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The molecular hopping of a lone 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecule adsorbed on a Ge(001) surface is studied by density functional theory calculations and the climbing-ima...

We have investigated the initial pentacene growth on the Si(111)--In surface using scanning tunneling microscopy. At a low coverage, the molecules lie down flat and form locally ordered molecular layers that are nucleated at the Si step edges. At a higher coverage, two kinds of pentacene crystals with the so-called herring-bone arrangement are grown directly on the surface with the longer molecular axis (‘c’ axis) being directed parallel to the surface. The pentacene growth on the surface is considered to be a 3D island growth mode. Two minor crystal structures that are poly-crystal and striped layer are also observed. All experimental results suggest that the surface is rather moderate compared with a reactive surface, which allows for molecular diffusion and rearrangement.

Initial growth process of pentacene molecules on clean Si(001)-2 × 1 substrate was investigated by scanning tunneling microscopy. It is found that the wetting layer, which is not crystalline but disordered, forms before the growth of a first crystalline layer. The wetting layer consists of double layer of the flatly adsorbed pentacene molecules. The formation of the wetting double layer is discussed. The first crystalline layer that is grown on the disordered wetting layer with standing-up pentacene molecules consists of some domains that differ in their crystal structures. Among them, a new pentacene crystal structure is found that can form only on the first layer. In contrast, the second crystalline layer has only single domain. Moreover, we investigated the electronic properties of the pentacene layers by the current–voltage measurements. The pentacene layers are semiconducting with a band gap of about 4 eV.

Hydrogen etching of a 4H-SiC(0001) surface at a moderate temperature of 1200 °C with molecular hydrogen gas was investigated to obtain enough flat and clean surface for large-scale high-quality epitaxial graphene synthesis. We found after a prolonged hydrogen etching that micro scratches, large depressions, and contaminations produced on the wafer in the manufacturing process disappeared and that a periodic array of atomic steps appeared, maintaining initial flat surface morphology. One hour of etching with a flow of 1.0 l/min was the optimum condition to obtain a flat and clean SiC surface in the present study. Using such surfaces, we were able to synthesize the so-called zero layer graphene by thermal annealing in ultrahigh vacuum.

Cu atom penetration through a defect in zero-layer graphene (ZLG) epitaxially grown on an SiC substrate was theoretically investigated, using density functional theory calculations, as a possible mechanism for pure single-layer graphene formation by Cu intercalation on an SiC surface. Our model calculation predicted that a Cu monolayer formed by Cu intercalation causes a lift of the graphene surface of about 0.2 nm, which supports our previous experimental observation. Our calculations on Cu intercalation through a graphene defect implied the possibility that a transition of the defect shape from a 5–8–5 to a double-vacancy model causes the timing of the passage of the Cu atom through the ZLG surface to reduce the potential barrier for the penetration. In addition, it was found that the SiC substrate stabilizes the Cu atom after penetration via an Si–Cu interaction. Furthermore, a preceding intercalated Cu atom was found to be capable of facilitating subsequent Cu penetration by suppressing its inverse re...

Adsorption of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on the Ge(001) surface was studied using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and the density-functional theory (DFT) calculations. Only single adsorption configuration of the PTCDA molecule was observed at low coverages on the Ge(001) at room temperature, unlike on the Si(001) where several adsorption configurations were reported. This indicates that the PTCDA molecules on the Ge(001) were more mobile than those on the Si(001). Atomic structure of the adsorption configuration on the Ge(001) was determined by comparison between the STM experiments and the DFT calculations. Bias-dependent STM images, STS, and calculated projected density of state curves show nontrivial hybridization of molecular orbitals with surface states of the Ge substrate. Interactions of the PTCDA molecule with the Ge and the Si surfaces were in detail analyzed by the DFT calculation, considering five main competing contributions...

Growth of a hybrid inorganic–organic layered structure on the Au(111) surface using a one-step solution growth is reported. The hybrid structure is consist of 4,4′-bipyridine [4,4′-BiPyH2]2 + cations, Cl anions and Au adatoms, provided from substrate by means of the adsorbate-induced surface phase transition of a surface reconstruction. Its surface and bulk structures were characterized by scanning tunneling microscopy (STM), secondary ion mass spectrometry (SIMS), and Raman spectroscopy. STM results reveal growth of the first [4,4′-BiPyH2]2 + layer on top of the p 3 × 3 R 30 ° chlorine overlayer formed on the Au(111) surface. These two layers are found to provide a platform for a following three-dimensional growth facilitated by hydrogen bonding, aurophilic and π–π stacking interactions.

The indium coverage of the Si(111)-$\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-In surface is investigated by means of x-ray photoelectron spectroscopy and first-principles density functional theory calculations. Both experimental and theoretical results indicate that the In coverage is a double layer rather than a single layer. Moreover, the atomic structure of the Si(111)-$\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-In surface is discussed by comparing experimental with simulated scanning tunneling microscopy (STM) images and scanning tunneling spectra with the calculated density of states. Our structural assignment agrees with previous studies, except for the interpretation of experimental STM images.

The empty-state scanning tunneling microscopy (STM) images of GaAs-c(4 × 4)α show symmetric features at positive biases, contrary to the naive prediction based on electron counting model. In this paper, we report that STM simulations based on first-principles electronic structure calculations successfully demonstrate symmetric images consistent with the STM observations. Furthermore, simple analysis has revealed that the origin of the symmetric images is the combined local electron density of multiple orbitals, and is essentially different from those on GaAs–c(4 × 4)β surfaces.

Adsorption structures of the 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecule on the clean Si(001) − 2 × 1 surface were investigated using scanning tunneling microscopy (STM) experiments in conjunction with first principles theoretical calculations. Four dominant adsorption structures were observed in the STM experiments and their atomic coordinates on the Si(001) surface were determined by comparison between the experimental STM images and the theoretical simulations. Maximizing the number of the Si—O bonds is more crucial than that of the Si—C bonds in the PTCDA adsorption.

Pd-intercalated graphene grown on a SiC(0001) substrate was investigated using STM, angle-resolved photoemission spectroscopy, and XPS. Pd atoms deposited at room temperature on a zero layer graphene grown on a SiC(0001) substrate were intercalated between the zero layer graphene and the SiC substrate after the thermal annealing above 700 °C, forming a Pd-intercalated single layer graphene. No charge transfer occurred between the intercalated Pd layer and the graphene, which resulted in the formation of the electrically neutral graphene. The Pd-intercalated graphene remained electrically neutral throughout the annealing temperature range between 700 and 1100 °C. The charge transfer, however, occurred between the intercalated Pd layer and the SiC substrate, which caused a band bending confirmed in the core level spectra measured by XPS.

Cr-adsorbed GaAs ( 0 0 1 ) ‐ c ( 4 × 4 ) α surfaces were investigated in view of a preparatory stage before studying the growth of zincblende CrAs. Cr was adsorbed on a GaAs ( 001 ) ‐ c ( 4 × 4 ) α surface at 200 °C followed by annealing for 2 min. Cr adsorbed surface was investigated with scanning tunneling microscopy at 80 K. Single Cr atom was identified after the classification of Cr dots grown on the surface. The results have suggested that a Cr atom adsorbs on a site between three Ga–As dimers. After further adsorption of Cr, the surface is covered by dots which are higher than a step height of the substrate.

Cu atoms deposited on a zero layer graphene grown on a SiC(0001) substrate, intercalate between the zero layer graphene and the SiC substrate after the thermal annealing above 600 °C, forming a Cu-intercalated single layer graphene. On the Cu-intercalated single layer graphene, a graphene lattice with superstructure due to moire pattern is observed by scanning tunneling microscopy, and specific linear dispersion at the K¯ point as well as a characteristic peak in a C1s core level spectrum, which is originated from a free-standing graphene, is confirmed by photoemission spectroscopy. The Cu-intercalated single layer graphene is found to be n-doped.

An epitaxial silicon-oxide monolayer of chemical composition of Si2O3 (the Si2O3 layer) formed on hexagonal SiC(0001¯) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si2O3 layer are found to be missing SiOn (n = 1, 2, 3) molecules. The band gap of the Si2O3 layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO2, 8.9 eV. It is proposed that the Si2O3 layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

Many studies have observed a clean GaAs(001)-c(4 × 4) surface using scanning tunneling microscopy. These studies have reported the observation of an asymmetric pattern formed from three asymmetric Ga–As dimers. In this study, however, a symmetric pattern was also observed depending on the applied bias voltage. These symmetric (asymmetric) patterns were observed at positive (negative) sample biases.