Abstract
Manipulation of artificial molecular rotors/motors is a key issue in the field of molecular nanomachines. Here we assemble non-planar SnPc molecules on an FeO film to form two kinds of rotors with different apparent morphologies, rotational speeds and stabilities. Both kinds of rotors can switch to each other via external field stimulation and the switch depends on the polarity of the applied bias voltage. Furthermore, we reveal that the molecular fragment has a great influence on the motions of molecules. Combining scanning tunneling microscopy and DFT calculations, two braking mechanisms are addressed for molecular rotors. One is the transformation of adsorption configurations under the external electric field stimulus that enables the molecular rotor to stop/restart its rotation. The other is the introduction of embedded molecular fragments that act as a brake pad and can stop the molecular rotation. We find that the rotation can be recovered by separating the molecule from the fragments. Our study suggests a good system for manipulating molecular rotors' properties in nanophysics and has important value for the design of controllable molecular machines.
Highlights
Our study suggests a good system for manipulating molecular rotors' properties in nanophysics and has important value for the design of controllable molecular machines
The detailed structures of molecular rotors are studied by scanning tunneling microscope (STM) and density functional theory (DFT) calculations
It's revealed that the rotors with high and low rotation speeds correspond to the shaped tin phthalocyanine (SnPc) molecules with the Sn ion pointing to FeO(111) and to the vacuum, respectively
Summary
Fabrication and manipulation of molecular rotors and motors are crucial for arti cial molecular machines,[1,2,3,4,5] which will most likely be used in the elds of intelligent materials, sensors, nano-medicine and so on.[6,7,8,9] mechanical motions at the molecular scale exist everywhere and play important roles in nature,[10,11] for example, the kinesin protein linear motion powered by adenosine triphosphate hydrolysis,[12] the transportation of cellular cytoplasm through vesicles and the whole bacterial locomotion driven by rotational agella.[13]. A cap-shaped tin phthalocyanine (SnPc) molecule adsorbed on the surface constitutes a singlemolecule switch, with the central metal ion pointed either down to the surface or up to the vacuum with different distances (d) to the surface[32,33] (Fig. 1(b)). This de nes two stable structural con gurations, denoted as jSn-dwi and jSn-upi, with the adsorption energy U(d) being a double-well potential with degenerate minima at ddw and dup. Via STM manipulation, we revealed that the molecular fragment has a great in uence on the motions of the molecules
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