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Item Open Access MECHANO-CHEMICAL PROPERTIES OF ELECTRON BEAM IRRADIATED POLYETHERETHERKETONE(Polymers, 2022) Almas, Nurlan; Kurbanova, Bayan; Zhakiyev, Nurkhat; Rakhadilov, Baurzhan; Sagdoldina, Zhuldyz; Andybayeva, Gaukhar; Serik, Nurzhan; Alsar, Zhanna; Utegulov, Zhandos; Insepov, ZinetulaIn this study, the mechano-chemical properties of aromatic polymer polyetheretherketone (PEEK) samples, irradiated by high energy electrons at 200 and 400 kGy doses, were investigated by Nanoindentation, Brillouin light scattering spectroscopy and Fourier-transform infrared spectroscopy (FTIR). Irradiating electrons penetrated down to a 5 mm depth inside the polymer, as shown numerically by the monte CArlo SImulation of electroN trajectory in sOlids (CASINO) method. The irradiation of PEEK samples at 200 kGy caused the enhancement of surface roughness by almost threefold. However, an increase in the irradiation dose to 400 kGy led to a decrease in the surface roughness of the sample. Most likely, this was due to the processes of erosion and melting of the sample surface induced by high dosage irradiation. It was found that electron irradiation led to a decrease of the elastic constant C11, as well as a slight decrease in the sample’s hardness, while the Young’s elastic modulus decrease was more noticeable. An intrinsic bulk property of PEEK is less radiation resistance than at its surface. The proportionality constant of Young’s modulus to indentation hardness for the pristine and irradiated samples were 0.039 and 0.038, respectively. In addition, a quasi-linear relationship between hardness and Young’s modulus was observed. The degradation of the polymer’s mechanical properties was attributed to electron irradiation-induced processes involving scission of macromolecular chains.Item Open Access SIZE-DEPENDENT PHONON-ASSISTED ANTI-STOKES PHOTOLUMINESCENCE IN NANOCRYSTALS OF ORGANOMETAL PEROVSKITES(Nanomaterials, 2022) Sekerbayev, Kairolla; Taurbayev, Yerzhan; Mussabek, Gauhar; Baktygerey, Saule; Pokryshkin, Nikolay S.; Yakunin, Valery G.; Utegulov, Zhandos; Timoshenko, Victor Yu.Anti-Stokes photoluminescence (ASPL), which is an up-conversion phonon-assisted process of the radiative recombination of photoexcited charge carriers, was investigated in methylammonium lead bromide (MALB) perovskite nanocrystals (NCs) with mean sizes that varied from about 6 to 120 nm. The structure properties of the MALB NCs were investigated by means of the scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. ASPL spectra of MALB NCs were measured under near-resonant laser excitation with a photon energy of 2.33 eV and they were compared with the results of the photoluminescence (PL) measurements under nonresonant excitation at 3.06 eV to reveal a contribution of phonon-assisted processes in ASPL. MALB NCs with a mean size of about 6 nm were found to demonstrate the most efficient ASPL, which is explained by an enhanced contribution of the phonon absorption process during the photoexcitation of small NCs. The obtained results can be useful for the application of nanocrystalline organometal perovskites in optoelectronic and all-optical solid-state cooling devices.Item Open Access IMPROVING PHOTOELECTROCHEMICAL ACTIVITY OF MAGNETRON-SPUTTERED DOUBLE-LAYER TUNGSTEN TRIOXIDE PHOTOANODES BY IRRADIATION WITH INTENSE PULSED ION BEAMS(Nanomaterials, 2022) Abduvalov, Alshyn; Kaikanov, Marat; Atabaev, Timur Sh.; Tikhonov, AlexanderThe photoelectrochemical (PEC) activity of metal oxide photoelectrodes for water-splitting applications can be boosted in several different ways. In this study, we showed that PEC activity can be significantly improved with a double-layer (crystalline-amorphous) configuration of WO3 thin films irradiated with intense pulsed ion beams (IPIB) of a nanosecond duration. It was found that IPIB irradiation promotes the formation of crystalline and sponge-like WO3 structures on the surface. Due to an increase in the active surface and light scattering in irradiated samples, photocurrent generation increased by ~80% at 1.23 reversible hydrogen electrodes (RHE).Item Open Access ELECTRICAL AND STRUCTURAL CHARACTERIZATION OF FEW-LAYER GRAPHENE SHEETS ON QUARTZ(Materials, 2022) Aimaganbetov, Kazybek; Almas, Nurlan; Kurbanova, Bayan; Muratov, Dauren; Serikkanov, Abay; Insepov, Zinetula; Tokmoldin, NurlanDespite 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.Item Open Access A REVIEW ON THE MATERIALS SCIENCE AND DEVICE PHYSICS OF SEMITRANSPARENT ORGANIC PHOTOVOLTAICS(Energies, 2022) Schopp, Nora; Brus, Viktor V.In this review, the current state of materials science and the device physics of semitransparent organic solar cells is summarized. Relevant synthetic strategies to narrow the band gap of organic semiconducting molecules are outlined, and recent developments in the polymer donor and near-infrared absorbing acceptor materials are discussed. Next, an overview of transparent electrodes is given, including oxides, multi-stacks, thin metal, and solution processed electrodes, as well as considerations that are unique to ST-OPVs. The remainder of this review focuses on the device engineering of ST-OPVs. The figures of merit and the theoretical limitations of ST-OPVs are covered, as well as strategies to improve the light utilization efficiency. Lastly, the importance of creating an in-depth understanding of the device physics of ST-OPVs is emphasized and the existing works that answer fundamental questions about the inherent changes in the optoelectronic processes in transparent devices are presented in a condensed way. This last part outlines the changes that are unique for devices with increased transparency and the resulting implications, serving as a point of reference for the systematic development of next-generation ST-OPVs.Item Open Access FABRICATION OF FLEXIBLE QUASI-INTERDIGITATED BACK-CONTACT PEROVSKITE SOLAR CELLS(Energies, 2022) 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.Item Open Access CONNECTION BETWEEN REGULAR BLACK HOLES IN NONLINEAR ELECTRODYNAMICS AND SEMICLASSICAL DUST COLLAPSE(PHYSICAL REVIEW D, 2022) Malafarina, Daniele; Toshmatov, BobirThere 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.Item Open Access UPON THE HORIZON'S VERGE: THERMAL PARTICLE CREATION BETWEEN AND APPROACHING HORIZONS(Classical and Quantum Gravity, 2022) Fernández-Silvestre, Diego; Good, Michael R R; Linder, Eric VQuantum particle creation from spacetime horizons, or accelerating boundaries in the dynamical Casimir effect, can have an equilibrium, or thermal, distribution. Using an accelerating boundary in flat spacetime (moving mirror), we investigate the production of thermal energy flux despite non-equilibrium accelerations, the evolution between equilibrium states, and the ‘interference’ between horizons. In particular, this allows us to give a complete solution to the particle spectrum of the accelerated boundary correspondence with Schwarzschild–de Sitter spacetime.Item Open Access MÖBIUS MIRRORS(Classical and Quantum Gravity, 2022) Good, Michael R R; Linder, Eric VAn accelerating boundary (mirror) acts as a horizon and black hole analog, radiating energy with some particle spectrum. We demonstrate that a Möbius transformation on the null coordinate advanced time mirror trajectory uniquely keeps invariant not only the energy flux but the particle spectrum. We clarify how the geometric entanglement entropy is also invariant. The transform allows generation of families of dynamically distinct trajectories, including $\mathcal{PT}$-symmetric ones, mapping from the eternally thermal mirror to the de Sitter horizon, and different boundary motions corresponding to Kerr or Schwarzschild black holes.Item Open Access DETERMINATION OF THE CHARGE CARRIER DENSITY IN ORGANIC SOLAR CELLS: A TUTORIAL(Journal of Applied Physics, 2022) Vollbrecht, Joachim; Tokmoldin, Nurlan; Sun, Bowen; Brus, Viktor V.; Shoaee, Safa; Neher, DieterThe increase in the performance of organic solar cells observed over the past few years has reinvigorated the search for a deeper understanding of the loss and extraction processes in this class of device. A detailed knowledge of the density of free charge carriers under different operating conditions and illumination intensities is a prerequisite to quantify the recombination and extraction dynamics. Differential charging techniques are a promising approach to experimentally obtain the charge carrier density under the aforementioned conditions. In particular, the combination of transient photovoltage and photocurrent as well as impedance and capacitance spectroscopy have been successfully used in past studies to determine the charge carrier density of organic solar cells. In this Tutorial, these experimental techniques will be discussed in detail, highlighting fundamental principles, practical considerations, necessary corrections, advantages, drawbacks, and ultimately their limitations. Relevant references introducing more advanced concepts will be provided as well. Therefore, the present Tutorial might act as an introduction and guideline aimed at new prospective users of these techniques as well as a point of reference for more experienced researchersItem Open Access STUDY OF THE ELECTRON–ATOM COLLISIONS IN DENSE SEMICLASSICAL PLASMA OF NOBLE GASES(Journal of Plasma Physics, 2022) 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.Item Open Access MaLeFiSenta: Machine Learning for FilamentS Identification and Orientation in the ISM(IEEE Access, 2022-07-22) Alina, Dana; Shomanov, Adai; Baimukhametova, SarahFilament 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...Item Open Access EFFECTS OF GRAVITATIONAL LENSING ON NEUTRINO OSCILLATION IN Γ-SPACETIME(The European Physical Journal C, 2022) Chakrabarty, Hrishikesh; Borah, Debasish; Abdujabbarov, Ahmadjon; Malafarina, Daniele; Ahmedov, BobomuratWe 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.Item Open Access CGHS BLACK HOLE ANALOG MOVING MIRROR AND ITS RELATIVISTIC QUANTUM INFORMATION AS RADIATION REACTION(Entropy, 2021) Myrzakul, Aizhan; Xiong, Chi; Good, Michael R RThe Callan-Giddings-Harvey-Strominger black hole has a spectrum and temperature that correspond to an accelerated reflecting boundary condition in flat spacetime. The beta coefficients are identical to a moving mirror model, where the acceleration is exponential in laboratory time. The center of the black hole is modeled by the perfectly reflecting regularity condition that red-shifts the field modes, which is the source of the particle creation. In addition to computing the energy flux, we find the corresponding moving mirror parameter associated with the black hole mass and the cosmological constant in the gravitational analog system. Generalized to any mirror trajectory, we derive the self-force (Lorentz-Abraham-Dirac), consistently, expressing it and the Larmor power in connection with entanglement entropy, inviting an interpretation of acceleration radiation in terms of information flow. The mirror self-force and radiative power are applied to the particular CGHS black hole analog moving mirror, which reveals the physics of information at the horizon during asymptotic approach to thermal equilibrium.Item Open Access OPTICAL RADIATION FROM THE SPUTTERED SPECIES UNDER EXCITATION OF TERNARY MIXTURES OF NOBLE GASES BY THE 6LI(N,Α)3H NUCLEAR REACTION PRODUCTS(EURASIAN CHEMICO-TECHNOLOGICAL JOURNAL, 2021-08-30) Samarkhanov, K.; Khasenov, M.; Batyrbekov, E.; Gordienko, Yu.; Baklanova, Yu.; Kenzhina, I.; Tulubayev, Ye.; Karambayeva, I.The present paper examines the luminescence of ternary Ar-Kr-Xe and Ne-Ar-Kr mixtures of noble gases in the spectral range from 300 to 970 nm, excited by the 6Li(n,α)3H nuclear reaction products in the core of a nuclear reactor. A thin layer of lithium applied on the walls of the experimental device, stabilized in the matrix of the capillary-porous structure, serves as a source of gas excitation. During in-pile tests, conducted at the IVG.1M research reactor, thermal neutrons interact via the 6Li(n,α)3H reaction, and the emergent alpha particles with a kinetic energy of 2.05 MeV and tritium ions with a kinetic energy of 2.73 MeV excite gaseous medium. The study was carried out in a wide temperature range. The temperature dependence of the intensity of the emission of the atoms of noble gases and alkali metals, heteronuclear ionic molecules of noble gases were studied. The obtained values of the activation energy of the emission process 1.58 eV for lithium and 0.72 eV for potassium agree well with the known values of evaporation energy. Excitation of alkali metals atoms occurs consequently of the Penning process of alkali metals atoms on noble gas atoms in the 1s-states and further ion-molecular reactions.Item Open Access LARGE-SCALE MAGNETIC FIELD IN THE MONOCEROS OB-1 EAST MOLECULAR CLOUD(Astronomy & Astrophysics manuscript, 2021) Alina, D.; Montillaud, J.; Hu, Y.; Lazarian, A.; Ristorcelli, I.; Abdikamalov, E.; Sagynbayeva, S.; Juvela, M.; Liu, T.; Carrière, J.-S.Context. The role of large-scale magnetic fields in the evolution of star forming regions remains elusive. Its understanding requires observational characterisation of well-constrained molecular clouds. The Monoceros OB1 molecular cloud is a large complex con taining several structures which were shown to be in an active interaction and to have a rich star formation history. However, magnetic fields in this region have only been studied on small scales. Aims. We study the large-scale magnetic field structure and its interplay with the gas dynamics in the Monoceros OB1 East molecular cloud. Methods. We combine observations of dust polarised emission from the Planck telescope and CO molecular line emission observa tions from the Taeduk Radio Astronomy Observatory 14-metre telescope. We calculate the strength of the plane-of-the-sky magnetic field using a modified Chandrasekhar-Fermi method and estimate mass over flux ratios in different regions of the cloud. We use the comparison of the velocity and intensity gradients of the molecular line observations with the polarimetric observations to trace dynamically active regions. Results. The molecular complex shows an ordered large-scale plane-of-the-sky magnetic field structure. In the Northern part, it is mostly orientated along the filamentary structures while the Southern part shows at least two regions with distinct magnetic field orientations. Our analysis reveals a shock region in the Northern part right in-between two filamentary clouds which were previously suggested to be in collision. The magnetic properties of the North-Main and North-Eastern filaments suggest that these filaments once formed one, and the magnetic field evolved together with the material and did not undergo major changes during the evolution of the cloud. In the Southern part, we find that either the magnetic field guides the accretion of interstellar matter towards the cloud or it is dragged by the matter falling towards the main cloud. Conclusions. The large-scale magnetic field in Monoceros OB-1 East molecular cloud is tightly connected to the global structure of the complex. In the Northern part, it seems to have a dynamically important role by possibly providing support against gravity in the direction perpendicular to the field and to the filament. In the Southern part, it is probably the most influencing factor which governs the morphological structure, guiding possible gas inflow. A study of the whole Monoceros OB-1 molecular complex at large scales is necessary in order to form a global picture of the formation and evolution of the Monoceros OB1 East cloud and the role of the magnetic field in this process.Item Open Access ACCRETION DISK LUMINOSITY FOR BLACK HOLES SURROUNDED BY DARK MATTER WITH ANISOTROPIC PRESSURE(The Astrophysical Journal, 2021) Boshkayev, Kuantay; Giamb`o, Roberto; Konysbayev, Talgar; Kurmanov, Ergali; Luongo, Orlando; Malafarina, Daniele; Quevedo, HernandoWe investigate the luminosity of the accretion disk for a static black hole surrounded by dark matter with anisotropic pressure. We calculate all basic orbital parameters of test particles in the accretion disk, such as angular velocity, angular momentum, energy and radius of the innermost circular stable orbit as functions of the dark matter density, radial pressure and anisotropic param eter, which establishes the relationship between the radial and tangential pressures. We show that the presence of dark matter with anisotropic pressure makes a noticeable difference in the geometry around a Schwarzschild black hole, affecting the radiative flux, differential luminosity and spectral luminosity of the accretion disk.Item Open Access SURFACE-ENHANCED RAMAN SCATTERING FROM DYE MOLECULES IN SILICON NANOWIRE STRUCTURES DECORATED BY GOLD NANOPARTICLES(International Journal of Molecular Sciences, 2022-02-26) Ikramova, Saltanat B.; Utegulov, Zhandos N.; Dikhanbayev, Kadyrjan K.; Gaipov, Abduzhappar E.; Nemkayeva, Renata R.; Yakunin, Valery G.; Savinov, Vladimir P.; Timoshenko, Victor YuSilicon nanowires (SiNWs) prepared by metal-assisted chemical etching of crystalline silicon wafers followed by deposition of plasmonic gold (Au) nanoparticles (NPs) were explored as templates for surface-enhanced Raman scattering (SERS) from probe molecules of Methylene blue and Rhodamine B. The filling factor by pores (porosity) of SiNW arrays was found to control the SERS efficiency, and the maximal enhancement was observed for the samples with porosity of 55%, which corresponded to dense arrays of SiNWs. The obtained results are discussed in terms of the electromagnetic enhancement of SERS related to the localized surface plasmon resonances in Au-NPs on SiNW’s surfaces accompanied with light scattering in the SiNW arrays. The observed SERS effect combined with the high stability of Au-NPs, scalability, and relatively simple preparation method are promising for the application of SiNW:Au-NP hybrid nanostructures as templates in molecular sensorics.Item Open Access QUANTUM POWER: A LORENTZ INVARIANT APPROACH TO HAWKING RADIATION(arxiv, 2021) Good, Michael R.R.; Linder, Eric V.The Equivalence Principle teaches us that gravitation, acceleration, and curvature are equivalent. Moreover we know that external effects on quantum fields creates par ticles, and this ties together black hole particle produc tion, thermal baths observed by accelerating observers, and moving mirror acceleration radiation, e.g. the Hawk ing [1], Unruh [2], and Davies-Fulling [3] effects. How ever, we also know that constant acceleration is insuf ficient: an electron sitting on a laboratory table in an eternal constant gravitational field of the Earth will not radiate. In the same way, an eternally exactly uniformly accelerating accelerated boundary (moving mirror) will not emit energy to an observer at infinity, e.g. [4]. Another aspect of great interest [5] is that asymptot ically static mirrors preserve unitarity and information [6]. We explore a model that merges these two regimes of uniform acceleration and zero acceleration and show that this system can radiate particles for an extended time with constant power. The system will not only pre serve information but emit thermal energy, conserve total radiated energy, and emit finite total particles, without infrared divergence. This model can serve as an analog for complete black hole evaporation.Item Open Access DEPTH-RESOLVED THERMAL CONDUCTIVITY AND DAMAGE IN SWIFT HEAVY ION IRRADIATED METAL OXIDES(Journal of Nuclear Materials, 2022) Abdullaev, Azat; Koshkinbayeva, Ainur; Chauhan, Vinay; Nurekeyev, Zhangatay; O’Connell, Jacques; van Vuuren, Arno Janse; Skuratov, Vladimir; Khafizov, Marat; Utegulov, Zhandos N.We investigated thermal transport in swift heavy ion (SHI) irradiated insulating single crystalline oxide materials: yttrium aluminum garnet- Y3Al5O12 (YAG), sapphire (Al2O3), zinc oxide (ZnO) and magnesium oxide (MgO) irradiated by 167 MeV Xe ions at 1012 – 1014 ions/cm2 fluences. Depth profiling of the ther mal transport on nano- and micro- meter scales was assessed by time-domain thermoreflectance (TDTR) and modulated thermoreflectance (MTR) methods, respectively. This combination allowed us to isolate the conductivities of different sub-surface damage-regions characterized by their distinct microstructure evolution regimes. Thermal conductivity degradation in SHI irradiated YAG and Al2O3 is attributed to for mation of ion tracks and subsequent amorphization, while in ZnO and MgO it is mostly due to point defects. Additionally, notably lower conductivity when probed by very low penetrating thermal waves is consistent with surface hillock formation. An analytical model based on Klemens-Callaway method for thermal conductivity coupled with a simplified microstructure evolution capturing saturation in defect concentration was used to obtain depth dependent damage across the ion impacted region. The studies showed that YAG has the highest damage profile resulting in the less dependence of thermal conductivity with the depth, while MgO on the contrary has the strongest dependence. The presented work sheds new light on how SHI induced defects affect thermal transport degradation and recovery of oxide ceramics as promising candidates for next generation nuclear reactor applications.