Slow-electron-energy-loss spectroscopy in the reflection mode, compared with electron-energy-loss spectroscopy of fast electrons

A5 evaporator. The surface properties were studied by Auger electron spectroscopy (AES) and by low energy electron diffraction (LEED). A novel LEED system employing position-sensitive detection was used. The Ge film surface gave a superposition of 7 x 7 and c(2 x 8) LEED patterns. A 7 x 7 ---,1 x 1 phase transition was observed at 425 _+10°C. An irreversible 7 x 7 --, c(2 x 8) transition was observed when the sample was heated above 500°C. The Ge film melted at 750_+ 30°C and formed a GexSil_ x ( x = 0.85+0.05) alloy whose surface gave a 7 x 7 LEED pattern. A 7 x 7 ~ 1 × 1 phase transition was observed at 600+0.15°C. Prolonged sputtering and annealing resulted in a GexSil_ x (x = 0.53+0.05) alloy whose surface gave a 5 x 5 LEED pattern. An apparent 5 x 5 --, 1 x 1 phase transition was observed at 870 + 10°C but at that temperature the film was converted irreversibly to one with a much lower Ge atom fraction (x = 0.025+0.005) whose surface gave a 7 x 7 LEED pattern. A surface with a 5 x 5 pattern identical to that for the x = 0.53 alloy was prepared by deposition or Ge on Si. A similar 5 x 5 surface was prepared by deposition of Ge on a facetted Ge-Si alloy surface originally showing a superposition of 5 x 5 and 7 x 7 patterns. The intensity distributions in all of the 7 x 7 LEED pattern were found to be similar to those for Si(111)-7 x 7 at nearly the same electron energies. The characteristics of the 7 x 7 -, 1 x 1 phase transitions were discussed in direct comparison with those of the Si(111)7 × 7 ~ 1 x 1 and Ge(111)-c(2 × 8) ---,] x 1 transitions observed with the same LEED system.

Surface Science 165 (1986) 203-220 North-Holland, Amsterdam

203

SLOW-ELECTRON-ENERGY-LOSS S P E C T R O S C O P Y IN THE REFLECTION MODE, COMPARED WITH ELECTRON-ENERGY-LOSS S P E C T R O S C O P Y OF FAST ELECTRONS A.G. N A S S I O P O U L O S and J. C A Z A U X Laboratoire de Spectroscopie Electronique, Universit@ de Reims, UER Sciences, BP 347, F-51062 Reims Cbdex, France Received 2 May 1985; accepted for publication 10 July 1985 Some experiments by slow-electron-energy-loss spectroscopy (SEELS) performed in the reflection mode are reported and the results are compared with the published data (when available) obtained by fast-electron-energy-loss spectroscopy in transmission through thin foils. This comparison illustrates similarities and differences between the two techniques with regard to (i) atomic and solid-state analysis and (ii) microanalytical properties. The experimental results concern the following core losses: L1, L2. 3 in A1 and SiC; Cls in graphite; Bls and NI~ in hexagonal boron nitride; M1, M2. 3 in nickel.

Surface Science 165 (1986) 221-233 North-Holland, Amsterdam

221

A D S O R P T I O N AND D E C O M P O S I T I O N OF ACETYLENE O N VANADIUM (100), (110), AND (111) SURFACES; THE EFFECT OF LARGE d ORBITALS Dae Bok KANG

a n d A l f r e d B. A N D E R S O N

Chemistry Department, Case Western Reserve University, Cleveland, Ohio 44106, USA Received 2 July 1985; accepted for publication 26 August 1985