Growth Behavior of Pristine and Potassium Doped Coronene Thin Films on Substrates with Tuned Coupling Strength

Abstract

The growth of polycyclic aromatic hydrocarbon (PAH) molecular coronene film on various substrates and the subsequent doping of potassium under ultrahigh vacuum (UHV) conditions have been systematically investigated by low-temperature scanning tunneling microscopy and spectroscopy (STM/STS). The crystalline structures and molecular orientations of coronene thin films are both thickness-dependent and substrate-sensitive due to the competition between molecule-substrate interaction and intermolecular interaction. In mono- or bilayer films, coronene molecules are flat-lying on the surface with hexagonal lattice, whereas in multilayer films, the topmost molecules are in a standing-up but tilted configuration with rectangular lattice. In particular, a 2 × 1 superstructure with respect to that of bulk coronene is formed on thick KCl film. Furthermore, we have studied the potassium doped coronene monolayer and multilayer on Ag(100) and KCl/Ag(100) surface. For K-doped coronene monolayer, at certain doping ratio x = 3, the lowest unoccupied molecular orbital (LUMO) of coronene film moves to the Fermi level, and a splitting of the LUMO state is observed. Increased potassium doping would result in a filled LUMO state below the Fermi level. By contrast, no well-ordered structures are obtained in the K-doped coronene multilayers which are vulnerable to rather moderate annealing processes owing to their relatively weak bonding with the supporting substrates, implying a big challenge of growth of PAH thick films in vacuum. The differences in the crystal structures of coronene thin films compared with that in bulk crystals might shed insight on the controversies in the experimental results on the electronic properties of alkali-metal-doped PAHs.

Hybridization vs decoupling: influence of an h-BN interlayer on the physical properties of a lander-type molecule on Ni(111)

“…Some applications, however, require to preserve the intrinsic properties of the molecules such as the typically rather narrow optical absorption and/or emission bands. To achieve this, one needs to electronically decouple the molecules from the substrate, which can be achieved through different ways such as the usage of wide-band-gap insulator thin films (e.g., oxides, alkali halides) [ 3 – 4 ], a molecular spacer layer [ 5 – 6 ], or sp 2 -hybridized two-dimensional interlayers (e.g., graphene and hexagonal boron nitride (h-BN)) [ 7 – 8 ]. The advantageous properties of an h-BN monolayer on metal single crystals are the high crystal quality, chemical inertness and the wide band gap of approx.…”

Scanning Tunneling Microscopy Studies of Potassium-Doped Picene Films on Au(111) Surface

“…However, the LUMO state in K 3 Picene does not reach the Fermi level. This could be caused by the film nature of the sample, the existence of an Au substrate, and the possible different crystal structure. ,,,,,, …”

“…Doped organic molecules provide a diverse platform to enrich the structural and electronic properties of organic materials, − which have wide applications in organic field effect transistors, , photovoltaic cells, , and so forth. Recently, doping of metal atoms, especially alkali metal atoms, into polycyclic aromatic hydrocarbon (PAH) materials attracts much attention because of the appearance of superconductivity. ,− As a typical PAH molecule, picene has an armchair aromatic molecular configuration composed of five benzene rings.…”

Tuning the electronic and magnetic properties of metal-doped phenanthrene by codoping method

“…Superconductivity in potassium-doped picene (C 22 H 14 ) with the transition temperature of 18 K was first reported in 2010, [1][2][3] In subsequent experiments, phenanthrene, coronene, dibenzopentacene, chrysene, anthracene and pentacene, as well as metal dopants, were employed to synthesize the samples to explore the superconductivity. [4][5][6][7][8][9][10][11][12] Very Recently, Xiao-Jia Chen's group reported potassium-doped p-terphenyl superconductor with surprisingly high transition temperatures of 43 Kelvin and 123 Kelvin. [13] Rosseinsky's group and Arčon's group synthesized the crystalline K 2 pentacene, K 2 picene and triphenylide-Based K 2 (C 18 H 12 ) 2 (DME), and the spin liquid state arising purely from carbon π electrons were reported.…”