SnPc Molecules on Surfaces Studied by Scanning Tunneling Microscopy

Using single molecule as a basic unit of storage devices is an appealing direction of device miniaturization. Tin-phthalocyanine (SnPc) molecules exhibit bistable adsorption configurations, Sn-up and Sn-down. A reversible conversion between these two configurations is readily manipulated and probed by scanning tunneling microscopy (STM). When SnPc molecules are used to form functional devices, they need to adsorb on supporting surfaces. So the growth mechanisms of ultra-thin films on metal surfaces or buffer layers have been investigated. Both layer-island (Stranski–Krastanov) and three-dimensional-island (Volmer–Weber) growth modes are observed in experiments. Because of an electronic decoupling of buffer layers, electronic and vibronic states of SnPc molecules are spectroscopically identified. Molecular switches between Sn-up and Sn-down configurations are achieved by either an electrical mean or mechanical forces. When the STM tip contacts SnPc molecules with controlled structures, electrons transports through single-molecule junctions are explored in detail. In addition, Ag–SnPc–Ag junction exhibits three conductance states at different voltages. These researches pave a way for further development of high-density data storage devices.