S. V. Savinov

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.

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.

Ex situ scanning tunneling microscopy investigations of the modification of titanium surface due to corrosion processes

Scanning tunneling microscopy was implemented for the comparative surface investigation of mechanically polished and electrochemically treated titanium samples. The titanium exposed to the phosphate buffered saline solution reveal the increased topography roughness (5–15 nm) of oxide thin layer on its surface. The introduction of H2O2 into the solution leads to the enhanced dissolution of the titanium oxide film resulting in a more defective surface. The I(V) dependencies obtained from spectroscopic measurements are indicative of the semiconducting properties of the thin oxide layer.

Noninvasive embedding of single Co atoms in Ge(111)2x1 surfaces

We report on a combined scanning tunneling microscopy (STM) and density functional theory (DFT) based investigation of Co atoms on Ge(111)2x1 surfaces. When deposited on cold surfaces, individual Co atoms have a limited diffusivity on the atomically flat areas and apparently reside on top of the upper pi-bonded chain rows exclusively. Voltage-dependent STM imaging reveals a highly anisotropic electronic perturbation of the Ge surface surrounding these Co atoms and pronounced one-dimensional confinement along the pi-bonded chains. DFT calculations reveal that the individual Co atoms are in fact embedded in the Ge surface, where they occupy a quasi-stationary position within the big 7-member Ge ring in between the 3rd and 4th atomic Ge layer. The energy needed for the Co atoms to overcome the potential barrier for penetration in the Ge surface is provided by the kinetic energy resulting from the deposition process. DFT calculations further demonstrate that the embedded Co atoms form four covalent Co-Ge bonds, resulting in a Co4+ valence state and a 3d5 electronic configuration. Calculated STM images are in perfect agreement with the experimental atomic resolution STM images for the broad range of applied tunneling voltages.

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.

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.

Many-particle interaction in tunneling spectroscopy of impurity states on the InAs(110) surface

We report on the direct observation by low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy of the d orbitals of a Mn p-type impurity appearing on a cleaved InAs(110) surface. We show that the crucial interplay between nonequilibrium charging effects and many-particle interaction leading to Coulomb singularities provides a consistent description of the experimental results.

Non-Equilibrium Tunneling Effects of Interacting Hubbard-Anderson Impurities

Nonequilibrium interaction effects of two Hubbard-Anderson impurities have been experimentally studied by means of STM/STS methods and theoretically analyzed using a self-consistent approach based on the Keldysh formalism.

Identifying the electronic properties of the Ge(111)-(2×1) surface by low-temperature scanning tunneling microscopy

We present the results of our low-temperature scanning tunneling microscopy (STM) investigation of the clean Ge(111) surface. Our experiments enable, for the first time, STM observation of one-dimensional surface screening around surface defects. We identify the dominating role of surface states in the low-temperature STM imaging as well as the important influence of nonequilibrium kinetics on the measured tunneling spectra.

Coulomb singularity effects in the tunneling spectroscopy of individual impurities

Nonequilibrium Coulomb effects in resonant tunneling through deep impurity states are analyzed. It is shown that Coulomb vertex corrections to the tunneling transfer amplitude lead to power law singularity in the current-voltage characteristics.Non-equilibrium Coulomb effects in resonant tunnelling processes through deep impurity states are analyzed. It is shown that Coulomb vertex corrections to the tunnelling transfer amplitude lead to a power-law singularity in current- voltage characteristics