Chemistry and Deposition Driven by Monoenergetic Synchrotron Radiation: Initial Studies of Condensed Silanes and Water o
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+Department of Chemistry, State University of New York, Stony Brook, N.Y. 11794-3400 *Physics Department, Brookhaven National Laboratory, Upton, N.Y. 11973 ABSTRACT
We extend previous work in broadband synchrotron radiation (SR) excitation of condensed multilayers to the study of reactions driven by monoenergetic SR. The long term goal of this work is to understand the importance of core-level excitation on the reactions that lead to materials growth. Results are presented for two systems of interest: formation of silica from Si(CH 3)4 and H20 mixtures with 90 eV irradiation (below the core levels) and the energy dependence of the reaction of SiI- 4 and H20. INTRODUCTION
Our research group is interested in understanding the reactions that occur in condensed layers composed of molecular precursors, which are supported on metallic or semiconductor substrates, during exposure to synchrotron radiation (SR). Prior research has shown that thin films (-30-40 A) of A120 3 and BN can be synthesized by exposing a condensed layer of AI(CH 3)3/H20' and B 2 H 6 /NH 32 , respectively, supported on a silver substrate to broadband SR. Core level excitation has been of interest for some time as a means of inducing site-selective chemistry 3, and synchrotron radiation has been extensively pursued as an excitation source for surface reactions (a comprehensive list is available in reference 4). Recent research by Rosenberg and coworkers' shows the effect of core level excitation in the adamantane (CIoH 16)/Si system. If this system is irradiated with photons with energies greater than 284 eV (above the C K-edge) decomposition of the carbon containing species is extensive and results in a surface that may be composed of SiC. Irradiation of the adamantane with photon energies less than 284 eV causes some decomposition, but much of the adamantane structure appears to persist. EXPERIMENTAL
The experiments presented in this note were carried out on the U7A and B beamlines at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory, which provide about 5x10" photons cm 2 sece' . The ultra-high vacuum chamber used in this study had a base pressure of 5x10 10 Torr, which was obtained with turbomolecular, Ti sublimation, and ion pumping. The sample used in this study was a Ta foil with either Ag or Au evaporated onto it in
561 Mat. Res. Soc. Symp. Proc. Vol. 354 01995 Materials Research Society
situ. X-ray photoelectron spectroscopy (XXPS) was performed with a hemispherical analyzer to verify that the surface 1500 was free of contaminants. The sample was attached to a liquid warmed to nitrogen cooled cryostat and could be cooled to -80 K. The reactants, (Si(CH 3)4 2 ho 1000 or SiH 4) and H1O were introduced into the chamber through stainless steel tubes of 1/16" 1 hoL inside diameter, directed at the cooled substrate. The resultant mixed layer on Ag or Au was TMVIS 0about 100 A thick as estimated by the attenuation of the substrate core levels level in XPS spectra. 90 95 100 105 110 Monoenergetic light from the (eV)
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