Local Barrier Height Imaging Research Articles

Unveiling Molecular Adsorption Geometry in Cyclohexanethiolate Self-Assembled Monolayers with Local Barrier Height Imaging

The Au–S interface of thiol-based, self-assembled monolayers grown on Au(111) surfaces is far less understood than it should be. Local barrier height imaging, which has recently resolved work function variations in the buried interface of alkanethiolate monolayers, is now used to study self-assembled monolayers on Au(111) formed by cyclohexanethiol, a molecule with a flexible aliphatic ring structure. Multiple ordered phases are observed, consistent with its conformational flexibility which makes multiple interadsorbate interactions possible. In one particular phase, the appearance of two readily distinguishable features in local barrier height images implies at least two types of adsorption sites. Correlation of simultaneously acquired topographic and local barrier height data allows for a preliminary structural model that accounts for adsorption geometry.

Fabrication of nano-pits and the measurement of their local surface potentials

An Au(1 1 1) surface was irradiated with 500 eV argon ions in a controlled manner to fabricate nano-pits. The surface morphology of nano-pits formed after 6 ML removal by ion irradiation under various temperatures was studied with STM. The depth distribution of pits at various irradiation temperatures was analyzed. There was a specific irradiation temperature at which the depth of pits became very deep in comparison with other temperatures. The results were compared with other fcc metals. The local barrier height (LBH) on surfaces with pits was measured. The LBH images were compared with the topographic images. The width where surface potential was modified near steps was found wider than the topographic width of steps. For pits lager than the critical size, the LBH value at the bottom of pits was same as that on a flat terrace except at step edges.

Modification of HF-treated silicon (100) surfaces by scanning tunneling microscopy in air under imaging conditions

The modification of HF-etched silicon (100) surface with a scanning tunneling microscope (STM) operated in air is studied for the first time in samples subjected to the standard HF etching without the follow-up rinsing in H2O. The modifications are produced in air under normal STM imaging conditions (Vt=−1.4 V and It=2 nA). The simultaneous acquisition of topographical, current image tunneling spectroscopy and local barrier-height images clearly shows that the nature of the modification is not only topographical but also chemical. The features produced with a resolution better than 25 nm are attributed to a tip-induced oxidation enhanced by the presence of fluorine on the surface.