S. I. Oreshkin

Metallic glass electronic structure peculiarities revealed by UHV STM/STS

We present the results of ultrahigh vacuum scanning tunneling microscopy/spectroscopy investigation of metallic glass surface. The topography and electronic structure of Ni63.5Nb36.5 have been studied. A great number of clusters with size about 5–10 nm have been found on constant current scanning tunneling microscopy images. The tunneling spectra of normalized tunneling conductivity revealed the energy pseudogap in the vicinity of Fermi energy. For energy values above 0.1 eV the normalized tunneling conductivity changes linearly with increasing of tunneling bias. The obtained results can be understood within suggested theoretical model based on the interplay of elastic electron scattering on random defects and weak intra-cluster Coulomb interaction. The effects of the finite edges of electron spectrum of each cluster have to be taken into account to explain the experimental data. The tunneling conductivity behavior and peculiarities in current images of individual clusters can also be qualitatively analyzed in the framework of suggested model.

Scanning tunneling spectroscopy of charge effects on semiconductor surfaces and atomic clusters

We have used scanning tunneling microscopy and scanning tunneling spectroscopy at liquid helium temperature to study the electronic structure of in situ cleaved, (110) oriented surfaces of InAs single crystals. Both unperturbed, atomically flat areas and areas with an atomic-size defect cluster have been investigated. We show that the anomalous behavior of the local tunneling conductivity, which indicates a pronounced enhancement of the semiconductor band gap for the flat areas, is consistent with band bending induced by charges localized at the apex of the tip. Atomic-size defect clusters contain additional charges which modify the band bending; this explains the different behavior of the tunneling conductivity near the defect cluster. The experimentally observed oscillations of the tunneling conductivity near the band gap edges can be directly related to resonant tunneling through quantized surface states which appear because of the band bending.

Effect of different impurity atoms on 1/fα tunneling current noise characteristics on InAs (110) surface

The results of UHV STM investigations of tunneling current noise spectra in the vicinity of individual impurity atoms on the InAs(110) surface are reported. It was found that the power law exponent of 1/fα noise depends on the presence of an impurity atom in the tunneling junction area. This is consistent with the proposed theoretical model considering tunneling current through a two-state impurity complex model system taking into account many-particle interaction.

Direct visualization of Ni-Nb bulk metallic glasses surface: From initial nucleation to full crystallization

This article is devoted to in situ investigation of the Ni-based bulk metallic glass structural evolution and crystallization behavior by scanning tunneling microscopy/spectroscopy. The possibility of different surface nanostructures formation is shown by annealing of an original bulk glassy alloy in ultra high vacuum. Atomic locations in these surface nanostructures are completely different from those formed according to Ni-Nb binary phase diagram in the bulk area of the sample. The validity of the results is also verified by transmission electron microscopy and nano-beam diffraction measurements.

A precise system for measuring weak optoacoustic perturbations

The practical implementation of a high-sensitivity measuring system based on an extended Fabry-Perot interferometer, which reacts to small variations of its optical length, is presented. The attained sensitivity is limited by the spectral noise density of optical pumping, which is lower than the resonance spectral density of thermal fluctuations of the interferometer base by one order of magnitude. Structurally, the system is an optoacoustic gravitational antenna without cooling (OGRAN). Extrapolating the results obtained for a pilot model to a large-size variant of the setup fo recasts a sensitivity sufficient for searching for gravitational bursts in the Galaxy and its nearest vicinity (within 100 kpc).

Ag-induced atomic structures on the Si(110) surface

We report the results of STM investigation of the initial stage of Ag adsorption on an Si(110) surface. At 0.21 ML Ag coverage, the size and orientation of the unit cell correspond to the parameters of a 16 × 2 unit cell of clean Si(110) surface. With increasing of the Ag coverage up to 0.42 ML, the type of surface reconstruction changes to a 4 × 1-Si(110)-Ag structure.

An optoacoustical gravitational antenna

An optoacoustical gravitational detector that structurally combines the principles of interferometric and solid-state gravitational antennas is described. A large acoustical resonator, which is matched to a commensurate Fabry-Perot (FP) optical interferometer, serves as the sensitive element for recording changes in the gravitational-field gradient. In a test experiment, the spectral density of recorded spatial deformations (metric variations) was 10−19 Hz−1/2 at a frequency of ∼1.3 kHz within a band of ∼4 Hz, which can be extended by an order of magnitude upon a corresponding increase in the sharpness of the interferometer mirrors. The new antenna is designed for detecting relativistic catastrophes (collapses) in the Galaxy and the nearest vicinity during complex (multichannel) monitoring with neutrino telescopes of the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences.

A high frequency resonance gravity gradiometer

A new setup OGRAN--the large scale opto-acoustical gravitational detector is described. As distinguished from known gravitational bar detectors it uses the optical interferometrical readout for registering weak variations of gravity gradient at the kilohetz frequency region. At room temperature, its sensitivity is limited only by the bar Brownian noise at the bandwidth close to 100 Hz. It is destined for a search for rare events--gravitational pulses coincident with signals of neutrino scintillator (BUST) in the deep underground of Baksan Neutrino Observatory of INR RAS.

Scanning tunneling microscopy/spectroscopy study of adsorption of C60F36 molecules on the 7 × 7-Si(111) surface

Spatially resolved images of an individual C60F36 fluorofullerene molecules on Si(111)-7 × 7 surface have been obtained by means of scanning tunneling microscopy/spectroscopy (STM/STS). The presence of isomers with different symmetry (T, C3, C1) has been revealed in STM investigation of initial adsorption stage of C60F36 on silicon surface Si(111)-(7 × 7). The adsorbed fluorofullerene molecule can occupy any adsorption site of silicon surface (corner site, faulted half, unfaulted half) that indicates for strong molecule-substrate interaction. The HOMO-LUMO gap of the adsorbed C60F36 molecules have been estimated from current image tunneling spectroscopy (CITS) and z(V) with engaged feedback measurements. The value of HOMO-LUMO gap observed experimentally was 3 eV. The C60F36 molecules adsorption on Si(111)-(7 × 7) surface was stable and kept equilibrium configuration during several hours.

Electronic structure of Ge(111)-(2 × 1) surface in the presence of doping atoms. Ab initio analysis of STM data

We present the result of ab initio modeling of the Ge(111)-(2 × 1) surface electronic structure in the presence of donor doping atom at certain position in the surface bilayer of (2 × 1) reconstruction. We briefly compare these results with the data of experimental low temperature STM investigations. Ab initio calculations demonstrate that doping atom strongly disturbs local electronic structure. The separate state, most probably split off conduction band, appears in the bandgap. Surface LDOS reveals spatial oscillations in vicinity of foreign atom. We also show that the spatial extent of non-negligible inter-atomic interaction between neighboring donor atoms is not less than 70 Å.