Semiconductor Research Articles

Semiconductor-ferromagnet-superconductor planar heterostructures for 1D topological superconductivity

Hybrid structures of semiconducting (SM) nanowires, epitaxially grown superconductors (SC), and ferromagnetic-insulator (FI) layers have been explored experimentally and theoretically as alternative platforms for topological superconductivity at zero magnetic field. Here, we analyze a tripartite SM/FI/SC heterostructure but realized in a planar stacking geometry, where the thin FI layer acts as a spin-polarized barrier between the SM and the SC. We optimize the system’s geometrical parameters using microscopic simulations, finding the range of FI thicknesses for which the hybrid system can be tuned into the topological regime. Within this range, and thanks to the vertical confinement provided by the stacking geometry, trivial and topological phases alternate regularly as the external gate is varied, displaying a hard topological gap that can reach half of the SC one. This is a significant improvement compared to setups using hexagonal nanowires, which show erratic topological regions with typically smaller and softer gaps. Our proposal provides a magnetic field-free planar design for quasi-one-dimensional topological superconductivity with attractive properties for experimental control and scalability.

New insights and advances on pyomelanin production: from microbial synthesis to applications.

Pyomelanin is a brown-black phenolic polymer and results from the oxidation of homogentisic acid (HGA) in the L-tyrosine pathway. As part of the research for natural and active ingredients issued from realistic bioprocesses, this work re-evaluates the HGA pigment and makes an updated inventory of its syntheses, microbial pathways, and properties, with tracks and recent advances for its large-scale production. The mechanism of the HGA polymerization is also well documented. In alkaptonuria, pyomelanin formation leads to connective tissue damage and arthritis, most probably due to the ROS issued from HGA oxidation. While UV radiation on human melanin may generate degradation products, pyomelanin is not photodegradable, is hyperthermostable, and has other properties better than L-Dopa melanin. This review aims to raise awareness about the potential of this pigment for various applications, not only for skin coloring and protection but also for other cells, materials, and as a promising (semi)conductor for bioelectronics and energy.

Conjugated Polymers for Microwave Applications: Untethered Sensing Platforms and Multifunctional Devices.

In the past two decades, organic electronic materials have enabled and accelerated a large and diverse set of technologies, from energy-harvesting devices and electromechanical actuators, to flexible and printed (opto)electronic circuitry. Among organic (semi)conductors, organic mixed ion-electronic conductors (OMIECs) are now at the center of renewed interest in organic electronics, as they are key drivers of recent developments in the fields of bioelectronics, energy storage, and neuromorphic computing. However, due to the relatively slow switching dynamics of organic electronics, their application in microwave technology, until recently, has been overlooked. Nonetheless, other unique properties of OMIECs, such as their substantial electrochemical tunability, charge-modulation range, and processability, make this field of use ripe with opportunities. In this work, the use of a series of solution-processed intrinsic OMIECs is demonstrated to actively tune the properties of metamaterial-inspired microwave devices, including an untethered bioelectrochemical sensing platform that requires no external power, and a tunable resonating structure with independent amplitude- and frequency-modulation. These devices showcase the considerable potential of OMIEC-based metadevices in autonomous bioelectronics and reconfigurable microwave optics.

Evolution of Selective Contacts in Photoelectrochemical Devices

The presence of a carrier selective contact is fundamental for photoelectrochemical (PEC) optoelectronic devices which convert solar energy to chemical/electrical energy. For example, during the overall water splitting (OWS) reaction in an acidic electrolyte, the generated electrons and holes must selectively transport to their respective contacts where they reduce protons and oxidize water, forming H2(g) and O2(g) respectively. Often, bare semiconductor (SEM) absorbers are poor catalysts and metals (or metal oxides) (CAT) are alternatively used, although forming a new junction with the underlying SEM. In some cases, the CAT/SEM junction does not theoretically form the required carrier selective junction. A real photocathode consisting of a p-InP and Pt junction should theoretically form an ohmic or non-selective junction, however, this photocathode efficiently reduces protons in operation. In extension, many single OWS particles decorated with cocatalysts theoretically would not form selective contacts producing sufficient open-circuit voltages required to split water (by simple thermionic-emission theory alone). This is further debated in the mechanism for carrier separation during photoelectrodeposition of catalyst in such OWS particles. Here, we exploited conductive probe microscopies and surface-sensitive spectroscopies to reveal the underlying mechanism driving carrier separation towards selective contacts such as alloying transformation and heterojunction formation in the Pt/p-InP system. Additionally, I will demonstrate the unique behavior of nanoscopic electrical contacts by individual characterization (operando and in-situ), demonstrating selectivity by a manifestation of the pinch-off effect. On the Pt/p-InP model system, individual contact selectivity, by the pinch-off effect, on a chemically controlled surface seen in Figure 1.a later evolves due to the formation of an InOx/p-InP heterojunction after operation (after CV). Furthermore, we investigate SrTiO3 as a planar model system proxy to OWS particles and show only small variation in the oxygen evolution reaction (OER) current in macroscopic cyclic voltammograms of <100> and <110> terminated surfaces (Figure 1.b). By revealing the underlying mechanisms and the degree that they play, PEC devices can be engineered utilizing an optimal absorber and catalyst whilst their pristine junction would theoretically be non-selective or producing an insufficient photovoltage. Figure 1

Investigation on effect of semiconducting screen on space charge behaviour of polypropylene‐based polymers for HVDC cables

High voltage direct current (HVDC) power transmission cable is critical for realising sustainability through renewable energy revolution. Eco-friendly thermoplastic polypropylene (PP)-based polymers/nanocomposites are regarded as promising candidates for replacing current thermoset crosslinked polyethylene (XLPE) cables. As an essential component of the extruded HVDC cable for improving conductor/insulation interface and suppressing charge injection to insulation at high DC electrical stresses, developing semiconducting (SC) screens that are compatible with PP-based insulation is of similar importance but has not been well studied yet. This work aims at designing PP-based semiconducting screens and investigating space charge behaviours of SC/PP/SC sandwich specimen to unfold the effect of semiconducting materials, bonding methods, applied DC electric field, and temperature on charge injection, accumulation, transportation, and dissipation in PP-based insulation. Although conventional thermal, mechanical, and low field electrical characterisations demonstrated that all of the developed semiconducting materials meet the performance criteria of commercial semiconducting materials, their space charge and local electric field distribution varied significantly at high DC fields. Compared with the traditional non-bonded configuration used at lab-scale, charge injection was enhanced in hot-pressed SC/PP/SC samples with tightly bonded interfaces, which better reflects the real situation in extruded cables. High temperature further intensified charge injections. Besides, our results also revealed that high temperature and electric field strongly influence charge mobilities and consequently their distribution and local electric field in PP-based insulations.

Excitonic insulators and Gross-Neveu models

We introduce a generalized Gross-Neveu (GN) model to describe the excitonic instabilities in two different systems: a small overlap semi-metal (SM) and a small gap semi-conductor (SMC), both in two (2d) and three-dimensions (3d). We identify the excitonic order parameter (EOP) and obtain the effective potential within the Large $N$ limit approach where the GN model can be exactly solved. We obtain the excitonic insulator (EI) phase diagrams as a function of temperature, chemical potential, overlap between bands and gaps of the system. We show that the EI may undergo first- or second-order thermal transitions depending on the regime whereupon this phase is approached. We also investigate the expected thermodynamic signatures for the specific heat above the fine-tuned excitonic quantum critical point (EQCP), in both 2d and 3d, in the SMC regime. We show that the EQCP is a different kind of critical point since although the EOP vanishes at the EQCP, there is always a finite gap in the SMC regime. We find that for high temperatures, the specific heat might exhibit a scaling behavior in the form $C_V/T \propto T^{(d-z)/z}$, where $d$ is the dimension of the system and $z$ is the dynamical critical exponent. The very low temperature behavior has a dominant exponential thermally activated term due to the presence of a gap that does not vanish at the excitonic transition.

Recent advances in wide solar spectrum active W18O49-based photocatalysts for energy and environmental applications

ABSTRACT Developing a facile and proficient strategy for photocatalysis using abundant solar light will result in a clean and renewable process for solving energy and environmental pollution issues. Semiconductor (SC)-based transition metal oxides are used widely, especially, oxygen-deficient tungsten oxide (W18O49) is expected to play an important role in photocatalytic applications because of its abundance, low cost, nontoxicity, surface plasmon resonance (SPR) response, chemical stability, and efficient charge transfer nature. This current review highlights the significance of different modifications in morphological, structural, SC coupling strategies and their influence on photocatalytic applications such as; H2 evaluation, CO2 reduction, and degradation of organics/heavy metal ion treatments. Further, the charge carrier pathways in different heterojunction mechanisms and their role on the photocatalytic activity also discussed in detail. This review highlights new directions and future advancements for developing highly efficient wide-spectrum active W18O49-based SC photocatalysts.

Light-Harvesting Novel Hierarchical Porous Cu9S5–MnWO4 Hybrid Structures in Photocatalytic Oxidative Homocoupling of Alkynes and Amines

The discovery of light-harvesting materials for use in photocatalytic organic reactions has recently attracted attention, indicating the potential for utilizing renewable energy sources. A hybrid semiconductor (SC)-SC structure, Cu9S5-MnWO4, was synthesized using a simple, efficient method. The novel hierarchical porous Cu9S5-MnWO4 hybrid structures were then applied in the photocatalysis of oxidative homocoupling of alkynes and amines. The design of a heterogeneous catalyst based on a porous, SC-SC hybrid structure and low-cost Cu should generate interest in the fabrication and modification of photocatalysts for a wide range of applications.

In situ metallic copper incorporation into novel g-C3N4/ZnWO4 nanocomposite semiconductor for efficient thin film solar cell application

Developing a noble metal-based solar energy conversion device is important in energy research. Again, nanocomposites consisting metal oxide-organic framework have received tremendous attention due to their excellent charge carrier transportability. Here, we have designed a nanocomposite by mixing π-conjugated sp2 hybridized g-C3N4 with ZnWO4 nanorods in which, Cu has been loaded. The red shift of the surface plasmon resonance (SPR) peak of Cu in case of g-C3N4/Cu/ZnWO4 (CCZ) is reflected in the photoluminescence (PL) lifetime data [CCZ (τ = 8.1 ns) > ZnWO4 (τ = 6.6 ns)]. Also, the PL intensity is found to get diminished for the composite owing to the delocalization of photoexcited electrons from the conduction band of g-C3N4 to the plasmonic metal (reservoir) through ZnWO4. Thin-film semiconductor (SC) photovoltaic (PV) devices on ITO coated surface have been successfully fabricated by spin coating the as-synthesized nanocomposites in conjunction with PEDOT: PSS and the power conversion efficiency (PCE) got improved from 1.8% (ZnWO4) to 8.4% (CCZ). Further, incident photon to current conversion efficiency (IPCE) for as-designed devices were obtained to be 73% (CCZ) > 47% (g-C3N4/ZnWO4) > 10% (ZnWO4) at 475 nm. In addition, CCZ has demonstrated high thermal stability without affecting the PCE value.

Characterizing the Geometry and Quantifying the Impact of Nanoscopic Electrocatalyst/Semiconductor Interfaces under Solar Water Splitting Conditions

AbstractThe materials that are receiving the most attention in photoelectrochemical water splitting are metallic nanoparticle electrocatalysts (np‐EC) attached to the surface of a semiconductor (SC) light absorber. In these multicomponent systems, the interface between the semiconductor and electrocatalysts critically affects performance. However, the np‐EC/SC interface remains poorly understood as it is complex on atomic scales, dynamic under reaction conditions, and inaccessible to direct experimental probes. This contribution sheds light on how the electrocatalyst/semiconductor interface evolves under reaction conditions by investigating the behavior of nickel electrocatalysts (as nanoparticles and films) deposited on silicon semiconductors. Rigorous electrochemical experiments, interfacial atomistic characterization, and computational modeling are combined to demonstrate critical links between the atomistic features of the interface and the overall performance. It is shown that electrolyte‐induced atomistic changes to the interface lead to (1) modulation of the charge carrier fluxes and a dramatic decrease in the electron/hole recombination rates and (2) a change in the barrier height of the interface. Furthermore, the critical roles of nonidealities and electrocatalyst coverage due to interfacial geometry are explored. Each of these factors must be considered to optimize the design of metal/semiconductor interfaces which are broadly applicable to photoelectrocatalysis and photovoltaic research.

Drude Dispersion in the Transmission Line Modeling of Bulk Absorbers at Sub-mm Wave Frequencies: A tool for absorber optimization

Semiconductor (SC)-based bulk absorbers operating in the (sub-) THz range are discussed. The conductivities of the bulk media are described by the Drude model for electron gas where the electron density is controlled. The Drude model predicts the existence of two frequencies of interest: one associated with the scattering time of the electrons and a second associated with the plasma frequency. The dimensions of the absorbers for a specific frequency range can be minimized by tuning the doping levels. Eventually, the maximum ohmic absorption from a bulk material is achieved when the real part of the characteristic impedance of the absorber is matched to the one of the surrounding medium and the imaginary part of the characteristic impedance is high so that the power entering the material is actually transformed in heat. Using a classic transmission line representation, a matching layer is introduced to further increase the absorption capabilities of an SC slab. Measurements using a time-domain spectroscopy (TDS) system show the increased accuracy of the Drude model

Photocatalytic Performance of Perovskite and Metal-Organic Framework Hybrid Material for the Reduction of N2 to Ammonia.

The orthorhombic phase of KNbO3 perovskite has been applied for nitrogen (N2) photoreduction to ammonia (NH3). However, this material suffers from a low surface area and low ammonia production efficiency under UV light irradiation. To eliminate these barriers, we used a metal-organic framework (MOF), named as TMU-5 ([Zn(OBA)(BPDH)0.5]n·1.5DMF, where H2OBA = 4,4'-oxybis(benzoic acid) and BPDH = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene), for the synthesis of the KNbO3@TMU-5 hybrid material. KNbO3@TMU-5 achieved a NH3 production rate of 39.9 μmol·L-1·h-1·g-1 upon UV light irradiation, as compared to 20.5 μmol·L-1·h-1·g-1 recorded for KNbO3 under similar experimental conditions. Using different characterization techniques especially gas adsorption, cyclic voltammetry, X-ray photoelectron spectroscopy, photocurrent measurements, and Fourier transform infrared spectroscopy, it has been found that the higher photoactivity of KNbO3@TMU-5 in ammonia production is due to its higher surface area, higher electron-hole separation efficiency, and higher density of negative charges on Nb sites. This work shows that hybridization of conventional semiconductors (SCs) with photoactive MOFs can improve the photoactivity of the SC@MOF hybrid material in different reactions, especially kinetically complex reactions like photoconversion of nitrogen to ammonia.

Microwave absorption analysis of graphene-based hybrid nanocomposites: experimental, numerical and component level testing studies

ABSTRACT An effective nanocomposite-based microwave absorber made of polyurethane /graphene/glass/epoxy with different weight percentages of graphene (0 to 2.5 wt%) is proposed. Microstructural characterization of samples is done with the help of XRD, FESEM and TEM. Graphene crystalline structure maximum diffraction peak is observed at 26o associated interlayer d-spacing is 0.341 nm (plane 002), the same affirmed with TEM analysis. Graphene flake structure is identified from FESEM results. Firstly, experimental investigation is done using wave guide setup, later numerical model is developed using RF module in COMSOL. The experimental results reveal more than 90% absorption capability in broad bandwidth i.e., 3 GHz and maximum Reflection loss -35.9 dB is attained at 12.1 GHz. Also, maximum shielding effectiveness is -47 dB for 2.5 wt% PU/graphene composite due to its semi conduction. Further, a composite concrete block using 2.5 wt% PU/graphene is analysed using numerical model for the application of anechoic.

Electrochemiluminescence with semiconductor (nano)materials.

Electrochemiluminescence (ECL) is the light production triggered by reactions at the electrode surface. Its intrinsic features based on a dual electrochemical/photophysical nature have made it an attractive and powerful method across diverse fields in applied and fundamental research. Herein, we review the combination of ECL with semiconductor (SC) materials presenting various typical dimensions and structures, which has opened new uses of ECL and offered exciting opportunities for (bio)sensing and imaging. In particular, we highlight this particularly rich domain at the interface between photoelectrochemistry, SC material chemistry and analytical chemistry. After an introduction to the ECL and SC fundamentals, we gather the recent advances with representative examples of new strategies to generate ECL in original configurations. Indeed, bulk SC can be used as electrode materials with unusual ECL properties or light-addressable systems. At the nanoscale, the SC nanocrystals or quantum dots (QDs) constitute excellent bright ECL nano-emitters with tuneable emission wavelengths and remarkable stability. Finally, the challenges and future prospects are discussed for the design of new detection strategies in (bio)analytical chemistry, light-addressable systems, imaging or infrared devices.

Integrated Sensing Arrays Based on Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs), as one of the most promising sensing techniques, have shown various advantages compared to traditional means, which include ultra-high sensitivity, low driving voltage, and excellent biocompatibility for different bioelectrical and biochemical sensing. Moreover, to fully unleash the potential of OECT sensors, integrated sensing systems, especially OECT-based sensing arrays, are widely investigated due to spatiotemporal resolution, mechanical flexibility, high optical transparency, low power dissipation, and ease of fabrication. These advantages are attributed to the unique working mechanism of OECT, novel mixed ionic-electronic (semi)conductors, adaptable device geometry/structure, etc. In this review, advances in OECT-based sensing systems are systematically summarized, with a focus on the OECT-based sensing array. Furthermore, perspectives, concerning stability, cut-off frequency, integrating density, and power dissipation, are discussed based on recent studies on OECTs and their relevant sensor arrays. Last, a summary and an outlook of this field are provided.

New perspectives of functional metal borohydrides

The chemistry of metal borohydrides and their derivatives has expanded signficantly during the past decade involving new compositions, structures, and the diversity of associated properties. Here we provide an overview of interesting results mainly from the past few years, discussed relative to previously published results. A range of new synthesis strategies has been developed to obtain pure samples, which has allowed very detailed structural, physical, and chemical investigations. A short overview of mono- and dimetallic borohydrides is provided, including a description of the complete series of rare-earth metal borohydrides and the recently discovered ammonium metal borohydrides, where the latter has attracted interest due to an extreme hydrogen content. Metal borohydrides appear to be the most promising class of materials to achieve high cationic conductivity of divalent metals, and particularly derivatives of metal borohydrides with neutral molecules show promise as future electrolytes for new types of solid-state batteries. Furthermore, metal borohydrides display a wide range of other properties, including optical, magnetic, semi conduction and possibly superconducting properties, and are also used as a new approach for carbon capture and conversion. The aim of the present review is to highlight new trends in properties and provide an outlook with possible future applications. Here, we focus on the more recently discovered materials.

Magnetoresistance ratio of more than 1% at room temperature in germanium vertical spin-valve devices with Co2FeSi

We report the highest two-terminal magnetoresistance (MR) ratio at room temperature in semiconductor (SC)-based vertical spin-valve (VSV) devices on a silicon (Si) platform. Here, we demonstrate all-epitaxial ferromagnet (FM)–germanium (Ge)–FM VSV devices with Co2FeSi as one of two FM electrodes. In addition to the high spin polarization of Co2FeSi, the relatively low resistance in the parallel magnetization state due to the strong Fermi-level-pinning effect at the p-type Ge/Co2FeSi interface causes the enhancement in the MR ratios. As a result, we achieve two-terminal MR ratios of over 1% even at room temperature through a 20-nm-thick Ge intermediate layer in VSV devices on Si. We emphasize that the use of Co-based Heusler alloys is effective even for SC-based VSV structures on Si to obtain high MR ratios at room temperature.

Diamond Coating Reduces Nuclear Fuel Rod Corrosion at Accidental Temperatures: The Role of Surface Electrochemistry and Semiconductivity.

If we want to decrease the probability of accidents in nuclear reactors, we must control the surface corrosion of the fuel rods. In this work we used a diamond coating containing <60% diamond and >40% sp2 “soft” carbon phase to protect Zr alloy fuel rods (ZIRLO®) against corrosion in steam at temperatures from 850 °C to 1000 °C. A diamond coating was grown in a pulse microwave plasma chemical vapor deposition apparatus and made a strong barrier against hydrogen uptake into ZIRLO® (ZIRLO) under all tested conditions. The coating also reduced ZIRLO corrosion in hot steam at 850 °C (for 60 min) and at 900 °C (for 30 min). However, the protective ability of the diamond coating decreased after 20 min in 1000 °C hot steam. The main goal of this work was to explain how diamond and sp2 “soft” carbon affect the ZIRLO fuel rod surface electrochemistry and semi conductivity and how these parameters influence the hot steam ZIRLO corrosion process. To achieve this goal, theoretical and experimental methods (scanning electron microscopy, Raman spectroscopy, electrochemical impedance spectroscopy, carrier gas hot extraction, oxidation kinetics, ab initio calculations) were applied. Deep understanding of ZIRLO surface processes and states enable us to reduce accidental temperature corrosion in nuclear reactors.

MOF-based nanoscale Pt catalyst decorated SnO2 porous nanofibers for acetone gas detection

Gas sensors fabricated by metal oxide semiconductors (SMOs) exhibited promising prospect for acetone detection due to their high sensitivity, small sizes, simple operation, facile fabrication and low cost. However, the current SMOs still face diverse challenges involving high power consumption, low response, poor anti-interfering ability and weak repeatability. In this work, in order to meet the ever-increasing requirements for acetone detection, Pt nanoparticles (NPs) were embedded into ZIF-8 templates then loaded on porous SnO2 nanofibers (NFs) via electrospinning and subsequent annealing process with a control of heating rate. The gas sensing characteristics of pristine SnO2, SnO2-ZnO, and Pt-ZnO-SnO2 porous NFs were investigated. The Pt-ZnO-SnO2 porous NFs displayed an ultrahigh response (Ra/Rg = 104.26–100 ppm at 170 °C), high selectivity and low detection limit (200 ppb) to acetone during dynamic measurements. In this study, the advanced sensing behavior can be ascribed to the multi-heterojunctions construction at the interface of SnO2-ZnO, ZnO/PtO2 and SnO2/PtO2, the increasement of oxygen vacancies, as well as the electronic and chemical sensitization of Pt NPs. The well-dispersed and ultrasmall-sized Pt NPs (~3 nm) functionalized on porous SnO2 NFs also play an essential role in fabricating high-performance acetone sensors.

Structural and Functional Behaviour of Ce-Doped Wide-Bandgap Semiconductors for Photo-Catalytic Applications

Increasing the photocatalytic efficiency of earth-abundant wide-bandgap semiconductors is of high interest for the development of cheap but effective light-driven chemical conversion processes. In this study, the coupling of ZnO and TiO2 with low contents of the rare-earth Ce species aimed to assess the photo-catalytic performance of the two semiconductors (SC). Structural and optical characterizations were performed to estimate the effect of the different interactions between Zn2+, Ti4+ and Ce4+ ions, and how the photo-responsive behaviour of Ce-Ti and Ce-Zn composites was affected. Therefore, photo-catalytic tests were performed for all Ce-modified SC to assess both their photo-oxidative and photo-reductive properties. Amongst all the tested materials, only Zn-based samples resulted in being suitable for the photo-oxidation of the methylene blue (MB) organic pollutant in a synthetic-dependent fashion.