Atomic scale chemistry on silicon surfaces studied with a variable temperature scanning tunneling mi...

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" Atomic scale chemistry on silicon surfaces studied with a variable temperature scanning tunneling microscope "
M. A. Rezaei W. Ho

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1113362
Doc. No	:	TLpq304419879
Main Entry	:	M. A. Rezaei
	:	W. Ho
Title & Author	:	Atomic scale chemistry on silicon surfaces studied with a variable temperature scanning tunneling microscope\ M. A. RezaeiW. Ho
College	:	Cornell University
Date	:	1998
student score	:	1998
Degree	:	Ph.D.
Page No	:	147
Abstract	:	Using a variable temperature scanning tunneling microscope, we have studied several adsorbates on silicon surfaces. We have studied the adsorption characteristics of H2S on Si(111)-(7 usd\timesusd 7). H2S adsorbs dissociatively at sub-monolayer coverage, from 50 to 300 K, with HS bonded to an adatom and H bonded to a rest atom. The adsorption is site selective and the adsorption site preference is temperature dependent. At 50 K, the faulted center sites are most favored for adsorption, followed by unfaulted center sites, faulted corner sites, and unfaulted corner sites. As the temperature is increased, the differences between the faulted and unfaulted halves diminish, but the center sites remain more reactive than the corner sites. We present an explanation to account for the non-Langmuir kinetics involved in this system. We have induced and imaged the dissociation of HS and DS on Si(111)-(7 usd\timesusd 7). Individual HS (or DS) fragments can be dissociated with the STM at low temperatures without affecting neighboring adsorbates. Near room temperature (297 K) and above, DS dissociates thermally, with an activation barrier of 0.73 0.15 eV. The activation barrier was calculated from atomistic studies of the dissociation rates at temperatures between 297 and 312 K. We have induced and imaged the dissociation of D2S on Si(100). D2S dissociates into DS and D below 200 K. Individual DS fragments can be dissociated with the STM at low temperatures. At 200 K or above, D2S dissociates into S and two D's. D2S adsorption affects the surface reconstruction on Si(100), from the buckled dimer configuration to the dynamically flipping configuration and vice versa. We have studied the adsorption and STM induced desorption of NO from Si(111)-(7 usd\timesusd 7). NO adsorbs preferentially on faulted corner sites, followed by faulted center sites, unfaulted corner sites and unfaulted center sites. The preference for the different adsorption sites is independent of temperature and correlates well with the local density of states at these sites. NO can be desorbed from Si(111) by the STM. The data suggest the desorption is induced by the electric field under the STM tip. The threshold positive electric field for desorption of NO is 0.114 0.009 V/A.
Subject	:	Adsorption
	:	Applied sciences
	:	Hydrogen silicide
	:	Pure sciences
	:	Scanning tunneling microscope
	:	Silicon