Pavel Kocán

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.

Continuous and correlated nucleation during nonstandard island growth at Ag/si(111)-7×7 heteroepitaxy

We present a combined experimental and theoretical study of submonolayer heteroepitaxial growth of Ag on Si(111)-

Epitaxially grown flat MnSi ultrathin film on Si(111)

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Early Stages of Submonolayer Growth of Ag on Si(111) 7×7 Observed by Scanning Tunneling Microscopy In Vivo

at temperatures from 420 K to 550 K when Ag atoms can easily diffuse on the surface and the reconstruction

Electric-field-controlled phase transition in a 2D molecular layer

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

remains stable. Scanning tunneling microscopy measurements for coverages from 0.05 ML to 0.6 ML (ML---monolayer) show that there is an excess of smallest islands (each of them fills up just one half unit cell---HUC) in all stages of growth. Formation of a two-dimensional (2D) wetting layer proceeds by continuous nucleation of the smallest islands in the proximity of larger 2D islands (extended over several HUCs) and following coalescence with them. Such a growth scenario is verified by kinetic Monte Carlo simulation which uses a coarse-grained model based on a limited capacity of HUC and a mechanism which increases nucleation probability in a neighborhood of already saturated HUCs (correlated nucleation). The model provides a good fit for experimental dependences of the relative number of Ag-occupied HUCs and the preference in occupation of faulted HUCs on temperature and amount of deposited Ag. Parameters obtained for the hopping of Ag adatoms between HUCs agree with those reported earlier for initial stages of growth. The model provides two parameters---maximum number of Ag atoms inside HUC, and on HUC boundary.

Reconstruction-Determined Diffusion of Ag Adatoms on the Si(111)-(7X7) Surface

Flat MnSi ultrathin films are epitaxially grown on the Si(111)-(7×7) surface by Mn deposition and subsequent annealing. Low-energy electron diffraction exhbits the brightest (3×3)R30° patterns when Mn atoms are deposited at ∼3 ML with subsequent annealing at 250°C. Scanning tunneling microscopy shows that atomically flat MnSi(111) surfaces with the (3×3)R30° periodicity are formed under above condition, and that the thickness of the flat MnSi films is ∼7A. The results support a recent theoretical prediction of flat-film formation of the B20-type MnSi on the Si(111) surface.

Pair Correlation Function of a 2D Molecular Gas Directly Visualized by Scanning Tunneling Microscopy

Scanning tunneling microscopy (STM) was used for directly imaging the early stages of heteroepitaxial growth of Ag on a Si(111) 7×7 surface during deposition by vacuum evaporation. Image sequences showed the behavior of single Ag adatoms after arriving on the surface and the formation of Ag clusters. STM measurements were performed at room temperature and 330 K. New data showed an attractive interaction between a cluster containing at least two Ag atoms and a monomer occupying an adjacent half-unit cell of surface reconstruction. The interaction modified the Ag adatom mobility on the surface and controled the growth scenario from the moment when the relative number of occupied half-unit cells is ≈0.5. The observation of the individual Ag adatom history on the surface enabled the interpretation of STM imaging of the smallest Ag objects, i.e., monomers, dimers, and trimers. The previously reported models of metal growth on the Si(111) 7×7 surface derived from in situ STM measurements are discussed with respect to the new data.

Adsorption of ethylene on Sn and In terminated Si(001) surface studied by photoelectron spectroscopy and scanning tunneling microscopy

Self-assembly of organic molecules is a mechanism crucial for design of molecular nanodevices. We demonstrate unprecedented control over the self-assembly, which could allow switching and patterning at scales accessible by lithography techniques. We use the scanning tunneling microscope (STM) to induce a reversible 2D-gas-solid phase transition of copper phthalocyanine molecules on technologically important silicon surface functionalized by a metal monolayer. By means of ab-initio calculations we show that the charge transfer in the system results in a dipole moment carried by the molecules. The dipole moment interacts with a non-uniform electric field of the STM tip and the interaction changes the local density of molecules. To model the transition, we perform kinetic Monte Carlo simulations which reveal that the ordered molecular structures can form even without any attractive intermolecular interaction.

Anomalous structural evolution and 3×3 reconstruction of a clean Si(111) surface observed after thermal desorption of thallium

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.