Spot Profile Analysis Of Electron Diffraction Research Articles

Growth of epitaxial monolayers

Due to scientific and technological interest many studies are concerned with growth modes for the first monolayers of epitaxial growth. By combination of microscopy (like STM) and diffraction (like spot profile analysis of LEED) the important steps of film formation via deposition, migration, nucleation and film completion are studied. Temperature, deposition rate and defects of substrate and of the growing film drastically influence the growth modes in homoepitaxial systems with respect to island density, roughness or facet appearance. For heteroepitaxial growth the misfit and the surface energies are decisive for the growth mode. Depending on the type of bonding the growing film is more or less determined by the structure of the substrate. For metals on metals the film is more or less floating where only the orientation is provided by the substrate. For metals on semiconductors some influence on the lattice constant is seen, which depends on the temperature of deposition. For semiconductors on semiconductors a one-to-one correspondence of film atoms to substrate atoms requires a clear transition from pseudomorphic to relaxed growth of the film by dislocations at the interface. For accommodation to the substrate each film has to develop special defects, which depend both on the system and on the growth parameters. The wide variety of growth modes and some specific film defects are qualitatively demonstrated with STM images and quantitatively described by spot profile analysis of electron diffraction (SPA-LEED).

SPA-LEED studies of defects in thin epitaxial NiSi2 layers on Si(111)

Thin epitaxial NiSi2 layers were formed by deposition of 2 up to 20 monolayers Ni at room temperature and following steps of annealing in the range of 550 to 750 K. These very thin layers show not only a rough surface but also inhomogeneities as domain boundaries, variations of stoichiometry and interface roughness. Step density and inhomogeneities are reduced by annealing at temperatures of less than 750 K. The continuous NiSi2 film breaks up into islands of three-fold symmetry above 800 K. It is shown that the process of film formation, annealing and disruption is quantitatively described by careful spot profile analysis of electron diffraction (SPA-LEED).

A new LEED instrument for quantitative spot profile analysis

A new instrument for spot profile analysis of electron diffraction (SPA-LEED) has been set up. The instrument works either with a transparent phosphor screen for visual inspection of the pattern or in its main mode with a channeltron for the measurement of the intensity. The diffraction pattern is recorded with a fixed channeltron position by scanning the beam over the channeltron aperture using two sets of electrostatic deflection plates. The scanning range covers about 30°. The intensity may vary over five orders of magnitude. The SPA-LEED system was checked with the Si(111) 7 × 7 surface. A full width at half maximum of 0.3% of the normal reflex distance corresponding to a transfer width of 110 nm is reproducibly obtained. Under optimum conditions the transfer width rose up to about 200 nm. Initial high resolution measurements have been performed on the system Pb on Cu(111). The results demonstrate the possibilities of the new instrument for qualitative and quantitative analysis.

A new LEED instrument for quantitative spot profile analysis

Abstract A new instrument for spot profile analysis of electron diffraction (SPA-LEED) has been set up. The instrument works either with a transparent phosphor screen for visual inspection of the pattern or in its main mode with a channeltron for the measurement of the intensity. The diffraction pattern is recorded with a fixed channeltron position by scanning the beam over the channeltron aperture using two sets of electrostatic deflection plates. The scanning range covers about 30°. The intensity may vary over five orders of magnitude. The SPA-LEED system was checked with the Si(111) 7 × 7 surface. A full width at half maximum of 0.3% of the normal reflex distance corresponding to a transfer width of 110 nm is reproducibly obtained. Under optimum conditions the transfer width rose up to about 200 nm. Initial high resolution measurements have been performed on the system Pb on Cu(111). The results demonstrate the possibilities of the new instrument for qualitative and quantitative analysis.