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Title:Novel reactions on halogen-terminated SI(100)
Author(s):Trenhaile, Brent Reid
Doctoral Committee Chair(s):Weaver, John H.
Department / Program:Physics
Subject(s):silicon SI(100)
hut formation
electron-stimulated Desorption
Abstract:The (100) surface of Si is an ideal surface on which to study fundamental processes because of its relative simplicity and its rich literature. In my research, I have sought to elucidate novel surface reactions on halogen-terminated Si(1OO). I have extensively utilized room-temperature and low-temperature scanning tunneling microscopes, as well as the variable-temperature instrument available in the Center of Microanalysis of Materials at the University of Illinois at Urbana Champaign, to get insights into atomic-level processes. My work has led to a new model for desorption of atoms from surfaces, has shown that halogens prevent hut formation during growth of Ge on Si(l00), and has demonstrated an innovative way that halogens can be used to investigate oxidation of Si(l00). Spontaneous desorption of Cl, Br, and I from n- and p-type Si(l00)-(2xl) was studied at temperatures of 620 - 800 K where conventional thermal bond breaking should be negligible. The activation energies and prefactors determined from Arrhenius plots indicate a novel reaction pathway that is initiated by the capture of electrons that have been excited by phonon processes into Si-halogen antibonding states. This configuration is on a repulsive potential energy surface, and it is sufficiently long-lived that desorption can occur, constituting phononactivated electron-stimulated-desorption. The desorption rates for I were nearly three orders of magnitude larger than the rates for Cl and Br. Here, the Si-I antibonding states overlap the conduction band minimum, so that conduction band electrons with this energy can be captured by the Si-I antibonding states. Together, these results reveal that a complex relationship exists between phonons and electronic excitations during chemical reactions at surfaces. The consequences of Ge deposition on Br-terminated Si(l00) were studied at ambient temperature after annealing at 650 K. One monolayer of Br was sufficient to prevent the formation of Ge huts beyond the critical thickness of 3 ML. This was possible because Br acts as a surfactant whose presence lowered the diffusivity of Ge adatoms. Hindered mobility was manifest at low coverage through the formation of short Ge chains. Further deposition resulted in the extension and connection of the Ge chains and gave rise to the buildup of incomplete layers. Finally, the initial stage of oxidation was studied for H20-exposed Si(l00) in the presence of Cl. Following H20 dissociation and saturation of the surface with Cl, a mild anneal allowed oxygen atoms to insert into Si dimer bonds. It was demonstrated that Cl allowed the bridge-bonded oxygen atoms to be imaged as a dark spot in the center of the dimer. The density of these "split dimer" defects correlated with the c-type defect density on the clean surface. These results also showed how to produce nearly defect free halogen-terminated Si(l00).
Issue Date:2006
Genre:Dissertation / Thesis
Other Identifier(s):5526384
Rights Information:©2006 Trenhaile
Date Available in IDEALS:2012-06-07

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