Atomistic interactions in STM atom manipulation
This thesis describes the study of two diverse systems, a cluster of silver atoms, and individual silver and bromine atoms, deposited on a metallic single crystal Ag(111)substrate, in the domain of atomic and molecular manipulation techniques, using a custom-built ultrahigh vacuum low temperature scanning tunneling microscope. A cluster of silver atoms was created by a controlled tip-sample contact. Single atoms were extracted from the cluster by using STM tip induced lateral manipulation. To investigate the mechanism of extraction in detail, atom extraction was carried out for different values of manipulation voltage and current. The threshold distance to pull an atom out from the cluster was determined. The tip-cluster distance proved to be the governing factor for the atom extraction mechanism. Lateral manipulation of a metal atom, silver, and a halogen atom, bromine, was carried out on a silver substrate with a silver coated tip apex. Silver atoms were extracted from a cluster of atoms, and bromine atoms were extracted from a cobalt porphyrin molecule using tunneling electron-induced bond dissociation technique. The threshold distance necessary to manipulate the silver atom and the bromine atom was determined. The lateral manipulation signals provided a value of the angle made by the tip with the surface at the first jump of the atom during manipulation. The interaction energy curves for these atoms were calculated using density functional theory. From a combination of all these results, a numerical value of force was obtained. This force corresponds to the threshold force necessary to move a silver atom and a bromine atom on the surface. The values of force provide an insight into the ionic and metallic interactions on the surface at the single atom level. The manipulation capability of the scanning tunneling microscope to build nanostructures was demonstrated by constructing a parabolic corral using locally extracted atoms. Since the surface vacancies and defects created during construction can be sealed off with the atoms and clusters after construction, this procedure resembles an atomic scale analog of a macroscale construction site.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:scanning tunneling microscope atom manipulation quantum corral extraction bond dissociation lateral ultra high vacuum system low temperature
Date of Publication:01/01/2007