| Nanometer material is a big hotspot of scientific research in recent decades. Nanometer material is a kind of solid material, it’s a composition of very fine grain size whose characteristic dimension size at most100nm. These materials have surface effect, small size effect, quantum size effect and macroscopic quantum tunnel effect, and has a strange mechanical, electrical, magnetic, optical, thermal and chemical properties due to the scale of the materials stay in the transition area of atom clusters and macro objects. With the development of science and technology, nanowires, nanotubes and nano film materials appeared, and showed their irreplaceable significance in the practical application. At present, the research of nanometer materials looks forward to be more popular, molecular motors has been born.Scanning tunneling microscopy (STM) is an advanced surface analysis, it can not only provide the atomic resolution images of surficial topography, but also reflects the electronic structure of nano-materials in real space. Ultrahigh vacuum system of the scanning tunneling microscopy (STM) can make the vacuum degree of the space where samples belong to achieve10-10mbar even better, reduce microscopic particles (such as electron, ion and photon, atoms and molecules, etc.) in the surrounding environment. And in the ultra high vacuum environment, the number of molecules per unit volume is less than1/1012of that in the normal pressure space. This is the ideal condition to research and produce nano-materials. Cryogenic system of STM, not only reduced the thermal motion of STM and samples, but reduce or even eliminate the noise from the external environment, and also improves the resolution of scanning tunneling spectrum, and even provides the possibilities for various controllable operation to be achieved, such as the manipulation of atoms or molecules, chemical reactions induced by tip, etc. Therefore, the STM has many advantages in the studies of nano materials.In this thesis, by utilizing the method of tip deposition and UHV-STM, we produced and studied the chain of ethanol molecules on the surface of HOPG. To make full use of its dimension effect to manipulate molecules in the space on the top of the substrate easily, molecular chain is fixed on high directional pyrolysis graphite substrate surface, rather than put it into the liquid or solid. Molecular motor are the nano-machines that convert the external energies into mechanical motion or rotations. Previous molecular rotors are almost based on single molecule. Here we present the self-assembled molecular rotors of ethanol chains connected by hydrogen bonds. By applying pulse voltage at one end of the chain, a H atom stripped from the molecular hydroxyl, O ion left will combine with C in the substrate, that’s the formation of the stable center of a rotor. Hydrogen-desorption can induce the rotation of ethanol chain around the C-O bond, leading to the formation of large-size of molecular rotors. When two positions with H-desorption appeared, the rotation of ethanol chains would be blocked due to the hindered torque, resulting in the rotor with fan-shape. Further investigation demonstrates that the rotation mechanism is the interplay of thermal fluctuation and inelastic electron tunneling. In the case of molecular thermal motion exist only, the speed of the rotation should be uniform, because of the isotropic substrate with a6fold symmetry, and the non-uniform rotation happened when the needle tip is too close to the molecular motor or the tunneling current is too large, what proved rotational speed of molecular motor is affected by the tunneling electronic. Our experiments showed:the needlepoint approached closer to the molecular chain, the motor rotated faster, and the distance increased the speed would be slower conversely; and at liquid helium temperature, we didn’t find signs of the rotation of the ethanol molecular chains on HOPG surface, what provided a sufficient evidence to verify the thermal motion mechanism of molecular motors. |
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