Optical Properties Of Materials Research Articles

Study Using the Brus Equation to Examine How Quantum Confinement Energy Affects the Optical Characteristics of Cadmium Sulfide and Zinc Selenide

In this paper, the Brus equation was used to study the effects of quantum confinement energy on the optical properties of material with quantum dot (QD). It was found that the wavelength and energy gap depend on the quantum confinement energy. With the increase in the energy of quantum confinement, the energy gap increases and the absorption wavelength decreases and shifts toward the UV region. This large blue shift observed in CdS and ZnSe QDs could be exploited for the potential applications as smart materials in photonic nanodevice and various other applications.

Hybrid Metasurfaces of Plasmonic Lattices and 2D Materials

AbstractPlasmonic metasurfaces can significantly enhance the interaction between light and 2D materials. Hybrid structures of plasmonic lattices and 2D materials show great promise for both fundamental and practical studies because of their unprecedented ability for precise manipulation of light at the nanoscale. This review starts with an overview of the basic concepts of plasmonic lattices and optical properties of 2D materials, as well as fabrication strategies for hybrid metasurfaces. Then, the enhanced photoluminescence, quantum emission, optoelectronic detection, nonlinear process, and valleytronics in hybrid metasurfaces are summarized, and their development for nanophotonic functional devices are reviewed. Further, several compelling topics are also outlined that provide outlooks for future directions of hybrid metasurfaces such as novel structural design and high‐quality fabrication, all‐dielectric metasurfaces, dynamic metasurfaces, and plasmonic mediation of chemical reactions and physical processes. It is believed that hybrid metasurfaces of plasmonic lattices and 2D materials can open prospects for versatile platforms for light‐matter interactions and contribute to the revolutions on nanophotonic devices.

Ultrasonic synthesis of controllable thin sheet-like BiPO4 assisted by ionic liquid and Bi-MOF with enhanced visible-light photocatalytic activity

Raw materials and synthesis strategies have great influence on the morphologies and optical properties of materials. In this study, ultrasonic synthesis of controllable thin sheet-like BiPO4 with an excessive visible-light response was synthesized, using Bi-based metal-organic frameworks (CAU-17) and ionic liquid [Omim]H2PO4 as raw materials. Compared with BiPO4-H (hydrothermal, solid rod shape) synthesized using inorganic salt, BiPO4-A (agitation, thin rod-like) and BiPO4-U (ultrasonic, thin sheet-like) have better visible-light absorption capacity and narrower band gap. Under visible-light, they could degrade 27.7 % (BiPO4-H), 73.0 % (BiPO4-A), and 76.3 % (BiPO4-U) tetracycline hydrochloride at 30 min, respectively. The speedy charge transfer at the photogenerated carrier interface, large specific surface areas, and improved light adsorption greatly enhance the photocatalytic performance. Cyclic experiments exhibit that the material has good photostability and repeatability. Finally, the feasible degradation mechanism of the material was proposed via a capture experiment. This paper provides a new technique for synthesizing BiPO4 or other photocatalysts, which can be used for high-efficiency wastewater purification under visible-light.

Anisotropic linear and nonlinear excitonic optical properties of buckled monolayer semiconductors

The optical properties of two-dimensional materials are exceptional in several respects. They are highly anisotropic and frequently dominated by excitonic effects. Dipole-allowed second-order nonlinear optical properties require broken inversion symmetry. Hence, several two-dimensional materials show strong in-plane (IP) nonlinearity but negligible out-of-plane (OOP) response due to vertical symmetry. By considering buckled hexagonal monolayers, we analyze the critical role of broken vertical symmetry on their excitonic optical response. Both linear as well as second-order shift current and second-harmonic response are studied. We demonstrate that substantial OOP nonlinear response can be obtained, in particular, through off-diagonal tensor elements coupling IP excitation to OOP response. Our findings are explained by excitonic selection rules for OOP response and the impact of dielectric screening on excitons is elucidated.

Extra-High Mechanical and Phononic Anisotropy in Black Phosphorus Blisters.

Strain is an effective strategy to modulate the electrical, optical, and optoelectronic properties of 2D materials. Conventional circular blisters could generate a biaxial stretching of 2D membranes with notable strain gradients along the hoop direction. However, such a deformation mode cannot be utilized to investigate mechanical responses of in-plane anisotropic 2D materials, for example, black phosphorus (BP), due to its crystallographic orientation dependence. Here, a novel rectangular-shaped bulge device is developed to uniaxially stretch the membrane, and further provide a promising platform to detect orientation-dependent mechanical and optical properties of anisotropic 2D materials. Impressively, the derived anisotropic ratio of Young's modulus of BP flakes is much higher than the values obtained via the nanoindentation method. The extra-high strain-dependent phononic anisotropy in Raman modes along different crystalline orientations is also observed. The designed rectangular budge device expands the uniaxial deformation methods available, allowing to explore the mechanical, and strain-dependent physical properties of other anisotropic 2D materials more broadly.

Structural, optical, and electrochromic properties of rare earth material (CeO2)/transitional metal oxide (WO3) thin film composite structure for electrochromic applications

Structural, optical, and electrochromic properties of rare earth material (CeO2)/transitional metal oxide (WO3) thin film composite structure for electrochromic applications

The effect of different strain on the structural and optical properties of multilayer γ-InSe

Strain engineering is one promising approach to tune electronic and optical properties of 2D materials. But which type mechanical strain is most efficient is unclear. Here we systematically investigate and compare the tuning effect from four different type strains for multilayer γ-InSe, including in-plane uniaxial tensile strain, in-plane biaxial tensile strain, hydrostatic compressive strain and out-of-plane axial compressive strain. The evolution of its phonon modes and luminescent properties upon strain were investigated using in situ Raman and photoluminescence (PL) spectroscopy. All phonon modes exhibit blue shift upon compression strain, while red shift upon tensile strain. Band gap reduction was observed for both compression strain and tensile strain. Strain type has great effect on the shift rate of Raman mode and band gap. Among four types strain, biaxial tensile strain exhibits the largest shift rates, being 8.49, 9.24 and 8.65 cm-1/% for three phonon modes and 85 meV/% for band gap. It suggests that biaxial tensile strain is more efficient for γ-InSe. This result is helpful for practical strain-based manipulation for 2D materials.

Tuning Oxide Properties by Oxygen Vacancy Control During Growth and Annealing.

Electrical, optical, and magnetic properties of oxide materials can often be controlled by varying the oxygen content. Here we outline two approaches for varying the oxygen content and provide concrete examples for tuning the electrical properties of SrTiO3-based heterostructures. In the first approach, the oxygen content is controlled by varying the deposition parameters during a pulsed laser deposition. In the second approach, the oxygen content is tuned by subjecting the samples to annealing in oxygen at elevated temperatures after the film growth. The approaches can be used for a wide range of oxides and nonoxide materials where the properties are sensitive to a change in the oxidation state. The approaches differ significantly from electrostatic gating, which is often used to change the electronic properties of confined electronic systems such as those observed in SrTiO3-based heterostructures. By controlling the oxygen vacancy concentration, we are able to control the carrier density over many orders of magnitude, even in nonconfined electronic systems. Moreover, properties can be controlled, which are not sensitive to the density of itinerant electrons.

Adaptive long wave-infrared camouflage using an all-dielectric metasurface

All-dielectric metamaterials consisting of high-index, sub-wavelength, and periodically decorated arrays allow for efficient manipulation of electromagnetic permittivity and permeability with lower losses at the optical frequencies. In this study, we propose a planar multilayer structure composed of dielectric interlayers (Al2O3/Ge/ITO/Soda Lime Glass) to achieve perfect and broadband absorption of mid- and long-infrared (IR) wavelengths. Analyzing the spectral properties of the designed structure proved that it possesses exquisite importance in thermal application when considering the IR signature reduction in the long wavelength range, as well as the reduced radiated energy dissipation along with the undetected band and the requirements for IR camouflage. This intrinsic merit of dielectric metamaterials stems from their inherent selective absorption/emission. In that respect, Kirchhoff's law states that the emissive and absorptive powers of all bodies are similar for radiation of the same wavelength at the same temperature. The temperature difference may occur not only from the properties of the surfaces but also from the optical properties of materials and environmental conditions. Studying the thermal camouflage at different background temperatures found that the camouflage material substantially reduces the contrast between the target and the background. Beyond that, extensive assessments validated that the contrast in the resulting short tips is due to the differences in the reflective properties of the material and the background. Our simulations and experiments lay the groundwork for structuring cost-effective all-dielectric thermal camouflage metaplatforms with high performance and the strong potential to be employed in practical military and defense applications.

Measurement of the conduction band spin-orbit splitting in WSe2 and WS2 monolayers

The conduction band spin-orbit splitting ∆${}_{c}$ has a strong impact on optical, transport, and spin-valley properties of 2D materials based on transition metal dichalcogenide monolayers. Here, the authors study charge tunable devices based on WSe${}_{2}$ and WS${}_{2}$ monolayers. In addition to the well-known radiative recombination of neutral and charged excitons, photoluminescence measurements highlight a weaker intensity optical transition. This line is interpreted as an impurity-assisted recombination of the negatively charged exciton (triplet trion), whose radiative recombination energy differs by ∆${}_{c}$ from that of the trion's direct optically active recombination.

Advances in ultrafast plasmonics

In the past 20 years, we have reached a broad understanding of many light-driven phenomena in nanoscale systems. The temporal dynamics of the excited states are instead quite challenging to explore, and, at the same time, crucial to study for understanding the origin of fundamental physical and chemical processes. In this review, we examine the current state and prospects of ultrafast phenomena driven by plasmons both from a fundamental and applied point of view. This research area is referred to as ultrafast plasmonics and represents an outstanding playground to tailor and control fast optical and electronic processes at the nanoscale, such as ultrafast optical switching, single photon emission, and strong coupling interactions to tailor photochemical reactions. Here, we provide an overview of the field and describe the methodologies to monitor and control nanoscale phenomena with plasmons at ultrafast timescales in terms of both modeling and experimental characterization. Various directions are showcased, among others recent advances in ultrafast plasmon-driven chemistry and multi-functional plasmonics, in which charge, spin, and lattice degrees of freedom are exploited to provide active control of the optical and electronic properties of nanoscale materials. As the focus shifts to the development of practical devices, such as all-optical transistors, we also emphasize new materials and applications in ultrafast plasmonics and highlight recent development in the relativistic realm. The latter is a promising research field with potential applications in fusion research or particle and light sources providing properties such as attosecond duration.

On Increasing Efficiency of UV Germicidal Recirculation for Air Sanitation

Enclosed germicidal irradiators, known as recirculators, have become widely used for air sanitation over the last years. The article presents the studies of the most common design of the device in terms of implementation of its target functionality. In the course of practical work, the role of shape and UV - C optical properties of material of the irradiation chamber walls for formation of efficient germicidal radiant flux inside it was studied. The significant effect of multiple reflections on the target functionality of the device was substantiated by calculations and confirmed by the test results. The article proposes the design of the irradiator and the analytical expressions for calculation of the irradiating chamber reflecting surface profile shape providing beneficial conditions for formation of an increased efficient germicidal flux inside it by means of multiple reflections.

Development and Characterization of Multi-Alkali Antimonide Photocathodes for High-Brightness RF Photoinjectors.

Due to their excellent photoemissive properties, especially low thermal emittance and high sensitivity in the green wavelength, multi-alkali antimonide photocathodes, in particular, cesium-potassium-antimonide, emerged as prominent photoemissive materials for the electron sources of high-repetition-rate FEL applications. To explore its feasibility of operating in a high-gradient RF gun, DESY collaborated with INFN LASA to develop multi-alkali photocathode materials. In this report, we describe the recipe of K-Cs-Sb photocathodes, which were grown on a Mo substrate by varying the foundational Sb layer thickness using sequential deposition techniques. This report also illustrates the information regarding the film thickness, substrate temperature, deposition rate, and its possible effects on the photocathode's properties. In addition, the influence of temperature on the cathode degradation is also summarized. Furthermore, in the framework of density functional theory (DFT), we investigated the electronic and optical properties of the K2CsSb material. The optical properties, such as dielectric function, reflectivity, refracting index, and extinction coefficient, were evaluated. The correlation between the calculated and measured optical properties, such as reflectivity, provides a better and more efficient strategy to rationalize and understand the photoemissive material's properties.

Optical and Electrical Properties of Low-Dimensional Crystalline Materials

Low-dimensional materials have experienced a real revolution in both the technological and research fields in recent decades [...]

Atomistic Simulation of Physical Vapor Deposition of Optical Thin Films.

A review of the methods and results of atomistic modeling of the deposition of thin optical films and a calculation of their characteristics is presented. The simulation of various processes in a vacuum chamber, including target sputtering and the formation of film layers, is considered. Methods for calculating the structural, mechanical, optical, and electronic properties of thin optical films and film-forming materials are discussed. The application of these methods to studying the dependences of the characteristics of thin optical films on the main deposition parameters is considered. The simulation results are compared with experimental data.

Planar Fourier optics for slab waveguides, surface plasmon polaritons, and 2D materials.

Recent experimental work has demonstrated the potential of combining the merits of diffractive and on-chip photonic information processing devices in a single chip by making use of planar (or slab) waveguides. Here, arguments are developed to show that diffraction formulas familiar from 3D Fourier optics can be adapted to 2D under certain mild conditions on the operating speeds of the devices in question. In addition to serving those working in on-chip photonics, this Letter provides analytical tools for the study of surface plasmon polaritons, surface waves, and the optical, acoustic, and crystallographic properties of 2D materials.

Recent Advances in 2D Material Theory, Synthesis, Properties, and Applications.

Two-dimensional (2D) material research is rapidly evolving to broaden the spectrum of emergent 2D systems. Here, we review recent advances in the theory, synthesis, characterization, device, and quantum physics of 2D materials and their heterostructures. First, we shed insight into modeling of defects and intercalants, focusing on their formation pathways and strategic functionalities. We also review machine learning for synthesis and sensing applications of 2D materials. In addition, we highlight important development in the synthesis, processing, and characterization of various 2D materials (e.g., MXnenes, magnetic compounds, epitaxial layers, low-symmetry crystals, etc.) and discuss oxidation and strain gradient engineering in 2D materials. Next, we discuss the optical and phonon properties of 2D materials controlled by material inhomogeneity and give examples of multidimensional imaging and biosensing equipped with machine learning analysis based on 2D platforms. We then provide updates on mix-dimensional heterostructures using 2D building blocks for next-generation logic/memory devices and the quantum anomalous Hall devices of high-quality magnetic topological insulators, followed by advances in small twist-angle homojunctions and their exciting quantum transport. Finally, we provide the perspectives and future work on several topics mentioned in this review.

Multifunctional Plasmonic Sensor for Excellent UV Photodetection and NO2 Gas Sensing by an Array of Al Nanocaps on GaN Truncated Nanocones

AbstractPlasmonics has been demonstrated to improve the performance of various optoelectronic devices operating in the infrared to visible wavelength regime. However, limited by optical properties of suitable plasmonic materials in ultraviolet (UV) regimes, rare works have been devoted to UV applications with plasmonic structures. This work deliberately fabricates a heterogeneous array of Al nanocaps (Al‐NC) on a wide‐bandgap semiconductor of GaN truncated nanocones (GaN‐TNC) and then presents a multifunctional plasmonic sensor for excellent UV photodetection and air‐quality‐index (AQI) gas sensing. As a UV photodetector, this work shows maximum responsivity (1.8 × 108 AW−1) and detectivity (1.2 × 1018 Jones) at the resonance wavelength of 355 nm, which based on the current knowledge, is the highest detectivity among GaN‐based UV photodetectors. Such a UV photodetector also introduces a decent response of rise time (78.3 ms) and fall time (303.5 ms), respectively. As a gas sensor, this work detects a key AQI gas of NO2 and provides a superior response of 28% and a detection limit of 500 ppb, respectively.

Field and temperature assisted DC/AC conduction measurements of PS/ZnO nanocomposite films

Electrical, optical and morphological properties of polymer nanocomposite materials are quite interesting to investigate due to their innovative characteristics and applications. Temperature dependent dc conductivity using different charge transport mechanisms like ionic hopping, Schottky and Poole-Frankel emissions has been investigated for pristine PS and PS/ZnO (at different wt% of ZnO) nanocomposite films in this research report. Non-ohmic conduction behaviour of these films developed an interest to carry out bulk and electrode limited conduction mechanisms. Ionic jump distance ‘a’ and conduction coefficient ‘βexp’ values for these films were calculated at various temperatures from the slopes of log I vs E and log I vs E1/2 plots respectively. The increase in dc conductivity of an order of 108 was observed by increasing the doping concentration up to 20 wt% of ZnO. The change in their ac conductivity was observed from 10−9 S/m to 10−6 S/m by varying the frequency from 1 to 300 kHz.

Experimental and DFT analysis of structural, optical, and electrical properties of Li3xLa2/3-xTiO3 (3x = 0.1, 0.3 and 0.5) solid electrolyte

The perovskite material, lithium lanthanum titanate Li3xLa2/3-xTiO3 (LLTO) is one of the interesting prospects that may be employed as a solid-state inorganic electrolyte for Li-ion batteries. Here, three various formulations corresponding to: (i) 3x = 0.1 (Li0.1La0.63TiO3), (ii) 3x = 0.3 (Li0.3La0.57TiO3), and (iii) 3x = 0.5 (Li0.5La0.5TiO3) were synthesized using sol-gel method. The impacts of lithium concentration, calcination temperature, elemental composition, microstructure, optical properties, and conductivity of the ceramics were studied using a plethora of techniques. DFT calculations were performed on Li0.5La0.5TiO3 to get an in-depth understanding on the relationship between the structure –electronic– optical properties of LLTO materials. Our results show that the grain and crystallite sizes behave inversely proportional to the band gap. Maximum grain ionic conductivity on the order of 10−3S/cm and grain boundary ionic conductivity on the order of 10−6S/cm were obtained for both samples (3x = 0.3 and 3x = 0.5) at higher temperatures. The total density of states indicates that the titanium d-bands (Ti-d) and oxygen p–bands (O-p) form covalent Ti-O bond character. The formation of localized states is suggested to result in the lowering of the band gap energy, when lithium content is increased. Finally, the calculated mechanical properties show that LLTO (3x = 0.5) possess high elastic moduli as compared to other solid electrolytes.