First-Principles Studies of Hydrogenated Si(111)--7×\times7

The relaxed geometries and electronic properties of the hydrogenated phases of the Si(111)-7$\times$7 surface are studied using first-principles molecular dynamics. A monohydride phase, with one H per dangling bond adsorbed on the bare surface is found to be energetically favorable. Another phase where 43 hydrogens saturate the dangling bonds created by the removal of the adatoms from the clean surface is found to be nearly equivalent energetically. Experimental STM and differential reflectance characteristics of the hydrogenated surfaces agree well with the calculated features.Comment: REVTEX manuscript with 3 postscript figures, all included in uu file. Also available at http://www.phy.ohiou.edu/~ulloa/ulloa.htm

A SOFT-X-RAY PHOTOEMISSION-STUDY OF IRON DEPOSITION ON SI(111)2X1 BY SYNCHROTRON RADIATION-EXCITED PHOTODECOMPOSITION OF ADSORBED FE(CO)5

We report a soft-X-ray photoemission investigation of the adsorption behaviour of Fe(CO)5 on Si(111)2 x 1 and of its photodecomposition to metallic Fe on Si. The system has been studied as a function of temperature in the 20-300 K range and at exposures in the 100-1000 langmuir range. Valence band and Si 2p, C 1s, O 1s, Fe 3p core level photoemission spectra are discussed, together with XAS (X-ray absorption spectroscopy) measurements at the Fe L2,3 edges, recorded in total electron yield (TEY) mode. In the present experimental conditions, we show that the initial adsorption of Fe(CO)5 is partially dissociative in the investigated temperature range. The reacted surfaces have been exposed to unmonochromatized synchrotron light ("white light") for different extents of time. At all investigated temperatures, the resulting product is metallic Fe on silicon, as clearly recognized from the appearance of a Fermi edge in the valence band, and by the XAS Fe L2,3 spectra. The process is shown to be locally excited by synchrotron light. The Fe overlayers obtained at low T's are stable, after room temperature (RT) annealing

A soft-X-ray photoemission study of iron deposition on Si(111)2×1 by synchrotron radiation-excited photodecomposition of adsorbed Fe(CO)5

We report a soft-X-ray photoemission investigation of the adsorption behaviour of Fe(CO)5on Si(111)2\uc3\u971 and of its photodecomposition to metallic Fe on Si. The system has been studied as a function of temperature in the 20-300 K range and at exposures in the 100-1000 langmuir range. Valence band and Si2p, C1s, O1s, Fe3p core level photoemission spectra are discussed, together with XAS (X-ray absorption spectroscopy) measurements at the FeI2.3edges, recorded in total electron yield (TEY) mod. In the present experimental conditions, we show that the initial adsorption of Fe(CO)5is partially dissociative in the investigated temperature range. The reacted surfaces have been exposed to unmonochromatized synchrotron light ("white light") for different extents of time. At all investigated temperatures, the resulting product is metallic Fe on silicon, as clearly recognized from the appearance of a Fermi edge in the valence band, and by the XAS FeL2.3spectra. The process is shown to be locally excited by synchrotron light. The Fe overlayers obtained at low T's are stable, after room temperature (RT) annealing

Topographic and spectroscopic analysis of ethylene adsorption on Si(111)7×7 by STM and STS

A study of the adsorption of ethylene C2H4 on Si(111)7 X 7 at room temperature by scanning tunneling microscopy and scanning tunneling spectroscopy is reported. No significant change in the surface reconstruction is observed. The spatial distribution of the surface reaction has been analyzed on an atom-by-atom basis. Reacted and unreacted sites have been selectively imaged. A higher reactivity of the adatoms in the faulted subunits with respect to those in the unfaulted subunits is reported. Furthermore, the center adatoms are more reactive than the corner adatoms. On the basis of this distribution of reacted atoms, the adsorption site is assigned. The proposed bond model implies that an ethylene molecule is bonded to a pair of adjacent Si adatom-rest atom. It is also shown that the adsorption process affects not only the surface atoms directly involved in the chemical bond with the ethylene molecules, but also some of the neighboring adatoms

Synchrotron radiation-induced Fe deposition on Si from organometallic precursors: Comparison with Fe silicides obtained by solid-phase epitaxy

The effect of exposing a Si(111)7\uc3\u977 surface reacted with Fe(CO)5to unmonochromatized synchrotron radiation ("white beam") has been followed by photoemission spectroscopy of core and valence levels. A silicide layer is obtained, as a result of partial decomposition of Fe(CO)5