19 Davey Lab
Penn State UniversityContacts:
Paul S. Weiss: stm@psu.eduGraduate Student:
Sanjini Nanayakkara: sun@stm1.chem.psu.eduDr. Tom Pearl : tpp1@psu.edu
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Our ultra-high vacuum (UHV) scanning tunneling microscope (STM) is capable of performing experiments at 300K, 77K and 4K. Experiments performed thus far range from studying substrate-mediated interactions between adsorbates on single crystal surfaces to investigating electronic properties of single conjugated molecules isolated in a self assembled monolayer (SAM) host matrix. The term, “substrate-mediated interactions”, indicates the crucial and fundamental role the substrate plays in determining the interaction between adsorbed molecules. One method by which the substrate can mediate interactions between adsorbates is by the perturbation of the electronic properties of the surface. The strongest perturbation involves smoothing of the electronic distribution at a step edge by charge transfer from the top of a step edge to the bottom, called the Smoluchowski effect. Studies performed on benzene on Cu{111} at 77K showed that benzene, a nucleophilic molecule adsorbs preferentially on the top of surface step edge. It was also shown that the perturbation of the electronic properties of the surface caused by the initial adsorption of benzene dictated the adsorption sites of other benzene molecules. Thus benzene molecules "communicate" with each other through the substrate. Future experiments will focus on further tuning this communication with the ultimate goal of building atomically precise surface structures.
Experiments are currently being performed on phenylene-ethynylene oligomers isolated by a host matrix of a SAM of alkanethiolates on Au(111). We are investigating their possible use as candidates for electronic devices. We are also investigating the fundamental electronic properties of passivated sub-nanometer gold particles tethered to a SAM by the use of alkanedithiolates. Previous experiments have shown that such particles display "Coulomb Blockade" effects due to their relatively small sizes..
The cleanliness and control over the environment in UHVand low temperatures is an advantage in terms of obtaining spectroscopic data and well as structural resolution of the surfaces.
Schema/Data