Web Release Date: November 6,
Controlled Manipulation of Self-Organized Ni(II)-Octaethylporphyrin Molecules Deposited from Solution on HOPG with a Scanning Tunneling Microscope
Department of Chemistry and Materials Science Program, Washington State University, Pullman, Washington 99164-4630
Received: July 3, 2007
In Final Form: September 19, 2007
Abstract:
The controlled manipulation of a physisorbed self-assembled monolayer is demonstrated at room temperature
for the first time. Patterns are drawn in a NiOEP monolayer supported on freshly cleaved highly ordered
pyrolytic graphite (HOPG) surface using a scanning tunneling microscope (STM) under ambient conditions.
STM images acquired before and after pattern formation at low gap resistance reveal the creation of molecule-free regions. In these cleared regions, STM images display the two-dimensional HOPG lattice with atomic
spacing of 2.5 Å and pattern depth of about 1.2 Å, typical of the STM apparent height for a monolayer
NiOEP film on graphite. These molecule-free regions are created by removal of NiOEP molecules from the
surface when the STM is operated at a very high current set point (tunneling resistance of about 120 M
or
less) as confirmed by the absence of molecular buildup around the patterned areas in the STM images. We
show that the removed molecules are not collecting at the boundaries of the scanned regions and discuss their
fate. Once the molecular film is damaged, the size of the uncovered area keeps on growing with subsequent
scans. We also observe that two different monolayer structures (triclinic and tetragonal) form under the same
experimental conditions.
Download the full text: PDF | HTML
