A. N. Titkov

InSb/InAs quantum dots grown by liquid phase epitaxy

The first original results on the growth of quantum dots (QDs) in the InSb/InAs system by liquid phase epitaxy (LPE) are reported. The density and dimensions of QDs were studied by methods of scanning probe microscopy and atomic force microscopy. The surface density, shapes, and dimensions of LPE-grown nanoislands depend on the growth conditions (temperature, cooling rate, and solution melt-substrate contact time). In the interval of temperatures T = 420–445°C, homogeneous arrays of InSb quantum dots on InAs(100) substrates were obtained with an average height of H = 3.4 ± 1nm, a radius of R = 27.2 ± 7.5 nm, and a density of up to 1.9 × 1010 cm−2.

Measurement of Young's modulus of GaAs nanowires growing obliquely on a substrate

A convenient and fast method for measuring Young’s modulus of semiconductor nanowires obliquely standing on the growth substrate is presented. In this method, the nanowire is elastically bent under the force exerted by the probe of an atomic-force microscope, and the load-unload dependences for the bending of the probe cantilever are recorded. Next, these curves are used to find the bending stiffness of the tilted nanowires, after which, taking into account the nanowire dimensions, Young’s modulus is obtained. The implementation of this method is demonstrated for tilted GaAs nanowires growing on a GaAs (111) substrate. Young’s modulus is determined by applying finite-element analysis to the problem of the stationary elastic bending of a nanowire taking into account the actual nanowire shape and faceting. It proves that a fairly accurate estimate of Young’s modulus can be obtained even if the nanowire shape is approximated by a circular cylinder with a single cross-sectional area. The values of Young’s modulus obtained for GaAs nanowires of cubic lattice symmetry are 2 to 3 times smaller than its value for bulk GaAs. This difference is attributed to the presence of stacking faults in the central part of the nanowires.

Identification of tetrahedral amorphous carbon clusters on atomic hydrogen-etched graphite surface by scanning tunneling microscopy/spectroscopy

Abstract Scanning tunneling microscopy and spectroscopy have been used to study the electronic states of the islands located at the edges of hydrogen-etched graphite surface. Spectroscopy results have shown the presence of additional electronic states, energy gap, and lowering of the Fermi level. The obtained results are in accordance with the theoretical prediction for the presence of p-type tetrahedral amorphous carbon clusters (ta-C/ta-C:H) in perfect sp 2 graphite network.

Study of multigraphene films prepared by sublimation on the sic surface

Graphene films were prepared by sublimation epitaxy of SiC under vacuum. The films were studied by Auger electron spectroscopy, reflection high-energy electron diffraction, atomic force microscopy, and Raman spectroscopy. It is concluded that the films prepared are polycrystalline and consist of graphene single crystals about 50 nm in size.

Staggered-lineup heterojunctions in the system of GaSbInAs

Abstract We present some results of investigations of the staggered-lineup (type II) heterojunctions between GaInSbAs solid solutions and GaSb. New bands have been observed in photoluminescence and electroluminescence spectra of the structures of different kind due to an existence of potential wells on both sides of a type II heteroboundary. An amplification of photocurrent has been found in the N-n structures, which we attribute to a modulation of transparency of a potential barrier for electrons at the heteroboundary by light induced holes captured in the potential well in the valence band. Features of the staggered-lineup heterojunctions were used for a development of some optoelectronic devices for a 1.5–2.5 μm spectral range.

Formation of Periodic Steps on 6H-SiC (0001) Surface by Annealing in a High Vacuum

Influence of high-vacuum annealing at temperatures in the range 1300-1400°C and residual pressure of ~10-6 Torr on the surface of 6H-SiC (0001) wafers has been studied. Auger spectroscopy and RHEED data show that the annealing conditions do not lead to any surface reconstruction of the wafers. Atomic force microscopy reveals atomically flat surface terraces separated by steps of unit-cell height (h = 1.5 nm).

Structural Properties of a Monolayer Graphite Film on the (111)Ir Surface

The structural properties of a monolayer graphite film prepared on the (111)Ir surface through thermal decomposition of benzene molecules were studied. The study was carried out in ultrahigh vacuum using scanning tunneling microscopy, which allowed observation of the atomic structure of the film. It is shown that, on extended smooth regions of the Ir surface, a continuous graphite film with a regular arrangement of carbon atoms in a planar hexagonal lattice is formed. The orientation of zigzag carbon atom chains coincides with the 〈110〉 direction on the Ir surface. Structural defects of the (5, 7) configuration were revealed in the film. A comparison of the topographies of the film and the (111)Ir surface shows that the graphite layer smoothly (without discontinuities) flows over subnanometer topographical features existing on the Ir surface and that the distance between the graphite film and the metal surface in this case can reach 1 nm.

Electronic Superstructures Observed by Scanning Tunneling Microscopy on Graphene Sheet in Vicinity of Nano-Defects of Ir(111) Substrate

Two-dimensional electronic and atomic superstructures (SS) on monolayer graphite (graphene) grown on a clean Ir(111) surface were observed near substrate nano-defect sites by scanning tunneling microscopy. These SS were found rotated 30° with respect to the undistorted areas (away from defects sites) of the graphene layer with a periodicity of ∼(√3 x √3) a (a = 2.46 A) and decay over a distance of few nanometers away from the defects. The observed SS were not due to real surface reconstruction, rather they just had an electronic nature.

Low-temperature transport properties of multigraphene films grown on the SiC surface by sublimation

Multigraphene films grown by sublimation on the surface of a semi-insulating 6H-SiC substrate have been studied. It is shown that pregrowth annealing of the substrate in a quasiclosed growth cell improves the structural quality of a multigraphene film. Ohmic contacts to the film have been fabricated, and the Hall effect has been studied at low temperatures. It is found that a 2D electron gas exists in the films. It is concluded that the conductivity of the film is determined by defects existing within the graphene layer or at the interface between the graphene film and a SiC substrate.

Formation of nanocarbon films on the SiC surface through sublimation in vacuum

The possibility of forming nanocarbon films on the SiC surface with the use of the technology employed in sublimation epitaxy of silicon carbide has been demonstrated. The temperature range in which nanocarbon films four to five lattice-cells thick form is found. The presence in films of two-dimensional graphite crystals is revealed.