Quantum Manipulation at Molecule Scale

Abstract

The properties of matters in the single-atom and single-molecule regime and the interactions among them are quantum mechanical in nature. Detecting and manipulating the quantum states on the molecular scale are important and essential for future applications in designing and constructing novel artificial structures and functional nanodevices in the “bottom-up” scheme (Feynman, 1960) because they have numbers of advantages as basic building blocks of matter and serve as good candidates for conceptually new device components when traditional microelectronics reaches the physical limit (Joachim et al., 2000). To realize novel functional nanodevices, controlled manipulation of quantum properties of molecules and nanoparticles are desired. As a local probe, scanning tunneling microscope (STM) has shown powerful ability in physical sciences and allows us to directly detect and manipulate single atoms, molecules and nanoparticles as well as their quantum states at the very basic level of matters since its invention by Binnig et al. (1982a,b). Although the concept of molecular electronics has been proposed for more than 30 years (Aviram and Ratner, 1974), to manipulate single molecules mechanically and quantum mechanically is still not easy. The basic issue in molecular electronics is to realize electronic devices employing only one or very few molecules, that requires controllable formation of transport junctions in which a single molecule can be precisely put between two electrodes and connect with both (Joachim and Ratner, 2005). It is extremely difficult for modern lithography to make electrode junctions as narrow as few nanometers, and more difficult to introduce a molecule into such a junction and connect well with both electrodes. While, an STM in which tip and substrate are two electrodes can provide such ability facilely owing to its atomic lateral resolution and vertical precision, and thus becomes a powerful tool for the study of quantum manipulation at the molecule scale. Controlled doping can alter the electronic properties of single molecules which can be readily investigated by STM. The facility and flexibility of STM also allows implementation of a diver-