Change Of SI(111) Surface Reconstruction Under Noble Metal Films
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CHANGE OF SI(l11) SURFACE RECONSTRUCTION UNDER NOBLE METAL FILMS HAWOONG HONG%, RICHARD ABURANO', D.-S. LIN', T.-C. CHIANG', HAYDN CHEN" P. ZSCHACK*" AND E. D. SPECHT-" *Materials Research Laboratory, University of Illinois, 104 S. Goodwin Ave, Urbana, IL 61801 **Metal and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
ABSTRACT Interface structures between Si(1 11) and thick noble metal overlayers are studied by grazing-angle-incidence x-ray diffraction and crystal truncation rods. The 7x7 reconstruction is only preserved under a Ag film deposited at room temperature. This capped 7x7 structure changed to a lxl structure upon annealing over 250 0 C. A thick overlayer of room temperature deposited Au film destroyed the 7x7 reconstruction and changed the interface structure to lxi. Our results are compared to a thick Cu/Si(1 11) interface structure'. INTRODUCTION There has been a great amount of work in the area of interface structure studies. Half of these studies are on clean surfaces or surfaces covered with mono- or submono-layers of foreign materials. The other half are on the "thin" films. There are very few studies focussed on the interface structure in the transition region between the substrate surface and the film. The structure of a clean surface or a monolayer covered surface is not necessarily preserved when the film becomes "thick", i.e. above the mono- or submono-layer regime. Some physical properties of resulting interfaces may not depend on the characteristics of the thin film. The structure of the transition region from the substrate to the bulk-like thin film may determine the properties. For example the Schottky barriers between semiconductors and metals can be controlled by the structure of the buried interfaces2 . Also, the structure of this transition region is a very important factor controlling the morphology of the thin film (considered as a thick film in this paper). Unfortunately, there are not many experimental techniques available to study buried interfaces. Using high resolution TEM, it is possible to study the cross-sectional structure of a buried interface3 . Although TEM gives real space images of buried interfaces, it is not simple to prepare a sample for TEM. Recently, x-ray scattering has been used to study buried interfaces4 . X-rays can penetrate fairly deep into the interface. With the prevailing brightness of synchrotron x-rays, there is a significant signal from the buried interface, so one can investigate the structure of the transition region of an interface much easier than before. The work by I. K. Robinson and his collaborators on Si(1 11) surfaces buried under a layer of amorphous silicon or a silicon oxide layer are among the first x-ray scattering studies on buried interfaces4 . Our study concerned the buried interfaces of Ag/Si(1 11) and Au/Si(l 11). Ag and Au have very simple phase diagrams when alloyed with Si?. These metals are known to have very small solubilities in solid Si. Thus the Ag/Si(111) and Au/Si(11l) interfaces are chosen in curr
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