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Epitaxial ferroelectric oxide thin films for optical applications
摘要： Ferroelectrics are non-centrosymmetric crystalline materials that possess a spontaneous polarization that can be switched by an electric field. The electric-field-dependent optical response of these materials makes them important for optical devices, such as modulators or beam deflectors. In the inexorable drive to miniaturization, the concept of integrated thin film optical devices has led to the incorporation of ferroelectric thin films on single-crystal substrates. These structures have appealing electro-optic modulation characteristics, interesting strain-dependent bandgaps and refractive index, as well as promising possibilities for solar harvesting. Here, we review the work on epitaxial ferroelectric (FE) films for optical applications. We first show that FE thin film materials are attractive for integrated electro-optic modulators and then show that epitaxial strain can be used to enhance the FE and optical functionality of films. Next, we describe some of the photovoltaic functionality of FE thin film materials’ systems and conclude the review by highlighting some thin-film devices that exploit the aforementioned optical effects.
关键词： epitaxial strain,electro-optic modulators,thin films,photovoltaic,optical applications,ferroelectric
更新于2025-09-09 09:28:46
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Comparative study on structure and properties of ZnO thin films prepared by RF magnetron sputtering using pure metallic Zn target and ZnO ceramic target
摘要： In this work, ZnO thin films was deposited onto Si substrate by ablation of different sputtering targets (ZnO ceramic target and pure metallic Zn target) under different substrate temperatures from 300°C to 600°C with intervals of 100°C, and the properties of ZnO thin films were analysed. The results showed that ZnO thin films had the c-axis preferred orientation and it also presented optimised properties owing to the reduction of thin film defects at a substrate temperature of 400°C. By analysing data, it could also be seen that the performance of ZnO thin films fabricated using the ZnO ceramic target was better than that of ZnO thin films fabricated using the pure metallic Zn target. It was considered that the excellent properties of ZnO thin films fabricated using the ZnO ceramic target were attributed to the decrease in oxygen vacancies and the reduction of film defects.
关键词： ZnO ceramic target,RF magnetron sputtering,pure metallic Zn target,ZnO,thin films
更新于2025-09-09 09:28:46
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Computational Investigation of the Morphology, Efficiency, and Properties of Silver Nano Wires Networks in Transparent Conductive Film
摘要： Random networks of silver nano wires have been considered for use in transparent conductive films as an alternative to Indium Tin Oxide (ITO), which is unsuitable for flexible devices. However, the random distribution of nano wires makes such conductive films non-uniform. As electrical conductivity is achieved through a percolation process, understanding the scale-dependency of the macroscopic properties (like electrical conductivity) and the exact efficiency of the network (the proportion of nano wires that participate in electrical conduction) is essential for optimizing the design. In this paper, we propose a computational method for identifying the representative volume element (RVE) of nano wire networks. This defines the minimum pixel size in devices using such transparent electrodes. The RVE is used to compute the macroscopic properties of films and to quantify the electrically conducting efficiency of networks. Then, the sheet resistance and transparency of networks are calculated based on the predicted RVEs, in order to analyze the effects of nano wire networks on the electrical and optical properties of conductive films. The results presented in this paper provide insights that help optimizing random nano wire networks in transparent conductive films for achieving better efficiencies.
关键词： electrical conductivity,representative volume element,silver nano wires,optical transmittance,transparent conductive films
更新于2025-09-09 09:28:46
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Effect of MIT in epitaxial VO <sub/>2</sub> films on THz transmittance
摘要： The development of THz technologies (communication, imaging, spectroscopy etc.) requires the design of materials for high-speed modulation of radiation in THz range. For such applications, the thin films based on oxides showed a metal-insulator transition (MIT) are interesting due to large different of optical transmittance before and after critical point. Among the oxide materials with MIT vanadium dioxide, which has a transition temperature the closest to the room temperature (68oC for bulk samples), is of particular interest, with the MIT characterized by a record speed (<1 ps) and a large amplitude (a change in the conductivity is 105 times for single crystals). It is known that the MIT transition in VO2 is accompanied by a first-order phase transition, while the crystalline structure from the monoclinic (crystal type MoO2) with the properties of the semiconductor transforms into a tetragonal (rutile type) with metallic conductivity. The electronic transition in the vanadium dioxide can be caused by the temperature, the electric field and laser radiation. A set of these unique properties makes vanadium dioxide a promising key component of optoelectronic devices (switches, modulators, lenses, etc.) for the THz range controlled by thermal action, electric voltage or laser pulse.
关键词： vanadium dioxide,epitaxial films,metal-insulator transition,THz transmittance,THz technologies
更新于2025-09-09 09:28:46
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Enhancement of the absorption bands in the infrared spectra of low-temperature uracil films by interference
摘要： An experimental method that enables significant enhancement of the bands in the IR absorption spectra of low-temperature films, using standard equipment for matrix isolation, was proposed. The effect is achieved due to the interference amplification of an electromagnetic wave using a sublayer of Ar film. IR Fourier spectra of low-temperature films of uracil (Ur) molecules were obtained in the range of 2000–500 cm–1, with a resolution of 3 cm–1. Thin Ur films with thickness of approximately 0.3 μm were grown at low temperatures on the surface of argon films of thickness of 2.3 and 1.1 μm. An enhancement in the spectral range of 1250–500 cm–1 was recorded for the first bilayer structure, and in the range of 2000–500 cm–1 for the second one. As a result of amplification in the spectrum of the low-temperature uracil film, absorption bands in the range of out-of-plane deformation vibrations of 1000–500 cm–1 were recorded for the first time. It was found that the out-of-plane fundamental NH modes of Ur groups are most sensitive to changes in the crystal structure of the film. It was shown that the absorption spectrum of the Ur film heated to room temperature differs from the spectrum of the Ur crystal obtained from the solution, which indicates a difference in their structures.
关键词： uracil,interference amplification,low-temperature films,absorption bands,infrared spectra
更新于2025-09-09 09:28:46
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and
摘要： The magnetoresistance of Ni81Fe19 and Co83Gd17 ferromagnetic thin films is measured in Corbino disk geometry, and compared to the magnetoresistance of the same films measured in the Hall-bar geometry. The symmetry of the magnetoresistance profiles is drastically modified by changing the geometry of the sample, i.e., by changing the boundary conditions. These properties are explained in a simple model, showing that the Corbino magnetoresistance is defined by the potentiostatic boundary conditions while the Hall-bar magnetoresistance is defined by galvanostatic boundary conditions.
关键词： boundary conditions,Corbino disk,ferromagnetic thin films,magnetoresistance,Hall-bar geometry
更新于2025-09-09 09:28:46
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[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Nonlinear Optical Properties of Oxide Thin Films
摘要： This work contains description of the oxide thin films fabricated by Physical Vapor Deposition technique in high vacuum on transparent (quartz) and semiconductor (n-type silicon) substrates kept at room temperature during the deposition process. Titanium, tin and indium oxides were chosen as the material for investigation. Selected films were annealed after fabrication in ambient atmosphere for 12 hours at the temperature equal to 100 °C, 150 °C, 250 °C and 450 °C. Structural properties were examined by optical images and AFM measurements. The films exhibit high structural dependence on the temperature of the annealing process. Quality of the films can be improved by using an appropriate temperature during the annealing process. Nonlinear optical effects were studied using Third Harmonic Generation with Nd:YAG laser at 1064 nm wavelength as a fundamental beam. The values of third-order NLO susceptibilities were calculated and analyzed. We find that the nonlinear optical properties were strictly connected with the morphology. Moreover the temperature of annealing process can change the structural and optical properties of the tested oxide thin films.
关键词： third harmonic generation,atomic force microscopy,oxide thin films,physical vapor deposition
更新于2025-09-09 09:28:46
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Visualizing topological edge states of single and double bilayer Bi supported on multibilayer Bi(111) films
摘要： Freestanding single bilayer Bi(111) is a two-dimensional topological insulator with edge states propagating along its perimeter. Given the interlayer coupling experimentally, the topological nature of Bi(111) thin films and the impact of the supporting substrate on the topmost Bi bilayer are still under debate. Here, combined with scanning tunneling microscopy and first-principles calculations, we systematically study the electronic properties of Bi(111) thin films grown on a NbSe2 substrate. Two types of nonmagnetic edge structures, i.e., a conventional zigzag edge and a 2 × 1 reconstructed edge, coexist alternately at the boundaries of single bilayer islands, the topological edge states of which exhibit remarkably different energy and spatial distributions. Prominent edge states are persistently visualized at the edges of both single and double bilayer Bi islands, regardless of the underlying thickness of Bi(111) thin films. We provide an explanation for the topological origin of the observed edge states that is verified with first-principles calculations. Our paper clarifies the long-standing controversy regarding the topology of Bi(111) thin films and reveals the tunability of topological edge states via edge modifications.
关键词： topological insulator,scanning tunneling microscopy,edge states,first-principles calculations,Bi(111) thin films
更新于2025-09-09 09:28:46
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Numerical Simulation of Plasmon Excitation in Gold Nanostructure of the Parabolic Nanoantenna Type
摘要： Experimentally obtained nanostructures shaped as a through hole with a particle at the center are considered. Their electrodynamic parameters are studied using numerical simulation methods. It is shown that such structures function similarly to parabolic antennas.
关键词： numerical simulation of electrodynamics,nanostructuring of thin films,parabolic nanoantennas
更新于2025-09-04 15:30:14
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A novel method for the determination of field output factors and output correction factors for small static fields for six diodes and a microdiamond detector in megavoltage photon beams
摘要： Purpose: The goal of this work is to provide a large and consistent set of data for detector specific output correction factors, (cid:1863)(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) , for small static fields for seven solid state detectors and to determine field output factors, Ω(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) , using EBT3 radiochromic films and W1 plastic scintillator as reference detectors on two different linear accelerators and four megavoltage photon beams. Consistent measurement conditions and recommendations given in the International Code of Practice TRS-483 for small field dosimetry were followed throughout the study. Methods: Ω(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) were determined on two linacs, Elekta Versa HD and Varian TrueBeam, for 6 and 10 MV beams with and without flattening filter and for nine fields ranging from 0.5 x 0.5 cm2 to 10 x 10 cm2. Signal readings obtained with EBT3 radiochromic films and W1 plastic scintillator were fitted by an analytical function. Volume averaging correction factors, determined from 2D dose matrices obtained with EBT3 films and fitted to bivariate Gaussian function, were used to correct measured signals. (cid:1863)(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) were determined empirically for six diodes, IBA SFD, IBA Razor, PTW 60008 P, PTW 60012 E, PTW 60018 SRS and SN EDGE and a PTW 60019 microDiamond detector. Results: Field output factors and detector specific (cid:1863)(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) are presented in the form of analytical functions as well as in the form of discrete values. It is found that in general, for a given linac, small field output factors need to be determined for every combination of beam energy and filtration (WFF or FFF) and field size as the differences between them can be statistically significant (p < 0.05). For different beam energies, the present data for (cid:1863)(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) are found to differ significantly (p < 0.05) from the corresponding data published in TRS-483 mostly for the smallest fields (< 1.5 cm). For the PTW microDiamond detector statistically significant differences (p < 0.05) between (cid:1863)(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) values were found for all investigated beams on Elekta Versa HD linac for field sizes 0.5 x 0.5 cm2 and 0.8 x 0.8 cm2. Significant differences in (cid:1863)(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) between beams of a given energy but with and without flattening filters are found for measurements made in small fields (< 1.5cm) at a given linac. Differences in (cid:1863)(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) are also found when measurements are made at different linacs using the same beam energy filtration combination; for the PTW microDiamond detector, these differences were found to be around 6% and were considered as significant. Conclusions: Selection of two reference detectors, EBT3 films and W1 plastic scintillator, and use of an analytical function, is a novel approach for the determination of Ω(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) for small static fields in megavoltage photon beams. Large set of (cid:1863)(cid:3018)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3018)(cid:3293)(cid:3280)(cid:3281) (cid:3033)(cid:3278)(cid:3287)(cid:3284)(cid:3289),(cid:3033)(cid:3293)(cid:3280)(cid:3281) data for seven solid-state detectors and four beam energies determined on two linacs by a single group of researchers can be considered a valuable supplement to the literature and the TRS-483 dataset.
关键词： EBT3 films,W1 scintillator,small fields,microDiamond,diodes
更新于2025-09-04 15:30:14