V. A. Gorbunov

Devil’s staircase behavior of a dimer adsorption model

We have constructed the simple two-dimensional adsorption model with short range non-competing interactions which demonstrates devil’s staircase of phase transitions. The main factor which leads to the appearance of infinite amount of ordered structures in our model is two competing forms of adsorption. The ground state properties of the model have been analyzed.

The effect of polyethylene glycol molecular weight on characteristics of the porous structure of silica materials

The effect of poly(ethylene glycol) (PEG) chain length on textural properties had been investigated. It is shown that mesoporous and microporous silica materials can be prepared based on PEG and TEOS. At fixed molar concentration of polymer using the PEG-1300 mesoporous silica material is formed but when increasing molecular weight to 3000—microporous silica material. With further increasing of the molecular weight of PEG to 20000 the micropore volume and total adsorption pore volume remain almost unchanged, so starting with a specific length of the PEG macromolecule the effect of molecular weight on the texture of the formed SiO2 becomes negligible. Based on the approach taken and the results we proved the possibility of purposeful control of the texture of silica materials.

Generalized lattice-gas model for adsorption of functional organic molecules in terms of pair directional interactions.

A generalized lattice-gas model that takes into account the directional character of pair interactions between the lattice sites is proposed. It is demonstrated that the proposed model can be successfully used to deeply understand the self-assembly process in adsorption monolayers of functional organic molecules driven by specified directional interactions between such molecules (e.g., hydrogen bonding). To illustrate the idea, representative cases of the general model with different numbers of identical functional groups in the chemical structure of the adsorbed molecule are investigated with Monte Carlo and the transfer-matrix methods. The model reveals that the phase behavior of the adsorption systems considered can be characterized as a hierarchical self-assembly process. It is predicted that in real adsorption systems of this type, the energy of hydrogen bonding sufficiently depends on the mutual orientation of the adsorbed molecules.

Adsorption thermodynamics of cross-shaped molecules with one attractive arm on random heterogeneous square lattice

Understanding the forces governing the arrangement of organic molecules on the solid surface is the key to control and creation of self-assembled organic nanostructures. In this paper we use the simple lattice gas model and grand canonical Monte Carlo method to demonstrate how the random surface heterogeneity affects both structural and thermodynamic properties of the adsorption overlayer of cross-shaped molecules with one attractive arm. The simulated results show that phase behavior of the adlayer on the random heterogeneous surface characterized by small energy difference between adsorption on the “weak” and “strong” sites and/or low concentration of the “strong” sites (0.1 and less) can be described as the hierarchical self-assembly process. On the other hand, the simulations performed for the system with large energy difference between adsorption on the “weak” and “strong” sites revealed that the stable phases appearing on the surface at coverage close to 0.5 and higher are the balance products of the “adsorbate–adsorbate” and “adsorbate–substrate” interactions.

Effect of nonmonotonic changing of surface coverage in multisite adsorption models with possibility of different orientations of molecules with respect to solid surface

The reasons for nonmonotonous changing of surface coverage as function of chemical potential in the multisite adsorption models (with allowance for the possibility that molecules can be oriented in a different manner with respect to the solid surface) are revealed in this work. It is demonstrated that this behavior of the surface coverage as function of chemical potential is determined by either the sequence of ordered structures being formed or by the emergence of a stable interface between the ordered phases at temperatures above the tricritical point.

The simulation of the adsorption of unsaturated cyclic hydrocarbons on the (001)-2 × 1 reconstructed silicon surface by the Monte Carlo and transfer-matrix methods

A model of the adsorption of cyclic unsaturated molecules on the Si(001)-2 × 1 reconstructed surface was developed for the example of 1,4-cyclohexadiene, which can be differently adsorbed on surface adsorption centers. Calculations were performed for a grand canonical ensemble by the Monte Carlo and transfer matrix methods. The structure of the ordered phases formed and the conditions of their appearance were studied in detail. It was shown that the suggested model reproduced all the qualitative special features of the system studied and similar systems.