Bozhko Sergey I, Walshe Killian, Shvets Igor V
Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow District, 142432, Russia.
School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Dublin 2, Ireland.
Sci Rep. 2019 Nov 5;9(1):16017. doi: 10.1038/s41598-019-52544-4.
We report on a transition in a monolayer of C molecules deposited on a WO/W(110) substrate. The transition from a static state, where the molecules are rigidly bound to the surface by a coordination bond, to a state where the molecules are loosely bound to the surface by van der Waals force and rotate continuously, has been studied using scanning tunnelling microscopy (STM). The separation between the molecules and the surface increases by 1.2 Å across the transition. The transition from the static state into the rotating state takes place at 259 K. The energy of the spinning state with respect to the lowest energy state, having a single coordinated bond, can be obtained from the statistics of the molecules switching. The binding energy of the molecule in the spinning state can be easily altered by changing the polarity of the bias voltage applied between the STM tip and the surface. The binding energy decreases by 80 meV when the bias polarity of the sample changes from positive to negative with respect to the tip. The results are consistent with the Coulomb blockade model: when electrons travel from the surface to the C molecule, and then to the tip; charge accumulates on the molecule due to the Coulomb blockade. This increases the electrostatic interaction between the molecule's charge and a corresponding image charge generated on the metallic surface.
我们报道了沉积在WO/W(110)衬底上的单层C分子的一种转变。利用扫描隧道显微镜（STM）研究了从静态（分子通过配位键刚性地结合在表面）到分子通过范德华力松散地结合在表面并持续旋转的状态的转变。在转变过程中，分子与表面之间的间距增加了1.2 Å。从静态到旋转状态的转变发生在259 K。相对于具有单个配位键的最低能量状态，旋转状态的能量可从分子切换的统计数据中获得。通过改变STM针尖与表面之间施加的偏置电压的极性，可以轻松改变旋转状态下分子的结合能。当样品相对于针尖的偏置极性从正变为负时，结合能降低80 meV。结果与库仑阻塞模型一致：当电子从表面传输到C分子，然后再到针尖时；由于库仑阻塞，电荷在分子上积累。这增加了分子电荷与金属表面上产生的相应镜像电荷之间的静电相互作用。
