Center for Functional Nanomaterials Seminar

Scanning tunneling microscopy (STM) is capable of detecting the structural and electronic properties of nanoscale materials on the atomic scale. Firstly, I will give a description of a newly-built laser-assisted variable temperature ultra-high vacuum (UHV) STM system with optical access for investigating optically active materials on the atomic scale. This system utilizes an integrated high numerical aperture (NA) optic that is mounted directly behind the sample stage under UHV (on the opposite side of the sample relative to the STM tip) in order to achieve sharp focusing of the laser beam in a stable geometry while maintaining excitation polarization integrity and high collection efficiency. Our setup allows recording the optical, topographic, and electronic properties of materials simultaneously. Secondly, I will present our STM investigations of molecular self-assembly, single-molecule physics and dynamics, and graphene on copper surfaces. Molecular self-assembly is an effective method for the fabrication of high quality thin films of conjugated molecules on metal surfaces. And the molecular arrangements can be tuned by changing the length of alkyl chains. Scanning tunneling spectroscopy of single iron phthalocyanine molecules on Au(111) shows Kondo resonances that depend sensitively on the molecular adsorption site. The thermally driven rotation of single tetra-tert-butyl zinc phthalocaynine molecules has been observed on Au(111) at 78 K with a fixed axis provided by the N-Au chemical bonding. The observation of the conductance switching for single rotaxane molecules confirms that the conductance switching in rotaxane thin films is an inherent property of rotaxane molecules. In our graphene research, we showed that carbon atoms nucleate into graphene islands with different lattice orientation on Cu(111),, leading to the formation of numerous domain boundaries at high coverage. Some interesting STM observations of graphene on Cu foil will also be discussed.