arXiv subjects
Publications and source records attributed to M. A. Korshunov.
Using the atom-atom potentials method, we have calculated the low-frequency Raman spectra of molecular crystal model with elements of disorder (Poly-Methyl-Methacrylate) PMMA that has a flexible molecule. Based on the results the coupling factor C(ν) has been calculated. Anharmonicity of vibrations, electro-optical anharmonicity, and disorder were taken into account.
We measured low-frequency Raman spectra of paradibromobenzene nanoparticles. With the reduction of the nanoparticles size frequencies of lines become smaller and the doubling of the most intensive lines takes place. Additional lines with increasing intensity appear in the spectrum. We did structure calculations for nanoparticles by the method of molecular dynamics and obtained histograms of lattice vibrations spectra by the Dyne's method. Calculations have shown that doubling of lines is due to the appearance of nanoparticles vibrations from borders of the Brillouin zone in the spectrum. Additional lines are caused by vibrations with $K \neq 0$. They have mixed orientation-translational character (that is evident from the eigenvectors of vibrations) that affects intensity of these lines. Upon reduction of the particles sizes change of vibration eigenvectors of molecules occurs $K \neq 0$. The greatest changes observed for a 20 cm$^{-1}$ paradibromobenzene line.
We measured the small frequencies Raman spectrum of the paradihlorobenzene and paradihlorobenzene solid solution nanoparticles with the size about 100 nanometers. Values of frequencies of lines decrease. The size of nanoparticles was determined by the electronic microscope. Calculations of nanoparticles structure were done using the method of molecular dynamics and histograms of nanoparticles spectra were calculated via the Dyne's method. The result is that the Raman spectrum is the sum of spectra from the central part of the nanoparticle and superficial structures with smaller concentration of paradihlorobenzene.
The method of molecular dynamics is used to investigate the distribution of DOBAMBC molecules in a capsule with the fixed border layer. Change of an arrangement of molecules in smectic layers depending on an inclination of molecules on border is considered.
We use a method of molecular dynamics to investigate the distribution of liquid crystal 5CB molecules in a polymeric matrix. Temperature dependences of parameters of an order are calculated. Calculations have shown that depending on the size of a capsule and on a time the transition temperature changes.
We have measured spectra of lattice fluctuations in p-dihlorbenzol nanoparticles of ~300nm size. Calculations of lattice frequencies and of these fluctuations in nanoparticles are done. It is shown that with reduction of nanoparticles sizes the spectrum of superficial fluctuations becomes prevailing.
We have obtained experimentally the low frequency Raman spectra of p-dihlorbenzol nanoparticles. Nanoparticle sizes are determined with the help of electron microscope. It was found that in the lattice vibration spectra from 70 nm the summary spectrum of α-paradihlorbenzola and β-paradihlorbenzol structures appears. It agrees with both calculations of nanoparticle structure by molecular dynamics and calculations of spectra histograms of the lattice vibrations by a Dyne's method.
Using Raman scattering, the solid solution nanoparticles of paradibrombenzol/paradihlorbenzol are investigated. It is found that in a spectrum of nanoparticles of solid solution frequencies of spectral lines are reduced in comparison with similar lines of a single crystal with the same concentration of components. Calculations of the lattice oscillations by Dyne's method are performed. It is shown that these modifications of frequencies can be caused by the increase of lattice parameters with the reduction of nanoparticles sizes.
P-dibromobenzene nanoparticles in a case of paradihlorbenzol molecules have been synthesized. Raman spectrums of these nanoparticles are measured. At diffusion of molecules of paradihlorbenzol in a pdibromobenzene nanoparticle solid solution formed. Modifications in structure of nanoparticles at diffusion are reflected in Raman spectrums. Unlike a solid solution single crystal, in nanoparticles the accelerated diffusion, $D = 1.3 \pm 0.02 10^{-11} cm^2/s$, is observed at room temperature. Calculations show that the accelerated diffusion is caused by magnification of parametres of a lattice at reduction of sizes of nanoparticles.
Raman spectrums of nanoparticles of a p-dibromobenzene with size of 300 nanometers and 50 nanometers are measured. It is found that frequencies of lines of stretching vibrations of C-Br at reduction of the sizes of nanoparticles below 300 nanometers are incremented. It is related to magnification of parameters of the lattice and interaction reduction between molecules.
Using a method Raman of spectroscopy and considering a non-uniformity of allocation of vacancies in a monocrystal, it is shown that lines with the small intensity (caused by presence of vacancies) have a major intensity in the sample of a larger size than in the sample of a smaller size. Increase of an intensity of lines at vacancy concentration increase can reveal which lines are related to presence of vacancies in the sample. For a p-dichlorobenzene, it is lines of a small intensity in a spectrum of the lattice oscillations in the field of 70 cm^{-1}.
The method of Raman scattering is used to investigate the cross edge of a p-dichlorobenzene monocrystal, which was grown up by a Bridgmen method. Comparison of intensities of additional lines of a spectrum of the lattice oscillations of certain parts of an edge of a monocrystal with density of these fields has allowed to relate some lines to presence of vacancies in structure.
Calculations of frequency spectra for organic molecular crystals taking various defects in their structure into account are carried out. It is shown how the presence of the vacancies, orientation disorder, and surface presence affects spectra. It was found, that each defect has the characteristic set of lines in the spectra.
Calculations of frequencies of the lattice and surface oscillations of organic nano-crystals are carried out. As the sample the para-dichlorobenzol has been chosen. Change of spectra of oscillations from the sizes of nano-particles is found. It is shown that with the reduction of the sizes of nano-particles a spectrum of the surface oscillations prevailing. Calculations have shown that for the correct interpretation of the observational spectra it is necessary to consider orientation disorder of the surface molecules and presence of vacancies in nano-particle volume.
Dependence of frequency spectra of the lattice oscillations of organic nano-crystals on temperature is studied at presence of vacancies in structure. In a frequency spectrum a number of additional lines monotonously changing with temperature is observed. Also, the spectrum of the surface oscillations is calculated at temperature change. At the same time, the low-frequency line has non-linear behavior with temperature change.
Computer modeling of formation of the one-dimensional and three-dimensional monatomic nanostructures by the method of atom-atom potentials was done. The arrangement of atoms was defined on the basis of the energy minimum. Our calculations have shown that the distance between the nearest atoms depends on number of atoms, thus atoms on boundary of grains of nanoparticles have more loose packing than in the volume. In three-dimensional nanostructures at reduction of their sizes increase of the disorder of atoms on positions is observed. Examination of model nanostructures constructed of bi-atomic molecules was also carried out. It is shown that distance between the nearest molecules and their orientation depend on number of molecules surrounding them. Molecules on boundary of grains of nanoparticles have more friable packing than in the volume. As in the linear chain, and three-dimensional nanostructures constructed of bi-atomic molecules, not only the disorder on positions of molecules depending on the sizes of nanoparticles, but also the orientation disorder is observed. At increase of the sizes of nanostructures the lattice in volume becomes more ordered than on boundaries of nanoparticles grains.
Computer modeling of the one-dimensional and three-dimensional nanoparticles with Van-der-Waals interaction was performed. The arrangement of atoms was defined on the grounds of an energy minimum. The calculations have shown that in the presence of vacancies in a nanoparticle and the account of a relaxation and oscillations the nanoparticle will pulse. This pulsation on distance between atoms of a nanoparticle is observed in both one-dimensional and a three-dimensional cases.
Influence of decrease of the sizes of crystallites of para-dichlorbenzol on Raman spectrums is studied. Lattice oscillations frequencies are calculated. On this basis the modification of lattice parameters for particles smaller than 5$μ$ and an incremented modification of nanodimension sized particles are studied. Magnification of lines intensities are related to transmitting oscillations and orientation oscillations frequency decrease is found.