiation-induced plastic flow of the Ag film enlarges pre-existing pin holes and separates the film at grain boundaries transforming the as-deposited thin Ag film into three-dimensional microcrystals having diameters greater than 30 nm. This plastic flow process is similar to that observed in free-standing Ag specimens during heavy ion irradiation. In addition to plastic flow, ballistic recoils inject Ag atoms into the SiO2 where they precipitate into nanoclusters. Both effects are greatly enhanced by simultaneous electron and ion irradiation