NEXAFS measurements indicating a tilted molecular orientation for methyl halides on GaAs(110)

The orientation of methyl halides (CH3X, 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 σ∗ resonance indicates that the molecules are oriented with the C-X axis tilted with respect to the surface normal. In the first monolayer, the molecules are inclined in the [01̄] direction, the C-X axis approximately 45° from the surface normal. In the second monolayer the molecules are inclined in the opposite [01] direction from the surface normal. Correlations between the orientation results obtained from these studies and other observations on these same surface adsorbate systems are discussed.