Articles
http://nur.nu.edu.kz:80/handle/123456789/4182
2024-03-29T12:57:54ZELECTRICAL AND STRUCTURAL CHARACTERIZATION OF FEW-LAYER GRAPHENE SHEETS ON QUARTZ
http://nur.nu.edu.kz:80/handle/123456789/7252
ELECTRICAL AND STRUCTURAL CHARACTERIZATION OF FEW-LAYER GRAPHENE SHEETS ON QUARTZ
Aimaganbetov, Kazybek; Almas, Nurlan; Kurbanova, Bayan; Muratov, Dauren; Serikkanov, Abay; Insepov, Zinetula; Tokmoldin, Nurlan
Despite the impressive performance and incredible promise for a variety of applications,
the wide-scale commercialization of graphene is still behind its full potential. One of the main
challenges is related to preserving graphene’s unique properties upon transfer onto practically
desirable substrates. In this work, few-layer graphene sheets deposited via liquid-phase transfer from
copper onto a quartz substrate have been studied using a suite of experimental techniques, including
scanning electron microscopy (SEM), Raman spectroscopy, admittance spectroscopy, and four-point
probe electrical measurements. SEM measurements suggest that the transfer of graphene from copper
foil to quartz using the aqueous solution of ammonium persulfate was accompanied by unintentional
etching of the entire surface of the quartz substrate and, as a result, the formation of microscopic
facet structures covering the etched surface of the substrate. As revealed by Raman spectroscopy
and the electrical measurements, the transfer process involving the etching of the copper foil in a
0.1Msolution of (NH4)2S2O8 resulted in its p-type doping. This was accompanied by the appearance
of an electronic gap of 0.022 eV, as evidenced by the Arrhenius analysis. The observed increase in
the conductance of the samples with temperature can be explained by thermally activated carrier
transport, dominating the scattering processes.
2022-01-01T00:00:00ZFABRICATION OF FLEXIBLE QUASI-INTERDIGITATED BACK-CONTACT PEROVSKITE SOLAR CELLS
http://nur.nu.edu.kz:80/handle/123456789/7014
FABRICATION OF FLEXIBLE QUASI-INTERDIGITATED BACK-CONTACT PEROVSKITE SOLAR CELLS
Parkhomenko, Hryhorii P.; Shalenov, Erik O.; Umatova, Zarina; Dzhumagulova, Karlygash N.; Jumabekov, Askhat N.
Perovskites are a promising class of semiconductor materials, which are being studied intensively for their applications in emerging new flexible optoelectronic devices. In this paper, device manufacturing and characterization of quasi-interdigitated back-contact perovskite solar cells fabricated on flexible substrates are studied. The photovoltaic parameters of the prepared flexible quasi-interdigitated back-contact perovskite solar cells (FQIBC PSCs) are obtained for the front- and rear-side illumination options. The dependences of the device’s open-circuit potential and short-circuit current on the illumination intensity are investigated to determine the main recombination pathways in the devices. Spectral response analysis of the devices demonstrates that the optical transmission losses can be minimized when FQIBC PSCs are illuminated from the front-side. Optoelectronic simulations are used to rationalize the experimental results. It is determined that the obtained FQIBC PSCs have high surface recombination losses, which hinder the device performance. The findings demonstrate a process for the fabrication of flexible back-contact PSCs and provide some directions for device performance improvements.
2022-01-01T00:00:00ZCONNECTION BETWEEN REGULAR BLACK HOLES IN NONLINEAR ELECTRODYNAMICS AND SEMICLASSICAL DUST COLLAPSE
http://nur.nu.edu.kz:80/handle/123456789/7005
CONNECTION BETWEEN REGULAR BLACK HOLES IN NONLINEAR ELECTRODYNAMICS AND SEMICLASSICAL DUST COLLAPSE
Malafarina, Daniele; Toshmatov, Bobir
There exists a correspondence between black holes in nonlinear electrodynamics (NLED) and gravitational collapse of homogeneous dust with semiclassical corrections in the strong curvature regime that to our knowledge has not been noticed until now. We discuss the nature of such correspondence and explore what insights may be gained from considering black holes in NLED in the context of semiclassical dust collapse and vice versa.
2022-01-01T00:00:00ZSTUDY OF THE ELECTRON–ATOM COLLISIONS IN DENSE SEMICLASSICAL PLASMA OF NOBLE GASES
http://nur.nu.edu.kz:80/handle/123456789/6949
STUDY OF THE ELECTRON–ATOM COLLISIONS IN DENSE SEMICLASSICAL PLASMA OF NOBLE GASES
Dzhumagulova, Karlygash N.; Shalenov, Erik O.; Tashkenbayev, Yerkhan A.; Ramazanov, Tlekkabyl S.
We present the effective optical potential of the interaction of an electron with an atom in
dense semiclassical plasma of noble gases. This potential takes into account the collective
screening effect and the quantum mechanical effect of diffraction. The influence of
diffraction and screening effects on the characteristics of electron–atom collisions was
investigated. Scattering phase shifts decrease with increase of the de Broglie wave. The
electron–atom momentum-transfer cross-section at λB → 0 tends to the data obtained
earlier with a neglecting of the diffraction effect.
2022-01-01T00:00:00ZMaLeFiSenta: Machine Learning for FilamentS Identification and Orientation in the ISM
http://nur.nu.edu.kz:80/handle/123456789/6898
MaLeFiSenta: Machine Learning for FilamentS Identification and Orientation in the ISM
Alina, Dana; Shomanov, Adai; Baimukhametova, Sarah
Filament identification became a pivotal step in tackling fundamental problems in various
fields of Astronomy. Nevertheless, existing filament identification algorithms are critically user-dependent and require individual parametrization. This study aimed to adapt the neural networks approach to elaborate on the best model for filament identification that would not require fine-tuning for a given astronomical map. First, we created training samples based on the most commonly used maps of the interstellar medium
obtained by Planck and Herschel space telescopes and the atomic hydrogen all-sky survey HI4PI. We used the Rolling Hough Transform, a widely used algorithm for filament identification, to produce training outputs. In the next step, we trained different neural network models. We discovered that a combination of the Mask R-CNN and U-Net architecture is most appropriate for filament identification and determination of their
orientation angles. We showed that neural network training might be performed efficiently on a relatively small training sample of only around 100 maps. Our approach eliminates the parametrization bias and facilitates filament identification and angle determination on large data sets...
2022-07-22T00:00:00ZEFFECTS OF GRAVITATIONAL LENSING ON NEUTRINO OSCILLATION IN Γ-SPACETIME
http://nur.nu.edu.kz:80/handle/123456789/6829
EFFECTS OF GRAVITATIONAL LENSING ON NEUTRINO OSCILLATION IN Γ-SPACETIME
Chakrabarty, Hrishikesh; Borah, Debasish; Abdujabbarov, Ahmadjon; Malafarina, Daniele; Ahmedov, Bobomurat
We study the effects of gravitational lensing on neutrino oscillations in the γ-spacetime which describes a static, axially-symmetric and asymptotically flat solution of the Einstein’s field equations in vacuum. Using the quantum-mechanical treatment for relativistic neutrinos, we calculate the phase of neutrino oscillations in this spacetime by considering both radial and non-radial propagation. We show the dependence of the oscillation probability on the absolute neutrino masses, which in the two-flavour case also depends upon the sign of mass squared difference, in sharp contrast with the well-known results of vacuum oscillation in flat spacetime. We also show the effects of the deformation parameter γ on neutrino oscillations and reproduce previously known results for the Schwarzschild metric. We then extend these to a more realistic three flavours neutrino scenario and study the effects of the parameter γ and the lightest neutrino mass while using best fit values of neutrino oscillation parameters.
2022-01-01T00:00:00Z