M. Sladecek

An ultrahigh vacuum system for in situ studies of thin films and nanostructures by nuclear resonance scattering of synchrotron radiation.

A multifunctional ultrahigh vacuum (UHV) system has been set up at the nuclear resonance beamline ID18 of the European Synchrotron Radiation Facility (ESRF). Thin and ultrathin films, nanoislands and -wires, multilayers, and stoichiometric oxides can be prepared by molecular beam epitaxy and characterized by low-energy electron diffraction, Auger electron spectroscopy, and reflection high-energy electron diffraction. Upon characterization the sample is transferred under UHV conditions to the chamber for experiments with the synchrotron beam. Electronic and magnetic properties, vibrational dynamics, and diffusion phenomena can be investigated by several synchrotron radiation based techniques, such as nuclear forward scattering, nuclear inelastic and quasielastic scattering, synchrotron radiation based perturbed angular correlations, and nuclear and electronic reflectivity. In addition, two portable UHV chambers serve to transfer the sample to other beamlines profiting from the available experimental techniques at the ESRF.

Enhanced iron self-diffusion in the near-surface region investigated by nuclear resonant scattering

The access to X-rays of third generation synchrotron radiation sources enables studies of dynamics in metallic systems in grazing incidence geometry. Combining grazing incidence reflection of X-rays with nuclear resonant scattering of synchrotron radiation allows depth-selective investigations of hyperfine parameters and diffusion phenomena of iron and iron compounds. The unique feature of this method is its sensitivity to near-surface motions of atoms and not exclusively to the atoms on the surface. The depth sensitivity can be varied between about two and more than 10 nm. A 300 nm thick 57 Fe sample grown by molecular beam epitaxy on a cleaved MgO(001) substrate was investigated. The diffusion coefficient of iron in the near-surface layer (thickness about 2 nm) is almost two orders of magnitude larger than in bulk bcc iron at the same temperature.

Diffusion Studies in Ordered Alloys

1. Introduction Diffusion is an important and fundamental phenomenon for the properties and the behavior of metals, alloys, semiconductors, ceramics, glasses and polymers at higher temperatures. It plays an important role in the kinetics of microstructural changes of a material. It is a driving force for nucleation of new phases, recrystallization and phase transformations with a wide use in current technology, e.g. surface hardening, changing of deformation behavior by nucleation, diffusion doping or sintering. Especially the intermetallic alloys attracted attention as suitable materials for high-temperature applications due to their corrosion stability and strength. Many of the physical processes, developed for intermetallics are applicable for diffusion in all crystalline solids. The knowledge of the diffusion behavior of intermetallic alloys is, therefore, of interest for basic material science and for their use in technological applications. [1]