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

Abstract

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.

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

“…Furthermore, it is observed from the high-resolution STM images that the two opposing lobes of each CuPc molecule still remain in the directions of principal axis of the Bi(111) substrate. The alignment of the CoPc chains is also parallel to the principal axes of the Bi(111) lattice, similar to the CoPc chain adsorbed on Bi(111) [ 44 ]. It indicates that the molecule–substrate interaction is not negligible, which may arise from the surface states of the Bi(111) substrate.…”

“…However, the chiral feature disappears in the STM image in Figure 3 b obtained at +0.5 V. This phenomenon is similar to CuPc/Ag (100) system [ 24 ], but different from the MnPc and CoPc molecules. The latter reveals no chirality at both positive and negative bias voltage in 2D domains on the Bi(111) surface [ 42 , 44 ]. The voltage-dependent chiral appearance indicates that the original effect of molecular chirality is not a molecular geometric effect, but an electronic effect.…”

Unveiling orbital coupling at the CoPc/Bi(111) surface by ab initio calculations and photoemission spectroscopy

“…A hexagonal slab was used to simulate the unit cell of the adsorption model, with a dimension of 22.74Å Â 22.74Å Â 20.96Å including four layers of Bi(111) and 15Å vacuum. As revealed from previous STM investigations of CoPc grown on Bi(111) surface, 35 the rst layer is at-lying absorbed on substrate surface. Thus, the isolated CoPc molecule was placed in the x-y plane with initial molecule-substrate distance of 3.5Å.…”

“…Different from noble metal surfaces such as Au(111) and Ag(111), semimetal Bi is relatively inert, indicating a rather weak molecule-substrate interaction in consistent with previous STM reports. 35 From the energy point of view, it can be seen that the top conguration is the most stable adsorption site with the adsorption energy of À2.83 eV, suggesting that the CoPc molecule is favored to be arranged at the top site. Interestingly, it is also notable that the adsorption energy for top site is lower by about 0.44 eV than the rest three congurations, which is apparently different from the CoPc/Ag(111) and CoPc/Au(111) adsorption system, for example, where the adsorption energy for top and hcp congurations is almost same, indicating that the atomic structure/properties of noble metal may hardly inuence the adsorption behaviors of MPc molecules.…”

“…20 Despite considerable investigations have been dedicated to the growth of MPcs on various substrates experimentally and theoretically, [4][5][6][7][8] however, less attention has been paid to the exploration of MPc/semimetal interface in the past. Besides, previous scarce reports mainly concentrate on the morphology investigation of MPc on semimetal surface, 3,35 while a systematic exploration of the interface electronic structures is still missing. In fact, bismuth (Bi), as one of the most studied semimetal elements, has exhibited fantastic characters, for example, the Bi(111) or Bi(110) surface with signicant spinorbit coupling have been served as the ideal platform in the exploitation of topological properties.…”