TEMPERATURE-DEPENDENT PHOTOEMISSION-STUDIES OF SI(100)2X1

We have studied the clean Si(100)2 X 1 surface with angle-resolved direct and inverse photoemission spectroscopy (ARUPS and KRIPES) as a function of temperature in the range 300 < T < 1215 K. We note four effects: (i) The dangling bond surface-state emission observed in ARUPS around - 0.8 eV below the Fermi level (E(F)) in normal emission gradually loses intensity as a function of temperature due to broadening, however, it is clearly discernible at 1215 K and appears at the same energy position (within 0.1 eV). We take this observation as evidence for the existence of asymmetric dimers over the whole temperature range studied. The reason for the observed broadening with temperature could be due either to an increasing buckle-flip frequency or to an increasing influence of electron-phonon interaction. (ii) The emission at the border of the surface Brillouin zone (SBZ) from a feature around - 1.0 eV and the small emission feature at the Fermi level in ARUPS in normal emission, which had been observed to be significant on highly-doped two-domain Si(100)2 X 1 surfaces but less pronounced on single-domain surfaces, vanish completely for T > 450 K. (iii) The dangling bond surface-state emission seen in KRIPES around + 0.35 eV above E(F) in normal emission has completely disappeared above 450 K. (iv) The dangling bond band in KRIPES, well described by models based on asymmetric dimers, is not affected by the temperature increase.