3.1 Introduction

In the last 5-10 years, we have been intensively working on computer simulations and experimental investigations of interface motion and transformation. With still continuously shrinking device structures, the question of how the microscopic laws may change on the nanoscale appears of utmost importance. This is not only interesting from fundamental point of view but also of practical interest. Planning and fabrication of nanoscale devices need better understanding of the atomic scale processes. A possibly new behaviour could help to improve the properties of devices or hinder their destruction.

Different examples for diffusional nanoscale effects, we have discovered recently, will be given in this contribution.[6,7,8,9,10,11] We will illustrate that interface shift kinetics may differ form the ones predicted by continuum approximations (anomalous kinetics). These findings led us to investigate solid state reaction kinetics. We will show that in many realistic cases reaction layers form and start to grow highly off-stoichiometrically. Moreover an initially existing stoichiometric compound layer may dissolve then re-form off-stoichiometrically.[11] We will also show that an initially diffused interface can sharpen even in completely miscible systems.[12,13]

A variety of different UHV-based techniques have been used to prove the above theoretical findings. The interface shift kinetics has been measured by means of surface analytical techniques (AES, XPS) during dissolution of thin films into semi-infinite substrates: Ni/Cu(111), Ni/Au(111), Si/Ge (111), a-Si/a-Ge. Solid state reactions in Co/Si system has been studied by synchrotron X-ray diffraction and also by using synchrotron facilities we have performed depth profiling and Extended X-ray Absorption Fine Structure (EXAFS) analysis in waveguide structure, which are rather new methods.[14] The interface sharpening has been measured by synchrotron X-ray diffraction.[15]