Researchers identify possible new material for nanoelectronics

A team from five Japanese and Taiwanese universities has characterised the structural and electronic properties of a thin layer of the molecule on a silver surface, demonstrating its potential for electronic applications. Picene's sister molecule pentacene has been widely studied because of its high carrier mobility. However, pentacene, which is made of five benzene molecules joined in a line, breaks down under normal environmental conditions. In Picene, however, these same five benzene rings are bonded together in a W shape. This simple structural change alters some of the molecule's other properties: Picene retains pentacene's high carrier mobility, but is more chemically stable and therefore better suited to practical applications. To test picene's properties when juxtaposed with a metal, as it would be in an electronic device, the researchers deposited a single layer of picene molecules onto a piece of silver. They then used scanning tunneling microscopy, an imaging technique that can visualise surfaces at the atomic level, to closely examine the interface between the picene and the silver. Though previous studies have shown a strong interaction between pentacene and metal surfaces, "we found that the zigzag-shaped picene basically just sits on the silver," said University of Tokyo researcher Yukio Hasegawa. Interactions between molecules can alter their shape and therefore their behavior, but the researchers found that picene's weak connection to the silver surface left its properties intact. "The weak interaction is advantageous for molecular [electronics] applications because the modification of the properties of molecular thin film by the presence of the [silver] is negligible and therefore [the] original properties of the molecule can be preserved very close to the interface," Hasegawa added. According to Hasegawa, picene's weak interactions with the silver allow it to deposit directly on the surface without a stabilising layer of molecules between, a quality he said is "essential for achieving high quality contact with metal electrodes." Because picene displays its high carrier mobility when exposed to oxygen, the researchers are now hopeing to investigate its properties under varying levels of oxygen exposure in order to elucidate a molecular mechanism behind the behaviour.