Min-Long Tao

Structural transitions in different monolayers of cobalt phthalocyanine film grown on Bi(1 1 1)

The structural evolution of cobalt phthalocyanine (CoPc) thin films grown on a Bi(1 1 1) surface from the sub-monolayer to the third layer has been investigated with low-temperature scanning tunneling microscopy (STM). Two crucial transitions have been identified during the film epitaxial growth: one is the structural transition from zigzag chains to linear dimerized chains in the monolayer regime; the other is the molecular orientational transition from a flat-lying to a standing-up configuration in the multilayer regime. These results are helpful in understanding the growth mechanism of transition-metal phthalocyanine films on semi-metallic surfaces.

STM STUDY OF THE ADSORPTION OF SINGLE-MOLECULE MAGNET Fe4 ON Bi(111) SURFACE

Single-molecule magnets (SMMs) have unique magnetic properties such as quantum tunneling of magnetization and quantum coherent oscillation, which have potential applications in quantum computation and information storage. In this paper, using the tip-deposition method, we have grafted individual Fe4 molecules onto the semi-metallic Bi(111) surface. Low temperature scanning tunneling microscope (LT-STM) was used to characterize the molecular morphology and electronic structures. It was found that individual Fe4 molecules reveal a triangle shape, which is consistent with the molecular structure of Fe4. Scanning tunneling spectroscopy (STS) analysis indicated that the HOMO–LUMO gap is 0.49 eV. These studies provide direct information about the adsorption of individual SMMs on semi-metal surfaces.

Monitoring and manipulating single molecule rotors on the Bi(111) surface by the scanning tunneling microscopy

We have investigated rotation and manipulation of manganese phthalocyanine (MnPc) molecules on the semimetallic Bi(111) surface by low-temperature scanning tunneling microscopy (STM). At liquid-helium temperature, individual MnPc molecules adsorb flat on the Bi(111) surface but with a slight bend toward the substrate. The in-plane orientation of the MnPc molecule can be changed by 60° by manipulation with the STM tip. At liquid-nitrogen temperature, the isolated MnPc molecules rotate around the central Mn ion because of the weak molecule–semimetal interaction. The MnPc rotor shows a flower-like feature with six lobes corresponding to the six-fold symmetry of Bi(111) lattice. Most importantly, the MnPc rotors can be started or stopped by controlling the intermolecular spacing with the STM tip. These results are important for understanding and controlling the performance of surface-mounted molecular rotors.

Off-Center Rotation of CuPc Molecular Rotor on a Bi(111) Surface and the Chiral Feature

Molecular rotors with an off-center axis and the chiral feature of achiral CuPc molecules on a semi-metallic Bi(111) surface have been investigated by means of a scanning tunneling microscopy (STM) at liquid nitrogen (LN2) temperature. The rotation axis of each CuPc molecular rotor is located at the end of a phthalocyanine group. As molecular coverage increases, the CuPc molecules are self-assembled into various nanoclusters and finally into two-dimensional (2D) domains, in which each CuPc molecule exhibits an apparent chiral feature. Such chiral features of the CuPc molecules can be attributed to the combined effect of asymmetric charge transfer between the CuPc and Bi(111) substrate, and the intermolecular van der Waals interactions.