D. Welipitiya

The adsorption and desorption of ferrocene on Ag(100)

The molecular adsorption and desorption of ferrocene, Fe(C5H5)2, on Ag(100) have been studied by both photoemission and thermal desorption. Photoemission results indicate that the initially adsorbed surface species closely resemble that of molecular ferrocene. The molecule is adsorbed with the cyclopentadienyl (C5H5) ring ligands parallel to the surface, as determined by electron energy-loss spectroscopy. The shift in photoemission binding energies relative to the gas phase is largely independent of the molecular orbital. The ultraviolet light does lead to partial fragmentation of the ferrocene, but fragmentation occurs only in the presence of incident radiation. The energetics of molecular desorption are influenced by lateral interactions within the molecularly adsorbed film.

Optical properties of boron carbide (B5C) thin films fabricated by plasma‐enhanced chemical‐vapor deposition

Variable angle of incidence spectroscopic ellipsometry was used to determine the optical constants near the band edge of boron carbide (B5C) thin films deposited on glass and n‐type Si(111) via plasma‐enhanced chemical‐vapor deposition. The index of refraction n, the extinction coefficient k, and the absorption coefficient are reported in the photon energy spectrum between 1.24 and 4 eV. Ellipsometry analysis of B5C films on silicon indicates a graded material, while the optical constants of B5C on glass are homogeneous. Line shape analyses of absorption data for the films on glass indicate an indirect transition at approximately 0.75 eV and a direct transition at about 1.5 eV.Variable angle of incidence spectroscopic ellipsometry was used to determine the optical constants near the band edge of boron carbide (B5C) thin films deposited on glass and n‐type Si(111) via plasma‐enhanced chemical‐vapor deposition. The index of refraction n, the extinction coefficient k, and the absorption coefficient are reported in the photon energy spectrum between 1.24 and 4 eV. Ellipsometry analysis of B5C films on silicon indicates a graded material, while the optical constants of B5C on glass are homogeneous. Line shape analyses of absorption data for the films on glass indicate an indirect transition at approximately 0.75 eV and a direct transition at about 1.5 eV.

Ultraviolet and electron radiation induced fragmentation of adsorbed ferrocene

From thermal desorption spectroscopy we find that ferrocene, Fe(C5H5)2, adsorbs and desorbs associatively on Ag(100). Photoemission results indicate that the initially adsorbed surface species closely resembles that of molecular ferrocene. The shift in photoemission binding energies relative to the gas phase is largely independent of the molecular orbital. We find that ultraviolet light does lead to partial fragmentation of the ferrocene and that the molecular fragments are much more strongly bound to the surface than the associatively adsorbed ferrocene. Since fragmentation occurs only in the presence of incident radiation, selective area deposition from this class of molecules is possible. Using a focused electron beam in a scanning transmission electron microscope, we show that selective area deposition of features with resolution of a few hundred angstroms is readily achieved.

The adsorption of nickelocene Part 1: molecular bonding on Ag(100)

Abstract The molecular adsorption and desorption of nickelocene, Ni(C 5 H 5 ) 2 , on Ag(100) have been studied by both angle-resolved photoemission and thermal desorption. Photoemission results indicate that the initially adsorbed surface species closely resemble that of molecular nickelocene. The molecular axis is not along the surface normal, as determined by angle-resolved photoemission and angle-resolved thermal desorption spectroscopy. This is a different bonding orientation than that adopted by molecular ferrocene on Ag(100). The molecular nickelocene desorption energies resemble those observed for ferrocene on Ag(100) but are complicated by multiple chemisorption states and steric effects in the desorption process. Nickelocene is unusual in that the molecular orientation is seen to affect the angular dependence of molecular desoprtion.

Fabrication of large arrays of micron-scale magnetic features by selective area organometallic chemical vapor deposition

We demonstrate that it is possible to deposit a wide range of magnetic features, using photoassisted selective area organometallic chemical vapor deposition. Large arrays of identical micron‐scale Ni features were deposited on a Si(111) wafer by this method. Their magnetic properties were studied by alternating gradient force magnetometry as well as magnetic force microscopy. Our morphological and magnetic measurements show that the structures are spatially well defined, and the magnetic properties are related to the structural shapes of the features. This method can be adapted to the fabrication of smaller‐scale magnetic and electronic devices.

Photoemission studies of Co‐ and Fe‐based compounds with the ThMn12 structure

The electronic structures of NdFe11Ti, NdCo10V2, and YCo10Cr2 have been studied with photoemission and spin‐polarized calculations. The changes in these electronic structures upon nitrogenation have also been investigated. In the Fe compound, the Fe 3d states dominate the calculated density of states near the Fermi‐edge, and the N(2p) peak is evident at around 6.3 eV. There is no shift in Fe 3d peaks visible in these compounds upon nitrogenation. Other than small energy shifts in the peak positions, there is an overall agreement between experimental data and the calculated density of states. The calculated density of states in the local‐density approximation for YCo10V2 is broadened to account for the well‐known many‐body effects and compared with the photoemission data.

Electronic structure of Sm2Fe17Nx compounds

Sm2Fe17Nx is of considerable current interest as a permanent‐magnet material because of its enhanced Curie temperature and uniaxial anisotropy. The electronic structures of Sm2Fe17Nx for x=0 and x∼2.6 have been studied with photoemission and spin‐polarized calculations. The materials are prepared by arc melting and nitrogen is introduced by ion implantation. The nitrogen concentration is quantified with Auger electron spectroscopy. The Sm 4f electrons with binding energies between 6 and 10 eV are investigated with resonant photoemission using photon energies near 140 eV. The major features of ultra‐violet photoemission spectra include the Fe 3d band with a strong peak at 0.8 eV and a small peak at 2.9 eV below the Fermi energy which agree quite well with the theoretical density of states calculation. The modification of the electronic structure with nitrogen concentration is studied to understand the effect of nitrogen addition on the magnetic properties.Sm[sub 2]Fe[sub 17]N[sub [ital x]] is of considerable current interest as a permanent-magnet material because of its enhanced Curie temperature and uniaxial anisotropy. The electronic structures of Sm[sub 2]Fe[sub 17]N[sub [ital x]] for [ital x]=0 and [ital x][similar to]2.6 have been studied with photoemission and spin-polarized calculations. The materials are prepared by arc melting and nitrogen is introduced by ion implantation. The nitrogen concentration is quantified with Auger electron spectroscopy. The Sm 4[ital f] electrons with binding energies between 6 and 10 eV are investigated with resonant photoemission using photon energies near 140 eV. The major features of ultra-violet photoemission spectra include the Fe 3[ital d] band with a strong peak at 0.8 eV and a small peak at 2.9 eV below the Fermi energy which agree quite well with the theoretical density of states calculation. The modification of the electronic structure with nitrogen concentration is studied to understand the effect of nitrogen addition on the magnetic properties.

Electronic structure of Sm[sub 2]Fe[sub 17]N[sub [ital x]] compounds

Sm2Fe17Nx is of considerable current interest as a permanent‐magnet material because of its enhanced Curie temperature and uniaxial anisotropy. The electronic structures of Sm2Fe17Nx for x=0 and x∼2.6 have been studied with photoemission and spin‐polarized calculations. The materials are prepared by arc melting and nitrogen is introduced by ion implantation. The nitrogen concentration is quantified with Auger electron spectroscopy. The Sm 4f electrons with binding energies between 6 and 10 eV are investigated with resonant photoemission using photon energies near 140 eV. The major features of ultra‐violet photoemission spectra include the Fe 3d band with a strong peak at 0.8 eV and a small peak at 2.9 eV below the Fermi energy which agree quite well with the theoretical density of states calculation. The modification of the electronic structure with nitrogen concentration is studied to understand the effect of nitrogen addition on the magnetic properties.Sm[sub 2]Fe[sub 17]N[sub [ital x]] is of considerable current interest as a permanent-magnet material because of its enhanced Curie temperature and uniaxial anisotropy. The electronic structures of Sm[sub 2]Fe[sub 17]N[sub [ital x]] for [ital x]=0 and [ital x][similar to]2.6 have been studied with photoemission and spin-polarized calculations. The materials are prepared by arc melting and nitrogen is introduced by ion implantation. The nitrogen concentration is quantified with Auger electron spectroscopy. The Sm 4[ital f] electrons with binding energies between 6 and 10 eV are investigated with resonant photoemission using photon energies near 140 eV. The major features of ultra-violet photoemission spectra include the Fe 3[ital d] band with a strong peak at 0.8 eV and a small peak at 2.9 eV below the Fermi energy which agree quite well with the theoretical density of states calculation. The modification of the electronic structure with nitrogen concentration is studied to understand the effect of nitrogen addition on the magnetic properties.

Finite size scaling in the thin film limit

The thickness dependent spin-polarized electronic structure of strained thin and ultrathin films of Gd is characterized by a distinct change in the critical exponent λ in the formalism of finite size scaling. The reduced critical exponent in the ultrathin films can be correlated to the increased dominance of the surface magnetic structure and the increasing paramagnetic-like behavior of the bulk.

Strain induced alteration of the gadolinium surface state

The electronic structure of strained and unstrained Gd(0001) has been studied with photoemission, inverse photoemission, and spin-polarized photoemission. A shift of the occupied majority and unoccupied minority surface states has been observed as a result of the strain, consistent with the phase accumulation model. There is a strain induced shift of the minority spin surface state across the Fermi level.