Ivan Ošt'ádal

Chemical identification of single atoms in heterogeneous III-IV chains on Si(100) surface by means of nc-AFM and DFT calculations.

Chemical identification of individual atoms in mixed In-Sn chains grown on a Si(100)-(2 × 1) surface was investigated by means of room temperature dynamic noncontact AFM measurements and DFT calculations. We demonstrate that the chemical nature of each atom in the chain can be identified by means of measurements of the short-range forces acting between an AFM tip and the atom. On the basis of this method, we revealed incorporation of silicon atoms from the substrate into the metal chains. Analysis of the measured and calculated short-range forces indicates that even different chemical states of a single atom can be distinguished.

Self-organized growth of Ag islands on Si(1 1 1)-(7 × 7)-optimization of an STM experiment by means of KMC simulations

A growth model and parameters obtained in our previous experimental (scanning tunneling microscopy, KMC) and theoretical (kinetic Monte Carlo simulations, KMC) studies of Ag/Si(111)-(7x7) heteroepitaxy were used to optimise growth conditions (temperature and deposition rate) for the most ordered self-organized growth of Ag island arrays on the (7x7) reconstructed surface. The conditions were estimated by means of KMC simulations using the preference in occupation of half unit cells (HUCs) of F-type as a criterion of island ordering. Morphology of experimentally prepared island structures was studied by STM. High degree of experimentally obtained island ordering is compared with the simulated data and results are discussed with respect to the model and parameters used at the KMC simulations.

Ag/Si(111)-(7X7) Heteroepitaxy—STM Experiment and KMC Simulations

Heteroepitaxial growth of Ag on Si(111)-(7X7) surface at various conditions was experimentally studied by scanning tunneling microscopy. A growth model based on experiments was used for kinetic Monte Carlo (KMC) simulations. The simulations of nucleation and island growth at low coverage and fitting experimental data provided basic growth parameters. Further growth—formation of a discontinuous transition film (wetting layer)—was implemented into the basic model. The suggested growth mechanism was successfully tested using the KMC simulations. The choice of experiments, the role of minimizing processes and parameters in the model, and efficiency of the used approach is demonstrated and discussed.

Electrical noise in MIM structures

Sandwich MIM structures Al/Al2O3/Au were measured before and after electroforming. I-V characteristics and noise of leakage and emission currents were measured in vacuum at various temperatures. Calculated power spectra of current noise of white, Lorentzian and 1/fa type reflect relaxation processes and dominating conduction mechanisms at various applied voltages.

Current noise in thin film Al/Al2O3/Au sandwiches

Abstract Information is presented about the mode of electrical conductance in a Me/MeO/Me sandwich, a type of structure that has been subject to extensive earlier investigations. The dynamics of the electrical current fluctuations were determined for the Al/Al2O3/Au sandwich. Sandwiches with a 17 nm thick alumina interlayer were measured under vacuum conditions at room and 100 K temperatures. I–V characteristics of leakage current were found not symmetric and contain linear parts in In (I) ∼ V 1 2 plot. Power spectra of leakage current noise show relaxation processes at low frequencies which depend on applied voltage and temperature. Amplitude distribution of the leakage current fluctuations is Gaussian at low voltages but at higher voltages (6 V) contains local maxima. The appearance of the multilevel fluctuations corresponds to the voltage region when sandwich structures begin to be unstable and shows qualitative changes in a conduction mechanism. The state indicated by increasing noise power can result in irreversible structural changes—electroformation—when critical conditions are reached. The noise spectra measured at the two different temperatures show an important role of heat dissipation in the structure.

STM study of epitaxial growth of Au on cleaved mica

Au films were evaporated on cleaved mica substrates at various temperatures. Morphology of epitaxial films was observed by scanning tunneling microscope (STM) under non-vacuum conditions. An influence of substrate temperature on a film has been studied and temperature dependence of surface roughness with a local minimum at temperature 0.6 Tm (Tm equals 1333 K -- temperature of melting point of Au) was found.