arXiv subjects

A. Vasil'ev

Publications and source records attributed to A. Vasil'ev.

4 recordsLinked to original sources

arXiv2026

Effect of Pb doping on the crystallization process and thermoelectric properties of Ge2Sb2Te5 phase change material

Phase change materials based on Ge-Sb-Te alloys are widely explored for their potential in both memory devices and thermoelectric applications. In this study, films of Ge2Sb2Te5 (GST) doped with varying concentrations of Pb were prepared and systematically investigated to trace the effect of Pb doping on crystallization-induced phase transformations and thermoelectric properties. Via X-ray diffraction and Raman spectroscopy, the impact of Pb doping on the crystallization behavior was revealed and examined. According to the specific electrical resistivity measurements, the Pb doping resulted in decreasing both the amorphous-to-cubic and cubic-to-hexagonal transition temperatures, thereby facilitating the formation of the hexagonal phase at a lower thermal regime. Furthermore, Seebeck coefficient and electrical resistivity data of hexagonal Pb-doped GST were used to calculate the power factor, PF. A PF maximum equal to 1.3 was found for 2.5 at. Pb-GST at 633 K, with the highest carrier mobility also observed for this composition. Controlled Pb doping effectively modulates both structural transitions and thermoelectric performance, highlighting the potential of Pb-GST for applications that combine phase-change memory and thermoelectric functionality, such as opto-thermoelectric devices and non-volatile thermoelectric sensors.

cond-mat.mtrl-sci↗

arXiv2025

Chemical vapor deposition synthesis of (GeTe)n(Sb2Te3) gradient crystalline films as promising planar heterostructures

Phase-change materials of the (GeTe)n (Sb2Te3) (GST) system are of high relevance in memory storage and energy conversion applications due to their fast-switching speed, high data retention, and tunable properties. Here, we report on a fast and efficient CVD-based method for the fabrication of crystalline GST films with variable Ge/Sb atomic content. In particular, the approach enables compositional control without changing the precursor, facilitating a gradient synthesis of Ge3Sb2Te6, Ge2Sb2Te5, and GeSb2Te4 phases in a single attempt. The analyses of their structural, optical, and electrical aspects highlight how compositional variation influences the film's properties. Our findings demonstrate a straightforward approach enabling the preparation of gradient crystalline GST films with tunable morphology and functionality. These gradient films can potentially provide in-plane multilevel and gradual switching thresholds for memory applications and altered refractive index and absorption for optical modulation and filtering applications.

cond-mat.mtrl-sci↗

arXiv2013

Boundary distortion estimates for holomorphic maps

We establish some estimates of the the angular derivatives from below for holomorphic self-maps of the unit disk at one and two fixed points of the unit circle provided there is no fixed point inside the unit disk. The results complement Cowen-Pommerenke and Anderson-Vasil'ev type estimates in the case of univalent functions. We use the method of extremal length and propose a new semigroup approach to deriving inequalities for holomorphic self-maps of the disk which are not necessarily univalent using known inequalities for univalent functions. This approach allowed us to receive a new Ossermans type estimate as well as inequalities for holomorphic self-maps which images do not separate the origin and the boundary.

math.CV↗

arXiv2011

Sub-Riemannian and sub-Lorentzian geometry on $\SU(1,1)$ and on its universal cover

We study sub-Riemannian and sub-Lorentzian geometry on the Lie group $\SU(1,1)$ and on its universal cover $\CSU(1,1)$. In the sub-Riemannian case we find the distance function and completely describe sub-Riemannian geodesics on both $\SU(1,1)$ and $\CSU(1,1)$, connecting two fixed points. In particular, we prove that there is a strong connection between the conjugate loci and the number of geodesics. In the sub-Lorentzian case, we describe the geodesics connecting two points on $\CSU(1,1)$, and compare them with Lorentzian ones. It turns out that the reachable sets for Lorentzian and sub-Lorentzian normal geodesics intersect but are not included one to the other. A description of the timelike future is obtained and compared in the Lorentzian and sub-Lorentzain cases.

math.DG↗