EELS Data Research Articles

A spectroscopic study of the coordination of dimethyl sulfoxide to a platinum (111) surface

Spectroscopic studies of the adsorption of dimethyl sulfoxide, ( CH 3) 2 S = O, on Pt(111) have shown that the molecule is bound to the surface via the sulfur atom in an inverted pyramid configuration. A comparison of XPS and EELS data for the adsorbed multilayer and monolayer with XPS and infrared data on the complex PtCl 2(DMSO) 2 is consistent with sulfur bonding. In addition, we detect a considerable increase of the v( S= O) frequency in the DMSO monolayer with decreasing coverage, indicating a coverage dependent heat of adsorption. UPS data show that on adsorption to form a monolayer, the highest occupied molecular orbital of DMSO, presumably the sulfur “lone pair” orbital, shifts to a higher binding energy. These results show a remarkable similarity between DMSO bonding to a metal surface and bonding to a single Pt 2+ species.

Effects of surface relaxation on the electronic structure of ZnO (101̄0)

We have investigated the effect of atomic relaxation on the electronic structure of the nonpolar ZnO (101̄0) surface using the tight binding scattering theoretical method. The bulk material is described by a realistic empirical tight binding Hamiltonian and the relaxation is taken into account by a d−2 scaling of the interaction matrix elements. We find that the ionic surface resonances and the covalent surface states, which we have reported about for the unrelaxed surface previously, are affected very differently by surface relaxation. The covalent surface states strongly shift in energy upon relaxation while the ionic resonances are only marginally affected. This result can easily be interpreted by correlating the changes in the surface electronic structure with the relaxation induced changes of the local binding environment near the surface. Our theoretical results are in good agreement with UPS and EELS data.

Interfacing of Computers to a STEM

There are many STEM applications where computer monitoring and control can enhance or provide new analytical capabilities. While x-ray detector systems have been available for many years, it is only recently that the system computer has had the capabilities extended to provide serial acquisition facilities suitable for EELS data and even scan control suitable for basic image processing requirements. The addition of a frame store opens up new possibilities for S/N improvement and is a useful intermediate stage toward quantitative image processing. With on-line processing of an image, automatic focussing and stigmation is a possibility and analysis of diffraction patterns can be faster and more convenient with computer assistance. A computer can co-ordinate the simultaneous acquisition of several signals, thus increasing the information gathered in an interval limited by contamination, drift or specimen damage and can supervise sequential, multi-signal analyses at pre-programmed points in the field of view. Where lens currents and alignment have to be specially adjusted for particular applications, settings can be recorded to enable conditions to be reproduced immediately under computer control.

The dynamical motion of atoms at the Ni(111) surface

One atom phonon spectral densities are presented for the vibrations of atoms at the Ni(111) surface both parallel and perpendicular to the surface. They are also presented for perpendicular motion of an adsorbed oxygen atom and the nickel atom immediately below it. The results are obtained using a continued fraction technique. They are compared with recent EELS data obtained by Ibach and Bruchmann.

The dynamical motion of atoms at the Ni(111) surface

Abstract One atom phonon spectral densities are presented for the vibrations of atoms at the Ni(111) surface both parallel and perpendicular to the surface. They are also presented for perpendicular motion of an adsorbed oxygen atom and the nickel atom immediately below it. The results are obtained using a continued fraction technique. They are compared with recent EELS data obtained by Ibach and Bruchmann.

First surface electronic structure of a wurtzite-type semiconductor the polar and nonpolar surfaces of ZnO

We report the first calculations of the surface electronic structure for a Wurtzite-type semiconductor, namely ZnO. The bulk electronic properties of the material are described by a realistic empirical tight binding Hamiltonian which we obtained by fitting a selfconsistent pseudopotential bulk band structure and experimental bulk XPS and UPS data. Using the scattering theoretical method, we have calculated the surface band structures and wavevector-integrated as well as wavevector-resolved layer densities of states for polar and nonpolar ZnO surfaces. In agreement with experiment, we find no surface states in the gap on clean ZnO surfaces. Within the projection of the bulk valence and conduction bands, however, distinct surface features occur. First, there are ionic O-2 p and Zn-4 s surface states which have predominantly resonance character. In addition, more covalent back bond and anti back bond surface states are found which are occupied and empty, respectively. We find very good agreement with recent EELS and UPS surface data.