Comparative STM study of azobenzene derivatives on bare and insulator coated metal surfaces

Photoactive molecules, such as azobenzene and its derivatives, have great potential for nanoscale opto-mechanical applications. However, one of the main difficulties in optical actuation of singe molecules at a surface is decoupling them from the electronic states of the substrate. One technique to accomplish this is to coat the substrate with a thin insulating layer, while another is to functionalize the molecule with ``spacer legs'' to lift it off the surface. We have conducted a comparative study of adsorption and self-assembly behavior of bare azobenzene, functionalized bis-tert-butyl-azobenzene, and functionalized tetra-tert-butyl-azobenzene molecules on bare and insulator coated metal surfaces using a variable temperature UHV STM. We observe a variety of temperature dependent molecular configurations, from which we infer the degree of molecule/surface decoupling due to surface modification and molecular functionalization.