Surface physics at the nano-scale via scanning probe microscopy and molecular dynamics simulations

Probe-based scanning microscopes, such as the STM and the AFM, are used to obtain the topographical and electronic structure maps of material surfaces, and to modify their morphologies on nanoscopic scales. They have generated new areas of research in condensed matter physics and materials science. We will review some examples from the fields of experimental nano-mechanics, nano-electronics and nano-magnetism. These now form the basis of the emerging field of Nano-technology. A parallel development has been brought about in the field of Computational Nano-science, using quantum-mechanical techniques and computer-based numerical modelling, such as the Molecular Dynamics (MD) simulation method. We will report on the simulation of nucleation and growth of nano-phase films on supporting substrates. Furthermore, a theoretical modelling of the formation of STM images of metallic clusters on metallic substrates will also be discussed within the non-equilibrium Keldysh Green function method to study the effects of coherent tunnelling through different atomic orbitals in a tip-sample geometry.

Development of numerical techniques for near-field aeroacoustic computations

This work is concerned with the development of a numerical scheme capable of producing accurate simulations of sound propagation in the presence of a mean flow field. The method is based on the concept of variable decomposition, which leads to two separate sets of equations. These equations are the linearised Euler equations and the Reynolds-averaged Navier–Stokes equations. This paper concentrates on the development of numerical schemes for the linearised Euler equations that leads to a computational aeroacoustics (CAA) code. The resulting CAA code is a non-diffusive, time- and space-staggered finite volume code for the acoustic perturbation, and it is validated against analytic results for pure 1D sound propagation and 2D benchmark problems involving sound scattering from a cylindrical obstacle. Predictions are also given for the case of prescribed source sound propagation in a laminar boundary layer as an illustration of the effects of mean convection. Copyright © 1999 John Wiley & Sons, Ltd.

Observation of C60 film formation on a highly oriented pyrolitic graphite substrate via scanning tunnelling microscopy

We have investigated the early stages in the adsorption process of C60 molecules on a highly oriented pyrolitic graphite (HOPG) substrate. C60 powder was thermally evaporated in UHV of 10−8 Pa conditions onto a freshly cleaved HOPG surface. We did not observe individual fullerenes on the substrate for the case of short deposition times and low evaporation rates. However, small islands of C60 molecules with an fcc structure could be observed when the deposition rate was about 0.2 nm/min and the total thickness was above 1 nm. The islands did not grow in the vicinity of the HOPG steps. The typical lateral dimensions of these islands were of the order of a few hundred square nanometers, having thickness of up to five monolayers. We modified the shapes and positions of these islands by the STM tip, using a small (less than 1 V) bias voltage.