Electronic Stopping Effects Research Articles

Effect of electronic stopping in molecular dynamics simulations of collision cascades in gallium arsenide

Understanding the generation and evolution of defects induced in matter by ion irradiation is of fundamental importance to estimate the degradation of functional properties of materials. Computational approaches used in dierent communities, from space radiation eects to nuclear energy experiments, are based on a number of approximations that, among others, traditionally neglect the coupling between electronic and ionic degrees of freedom in the description of displacements. In this work, we study collision cascades in GaAs, including the electronic stopping power for selfprojectiles in dierent directions obtained via real time Time Dependent Density Functional Theory in Molecular Dynamics simulations of collision cascades, using the recent electron-phonon model and the previously developed two-temperature model. We show that the former can be well applied to describe the eects of electronic stopping in molecular dynamics simulations of collision cascades in a multielement semiconductor and that the number of defects is considerably aected by electronic stopping eects. The results are also discussed in the wider context of the commonly used non-ionizing energy loss model to estimate degradation of materials by cumulative displacements.

Electronic stopping in molecular dynamics simulations of cascades in 3C–SiC

We investigate the effect of the electronic stopping power on defect production due to ion irradiation of cubic silicon carbide using molecular dynamics simulations. We simulate 20 keV and 30 keV Si and C ions, with and without the electronic energy loss. The results show that the electronic stopping effects are more profound in the case of C irradiation, where the ratio of the electronic energy loss Se to the nuclear energy loss Sn is much larger compared to the ratio for Si ions. These findings indicate that this ratio plays a role in the effect of the electronic stopping on ion irradiation.

Extension and applications of switching model: Range theory, multiple scattering model of Goudsmit–Saunderson, and lateral spread treatment of Marwick–Sigmund

The switching model (PSM) developed in the previous paper is extended to obtain an “extended switching model (ESM). In the ESM, the mixt electronic-and-nuclear energy-loss region, in addition to the electronic and nuclear energy-loss regions in PSM, is taken into account analytically and appropriately. This model is combined with a small-angle multiple scattering range theory considering both nuclear and electronic stopping effects developed by Marwick–Sigmund and Valdes–Arista to formulate a improved range theory. The ESM is also combined with the multiple scattering theory with non-small angle approximation by Goudsmit–Saunderson. Furthermore, we applied ESM to lateral spread model of Marwick–Sigmund. Numerical calculations of the entire distribution functions including one of the mixt region are roughly and approximately possible. However, exact numerical calculation may be impossible. Consequently, several preliminary numerical calculations of the electronic, mixt, and nuclear regions are performed to examine their underlying behavior with respect to the incident energy, the scattering angle, the outgoing projectile intensity, and the target thickness. We show the numerical results not only of PSM and but also of ESM. Both numerical results are shown in the present paper for the first time. Since the theoretical relations are constructed using reduced variables, the calculations are made only on the case of C colliding on C.

Electronic effects in high-energy radiation damage in tungsten

Although the effects of the electronic excitations during high-energy radiation damage processes are not currently understood, it is shown that their role in the interaction of radiation with matter is important. We perform molecular dynamics simulations of high-energy collision cascades in bcc-tungsten using the coupled two-temperature molecular dynamics (2T-MD) model that incorporates both the effects of electronic stopping and electron–phonon interaction. We compare the combination of these effects on the induced damage with only the effect of electronic stopping, and conclude in several novel insights. In the 2T-MD model, the electron–phonon coupling results in less damage production in the molten region and in faster relaxation of the damage at short times. These two effects lead to a significantly smaller amount of the final damage at longer times.

Sputtering induced by cluster impact on metal targets: Influenceof electronic stopping

The effect of electronic stopping on the sputtering of metals by cluster impact is discussed. We focus on the specific case of Au 13 impact on a Au surface. Using molecular-dynamics simulation, we study several strategies to include electronic stopping. Electronic stopping influences both the magnitude of the sputter yield and the duration of the sputter process. In the usual procedure, electronic stopping only affects sufficiently fast atoms with kinetic energies above a threshold energy, which is of the order of the target cohesive energy. When assuming that electronic stopping holds down to thermal energies <1 eV, or even to 0 eV, the collision spike is rapidly quenched and the sputter yields become unrealistically small. Furthermore, we implement a scheme to include electronic stopping based on local (electron) density information readily available in a simulation.

Influence of electronic stopping on amorphization energies

The effect of electronic stopping on amorphization energies in germanium and silicon carbide is investigated by determining critical damage energies from the boundary positions of buried amorphous layers of carbon implants and relating them to the accompanying inelastic energy densities. Additional results were obtained by re-analyzing previously published results of damage profiles obtained by other workers for different ions in silicon, indium phosphide and gallium arsenide. Results show that electronic stopping reduces damage efficiency in mono-elemental targets, although this effect becomes less important with increasing target mass. Contrary to this, an enhancement of damage efficiency is observed in the lighter two binary targets, while a rather weak reduction is observed in gallium arsenide.

Effect of electronic stopping on the irradiation-induced changes in hybrid modified silicate thin films

Ion beam processing of organic/inorganic thin films can provide an alterative means to heat treatment in converting the films to their final desired mechanical properties. In this study, hybrid sol–gel derived thin films based on TEOS (tetraethylorthosilicate Si(OC2H5)4) and MTES (methyltriethoxysilane CH3Si(OC2H5)3) were prepared and deposited on Si substrates by spin coating. After the films were allowed to air dry they were heat treated at 300°C for 10min. Ion irradiation was carried out at room temperature using 2MeV Cu2+, 115keV He+ and 115keV H+ ions. Ion fluence was varied such that the electronic energy deposited to the film surface region was kept constant for the three different ions. Hardness and H loss in the films were measured after irradiation and were found to depend on the incident ion species. Both hardness and H loss were found to have a linear dependence with ion electronic stopping power.

Microstructural modifications of Ni–Ti shape memory alloy thin films induced by electronic stopping of high-energy heavy ions

The current study is part of an overarching goal to develop an ion implantation process for producing cyclic actuating elements used in microelectromechanical systems. The damage produced by high-energy ions can be used as a means to selectively suppress the martensitic transformation and bias the motion of shape memory alloy thin films Ni–Ti. In order to optimize the performance of these devices, detailed knowledge of the influence of ion implantation on the microstructure is needed. Recent experiments have shown that complex microstructures are formed after 5 MeV Ni ion implantation. In particular, the extensive surface amorphization and the depth distributions of the irradiation induced phase transformations, which were more prominent at shallower depths than expected, did not correlate with ion transport theories involving nuclear stopping damage distributions. Although electronic stopping effects are normally neglected in metals in these energy regimes, they may explain the unexpected surface amorphization since electronic stopping is the prevalent mode of ion energy transfer at shallow depths. Therefore, swift ion irradiation experiments were conducted to assess the effects of electronic stopping on the damage production. Microstructural observations showed that significant damage was produced from ions possessing low electronic stopping powers (<9 keV/nm) near those of 5 MeV Ni ions (3 keV/nm), confirming, in part, that electronic stopping effects contribute to the damage processes.

Irradiation-induced phase transformation in undeformed and deformed NiTi shape memory thin films by high-energy ion beams

Irradiation-induced transformations in sputter-deposited Ti-rich NiTi thin films have been investigated with special attention given to the effects of prior deformation on the response of martensite phase. Irradiation at low fluence was carried out at room temperature with Au ions at 350 MeV, such that the projected ion range greatly exceeded the film thickness and lattice damage was attributable mainly to electronic stopping effects (43 keV nm−1). Ion-beam modified microstructures were investigated using transmission electron microscopy, X-ray diffraction, and differential scanning calorimetry. Amorphous tracks were observed in both Ti2Ni precipitates and martensite. The track diameter and the amount of amorphization were larger in the pre-deformed sample as compared to the undeformed sample. In both cases the displacive transformation temperatures and transformation enthalpies were depressed by irradiation, but to a greater degree in the pre-deformed material. Similarly, the extent of austenitic and R-phase regions observed to surround individual ion tracks was substantially greater for the pre-deformed films. These observations are discussed in terms of differences between the deformed and undeformed cases with respect to microstructure.

New method based on atomic force microscopy for in-depth characterization of damage in Si irradiated with 209 MeV Kr

Si was irradiated with 209 MeV Kr ions on an (010) oriented surface. Then atomic force microscopy (AFM) was used to measure the roughness on the adjacent (100) plane (the original wafer surface). The distance on this later plane is called “depth” as measured from the (010) (100) edge. Good agreement is found in projected range values between AFM, spreading resistance (SR) data, and Monte Carlo (TRIM) simulation. Four distinct damage zones are found: zone A, dominated by electronic stopping effects; zone B, electronically assisted elastic collisions; zone C, dominant nuclear stopping; and zone D, defects created by the channeled fraction of the beam.

Atomic scale investigation of surface modification induced by 215 MeV Ne irradiation on graphite

Graphite irradiated by 10 12 cm −2 215 MeV Ne ions was investigated by STM. Both, Samples irradiated perpendicular and parallel with the c-plane of graphite were prepared. Four different types of surface features were found. Type 0 features attributed to the Ne ions, type I, due to nuclear cascades of knocked on C atoms, type II, and III attributed to electronic stopping effects of knocked on C atoms. A structure showing a mixed character of II, and III type feature was found over HOPG irradiated parallel with the c-plane. A value in the range of 100–200 Å was found for the radius of the core region of the electronic cascade.

Novel beam effect: mass transport due to the lateral component of the ion momentum

A new effect in ion beam-solid interaction is described, namely mass transport in the bombarded solid due to lateral momentum transfer from the ions. It manifests itself, after high energy (several MeV) ion implantation at low temperature through a contact mask, as a surface depression at one end, and an elevated surface at the other end of the masked region. It is only evident for off-normal implantations, and then the depressed surface is always on the windward side of the mask and the elevated surface region is always on the downwind side, and it increases superlinearly with ion energy. Electronic stopping effects play a major role not only for the momentum transfer but also for the plastic deformation of the solid.

Electronic stopping effects in Fe 60Co 40 films irradiated with high energy ions

Thin films of the Fe 60Co 40 alloy produced by electron beam deposition under ultrahigh vacuum have been irradiated at liquid nitrogen temperature with high energy ions, 40–186 MeV N ions and 445 MeV Ag ions, on the French accelerator GANIL in Caen. The damage production has been continuously measured as a function of the ion fluence at 77 K using in situ electrical resistivity measurements. The experimental results are analyzed to obtain the defect production efficiency which is the ratio of the experimental to the theoretical displacement cross section. It is found for the lightest ions, 40–186 MeV N, that the defect production efficiency is lower than unity and can be understood on the basis of elastic collision effects only. On the contrary, an important defect production efficiency much higher than unity is observed in the case of the 445 MeV Ag irradiation where the slowing down of ions occurs mainly via inelastic collisions. These observations are new evidence of the spectacular damage creation which can be induced by very high energy deposition in electronic excitation in some metallic targets. A comparison and discussion are made regarding previous damage rate studies for other types of high electronic energy deposition in metallic targets.