Konstantin Romanyuk

Inertness and degradation of (0001) surface of Bi2Se3 topological insulator

Inertness of the cleaved (0001) surface of the Bi2Se3 single crystal, grown by modified Bridgman method, to oxidation has been demonstrated by X-ray photoelectron spectroscopy, scanning tunneling microscopy, and by ab initio DFT calculations. No intrinsic bismuth and selenium oxides are formed on the low-defect, atomically flat Bi2Se3(0001)-(1×1) surface after a long-time air exposure. The inertness of Bi2Se3(0001) to O2 and NO2, as well as bismuth-oxygen bonding formation under molecular adsorption in the Se vacancy was supported by DFT calculations.

Strong piezoelectricity in single-layer graphene deposited on SiO2 grating substrates

Electromechanical response of materials is a key property for various applications ranging from actuators to sophisticated nanoelectromechanical systems. Here electromechanical properties of the single-layer graphene transferred onto SiO2 calibration grating substrates is studied via piezoresponse force microscopy and confocal Raman spectroscopy. The correlation of mechanical strains in graphene layer with the substrate morphology is established via Raman mapping. Apparent vertical piezoresponse from the single-layer graphene supported by underlying SiO2 structure is observed by piezoresponse force microscopy. The calculated vertical piezocoefficient is about 1.4 nm V−1, that is, much higher than that of the conventional piezoelectric materials such as lead zirconate titanate and comparable to that of relaxor single crystals. The observed piezoresponse and achieved strain in graphene are associated with the chemical interaction of graphenes carbon atoms with the oxygen from underlying SiO2. The results provide a basis for future applications of graphene layers for sensing, actuating and energy harvesting.

Stability of the (0001) surface of the Bi2Se3 topological insulator

The inertness of the cleaved (0001) surface of a Bi2Se3 single crystal to oxidation has been demonstrated using X-ray photoelectron spectroscopy, as well as atomic-force and scanning tunneling microscopy and spectroscopy. No intrinsic bismuth and selenium oxides are formed on the surface after a month of storage in air. Atomically flat surfaces with macroscopic sizes (∼1 cm2) and rms roughness less than 0.1 nm have been prepared, and (1 × 1)-(0001) Bi2Se3 atomic structure has been resolved. The tunneling conductance measurements have shown that the energy dependence of the surface density of states is quasilinear in the band gap of Bi2Se3.

Single- and multi-frequency detection of surface displacements via scanning probe microscopy.

Piezoresponse force microscopy (PFM) provides a novel opportunity to detect picometer-level displacements induced by an electric field applied through a conducting tip of an atomic force microscope (AFM). Recently, it was discovered that superb vertical sensitivity provided by PFM is high enough to monitor electric-field-induced ionic displacements in solids, the technique being referred to as electrochemical strain microscopy (ESM). ESM has been implemented only in multi-frequency detection modes such as dual AC resonance tracking (DART) and band excitation, where the response is recorded within a finite frequency range, typically around the first contact resonance. In this paper, we analyze and compare signal-to-noise ratios of the conventional single-frequency method with multi-frequency regimes of measuring surface displacements. Single-frequency detection ESM is demonstrated using a commercial AFM.

Scanning tunneling microscopy study of the growth and self-organization of Ge nanostructures on vicinal Si(111) surfaces

AbstractThe initial stages of Ge growth on Si(111) vicinal surfaces tilted in the [

Effect of dislocations on the shape of islands during silicon growth on the oxidized Si(111) surface

\overline 1 \overline 1 2

Formation of Ge clusters at a Si(111)-Bi-

] and [