arXiv subjects

Zhandos Utegulov

Publications and source records attributed to Zhandos Utegulov.

3 recordsLinked to original sources

arXiv2026

Probing optical and acoustic phonons in heated nano-Si/epoxy composites

Understanding the thermal response of optical and acoustic phonons is crucial for designing functional polymer nanocomposites. We study silicon nanoparticle (Si NP)-epoxy composites using combined Raman and Brillouin spectroscopy under local(laser-induced) and global(stage-controlled) heating. Raman spectra reveal THz longitudinal optical(LO) phonon softening and spectral broadening under local heating, indicating nanoscale hot-spots and interfacial scattering. Brillouin data track GHz longitudinal acoustic(LA) phonons, showing temperature- and concentration-dependent evolution of elasticity and damping. Contrasting heating methods unravels Si loading thresholds for isolated thermal absorbers, thermal percolation, acoustic attenuation and elastic homogenization. Local heating induces greater phonon softening and damping than global heating, with this disparity amplified at higher loadings by thermal gradients and interfacial dissipation. Global heating correlates with viscoelastic relaxation, showing intensified acoustic attenuation near the glass transition. Raman thermometry coupled with finite-element opto-thermal modeling allows evaluation of thermal conductivity of the composites characterized by increase from 0.09 to 0.46 W/(mK) for 0.07 up to 2 wt% of Si NPs, respectively, outperforming SiC nanowires at 2 wt% [D. Shen et al, Sci. Rep. 7, 2606 (2017)] despite bulk conductivity of Si being more than 3 times smaller than that of SiC. However, effective heat conductivity of our nanocomposites remain far below bulk Si, confirming that interfacial thermal resistance, not filler conductivity, governs heat transport.

physics.app-ph↗

arXiv2025

Ions leaving no tracks

The paths of swift heavy ions are typically traceable in solids, because of confined electronic interactions along the paths, inducing what is known in literature as 'ion tracks', i.e. nano-sized in cross-section cylindrical zones of modified material extending for microns in length. Such tracks readily form in materials exhibiting low thermal conductivities, in particular insulators or semiconductors, altering the homogeneity of materials. In this work, using recently discovered gamma/beta-Ga2O3 polymorph heterostructures we show that, in contrast to the trends in many other materials, including that in beta-Ga2O3, swift heavy ions leave no tracks in gamma-Ga2O3. We explained this trend in terms of amazingly fast disorder recovery, occurring because of multiple configurations in the gamma-Ga2O3 lattice itself, so that the disorder formed by ion impacts gets rapidly erased, giving a perception of ions leaving no tracks. As such, gamma-Ga2O3, readily integrated with beta-Ga2O3 in polymorph heterostructures, may become a promising semiconductor platform for devices capable to operate in extremely harsh radiation environments.

cond-mat.mtrl-sci↗

arXiv2024

Thermal Conductivity of Double Polymorph Ga2O3 Structures

Recently discovered double gamma/beta (γ/\b{eta}) polymorph Ga2O3 structures constitute a class of novel materials providing an option to modulate functional properties across interfaces without changing chemical compositions of materials, in contrast to that in conventional heterostructures. In this work, for the first time, we investigate thermal transport in such homo-interface structures as an example of their physical properties. Specifically, the cross-plane thermal conductivity (k) was measured by femtosecond laser-based time-domain thermoreflectance with MHz modulation rates, effectively obtaining depth profiles of the thermal conductivity across the γ/\b{eta}-Ga2O3 structures. In this way, the thermal conductivity of γ-Ga2O3 k=1.84÷2.11 W m-1K-1 was found to be independent of the initial \b{eta}-substrates orientations, in accordance with the cubic spinel structure of the γ-phase and consistently with the molecular dynamics simulation data. In its turn, the thermal conductivity of monoclinic \b{eta}-Ga2O3 showed a distinct anisotropy, with values ranging from 10 W m-1K-1 for [201] to 20 Wm-1K-1 for [010] orientations. Thus, for double γ/\b{eta} Ga2O3 polymorph structures formed on [010] \b{eta}-substrates, there is an order of magnitude difference in thermal conductivity across the γ/\b{eta} interface, which potentially can be exploited in thermal energy conversion applications.

cond-mat.mtrl-sci↗