Dioxide Substrates Research Articles

VO2 based polarization-independent dual-wavelength plasmonic switches using U and C shaped nanostructures.

We have proposed vanadium dioxide (VO2) based polarization-independent dual-wavelength plasmonic switches using a periodic combination of U and C shaped gold nanostructures on a gold coated silicon dioxide (SiO2) substrate with a thin VO2 film as spacer between the nanostructures and the underlying substrate. A spatial offset between the two nanostructures is taken such that high switching efficiency is obtained simultaneously at two wavelengths for all polarization angles of incident light. The switching mechanism is based on the transformation of the phase change material, VO2, from its monoclinic semiconductor state to its tetragonal metal state when exposed to an external stimulus. This transformation leads to a significant change in the optical behavior of the proposed switch, leading to an effective transition from ON to OFF state. Finite difference time domain (FDTD) modelling shows that the proposed switches are capable of achieving a high extinction ratio of ~ 20 dB at two wavelengths-1560nm and 2130nm-for incident light with any polarization angle. To demonstrate the spectral tunability of switching wavelengths, the optimization of the geometrical parameters is also carried out. These switches can be employed in telecommunication networks, optical communications, and integrated photonic circuits.

Dynamically switchable multifunctional device for terahertz application using vanadium dioxide and graphene-based metasurface

Abstract In this article, a dynamically switchable and multifunctional metasurface is realized using a combination of vanadium dioxide (VO2) and graphene-based structures. The device can be tuned using the temperature transition property of vanadium dioxide from a wideband linear-to-circular polarization converter (LTCPC) to a wideband linear-to-linear cross polarization converter (LTLPC) and a dual-band absorber. The unit cell is designed with a gold-backed lossy-silicon dioxide (SiO2) substrate with a permittivity of 3.9, and the top metasurface layer is designed with a graphene-based dual triangle loaded split ring (DTLSR) and two stripes of vanadium oxide to cover the split partially. The proposed device can be used as a wideband LTCPC at normal temperature (298 K) from 1.43 THz to 2.85 THz, i.e., 66.35% fractional bandwidth (FBW). At temperatures greater than 341 K, VO2 exhibits metallic properties, and the structure functions as LTLPC from 1.82 THz to 3.31 THz (PCR ≥ 80%), i.e., 58.08 % FBW and maximum polarization conversion ratio (PCR) reported as high as 99.65 %. Furthermore, at this metallic condition, two absorption peaks are obtained at 1.22 THz and 3.30 THz with absorptivity of 93.5% and 100%, respectively. The device offers incident angle invariability up to 40° for LTCPC and up to 50° for LTLPC operation. Further insight into the mechanism of operation is developed using the surface current density and electric field distribution analysis. The advantage of the proposed metasurface over other similar structures is assessed with respect to multifunctional behavior, bandwidth, and stability under oblique incidence.

Tunable mid-infrared absorber based on Dirac metamaterials

In this paper, a tunable metamaterial absorber based on a Dirac semimetal is proposed. It consists of three different structures, from top to bottom, namely a double semicircular Dirac semimetal resonator, a silicon dioxide substrate and a continuous vanadium dioxide (VO2) reflector layer. When the Fermi energy level of the Dirac semimetal is 10meV, the absorber absorbs more than 90% in the 39.06–84.76 THz range. Firstly, taking advantage of the tunability of the conductivity of the Dirac semimetal, dynamic tuning of the absorption frequency can be achieved by changing the Fermi energy level of the Dirac semimetal without the need to optimise the geometry and remanufacture the structure. Secondly, the structure has been improved by the addition of the phase change material VO2, resulting in a much higher absorption performance of the absorber. Since VO2 is a temperature-sensitive metal oxide with an insulating phase below the phase transition temperature (about 68 °C) and a metallic phase above the phase transition temperature, this paper also analyses the effect of VO2 on the absorptive performance at different temperatures, with the aim of further improving absorber performance.

A metasurface integrated self-decoupled multiport tunable antenna for THz applications

Abstract A four port multiple-input multiple-output (MIMO) antenna is initially designed on silicon dioxide (quartz) substrate by arranging the antenna elements in an orthogonal configuration by using self-decoupling mechanism. Mean effective gain lower than 0.5 and radiation efficiency greater than 95% are obtained. Characteristic mode analysis of the proposed MIMO antenna has been performed using finite integration technique to validate the resonant modes. Further, a dual band self-multiplexing MIMO antenna has been constructed by loading each antenna element with a graphene constituted stub. Graphene loading in the antenna elements is done to introduce tunability in the MIMO operation in two frequency bands. The dual resonance frequencies range from 4.3–4.6 THz and 5.2–5.6 THz while the chemical potential is varied from 0.1 eV to 0.9 eV. The diversity performance of the MIMO antenna with and without graphene loading have been analyzed through numerical simulations. Envelope correlation coefficient lower than 0.0002 and diversity gain of 10 dB have been obtained. By biasing each of the antenna elements with different voltages, quadruplexing mechanism can be performed since each antenna resonates at a different frequency. Finally, a metasurface is designed on silicon dioxide (quartz) substrate to function as a reflective surface from 3.75–6.42 THz covering the resonance band of the tunable MIMO antenna for enhancing its gain to 14 dBi.

Dual-band circular dichroism in chiral metamaterial absorber based on vanadium dioxide

Abstract Chiral metamaterial absorbers are instrumental in a wide array of applications, encompassing multifaceted optoelectronic devices, information-encrypting metamaterials, and thermal-controlled imaging and detection systems. In this study, we showcase a Ꞩ-shaped chiral metamaterial integrated with a vanadium dioxide substrate, which enables dynamic tuning of terahertz (THz) dual-band circular dichroism (CD). This absorber boasts spin-selective absorption, stemming from the selective excitation of the plasmon polaron mode on its horizontal microrod. Notably, right-handed circularly polarized light (CPL) experiences near-perfect absorption at resonance, whereas left-handed circular polarization is absorbed to a much lesser degree, yielding pronounced CD. This exceptional chiral selectivity facilitates dual-band CD effects, with peak values reaching 0.814 and 0.784. Furthermore, by manipulating the conductivity of vanadium dioxide, we can dynamically adjust both the CD and absorption peaks of the chiral metamaterial. The maximum modulation depth of the CD response can attain values as high as 0.807 and 0.776. Our work presents a novel design strategy for the active control and modulation of CPL, thereby expanding the horizons of metamaterial absorber applications within the THz spectrum.

Modeling and experimental characterization of a compact Mach–Zehnder electro-optic modulator on the SOI

The Mach–Zehnder electro-optic modulator (MZM) plays a crucial role in photonics integration technology during signal transmission. We propose the design and fabrication of a silicon-based electro-optic modulator based on the M-Z structure and design a modulator using silicon as the waveguide core layer on a silicon dioxide substrate. The detailed design involves a 1×2 splitter, branch waveguides, modulating arm waveguides, and a 2×1 combiner. The MZM fabrication and characterization results reveal that the half-wave voltage of the silicon-based MZM is 2 V, with an optical loss of −2.464dB and a device core size of 450µm×2800µm. The experimental results indicate that the MZM with a low half-wave voltage, a low loss, and high integration has significant value. The proposed MZM exhibits considerable improvements, featuring a low half-wave voltage and a low loss, and this device may serve as a fundamental component in wearable large-scale photonic integrated circuits for weak ECG real-time detection.

A broadband tunable THz sensor based on graphene metasurface

In this paper, we design a polarization-independent and angle-insensitive wideband THz graphene metamaterial sensor. The proposed metasurface sensor consists of six layers, which are silicon dioxide substrate, metal reflector, air layer, graphene metasurface with microstructure, ion-gel layer and silicon dioxide dielectric layer from bottom to top. The sensor was simulated by using CST Microwave Studio software, and the absorption and sensing performance were analyzed. The results show that the absorption rate is more than 95 % in the range of 1.05–4.07 THz. In addition, when the Fermi energy level of graphene is changed, the absorption rate can be adjusted from 20 % to more than 95 %. At the same time, the absorptivity of the device can be maintained above 80 % before 60° when the TE and TM waves are incident, and it is insensitive to the polarization angle due to the central symmetry of the graphene surface microstructure. By changing the thickness of the air layer, the device can achieve maximum absorption at h2=30μm, where the maximum frequency shift sensitivity is 2.179 THz/RIU. The influence of structure parameters and incident angle on the absorption spectrum shows that the proposed structure has good stability. The proposed metasurface sensor has potential application prospects in biological detection and medical monitoring, broadening the application range of THz functional devices.

No evidence of improvements in energy metabolism after 1week of nitrate and citrulline co-supplementation in elite rowers.

Citrulline (CIT) and beetroot extract (BR) supplements positively impacts exercise performance in elite rowers. However, its influence on metabolic outcomes such as whole-body volumes of oxygen consumption (VO2) and carbon dioxide production (VCO2), substrate oxidation, energy expenditure (EE), and gross efficiency remains unknown. We studied the effects of 1week of daily co-supplementation of 3.5g BR (500mg NO3-) plus 6g CIT on VO2 and VCO2 kinetics, substrate utilization, EE, and gross efficiency in elite male rowers compared to a placebo and to a BR supplementation. Twenty elite rowers participated in this randomized, double-blind, placebo-controlled crossover trial completing 1week of supplementation in each group of study: Placebo (PLAG); BRG; and BR-CITG. Efficiency (70% VO2max) and performance (incremental maximal) tests were performed, and gas-exchange data were collected via indirect calorimetry. Analysis of covariance (ANCOVA) showed no mean between-condition differences on respiratory exchange ratio (RER), EE, and gross efficiency in the efficiency test (all P > 0.06), and in the performance test (all P > 0.28). Moreover, in both tests no interaction Time × Supplement effects were observed for VO2, VCO2, RER, EE, substrate oxidation, and, gross efficiency (all P > 0.12). After 1week, no effects on energy metabolism and substrate utilization were observed after the daily co-ingestion of BR extract plus CIT supplement, therefore longer (> 7days) and higher doses of supplementation might be needed to influence metabolism.

Investigating the impact of graphene patch width on performance and bandwidth enhancement in nano-patch antennas

This study investigates how varying the width of a graphene patch affects the performance and bandwidth of a nano-patch antenna. High-Frequency Structural Simulator (HFSS) software was employed for simulation, evaluating parameters such as voltage standing wave ratio (VSWR), gain, and return loss. The graphene patch of 0.690nm thick was placed on a silicon dioxide substrate with a thickness of 10 µm, while the patch width was systematically varied at 30 µm, 32 µm, 34 µm, 38 µm, and 42 µm. Surprisingly, the resonating frequency remained unaffected by changes in patch width. The results revealed that the patch widths of 32 µm, 34 µm, and 38 µm produced the highest return losses of -24.5482, -24.4774, and -24.4001, respectively. Additionally, these configurations exhibited impeccable VSWR values of 1.0302, 1.0387, and 1.0480. Notably, a substantial bandwidth improvement exceeding 500 GHz was achieved for these patch widths. This finding underscores the significant relationship between gain, directivity, and patch width in graphene nano-patch antennas. Furthermore, both 32 µm and 34 µm patch widths demonstrated gain and directivity exceeding 7 dB.

Controllable Fabrication of Gallium Ion Beam on Quartz Nanogrooves.

Nanogrooves with high aspect ratios possess small size effects and high-precision optical control capabilities, as well as high specific surface area and catalytic performance, demonstrating significant application value in the fields of optics, semiconductor processes, and biosensing. However, existing manufacturing methods face issues such as complexity, high costs, low efficiency, and low precision, especially in the difficulty of fabricating nanogrooves with high resolution on the nanoscale. This study proposes a method based on focused ion beam technology and a layer-by-layer etching process, successfully preparing V-shaped and rectangular nanogrooves on a silicon dioxide substrate. Combining with cellular automaton algorithm, the ion sputtering flux and redeposition model was simulated. By converting three-dimensional grooves to discrete rectangular slices through a continuous etching process and utilizing the sputtering and redeposition effects of gallium ion beams, high-aspect-ratio V-shaped grooves with up to 9.6:1 and rectangular grooves with nearly vertical sidewalls were achieved. In addition, the morphology and composition of the V-shaped groove sidewall were analyzed in detail using transmission electron microscopy (TEM) and tomography techniques. The influence of the etching process parameters (ion current, dwell time, scan times, and pixel overlap ratio) on groove size was analyzed, and the optimized process parameters were obtained.

4 × 4 graphene nano-antenna array for plasmonic sensing applications

The manuscript presents the design and investigation of square and L-shaped graphene plasmonic nano-antenna arrays on a silicon dioxide substrate for plasmonic biosensing applications. The design parameters, such as the shape of the nanostructure, spacing between the antenna array elements, size of the antenna array and chemical potential of the graphene are used to analyze the plasmonic resonance characteristics of the proposed plasmonic nano-antenna array. Initially, dispersive characteristics of graphene, such as conductivity, permittivity and refractive index are analyzed using its chemical potential for the validation of the graphene material for plasmonic sensing applications. The proposed square and L-shaped nanopatch antenna structures are radiating at 30 THz with a reflection coefficient of -28.4 dB and − 44.6 dB respectively at 0.1 eV chemical potential. It is observed that graphene nanopatch antenna radiates at 30 THz, 115 THz and 176 THz at a chemical potential of 1.3 eV. Further, the study demonstrated that the designed square and L-shaped nano-antenna exhibit a gain of 3.52 dB and 9.51 dB respectively at 30 THz. The gain can be increased further using a square and L-shaped nano-antenna array of dimensions 2 × 2, 3 × 3 and 4 × 4. It is observed that maximum gains of 33.44 dB and 30.86 dB are obtained for the square and L-shaped 4 × 4 plasmonic nanoarray antenna respectively. Finally, a nanocircuit model of square and L-shaped nano-antennas is proposed and validated through CST simulations.

Design of encoded graphene-gold metasurface-based circular ring and square sensors for brain tumor detection and optimization using XGBoost algorithm

This study introduces a circular ring and square metasurfaces-based sensor employing graphene and gold layers for enhanced brain tumor detection. The sensor architecture includes dual graphene circular metasurfaces and a gold square resonator layer on a silicon dioxide substrate. A comprehensive parametric investigation explores the influence of geometric parameters and graphene chemical potential on sensor performance. The sensor achieves a remarkable sensitivity of 769 GHzRIU−1, a high-quality factor of 6.514, a low detection limit of 0.182 RIU, and an FOM of 1.148RIU−1. Electric field intensity analysis identifies optimal transmission frequencies. By employing the XGBoost regressor, the analysis significantly reduces simulation time and resource consumption by at least 80 %. Simulation validation confirms that despite 80 % reduction in simulation time, high prediction accuracy remains achievable, with an impressive R2 score ranging from 0.9 to 1. The proposed sensor presents a promising non-invasive approach for early brain tumor diagnosis, with potential applications in biomedical imaging and other related fields.

Multi-wavelength and broadband plasmonic switching with V-shaped plasmonic nanostructures on a VO2 coated plasmonic substrate

In this paper, periodic arrays of identical V-shaped gold nanostructures and variable V-shaped gold nanostructures are designed on top of a gold-coated silicon dioxide (SiO2) substrate with a thin spacer layer of vanadium dioxide (VO2) to realize multi-wavelength and broadband plasmonic switches, respectively. The periodic array of identical V-shaped nanostructures (IVNSs) with small inter-particle separation leads to coupled interactions of the elementary plasmons of a V-shaped nanostructure (VNS), resulting in a hybridized plasmon response with two longitudinal plasmonic modes in the reflectance spectra of the proposed switches when the incident light is polarized in the x-direction. The x-direction is oriented along the axis that joins the V-junctions of all VNSs in one unit cell of the periodic array. On exposure to temperature, electric field, or optical stimulus, the VO2 layer transforms from its monoclinic semiconducting state to its rutile metallic state, leading to an overall change in the reflectance spectra obtained from the proposed nanostructures and resulting in an efficient multi-wavelength switching action. Finite difference time domain modelling is employed to demonstrate that an extinction ratio (ER) >12 dB at two wavelengths can be achieved by employing the proposed switches based on periodic arrays of IVNSs. Further, plasmonic switches based on variable V-shaped nanostructures—i.e. multiple VNSs with variable arm lengths in one unit cell of a periodic array—are proposed for broadband switching. In the broadband operation mode, we report an ER >5 dB over an operational wavelength range >1400 nm in the near-IR spectral range spanning over all optical communication bands, i.e. the O, E, S, C, L and U bands. Further, it is also demonstrated that the wavelength of operation for these switches can be tuned by varying the geometrical parameters of the proposed switches. These switches have the potential to be employed in communication networks where ultrasmall and ultrafast switches with multi-wavelength operation or switching over a wide operational bandwidth are inevitably required.

Three-dimensional integrated metal-oxide transistors

AbstractThe monolithic three-dimensional vertical integration of thin-film transistor (TFT) technologies could be used to create high-density, energy-efficient and low-cost integrated circuits. However, the development of scalable processes for integrating three-dimensional TFT devices is challenging. Here, we report the monolithic three-dimensional integration of indium oxide (In2O3) TFTs on a silicon/silicon dioxide (Si/SiO2) substrate at room temperature. We use an approach that is compatible with complementary metal–oxide–semiconductor (CMOS) processes to stack ten n-channel In2O3 TFTs. Different architectures—including bottom-, top- and dual-gate TFTs—can be fabricated at different layers in the stack. Our dual-gate devices exhibit enhanced electrical performance with a maximum field-effect mobility of 15 cm2 V−1 s−1, a subthreshold swing of 0.4 V dec−1 and a current on/off ratio of 108. By monolithically integrating dual-gate In2O3 TFTs at different locations in the stack, we created unipolar invertor circuits with a signal gain of around 50 and wide noise margins. The dual-gate devices also allow fine-tuning of the invertors to achieve symmetric voltage-transfer characteristics and optimal noise margins.

Highly efficient, selective, and stable photocatalytic methane coupling to ethane enabled by lattice oxygen looping.

Light-driven oxidative coupling of methane (OCM) for multi-carbon (C2+) product evolution is a promising approach toward the sustainable production of value-added chemicals, yet remains challenging due to its low intrinsic activity. Here, we demonstrate the integration of bismuth oxide (BiOx) and gold (Au) on titanium dioxide (TiO2) substrate to achieve a high conversion rate, product selectivity, and catalytic durability toward photocatalytic OCM through rational catalytic site engineering. Mechanistic investigations reveal that the lattice oxygen in BiOx is effectively activated as the localized oxidant to promote methane dissociation, while Au governs the methyl transfer to avoid undesirable overoxidation and promote carbon─carbon coupling. The optimal Au/BiOx-TiO2 hybrid delivers a conversion rate of 20.8 millimoles per gram per hour with C2+ product selectivity high to 97% in the flow reactor. More specifically, the veritable participation of lattice oxygen during OCM is chemically looped by introduced dioxygen via the Mars-van Krevelen mechanism, endowing superior catalyst stability.

Realization of high transparent mobility zinc‐doped indium oxide (IZO) thin films by RF‐magnetron sputtering

AbstractZinc‐doped indium oxide (IZO) thin films were deposited on silicon dioxide substrates by radio‐frequency magnetron sputtering using an IZO ceramic target with In2O3/ZnO weight ratio of 9:1. The effects of power, pressure, and distance between target and substrate on microstructure and photoelectric properties of IZO films were investigated. The results show the performance of IZO films prepared under the conditions of power 80 W, air pressure .5 Pa, and target base distance 80 mm are the best, and the IZO films are amorphous with high transmittance (>86.0%), high mobility (>45.0 cm2/V s), and low resistivity (less than 2.0 × 10−4 Ω cm), which are the best photoelectric performance reported at present. This work provides a feasible research approach for preparing high‐performance IZO thin films.

Generating terahertz multiple vortex beams using graphene metasurfaces

This paper investigates the generation of orbital angular momentum vortex beams using a graphene metasurface in the terahertz frequency band. The proposed design consists of 20 × 20 unit-cell elements to operate in 1.2 THz applications. Each element is a graphene ring patch printed on a silicon dioxide substrate backed with a polysilicon ground plane of size 75 × 75 × 25 µm3. The graphene reconfigurable surface conductivity is used to control the beam shape, direction, and directivity radiated from the metasurface, through the application of DC biasing voltages. A parametric study on the effect of graphene chemical potential, relaxation time and temperature on the unit-cell reflection properties is introduced. The reflection magnitude varies from − 2.1 dB to -0.8 dB with a 350-degree phase variation for µc ranging from 0.25 eV to 1.6 eV at \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au$$\\end{document} =5 ps, and T = 300 K. The effect of graphene relaxation time from 0.3 ps to 10 ps on the reflection coefficient at µc = 0.7 eV, and T = 300 K is investigated. The metasurface radiation characteristics are investigated under the illumination of two types of incidence sources, plane-wave, and focused-waves. A depiction of a single vortex beam in various orientations θ = 0, 30o, 50o, and 70o, φ = 90o for l = 1 is presented. The purity of the OAM single beam shows that 94% of the power is concentrated in the designed mode. A graphene metasurface can to convert linearly polarized input into multiple beams exhibiting orthogonal modes. Two/four vortex beams in different directions are demonstrated. The capacity for wireless communication in the terahertz band can be enhanced by utilizing a graphene metasurface.

Fabrication and application of two-dimensional tungsten disulfide thin film

To form a tungsten disulfide film, a tungsten trioxide film is deposited first and then hydrogen sulfide is injected into the furnace tube to sulfide the tungsten trioxide film in a high-temperature environment. Due to the need to accurately control the thickness of tungsten trioxide, the power of the RF sputtering machine was reduced as much as possible in a stable condition in the experiment and the bias voltage during each process was monitored. In this experiment, a sapphire substrate and a silicon substrate with 200[Formula: see text]nm silicon dioxide are used. Then use optical instruments such as Raman optics, ellipsometers and high-resolution electron transmission microscopes, atomic force microscopes and other instruments for further measurement. The analysis results show that we have successfully made tungsten disulfide films of different thicknesses. Moreover, two-dimensional tungsten disulfide thin film has a response to light, gas and pH and related devices have been successfully fabricated in experiments. Among them, comparing the single-layer film and the double-layer film, the film quality of the double-layer film is better. The quality of the film grown on the sapphire substrate is also better than the quality of the film grown on the silicon dioxide substrate.

Interpretability of high-resolution transmission electron microscopy images

High-resolution electron microscopy is a well-suited tool for characterizing the nanoscale structure of materials. However, the interaction of the sample and the high-energy electrons of the beam can often have a detrimental impact on the sample structure. This effect can only be alleviated by decreasing the number of electrons to which the sample is exposed but will come at the cost of a decreased signal-to-noise ratio in the resulting image. Images with low signal to noise ratios are often challenging to interpret as parts of the sample with a low interaction with the electron beam are reproduced with very low contrast. Here we suggest simple measures as alternatives to the conventional signal-to-noise ratio and investigate how these can be used to predict the interpretability of the electron microscopy images. We test the models on a sample consisting of gold nanoparticles supported on a cerium dioxide substrate. The models are evaluated based on series of images acquired at varying electron dose.

Ultrathin tunable UWB metasurface absorber design by exciting plasmonic modes in bilayer graphene stack

This work presents a graphene-based ultra-wideband (UWB) tunable metasurface absorber (MSA) consisting of top patterned graphene (Gpat) and bottom continuous graphene (Gcont) separated by a 2 μm thick silicon dioxide (SiO2) substrate. An absorptivity (Af) ≥ 90 % from 0.1 to 14 THz (fractional bandwidth = 197.2 %) has been achieved in three steps: (i) Fabry-Perot cavity mode has been generated near 0.1 THz using bilayer graphene stack, (ii) multiple plasmonic modes have been excited by engraving resonant slots on Gpat and (iii) plasmonic coupling strength has been enhanced between Gpat and Gcont by adjusting SiO2 substrate's thickness. The excited plasmonic modes show high absorption due to the generation of localized surface plasmon polariton (LSPP) waves. The fourfold symmetry in design nullifies the effect of the polarization angle (ϕ). Interestingly, the orthogonal modes' excitation helps to achieve similar Af response under both transverse electric and transverse magnetic polarizations for incidence angle (θ) up to 60°. Further, an effective DC biasing mechanism has been devised to tune the chemical potential (μc) of the interconnected Gcont, which ensures common DC bias between unit cells. A DC voltage from 0 to 10.2 V can vary μc (Bottom) from 0 to 1 eV to provide frequency tunability.