Natalie A. Kautz

Alkanethiol/Au(111) Self-Assembled Monolayers Contain Gold Adatoms : Scanning Tunneling Microscopy before and after Reaction with Atomic Hydrogen

Alkanethiol self-assembled monolayers on Au(111) are widely studied, yet the exact nature of the sulfur-gold bond is still debated. Recent studies suggest that Au(111) is significantly reconstructed, with alkanethiol molecules binding to gold adatoms on the surface. These adatoms are observed using scanning tunneling microscopy before and after removing the organic monolayer with an atomic hydrogen beam. Upon monolayer removal, changes in the gold substrate are seen in the formation of bright, triangularly shaped islands, decreasing size of surface vacancy islands, and faceting of terrace edges. A 0.143 +/- 0.033 increase in gold coverage after monolayer removal shows that there is one additional gold adatom for every two octanethiol molecules on the surface.

Minimizing image-processing artifacts in scanning tunneling microscopy using linear-regression fitting

We present a method for removing noise from scanning tunneling microscopy images based on least-squares fitting of spatial data. Modeling the known structure of the surface, including isolated features and surface steps, allows for effective discrimination of signal from noise and produces minimal processing artifacts, even for very noisy images. This approach is effective for removing external noise due to vibrational or acoustic interference, and can also be applied to correct for tip-related height jumps as well as to flatten images warped by thermal effects or nonlinearity of the microscope scanner.

Formation of rectangular packing and one-dimensional lines of C60 on 11-phenoxyundecanethiol self-assembled monolayers on Au(111).

The behavior of C(60) molecules deposited onto 11-phenoxyundecanethiol (phenoxy) self-assembled monolayers (SAMs) is studied using ultrahigh vacuum scanning tunneling microscopy (UHV-STM) and spectroscopy. We observe that after thermally annealing between 350 and 400 K in vacuum a combination of hexagonally close-packed islands, rectangularly packed islands, and isolated single lines of C(60) is observed when the C(60) is initially deposited on an unannealed phenoxy SAM. However, only rectangularly packed islands are found when they are deposited on a preannealed phenoxy SAM. We determine the rectangular packing to have a (2√3 × 4) rectangular unit cell with respect to the underlying Au(111) substrate. This type of C(60) structure has not been observed previously for multicomponent self-assemblies on a surface. We discuss the possible causes for the formation of this structure as well as the differences between starting on an unannealed SAM and an annealed one. This study demonstrates the capability of functionalized alkanethiol SAMs to control the growth and structure of C(60) islands during annealing depending on the structural changes of the SAM itself; by preannealing the SAM, the motion of the C(60) can be confined and unique structures resulting from interactions between the SAM molecules and C(60) can be produced.