We deposited low-energy 111In atoms on a vicinal Cu(100) surface at 82K, and measured the atomic sites by means of the perturbed angular correlations technique (PAC). The sites of the as-deposited In atoms were determined for deposition energies ranging from 5 to 100 eV. The results are coinpared to Molecular Dynamics simulations of the deposition process.

We investigate the behaviour of submonolayer amounts of indium at steps and in terraces on Cu(001) and Cu(1117) surfaces at temperatures between 120 and 300 K by means of variable temperature scanning tunneling microscopy (STM). We find that after deposition all indium atoms attach to steps and that they are eventually incorporated in the first atomic layer to form a surface alloy. At 120 K indium atoms have a clear preference to form rows of specific lengths along steps. At higher temperature the mobility of indium at steps increases, resulting in an apparent decrease in the average length of indium rows. The indium atoms are incorporated in the first layer at room temperature. At the low coverages of our experiment, they exhibit only moderate ordering after being incorporated. To substantiate the picture that emerges from the STM-measurements, we provide a detailed comparison with perturbed angular correlation spectroscopy (PACS) results that have been obtained previously on the same system. When the PACS spectra are partly reinterpreted, the results from both techniques are in agreement and provide the full scenario of the incorporation of indium in Cu(001) surfaces.

Perturbed angular correlation spectroscopy offers a detailed picture of the sites and mobility of individual In-111 probe atoms deposited under various conditions onto Cu(100) surfaces. Generally four sites can be distinguished: the adatomic terrace and step sites, plus the substitutional terrace and step sites. After investigating the behavior of In on flat Cu(100) surfaces we address some specific issues: the interaction between In adatoms and Cu islands, the surface segregation of In after deposition of extra Cu layers, and the interaction between substitutional In terrace atoms with Cu adatoms. We conclude that In atoms strongly prefer substitutional terrace sites; they try to keep this environment during subsequent Cu deposition. Our measurements do not support the proposed surfactant mechanism of In on Cu(100), in which Cu adatoms reach a lower terrace by pushing out an In atom at a step edge.

We present a method to deposit a wide range of radioactive probe atoms on surfaces, without introducing lattice damage or contaminating the surface with other elements or isotopes. In this method, the probe atoms are mass-separated using an isotope separator, decelerated to 5 eV, and directly deposited on the surface. The method allows for performing hyperfine interactions experiments using trace amounts of radioactive probes located at surfaces and interfaces. The characteristics of the deposition method will be described, with particular attention to the deceleration stage of the isotope separator. The method was tested with perturbed angular correlation (PAC) experiments on the system In on Cu(17,1,1). The results are in agreement with molecular dynamics simulations of the deposition process. New developments, in particular the study of the self-diffusion of Ag atoms on Ag(100) by means of PAC with the 111 Ag probe, are briefly discussed.

Perturbed angular correlation experiments using soft-landed Ag-111 probe atoms on a Ag(100) surface allow monitoring of the self-diffusion of Ag on the surface. Tn total, three different sites are observed as a function of substrate temperature: the adatomic terrace site in the temperature interval between XO and 150 K, the adatomic step site between 130 and 180 K, and the substitutional terrace site starting from 150 K, where adatoms are still present on the surface. These data could be explained only by assuming that the hopping diffusion mechanism is active at low temperatures, while the exchange diffusion mechanism is responsible for the observed substitutional terrace site at 150 It. [S0031-9007(98)07711-4].

The magnetic behavior of epitaxial probe layers of Fe-57 down to a thickness of 1 monolayer (ML) has been investigated with the technique of nuclear resonant scattering by synchrotron radiation (NRS) in a grazing: incidence geometry. The samples consisted of 10-55 ML Fe deposited onto a Ge(100) substrate and covered with 2 nm Au. Probe layers of 1-10 ML Fe-57 were inserted at different depths in the Fe film. The technique yields spectroscopic information, i.e., magnetic hyperfine fields and isomer shifts, as well as structural information, such as layer thicknesses and interface roughness. The results show the existence of a nonmagnetic Ge/Fe interlayer of at least 10 ML thick after deposition at room temperature. Subsequent conversion electron Mossbauer spectroscopy (CEMS) data show that, although the samples were stored at room temperature, the interlayer diffusion proceeds as a function of time. The relative merits of NRS and CEMS for the investigation of ultrathin layers are discussed.

In this paper we give a short introduction to the Perturbed Angular Correlation technique and present a novel deposition method for radioactive atoms that probe their surroundings via the hyperfine interaction. Recently obtained results for In depositions on Cu(17 1 1) with energies varying from 5 to 100 eV are discussed and compared with results obtained by evaporation. The experimental results are also compared with molecular dynamics simulations of the low energy deposition process.

Bulk copper and nickel samples containing 2.5 and 5 at.% krypton present in overpressurized bubbles have been studied by EXAFS spectroscopy. A fit to the experimental data yields krypton nearest-neighbour distances of 3.62(4) and 3.69(4) Å in a copper and a nickel matrix respectively. These values confirm that krypton bubbles are overpressurized. Calculated krypton packing densities are in good agreement with results from other techniques. In addition, average krypton - metal nearest-neighbour distances of 3.0(1) Å were determined. Atomistic calculations show a wide variation of krypton - metal distances, in agreement with the experiment.

In this paper we give a short introduction to the Perturbed Angular Correlation technique and present a novel deposition method for radioactive atoms that probe their surroundings via the hyperfine interaction. Recently obtained results for In depositions on Cu(17 1 1) with energies varying from 5 to 100 eV are discussed and compared with results obtained by evaporation. The experimental results are also compared with molecular dynamics simulations of the low energy deposition process.

Krypton atoms incorporated in sputtered a-silicon films are investigated by means of Mössbauer spectroscopy. The hyperfine parameters of the source were determined by taking a spectrum against solid krypton. Mössbauer spectra were taken for films containing krypton concentrations up to 7 at.%. A Debye temperature of 116(4) K has been measured for a sample containing 2.83 at.% Kr. The isomer shifts found for all spectra and the high Debye temperature indicate that krypton resides in small highly pressurized precipitates.