arXiv subjects

Alexander Sobolev

Publications and source records attributed to Alexander Sobolev.

5 recordsLinked to original sources

arXiv2025

Multifunctional 2d infrared photodetectors enabled by asymmetric singular metasurfaces

Two-dimensional materials offering ultrafast photoresponse suffer from low intrinsic absorbance, especially in the mid-infrared wavelength range. Challenges in 2d material doping further complicate the creation of light-sensitive $p-n$ junctions. Here, we experimentally demonstrate a graphene-based infrared detector with simultaneously enhanced absorption and strong structural asymmetry enabling zero-bias photocurrent. A key element for those properties is an asymmetric singular metasurface (ASMS) atop graphene with keen metal wedges providing singular enhancement of local absorbance. The ASMS geometry predefines extra device functionalities. The structures with connected metallic wedges demonstrate polarization ratios up to 200 in a broad range of carrier densities at a wavelength of 8.6 $μ$m. The structures with isolated wedges display gate-controlled switching between polarization-discerning and polarization-stable photoresponse, a highly desirable yet scarce property for polarized imaging.

cond-mat.mes-hall↗

arXiv2024

Hankel operators with band spectra and elliptic functions

We consider the class of bounded self-adjoint Hankel operators $\mathbf H$, realised as integral operators on the positive semi-axis, that commute with dilations by a fixed factor. By analogy with the spectral theory of periodic Schrödinger operators, we develop a Floquet-Bloch decomposition for this class of Hankel operators $\mathbf H$, which represents $\mathbf H$ as a direct integral of certain compact fiber operators. As a consequence, $\mathbf H$ has a band spectrum. We establish main properties of the corresponding band functions, i.e. the eigenvalues of the fiber operators in the Floquet-Bloch decomposition. A striking feature of this model is that one may have flat bands that co-exist with non-flat bands; we consider some simple explicit examples of this nature. Furthermore, we prove that the analytic continuation of the secular determinant for the fiber operator is an elliptic function; this link to elliptic functions is our main tool.

math.SP↗

arXiv2018

Coating of Aluminum Alloys by Micro Arc Oxidation in Nitrate Salt

Plasma electrolytic oxidation (PEO) is a process for obtaining oxide coatings on valve metals. Mostly PEO is done in an aqueous solution electrolyte which limits the size of treated parts due to the system heating up. In presented work an alternative method of PEO processing applied in aluminum 1050 alloy in nitrate molten salt was investigated. The morphology, phase and chemical compositions, micro-hardness, and corrosion resistance were examined using. The obtained results showed that formed coating contains from two sub-layers, outer soft layer with the thickness of 4 micrometer and inner, denser layer with the thickness of 5 micrometer. The formed coating consists of corundum, γ - Al2O3, θ - Al2O3 and is free of any contaminants originated from the electrolyte.

physics.app-ph↗

arXiv2018

Creation of oxide coating on Al 1050 alloy

Plasma electrolytic oxidation (PEO) is a surface processing for oxide coatings formation with advanced properties. Mostly, PEO is performed in an aqueous solution electrolyte which limits the dimension of treated parts due to the system heating up. Therefore, treatment of large surfaces cannot be applied in aqueous electrolyte. In current work an alternative approach of PEO treatment applied in aluminum 1050 alloy in nitrate molten salt was investigated. The structure, phase and chemical compositions, and micro-hardness were examined using XRD, SEM, EDS and micro-hardness tests. The obtained results showed that formed coating contains from two phases of α- Al2O3 and γ- Al2O3. It was found that formed coating is free of any contaminants originated from the electrolyte and has no damages, which are usually present in coatings formed in PEO treatment in aqueous solution electrolyte.

physics.app-ph↗

arXiv2015

A Frequency Selective Surface based focal plane receiver for the OLIMPO balloon-borne telescope

We describe here a focal plane array of Cold-Electron Bolometer (CEB) detectors integrated in a Frequency Selective Surface (FSS) for the 350 GHz detection band of the OLIMPO balloon-borne telescope. In our architecture, the two terminal CEB has been integrated in the periodic unit cell of the FSS structure and is impedance matched to the embedding impedance seen by it and provides a resonant interaction with the incident sub-mm radiation. The detector array has been designed to operate in background noise limited condition for incident powers of 20 pW to 80 pW, making it possible to use the same pixel in both photometric and spectrometric configurations. We present high frequency and dc simulations of our system, together with fabrication details. The frequency response of the FSS array, optical response measurements with hot/cold load in front of optical window and with variable temperature black body source inside cryostat are presented. A comparison of the optical response to the CEB model and estimations of Noise Equivalent power (NEP) is also presented.

astro-ph.IM↗