Surface Effects During Ion Beam Processing of Materials
- PDF / 3,177,443 Bytes
- 11 Pages / 414.72 x 648 pts Page_size
- 79 Downloads / 209 Views
ABSTRACT Microstructural changes of surfaces during ion implantation have been investigated on the atomic level by molecular dynamics computer simulations. Unlike past surface studies, which have been focused on the problem of sputtering, the current work examines the effects of collective materials response on surface topography. Collective behavior has been noted for the crystal interior in the context of thermal spikes, but we show here that it can lead to far more dramatic consequences at the surface. The investigation includes implantation in several metals, but emphasizing Pt, Si and Ge. In addition, the study includes the first simulations of implantations of a metallic glass, CuTi, and amorphous Si.
INTRODUCTION Although the formal theory of atomic collisions in solids is now well established, and calculations of ion stopping, ion ranges, defect production, atomic mixing, sputtering and channeling are now all possible, the difficulties of treating the complexities of real materials can only be handled through computer simulation. Vineyard and co-workers at Brookhaven were first to realize the enormous potential of molecular dynamics simulations for treating radiation damage problems nearly forty years ago [1], but it has only been in the past decade with the advances in computational facilities and development of realistic potentials that this technique has become a practical means to solve the many body problems in question. Various review articles highlight the progress in this field [2]. Most of this work has considered radiation damage problems in bulk crystals, such as defect production and atomic mixing. The work described here focuses on changes which occur at the crystal surface during ion implantation and ion sputtering. Ion beam sputtering has been extensively studied over the past forty years and an extensive body of knowledge has been developed by experimental, theoretical, and computer simulation methods. Past studies have been primarily concerned with the emitted particles, while more recent works have investigated topographical development of the surface during prolonged bombardment at elevated temperatures [3]. A topic that has been far less considered is the topographical changes associated with individual ion impacts, although notable exceptions are found in the literature [4]. Two recently published papers, however, one computer simulation, using molecular dynamics (MD) [5], and the other experimental, using scanning tunneling microscopy (STM) [6], have illustrated that the morphological changes stemming from single impacts can indeed be profound. To illustrate this point, we note that the average sputtering yield of a 10 keV Au atom implanted into Au is = 10. The MD simulations showed, on the other hand, that in addition to these some 10 sputtered atoms, 550 atoms were transported to the surface as adadoms, a crater was formed in the surface and a dislocation loop was created just below the surface [5]. From another perspective, a 10 keV cascade event initiated in the interior of a crys
Data Loading...
