Small Active Area Research Articles

A programmable compound prism powered by triboelectric nanogenerator for highly efficient solar beam steering

Abstract Concentrator photovoltaics (CPV) has great competitiveness in replacing the conventional flat-panel PV system due to its high conversion efficiency and small cell active area. However, the accessory beam steering and concentrating optics are bulky and costly. Here we propose a programmable compound prism (PCP) powered by triboelectric nanogenerator (TENG) for solar beam steering. A disc TENG with a RC circuit could produce DC voltage signal, and the voltage signal could be tuned by varying the resistance in RC circuit. By connecting the variable DC output to the left, right and back walls of the PCP filled with DC 550 silicone oil, DI water and PMX 200 silicone oil, the two oil/water interfaces could be modulated in a programmable manner. A maximum deflection angle range of 15° was achieved in the PCP, which is 38% greater than conventional single prism with only one oil/water interface. The proposed TENG-PCP was employed to deflect an oblique incident laser beam to trigger the power generation in a multi-junction solar cell. With the operation of the proposed TENG-PCP, a 1.2 mW increment was achieved by the multi-junction solar cell, indicating the potential of boosting the CPV by the presented TENG−PCP.

Towards portable muography with small-area, gas-tight glass Resistive Plate Chambers

Imaging techniques that use atmospheric muons, collectively named under the neologism “muography”, have seen a tremendous growth in recent times, mainly due to their diverse range of applications. The most well-known ones include but are not limited to: volcanology, archaeology, civil engineering, nuclear reactor monitoring, nuclear waste characterization, underground mapping, etc. These methods are based on the attenuation or deviation of muons to image large and/or dense objects where conventional techniques cannot work or their use becomes challenging. In this context, we have constructed a muography telescope based on “mini glass-RPC” planes following a design similar to the glass-RPC detectors developed by the CALICE Collaboration and used by the TOMUVOL experiment in the context of volcano radiography, but with smaller active area (16× 16 cm2). The compact size makes it an attractive choice with respect to other detectors previously employed for imaging on similar scales. An important innovation in this design is that the detectors are sealed. This makes the detector more portable and solves the usual safety and logistic issues for gas detectors operated underground and/or inside small rooms. This paper provides an overview on our guiding principles, the detector development and our operational experiences. Drawing on the lessons learnt from the first prototype, we also discuss our future direction for an improved second prototype, focusing primarily on a recently adopted serigraphy technique for the resistive coating of the glass plates.

Plasmonic antenna coupling to hyperbolic phonon-polaritons for sensitive and fast mid-infrared photodetection with graphene

Integrating and manipulating the nano-optoelectronic properties of Van der Waals heterostructures can enable unprecedented platforms for photodetection and sensing. The main challenge of infrared photodetectors is to funnel the light into a small nanoscale active area and efficiently convert it into an electrical signal. Here, we overcome all of those challenges in one device, by efficient coupling of a plasmonic antenna to hyperbolic phonon-polaritons in hexagonal-BN to highly concentrate mid-infrared light into a graphene pn-junction. We balance the interplay of the absorption, electrical and thermal conductivity of graphene via the device geometry. This approach yields remarkable device performance featuring room temperature high sensitivity (NEP of 82 pW/sqrt{{bf{Hz}}}) and fast rise time of 17 nanoseconds (setup-limited), among others, hence achieving a combination currently not present in the state-of-the-art graphene and commercial mid-infrared detectors. We also develop a multiphysics model that shows very good quantitative agreement with our experimental results and reveals the different contributions to our photoresponse, thus paving the way for further improvement of these types of photodetectors even beyond mid-infrared range.

Dipole-dominated dissipative magnetic solitons in quasi-one-dimensional spin-torque oscillators

It is well-known that a spin-transfer torque caused by a dc electric current can excite in a two-dimensional ferromagnetic film exchange-dominated magnetic solitons, often called “spin-wave bullets”, under the condition of a negative nonlinear shift of spin wave frequency. In this work, we demonstrate that in a quasi-one-dimensional (1D) case, e.g., in a nanowire spin-Hall oscillator, it is possible to excite a stable dissipative magnetic soliton, which is dominated by the dipole-dipole interaction. This dissipative magnetic soliton can be described in the framework of a 1D Ginzburg-Landau auto-oscillator model, and has the shape similar to that of the exchange-dominated spin wave bullet, but with a different spatial localization law. The influence of the dipolar interaction makes possible the stabilization of a dissipative soliton in a relatively large (micron-sized) active area of the oscillator, which is in a sharp contrast with the two-dimensional case, where the excitation of a stable spin-wave bullet was observed only in relatively small active areas having typical sizes of the order of 100 nm. The characteristics and possible applications of these dipole-dominated spin wave bullets are discussed.

High concentration factor diffractive microlenses integrated with CMOS single-photon avalanche diode detector arrays for fill-factor improvement

Large-format single-photon avalanche diode (SPAD) arrays often suffer from low fill-factors—the ratio of the active area to the overall pixel area. The detection efficiency of these detector arrays can be vastly increased with the integration of microlens arrays designed to concentrate incident light onto the active areas and may be refractive or diffractive in nature. The ability of diffractive optical elements (DOEs) to efficiently cover a square or rectangular pixel, combined with their capability of working as fast lenses (i.e., ) makes them versatile and practical lens designs for use in sparse photon applications using microscale, large-format detector arrays. Binary-mask-based photolithography was employed to fabricate fast diffractive microlenses for two designs of SPAD detector arrays, each design having a different pixel pitch and fill-factor. A spectral characterization of the lenses is performed, as well as analysis of performance under different illumination conditions from wide- to narrow-angle illumination (i.e., to optics). The performance of the microlenses presented exceeds previous designs in terms of both concentration factor (i.e., increase in light collection capability) and lens speed. Concentration factors greater than are achieved for focal lengths in the substrate material as short as , representing a microlens f-number of 3.8 and providing a focal spot diameter of . These results were achieved while retaining an extremely high degree of performance uniformity across the 1024 devices in each case, which demonstrates the significant benefits to be gained by the implementation of DOEs as part of an integrated detector system using SPAD arrays with very small active areas.

Biosensing: Tunable Fano‐Resonant Metasurfaces on a Disposable Plastic‐Template for Multimodal and Multiplex Biosensing (Adv. Mater. 19/2020)

Metasurface fabrication techniques are costly and time consuming since they require multiple complex deposition and patterning steps to build devices with only a small active area. Digital versatile disks (DVDs) are commonly available and are used to play movies. In article number 1907160, Fatih Inci, Utkan Demirci, and co-workers utilize these DVDs to create a plastic-templated metasurface allowing the fabrication of cost-effective Fano-resonant biosensors over a large active area with layer-by-layer bio-sensing of binding intact viruses, i.e., HIV, proteins, and antibodies. Image credit: M. Giray Ögüt.

Tunable Fano-Resonant Metasurfaces on a Disposable Plastic-Template for Multimodal and Multiplex Biosensing.

Metasurfaces are engineered nanostructured interfaces that extend the photonic behavior of natural materials, and they spur many breakthroughs in multiple fields, including quantum optics, optoelectronics, and biosensing. Recent advances in metasurface nanofabrication enable precise manipulation of light-matter interactions at subwavelength scales. However, current fabrication methods are costly and time-consuming and have a small active area with low reproducibility due to limitations in lithography, where sensing nanosized rare biotargets requires a wide active surface area for efficient binding and detection. Here, a plastic-templated tunable metasurface with a large active area and periodic metal-dielectric layers to excite plasmonic Fano resonance transitions providing multimodal and multiplex sensing of small biotargets, such as proteins and viruses, is introduced. The tunable Fano resonance feature of the metasurface is enabled via chemical etching steps to manage nanoperiodicity of the plastic template decorated with plasmonic layers and surrounding dielectric medium. This metasurface integrated with microfluidics further enhances the light-matter interactions over a wide sensing area, extending data collection from 3D to 4D by tracking real-time biomolecular binding events. Overall, this work resolves cost- and complexity-related large-scale fabrication challenges and improves multilayer sensitivity of detection in biosensing applications.

Membrane InGaAsP Mach–Zehnder Modulator Integrated With Optical Amplifier on Si Platform

A high-efficiency Mach-Zehnder modulator (MZM) using InGaAsP phase shifters and a semiconductor optical amplifier (SOA) using multiple-quantum-well (MQW) are integrated on Si-waveguide circuits. Membrane structure is easy to optically couple to the widely-used 220-nm-thick Si waveguides, because both layers have comparable effective refractive indices. To integrate different bandgap III-V compound semiconductors; InGaAsP-based MQW for SOA and InGaAsP bulk for MZM, we employ epitaxial regrowth on thin-InP layer that is directly bonded on a silicon-on-insulator (SOI) wafer. Their thicknesses are smaller than the critical thickness (∼430 nm) for epitaxial growth of the InP-based layers bonded on the SOI wafer. This fabrication procedure is beneficial for the wafer-level integration of InP-based devices with different bandgaps on Si-photonic circuits. Furthermore, membrane lateral p-n and p-i-n diode structures improve the modulation efficiency of the MZM and reduce the power consumption of the SOA due to the high optical confinement factor and small active area. The integrated 300-μm-long SOA and MZM with 500-μm-long phase shifters show a fiber-to-fiber lossless operation with the SOA current of only 24 mA at room temperature. The modulation efficiency of the compact MZM is high enough for eye opening with non-return-to-zero (NRZ) signals from 28 to 40 Gbit/s. By using the SOA to amplify the signals modulated by the MZM, the fiber output power of −3.4 dBm was obtained without any significant pattern effect.

Facile one-step room temperature synthesis of PdAg nanocatalysts supported on multi-walled carbon nanotubes towards electro-oxidation of methanol and ethanol

Pd nanocatalysts still suffer from poor activity and rapid stability degradation due to incomplete oxidation reaction of methanol and ethanol. Herein, we report the facile synthesis of bimetallic PdAg supported on multi-walled carbon nanotube (MWCNT) nanocatalysts prepared via one-step room temperature chemical reduction strategy without additional of any capping agents towards the electrooxidation of methanol and ethanol in alkaline medium. During the synthesis process, reduction reaction between PdCl2, AgNO3 and NaBH4 led to bimetallic PdAg/MWCNT electrocatalysts. The results revealed that the PdAg NPs are uniformly-dispersed on the surface of MWCNT with a well-defined structure, small particle size (5.5 nm) and high surface active area (117.49 m2gPd−1). XPS results showed a strong charge transfer interaction between Pd and Ag atoms on catalytic surface. Cyclic voltammetry (CVs) results demonstrate that as-obtained PdAg/MWCNT electrocatalysts exhibit higher electrochemical activity and long-term durability for methanol and ethanol oxidation than the Pd/C (JM) electrocatalysts. Moreover, Pd3·5Ag/MWCNT electrocatalyst exhibit higher electrochemical performance in ethanol (3722mA mgPd−1) than methanol (1619.52 mA mgPd−1). This method has shown promising effect as advance strategy for the synthesis of low cost and high-performance Pd-based nanocatalysts, and for large-scale application as well.

Nitrogen-doped Diamond Nanowire Gas Sensor for the Detection of Methane

Diamond-based sensors have shown great potential in the past few years due to their unique physicochemical properties. We report on the development of high-performance nitrogen-doped ultrananocrystalline diamond (UNCD) nanowire-based methane (CH4) gas sensors, taking advantage of a large surface-to-volume ratio and a small active area offered by the 1D nanowire geometry. The morphologic surface and crystalline structures of UNCD are also characterized by using scanning electron microscopy (SEM) and Raman scattering, respectively. By using synthesized nanowire arrays combined with 4-pin electrical electrodes, prototypic highly sensitive CH4 gas sensors have been designed, fabricated and tested. Various parameters including the sensitivity, response and recovery times, and thermal effect on the performance of the gas sensor have also been investigated in order to quantitate the sensing ability. Enhanced by the small grain size and porosity of the nanowire structure, fabricated nanowire UNCD sensors demonstrated a high sensitivity to CH4 gas at room temperature down to 2 ppm, as well as fast response and recovery times which are almost 10 times faster than that of regular nanodiamond thin film based sensors.

Large-area solid oxide cells with La0.6Sr0.4CoO3-δ infiltrated oxygen electrodes for electricity generation and hydrogen production

Infiltration is an effective way to improve the performance of the oxygen electrode for solid oxide cells (SOCs). Most studies on infiltrated SOCs are carried out on button cells with a small active area. Here, we report on the preparation of large-area fuel-electrode-supported SOCs with a La0.6Sr0.4CoO3-δ (LSC) infiltrated gadolinia-doped ceria (CGO) oxygen electrode. The electrochemical performance of the resulting SOCs is examined at 4 × 4 cm2 level (active area). The cell delivers a power density of 1.08 W cm−2 at 0.6 V and 750 °C in fuel cell mode with high fuel and oxygen utilization of 52 and 57%, respectively; in electrolysis mode, the current density reaches 1.07 A cm−2 at 1.3 V and 750 °C with a steam utilization of 60%. Additionally, the influence of feed gas composition on cell performance and the short-term durability of the cell in electrolysis mode are studied. Electrochemical impedance spectroscopy (EIS) results and the post-test microstructural characterization demonstrate that there is no visible degradation of the LSC infiltrated CGO oxygen electrode after the durability test. These results highlight the potential of large-scale production of high-performance SOCs by designing nanostructured electrode via infiltration.

An 8-nW Resistor-Less Bandgap Reference Based on a Single-Branch Floating PTAT Voltage

This letter presents an ultra low-power resistor-less bandgap reference circuit, which is based on the topology of a single-branch floating proportional-to-absolute-temperature (PTAT) voltage. By using a cascode high impedance current bias technique, the single-branch PTAT voltage can be directly floating on the complementary-to-absolute-temperature (CTAT) voltage generated by the $V_{EB}$ of the bipolar transistor. Ultra low power consumption is realized by the simple topology in the proposed method, which only needs a few current branches. Fabricated in 0.13- $\mu \text{m}$ CMOS process, this letter generates a 1.252-V bandgap reference voltage. The total power consumption is 8.26 nW with a 1.4-V supply voltage. Without a resistor, this letter can achieve a small active area of 0.017 mm2. The average value of the temperature coefficient is 68 ppm/°C from −20 °C to 110 °C, and the line regulation is 0.019 %/V.

Flow-induced snap-through triboelectric nanogenerator

Recently, flow-induced vibration and aeroelastic flutter have been considered to be an attractive energy source in renewable energy harvesting systems. However, irregular and random motions in the fluid-structure coupled dynamics greatly deteriorate the consistency and efficiency of the output power performance. Here, we report a novel mechanism of a periodic snap-through triboelectric energy harvester based on the bi-stable property of structural buckling and integrated dielectric-electrode layers made of PDMS-sealed Cu nanowire-Cu mesh. Under wind, a buckled elastic sheet experiences a periodic snap-through oscillation with a rapid transition between two opposite phases. In a regime with a large distance between two side walls, the critical free-stream velocity needed to initiate snapping increases as the wall distance becomes larger. By contrast, for a small wall-distance regime, the critical velocity decreases in an inverse manner with the wall distance. In a post-equilibrium state, three contact modes including rolling contact, head-on contact, and touch and sliding contact are identified, and their appearances strongly depend on the wall distance and free-stream velocity. The electrode layer with a small active area of 5 cm by 1 cm can deliver a maximum output power of 7.3 mW at the optimal wall distance with a free-stream velocity of 9.1 m/s. The proposed snap-through TENG system exhibits power generation performance superior to that of existing flutter-based systems, suggesting its potential applications in powering electric devices.

A New Methodology Based on Hill of Value for Ore Reserve Selection in Long-Term Planning for Block Caving

The underground mining evolution for block cave mines in Chile and worldwide has made important strides in the last decades. Nonetheless, reserves determination in the initial stages of these types of projects—mainly for long-term planning—is not studied in as much detail as it should be, especially regarding the impact on the final value of the enterprise. Today, the first estimation of the size of a block cave mine, typically expressed in tons, tends to determine very large footprints and ore bodies. The resulting large-scale mine is obtained by applying the marginal cut-off grade (COG) to determine reserves. Yet, in many cases, it is possible to obtain an equal or higher benefit, extracting fewer reserves in less time, with a smaller active area, which significantly reduces the project’s uncertainty. To explore scenarios obtained by applying a higher marginal COG in the initial phases of the project, the Hill of Value methodology is used to estimate the net present value (NPV) in relation to the production rate and the COG. However, the application of this methodology considers certain simplifications that generate results which are not completely satisfactory in specific cases. This paper suggests an improvement of this method to obtain more reliable results regarding determination of a COG profile that will optimize the NPV of a block-cave project. The methodology was developed and applied in a massive polymetallic deposit with zinc, lead, and silver mineralization, corresponding to a real block caving project. The methodology provides NPV results that differ by approximately 15% in comparison to the real mine plan, while also being considerably simpler and faster to calculate. In summary, the proposed methodology provides a reasonable and fast procedure to estimate higher than marginal COG that increases the NPV of block cave mine projects.

Optimization of the TiO2 layer in DSSCs by a nonionic surfactant

Developing dye-sensitized solar cells (DSSCs) further is of utmost importance in a time of increasing energy consumption and the necessity to change to renewable energy sources. Opposite to silicon-based solar cells, DSSCs can be produced from low-cost, non-toxic materials. In addition, they can be applied on flexible substrates, enabling even utilization on textile architecture. On the other hand, reaching efficiencies in a similar order of magnitude as with silicon-based solar cells is only possible by highly pure and toxic materials. This is why optimization of DSSCs with non-toxic and affordable materials is of high interest. Here we report on the possibility to increase the TiO2 layer performance by adding a nonionic surfactant, focusing on a non-toxic electrolyte and a natural dye. Our results show that coating the semiconducting layer from a solvent including a surfactant increases the efficiency of the DSSC. To enable comparison with results of other groups which are often reported for very small active areas, we compare three different areas between 0.25 cm² and 6.0 cm² and show that the efficiencies are more than doubled for the smallest active area in comparison to the largest one. This underlines the necessity to perform more research on large-area DSSCs, e.g. by combining several smaller cells, aiming at possible applications on tents or other large textile areas.

Wearable SiPM-Based NIRS Interface Integrated With Pulsed Laser Source.

We present the design of a miniaturized probe integrating silicon photomultiplier and light-pulsing electronics in a single 2 × 2mm2 complementary metal-oxide-semiconductor (CMOS) chip which includes functional blocks such as a fast pulse-laser driver and synchronized single-photon detection circuit. The photon pulses can be either counted on-chip or processed by an external high-speed electronic module such as time-corelated single photon counting (TCSPC) unit. The integrated circuit was assembled on a printed circuit board (PCB) and also on a 2.5D silicon interposer platform of size 1 cm and interfaced with a silicon photomultiplier (SiPM), vertical cavity surface emitting laser (VCSEL) and other ancillary components such as capacitors and resistors. Our approach of integrating an optical interface to optimize light collection on the small active area and light emission from the vertical-cavity surface-emitting laser (VSCEL) will facilitate clinical adoption in many applications and change the landscape of Near Infrared Spectroscopy (NIRS) hardware commercially due to significant optode-size reduction and the elimination of optical fibers.

Nitrogen-rich graphitic carbon nitride nanotubes for photocatalytic hydrogen evolution with simultaneous contaminant degradation

Graphitic carbon nitride (g-C3N4) has aroused great concern since it applied to the photocatalytic process. However, the inherent shortcomings of bulk g-C3N4, such as small active surface area, low separation efficiency of photogenerated carriers, sluggish charge transport process, etc., result in low-level photocatalytic performance. The rich-nitrogen carbon nitride nanotubes (CNNTs) made by an easy supermolecule self-assembly method could slove these subsisting problems. The CNNTs with unique morphology possess superior separation/migration of photo-excited charge carriers and enhanced photocatalytic performance. Under irradiation with visible light (λ > 400 nm), measured with Pt (3 wt%) as co-catalyst, the CNNTs have a hydrogen evolution rate of 18.06 mmol h−1 g−1 and its apparent quantum yield (AQY) is 12.55% (420 nm). The CNNTs are also applied to degrade antibiotics with simultaneous hydrogen production, providing a method for alleviating energy crisis and environmental pollution issues. The degradation rate of bisphenol A (BPA) is 92% and simultaneously with 13.63 μmol photocatalytic hydrogen generation after irradiation for 5 h.

Porous Ultrathin NiSe Nanosheet Networks on Nickel Foam for High‐Performance Hybrid Supercapacitors

Transition metal selenides (TMSs) with excellent electrochemical activity and high intrinsic electrical conductivity have attracted considerable attention owing to their potential use in energy storage devices. However, the low energy densities of the reported TMSs, which originate from the small active surface area and poor electrolyte ion mobility, substantially restrict their application potential. In this work, porous ultrathin nickel selenide nanosheet networks (NiSe NNs) on nickel foam are fabricated by using a novel, facile method, that is, selenylation/pickling of the pre-formed manganese-doped α-Ni(OH)2 . Removal of Mn resulted in NNs with a highly porous structure. The 3D framework of the NNs and the inherent nature of the NiSe affords high ion mobility, abundant accessible activated sites, vigorous electrochemical activity, and low resistance. One of the highest specific capacities of TMSs ever reported, that is, 443 mA h g-1 (807 μAh cm-2 ) at 3.0 A g-1 , is achieved with the NNs as electrodes. The assembled NiSe NNs//porous carbon hybrid supercapacitor delivers a high energy density of 66.6 Wh kg-1 at a power density of 425 W kg-1 , with excellent cycling stability. This work provides a new strategy for the production of novel electrode materials that can be applied in high-performance hybrid supercapacitors, and a fresh pathway towards commercial applications of hybrid supercapacitors based on TMS electrodes.

Characteristics of Large Area Perovskite Solar Cells from Electrodes of Used Car Batteries

Power conversion efficiency (PCE) of perovskite solar cells increases very rapidly and more than 22% is already achieved. However, some problems still need to be resolved for mass production and commercialization, including reducing production costs and development of large area solar cells. The best PCE is reached by very small active area, mostly below 0.5 cm2 which is mostly produced by spin-coating technique. Moreover, the perovskite precursor materials, mostly lead (II) iodide (PbI2) and hole-transport materials (HTM) Spiro-OMeTAD are expensive material in perovskite solar cells. Therefore, the use of low-cost perovskite precursors and low-cost HTM materials is one way to reduce the whole production costs of perovskite solar cells. Nowadays, many groups have been developed HTM-free perovskite solar cells using carbon-based mesoscopic solar cells for low cost production and large area perovskite solar cells, although the PCE of large area perovskite solar cells is still half than that very small area prepared by spin-coating technique. Here, we report our recent study to fabricate perovskite solar cells using mesoscopic carbon-based structure consisting of glass/ITO/TiO2/ZrO2/perovskite/carbon with active area larger than 1 cm2 by use of simple screen printing technique in ambient air with high humidity. We also synthesize PbI2 as perovskite precursor material from electrodes of used car battery to reduce the cost of solar cells production. Although, the PCE is still much lower than that reported by other groups, however, our study shows that perovskite solar cells from used car battery and with active area more than 1 cm2 can be fabricated in ambient air with high humidity by use of simple screen printing technique.

Dependence of ITO‐Coated Flexible Substrates in the Performance and Bending Durability of Perovskite Solar Cells

Flexible perovskite solar cells (PSCs) is being reported on different kinds of indium tin oxide (ITO)‐coated flexible substrates such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) with varying sheet resistance. High sheet resistance and low transmittance of these substrates in comparison to glass‐ITO based rigid substrate are among the major issues in achieving high power conversion efficiency (PCE), especially with large active area due to considerably low fill factor (FF) values. With a small active cell area of 0.1 cm2, it is found that sheet resistance of these substrates do not play a dominant role and the short circuit current density (JSC) depends on the transmittance of these conducting flexible substrates producing average PCE of 12.1% with PEN‐ITO (12 Ω/□) and 11.74% for PET‐ITO (49 Ω/□). When the active cell area is increased to 1 cm2, sheet resistance seems to play a major role to maintain JSC as well as FF of the flexible PSCs giving PCE of ∼10% with PEN‐ITO (12 Ω/□) in comparison to 3.4% for PET‐ITO (49 Ω/□). In contrast to PCE results, bending durability test for 1000 cycles showed that the flexible substrates with highest sheet resistance can retain maximum PCE.