The dissertation is devoted to establishing the correlation between the sizes of nanostructured objects and their properties: the structure, phase states and transformations in atomic and molecular nanosystems, sorption capacities of carbon honeycombs, as well as studying the effect of geometrically spatial limitation on the surface characteristics of solidified gases and perovskites. It is shown that this correlation has a significant effect on the behavior of nanoscale formations depending on the type of interatomic interaction. To attain the goal of the work, new methods of performing and analyzing the experiment, as well as the new theoretical approaches, were developed.
The dissertation established for the first time the complete sequence of the most energetically favorable structures of atomic nanoclusters in a wide size range from 13 to ~ 105 atoms, in which the advantage of decahedra over icosahedra at cluster sizes N ~ 2000 atoms was shown. It was demonstrated that the obtained macroscopic samples of noble gas nanoclusters by the methods of impurity–helium mixtures injection into superfluid helium consist of weakly interacting nanoclusters with fivefold symmetry axes, such as icosahedra and decahedra.
Considering the optimized hcp clusters, it was found for the first time that at sizes N ~ 105 atoms, the hcp structure forms in accordance with direct theoretical predictions. This result is confirmed in the experimental X–ray study of the evolution of macroscopic ensembles of argon nanoclusters stabilized in superfluid helium during cluster growth outside liquid helium. Due to the proposed original theoretical approach based on the study of the quasiharmonic instability of crystals of inert elements Ne, Ar, Kr and Xe and their surfaces, the reasons and mechanisms leading to transformations in systems of atomic nanoclusters that are impossible in bulk crystals have been clarified.
In the experimental study of clusters of a quantum object – deuterium, immersed in superfluid helium, it was found that at temperatures close to the λ point, small clusters with the number of molecules N < 300 lose their stability, and clusters less than 100 molecules in size are unstable even in the ground state.
The studied relaxation of the surface structures of nitrogen and carbon monoxide has shown a very low probability of the formation of large nitrogen clusters with fivefold symmetry axes, such as icosahedra and decahedra. This conclusion was confirmed by known experiments. In the low–temperature nanocluster condensates of N2O on a substrate, the formation of the most energetically favorable structure P213, which is ordered by the asymmetric ends of linear molecules, was found. When studying low–temperature condensates of nitrous oxide N2O with asymmetric molecules, two fundamentally different types of amorphous states were found, one is similar to a frozen liquid, and the other is a polycluster formation.
By means of the reflection high–energy electron diffraction (RHEED) method a full image of quasi–two–dimensional surface inverse lattice of strontium titanate in the form of rods perpendicular to single–crystal surfaces and modulated in thickness was obtained for the first time. The effect of contraction of the crystal lattice parallel to the surface of an unexcited SrTiO3 crystal in the temperature range 5 – 300 K was found. This effect increases with lowering temperature.
A new low–density carbon honeycomb structure is synthesized, it is obtained from vacuum sublimated graphite, in which the walls between cells are formed from only one graphene layer. Methods of saturation of a new honeycomb carbon structure – carbon honeycombs with record amounts of sorbed heavy inert gases Ar, Kr and Xe, which are 4– 7 percents of the number of carbon atoms in the matrix, have been found and applied. A two – stage character of carbon dioxide desorption from carbon honeycombs was found. It is associated with different interactions of molecules with the matrix in narrow and wide channels. It was found that, due to the strong binding to the channel walls, the desorption of CO2 from the honeycomb structure is not completed even at temperatures almost three times higher than the temperature of sublimation from flat substrates in vacuum.
