Browsing by Author "Zakhidov, Anvar A."
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Item A Few-Minute Synthesis of CsPbBr₃ Nanolasers with a High Quality Factor by Spraying at Ambient Conditions(Amer Chemical Soc, 2018-12-12) Pushkarev, Anatoly P.; Korolev, Viacheslav, I.; Markina, Daria, I.; Komissarenko, Filipp E.; Naujokaitis, Arnas; Drabavicius, Audrius; Pakstas, Vidas; Franckevicius, Marius; Khubezhov, Soslan A.; Sannikov, Denis A.; Zasedatelev, Anton, V.; Lagoudakis, Pavlos G.; Zakhidov, Anvar A.; Makarov, Sergey, V.; 0000-0003-3983-2229 (Zakhidov, AA); Zakhidov, Anvar A.Inorganic cesium lead halide perovskite nanowires, generating laser emission in the broad spectral range at room temperature and low threshold, have become powerful tools for the cutting-edge applications in the optoelectronics and nanophotonics. However, to achieve high-quality nanowires with the outstanding optical properties, it was necessary to employ long-lasting and costly methods of their synthesis, as well as postsynthetic separation and transfer procedures that are not convenient for large-scale production. Here we report a novel approach to fabricate high quality CsPbBr₃ nanolasers obtained by rapid precipitation from dimethyl sulfoxide solution sprayed onto hydrophobic substrates at ambient conditions. The synthesis technique allows producing the well-separated nanowires with a broad size distribution of 2-50 μm in 5-7 min, being the fastest method to the best of our knowledge. The formation of nanowires occurs via ligand-assisted reprecipitation triggered by intermolecular proton transfer from (CH₃)₂CHOH to H₂O in the presence of a minor amount of water. The XRD patterns confirm an orthorhombic crystal structure of the as-grown CsPbBr₃ single nanowires. Scanning electron microscopy images reveal their regular shape and truncated pyramidal end facets, while high-resolution transmission electron microscopy ones demonstrate their single-crystal structure. The lifetime of excitonic emission of the nanowires is found to be 7 ns, when the samples are excited with energy below the lasing threshold, manifesting the low concentration of defect states. The measured nanolasers of different lengths exhibit pronounced stimulated emission above 13 μJ cm⁻² excitation threshold with quality factor Q = 1017-6166. Their high performance is assumed to be related to their monocrystalline structure, low concentration of defect states, and improved end facet reflectivity.Item Beyond Quantum Confinement: Excitonic Nonlocality in Halide Perovskite Nanoparticles with Mie Resonances(Royal Society of Chemistry) Berestennikov, A. S.; Li, Y.; Iorsh, I. V.; Zakhidov, Anvar A.; Rogach, A. L.; Makarov, S. V.; Zakhidov, Anvar A.Halide perovskite nanoparticles have demonstrated pronounced quantum confinement properties for nanometer-scale sizes and strong Mie resonances for 10 2 nm sizes. Here we studied the intermediate sizes where the nonlocal response of the exciton affects the spectral properties of Mie modes. The mechanism of this effect is associated with the fact that excitons in nanoparticles have an additional kinetic energy that is proportional to k 2 , where k is the wavenumber. Therefore, they possess higher energy than in the case of static excitons. The obtained experimental and theoretical results for MAPbBr 3 nanoparticles of various sizes (2-200 nm) show that for particle radii comparable with the Bohr radius of the exciton (a few nanometers in perovskites), the blue-shift of the photoluminescence, scattering, and absorption cross-section peaks related to quantum confinement should be dominating due to the weakness of Mie resonances for such small sizes. On the other hand, for larger sizes (more than 50-100 nm), the influence of Mie modes increases, and the blue shift remains despite the fact that the effect of quantum confinement becomes much weaker. ©2019 The Royal Society of Chemistry.Item Differential Ion Motion in Perovskite Light Emitting Electrochemical Cells(2022-05-01T05:00:00.000Z) Mishra, Aditya; Slinker, Jason D; Moheimani, Reza; Hsu, Julia W.P.; Young, Chadwin D.; Zakhidov, Anvar A.Perovskite light emitting diodes (PeLED) have shown promising progress as next-generation efficient electroluminescent devices. However, PeLEDs suffer from low lifetimes and color instability during operation that limits its insertion into most practical applications. To address this concern, I investigated a form of perovskite light-emitting device termed perovskite light-emitting electrochemical cells (PeLECs) that utilize a phenomenon of selective differential ion motion in perovskite devices. I have been exploring an interesting phenomenon of “differential ion motion” in PeLECs, where under applied bias, additive ions (LiPF6) selectively move while restricting the motion of intrinsic perovskite ions. This interplay of intrinsic and additive ions enhances the efficiency and operational stability of PeLECs. In differential ion motion, the perovskite structure remains stable while sacrificial additive ions move in response to the applied electric field. These additive ions accumulate at respective electrodes (anions at anode and cations at the cathode) and improve electronic charge injection (electron and holes) by the formation of electrical double layers (EDLs) at the electrode interfaces. Specifically, I fabricated and characterized PeLECs, directly measuring their luminance-currentvoltage characteristics, quantum efficiency, power efficiency, electroluminescence (EL) spectra, operational stability. To understand the fundamental materials science behind device performance, I have performed numerous materials and device characterizations such as electron microscopy (SEM, TEM), spectroscopy (XPS, UV-Vis), crystallography (XRD), force microscopy (AFM), reliability testing, electrochemical circuit design, and photoluminescence (PL) spectra, lifetime, and quantum yield. We demonstrated that optimized Li salt additive improves thin film morphology, increases PL stability and quantum yield, reduces charge traps, and strengthens the perovskite chemical bonding. Then, we hypothesized differential ion motion phenomenon and showed long lifetimes at constant current, calculated EDLs thickness by using electrochemical impedance circuit model. We also demonstrated voltage-controlled color-tunable perovskite host-ionic guest (Ir-ionic transition metal complex) LECs. We observed the benefits of differential ion motion in pure blue light-emitting mixed-halide perovskite, where we effectively suppressed detrimental halide segregation under intense photoexcitation and electrical bias that facilitated us to obtain longawaited stable blue PeLECs satisfying technological emission standards. Additionally, we integrated highly emissive zero-dimensional perovskite into a 3D perovskite matrix through a novel solvent engineering method that demonstrated high quantum efficiency and operational stability facilitated by differential ion motion. PeLECs have shown superior operational stability (initial luminance level of 3200 cd/m2, 120 h— extrapolates to 30,000 h half-life at 100 cd/m2, the common industrial benchmark for a lifetime) and high color-purity (Full-width half maximum of EL spectra ≤ 18 nm). Pure Blue emission from PeLECs meets all the National Television System Committee (NTSC) requirements. These PeLECs are simple single-layer devices that offer ease of processing (low-temperature and costeffective) for facile fabrication of large-area display and lighting applications. Leveraging differential ion motion in PeLECs demonstrates a new pathway of utilizing simple and smart, wearable devices for the internet of things (IoT) for digital communication and fashion.Item Effects of Nanostructure Geometry on Nanoimprinted Polymer Photovoltaics(RSC Pub, 2014-04-23) Yang, Yi; Mielczarek, Kamil; Aryal, Mukti; Zakhidov, Anvar A.; Hu, Wenchuang (Walter); 0000 0003 5287 0481 (Zakhidov, AA); 2005061514 (Hu, W); Zakhidov, Anvar A.; Hu, Wenchuang (Walter)We demonstrate the effects of nanostructure geometry on the nanoimprint induced poly(3-hexylthiophene-2,5-diyl) (P3HT) chain alignment and the performance of nanoimprinted photovoltaic devices. Out-of-plane and in-plane grazing incident X-ray diffraction techniques are employed to characterize the nanoimprint induced chain alignment in P3HT nanogratings with different widths, spacings and heights. We observe the dependence of the crystallite orientation on nanostructure geometry such that a larger width of P3HT nanogratings leads to more edge-on chain alignment while the increase in height gives more vertical alignment. Consequently, P3HT/6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) solar cells with the highest density and aspect ratio P3HT nanostructures show the highest power conversion efficiency among others, which is attributed to the efficient charge separation, transport and light absorption.Item Electrochemically Gated Organic Photovoltaic with Tunable Carbon Nanotube Cathodes(2013-10-18) Cook, Alexander B.; Yuen, Jonathan D.; Zakhidov, Anvar A.; 0000 0003 5287 0481 (Zakhidov, AA); Zakhidov, Anvar A.We demonstrate an organic photovoltaic (OPV) device with an electrochemically gated carbon nanotube (CNT) charge collector. Bias voltages applied to the gate electrode reconfigure the common CNT electrode from an anode into a cathode which effectively collects photogenerated electrons, dramatically increasing all solar cell parameters to achieve a power conversion efficiency of ∼3%. This device requires very little current to initially charge and the leakage current is negligible compared to the photocurrent. This device can also be viewed as a hybrid tandem OPV-supercapacitor with a common CNT electrode. Other regimes of operation are briefly discussed.Item Extended-gate MOSFET for High Sensitivity Photodetectors and pH Sensors(2021-12-01T06:00:00.000Z) Liu, Jinbo; Young, Chadwin D.; Hu, Walter; Anderson, William; Frensley, William R.; Zakhidov, Anvar A.; Gu, QingOver the past years, semiconductors have been greatly used in sensors. With the development semiconductor technology, the semiconductor sensors showed high sensitivity, large integration and reliable stability. Ion-Sensitive Field Effect Transistor (ISFET) changed the gate electrode of Metal-oxide-semiconductor Field Effect Transistor (MOSFET) from metals to electrolyte. In this dissertation, the perovskite, which is a kind of material with large light absorption coefficient, is used to replace the electrolyte in ISFET based on the structure of ISFET to create high sensitivity photodetector. The perovskite is deposited on a silicon wafer and physically separated with MOSFET. Besides taking both advantages of perovskite with excellent optoelectrical property and silicon as a single crystal with good electrical property to get high responsivity, this extended-gate structure provides convenience for changing the capacitance of perovskite and removing the influence of light on MOSFET. The frequency of electrical signal on perovskite can modulate the capacitance of perovskite, which can be used when the capacitance of perovskite is too high compared with MOSFET. The ionic movement influence, which degrees the performance of this photodetector, can be reduced by adding another MOSFET served as current source at the gate of original MOSFET. Inspired by the ionic movement of perovskite, this dissertation also proves ionic movement in pH electrolyte deteriorates the sensitivity of ISFET by electrical measurement. The extended gate structure is utilized to separate the MOSFET and pH capacitance so the MOSFET is free from changing of temperature. Low temperature can decrease the mobility of ions in pH electrolyte especially after the phase change from liquid to solid. The ions in electrolyte can’t follow the high frequency bias voltage so the ionic movement is less at high frequency. Our results show that the ISFETs have larger sensitivity in low temperature and high frequency since the ionic movement can be suppressed by low temperature and high frequency.Item Halide-Perovskite Resonant Nanophotonics(Wiley-vch Verlag) Makarov, S.; Furasova, A.; Tiguntseva, E.; Hemmetter, A.; Berestennikov, A.; Pushkarev, A.; Zakhidov, Anvar A.; Kivshar, Y.; 0000 0003 5287 0481 (Zakhidov, AA); 0000-0003-3983-2229 (Zakhidov, AA); Zakhidov, Anvar A.Halide perovskites have emerged recently as promising materials for many applications in photovoltaics and optoelectronics. Recent studies of optical properties of halide perovskites suggest many novel opportunities for a design of advanced nanophotonic devices due to their low-cost fabrication, relatively high values of the refractive index, existence of excitons at room temperatures, broadband bandgap tunability, high optical gain, and strong nonlinear response, as well as simplicity of their integration with other types of optical and electronic structures. This paper provides an overview of the recent progress in the study of optical effects originating from nanostructured perovskites, and it also oversees a range of potential applications of resonant nanophotonics with halide perovskites.Item Investigation Into Higher Dimensional Rotations(2022-12-01T06:00:00.000Z) Bal, Sabindra Singh 1981-; Zakhidov, Anvar A.; Ramakrishna, Viswanath; Cao, Yan; Dabkowski, Mieczyslaw K.; Choudhary, Pankaj K.Axis-angle representations provides efficient methods to study three dimensional rotations. The representation imparts visualization and thus aids the analysis of a three-dimensional proper rotation by reducing its study to that of a two dimensional one. In this dissertation, we accomplish a similar result for five dimensional proper rotation by reducing its study to that of either two or four dimensional proper rotations. For a matrix in SO(5, R), we complete a closed from formula for the axis which is the fixed point set of the matrix as well as the formula for the angle which is the complementary proper rotation that the matrix performs in the orthogonal complement to the axis. In fact, two such derivations are provided. The first is based on the properties of a matrix in SO(5, R) such as the special structure of its characteristic polynomial being skew palindromic while the second utilizes the structure of the Lie algebra of the covering group. Closed form formula for the logarithm in the covering group of SO(5, R) is also derived as it is essential for the second method. Further, we study indefinite rotations with signature (1,9) and come close to establish that the group of such rotations is isomorphic to 2x2 octonion matrices with determinant 1.Item Lambertian White Top-Emitting Organic Light Emitting Device with Carbon Nanotube Cathode(2012-12-04) Freitag, P.; Zakhidov, Al A.; Luessem, B.; Zakhidov, Anvar A.; Leo, K.; 0000 0003 5287 0481 (Zakhidov, AA); Zakhidov, Anvar A.We demonstrate that white organic light emitting devices (OLEDs) with top carbon nanotube (CNT) electrodes show almost no microcavity effect and exhibit essentially Lambertian emission. CNT top electrodes were applied by direct lamination of multiwall CNT sheets onto white small molecule OLED stack. The devices show an external quantum efficiency of 1.5% and high color rendering index of 70. Due to elimination of the cavity effect, the devices show good color stability for different viewing angles. Thus, CNT electrodes are a viable alternative to thin semitransparent metallic films, where the strong cavity effect causes spectral shift and non-Lambertian angular dependence. Our method of the device fabrication is simple yet effective and compatible with virtually any small molecule organic semiconductor stack. It is also compatible with flexible substrates and roll-to-roll fabrication.Item Laser Post-Processing of Halide Perovskites for Enhanced Photoluminescence and Absorbance(IOP Publishing Ltd, 2018-11-05) Tiguntseva, E. Y.; Saraeva, I. N.; Kudryashov, S. I.; Ushakova, E. V.; Komissarenko, F. E.; Ishteev, A. R.; Tsypkin, A. N.; Haroldson, Ross; Milichko, V. A.; Zuev, D. A.; Makarov, S. V.; Zakhidov, Anvar A.; 0000 0003 5287 0481 (Zakhidov, AA); 0000-0003-3983-2229 (Zakhidov, AA); Haroldson, Ross; Zakhidov, Anvar A.Hybrid halide perovskites have emerged as one of the most promising type of materials for thin-film photovoltaic and light-emitting devices. Further boosting their performance is critically important for commercialization. Here we use femtosecond laser for post-processing of organo-metalic perovskite (MAPbI3) films. The high throughput laser approaches include both ablative silicon nanoparticles integration and laser-induced annealing. By using these techniques, we achieve strong enhancement of photoluminescence as well as useful light absorption. As a result, we observed experimentally 10-fold enhancement of absorbance in a perovskite layer with the silicon nanoparticles. Direct laser annealing allows for increasing of photoluminescence over 130%, and increase absorbance over 300% in near-IR range. We believe that the developed approaches pave the way to novel scalable and highly effective designs of perovskite based devices.Item Microwave Conductance of Aligned Multiwall Carbon Nanotube Textile Sheets(2014-12-30) Brown, Brian L.; Bykova, Julia S.; Howard, Austin R.; Zakhidov, Anvar A.; Shaner, Eric A.; Lee, Mark; Brown, Brian L.; Bykova, Julia S.; Howard, Austin R.; Zakhidov, Anvar A.; Lee, MarkMultiwall carbon nanotube (MWNT) sheets are a class of nanomaterial-based multifunctional textile with potentially useful microwave properties. To understand better the microwave electrodynamics, complex AC conductance measurements from 0.01 to 50 GHz were made on sheets of highly aligned MWNTs with the alignment texture both parallel and perpendicular to the microwave electric field polarization. In both orientations, the AC conductance is modeled to first order by a parallel frequency-independent conductance and capacitance with no inductive contribution. This is consistent with low-frequency diffusive Drude AC conduction up to 50 GHz, in contrast to the "universal disorder" AC conduction reported in many types of single-wall nanotube materials.Item Molecular Beam Epitaxy of La2-xSrxCuO4 Films and Heterostructures(2022-08-01T05:00:00.000Z) Xu, Xiaotao; Shi, Xiaoyan; Morcos, Faruck; Lv, Bing; Lumata, Lloyd; Zakhidov, Anvar A.; Zhang, FanSince 1986, the study of high-temperature superconductivity (HTS) in cuprates has revealed a massive amount of discoveries, such as pseudogap, charge density wave, d-wave superconductivity, etc. These novel states of matter trigger even more unknowns in fundamental science and inspire enormous emergent applications. This dissertation presents our research on the archetypical La2-xSrxCuO4 (LSCO) thin films and heterostructures. Specifically, the research has been driven by several fundamental questions. For example, can we create c-axis Josephson junctions for scientific research and superconductor-based quantum computation? What controls the fundamental behaviors of interface superconductivity? To answer those questions, high-quality crystals are required. Here we utilized and improved the oxide atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) technique to grow atomically smooth cuprate films and heterostructures to answer the proposed research questions. The main results are presented as follows. First, we improved the ALL-MBE growth in several ways to enhance the film quality significantly. Specifically, we studied the thermal annealing of oxide substrates and developed treatment methods for LaSrAlO4(LSAO) and SrTiO3(STO) substrates. Ramp-up rate and annealing temperature are found to be the most critical parameters. We then studied the synthesis of LSCO thin films via the ALL-MBE system. A detailed recipe for the growth of LSCO thin films on LSAO substrates is presented. Unique reflection high energy electron diffraction (RHEED) pattern features are observed in LSCO films. A strategy to monitor the film growth and maintain the correct stoichiometry is developed based on the real-time RHEED feedback. We also investigated the power and stability of ozone oxidation and compiled empirical post-annealing procedures suitable for various doping levels. Substrates and LSCO films were evaluated using atomic force microscopy (AFM) and RHEED. The results indicate that they are atomically perfect with high crystallinity. Mutual inductance (MI) tests reveal that the LSCO films are uniform over the whole sample area with a sharp superconducting transition. Second, LSCO heterostructures and superlattices have been synthesized to study the HTS c-axis Josephson junction and interfacial superconductivity. The method to probe the superconducting dead layer number near the interface is introduced using a series of superlattices. At the LSCO-LSAO interface, MI and transport measurements imply that the first two LSCO layers that are near the LSAO exhibit a substantial suppression of superconductivity, resulting in a barrier that is five layers thick in total. And an overdoped LSCO protective layer is found to be effective against carrier depletion in superconducting layers. Within LSAO barriers, a thickness of 2 unit-cells of LSCO interface superconductor is synthesized. The superconducting transition of the sample is tunable with doping and demonstrates the highest transition temperature of 34 K.Item Multifunctional Carbon Nanotube Yarns for Artificial Muscles and Energy Harvesters(2021-08-01T05:00:00.000Z) Wang, Zhong; Baughman, Ray H.; Da Silveira Rodrigues, Fabiano; Zakhidov, Anvar A.; Ferrairs, John P.; Pantano, PaulThe superb mechanical, physical, and chemical properties of carbon nanotube (CNT) yarns have promoted their application as function components that program actuation, sensing, and power management for soft robotics and smart systems. Success in making artificial muscles that are faster, more powerful, and that can provide larger strokes would expand their applications. Efficient conversion of ambient mechanical energy into electrical energy is needed for diverse applications, including self-powered wireless sensors, structural and human health monitoring systems, and the extraction of energy from ocean waves. Herein, the development of CNT yarn artificial muscles and mechanical energy harvesters are first discussed, and the obtained understanding of underlying mechanisms provide guidance for optimizing muscle and harvester performances. Next, unipolar stroke CNT yarn muscles are described, in which muscle stroke changes between extreme potentials are additive and muscle stroke remarkably increases with increasing potential scan rate. The normal decrease in stroke with increasing scan rate, because of decreased capacitance, is overwhelmed by a dramatic increase in effective ion size caused by electroosmotic pumping of solvent. These coiled carbon nanotube yarn muscles contain a yarn guest that shifts the yarn’s potential of zero charge (pzc) by over a volt, either positively or negatively. Such pzc shift agents include ion-exchange membrane polymers, oxidized graphene platelets, and surfactants. Record muscle strokes, contractile work-per-cycle, contractile power densities, and energy conversion efficiencies are obtained for unipolar muscles. Then, powerful CNT yarn mechanical energy harvesters (we call twistrons) are described, which are electrochemical artificial muscles run in reverse. Stretching a coiled CNT yarn can provide large, reversible changes in electrochemical capacitance, which enables conversion of mechanical energy to electrical energy. The performance of these twistron harvesters can be increased by diverse fabrication methods: optimizing the structure of the precursor CNT forest, using stretchinduced alignment, thermal annealing under tension, and incorporating reduced graphene oxide nanoplates. The peak output power at 1 Hz and at 30 Hz for a sinusoidal stretch were 0.73 and 3.19 kW/kg, which are 15- and 13-fold higher than for previous twistron harvesters at these respective frequencies. This performance at 30 Hz was over 12-fold that of other prior-art mechanical energy harvesters for frequencies between 1 Hz and 600 Hz. Last, the opportunities and challenges for future practical applications of CNT yarns are highlighted.Item Nanoimprinted Perovskite Metasurface for Enhanced Photoluminescence(Optical Soc Amer, 2018-11-05) Wang, Honglei; Liu, Shih-Chia; Balachandran, Balasubramaniam; Moon, Jiyoung; Haroldson, Ross; Li, Zhitong; Ishteev, Artur; Gu, Qing; Zhou, Weidong; Zakhidov, Anvar A.; Hu, Wenchuang (Walter); 0000 0003 5287 0481 (Zakhidov, AA); 0000-0003-3983-2229 (Zakhidov, AA); Wang, Honglei; Balachandran, Balasubramaniam; Moon, Jiyoung; Haroldson, Ross; Li, Zhitong; Gu, Qing; Zakhidov, Anvar A.; Hu, Wenchuang (Walter)Recently, solution-processed hybrid halide perovskite has emerged as promising materials for advanced optoelectronic devices such as photovoltaics, photodetectors, light emitting diodes and lasers. In the mean time, all-dielectric metasurfaces with high-index materials have attracted attention due to their low-loss and high-efficient optical resonances. Because of its tunable by composition band gap in the visible frequencies, organolead halide perovskite could serve as a powerful platform for realizing high-index, low-loss metasurfaces. However, direct patterning of perovskite by lithography-based technique is not feasible due to material instability under moisture. Here we report novel organolead halide perovskite metasurfaces created by the cost-effective thermal nanoimprint technology. The nanoimprinted perovskite metasurface showed improved surface morphology and enhanced optical absorption properties. Significantly enhanced optical emission with an eight-fold enhancement in photoluminescence (PL) intensity was observed under room temperature. Temperature-dependent PL of perovskite nanograting metasurface was also investigated. Based on our results, we believe that thermal nanoimprint is a simple and cost-effective technique to fabricate perovskite-based metasurfaces, which could have broad impact on optoelectronic and photonic applications.Item Perovskite Nanophotonic Devices and Topological Photonic Devices(2021-05-01T05:00:00.000Z) Li, Zhitong; Gu, Qing; Minary, Majid; Zhang, Chuanwei; Lee, Jeong-Bong; Zakhidov, Anvar A.Solution processed organic-inorganic lead halide perovskites have rapidly emerged as a promising gain material for development of the next generation of nanophotonic device ranging from nanolasers, nano LEDs, and solar cells. Here, continuous-wave operation of MAPbI3 perovskite nanolaser is achieved at room temperature with ultralow threshold, which is enabled by thermal nanoimprint lithography that directly patterns perovskite into laser cavities and improves perovskite’s emission characteristics. In the meantime, hyperbolic metamaterials and metasurfaces (HMMs), a special class of anisotropic media, has drawn tremendous research attention recently owing to its remarkable ability to manipulate electromagnetic waves at the subwavelength scale. However, the inevitable metal loss hinders the development of HMMs. Here, a luminescent perovskite HMM operating at 760 nm is achieved using alternating layers of MAPbI3 perovskite and Au, where the loss in Au is maximally compensated by MAPbI3. Simultaneously, topological photonics is a rapidly emerging field, aiming to apply topological physics in photonic systems. The topological protected photonic edge mode is immune to the system disorders and imperfections. However, all photonic edge modes reported in the pioneering works are from lattice systems. Here, a topological band theory is developed in continuous HMM through a nonHermitian Hamiltonian formulated Maxwell’s equations. Two types of edge mode can be induced by including gyromagnetic and chiral effect in HMM and can be numerically observed. Finally, a topological micro ring laser array that possesses edge mode lasing is designed and experimentally achieved on the III-V semiconductor platform.Item Photoinduced Migration of Ions in Optically Resonant Perovskite Nanoparticles(Pleiades Publishing) Gets, D. S.; Tiguntseva, E. Y.; Berestennikov, A. S.; Lyashenko, T. G.; Pushkarev, A. P.; Makarov, S. V.; Zakhidov, Anvar A.; Zakhidov, Anvar A.Organic–inorganic perovskites with a mixed anion composition are widely used in solar cells, light-emitting diodes, and nanophotonic structures. Light nanosources based on resonant perovskite nanoparticles are of particular interest. However, perovskites with such a composition demonstrate the light-induced segregation of anions, which leads to a reversible dynamic rearrangement of the optical properties of a material and photoluminescence spectra. In this work, the photoinduced process of change in optical properties in resonant hybrid perovskite nanoparticles with a mixed anion composition (MAPbBr₁.₅I₁.₅, where MA = NH₃CH₃⁺) has been studied. Comparison with a similar process in a perovskite thin film with a similar composition has shown that the photoinduced migration of halogen ions in a nanoparticle occurs cyclically. This is due to the competition of two processes: the concentration of ions near the boundaries of the particle and migration caused by the gradient of the density of light-generated electron–hole pairs. This effect in resonant nanoparticles makes it possible to obtain optically tunable nanoantennas.Item Resonant Silicon Nanoparticles for Enhanced Light Harvesting in Halide Perovskite Solar Cells(Wiley-VCH Verlag) Furasova, A.; Calabró, E.; Lamanna, E.; Tiguntseva, E.; Ushakova, E.; Ubyivovk, E.; Mikhailovskii, V.; Zakhidov, Anvar A.; Makarov, S.; Di Carlo, A.; Zakhidov, Anvar A.Implementation of resonant nanoparticles (NPs) for improving performance of organometal halide perovskites solar cells is highly prospective approach, because it is compatible with the solution processing techniques used for any organic materials. Previously, resonant metallic NPs have been incorporated into perovskite solar cells for better light absorption and charge separation. However, high inherent optical losses and high reactivity of noble metals with halides in perovskites are main limiting factors for this approach. Incidentally, low-loss and chemically inert resonant silicon NPs allow for light trapping and enhancement at nanoscale, being suitable for thin film photovoltaics. Here photocurrent and fill-factor (FF) enhancements in meso-superstructured perovskite solar cells, incorporating resonant silicon NPs between mesoporous TiO₂ transport and active layers, are demonstrated. This results in a boost of device efficiency up to 18.8% and FF up to 79%, being a record among the previously reported values on NPs incorporation into CH₃NH₃PbI₃ perovskite-based solar cells. Theoretical modeling and optical characterization reveal the significant role of Si NPs for increased light absorption in the active layer rather than for better charge separation. The proposed strategy is universal and can be applied in perovskite solar cells with various compositions, as well as in other optoelectronic devices. ©2018 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Room Temperature Operation of Directly Patterned Perovskite Distributed Feedback Light Source under Continuous-Wave Optical Pumping(Institute of Electrical and Electronics Engineers Inc.) Gharajeh, Abouzar; Haroldson, Ross; Li, Zhitong; Moon, Jiyoung; Balachandran, Balasubramaniam; Hu, Wenchuang (Walter); Zakhidov, Anvar A.; Gu, Qing; 0000 0003 5287 0481 (Zakhidov, AA); 0000-0003-3983-2229 (Zakhidov, AA); 0000-0003-3855-3690 (Gu, Q); Gharajeh, Abouzar; Haroldson, Ross; Li, Zhitong; Moon, Jiyoung; Balachandran, Balasubramaniam; Hu, Wenchuang (Walter); Zakhidov, Anvar A.; Gu, QingWe report the first directly patterned perovskite distributed feedback (DFB) resonator with a narrow amplified spontaneous emission (ASE) at pump powers as low as 0.1W/cm², under continuous-wave (CW) optical pumping condition at room temperature.Item Stable Doping of Carbon Nanotubes via Molecular Self Assembly(2014-10-13) Lee, B.; Chen, Y.; Cook, Alex; Zakhidov, Anvar A.; Podzorov, V.; 0000 0003 5287 0481 (Zakhidov, AA); Zakhidov, Anvar A.We report a novel method for stable doping of carbon nanotubes (CNT) based on methods of molecular self assembly. A conformal growth of a self-assembled monolayer of fluoroalkyl tri-chloro-silane (FTS) at CNT surfaces results in a strong increase of the sheet conductivity of CNT electrodes by 60-300%, depending on the CNT chirality and composition. The charge carrier mobility of undoped partially aligned CNT films was independently estimated in a field-effect transistor geometry (~100 cm² V⁻¹ s⁻¹). The hole density induced by the FTS monolayer in CNT sheets is estimated to be similar to 1.8 x 10¹⁴ cm⁻². We also show that FTS doping of CNT anodes greatly improves the performance of organic solar cells. This large and stable doping effect, easily achieved in large area samples, makes this approach very attractive for applications of CNTs in transparent and flexible electronics.Item Superconductivity in an inhomogeneous bundle of metallic and semiconducting nanotubes(2013-09-06) Grigorenko, I.; Zakhidov, Anvar A.; 0000 0003 5287 0481 (Zakhidov, AA); Zakhidov, Anvar A.Using Bogoliubov-de Gennes formalism for inhomogeneous systems, we have studied superconducting properties of a bundle of packed carbon nanotubes, making a triangular lattice in the bundle's transverse cross-section. The bundle consists of a mixture of metallic and doped semiconducting nanotubes, which have different critical transition temperatures. We investigate how a spatially averaged superconducting order parameter and the critical transition temperature depend on the fraction of the doped semiconducting carbon nanotubes in the bundle. Our simulations suggest that the superconductivity in the bundle will be suppressed when the fraction of the doped semiconducting carbon nanotubes will be less than 0.5, which is the percolation threshold for a two-dimensional triangular lattice.