Ion Irradiation Of Materials Research Articles

Improvement of new electronic materials using computer modeling

Porous materials occupy an important place among the materials of electronic equipment. Nanopores, which are obtained by ion irradiation of materials, have a complex internal structure that depends on the interaction of fast ions with the substance. Obtaining such structures is important, in particular, in the manufacture of biosensor devices based on them. The most effective methods of studying their properties are computer simulations. However, effective computer models of track structures, necessary for the development and improvement of modern biosensors, are not being created actively enough. The approach proposed here involves a detailed study of the interaction of ion flows with the inner surface of the nanotrack. This approach takes into account the structural features of the inner surface of the track as well as the role of adsorption and scattering centers and other local centers. In the existing approaches, the processes mentioned above are mainly described phenomenologically, which does not indicate the ways of modifying the characteristics of the material that is necessary for the device improvement.

Understanding the effects of ion irradiation using nanoindentation techniques

The effects of ion irradiation in materials for research are usually limited to a shallow surface layer of the order of one micrometre in depth. Determining the mechanical properties of such irradiated materials requires techniques with high spatial resolution. Nanoindentation is a relatively simple method for investigating these shallow layers with the advantage that statistically rich data sets for elastic and plastic property values can be generated. However, interpretation of the results requires and understanding of the material response, including the extent of the plastic zone with respect to the irradiated layer, pile-up or sink-in of material around the indentation site that affect the calculated contact area and hence derived mechanical property values. An Fe+ self-irradiated Fe12%Cr alloy was investigated with three different indenter tip geometries, a cube corner, Berkovich and 10μm radius indenter. Sharp indenters provide sufficiently small plastic zones to be contained within the irradiated layer but pop-in events and pile-up need to be taken into account for correct interpretation of the mechanical properties of the irradiated material.

Time-dependent quantum dynamical simulations of C2condensation under extreme conditions

We report theoretical studies of the initial phase of bulk C(2) condensation into carbon nano-structures by means of Born-Oppenheimer and time-dependent quantum mechanical Liouville-von Neumann molecular dynamics based on the density-functional tight-binding (DFTB) framework for electrons. We observe that the time-dependent quantum mechanical approach leads to faster formation of carbon nanostructures than analogous Born-Oppenheimer simulations. Our results suggest that the condensation of bulk carbon is nonadiabatic in nature, with the critical role of electronic stopping as in ion-irradiation of materials. Contrary to time-dependent quantum mechanical simulations, Born-Oppenheimer dynamics incorrectly predict that the short carbon chains obtained from initial reactive collisions between C(2) quickly evaporate, leading to much lower probability of secondary collisions and condensation. We also discuss some deficiencies in Born-Oppenheimer dynamics that lead to unphysical charge polarization and electron transfer.

A new tool to compare neutron and ion irradiation in materials

The slowing down of neutrons produced in nuclear plants or in spallation sources generates many defects in a material, driving this material far from its equilibrium state. This concentration of defects leads to important structural modifications of solids. To model the impact of radiation in solids, particle accelerators are useful tools. The nature and the energy of ions in accelerators must be chosen to produce similar effects to those occurring in nuclear plants. A new program, DART, based on the binary collision approximation, has been developed to optimize the choice of incident particles. In this program, the anisotropy of the neutron atom interaction is treated with a new formalism. Such a formalism allows us to compute accurate displacement cross sections and recoil spectra for all kinds of particles (ions, neutrons, or electrons). The comparison of these displacement cross sections as well as recoil spectra due to ions, electrons and neutrons permits to define the nature and the energy of ions able to simulate damages in reactors.

Modelling of a selforganization process leading to periodic arrays of nanometric amorphous precipitates by ion irradiation

Ion irradiation of materials, which undergo a drastic density change upon amorphization have been shown to exhibit selforganized, nanometric structures of the amorphous phase in the crystalline host lattice. In order to better understand the process a Monte-Carlo-simulation code based on a simple model is developed. In the present work we focus on high-dose carbon implantations into silicon. The simulation is able to reproduce results gained by cross-sectional TEM measurements of high-dose carbon implanted silicon. Necessary conditions can be specified for the selforganization process and information is gained about the compositional and structural state during the ordering process which is difficult to be obtained by experiment.

Phase transformations and compound formation during ion irradiation of materials

This paper summarises new results which illustrate some important concepts in phase transformation and compound formation under ion irradiation. Firstly, the amorphization behaviour in typical semiconductors and metals is contrasted by examining different modes of nucleation of the amorphous phase. Secondly, silicon dioxide formation within amorphous silicon during low temperature, high dose oxygen bombardment is examined. Finally, we illustrate the formation of epitaxial Ni 3Si on Ni(100) by high dose Si implantation and subsequent annealing.