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Item Open Access 2D BI2SE3 VAN DER WAALS EPITAXY ON MICA FOR OPTOELECTRONICS APPLICATIONS(MDPI, 2020-08-22) Wang, Shifeng; Li, Yong; Ng, Annie; Hu, Qing; Zhou, Qianyu; Li, Xin; Liu, HaoBi2Se3 possesses a two-dimensional layered rhombohedral crystal structure, where the quintuple layers (QLs) are covalently bonded within the layers but weakly held together by van der Waals forces between the adjacent QLs. It is also pointed out that Bi2Se3 is a topological insulator, making it a promising candidate for a wide range of electronic and optoelectronic applications. In this study, we investigate the growth of high-quality Bi2Se3 thin films on mica by the molecular beam epitaxy technique. The films exhibited a layered structure and highly c-axis-preferred growth orientation with an XRD rocking curve full-width at half-maximum (FWHM) of 0.088◦ , clearly demonstrating excellent crystallinity for the Bi2Se3 deposited on the mica substrate. The growth mechanism was studied by using an interface model associated with the coincidence site lattice unit (CSLU) developed for van der Waals epitaxies. This high (001) texture favors electron transport in the material. Hall measurements revealed a mobility of 726 cm2 /(Vs) at room temperature and up to 1469 cm2 /(Vs) at 12 K. The results illustrate excellent electron mobility arising from the superior crystallinity of the films with significant implications for applications in conducting electrodes in optoelectronic devices on flexible substrates.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 ACCRETION DISK LUMINOSITY FOR BLACK HOLES SURROUNDED BY DARK MATTER WITH ANISOTROPIC PRESSURE(The Astrophysical Journal, 2022) Kurmanov, E.; Boshkayev, K.; Giambò, R.; Konysbayev, T.; Luongo, O.; Malafarina, D.; Quevedo, H.We investigate the luminosity of the accretion disk of 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 parameter, 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 ACOUSTIC WAVE GENERATION IN COLLAPSING MASSIVE STARS WITH CONVECTIVE SHELLS(Monthly Notices of the Royal Astronomical Society, 2020) Abdikamalov, Ernazar; Foglizzo, ThierryThe convection that takes place in the innermost shells of massive stars plays an important role in the formation of core-collapse supernova explosions. Upon encountering the supernova shock, additional turbulence is generated, amplifying the explosion. In this work, we study how the convective perturbations evolve during the stellar collapse. Our main aim is to establish their physical properties right before they reach the supernova shock. To this end, we solve the linearized hydrodynamics equations perturbed on a stationary background flow. The latter is approximated by the spherical transonic Bondi accretion, while the convective perturbations are modelled as a combination of entropy and vorticity waves. We follow their evolution from large radii, where convective shells are initially located, down to small radii, where they are expected to encounter the accretion shock above the proto-neutron star. Considering typical vorticity perturbations with a Mach number ∼0.1 and entropy perturbations with magnitude ∼0.05kb/baryon, we find that the advection of these perturbations down to the shock generates acoustic waves with a relative amplitude δp/γ p 10 per cent, in agreement with published numerical simulations. The velocity perturbations consist of contributions from acoustic and vorticity waves with values reaching ∼10 per cent of the sound speed ahead of the shock. The perturbation amplitudes decrease with increasing and initial radii of the convective shellsItem Open Access ANALYTICAL INVERSE DESIGN OF POLARIZATION-INSENSITIVE PHOTONIC FILTERS BY TAILORING FABRY-PEROT INTERFERENCE(Institute of Electrical and Electronics Engineers, 2020-07-28) Valagiannopoulos, ConstantinosFiltering of photonic signals of a certain frequency while suppressing all the others of a specific band for both electromagnetic signal polarizations, becomes possible with a single dielectric layer by properly engineering the occurred Fabry-Perot interference. Analytical formulas for combinations of cavity size, material texture and incoming angle are given so that the filtering purpose is optimally served. In this way, inverse design for a simple class of optical setups is rigorously performed and, if the employed medium is very dense and the working band narrow enough, sharp filters with increased frequency selectivity are obtained.Item Open Access ANOMALOUS DIFFRACTION OF MATTER WAVES WITH MINIMAL QUANTUM METASURFACES(EPJ Quantum Technol., 2021-02-06) Valagiannopoulos, ConstantinosIn the last few years, there is a huge upsurge in the number of closed deals regarding quantum technologies for materials, computing, communication and instrumentation. Such a trend has inevitably affected the research funding market; thus, large state initiatives are taken that are directly expected to drive the formulation of novel research concepts and the development of quantum device prototypes from sensors and circuitry to quantum memory and repeaters.....Item Open Access ANOMALOUS DIFFRACTION OF MATTER WAVES WITH MINIMAL QUANTUM METASURFACES(Springer Science and Business Media Deutschland GmbH, 2021-02-06) Valagiannopoulos, ConstantinosIn the last few years, there is a huge upsurge in the number of closed deals regarding quantum technologies for materials, computing, communication and instrumentation. Such a trend has inevitably affected the research funding market; thus, large state initiatives are taken that are directly expected to drive the formulation of novel research concepts and the development of quantum device prototypes from sensors and circuitry to quantum memory and repeaters. A fundamental operation behind all these applications is the effective steering of electrons, constituting matter waves, along specific directions and with certain magnitudes, due to development of various reflective and refractive orders. The objective of this study is to optimize the simplest structure that supports such anomalous diffraction, namely a quantum metasurface comprising cylindrical rods embedded in suitable crystalline matter. Several highly-performing designs from these minimal setups are proven to work exceptionally as multiport components, employable to a variety of quantum engineering implementations.Item Open Access ANOMALOUS REFRACTION INTO FREE SPACE WITH ALL-DIELECTRIC BINARY METAGRATINGS(PHYSICAL REVIEW RESEARCH, 2020-09-30) Tsitsas, Nikolaos L.; Valagiannopoulos, ConstantinosSteering the incoming photonic power toward unusual directions, not predicted by Snell’s laws of reflection and refraction, is a fundamental operation behind numerous wavefront engineering applications. In this study, strong anomalous transmission is reported to all-dielectric electrically thin structures comprising only two materials in alternating rectangular posts. These binary metagratings have been thoroughly optimized to support almost perfect negative refraction by suppressing all the rest of diffraction orders; such an effect is found to be very robust with respect to oscillation frequency, incident beam angle, and structural defects. In this way, easy-to-fabricate setups working at different colors of the visible spectrum are determined and may be directly incorporated in various optical integrated systems from lenses and beamformers to field enhancers and power splittersItem Open Access Antiresonances and Ultrafast Resonances in a Twin Photonic Oscillator(Institute of Electrical and Electronics Engineers, 2019-02) Kominis, Yannis; Choquette, Kent D.; Bountis, Anastassios; Kovanis, VassiliosWe consider the properties of the small-signal modulation response of symmetry-breaking phase-locked states of twin coupled semiconductor lasers. The extended stability and the varying asymmetry of these modes allows for the introduction of a rich set of interesting modulation response features, such as sharp resonances and antiresonances as well as efficient modulation at very high frequencies exceeding the free running relaxation frequencies by orders of magnitude.Item Open Access CDTE X/Γ-RAY DETECTORS WITH DIFFERENT CONTACT MATERIALS(MDPI AG, 2021-05-18) Gnatyuk, Volodymyr; Maslyanchuk, Olena; Solovan, Mykhailo; Brus, Viktor; Aoki, ToruDifferent contact materials and optimization of techniques of their depositions expand the possibilities to obtain high performance room temperature CdTe-based X/γ-ray detectors. The heterostructures with ohmic (MoOx) and Schottky (MoOx, TiOx, TiN, and In) contacts, created by DC reactive magnetron sputtering and vacuum thermal evaporation, as well as In/CdTe/Au diodes with a p-n junction, formed by laser-induced doping, have been developed and investigated. De-pending on the surface pre-treatment of semi-insulating p-CdTe crystals, the deposition of a MoOx film formed either ohmic or Schottky contacts. Based on the calculations and I-V characteristics of the Mo-MoOx/р-CdTe/MoOx-Mo, In/р-CdTe/MoOx-Mo, Ti-TiOx/р-CdTe/MoOx-Mo, and Ti-TiN/р-CdTe/MoOx-Mo Schottky-diode detectors, the current transport processes were described in the models of the carrier generation–recombination within the space-charge region (SCR) at low bias, and space-charge limited current incorporating the Poole–Frenkel effect at higher voltages, respectively. The energies of generation–recombination centers, density of trapping centers, and effective carrier lifetimes were determined. Nanosecond laser irradiation of the In electrode, pre-deposited on the p-CdTe crystals, resulted in extending the voltage range, corresponding to the carrier generation–recombination in the SCR in the I-V characteristics of the In/CdTe/Au diodes. Such In/CdTe/Au p-n junction diode detectors demonstrated high energy resolutions (7%@59.5 keV, 4%@122 keV, and 1.6%@662 keV).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 Conformal High-K Dielectric Coating of Suspended Single-Walled Carbon Nanotubes by Atomic Layer Deposition(MDPI, 2019-08) Kemelbay, Aidar; Tikhonov, Alexander; Aloni, Shaul; Kuykendall, Tevye R.As one of the highest mobility semiconductor materials, carbon nanotubes (CNTs) have been extensively studied for use in field effect transistors (FETs). To fabricate surround-gate FETs— which offer the best switching performance—deposition of conformal, weakly-interacting dielectric layers is necessary. This is challenging due to the chemically inert surface of CNTs and a lack of nucleation sites—especially for defect-free CNTs. As a result, a technique that enables integration of uniform high-k dielectrics, while preserving the CNT’s exceptional properties is required. In this work, we show a method that enables conformal atomic layer deposition (ALD) of high-k dielectrics on defect-free CNTs. By depositing a thin Ti metal film, followed by oxidation to TiO2 under ambient conditions, a nucleation layer is formed for subsequent ALD deposition of Al2O3. The technique is easy to implement and is VLSI-compatible. We show that the ALD coatings are uniform, continuous and conformal, and Raman spectroscopy reveals that the technique does not induce defects in the CNT. The resulting bilayer TiO2/Al2O3 thin-film shows an improved dielectric constant of 21.7 and an equivalent oxide thickness of 2.7 nm. The electrical properties of back-gated and top-gated devices fabricated using this method are presented.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 Data Acquisition System for Microwave Kinetic Inductance Detectors(IOP PUBLISHING LTD, 2019) Bekbalanova, Marzhan; Shafiee, Mehdi; Kizheppatt, Vipin; Kazykenov, Zhaksylyk; Alzhanov, Baurzhan; Smoot, George F.; Grossan, BruceEnergetic Cosmos Laboratory is developing Kinetic Inductance Detectors (MKID) for mm/submm astronomy purposes. In order to measure the instantaneous resonance frequency and dissipation of superconducting microresonators of the MKID arrays, we have developed a data acquisition system with emphasis on precision, readout speed and digital processing capabilities. We use IQ mixer to down convert the MKIDs signal in the range of 20-80 MHz, then digitize them by 250 MSPS ADC. Processed data at FPGA-Kintex 7 will be transferred to the PC for further analysis by the rate of 10 Gbit/sec. In this report, we describe the technical details and the algorithm we developed.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.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; Chauhanb, Vinay; Nurekeyev, Zhangatay; O’Connell, Jacques; Janse van Vuuren, Arno; 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 applicationsItem Open Access DESIGNING NANOINCLUSIONS FOR QUANTUM SENSING BASED ON ELECTROMAGNETIC SCATTERING FORMALISM(Progress In Electromagnetics Research, 2021) Valagiannopoulos, ConstantinosQuantum interactions between a single particle and nanoinclusions of spherical or cylindrical shape are optimized to produce scattering lineshapes of high selectivity with respect to impinging energies, excitation directions, and cavity sizes. The optimization uses a rigorous solution derived via electromagnetic scattering formalism while the adopted scheme rejects boundary extrema corresponding to resonances that occur outside of the permissible parametric domains. The reported effects may inspire experimental efforts towards designing quantum sensing systems employed in applications spanning from quantum switching and filtering to single-photon detection and quantum memory.Item Open Access DETECTING THE EVENT OF A SINGLE PHOTON LOSS ON QUANTUM SIGNALS(Journal of Physics B Atomic Molecular and Optical Physics, 2021-05) Mandilara, A.; Balkybek, Y.; Akulin, V. M.We design a scheme for detecting a single photon loss from multi-modal quantum signals transmitted via a fiber or in free space. This consists of a special type of unitary coding transformation, the parity controlled-squeezing, applied prior to the transmission on the signal composed by information and ancilla modes. At the receiver, the inverse unitary transformation is applied—decoding, and the ancilla mode is measured via photon detection. The outcome reveals whether a photon loss has occurred. Distortion of the information part of the signal caused by an ancilla photon loss can be corrected via unitary transformation while loss of a photon from the information part of the signal can be detected with the probability exponentially close to unity but cannot be corrected. In contrast to the schemes of decoherence free subspaces and quantum error correction protocols, this method allows one to make use in principle of entire Hilbert space dimensionality. We discuss possible ways of synthesizing the required encoding–decoding transformation.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 DISPERSION RELATIONS IN FINITE-BOOST DSR(Elsevier, 2020-10-10) Jafari, Nosratollah; Good, Michael R.R.We find finite-boost transformations DSR theories in first order of the Planck length , by solving differential equations for the modified generators. We obtain corresponding dispersion relations for these transformations, which help us classify the DSR theories via four types. The final type of our classification has the same special relativistic dispersion relation but the transformations are not Lorentz. In DSR theories, the velocity of photons is generally different from the ordinary speed c and possess time delay, however in this new DSR light has the same special relativistic speed with no delay. A special case demonstrates that any search for quantum gravity effects in observations which gives a special relativistic dispersion relation is consistent with DSR.