Laser Irradiation of Atomic Chains: A Show-Case Study Based on the Density Functional Theory
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0960-N09-05
Laser Irradiation of Atomic Chains: A Show-Case Study Based on the Density Functional Theory Anna M. Mazzone and Marco Bianconi IMM Sezione di Bologna, CNR, via Gobetti 101, Bologna, 40129, Italy
ABSTRACT This study is motivated by recent applications of short laser pulses to the manipulation of structures at the atomic scale and is based on the Density Functional theory. The structures considered are linear monoatomic chains formed by covalent and metallic atoms (i.e. Si, As and Al, Ag) and the calculations illustrate their evolution under laser irradiation. The results show that the modification of the chain structure spans from a slightly relaxation of the internuclear distances to fragmentation and illustrate the energies and the times needed to induce those changes.
1. INTRODUCTION A very active field of current research is the application of ultra-short laser pulses to induce and control chemical reactions and some of these novel processes are dissociation and/or molecular alignment [1]. Among currently discussed systems there are clusters, nanowires and nanotubes. For the manipulation of these structures the use of an energy input is considered with the double aim of obtaining substantial structural modifications, suitable for the production of new materials, and of gaining insight, at a basic level, into the processes leading to atomic displacements and into the dependence of these processes on the structural properties of the nanostructure and on its composition. These are also the purposes which have motivated the present study. The structures considered below are free-standing chains formed by covalent and metallic atoms,i.e. Si, As and Al, Ag. The calculations are based on the Density Functional Theory and an analysis is made of the chain evolution under laser irradiation with the purpose of stating a correlation, if any, among the chain length and composition, the parameters of the laser light and the final output of the transient.
2. COMPUTATIONAL DETAILS In spite of the significant progresses in this field, most of the present studies on nanowires is based on gold. Furthermore experimental conditions refer to deposited structures or to structures suspended between metallic contacts
and the use of these complex geometries complicates the understanding of the inherent properties of the nanowires. Therefore an extensive analysis of simple models seems required in order to progress towards a systematic view of the nanowire's properties. In theoretical studies, two structural models are generally referred to, i.e. thick, short wires with a section formed by many atoms with a complex arrangement or thin wires infinitely long. However the purpose of the current technologies is the attainment of the 1D limit and therefore the assessment of the performances of structures of this type is an important prerequisite to any experimental step. Owing to this state of the art, the structures used in the following calculations are free-standing chains formed by n equispaced atoms and the elements form
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