arXiv subjects

S. I. Bozhko

Publications and source records attributed to S. I. Bozhko.

11 recordsLinked to original sources

arXiv2026

Period-dependent suppression of Fourier peaks for topography images: Analysis of periodicity of triple-step arrays on vicinal Si(h h m) surfaces

Reliable determination of the periodicity of multiatomic steps on high-Miller-index vicinal surfaces is often complicated by (i) the presence of relatively narrow terraces tilted at large angles relative to the scanning plane, and (ii) unavoidable distortions in the lateral direction resulting from creep and improper calibration of a piezo scanner. We argue that the period of the triple-step arrays on vicinal Si(5\,5\,6) and Si(5 5 7) single-crystal wafers can be determined from raw scanning tunneling microscopy data, without preliminary corrections, with precision approaching the interatomic distance. We demonstrate that the intensity of the Fourier peaks of the differential maps, derived from raw topography images by the difference-of-Gaussians approach, strongly depends on the period of the ordered triple-step arrays. This suppression of the ninth Fourier peak indicates that the regular array of triple steps has a period of $18b=5.99$ nm in projection onto the Si(1 1 1) terrace plane, where $b=0.333$ nm is the distance between atomic rows of the $1\times 1$ lattice in the $[\bar{1}\,\bar{1}\,2]$ direction. This means that the nominally (5\,5\,7)-oriented Si wafers may correspond locally to the Si(8 8 11) orientation. The method can be applied to the precise analysis of other vicinal surfaces with narrow and wide terraces containing an integer number of Si(1 1 1)$7\times 7$ unit cells.

cond-mat.mtrl-sci↗

arXiv2026

Atomically precise triple-step staircase on a vicinal silicon surface: Is it Si(5 5 7), Si(7 7 10) or Si(8 8 11)?

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.

cond-mat.mtrl-sci↗

arXiv2025

Electronic localization on the structural inhomogeneities formed due to Bi and Te deficiency in the MBE grown films of AFM topological insulator MnBi2Te4: Evidence from spectroscopic ellipsometry and infrared studies

The intrinsic substitutional and antisite defects cause unintentional doping and shift of the E_F position above the conduction band minimum in the AFM topological insulator (TI) MnBi2Te4. This prevents measurements of the quantum anomalous Hall effect (QAH) and investigation of the topological Dirac states. In the present study, the Mn-Bi-Te films grown by the MBE technique onto Si(111) substrates with decreasing Bi and Te contents and increasing Mn content were investigated by 0.5-6.5 eV spectroscopic ellipsometry. In addition, the 0.004-0.9 eV infrared (IR) transmittance spectra were examined. An effective medium model was used to reproduce the measured ellipsometric angles, Psi(omega) and Delta(omega), of the Mn-Bi-Te films in terms of the constructed model, including film thickness, surface roughness, and volume fractions of two (MnTe and Bi2Te3) or three constituents, the latter being associated with the structural inhomogeneities contribution. The results obtained for the inhomogeneous Mn-Bi-Te films using the three-phase EMA model indicate that the defect-associated optical response systematically shifts to higher photon energies from ~1.95 to ~2.43 eV with decreasing Te and Bi contents and increasing Mn content, pointing out that the electrons become more deeply localized in the formed structural inhomogeneities. The obtained results indicate that the structure of the non-stoichiometric Mn-Bi-Te films is not continuous but represented by regions of nearly stoichiometric MnBi2Te4 phase, which includes hollows or quantum anti-dots (QADs). The measured FIR transmittance spectra for the non-stoichiometric Mn-Bi-Te films show substantially reduced (or absent) contribution(s) from free charge carriers, which supports the relevance of localization effects.

cond-mat.str-el↗

arXiv2024

Effective removal of global tilt from topography images of vicinal surfaces with narrow terraces

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 on sample surface. 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.

cond-mat.mtrl-sci↗

arXiv2024

Visualization of Atomic Structures on Faceted and Nonflat Surfaces by the Difference-of-Gaussians Approach

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.

cond-mat.mtrl-sci↗

arXiv2022

Observation of hidden parts of dislocation loops in thin Pb films by means of scanning tunneling spectroscopy

Local electronic properties of quasi-two-dimensional Pb(111) islands with screw dislocations of different types on their surfaces were experimentally studied by means of low-temperature scanning tunneling microscopy and spectroscopy in the regime of constant current. A comparison of the topography map, the maps of tunneling current variation and the differential tunneling conductance acquired simultaneously allows one to visualize the hidden parts of the dislocation loops under the sample surface. We demonstrate that two closely-positioned screw dislocations with the opposite Burgers vectors can either (i) connect to each other by the sub-surface dislocation loop or (ii) generate independent hidden edge dislocation lines which run towards the perimeter of the Pb island. In addition, we found a screw dislocation, which does not produce outcoming sub-surface dislocation loops. Screw dislocations and the hidden dislocations lines are the source of the non-quantized variation of the local thickness of the Pb terraces, affecting the local electronic properties.

cond-mat.mes-hall↗

arXiv2020

Memory effect in the charge transport in strongly disordered antimony films

We study conductivity of strongly disordered amorphous antimony films under high bias voltages. We observe non-linear current-voltage characteristic, where the conductivity value at zero bias is one of two distinct values, being determined by the sign of previously applied voltage. Relaxation curves demonstrate high stability of these conductivity values on a large timescale. Investigations of the antimony film structure allows to determine the percolation character of electron transport in strongly disordered films. We connect the memory effect in conductivity with modification of the percolation pattern due to recharging of some film regions at high bias voltages.

cond-mat.mes-hall↗

arXiv2019

Nonuniform quantum-confined states and visualization of hidden defects in thin Pb(111) films

The spatial distribution of the differential conductance for ultrathin Pb films grown on Si(111)7x7 substrate is studied by means of low-temperature scanning tunneling microscopy and spectroscopy. The formation of the quantum--confined states for conduction electrons and, correspondingly, the appearance of local maxima of the differential tunneling conductance are typical for Pb films; the energy of such states is determined mainly by the local thickness of Pb film. We demonstrate that the magnitude of the tunneling conductivity within atomically flat terraces can be spatially nonuniform and the period of the small-scale modulation coincides with the period of Si(111)7x7 reconstruction. For relatively thick Pb films we observe large-scale inhomogeneities of the tunneling conductance, which reveal itself as a gradual shift of the quantized levels at a value of the order of 50 meV at distances of the order of 100 nm. We believe that such large-scale variations of the tunneling conductance and, respectively, local density of states in Pb films can be related to presence of internal defects of crystalline structure, for instance, local electrical potentials and stresses.

cond-mat.mes-hall↗

arXiv2017

Double Fe-impurity charge state in the topological insulator Bi$_2$Se$_3$

The influence of individual impurities of Fe on the electronic properties of topological insulator Bi$_2$Se$_3$ is studied by Scanning Tunneling Microscopy. The microscope tip is used in order to remotely charge/discharge Fe impurities. The charging process is shown to depend on the impurity location in the crystallographic unit cell, on the presence of other Fe impurities in the close vicinity, as well as on the overall doping level of the crystal. We present a qualitative explanation of the observed phenomena in terms of tip-induced local band bending. Our observations evidence that the specific impurity neighborhood and the position of the Fermi energy with respect to the Dirac point and bulk bands have both to be taken into account when considering the electron scattering on the disorder in topological insulators.

cond-mat.mes-hall↗

arXiv2014

Surface states in a 3D topological insulator: The role of hexagonal warping and curvature

We explore a combined effect of hexagonal warping and of finite effective mass on both the tunneling density of electronic states (TDOS) and structure of Landau levels (LLs) of 3D topological insulators. We find the increasing warping to transform the square-root van Hove singularity into a logarithmic one. For moderate warping an additional logarithmic singularity and a jump in the TDOS appear. This phenomenon is experimentally verified by direct measurements of the local TDOS in Bi$_2$Te$_3$. By combining the perturbation theory and the WKB approximation we calculate the LLs in the presence of hexagonal warping. We predict that due to the degeneracy removal the evolution of LLs in the magnetic field is drastically modified.

cond-mat.mes-hall↗

arXiv2011

Structure and magnetic properties of nanostructured Pd-Fe thin films produced by pulse electrodeposition

Nanostructured Pd-Fe thin films with varied Fe content were prepared by electrodeposition technique from organic electrolytes on Cu and brass substrates. The structure and the magnetic properties of the films were investigated prior to post-deposition annealing. The structure of the Pd1-xFex thin films with x = 0.14, 0.24, and 0.52 was determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM) as a solid solution of iron in palladium face-centered cubic lattice with the (111) orientation of nanograins relatively to the substrate surface. The films with higher iron concentration, x = 0.74, 0.91, have structure of a solid solution based on the body-centered cubic lattice. The average grain size determined by the scanning electron microscopy (SEM) for the first two alloys is 7-10 nm, and for the latter ones it is about 120 nm. The saturation magnetization of the films has linear dependence on the iron content, but coercivity has non-monotonic dependence on x, i.e. the films with x = 0.68 show highest coercivity. The magnetic anisotropy of the samples is studied by ferromagnetic resonance (FMR) spectroscopy.

cond-mat.mtrl-sci↗