Monolithic Perovskite-Silicon Dual-Band Photodetector for Efficient Spectral Light Discrimination.

Selective spectral discrimination of visible and near-infrared light, which accurately distinguishes different light wavelengths, holds considerable promise in various fields, such as automobiles, defense, and environmental monitoring. However, conventional imaging technologies suffer from various issues, including insufficient spatial optimization, low definition, and optical loss. Herein, a groundbreaking advancement is demonstrated in the form of a dual-band photodiode with distinct near-infrared- and visible-light discrimination obtained via simple voltage control. The approach involves the monolithic stacking integration of methylammonium lead iodide (MAPbI3) and Si semiconductors, resulting in a p-Si/n-phenyl-C61-butyric acid methyl ester/i-MAPbI3/p-spiro-MeOTAD (PNIP) device. Remarkably, the PNIP configuration can independently detect the visible and near-infrared regions without traditional optical filters under a voltage range of 3 to -3 V. In addition, an imaging system for a prototype autonomous vehicle confirms the capability of the device to separate visible and near-infrared light via an electrical bias and practicality of this mechanism. Therefore, this study pushes the boundaries of image sensor development and sets the stage for fabricating compact and power-efficient photonic devices with superior performance and diverse functionality.

Hydrothermally Grown Dual-Phase Heterogeneous Electrocatalysts for Highly Efficient Rechargeable Metal-Air Batteries with Long-Term Stability.

Metal-air batteries as alternatives to the existing lithium-ion battery are becoming increasingly attractive sources of power due to their high energy-cost competitiveness and inherent safety; however, their low oxygen evolution and reduction reaction (OER/ORR) performance and poor operational stability must be overcome prior to commercialization. Herein, it is demonstrated that a novel class of hydrothermally grown dual-phase heterogeneous electrocatalysts, in which silver-manganese (AgMn) heterometal nanoparticles are anchored on top of 2D nanosheet-like nickel vanadium oxide (NiV2 O6 ), allows an enlarged surface area and efficient charge transfer/redistribution, resulting in a bifunctional OER/ORR superior to those of conventional Pt/C or RuO2 . The dual-phase NiV2 O6 /AgMn catalysts on the air cathode of a zinc-air battery lead to a stable discharge-charge voltage gap of 0.83 V at 50 mA cm-2 , with a specific capacity of 660 mAh g-1 and life cycle stabilities of more than 146 h at 10 mA cm-2 and 11 h at 50 mA cm-2 . The proposed new class of dual-phase NiV2 O6 /AgMn catalysts are successfully applied as pouch-type zinc-air batteries with long-term stability over 33.9 h at 10 mA cm-2 .

Photosensitive Nanodiscs Composed of Human Photoreceptors for Refractive Index Modulation at Selective Wavelengths.

A photoreceptor on the retina acts as an optical waveguide to transfer an individual photonic signal to the cell inside, which is determined by the refractive index of internal materials. Under the photoactivation of photoreceptors making conformational and chemical variation in a visual cell, the optical signal modulation is demonstrated using an artificial photoreceptor-based waveguide with a controlling beam refraction. Two types of nanodiscs are made of human photoreceptor proteins, short-wavelength-sensitive opsin and rhodopsin, with spectral sensitivity. The refractive index and nonlinear features of those two photosensitive nanodiscs are investigated as fundamental properties. The photonanodiscs are photoactivated in such a way that allow refractive index tuning over 0.18 according to the biological function of the respective proteins with color-dependent response.

Template-Free Preparation of a Mesopore-Rich Hierarchically Porous Carbon Monolith from a Thermally Rearrangeable Polyurea Network.

A mesopore-rich, hierarchically porous carbon monolith was prepared by carbonizing a polyisocyanurate network derived by thermal rearrangement of a polyurea network. The initial polyurea network was synthesized by the cross-linking polymerization of tetrakis(4-aminophenyl)methane (TAPM) and hexamethylene diisocyanate (HDI) in the sol-forming condition, followed by precipitation into nanoparticulate solids in a nonsolvent. The powder was molded into a shape and then heated at 200-400 °C to obtain the porous carbon precursor composed of the rearranged network. The thermolysis of urea bonds to amine and isocyanate groups, the subsequent cyclization of isocyanates to isocyanurates, and the vaporization of volatiles caused sintering of the nanoparticles into a monolithic network with micro-, meso-, and macropores. The rearranged network was carbonized to obtain a carbon monolith. It was found that the rearranged network, with a high isocyanurate ratio, led to a porous carbon with a high mesopore ratio. The electrical conductivity of the resulting carbon monoliths exhibited a rapid response to carbon dioxide adsorption, indicating efficient gas transport through the hierarchical pore structure.

Perovskite multifunctional logic gates via bipolar photoresponse of single photodetector.

The explosive demand for a wide range of data processing has sparked interest towards a new logic gate platform as the existing electronic logic gates face limitations in accurate and fast computing. Accordingly, optoelectronic logic gates (OELGs) using photodiodes are of significant interest due to their broad bandwidth and fast data transmission, but complex configuration, power consumption, and low reliability issues are still inherent in these systems. Herein, we present a novel all-in-one OELG based on the bipolar spectral photoresponse characteristics of a self-powered perovskite photodetector (SPPD) having a back-to-back p+-i-n-p-p+ diode structure. Five representative logic gates ("AND", "OR", "NAND", "NOR", and "NOT") are demonstrated with only a single SPPD via the photocurrent polarity control. For practical applications, we propose a universal OELG platform of integrated 8 × 8 SPPD pixels, demonstrating the 100% accuracy in five logic gate operations irrelevant to current variation between pixels.

Enhanced NO2 Sensing Performance of Graphene with Thermally Induced Defects.

This paper demonstrates the enhanced NO2 sensing performance of graphene with defects generated by rapid thermal annealing (RTA). A high temperature of RTA (300-700 °C) was applied to graphene under an argon atmosphere to form defects on sp2 carbon lattices. The density of defects proportionally increased with increasing the RTA temperature. Raman scattering results confirmed significant changes in sp2 bonding. After 700 °C RTA, ID/IG, I2D/IG, and FWHM (full width at half maximum)(G) values, which are used to indirectly investigate carbon-carbon bonds' chemical and physical properties, were markedly changed compared to the pristine graphene. Further evidence of the thermally-induced defects on graphene was found via electrical resistance measurements. The electrical resistance of the RTA-treated graphene linearly increased with increasing RTA temperature. Meanwhile, the NO2 response of graphene sensors increased from 0 to 500 °C and reached maximum (R = ~24%) at 500 °C. Then, the response rather decreased at 700 °C (R = ~14%). The results imply that rich defects formed at above a critical temperature (~500 °C) may damage electrical paths of sp2 chains and thus deteriorate NO2 response. Compared to the existing functionalization process, the RTA treatment is very facile and allows precise control of the NO2 sensing characteristics, contributing to manufacturing commercial low-cost, high-performance, integrated sensors.

Identifying Carrier Behavior in Ultrathin Indirect-Bandgap CsPbX3 Nanocrystal Films for Use in UV/Visible-Blind High-Energy Detectors.

High-energy radiation detectors such as X-ray detectors with low light photoresponse characteristics are used for several applications including, space, medical, and military devices. Here, an indirect bandgap inorganic perovskite-based X-ray detector is reported. The indirect bandgap nature of perovskite materials is revealed through optical characterizations, time-resolved photoluminescence (TRPL), and theoretical simulations, demonstrating that the differences in temperature-dependent carrier lifetime related to CsPbX3 (X = Br, I) perovskite composition are due to the changes in the bandgap structure. TRPL, theoretical analyses, and X-ray radiation measurements reveal that the high response of the UV/visible-blind yellow-phase CsPbI3 under high-energy X-ray exposure is attributed to the nature of the indirect bandgap structure of CsPbX3 . The yellow-phase CsPbI3 -based X-ray detector achieves a relatively high sensitivity of 83.6 µCGyair-1 cm-2 (under 1.7 mGyair s-1 at an electron field of 0.17 V µm-1 used for medical diagnostics) although the active layer is based solely on an ultrathin (≈6.6 µm) CsPbI3 nanocrystal film, exceeding the values obtained for commercial X-ray detectors, and further confirming good material quality. This CsPbX3 X-ray detector is sufficient for cost-effective device miniaturization based on a simple design.

High-Performance Photovoltaic Hydrogen Sensing Platform with a Light-Intensity Calibration Module.

Although battery-free gas sensors (e.g., photovoltaic or triboelectric sensors) have recently appeared to resolve the power consumption issue of conventional chemiresistors, severe technical barriers still remain. Especially, their signals varying under ambient conditions such as light intensity restrict the utilization of these sensors. Insufficient sensing performances (low response and slow sensing rate) of previous battery-free sensors are also an obstacle for practical use. Herein, a photovoltaic hydrogen (H2)-sensing platform having constant sensing responses regardless of light conditions is demonstrated. The platform consists of two photovoltaic units: (1) a palladium (Pd)-decorated n-IGZO/p-Si photodiode covered with a microporous zeolitic imidazolate framework-8 (ZIF-8) film and (2) a device with the same configuration, but without the Pd catalyst as a reference to calibrate the base current of sensor (1). The platform after calibration yields accurate response values in real time regardless of unknown irradiance. Besides, the sensing performances (e.g., sensing response of 1.57 × 104% at 1% H2 with a response time <15 s) of our platform are comparable with those of the conventional resistive H2 sensors, which yield unprecedented results in photovoltaic H2 sensors.

Optimized performance III-nitride-perovskite-based heterojunction photodetector via asymmetric electrode configuration.

Organometal halide perovskite photodetectors have recently drawn significant attention due to their excellent potential to perform as broadband photodetectors. However, the photoresponse in the ultraviolet (UV) spectrum can be improved by introducing wide bandgap semiconductors. In this work, we report on a methylammonium lead iodide/p-type gallium nitride (MAPI/p-GaN) heterojunction photodetector. We demonstrate that the device is capable of detecting in the UV region by p-GaN being hybridized with MAPI. We further investigate different symmetric and asymmetric metal-electrode contacts to enhance the device performance including the response time. The asymmetric electrode configuration is found to be the most optimal configuration which results in high photoresponse (photo-responsivity is 55 mA W-1 and fall time < 80 ms). As the light illumination occurs through the GaN side, its presence ultimately reduces MAPI degradation due to efficient absorption of the UV photons by GaN film.

Solar-Blind Self-Powered Photodetector Using Solution-Processed Amorphous Core-Shell Gallium Oxide Nanoparticles.

Solution-processed deep ultraviolet (DUV) photodetectors based on wide band gap oxide semiconductors (WBGS) working in the <280 nm wavelength range are drawing increasing attention of the research community because of their cost-effective production and potential use in diverse applications. Here, we report on the synthesis of novel core-shell amorphous gallium oxide nanoparticles (NPs) (a-Ga2Ox/GaOx NPs) that have not been previously obtained. The amorphous gallium oxide NPs were synthesized from gallium nitride using the femtosecond laser ablation in liquid technique. Transmission electron microscopy and electron energy-loss spectroscopy measurements revealed the amorphous NP nature with a Ga-rich core and oxide-rich shell. Optical properties of these core-shell amorphous gallium oxide NPs were investigated by time-resolved spectroscopy and photoluminescence. As a proof of concept, the amorphous gallium oxide NPs were used as an active layer in a solar-blind DUV photodetector with high responsivity (778 mA/W) at 244 nm, which is the highest responsivity recorded to date for any solution-processed DUV photodetector. This work on a high-performance solution-processed device paves the way for large-scale industrial application of the WBGS.

Improvement of the Bias Stress Stability in 2D MoS2 and WS2 Transistors with a TiO2 Interfacial Layer.

The fermi-level pinning phenomenon, which occurs at the metal-semiconductor interface, not only obstructs the achievement of high-performance field effect transistors (FETs) but also results in poor long-term stability. This paper reports on the improvement in gate-bias stress stability in two-dimensional (2D) transition metal dichalcogenide (TMD) FETs with a titanium dioxide (TiO2) interfacial layer inserted between the 2D TMDs (MoS2 or WS2) and metal electrodes. Compared to the control MoS2, the device without the TiO2 layer, the TiO2 interfacial layer deposited on 2D TMDs could lead to more effective carrier modulation by simply changing the contact metal, thereby improving the performance of the Schottky-barrier-modulated FET device. The TiO2 layer could also suppress the Fermi-level pinning phenomenon usually fixed to the metal-semiconductor interface, resulting in an improvement in transistor performance. Especially, the introduction of the TiO2 layer contributed to achieving stable device performance. Threshold voltage variation of MoS2 and WS2 FETs with the TiO2 interfacial layer was ~2 V and ~3.6 V, respectively. The theoretical result of the density function theory validated that mid-gap energy states created within the bandgap of 2D MoS2 can cause a doping effect. The simple approach of introducing a thin interfacial oxide layer offers a promising way toward the implementation of high-performance 2D TMD-based logic circuits.

Self-Patterned CsPbBr3 Nanocrystals for High-Performance Optoelectronics.

All-inorganic lead halide perovskites are promising materials for many optoelectronic applications. However, two issues that arise during device fabrication hinder their practical use, namely, inadequate continuity of coated inorganic perovskite films across large areas and inability to integrate these films with traditional photolithography due to poor adhesion to wafers. Herein, for the first time, to address these issues, we show a room-temperature synthesis process employed to produce CsPbBr3 perovskite nanocrystals with two-dimensional (2D) nanosheet features. Due to the unique properties of these 2D nanocrystals, including the "self-assembly" characteristic, the "double solvent evaporation inducing self-patterning" strategy is used to generate high-quality patterned thin films in selected areas automatically after drop-casting, enabling fabrication of high-performance devices without using complex and expensive fabrication processing techniques. The films are free from microcracks. In a proof-of-concept experiment, photodetector arrays are used to demonstrate the superior properties of such films. We provide evidence of both high responsivity (9.04 A/W) and high stability across large areas. The photodetectors fabricated on a flexible substrate exhibit outstanding photoresponse stability. Advanced optical and structural studies reveal the possible mechanism. Our simple and cost-effective method paves the way for the next-generation nanotechnology based on high-performance, cost-effective optoelectronic devices.

Facile fabrication of ZnO nanowire memory device based on chemically-treated surface defects.

In this study, we demonstrate a transistor-type ZnO nanowire (NW) memory device based on the surface defect states of a rough ZnO NW, which is obtained by introducing facile H2O2 solution treatment. The surface defect states of the ZnO NW are validated by photoluminescence characterisation. A memory device based on the rough ZnO NW exhibits clearly separated bi-stable states (ON and OFF states). A significant current fluctuation does not exist during repetitive endurance cycling test. Stable memory retention characteristics are also achieved at a high temperature of 85 °C and at room temperature. The surface-treated ZnO NW device also exhibits dynamically well-responsive pulse switching under a sequential pulse test configuration, thereby indicating its potential practical memory applications. The simple chemical treatment strategy can be widely used for modulating the surface states of diverse low-dimensional materials.

Enhanced Performance of MoS2 Photodetectors by Inserting an ALD-Processed TiO2 Interlayer.

2D molybdenum disulfide (MoS2 ) possesses excellent optoelectronic properties that make it a promising candidate for use in high-performance photodetectors. Yet, to meet the growing demand for practical and reliable MoS2 photodetectors, the critical issue of defect introduction to the interface between the exfoliated MoS2 and the electrode metal during fabrication must be addressed, because defects deteriorate the device performance. To achieve this objective, the use of an atomic layer-deposited TiO2 interlayer (between exfoliated MoS2 and electrode) is reported in this work, for the first time, to enhance the performance of MoS2 photodetectors. The TiO2 interlayer is inserted through 20 atomic layer deposition cycles before depositing the electrode metal on MoS2 /SiO2 substrate, leading to significantly enhanced photoresponsivity and response speed. These results pave the way for practical applications and provide a novel direction for optimizing the interlayer material.

Tunable graphene doping by modulating the nanopore geometry on a SiO2/Si substrate.

A tunable graphene doping method utilizing a SiO2/Si substrate with nanopores (NP) was introduced. Laser interference lithography (LIL) using a He-Cd laser (λ = 325 nm) was used to prepare pore size- and pitch-controllable NP SiO2/Si substrates. Then, bottom-contact graphene field effect transistors (G-FETs) were fabricated on the NP SiO2/Si substrate to measure the transfer curves. The graphene transferred onto the NP SiO2/Si substrate showed relatively n-doped behavior compared to the graphene transferred onto a flat SiO2/Si substrate, as evidenced by the blue-shift of the 2D peak position (∼2700 cm-1) in the Raman spectra due to contact doping. As the porosity increased within the substrate, the Dirac voltage shifted to a more positive or negative value, depending on the initial doping type (p- or n-type, respectively) of the contact doping. The Dirac voltage shifts with porosity were ascribed mainly to the compensation for the reduced capacitance owing to the SiO2-air hetero-structured dielectric layer within the periodically aligned nanopores capped by the suspended graphene (electrostatic doping). The hysteresis (Dirac voltage difference during the forward and backward scans) was reduced when utilizing an NP SiO2/Si substrate with smaller pores and/or a low porosity because fewer H2O or O2 molecules could be trapped inside the smaller pores.

High-Performance Ultraviolet-to-Infrared Broadband Perovskite Photodetectors Achieved via Inter-/Intraband Transitions.

A high-performance vertically injected broadband UV-to-IR photodetector based on Gd-doped ZnO nanorods (NRs)/CH3NH3PbI3 perovskite heterojunction was fabricated on metal substrates. Our perovskite-based photodetector is sensitive to a broad spectral range, from ultraviolet to infrared light region (λ = 250-1357 nm). Such structure leads to a high photoresponsivity of 28 and 0.22 A/W, for white light and IR illumination, respectively, with high detectivity values of 1.1 × 1012 and 9.3 × 109 Jones. Optical characterizations demonstrate that the IR detection is due to intraband transition in the perovskite material. Metal substrate boosts carrier injection, resulting in higher responsivity compared to the conventional devices grown on glass, whereas the presence of Gd increases the ZnO NRs performance. For the first time, the perovskite-based photodetector is demonstrated to extend its detection capability to IR (>1000 nm) with high room temperature responsivity across the detected spectrum, leading to a high-performance ingenious cost-effective UV-to-IR broadband photodetector design for large-scale applications.

Highly Bendable In-Ga-ZnO Thin Film Transistors by Using a Thermally Stable Organic Dielectric Layer.

Flexible In-Ga-ZnO (IGZO) thin film transistor (TFT) on a polyimide substrate is produced by employing a thermally stable SA7 organic material as the multi-functional barrier and dielectric layers. The IGZO channel layer was sputtered at Ar:O2 gas flow rate of 100:1 sccm and the fabricated TFT exhibited excellent transistor performances with a mobility of 15.67 cm2/Vs, a threshold voltage of 6.4 V and an on/off current ratio of 4.5 × 105. Further, high mechanical stability was achieved by the use of organic/inorganic stacking of dielectric and channel layers. Thus, the IGZO transistor endured unprecedented bending strain up to 3.33% at a bending radius of 1.5 mm with no significant degradation in transistor performances along with a superior reliability up to 1000 cycles.

Effect of Channel Thickness, Annealing Temperature and Channel Length on Nanoscale Ga2O3-In2O3-ZnO Thin Film Transistor Performance.

We demonstrated the effect of active layer (channel) thickness and annealing temperature on the electrical performances of Ga2O3-In2O3-ZnO (GIZO) thin film transistor (TFT) having nanoscale channel width (W/L: 500 nm/100 µm). We found that the electron carrier concentration of the channel was decreased significantly with increasing the annealing temperature (100 degrees C to 300 degrees C). Accordingly, the threshold voltage (V(T)) was shifted towards positive voltage (-12.2 V to 10.8 V). In case of channel thickness, the V(T) was shifted towards negative voltage with increasing the channel thickness. The device with channel thickness of 90 nm annealed at 200 degrees C revealed the best device performances in terms of mobility (10.86 cm2/Vs) and V(T) (0.8 V). The effect of channel length was also studied, in which the channel width, thickness and annealing temperature were kept constant such as 500 nm, 90 nm and 200 degrees C, respectively. The channel length influenced the on-current level significantly with small variation of V(T), resulting in lower value of on/off current ratio with increasing the channel length. The device with channel length of 0.5 µm showed enhanced on/off current ratio of 10(6) with minimum V(T) of 0.26 V.

Palladium Nanoribbon Array for Fast Hydrogen Gas Sensing with Ultrahigh Sensitivity.

A lithographically aligned palladium nano-ribbon (Pd-NRB) array with gaps of less than 40 nm is fabricated on a poly(ethylene terephthalate) substrate using the direct metal transfer method. The 200 µm Pd-NRB hydrogen gas sensor exhibits an unprecedented sensitivity of 10(9) % after bending treatment, along with fast sensing behavior (80% response time of 3.6 s and 80% recovery time of 8.7 s) at room temperature.

Large-Scale Nanoelectrode Arrays to Monitor the Dopaminergic Differentiation of Human Neural Stem Cells.

A novel cell-based biosensing platform is developed using a combination of sequential laser interference lithography and electrochemical deposition methods. This enables the sensitive discrimination of dopaminergic cells from other types of neural cells in a completely nondestructive manner. This platform and detection strategy may become an effective noninvasive in situ monitoring tool that can be used to determine stem cell fate for various regenerative applications.