Patterned Indium Tin Oxide Research Articles

A skin-beyond multifrequency camouflage system with self-adaptive discoloration and radar-infrared stealth

Camouflage technology could enhance the safety and security of desirable targets by concealing their signatures from the microwave, vision, infrared detection methods. However, conventional single-band camouflage fails to align with the current trends toward multi-band compatibility and intelligent adaptation. Here a bioskin-inspired multifrequency camouflaging system, including an artificial multispectral camouflage skin and an adaptive processing unit, was designed to simultaneously achieve infrared, radar, and adaptive visual stealth. This skin adopts a vertically stacked structure and utilizes a square patterned indium tin oxide for infrared stealth, a sector-box nesting silver nanowire-graphene (AgGr) metasurface for radar stealth, and a light-controlled AgGr heater to drive thermochromic displays for visible stealth. The system achieves multiband compatible properties with ultralow infrared emissivity of 0.24, high and broad microwave absorption in the 10 GHz-37.5 GHz region, and highly self-adaptive discoloration in response to background-color changes. Our work provides a reliable all-in-one design in flexible smart optoelectronics for future camouflage skin.

An Optically Transparent Metamaterial Absorber with Tunable Absorption Bandwidth and Low Infrared Emissivity

A transparent metamaterial absorber (MMA) with both tunable absorption bandwidth and low infrared (IR) emissivity is proposed in this paper. The MMA is hierarchical, which consists of an infrared shielding layer (IRSL), two radar-absorption layers (RALs), an air/water layer, and an indium–tin–oxide (ITO) backplane from the top downwards. The IRSL and the RALs are made of ITO patterns etched on polyethylene terephthalate (PET) substrates. By changing the thickness of the water, the 90% absorption bandwidth can be tuned from 6.4–11.3 GHz to 12.7–20.6 GHz, while retaining good polarization and angular stability. An equivalent circuit model (ECM) is present, to reveal the physical mechanism of absorption. The proposed MMA has a low theoretical IR emissivity of about 0.24. A sample was fabricated and measured, and the experimental results are consistent with the simulation results, showing its potential applications in stealth glass and multifunctional radome.

Fast Reconfigurable Electrode Array Based on Titanium Oxide for Localized Stimulation of Cultured Neural Network

Planar microelectrode arrays have become standard tools for in vitro neural-network analysis. However, these predefined micropatterned devices lack adaptability to target-specific cells within a cultured network. Herein, we fabricated a reconfigurable TiO2 electrode array with an anatase-brookite bicrystalline polymorphous mesoporous layer. Because of its selective absorption of ultraviolet (UV) light and corresponding photoconductivity, TiO2 electrode array was identified as a promising tool for high-resolution light-addressing. The TiO2 film was used as a semitransparent semiconductor with a high Roff/Ron ratio of 105 and a fast response time of 400 ms. In addition, the effect of UV radiation on the resistance of the TiO2 film over 30 d in an aqueous environment was analyzed, with the film exhibiting high stability. An arbitrary UV pattern was applied to a reconfigurable TiO2 electrode using a digital micromirror device (DMD), affording highly localized neural stimulation at the single-cell level. The reconfigurable TiO2 electrode with a patterned indium tin oxide (ITO) substrate enabled the independent connection of up to 60 points with external stimulators and signal recorders. We believe this technique would be helpful for electrophysiological research requiring the analysis of cell and neural-network features using a highly localized neural interface.

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.

Zooming optimization for fractional Fourier holographic parallel laser microprocessing

In this paper, a zooming relationship for holographic parallel laser foci with the fractional Fourier transform is revealed and optimized, which is beneficial for accurate control of the microfabrication of structures and micropatterning of material surfaces. Using a spatial light modulator (SLM) and a dedicated computer-generated hologram (CGH), a single Gaussian beam can be modulated into multiple laser foci to improve the microprocessing efficiency. As a new extension of fractional Fourier holography, the adjustment of the multifocal position and the detail scaling of the design target by different fractional orders was investigated by means of theoretical analysis and numerical simulation. The processing experiments for microwire pairs on a glass surface verify that the consistency between parallel microstructures is jointly determined by sampling intervals and fractional orders. Then, zooming optimization was performed for the precise and rapid patterning of indium tin oxide (ITO) films. The fractional holographic parallel laser multifocus processing method shows great potential for the processing of multilayer structural materials and complex surface topography.

Direct Emission of Focused Terahertz Vortex Beams Using Indium‐Tin‐Oxide‐Based Fresnel Zone Plates

AbstractTerahertz (THz) vortex beams with helical wavefronts promise many important applications ranging from high‐speed wireless communications to super‐resolution imaging. Conventional methods to generate THz beams mostly rely on manipulating and converting the incident THz beams. Herein is proposed and experimentally demonstrated how the patterned indium tin oxide (ITO) film, i.e., ITO Fresnel zone plate (ITO‐FZP), enables direct emission of focused THz vortex beams with desired orbital angular momentums. Such THz vortex‐beam emitters are based on the straightforward nonlinear THz emission through the patterned ITO film under femtosecond laser excitation. The proposed approach greatly integrates THz emission and vortex‐beam generation processes, which is low cost, robust, and easy to fabricate.

Disposal Immunosensor for Sensitive Electrochemical Detection of Prostate-Specific Antigen Based on Amino-Rich Nanochannels Array-Modified Patterned Indium Tin Oxide Electrode.

Sensitive detection of prostate-specific antigens (PSA) in serum is essential for the prevention and early treatment of prostate cancer. Simple and disposable electrochemical immunosensors are highly desirable for screening and mobile detection of PSAs in high-risk populations. Here, an electrochemical immunosensor was constructed based on amino-rich nanochannels array-modified patterned, inexpensive, and disposable indium tin oxide (ITO) electrodes, which can be employed for the sensitive detection of PSA. Using an amino-group-containing precursor, a vertically ordered mesoporous silica nanochannel film (VMSF) containing amino groups (NH2-VMSF) was rapidly grown on ITO. When NH2-VMSF contained template surfactant micelle (SM), the outer surface of NH2-VMSF was directionally modified by aldehyde groups, which enabled further covalent immobilization of the recognitive antibody to prepare the immuno-recognitive interface. Owing to the charge-based selective permeability, NH2-VMSF can electrostatically adsorb negatively charged redox probes in solution (Fe(CN)63-/4-). The electrochemical detection of PSA is realized based on the mechanism that the antigen-antibody complex can reduce the diffusion of redox probes in solution to the underlying electrode, leading to the decrease in electrochemical signal. The constructed immunosensor can achieve sensitive detection of PSA in the range from 10 pg/mL to 1 μg/mL with a limit of detection (LOD) of 8.1 pg/mL. Sensitive detection of PSA in human serum was also achieved. The proposed disposable immunosensor based on cheap electrode and nanochannel array is expected to provide a new idea for developing a universal immunosensing platform for sensitive detection of tumor markers.

A High-Performance Ultra-Broadband Transparent Absorber With a Patterned ITO Metasurface

A high-performance microwave absorber with simultaneously ultra-broadband microwave absorption, mechanical flexibility and high optical transparency is proposed. A patterned indium–tin–oxide (ITO) conductive metasurface is used as the upper surface resonance layer. ANSYS HFSS 15.0 was used for the infinite period structures of the absorber simulation, and the Floquet port, master-slave boundary condition and adaptive meshing were set in the software. As a result, the absorber features >90% broadband absorption, which covers a wide frequency range of 17.6 GHz (21.6-39.2 GHz) and includes part of the K and Ka frequency bands. What is more, the absorption is above 99% in the range from 30 GHz to 33.6 GHz. The optical transmittance of the absorber in the visible light band is 85%. The thickness of the absorber is only 0.1 times of the wavelength corresponding to the lowest absorption frequency (13.89 mm). Furthermore, the absorber maintains stable absorption at different incident and polarization angles due to the quadruple centrosymmetric pattern.

Polarization-Independent, tunable, broadband perfect absorber based on semi-sphere patterned Epsilon-Near-Zero films

Epsilon-near-zero (ENZ) optical materials, whose real part of the dielectric constant crosses zero, have been demonstrated to enhance linear and nonlinear optical responses in the ENZ region. Here, a new broadband light absorption design concept based on the coupling of ENZ and localized surface plasmon resonance (LSPR) modes is proposed. It is verified by a single-layer semi-sphere patterned indium tin oxide (ITO) film based on large-area and low-cost self-assembly technology. Simulation and experimental results show that the 91 nm thick ITO film on the two-dimensional microsphere array can simultaneously excite the ENZ and LSPR modes without complex coupling structures, which enable >98% light absorption in the range of 1435–1680 nm. The perfect absorber based on a corrugated ITO film has typical polarization-independent, large-angular-spectrum, adjustable-absorption-bandwidth, and field-enhanced resonance absorption characteristics. These findings provide a new design solution for low-cost broadband perfect absorbers based on ENZ materials, which have wide prospects for application in near-infrared sensors, photoelectric detection, and ENZ photonics.

A transparent ultra-broadband microwave absorber based on flexible multilayer structure

In this work, a transparent ultra-broadband microwave absorber (MA) based on flexible multilayer structure was demonstrated. The designed resonant structure consists of a resistive film pattern of indium tin oxide (ITO) on a flexible substrate PET. By adjusting the size of the resonant layer ITO pattern and the array position arrangement, an ultra-broadband absorption of over 90% is achieved in the frequency range 8.6–75.8 GHz, with a relative absorption bandwidth of 159%. At the same time, the transparent flexible medium polydimethy-lsiloxane (PDMS) and PET substrate are used to obtain good optical transmittance. Due to the quadruple symmetry of the resistive film resonance pattern, MA shows high polarization insensitivity. For TE and TM polarised waves, the proposed MA can maintain an absorption rate greater than 80% as the angle of incidence is increased to 40°. The current distribution of each resonant layer at strong resonant frequency is simulated and analysed to determine the absorption mechanism of MA. A sample consisting of 11 × 11 cells was produced and the experimental measurements were in general consistent with the numerical simulation results. Due to its ultra-wideband absorption characteristics and wide incident angle stability, it has potential application value in the fields of radar stealth system and transparent electromagnetic shielding.

Patterning Indium Tin Oxide Using Self-Assembled Monolayers as Etch Resists for Photovoltaic and Display Devices

Patterning Indium Tin Oxide Using Self-Assembled Monolayers as Etch Resists for Photovoltaic and Display Devices

Accelerated Osteogenesis of Heterogeneous Electric Potential Gradient on CFO/P(VDF‐TrFE) Membranes

AbstractPiezoelectric biomaterials are considered to be able to mimic the electrophysiological microenvironment of natural bone tissue, thus enhancing the bone regeneration. However, the effects of heterogeneous electric potential gradient of piezoelectric biomaterials on their osteogenic performance still remain elusive, largely because of the challenge of harassing the distribution of electric potential gradient on the surface of piezoelectric biomaterials. This study controls the heterogeneous electric potential gradient on the CoFe2O4/poly(vinylidene fluoride‐trifluoroethylene (CFO/P(VDF‐TrFE)) membrane by using an alternatively positive–negative polarization processing on microscaled straight‐stripe patterned indium tin oxide coated glass (ITO) electrodes. The potential gradient (Δζ) on membranes can be controlled by the stripe width and polarization parameters. Interestingly, Δζshows a significant influence on the cellular osteogenic potential of mesenchymal stem cells (MSCs) and the bone regeneration performance in vivo. The Δζof 0.672 pm/(V*µm) shows the optimal osteogenic performance both in vitro and in vivo, which can be attributed to the boost of integrins α5β1expression as well as the orientated arrangement and contractility of the cytoskeletons via mechanotransduction signaling cascades. This work therefore shows the importance of heterogeneous electric potential and provides a novel strategy to accelerate the osteogenic performances of piezoelectric biomaterials.

Laser direct patterning induced the tunable optical properties of indium tin oxide micro-hole arrays films

Here we introduce a facile method to fabricate patterned indium tin oxide (ITO) thin films via selective laser ablation at ambient conditions. By scanning the ITO thin films with focused Nd: YAG pulsed laser, the ITO thin films were selective ablated and patterned without using any conventional chemical etching or photolithography steps. Then we investigated the effects of scanning rate for the structure, morphology and optical properties of patterned ITO thin film. These results indicate that the epsilon-near-zero (ENZ) wavelength of ITO thin films can be tuned from 1100 nm to 1340 nm by adjusting the period of the micro-hole array in microstructure. The nonlinear absorption response of patterned ITO films was about 2.85 time than of the as-deposited ITO thin film. Additionally, the results of the Finite-Difference Time-Domain (FDTD) simulation are in good agreement with those of the experiments.

Heterogeneous Amplitude−Phase Metasurface for Distinct Wavefront Manipulation

Achieving simultaneously multiple distinct wavefront manipulations using a single flat plate is pivotal in increasing the integration level and information capacity of an optoelectronic system. As of today, the state‐of‐the‐art metadevices have been devoted to multiple functionalities by imparting two independent phase patterns triggered at two orthogonal polarization states. However, in fact, it is terribly challenging to realize individual amplitude−phase (A−P) control using an anisotropic metasurface. Herein, a heterogeneous strategy for achieving an A−P manipulation utilizing heterogeneous indium tin oxide (ITO) resistive films and metal patterns is demonstrated. By synergizing dual‐layer ITO films and a sandwiched dual‐mode metallic layer on a back metallic ground, the proposed meta‐atom exhibits near‐zero and near‐unity reflections for dual‐orthogonal linear polarizations. The above feature can be utilized to trigger polarization‐dependent functionalities by uniformly and inhomogeneously distributing the ITO and metallic pattern, respectively. Using this proposed architecture, two metasurfaces with integrated radiation−absorption and integrated diffusion−absorption function are implemented. Both numerical and experimental results demonstrate that two well‐designed metadevices enable to achieve a similar broadband absorptivity (above 90% within 7.8−18.5 GHz) but completely distinct wavefront manipulations triggered by two polarizations. The heterogeneous metasurface concept paves the way toward realizing high‐performance multifunctionalities with complex wavefront manipulation capabilities.

Invisible and Flexible Printed Sensors Based on ITO Nanoparticle Ink for Security Applications

Here, we propose a method to create a transparent security system based on printed conductive indium tin oxide (ITO)—the most widely used transparent conducting oxide material integrated into the devices with high transparency. Commonly used solution-processed ITO annealing methods are utilizing temperatures which are limiting the use of flexible polymeric substrates. Our method combines inkjet printing on flexible temperature-stable colorless polyimide (CPI) substrate with fast flash lamp annealing (FLA). In this study, millisecond pulses of visible light from a xenon lamp induce rapid heating of the ITO films up to 650°C through the light-absorbing additional layer of a colored organic dye onto printed ITO, whereas the CPI bulk never exceeds the melting point. Fabricated flexible ITO patterns on CPI film processed with the flash lamp annealing through the dye layer exhibit a transmittance of up to 85% at the wavelength of 550 nm and sheet resistance of 520 Ω/sq for a 70 nm layer thickness. With the proposed technology of our demonstrator realization—transparent glass/window or any other object such as a curved door lock can be used for integrating a touch-enabled transparent security access system, which would be completely invisible.

Compact multi-functional frequency-selective absorber based on customizable impedance films.

Multi-functional metamaterial absorbers have attracted considerable attention for applications in the microwave frequency regime. In this paper, we report the design, fabrication, and characterization of frequency-selective absorbers, which exhibit substantial absorption property within a pre-defined frequency band, while at the same time behaving as a highly transparent screen in another targeted frequency band. The proposed designs consist of a symmetrically patterned indium tin oxide film acting as an absorbing layer, two dielectric substrates, and a cross-slot metal sheet frequency selective surface playing the role of a transmitting layer. In order to validate the functionalities of the designed absorbers, equivalent circuit models, full-wave numerical simulations and measurements are presented. The measured results, in good agreement with the numerical ones, show that the proposed designs realize 80% broadband absorption over the desired frequency range and possess a transparent window in a higher or lower frequency band for a wide range of incidence angles up to 60°. These performances suggest that the proposed designs are promising candidates for multi-functional scattering control and communication applications.

Broadband and wide angle microwave absorption with optically transparent metamaterial

Abstract An optically transparent metamaterial for microwave absorber with wide operation angle, polarization insensitivity, broadband and high absorptivity was demonstrated. The metamaterial is composed of planar indium tin oxide (ITO) structures and low-loss glass substrates. By tailoring the reflection response of ITO patterns and the position of arrayed ITO resonators between quartz glass dielectric substrates, more than 90% absorption in the frequency ranges of 8–20 GHz and within a wide angular range from 0° to 60° is achieved. Meanwhile, by employing transparent substrates, including soda-lime glass and quartz glass, good optical transmittance (80%) is obtained. The dielectric loss of quartz glass is lower than other dielectric substrates, which implies that the high absorptivity was achieved mainly due to the contribution of planar ITO metamaterial structure. The reflectivity of proposed MMAs is simulated and measured experimentally. Both of which demonstrate excellent absorption performance of the metamaterial. The optically transparent broadband metamaterials absorber with high absorptivity and polarization insensitivity opens a horizon of potential applications in many fields.

Development of MALDI MS peptide array for thrombin inhibitor screening

The development of in situ methods for the analysis and visualization of enzyme activity is of paramount importance in drug discovery, research, and development. In this work, the functionalized and array patterned indium tin oxide (ITO) glass slides were fabricated by non-covalent immobilization of amphipathic phospholipid-tagged peptides encompassing the thrombin cleavage site on steric acid-modified ITO slides. The fabricated peptide arrays provide 60 spots per slide, and are compatible with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) measurement, free matrix peak interference, and tolerance to repeated aqueous washing. The peptide arrays were used for the investigation of thrombin activity and screening for its potential inhibitors. The thrombin activity and its Michaelis-Menten constant (Km) for immobilized peptide substrate was determined using developed MALDI MS peptide array. To investigate the applicability and effectiveness of peptide arrays, the anti-thrombin activity of grape seed proanthocyanidins with different degrees of polymerization (DP) was monitored and visualized. MALDI MS imaging results showed that the fractions of proanthocyanidins with the mean DP of 4.61–6.82 had good thrombin inhibitory activity and their half-maximal inhibitory concentration (IC50) were below 10 μg/mL. Therefore, the developed peptide array is a reliable platform for the discovery of natural thrombin inhibitors.

Indium Tin Oxide optical access for magnetic tunnel junctions in hybrid spintronic–photonic circuits

The all-optical magnetization reversal of magnetic layers, by picosecond optical pulses, is of particular interest as it shows the potential for energy-efficient and fast magnetic tunnel junction (MTJ) elements. This approach requires memory elements that are optically and electronically accessible, for optical writing and electronic read-out. In this paper, we propose the integration of indium tin oxide (ITO) as a transparent conducting electrode for magnetic tunnel junctions in integrated spintronic–photonic circuits. To provide light with sufficient energy to the MTJ free layer and allow electrical read-out of the MTJ state, we successfully integrated indium tin oxide as a top transparent electrode. The study shows that ITO film deposition by physical vapor deposition with conditions such as high source power and low O2 flow achieves smooth and conductive thin films. Increase in grain size was associated with low resistivity. Deposition of 150 nm ITO at 300 W, O2 flow of 1 sccm and 8.10−3 mbar vacuum pressure results in 4.8 × 10−4 Ω.cm resistivity and up to 80% transmittance at 800 nm wavelength. The patterning of ITO using CH4/H2 chemistry in a reactive ion etch process was investigated showing almost vertical sidewalls for diameters down to 50 nm. The ITO based process flow was compared to a standard magnetic tunnel junctions fabrication process flow based on Ta hard mask. Electrical measurements validate that the proposed process based on ITO results in properties equivalent to the standard process. We also show electrical results of magnetic tunnel junctions having all-optical switching top electrode fabricated with ITO for optical access. The developed ITO process flow shows very promising initial results and provides a way to fabricate these new devices to integrate all-optical switching magnetic tunnel junctions with electronic and photonic elements.

Study of indium tin oxide films deposited on colorless polyimide film by magnetron sputtering

Polyimide attracted most interest for its high performance as a flexible substrate of touch panels. Experimental models were built to evaluate production feasibility. The solution with monomer was coated on a glass substrate, cured at 250 °C to form a solid colorless polyimide (CPI) film. Then, a supporting layer with silicon oxide and a conducting layer with indium tin oxide (ITO) were deposited on the CPI film by magnetron sputtering. Composite with a CPI substrate and ITO patterns were prepared via a series of procedures. Test results indicated ITO film thickness and sheet resistance could be controlled by adjusting sputtering power, and the film showed smooth curves on the contour line chart. The transmittance of CPI/ITO film composite was up to 80%. The bending durability of the film was evaluated by two-point bending method, and it could be significantly improved by shielding the ITO pattern with ultraviolet cured resin as an external buffer layer. Samples with buffer layers passed 64,000 cycles bend test, and the minimum fracture radius reached 4 mm. The increase of ITO film thickness had no significant negative impact on the performance of flexible devices.