arXiv subjects

Vitaly I. Korepanov

Publications and source records attributed to Vitaly I. Korepanov.

7 recordsLinked to original sources

arXiv2025

Rapid Determination of Nanodiamond Size Distribution and Impurity Concentration from Raman Spectra Using an Open Machine-Learning Toolbox

Ready-to-use numerical toolbox for nanodiamond Raman spectra calculation and fit is presented. The developed theoretical approach allows accounting for arbitrary nanoparticle size-distribution and the microscopic line broadening mechanisms for the optical phonons. The two tools for solving the inverse problem of the nanodiamond properties reconstruction using a known Raman spectrum are provided. The first one utilizes a dense neural network trained on a vast array of synthetic Raman spectra. The second approach is based on the stochastic Metropolis algorithm, which updates the ensemble parameters by small quantities, tending to the state with minimal error. Both methods are available thanks to the computationally instant elasticity theory-like model for optical phonon modes in diamond nanocrystals that accurately reproduces the results of the atomistic approaches. Using experimental Raman spectra for nanodiamonds prepared by various techniques, we tested our tools and observed a faithful agreement with the data as well as between the two methods. The open and documented software is accessible online (nanoraman.pythonanywhere.com) and as a Python module (github.com/KoniakhinSV/Nanoparticle_Raman).

cond-mat.mes-hall↗

arXiv2019

Phonon propagation scale and nanoscale order in vitreous silica from Raman spectroscopy

For nanoscale systems such as nanoparticles and 3D-bonded networks, the range of spatial coherence is well reflected in the Raman spectral pattern. For confined, or localized, phonons, the range of q-points contributing to the spectrum depends on the phonon confinement length, which makes possible to derive the size information from the spectra. In this work, Raman spectrum of vitreous silica is described as localized phonons of SiO2 network. The convergence of the spectral pattern with the confinement size is studied. It is shown that the phonon propagation scale in vitreous silica is within the 0.5-2 nm range.

physics.chem-ph↗

arXiv2019

2D polyphthalocyanines (PPCs) of different structure and polymerization degree: chemical factors, characterization and processability

2D conjugated polyphthalocyanines can be obtained as two distinctly different types of material with specific molecular structures and different morphological properties. It was believed that the temperature is the key factor affecting the chemical reaction, but we show that even at the optimal temperature (420°C), the reaction on vapor/solid interface and liquid/solid interface yields different products: while the former is well-polymerized and ordered, the latter is amorphous and cross-linked with the typical conjugation scale of single PC ring. IR spectroscopy is most sensitive tool for identifying the molecular structure, providing the information on polymerization degree, structural uniformity and content of terminal groups. We show that, unlike the ordered PPCs, the cross-linked product can be reproducibly obtained as continuous conductive material.

cond-mat.mtrl-sci↗

arXiv2018

Spectroscopic identification of conjugated polymeric phthalocyanines

Since the discovery of polyphthalocyanines (PPCs) in late 1950s, numerous attempts have been made to synthesize this 2D polymer by different approaches. Interestingly, the reported IR, Raman and UV-vis spectra of PPCs show drastic variation depending on the synthesis conditions. In this work, we show that the spectral data obtained in some works should be assigned not to the target polymer, but rather to octacyano phthalocyanine (OCP), which is an early step of the reaction. We discuss the spectral signatures of the well-polymerized and monomeric PCs based on reliable experimental data and support the spectral assignments with DFT calculations.

cond-mat.mtrl-sci↗

arXiv2018

Asymmetric fitting function for condensed-phase Raman spectroscopy

Asymmetric lineshapes are experimentally observed in Raman spectra of different classes of condensed matter. Determination of the peak parameters, typically done with symmetric pseudo-Voigt functions, in such situations yields unreliable results. While wide choice of asymmetric fitting functions is possible, for the function to be practically useful, it should satisfy several criteria: simple analytic form, minimum of parameters, description of the symmetric shape as "zero case", estimation of the desired peak parameters in a straightforward way and, above all, adequate description of the experimental data. In this work we formulate the asymmetric pseudo-Voigt function by damped perturbation of the original symmetric shapes with one asymmetry-related parameter. The damped character of the perturbation ensures by construction the consistent behavior of the line tails. We test the asymmetric function by fitting the experimental Raman spectra. The results show that the function is able to describe a wide range of experimentally observed asymmetries for different nature of asymmetric broadening, including 3D and 2D crystals, nanoparticles, polymer, molecular solid and liquid.

cond-mat.other↗

arXiv2016

Quantum-chemical perspective of nanoscale Raman spectroscopy with three-dimensional phonon confinement model

Raman spectroscopy of crystalline/molecular systems is well backed with quantum chemical calculations and group theory, making it a unique characterization tool. For the "intermediate" case of nanoscale systems, however, the use of Raman spectroscopy is limited by the lack of such theoretical bases. Here, we suggest to couple a scaled quantum-mechanical (SQM) calculation with the phonon confinement model (PCM) to construct a universal and physically consistent basis for nanoscale Raman spectroscopy. Unlike the commonly used one-dimensional dispersion PCM, we take into account the confinement along all the three dimensions of the k-space. We apply it to diamond nanoparticles of sub-50nm size, a system with pronounced anisotropy of dispersion for which the use of three-dimensional dispersion is a requisite. The model excellently reproduces size-sensitive spectral features, including the peak position, bandwidth and asymmetry of the sp3 C-C Raman band. This fundamental approach can be easily generalized to other nanocrystalline solids to hopefully contribute the future development of quantitative nanoscale Raman spectroscopy.

physics.chem-ph↗

arXiv2013

Synthesis and structure of high-quality films of copper polyphthalocyanine - 2D conductive polymer

We propose an experimental approach, by which thin films of copper polyphthalocyanine (CuPPC) can be directly synthesized in a chemical vapor deposition (CVD) set-up at mild temperature (420 °C). High polymerization degree and high crystallinity of the films was confirmed by TEM, FTIR and UV-VIS studies; the stacking structure of CuPPC layers was determined, inter-layer spacing was estimated from XRD and TEM electron-diffraction. Quantum-chemical study performed providing support for experimental structure determination and yielding information on the electronic structure.

cond-mat.mtrl-sci↗