Indium Tin Oxide Layer Research Articles

Time-varying gradient metasurface with applications in all-optical beam steering

Abstract Integrating the large, subpicosecond nonlinear optical response of epsilon-near-zero (ENZ) materials with the broad design freedoms of plasmonic metasurfaces shows potential for creating rapidly modulated optical devices with possible applications in telecommunications, sensing, and reactive beam steering. In this work, we experimentally investigate a metasurface consisting of a plasmonic gradient array on a thin layer of indium tin oxide (ITO), characterize how incident probe pulses diffract from a system as it is being dynamically modulated by a pump pulse at wavelengths near the ENZ region. Angular shifts in the diffraction orders are observed and can be principally attributed to the adiabatic wavelength conversion of the probe as it witnesses the temporal change of index induced by the pump. Of note, the asymmetric gradient metasurface, considered to be a blazed diffraction grating, shows significantly different dynamic responses for different diffraction orders. The free-space wavelength shift to +1 and −1 diffraction orders is 6 and 12 nm, resulting in steering angle changes of 0.65 and 1.5°, respectively.

Piezoelectric Energy Harvesting Using Solar Radiation Pressure Enhanced by Surface Plasmons at Visible to Near‐Infrared Wavelengths

A light‐pressure electric generator (LPEG) device, which harvests piezoelectric energy using solar radiation enhanced by surface plasmons (SPs), is demonstrated. The design of the device is motivated by the need to drastically increase the power output of existing piezoelectric devices based on SP resonance. The solar radiation pressure can be used as an energy source by employing an indium tin oxide (ITO)/Ag double layer to excite the SPs in the near‐infrared (NIR) and visible light regions. The LPEG with the ITO layer generates an open‐circuit voltage of 295 mV, a short‐circuit current of 3.78 μA, and a power of 532.3 μW cm−2 under a solar simulator. The power of the LPEG device incorporating the ITO layer increased by 38% compared to the device without the ITO layer. The effect of the ITO layer on the electrical output of the LPEG was analyzed in detail by measuring the electrical output when visible and NIR lights are incident on the device using optical bandpass filters. In addition, finite‐difference time‐domain simulation confirmed that the pressure of the incident light can be further amplified by the ITO/Ag double layer. Finally, the energy harvested from the LPEG was stored in capacitors to successfully illuminate red light‐emitting diodes.

Study of domain structure of thin ferroelectric films with a pulse laser

We studied the domain structure of thin ferroelectric films from the pyroelectric response to heating by a pulsed laser. Barium-strontium niobate SrxBa1-xNb2O6 (SBN) films grown by plasma spraying on a layer of indium-tin oxide (ITO), which was deposited on a sapphire substrate, were studied. This technique makes it possible to determine the magnitude of the spontaneous polarization of the film and the distribution of the pyroelectric coefficient over the depth of the sample.

Design Considerations of an ITO-Coated U-Shaped Fiber Optic LMR Biosensor for the Detection of Antibiotic Ciprofloxacin

The extensive use of antibiotics has become a serious concern due to certain deficiencies in wastewater facilities, their resistance to removal, and their toxic effects on the natural environment. Therefore, substantial attention has been given to the detection of antibiotics because of their potential detriment to the ecosystem and human health. In the present study, a novel design of indium tin oxide (ITO) coated U-shaped fiber optic lossy mode resonance (LMR) biosensor is presented for the sensitive detection of the antibiotic ciprofloxacin (CIP). The performance of the designed U-shaped LMR sensor is characterized in terms of its sensitivity, full width at half maximum (FWHM), the figure of merit (FOM), and the limit of detection (LOD). For the proposed U-shaped LMR sensing probe, the various crucial factors such as the thickness (d) of the ITO layer, sensing region length (L), and bending radius (R) are optimized. The thickness of the ITO layer is optimized in such a way that two LMR curves are observed in the transmission spectrum and, thereafter, the performance parameters are evaluated for each LMR. It is observed that the designed U-shaped LMR sensor with optimized parameters shows an approximately seven-fold enhancement in sensitivity compared to the straight-core fiber optic LMR sensor. The numerical results revealed that the designed U-shaped fiber optic LMR biosensor can provide a maximum sensitivity of 17,209.9 nm/RIU with the highest FOM of 91.42 RIU-1, and LOD of 6.3 × 10-5 RIU for the detection of CIP hydrochloride in the concentration range of 0.001 to 0.029 mol∙dm-3. Thus, it is believed that the designed LMR biosensor can practically explore its potential use in environmental monitoring and biomedical applications and hence, opens a new window of opportunity for the researchers working in the field of U-shaped fiber optic LMR biosensing.

Voltage-Dependent FTIR and 2D Infrared Spectroscopies within the Electric Double Layer Using a Plasmonic and Conductive Electrode.

Strong electric fields exist between the electric double layer and charged surfaces. These fields impact molecular structures and chemistry at interfaces. We have developed a transparent electrode with infrared plasmonic enhancement sufficient to measure FTIR and two-dimensional infrared spectra at submonolayer coverages on the surface to which a voltage can be applied. Our device consists of an infrared transparent substrate, a 10-20 nm layer of conductive indium tin oxide (ITO), an electrically resistive layer of 3-5 nm Al2O3, and a 3 nm layer of nonconductive plasmonic gold. The materials and thicknesses are set to maximize the surface number density of the monolayer molecules, electrical conductivity, and plasmonic enhancement while minimizing background signals and avoiding Fano line shape distortions. The design was optimized by iteratively characterizing the material roughness and thickness with atomic force microscopy and electron microscopy and by monitoring the plasmon resonance enhancement with spectroscopy. The design is robust to repeated fabrication. This new electrode is tested on nitrile functional groups using a monolayer of 4-mercaptobenzonitrile as well as on CO and CC stretching modes using 4-mercaptobenzoic acid methyl ester. A voltage-dependent Stark shift is observed on both monolayers. We also observe that the transition dipole strength of the CN mode scales linearly with the applied voltage, providing a second way of measuring the surface electric field strength. We anticipate that this cell will enable many new voltage-dependent infrared experiments under applied voltages.

Reducing Nonradiative Losses in Perovskite LEDs through Atomic Layer Deposition of Al2O3 on the Hole-Injection Contact.

Halide perovskite light-emitting diodes (PeLEDs) exhibit great potential for use in next-generation display technologies. However, scale-up will be challenging due to the requirement of very thin transport layers for high efficiencies, which often present spatial inhomogeneities from improper wetting and drying during solution processing. Here, we show how a thin Al2O3 layer grown by atomic layer deposition can be used to preferentially cover regions of imperfect hole transport layer deposition and form an intermixed composite with the organic transport layer, allowing hole conduction and injection to persist through the organic hole transporter. This has the dual effect of reducing nonradiative recombination at the heterojunction and improving carrier selectivity, which we infer to be due to the inhibition of direct contact between the indium tin oxide and perovskite layers. We observe an immediate improvement in electroluminescent external quantum efficiency in our p-i-n LEDs from an average of 9.8% to 13.5%, with a champion efficiency of 15.0%. The technique uses industrially available equipment and can readily be scaled up to larger areas and incorporated in other applications such as thin-film photovoltaic cells.

Inside the ovonic threshold switching (OTS) device based on GeSbSeN: Structural analysis under electrical and thermal stress

In this article, we present the structural investigation by Raman spectroscopy of GeSbSeN ovonic threshold switching (OTS) material once integrated in selector devices featuring a top electrode based on a transparent and conductive indium tin oxide layer. The devices are characterized by standard electrical protocols, and the structural evolution of the material is investigated after several switching operations. The results are correlated with the spectra obtained from blanket samples annealed at increasing temperature and are supported by XRD and TEM analyses. We establish a link between the evolution of the material structure with the annealing process and the device behavior along cycling, bringing important advancement in the understanding of the switching mechanism and of the origin of the failure in OTS devices.

Characteristics of High-Power Impulse Magnetron Sputtering ITO/Ag/ITO Films for Application in Transparent Micro-LED Displays

In this study, a blue transparent micro-LED display with a chip size of 20 μm × 20 μm, a pixel density of 152 PPI, a pixel spacing of 150 μm, and a resolution of 64 × 32 has been fabricated. ITO/Ag/ITO transparent layers were deposited by high-power impulse magnetron sputtering. Sheet resistance was used to analyze the electrical properties of the indium tin oxide (ITO) layers, whereas scanning electron microscopy, transmission electron microscopy, and atomic force microscopy were used to examine the surface morphology. These results demonstrate that the ITO/Ag/ITO structure with 20 nm thick Ag has a lower sheet resistance (3.36 Ω/sq) and sufficient visible light transmittance (80.45%). The visible light transmittance of the ITO/Ag/ITO layers increased to 86% after rapid thermal annealing. In addition, surface roughness was minimized, and sheet resistance was further reduced, resulting in ohmic contact on n-GaN that is suited for applications involving transparent micro-LED displays.

Simple electrically tunable liquid crystal spatial phase modulator.

We describe multiple optical functionalities obtained with a simple electrically tunable liquid crystal element that can be controlled by 4 electrodes, which are connected to a serpentine shaped transparent indium tin oxide layer. We experimentally demonstrate that the device is capable of dynamically generating refractive index distributions corresponding to a standard spherical lens, axicon, cylindrical lens, and prism. The dynamic switching of the device between these different operation modes is done in a very simple electronic way. We think that this element has a significant potential for applications in adaptive imaging, optogenetics, photonic integrated circuits, etc.

Understanding Silicon Heterojunction Solar Cells with nc‐SiC/SiO2as an Alternate Transparent Passivating Front Contact and Computational Design Optimization

The potential performance of silicon heterojunction solar cells applying transparent passivating contact (TPC) at the front side, based on a nc‐SiC:H/SiO2layer stack, is modeled and investigated. Herein, a complete multiscale electro‐optical device model of TPC solar cells is developed. The model is then used to understand and analyze such cells and search for potential conversion efficiency improvement paths. The influences of contact layer thicknesses and other properties on device performance are studied. An algorithm‐based optimization of cell electro‐optical performance is performed. It is implemented by coupling a genetic algorithm with a finite element method‐based TPC solar cell device model. Optimum front contact layer thicknesses are calculated. For optically optimized TPC contact layer thicknesses, an optical improvement of around 0.5 mA cm−2is found. Moreover, for complete electro‐optical optimization of TPC layers, about 0.27% absolute value increment in power conversion efficiency is calculated. At the rear side, proper designing of optimizing carrier transport using active dopant concentration of p‐type a‐Si:H layer and indium tin oxide layer has shown a potential to reach power conversion efficiency beyond 25%.

Electrically tunable conducting oxide metasurfaces for high power applications

Abstract Active metasurfaces designed to operate at optical frequencies are flat optical elements that can dynamic, subwavelength-scale wavefront control of reflected or transmitted light. The practical and fundamental power-handling limits of active metasurfaces at high pulse energies and high average powers determine the potential applications for these emerging photonic components. Here, we investigate thermal performance limits of reflective gate-tunable conducting oxide metasurfaces illuminated with high power density laser beams, for both continuous wave (CW) and pulsed laser illumination. Our gate-tunable metasurfaces use indium tin oxide (ITO) as an active material, which undergoes an epsilon-near-zero (ENZ) transition under applied electrical bias. We experimentally show that under CW illumination, there is no significant change in the electrically tunable metasurface optical response for high irradiances ranging from 1.6 kW/cm2 to 9.1 kW/cm2 when the illuminating laser beam diameter is 7 μm. Even under an applied bias, when over 60% of the incoming light is absorbed in a 1 nm–thick charge accumulation layer within ITO, the local temperature rise in the metasurface is modest, supporting its robustness for high-power applications. Additionally, we theoretically show that in the ENZ regime, the metasurface reflectance can be increased by a factor of 10 by replacing the active ITO layer with cadmium oxide (CdO). Thus conducting oxide metasurfaces can tolerate the power densities needed in higher power applications, including free space optical communications, to light detection and ranging (LiDAR), as well as laser-based additive manufacturing.

Ultra-wideband flexible radar-infrared bi-stealth absorber based on a patterned graphene.

In this work, an ultra-wideband flexible radar absorber with low infrared emissivity for a radar-infrared bi-stealth application utilizing multilayer patterned graphene is proposed. The proposed absorber consists of three layers of graphene films with different patterns, flexible substrates, lightweight foam, and a ground layer. The flexible graphene films, rather than the conventional lumped resistors, are adopted as omnidirectional resistors to achieve dual polarization and flexibility. On the top of the absorber, an infrared shielding layer (IRSL) consists of patterned Indium tin oxide (ITO) separated by a thin foam layer. Due to the low-pass characteristics and the high filling ratio of the top ITO layer, the infrared emissivity of the whole structure is reduced effectively while the radar absorption property is slightly affected. As a result, the 90% absorption band is from 1.96 GHz to 20.72 GHz (fractional bandwidth 165.4%), with a low infrared emissivity of about 0.35. Besides, a miniaturized unit is achieved with the period of 0.079 λl at the lowest absorption frequency, and the oblique angle incidence response is up to 45° for TE mode and 60° for TM mode. A plane and a bending prototype are fabricated and measured, respectively. The screen-printing technology is adopted to print the graphene resistive films, and the measurement results agree well with the simulation.

Realization of tuneable ultrabroadband interconnection for solitonic-plasmonic synapsis by exploiting epsilon near zero conducting oxides

This research introduces a novel highly efficient method to interconnect two metallic nanostrips that support the propagation of surface plasmon polariton (SPP) waves exploiting photorefractive soliton guide. The intricate design of the multilayer geometry enables light control diffraction at the metallic nanostrip’s end and reduces its angular dispersion. Moreover, the system’s on/off state can be switched by exploiting the epsilon near zero properties of the indium tin oxide (ITO) layer. The photorefractive crystal positioned between the two plasmonic waveguides enables the self-confinement of light, generating a waveguide that can be utilized by both the writing light and other wavelengths transmitted as signals. The resulting SPP waves can be efficiently recoupled in the second nanostrip, with an efficiency of around 40% across a broad range of wavelengths. This cutting-edge approach paves the way for significant advancements in the field of nanophotonics and provides a fundamental framework for the development of new, highly efficient optical interconnects in nanoscale systems. The findings of this study have implications for a wide range of applications, including nanoscale sensing, optical computing, and data communication.

Fabrication of ITO microelectrodes and electrode arrays using a low-cost CO2 laser plotter.

Good electronic (Rs = ∼5 Ω sq-1) and optical properties (transmittance: >83%) make indium tin oxide (ITO) an attractive electrode substrate. Despite the commercial availability of high-quality ITO and some low-cost methods for direct deposition being in use by now, the definition of patterns is still a concern. Putting their popularity and extensive use aside, the manufacturing of ITO electrodes so far lacks a rapid, highly reproducible, flexible, cost-effective, easy patterning process that could surpass difficult, time-consuming techniques such as lithography. Herein, we present a low-cost method based on CO2 laser irradiation for preparing ITO microelectrodes and electrode arrays. Electrodes of different sizes and shapes were examined to identify the performance of the proposed methods. Direct ablation of the ITO layer was optimized for rectangular electrodes of 25, 50, and 100 μm in width, while laser cutting of scotch tape stencils and subsequent wet etching were used to create circular electrodes with a diameter of 1.75 mm. A multielectrode array system consisting 8 of these circular electrodes was fabricated on a (25 × 25) mm2 plate, characterized electrochemically through cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM), and as an example application used for monitoring the anchoring behavior of HeLa and HepG2 cell cultures through cell-based electrochemical impedance spectroscopy. Together, the direct ablation method and preparation of laser cut stencils form a complete toolbox, which allows for low-cost and fast fabrication of ITO electrodes for a wide variety of applications. To demonstrate the general availability of the method, we have also prepared a batch of electrodes using a laser plotter in a local printing shop, achieving high intra-workshop reproducibility.

Influence of Post Processing on Thermal Conductivity of ITO Thin Films

This work presents the influence of post processing on morphology, thermal and electrical properties of indium tin oxide (ITO) thin films annealed at 400 °C in different atmospheres. The commercially available 170 nm thick ITO layers deposited on glass were used as a starting material. The X-ray diffraction measurements revealed polycrystalline structure with dominant signal from (222) plane for all samples. The annealing reduces the intensity of this peak and causes increase of (221) and (440) peaks. Atomic force microscopy images showed that the surface morphology is typical for polycrystalline layers with roughness not exceeding few nm. Annealing in the oxygen and the nitrogen-hydrogen mixture (NHM) changes shapes of grains. The electrical conductivity decreases after annealing except the one of layer annealed in NHM. Thermal conductivities of annealed ITO thin films were in range from 6.4 to 10.6 W·m-1·K-1, and they were higher than the one for starting material-5.1 W·m-1·K-1. Present work showed that annealing can be used to modify properties of ITO layers to make them useful for specific applications e.g., in ITO based solar cells.

Neural Network Design of Multilayer Metamaterial for Temporal Differentiation

AbstractControlling wave−matter interactions with metamaterials (MTMs) for the calculation of mathematical operations has become an important paradigm for analogue computing given their ability to dramatically increase computational processing speeds. Here, motivated by the importance of performing mathematical operations on temporal signals, multilayer MTMs with the ability to calculate the derivative of temporally modulated signals are proposed, designed, and studied. To do this, a neural network (NN) based algorithm is used to design the multilayer structures (alternating layers of indium tin oxide (ITO) and titanium dioxide (TiO2)) that can calculate the first temporal derivative of the envelope of an impinging electromagnetic signal modulated at telecom wavelengths (1550 nm). Different designs are presented using multiple incident temporal signals including a modulated Gaussian as well as modulated arbitrary functions, demonstrating an excellent agreement between the predicted results (NN results) and the theoretical (ideal) values. It is shown how the proposed NN‐based algorithm can complete its search of the design space for the layer thicknesses of the multilayer MTM after just a few seconds, with a low mean square error in the order of (or below) 10−4 when comparing the predicted results with the theoretical spectrum of the ideal temporal derivative.

Effects of voltage variation on heat and stress distributions in the electrochromic glass

Electrochromic glass has been used in many applications, such as the building envelope, because its light filtration can be adjusted in a controllable manner using low input energy. Electrochromic glass is a composite glass that consists of five layers. These five layers have two layers of glass, two layers of Indium Tin Oxide (ITO) and a layer of Poly (3-hexylthiophene), which is an electrochromic film. When a current passes through the glass, a voltage difference occurs, resulting in a redox reaction at an electrode layer. This causes the glass to change colour from transparent to opaque, resulting in a change in radiation absorption, which affects the heat transfer process. The study investigates temperature and thermal stress distributions in electrochromic glass by adjusting an input voltage in a range of 0–2.6 V. The spectral absorbance data at all light spectrum ranges were experimentally obtained. The averaged absorbance data were used for calculating the heat generation rate, and used as the input parameter for three-dimensional (3D) multiphysics simulations. The maximum temperature and thermal stress of the electrochromic glass are reached at 1.8 V according to the high rate of heat generation. The peak value of stress occurs at the interface between ITO and electrochromic layers. This study provides information regarding the heat transfer process and the stress induced in the electrochromic glass which varies with the applied voltages and can be applied to glass industries and many other related fields.

Mapping the Optomechanical Coupling Mediated by Light among Mechanical Resonators Including Multilayer Cavity and Molecules

For a wide range of health applications, label-free sensing is essential, and microphotonics offers innovative technical solutions for pursuing important objectives. It has been shown that the strong light/matter coupling formed between a cavity and molecules through light excitation enhances biological and clinical applications by providing deep insights into molecular analysis. The multilayer cavity’s proposed architecture is meant to promote a robust interaction between light and matter. The top layer was made of silver Ag multishape features that, after being synthesized and characterized, were immobilized on the surface of a multilayer system. A layer of indium tin oxide (ITO) was flipped to produce two distinct layouts. An investigation of the mode behavior was conducted to describe the two layouts; experimental and numerical results point to a strong light/matter interaction by the ITO/SiO2/spacer/Ag design. For the characterization of light/matter coupling, a fluorophore was adsorbed on the surface; the anticrossing energy was then examined by integrating the experimental data with a three mechanical oscillator model. To show the system’s sensitivity, the analysis was carried out again using bovine serum albumin (BSA). The protein is water-soluble and exhibits an infrared absorption band (amide I), while also being active in the Raman region. In addition, it may consistently bind to Ag multishape features. The excellent sensitivity was demonstrated, enabling the use of image analysis to capture the surface-enhanced Raman scattering of BSA. In conclusion, the suggested sensing approach raises fresh possibilities for highly sensitive biomolecule detection method and encourages results when used as a fundamental sensing technique to investigate molecular patterns.

THz Radiation Efficiency Enhancement from Metal-ITO Nonlinear Metasurfaces.

Strong single-cycle THz emission has been demonstrated from nonlinear plasmonic metasurfaces, when excited by femtosecond laser pulses. In order to invoke a higher nonlinear response, such metasurfaces have been coupled to thin indium-tin-oxide (ITO) films, which exhibit an epsilon-near zero (ENZ) behavior in the excitation wavelength range and enhance the nonlinear conversion. However, the THz conductivity of the ITO film also reduces the radiation efficiency of the meta-atoms constituting the metasurface. To overcome this, we etch the ITO layer around the plasmonic meta-atoms, which allows harnessing of the enhanced localized fields due to the ENZ behavior of the remaining ITO film, while improving the THz radiation efficiency. We report an increase of more than 1 order of magnitude in the emitted THz spectral power density, while the energy conversion efficiency approaches 10-6. This simple yet very effective fabrication scheme provides important progress toward increasing the range of applications of nonlinear plasmonic metasurface THz emitters.

A novel passivating contact approach for enhanced performance of crystalline silicon solar cells

Passivated contacts based on ultrathin silicon oxide (SiOx) layers and phosphorus-doped nanocrystalline silicon oxide (nc-SiOx(n)) layers have been examined for their application in tunnel oxide-passivated contact (TOPCon) solar cells. Passivated contact nc-SiOx(n)/SiOx, is accomplished by implementing a thermally grown SiOx tunnel layer and a plasma-enhanced chemical vapor deposited (PECVD)-grown nc-SiOx(n) layer, which are subsequently transformed into a more crystalline phase by annealing at a higher temperature. In this research, a 3.2 × 3.2 cm solar cell was fabricated, where the base material was n-type crystalline silicon (c-Si(n)), and an aluminum oxide (Al2O3) acts as a passivation layer which helps to enhanced the passivation properties and indium tin oxide (ITO) layer was used on the front side, which could serve as an anti-reflection coating (ARC), respectively. The influence of the temperature, doping level, and thickness of nc-SiOx(n) on the surface passivation of the contacts was investigated. Superior recombination current density (Jo) values of up to 2.9 fA/cm2 were assessed for the nc-SiOx(n)/SiOx contacts. TOPCon solar cells with top boron-doped emitter, Al2O3, and ITO/rear stack of nc-SiOx(n)/SiOx passivation contacts were formed and resulted in Voc = 650 mV and FF = 78%. Furthermore, we focused on ameliorating the achievements of solar cells using a transparent passivating contact-based nc-SiOx(n), as well as the passivation process and operating principle.