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• The VOPc molecules adsorbed on Bi(111) surface adopt the bilayer-by-bilayer mode from the beginning of growth. • The VOPc bilayer possesses a nested flat laying structure, where the molecules have the orientation O-up in the lower layer and O-down in the upper layer. • The isolated VOPc molecules adsorbed on Bi(111) rotate around the center stemming from the weak interaction between the molecules and Bi(111) surface. The self-assembly of vanadyl phthalocyanine (VOPc) molecules grown on Bi(111) surfaces has been studied using low-temperature scanning tunneling microscopy (STM). It is found that the isolated VOPc molecules adsorbed on Bi(111) rotate around the center stemming from the weak interaction between the molecules and Bi(111) surface. When VOPc molecules assemble into 2D domains, they adopt the bilayer-by-bilayer mode from the beginning of growth. In VOPc ultrathin films, there are almost no domains with one molecular layer (ML) or 3 ML, only domains with 2 ML and 4 ML. Furthermore, the VOPc bilayer possesses a nested flat-laying structure, where the molecules have the orientation O-up in the lower layer and O-down in the upper layer. This results in a strong interlayer coupling within the nested bilayer and a relatively weak coupling between the bilayers, leading to bilayer-by-bilayer growth. [Display omitted] [ABSTRACT FROM AUTHOR]

Self-assembly of functional molecules on solid substrate has been recognized as an appealing approach for the fabrication of diverse nanostructures for nanoelectronics. Herein, we investigate the growth of cobalt phthalocyanine (CoPc) on a Bi(111) surface with focus on the interface electronic structures utilizing photoelectron spectroscopy. While charge transfer from bismuth substrate to the molecule results in the emergence of an interface component in the Co 3p core level at lower binding energy, core-levels associated to the molecular ligand (C 1s and N 1s) are less influenced by the adsorption. In addition, density functional theory (DFT) calculations also support the empirical inference that the molecule-substrate interaction mainly involves the out-of-plane empty Co 3d orbital and bismuth states. Finally, valence band spectra demonstrate the molecule-substrate interaction is induced by interface charge transfer, agreeing well with core level measurements. Charge transfer is shown to be mainly from the underlying bismuth substrate to the empty states located at the central Co atom in the CoPc molecules. This report may provide a fundamental basis to the on-surface engineering of interfaces for molecular devices and spintronics. [ABSTRACT FROM AUTHOR]

Fully relativistic density-functional-theory calculations of Bi(111) thin films are analyzed to revisit their two metallic surface-states branches. We first contrast these metallic branches with surface states arising at gaps in the valence band opened by the spin-orbit coupling (SOC). We find that the two metallic branches alongΓM‾do not overlap with the bulk band at the zone boundary, M . We show that the spin texture observed in such states cannot be traced to the lifting of Kramers' degeneracy. Instead, we track them to themj=±1/2-mj=±3/2SOC splitting, the potential anisotropy for in-plane and out-of-plane states, and the coupling between the opposite surfaces of a slab occurring near M , which is driven by a spatial redistribution of the four metallic states composing the two metallic branches. Each of these branches appears to be non-degenerate at the tested surface, yet each is degenerate with another state of opposite spin at the other surface. Nevertheless, the four metallic states bear some contribution on both surfaces of the film because of their spatial redistribution near M . The overlapping among these states near M , afforded by their spatial redistribution on both surfaces, causes a hybridization that perpetuates the splitting between the two branches, makes the film's electronic structure thickness dependent near M , extinguishes the magnetic moment of the metallic states avoiding the magnetic-moment discontinuity at M , and denies the need or expectancy of the metallic branches becoming degenerate at M . We propose that the opposite spin polarization observed for the two metallic branches occurs because the surface atoms retain their covalent bonds and thus cannot afford magnetic polarization. We show that the Rashba-splitting of the metallic states for inversion-asymmetric films does not have a fixed magnitude but can be tuned by changing the perturbation breaking inversion symmetry., (© 2023 IOP Publishing Ltd.)

The Bi(111) | 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF 4 ) interface has been studied by in situ scanning tunnelling microscopy (STM), cyclic voltammetry and impedance spectroscopy methods within the electrode potential region from − 1.2 V to 0.0 V ( vs. Ag | AgCl in EMImBF 4 ) for 60 h. The Bi(111) | EMImBF 4 interface is ideally polarisable from − 0.8 V to − 0.2 V and the atomic resolution data were established and analysed. After some oxidation/dissolution and reduction cycles within the potential region from 0.0 V to − 1.2 V the roughening of the Bi(111) surface was observed. Differently from Au(hkl) | room temperature ionic liquid interfaces, there is no potential-induced surface reconstruction at Bi(111) | EMImBF 4 interface, and therefore it is not possible to restore the atomically flat Bi(111) surface by applying moderate negative potentials, observed for Au(hkl). Slow electrical double layer (EDL) formation kinetics limited by the finite-length mass transfer and adsorption steps of EMImBF 4 onto the Bi(111) surface has been analysed by the impedance method. The higher series, double layer and adsorption capacitance values, calculated using non-linear least squares fitting method of impedance data, for the Bi(111) | EMImBF 4 interface compared to the Bi(111) | 1-butyl-4-methylpyridinium tetrafluoroborate (BMPyBF 4 ) interface has been explained by the lower molar volume, higher dielectric constant and lower thickness of the EDL formed. [ABSTRACT FROM AUTHOR]

Highlights: [•] 4,4′-bipyridine adsorption at Bi(111) single crystal. [•] Two different molecular patterns observed depending on the electrolyte concentration. [•] DFT calculations provide possible adsorbate orientations and adsorption patterns. [•] Good agreement between modeled and measured in situ STM data. [•] 4,4’-bipyridine molecules are oriented perpendicular to the Bi(111) surface. [ABSTRACT FROM AUTHOR]

Here we present two techniques which give insight on transport phenomena with atomic resolution. Ballistic electron emission microscopy is used to study the ballistic transport through layered heterogeneous systems. The measured ballistic fraction of the tunneling current provides information about lossless transport channels through metallic layers and organic adsorbates. The transport characteristics of Bi(111)/Si Schottky devices and the influence of the organic adsorbates perylene tetracaboxylic dianhydride acid and C60 on the ballistic current are discussed. Scanning tunneling potentiometry gives access to the lateral transport along a surface, thus scattering processes within two-dimensional electron systems for the Bi(111) surface and the Si(111)(?3 × ?3)-Ag surface could be visualized.

Highlights: [•] The stable adsorbate adlayer of TU on Bi(111) was detected by using the in situ STM method. [•] The Nyquist plots can be simulated with the MFMG-R circuit. [•] The Cole–Cole plots form two clearly visible, with kinetically different, TU adsorption areas. [ABSTRACT FROM AUTHOR]

Abstract: Impedance spectroscopy and in situ STM methods have been used for investigation of the camphor and 2,2′-bipyridine (2,2′-BP) adsorption at the electrochemically polished Bi(111) electrode from weakly acidified Na2SO4 supporting electrolyte solution. The influence of electrode potential on the adsorption kinetics of camphor and 2,2′-BP on Bi(111) has been demonstrated. In the region of maximal adsorption, i.e. capacitance pit in the differential capacitance versus electrode potential curve, the heterogeneous adsorption and diffusion steps are the rate determining stages for camphor and 2,2′-BP adsorption at the Bi(111) electrode. It was found that for camphor|Bi(111) interface the stable adsorbate adlayer detectable by using the in situ STM method has been observed only at the positively charged electrode surface, where the weak co-adsorption of SO4 2− anions and camphor molecules is possible. At the weakly negatively charged Bi(111) electrode surface there are only physically adsorbed camphor molecules forming the compact adsorption layer. The in situ STM data in a good agreement with impedance data indicate that a very well detectable 2,2′-BP adsorption layer is formed at Bi(111) electrode in the wide region of charge densities around the zero charge potential. [Copyright &y& Elsevier]

Abstract: The in situ STM studies of Bi(111)C, cleaved at the temperature of liquid nitrogen inside the glove box, have been performed under negative polarisation from −0.1 to −0.7V (versus Ag|AgCl in sat. KCl aqueous solution). The 0.05M Na2SO4 +0.0005M H2SO4 aqueous solution has been used for in situ STM studies. The atomic resolution has been achieved. The in situ STM data show that the surface structure of Bi(111)C and electrochemically polished Bi(111)EP is stable within the potential region investigated and there are no quick surface reconstruction processes as observed for Au(h k l) and discussed in the works [A. Hamelin, in: J.O’M. Bockris, B.E. Conway, R.E. White (Eds.), Modern Aspects of Electrochemistry, vol. 16, Plenum, New York, 1985, p. 1; D.M. Kolb, Ber. Bunsen. Phys. Chem. 92 (1988) 1175; D.M. Kolb, in: J. Lipkowski, P.N. Ross (Eds.), Structure of Electrified Interfaces, VCH, New York, 1993, p. 65; S. Trasatti, E. Lust, in: R.E. White, J.O’M. Bockris, B.E. Conway (Eds.), Modern Aspects of Electrochemistry, vol. 33, Kluwer Academic/Plenum Publishers, New York, 1999, p. 1]. [Copyright &y& Elsevier]

Azobenzene is a prototypical molecular switch which can be interconverted with UV and visible light between a trans and a cis isomer in solution. While the ability to control their conformation with light is lost for many molecular photoswitches in the adsorbed state, there are some examples for successful photoisomerization in direct contact with a surface. However, there the process is often driven by a different mechanism than in solution. For instance, photoisomerization of a cyano-substituted azobenzene directly adsorbed on Bi(111) occurs via electronic excitations in the substrate and subsequent charge transfer. In the present study we observe two substrate-mediated trans – cis photoisomerization reactions of the same azobenzene derivative in two different environments within a multilayer thin film on Bi(111). Both processes are associated with photoisomerization and one is around two orders of magnitude more efficient than the other. Furthermore, the cis isomers perform a thermally induced reaction which may be ascribed to a back-isomerization in the electronic ground state or to a phenyl ring rotation of the cis isomer.