Surface Science 287/288 (1993) 713-717 Noah-lowland zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA surface scienck tt.:..>... . “‘<..’ ““;;;..,‘~.~.i.:.: . . . . . . . . . .,,,.... .:.:.:.:.:,:~::~:j??~: “~Y+:~.~rA: ‘..‘~i..‘.~...........:~.:.~ . . . . . ,_. :.:*z . . . . . ..h. . . . . . . . . . :y,,,..:.:.: . . . . . . . . . . . . . . “‘!‘.‘:‘.:.:.~.:.:.~:.~.:.:.::::~ ,::::::: ::::.:::::::: . . . . . I.. . . ~ .,.:,~,~‘:‘,.,,.,.,.,..;,.,, . I .:.:,:.:r.,,;.,. ,; . . . . . . . . Au structures on Sit 111) studied by spectroscopic e~~ipsomet~ and optical second harmonic generation J.D. O’Mahony, J.F. McGilp * zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ~ar&~eni of Pure and zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Applied Physics, U~~vers~~ of Dub& Trinity College, Dublin .Z2 Ireland M.H.W. Verbruggen and C.F.J. Flipse Faculty of Physics, Eindhoven University of Technology, P.0. Box 513, 5600 MB Eindhoven, Netherlands Received 1 September 1992; accepted for publication 11 October 1992 Two optical techniques, spectroscopic ellipsometty (SE) and second harmonic generation (SHG), have been used to follow the initial stages of ordered growth of Au on the Si(ll1) surface under ultra-high vacuum conditions. Comparison of the linear and nontinear optical response, as a function of coverage, shows that the nonlinear response is more sensitive to submonolayer structural changes, for this system. Differences in the linear optical response of amorphous and ordered interfaces indicate the necessity for more sophisticated approaches to microscopic modelling of ultra-thin film growth. 1. Introduction Epioptic [ll techniques, where photons are used as both probe and signal, are proving to be of considerable value in the study of the funda- mental physics involved in the formation of the Mets-semiconductor interface. In this paper the linear optical response, probed by spectroscopic ellipsometry (SE), and the nonlinear optical re- sponse, leading to optical second harmonic gen- eration (SHG), have been used to study the growth of Au on the Si(l11) surface in the mono- layer (ML) rkgime. The results show the potential of non-destructive optical probes for in situ char- acterisation of growth with submonolayer sensi- tivity. This work extends previous studies of the Si(lll)-Au system by SHG alone 121. * To whom correspondence should be addressed. 2. Theory The rotating polariser method of SE [3,4] was used to measure the linear optical response of the system. The reflected beam intensity at time t, I&>, is given by f,(t) =1,[1 +ru cos(Zo,t)+p sin(2o,t)], (1) where I, is the average intensity, wP is the input polariser rotation frequency and cu(w) and p(w) are the normalised Fourier coefficients at photon frequency w, given by a(W) = cos(2A) - cos(2?P) zyxwvutsrqponmlkjihgfedcb 1 - cos(2A) cos(2’Iy) ’ P(w) = sin(2A) sin(2?V) cos(A) 1 - cos(2A) cos(2Q) * The polarisation analyser angle, A, is chosen as f45” and the conventional ellipsometric angles 0039~6028/93/$06.00 0 1993 - Elsevier Science Publishers B.V. All rights reserved