NEXAFS MEASUREMENTS INDICATING A TILTED MOLECULAR-ORIENTATION FOR METHYL HALIDES ON GAAS(110)

The orientation of methyl halides (CH(3)X, X = Cl, Br, I) molecularly adsorbed at 80 K on GaAs(110) has been investigated by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the carbon K edge. Analysis of the angular dependence of the C-X sigma() resonance indi cates that the molecules are oriented with the C-X axis tilted with re spect to the surface normal. In the first monolayer, the molecules are inclined in the [0 (1) over bar] direction, the C-X axis approximatel y 45 degrees from the surface normal. Tn the second monolayer the mole cules are inclined in the opposite [01] direction from the surface nor mal. Correlations between the orientation results obtained from these studies and other observations on these same surface adsorbate systems are discussed.