Voltage dependent STM imaging of inorganic adsorbates

Abstract

Scanning tunneling microscopy is sensitive to surface adsorbates to a much lower impurity level than most other surface science techniques. Even under the best vacuum and preparation conditions, a very low concentration of depressions of unknown origin is often observed in STM images of the coin metal surfaces. We outline a procedure to identify impurities by apparent height spectroscopy; a technique that can be easily performed by standard scanning tunneling microscopes. Apparent height spectroscopy, performed with a low-temperature scanning tunneling microscope, records the apparent height of an adsorbate with respect to the surface level over an extended voltage range at distinct voltage intervals. The spectra show characteristic features that can be used to identify adsorbates. We exemplify our method for two common impurities on Cu(111), oxygen atoms and carbon monoxide molecules. We reveal three characteristic differences in the apparent height spectroscopy of the two adsorbates: the dark region, the voltage of contrast reversal, and the onset of the lowest unoccupied molecular orbital. Each of these features is characteristic for the specific adsorbate/substrate system; giving three possibilities to identify the two species. The procedure can easily be extended to other impurities.

Characteristics of sulfur atoms adsorbed on Ag(100), Ag(110), and Ag(111) as probed with scanning tunneling microscopy: experiment and theory

“…[23][24][25] It has been proposed recently that such voltage-dependent imaging can be used as a tool to differentiate between adsorbates on surfaces. 10 To this end, one must either have a basis of past experimental work for comparison, or confidence that theoretical work can make reliable predictions. In this paper we focus on STM images of S atoms on the three low-index surfaces of Ag.…”

Considerably Increased Dynamics of CO–Water Complexes over CO and Water Alone

“…Depressions and protrusions are randomly distributed across the surface (Figure a,b). At the tunneling parameters used here, water and CO are imaged on Cu(111) as protrusions and depressions, respectively. Previous work revealed that water and CO monomers preferentially adsorb at atop adsorption sites on most metal surfaces, including Cu(111).…”