Progress toward single-molecule electronics relies on a thorough understanding of local physico-chemical processes and development of synthetic routines for controlled hetero-coupling. We demonstrate a structurally unexpected ring closure process for a homo-coupled 4,4'-bipicenyl, realized in on-surface synthesis. An initial covalent C-C coupling of 4-bromopicene locks at lower temperatures the position and geometrically shields part of 4,4'-bipicenyl. Employing this effect of shielding might offer a path toward controlled stepwise hetero-coupling. At higher temperatures, a thermally activated three-dimensional rotation upon hydrogen dissociation, a dehydrogenative roto-cyclization, lifts the surface-dimensionality restriction, and leads to the formation of a perylene. Thereby, the shielded molecular part becomes accessible again.

Organic electronics are a growing field of research involving the design of devices using organic molecules instead of traditional semiconductor materials. Organic molecules are more versatile and can be tailored to possess the desired electronic, mechanical, optical, and chemical properties. Herein, dibenzo[6]phenacene (DB6P) is addressed, which is an organic molecule with a phenacene skeleton linearly extended with additional benzene rings. Employing scanning tunneling microscopy and spectroscopy, we studied the growth of DB6P on a Ag(111) surface and the emerging electronic states. Molecules grew initially planar on the surface, while the growth of the second layer continued in a stacked configuration with a rotated unit cell. This rotation resulted in a Moire-like modulation, providing experimental access to the vertical electronic interaction between molecules in different layers. The study findings are important because they could lead to the development of new types of organic electronic devices with improved performance and functionality.

The physical investigation of surfaces and their properties crucially depends on their quality. Such investigations are commonly performed in an ultra-high vacuum environment. Thereby, the transfer of samples among different setups and under ambient conditions is desirable. The usage of a capping layer for the protection of surfaces against contaminations during long-time storage and transfer, and the subsequent temperature-controlled decapping is an established approach. However, a residual-free removal of the capping layer may present a challenge. Here, we systematically investigate the decapping process of a tellurium protected topological insulator Bi2Te3. We give evidence for the material segregation from the contaminated capping layer surface to the substrates. Therefore, a simple, temperature controlled decapping is not sufficient. We demonstrate that near perfect surfaces can be reliably obtained even after long-time storage through a combination of an initial argon ion sputtering process and a following heating for decapping. This approach is suitable for dedicated analysis systems as well as for industrial applications, large throughput of samples of arbitrary shapes, and is easily implemented in existing setups.

Layered MoS 2 is considered as one of the most promising two-dimensional photocatalytic materials for hydrogen evolution and water splitting; however, the electronic structure at the MoS 2 -liquid interface is so far insufficiently resolved. Measuring and understanding the band offset at the surfaces of MoS 2 are crucial for understanding catalytic reactions and to achieve further improvements in performance. Herein, the heterogeneous charge transfer behavior of MoS 2 flakes of various layer numbers and sizes is addressed with high spatial resolution in organic solutions using the ferrocene/ferrocenium (Fc/Fc + ) redox pair as a probe in near-field scanning electrochemical microscopy, i.e. in close nm probe-sample proximity. Redox mapping reveals an area and layer dependent reactivity for MoS 2 with a detailed insight into the local processes as band offset and confinement of the faradaic current obtained. In combination with additional characterization methods, we deduce a band alignment occurring at the liquid-solid interface.

Ditetradecyl-substituted [7]phenacene was prepared and applied in thin-film FET devices, displaying higher mobility compared to parent [7]phenacene.

The [10]phenacene and [11]phenacene molecules have been synthesized using a simple repetition of Wittig reactions followed by photocyclization. Sufficient amounts of [10]phenacene and [11]phenacene were obtained, and thin-film FETs using these molecules have been fabricated with SiO 2 and ionic liquid gate dielectrics. These FETs operated in p-channel. The averaged measurements of field-effect mobility, < μ >, were 3.1(7) × 10 −2 and 1.11(4) × 10 −1 cm 2 V −1 s −1 , respectively, for [10]phenacene and [11]phenacene thin-film FETs with SiO 2 gate dielectrics. Furthermore, [10]phenacene and [11]phenacene thin-film electric-double-layer (EDL) FETs with ionic liquid showed low-voltage p-channel FET properties, with < μ > values of 3(1) and 1(1) cm 2 V −1 s −1 , respectively. This study also discusses the future utility of the extremely extended π-network molecules [10]phenacene and [11]phenacene as the active layer of FET devices, based on the experimental results obtained.

We elucidate that the tip sharpness in scanning tunneling microscopy (STM) can be characterized through the number of field-emission (FE) resonances. A higher number of FE resonances indicates higher sharpness. We observe empty quantum well (QW) states in Pb islands on Cu(111) under different tip sharpness levels. We found that QW states observed by sharper tips always had lower energies, revealing negative energy shifts. This sharpness-induced energy shift originates from an inhomogeneous electric field in the STM gap. An increase in sharpness increases the electric field inhomogeneity, that is, enhances the electric field near the tip apex, but weakens the electric field near the sample. As a result, higher sharpness can increase the electronic phase in vacuum, causing the lowering of QW state energies. Moreover, the behaviors of negative energy shift as a function of state energy are entirely different for Pb islands with a thickness of two and nine atomic layers. This thickness-dependent behavior results from the electrostatic force in the STM gap decreasing with increasing tip sharpness. The variation of the phase contributed from the expansion deformation induced by the electrostatic force in a nine-layer Pb island is significantly greater, sufficient to effectively negate the increase of electronic phase in vacuum.

Phenacenes represent.a class of simple hydrocarbons with appealing physical properties ranging from high charge mobility to superconductivity in combination with chemical robustness that are easily modified to serve as versatile building blocks for tailored structures. As a promising candidate for applications in organic devices, phenacenes are the focus of recent investigations. Thereby, the initial growth behavior starting from a single molecule is controversial. Here, we address the growth of [7]phenacene and [9]phenacene on a Ag(111) surface, studying the details of the initial stage of growth by scanning tunneling microscopy. According to our results, a previously introduced model involving a coverage-dependent phase change with the out-of-plane rotation of molecules in the initial growth stage can be disregarded. Instead, we find evidence for the formation of a new phase on top of an in-plane wetting layer during the initial stage of growth.

The influence of geometric parameters on the magnetic fine structure of domain walls in bent nanowires is investigated. The domain pattern in the soft-magnetic Co39Fe54Si7 alloy is studied via scanning electron microscopy with polarization analysis and modeled via micromagnetic simulations. It is demonstrated that the bending angle affects details of the microstructure as well as the preponderant domain-wall type. A phenomenological model is developed that provides the global energy minimum of individual types of domain walls as a function of the geometric parameters of the wire. The results can be directly transferred to permalloy wires, as permalloy and Co39Fe54Si7 alloy have a comparable magnetostatic exchange length.

As promising building blocks in spintronics, organic molecules have shown a variety of advantages including long spin coherence time and length as well as superparamagnetism. In addition, contacting with ferromagnetic (FM) materials, molecules induce so-called “spinterfaces” at the organic-FM boundaries, at which new spin-polarized states appear and change the magnetic properties in these hybrid systems. While the spinterface may influence performance in spinctronic devices, it may also extend the possibility of organic spintronics. To conduct an investigation into spinterfaces, we visualized the spin-distribution within single pentacene (PEN, C 22 H 14 ) on FM Co nanoislands on Cu(111) via spin-polarized scanning tunnelling microscopy (SP-STM) [1]. Near the Fermi level, the widely-used semiconducting PEN molecules show not only spin-polarization opposite to the Co substrate, but also spin-dependent symmetries. Combined with first-principles calculations, the experimental findings agree with the pz-d hybridization model, in which spin-dependent bonding types can result in different molecule symmetries. Our observations exhibit locally-reversed spin-polarization after molecule deposition, and reveal a concise way to predict molecular spin-distribution for π -conjugated molecules such as PEN in organic-FM hybrid structures.

Incorporating spin-polarized scanning tunneling microscopy (SP-STM) measurements and first-principles calculations, we resolve spin-polarized states and consequent features in a pentacene(PEN)-Co hybrid system. Symmetry reduction of PEN clarifies the PEN adsorption site and the Co stacking methods. Near the Fermi energy, the molecular symmetry is spin-dependently recovered and an inversion of spin-polarization in PEN with respect to Co is observed. The experimental findings and calculation results are interpreted by a pz-d hybridization model, in which spin-dependent bonding-antibonding splitting of molecular orbitals happens at metal-organic spinterfaces.

We study the magnetostatic interaction of submicron Ni-81 Fe-19 rectangles arranged in a linear chain by measuring the anisotropic magnetoresistance (AMR) of a single rectangle. The rectangles have a lateral aspect ratio of 2 : 1 and are lined up with the long axis oriented side by side varying the interelement distance down to 60 nm. The energy density of the Landau state is determined from the hard-axis magnetization reversal for a field applied along the chain direction. As a second approach identical energy densities are deduced from the switching field (Landau to quasisingle domain state) like in the case of a Stoner-Wohlfarth particle. The results show that the impact of the magnetostatic interaction on the energy density of the Landau state in remanence is negligibly small (<1 kJ/m(3)). The magnetostatic interaction between field-distorted Landau states, however, is the same as for rectangles in a single domain state and is therefore governed by the compensation of surface charges at the rim. By studying rectangles with only one neighbor, the important role of symmetry on the magnetostatic interaction is shown.

Using ultrahigh-vacuum low-temperature scanning tunneling microscopy and spectroscopy combined with first principles density functional theory calculations, we have investigated structural and electronic properties of pristine and potassium (K)-deposited picene thin films formed in situ on a Ag(111) substrate. At low coverages, the molecules are uniformly distributed with the long axis aligned along the [112̄] direction of the substrate. At higher coverages, ordered structures composed of monolayer molecules are observed, one of which is a monolayer with tilted and flat-lying molecules resembling a (11̄0) plane of the bulk crystalline picene. Between the molecules and the substrate, the van der Waals interaction is dominant with negligible hybridization between their electronic states; a conclusion that contrasts with the chemisorption exhibited by pentacene molecules on the same substrate. We also observed a monolayer picene thin film in which all molecules were standing to form an intermolecular π stacking. Two-dimensional delocalized electronic states are found on the K-deposited π stacking structure.

Ge films can be grown between the Pb overlayer and Si(111) substrate by the surfactant-mediated epitaxy. We detect the high-order Gundlach oscillation revealed in scanning tunneling microscopy (STM) to measure the work function difference between Pb/Si(111) and Pb/Ge/Si(111). Owing to different dielectric responses of Si and Ge, the tunneling current on Pb/Si has to be larger than that on Pb/Ge/Si by a factor of 2–3 to establish the same electric field in STM gap on both regions. This condition leads us to obtain a work function difference of 200 meV from observing Gundlach oscillation. It is believed that the method developed in this work can be extended to measure the surface work function difference of bulk conductors as well.

In this study, we use low-temperature scanning tunneling microscopy and X-ray photoemission spectroscopy to study two closely related molecules, pentacene (PEN) and perfluoropentacene (PFP), adsorbed on a herringbone reconstructed Au(111) surface. PEN molecules are mobile under the probe tip at an elevated positive sample bias voltage with the direction of diffusion being correlated to the surface structure and the initial molecular orientation. Moreover, an induced rearrangement of the herringbone reconstruction is observable after manipulation. PFP molecules rearrange into flat, densely packed islands and the herringbone structure is undisturbed by the adsorbed PFP molecules. In addition, the X-ray photoelectron spectroscopy (XPS) C 1s and F 1s core level spectra of PFP show a shift toward high binding energy at high coverage. In comparison only a subtle shift for the C 1s core level of PEN at high coverage is seen. This indicates a different molecular arrangement for PFP in the bulk and in close proximity to the gold substrate.

It is known that the energy spacing between adjacent empty quantum well (QW) states in Pb islands on Cu(111) would reveal the shrinking characteristic originating from the effect of the image potential. Using the phase accumulation model, including a phase factor contributed from the image potential, the shrinking energy spacing can be quantitatively explained with the assumption of the parabolic energy versus wave vector (E–k) dispersion. However, an experimental dispersion acquired from analyzing the energies of the QW state reveals a linearE–krelationship corresponding to the Pb bulk band structure, implying the assumed parabolic dispersion is not appropriate. By combining the linear dispersion with the image potential effect in the calculation, it is found that the calculated values of energy spacing of island thickness below eight atomic layers are not in agreement with the experimental measurements. This implies that the electronic structure of Pb islands would be similar to that of the bulk when their thicknesses reach eight-atomic layers.

Well-ordered metal-organic nanostructures of Fe-PTCDA (perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride) chains and networks are grown on a Au(111) surface. These structures are investigated by high-resolution scanning tunneling microscopy. Digitized frontier orbital shifts are followed in scanning tunneling spectroscopy. By comparing the frontier energies with the molecular coordination environments, we conclude that the specific coordination affects the magnitude of charge transfer onto each PTCDA in the Fe-PTCDA hybridization system. A basic model is derived, which captures the essential underlying physics and correlates the observed energetic shift of the frontier orbital with the charge transfer.

The unoccupied states of Pb dense overlayers on Si(111) reveal an oscillatory character with two electronic resonance peaks that can be observed by scanning tunneling spectroscopy. By measuring the energy spacing between resonance peaks, it is found that the energy spacing is reduced with increasing the coverage of dense overlayer. The change of energy spacing originates from that the movement of the high-energy resonance peak is more pronounced than that of the low-energy peak with varying coverage. The authors demonstrate that this phase-dependent energy spacing is a useful quantity to identify that the room-temperature 1 × 1 and the low-temperature 7 × 3 phases have an identical coverage of 1.2 ML.