Interactions of methyl halides (Cl, Br and I) with Ag(111)

A437 Surface Science 219 (1989) 277-293 North-Holland, Amsterdam

277

ANTIMONY ADSORPTION ON SILICON (111) ANALYZED IN REAL TIME BY IN SITU ELLIPSOMETRY S. ANDRIEU ISA RIBER,

*

133 - 137, Bd National, 92503 Rueil-Malmaison,

France

and F. ARNAUD

d’AVITAYA

CNET CNS, Chemin du vieux chLe,

38243 Meylan, France

Received

for publication

23 January

1989; accepted

17 April 1989

In this work spectroscopic ellipsometry is used as a technique for crystal surface analysis, here applied to the study of Sb, adsorption on silicon (111). Perfect initial Si(ll1) surfaces are obtained by removing a 150 A thick oxide at high temperature under a silicon flux. This cleaning is controlled in real time by ellipsometry. Sb, adsorption-desorption kinetics in the monolayer range are thus presented, varying the incident antimony flw and substrate temperature. Adsorption kinetics at low substrate temperature allow calibration of the antimony flux impinging on the substrate. In all cases the desorption is found to be described by an Arrhenius law which is typical of a monomer Sb evaporation from the substrate. Moreover, the study of the adsorption kinetics and coverages at steady state shows that the adsorption phenomenon can be approximated to a monomer Sb adsorption for substrate temperatures higher than 725 OC. However, a discrepancy with the monomer adsorption model is observed below this temperature. This may be explained in terms of Sb, sorption and dissociation on the surface. A simple model based on first-order dissociation kinetics of adsorbed Sb, is proposed to explain the observations at low coverages. An activation energy analysis is proposed that allows a better understanding of the Sb, interaction with a silicon surface.

294

Surface

INTERACTIONS

OF METHYL

X.-L. ZHOU, F. SOLYMOSI and J.M. WHITE Department Received

of Chemistry, 22 December

HALIDES

Science 219 (1989) 294-316 North-Holland, Amsterdam

(Cl, Br AND I) WITH Ag(ll1)

*, P.M. BLASS, K.C. CANNON

University of Texas, Austin, TX 78712, USA 1988; accepted

for publication

19 April 1989

The adsorption of methyl halides (Cl, Br and I) on a Ag(ll1) surface has been investigated by temperature programmed desorption (TPD), work function change (A+), ultraviolet photoelectron spectroscopy (UPS), and X-ray photoelectron spectroscopy (XPS). All three compounds adsorb with high sticking probability at 100 K, even up to multilayer coverages. The absolute coverage at one monolayer of CH,X is independent of X and is (4.6*O.3)X1O14 molecules/cm*. UPS and XPS spectra suggest that the adsorption of methyl halides is molecular at 100 K and with little distortion of the corresponding gas-phase molecular electronic structures. Submonolayer adsorption is accompanied by a significant work function decrease (A+ between - 0.83 and - 1.25 eV) indicating a dipole with the positive end pointed away from the surface. At high exposures, multilayers form and desorb at 113 (Cl), 121 (Br), and 136 K (I). Whereas chemisorbed monolayer coverages of CHsCl and CHsBr desorb, with TP = 126 and 142 K, without detectable decomposition, a significant fraction ( = 35%) of monolayer CHsI dissociates between 130 and 190 K to give adsorbed CH, and I. The dissociation of CHsI is accompanied by a decrease in the binding energy of the 1(3d,,,) core electrons. The adsorbed CH, does not dehydrogenate on Ag(lll), but recombines above 190 K to yield C,H, which immediately desorbs.