title: The puzzle of contrast inversion in DNA STM imaging.
abstract: DNA has been at the center of an imaging effort since the invention of the scanning tunneling microscope (STM). In some of the STM imaging reports the molecules appeared with negative contrast, i.e., "submerged" under the metal background and darker. We demonstrate the phenomenon of contrast inversion in DNA STM imaging by controlled and spontaneous contrast inversions and by the dependence of the DNA apparent height with respect to the surface on the imaging bias voltage. Using these characterizations, we formulate a model explaining the above phenomenon by resonant tunneling through virtual states in the vacuum between the STM tip and the DNA molecule.
authors.forename: Errez
authors.initials: E
authors.lastname: Shapir
authors.forename: Juyeon
authors.initials: J
authors.lastname: Yi
authors.forename: Hezy
authors.initials: H
authors.lastname: Cohen
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Kotlyar
authors.forename: Gianaurelio
authors.initials: G
authors.lastname: Cuniberti
authors.forename: Danny
authors.initials: D
authors.lastname: Porath
mesh_terms: D004247:DNA / Q000648:ultrastructure*; D016252:Microscopy, Scanning Tunneling
chemical_list: D004247:DNA