Scanning tunneling microscopy studies of periodic arrays of triple steps fabricated on single-crystalline Si(5 5 7) wafers demonstrate several possible atomic structures of consecutive steps and Si(1 1 1) terraces maintaining the same periodicity on micrometer-sized surface areas. Detailed analysis of the atomically resolved data reveals the formation of Si(8 8 11) triple-step staircase with a period of 18b=5.99 nm in projection onto the terrace plane, where b=0.333 nm is the distance between atomic rows for the Si(1 1 1)1x1 surface. Schematic models for several possible configurations of either 7x7 or 5x5-reconstructed terraces and triple steps are proposed.

Detailed analysis of scanning probe microscopy (SPM) data acquired for faceted and non-flat surfaces is usually complicated due to the presence of a large number of surface areas tilted by large/variable angles relative to the scanning plane. As a consequence, standard methods of elimination of global or local slopes by either a plane subtraction or numerical differentiation seem to be ineffective. We demonstrate that a simple difference-of-Gaussians procedure provides output data corresponding to projection of a considered surface onto the scanning plane without undesirable contrast modifications. This method allows us to suppress small-scale noise, minimize effects of finite slopes in the SPM images along both fast and slow scanning directions and removes surface ripples without active participation of the operator. This method can be applied for fast on-the-fly visualization of experimental data, and for more detailed analysis, including high-precision determination of lattice parameters and angles between translation vectors for surface reconstruction of different terraces or surface domains. In order to estimate geometrical distortions introduced by our procedure, we compare the results obtained by the difference-of-Gaussians approach for the tilted surfaces with direct image rotation in 3D space.

The main feature of vicinal surfaces of crystals characterized by the Miller indices (hhm) is rather small width (less than 10 nm) and substantially large length (more than 200 nm) of atomically-flat terraces. This makes difficult to apply standard methods of image processing and correct visualization of crystalline lattices at the terraces and multiatomic steps. Here we consider two procedures allowing us to minimize effects of both small-scale noise and global tilt of sample: (i) analysis of the difference of two Gaussian blurred images, and (ii) subtraction of the plane, whose parameters are determined by optimization of the histogram of the visible heights, from raw topography image. It is shown that both methods provide nondistorted images demonstrating atomic structures on vicinal Si(556) and Si(557) surfaces.

Graphene layers on semiconducting substrates, modified using covalent and noncovalent chemical functionalization, can be utilized for the fabrication of hybrid structures combining the physical properties of graphene and organic molecules. In this paper the results of investigations of the atomic and electronic structure of ultrathin graphene layers on β-SiC/Si(001) wafers modified using the phenazine dye Neutral Red are presented. Continuous graphene films consisting of several atomic layers are synthesized on β‑SiC/Si(001) wafers using high temperature annealing in ultrahigh vacuum. The synthesized graphene layers were chemically modified in a solution of diazonium salt of the Neutral Red dye under white-light illumination. The results of scanning tunneling microscopy and spectroscopy demonstrate the formation of a composite phenazine–graphene structure with a large energy gap in all surface regions. The molecules can be oriented preferentially parallel and perpendicular to the graphene layers and form locally ordered structures with rectangular and oblique unit cells. The electronic energy spectrum and band gap in different surface areas depend on the local atomic structure and the molecule’s orientation relative to the surface. According to density-functional-theory calculations, the local modifications of the electronic structure and band gap can be related to deformations (compression or extension) of the phenazine dye molecules because of their interaction with the uppermost graphene layer.

The studies of the properties of graphene synthesized on the surface of epitaxial films of cubic single-crystal silicon carbide preliminarily grown on Si(001) wafers have been reviewed. These studies were supported by the Russian Foundation for Basic Research, project no. 17-02-01139. The results of these studies demonstrate that graphene layers synthesized on β-SiC/Si(001) substrates have the atomic structure and electronic properties of a quasi-freestanding graphene sheet. Continuous graphene layers with a preferential direction of nanodomain boundaries, which is determined by the orientation of steps on the initial surface, can be synthesized on vicinal SiC(001) substrates. The possibility of controlled growth of mono-, bi-, and trilayer graphene on β-SiC/Si(001) wafers has been demonstrated. The studies have shown the opening of a transport gap and a high positive magnetoresistance in a parallel magnetic field in an ordered system of graphene nanoribbons on the vicinal SiC(001) surface. It has been shown that the functionalization of graphene with organic compounds changes the electronic properties of graphene on SiC(001), modifying it to a semiconductor with given properties, which allows applications in modern micro- and nanoelectronics.

We have studied the solid state dewetting of ten monolayers thick Ag film deposited on periodically patterned Si(557) surface. The annealing of the system in the ultra-high vacuum at the temperatures between 300 and 400 °C resulted in full agglomeration of the film and formation of faceted single crystalline Ag nanoparticles exhibiting bimodal size distribution. We demonstrated that some particles contain screw dislocations producing a step on the upper particle facet. We related the bimodality in particles distribution with the ability of dislocation-containing Ag particles to evolve by Ostwald ripening mechanism.

We study the in-situ growth of a nanocomposite material consisting of a thin CuPcF4 film and multiphase/multidimensional indium nanoparticles, self-organizing on the surface and in the bulk, at various stages of thermal deposition of metal on an organic film under ultrahigh vacuum conditions. The analysis of high-resolution transmission electron microscopy (HR-TEM) images provided valuable information about the evolution of morphology, size, density, and distribution of indium nanoparticles upon indium deposition. These 2D/3D ultra-small nano-objects turned out to have not only body-centered tetragonal (bct) crystal structure, typical for bulk indium, but also unusual face-centered cubic (fcc) one. Using a synchrotron facility, the study of the electronic structure of the hybrid nanocomposite on variable stages of metal deposition was performed by XPS and NEXAFS. Core-level spectra related to the organics indicated reasonably weak chemical interaction of indium with CuPcF4 molecules, which is not the case for a number of metal/organic semiconductor systems, while valence band spectra have shown a considerable change of the material electronic properties. The energy level diagrams, derived from the experiment, can be applied for the creation of new prototypes of metal-organic memory devices.

Using spin- and angle-resolved photoemission spectroscopy and relativistic many-body calculations, we investigate the evolution of the electronic structure of (Bi1-xInx)(2)Se-3)(2)Se-3 bulk single crystals around the critical point of the trivial to topological insulator quantum-phase transition. By increasing x, we observe how a surface gap opens at the Dirac point of the initially gapless topological surface state of Bi2Se3, leading to the existence of massive fermions. The surface gap monotonically increases for a wide range of x values across the topological and trivial sides of the quantum-phase transition. By means of photon-energy-dependent measurements, we demonstrate that the gapped surface state survives the inversion of the bulk bands which occurs at a critical point near x = 0.055. The surface state exhibits a nonzero in-plane spin polarization which decays exponentially with increasing x, and which persists in both the topological and trivial insulator phases. Our calculations reveal qualitative agreement with the experimental results all across the quantum-phase transition upon the systematic variation of the spin-orbit coupling strength. A non-time-reversal symmetry-breaking mechanism of bulk-mediated scattering processes that increase with decreasing spin-orbit coupling strength is proposed as explanation.

The growth of Fe nanostructures on the stoichiometric MoO2/Mo(110) and oxygen-rich MoO2+x/Mo(110) surfaces has been studied using low-temperature scanning tunnelling microscopy (STM) and density functional theory calculations. STM results indicate that at low coverage Fe nucleates on the MoO2/Mo(110) surface, forming small, well-ordered nanoclusters of uniform size, each consisting of five Fe atoms. These five-atom clusters can agglomerate into larger nanostructures reflecting the substrate geometry, but they retain their individual character within the structure. Linear Fe nanocluster arrays are formed on the MoO2/Mo(110) surface at room temperature when the surface coverage is greater than 0.6 monolayers. These nanocluster arrays follow the direction of the oxide rows of the strained MoO2/Mo(110) surface. Slightly altering the preparation procedure of MoO2/Mo(110) leads to the presence of oxygen adatoms on this surface. Fe deposition onto the oxygen-rich MoO2+x/Mo(110) surface results in elongated nanostructures that reach up to 24 nm in length. These nanolines have a zigzag shape and are likely composed of partially oxidised Fe formed upon reaction with the oxygen-rich surface.

The fabrication of ordered low-dimensional structures on clean and metal-atom-decorated stepped Si(557) and Si(556) surfaces is discussed. The formation conditions and atomic structure of regular step systems on clean Si(557) 7 × 7 and Si(556) 7 × 7 surfaces are studied. The atomic structure of stepped Si(hhm), Ag/Si(557), and Gd/Si(557) surfaces is studied using high-resolution scanning tunneling microscopy and low-energy electron diffraction. The possibility of fabricating 1D and 2D structures of gadolinium and silver atoms on the Si(557) surface is demonstrated.

Scanning tunneling microscopy (STM) is one of the main techniques for direct visualization of the surface electronic structure and chemical analysis of multi-component surfaces at the atomic scale. This review is focused on the role of the tip orbital structure and tip-surface interaction in STM imaging with picometer spatial resolution. Fabrication of STM probes with well-defined structure and selective visualization of individual electron orbitals in the STM experiments with controlled tunneling gap and probe structure are demonstrated.

The structure of the [001]-oriented single crystalline tungsten probes sharpened in ultra-high vacuum using electron beam heating and ion sputtering has been studied using scanning and transmission electron microscopy. The electron microscopy data prove reproducible fabrication of the single-apex tips with nanoscale pyramids grained by the {011} planes at the apexes. These sharp, [001]-oriented tungsten tips have been successfully utilized in high resolution scanning tunneling microscopy imaging of HOPG(0001), SiC(001) and graphene/SiC(001) surfaces. The electron microscopy characterization performed before and after the high resolution STM experiments provides direct correlation between the tip structure and picoscale spatial resolution achieved in the experiments.

The results of studying the structure of diamond single crystals grown by the temperature gradient method with the aim to obtain samples having maximum uniform characteristics for manufacturing probes for scanning electron microscopes with a specified axial orientation and controlled distribution of the dopant have been considered. It has been shown that the use of similar probes in scanning tunneling microscopy decreases the probability of incidental tunneling channels with participation of the surface states caused by the presence of boron atoms in the diamond structure and increases the reliability of experimental data. The high stability of monocrystalline diamond probes and the possibility to attain the atomic resolution with the help of them have been demonstrated by the investigations of the (0001) graphite plane using scanning tunneling microscopy.

The spatial resolution of a scanning tunneling microscope (STM) can be enhanced using light element-terminated probes with spatially localized electron orbitals at the apex atom. Conductive diamond probes can provide carbon atomic orbitals suitable for STM imaging with sub-Ångström lateral resolution and high apex stability crucial for the small tunneling gaps necessary for high-resolution experiments. Here we demonstrate that high spatial resolution can be achieved in STM experiments with single-crystal diamond tips, which are generally only considered for use as probes for atomic force microscopy. The results of STM experiments with a heavily boron-doped, diamond probe on a graphite surface; density functional theory calculations of the tip and surface electronic structure; and first-principles tunneling current calculations demonstrate that the highest spatial resolution can be achieved with diamond tips at tip-sample distances of 3-5 Å when frontier p-orbitals of the tip provide their maximum contribution to the tunneling current. At the same time, atomic resolution is feasible even at extremely small gaps with very high noise in the tunneling current.

Precise knowledge of the atomic and electronic structure of scanning tunneling microscopy (STM) tips is crucial for a correct interpretation of atomically resolved STM data and an improvement of the spatial resolution. Here we demonstrate that tungsten probes with controllable electronic structure can be fabricated using oriented single crystalline tips. High quality of the [001]-oriented W tips sharpened in ultra high vacuum was proved by electron microscopy. Distance dependent STM studies carried out on a graphite (0001) surface demonstrate that application of crystallographically oriented single crystalline tips allows one to control the tip electron orbitals responsible for high resolution imaging under specific tunneling conditions.

The natural cleavage plane (10 (2) over bar) of a layered compound GaTe possesses unique properties due to high in-plain anisotropy with the corresponding lattice constant of 1.18 nm. The structure and electronic properties of the GaTe (10 (2) over bar) clean surfaces have been studied both experimentally, using photoelectron spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy, and theoretically, using density functional theory. The results clearly indicate a monoclinic structure of the surface layer, with no pronounced reconstruction or relaxation of the surface observed. This finding contradicts the previous LEED study, where a surface monoclinic-hexagonal phase transformation was reported. The GaTe (10 (2) over bar) surface is found to be quite stable in time and resistant to oxidation. This makes gallium monotelluride an attractive substrate for growth of one-dimensional metal structures.

The natural cleavage plane $(10\overline{2})$ of a layered compound GaTe possesses unique properties due to high in-plain anisotropy with the corresponding lattice constant of 1.18 nm. The structure and electronic properties of the GaTe $(10\overline{2})$ clean surfaces have been studied both experimentally, using photoelectron spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy, and theoretically, using density functional theory. The results clearly indicate a monoclinic structure of the surface layer, with no pronounced reconstruction or relaxation of the surface observed. This finding contradicts the previous LEED study, where a surface monoclinic-hexagonal phase transformation was reported. The GaTe $(10\overline{2})$ surface is found to be quite stable in time and resistant to oxidation. This makes gallium monotelluride an attractive substrate for growth of one-dimensional metal structures.

We report high resolution scanning tunneling microscopy (STM) studies performed with [001]-oriented single crystalline tungsten tips. The sharpness of the W[001] tips cleaned by electron beam heating and ion sputtering is confirmed by electron microscopy data. Distance dependent STM experiments with the W[001] tips on a graphite surface demonstrate possibility to select the tip electron orbitals responsible for high resolution imaging using single crystalline probes. This is confirmed by imaging two-fold and four-fold split subatomic features reproducing the shapes of tungsten dxz and dxy atomic orbitals at specific tunneling conditions.