Sensitive Semiconductor Research Articles

Synthesis and Photo/Radiation Chemical Characterization of a New Redox-Stable Pyridine-Triazole Ligand.

Photocatalysis using transition-metal complexes is widely considered the future of effective and affordable clean-air technology. In particular, redox-stable, easily accessible ligands are decisive. Here, we report a straightforward and facile synthesis of a new highly stable 2,6-bis(triazolyl)pyridine ligand, containing a nitrile moiety as a masked anchoring group, using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The reported structure mimics the binding motif of uneasy to synthesize ligands. Pulse radiolysis under oxidizing and reducing conditions provided evidence for the high stability of the formed radical cation and radical anion 2,6-di(1,2,3-triazol-1-yl)-pyridine compound, thus indicating the feasibility of utilizing this as a ligand for redox active metal complexes and the sensitization of metal-oxide semiconductors (e. g., TiO2 nanoparticles or nanotubes).

Progress toward absolute calibrations of DC x-ray sources from 1keV to >30keV for Z diagnostics applications.

Numerous x-ray diagnostics at the Z facility, time-resolved and time-integrated, would benefit from a local calibrated x-ray source. For many years, Z has used low-power Manson x-ray sources to provide some characterization information for components of Z diagnostics below 30keV. More recently, we have acquired TruFocus x-ray sources, which operate at voltages up to 100kV depending on the anode material and model. These DC sources have demonstrated good stability and repeatability. Absolute calibrations of either sources or detectors usually involve another calibrated detector from another source, which has not been readily available locally. Therefore, we have adopted the strategy of characterizing a sensitive semiconductor diode detector by controlling or inferring the active volume. This characterized detector is then used to scale the Manson x-ray spectral shape as measured by an Amptek energy-resolving detector. The result agrees well with the modeled source spectrum. We can apply this technique to the TruFocus as well.

Nanomaterials: History, Production, Properties, Applications, and Toxicities

Environmental sustainability is a pressing issue that needs to be addressed immediately due to issues like climate change, pollution, and disturbances to biodiversity. These environmental problems are significantly influenced by pollutants in the atmosphere and on the ground. Semiconducting metal oxide nanostructures are crucial for the creation of smart materials that are efficient for sensing and purging hazardous chemical pollutants from our environment. Aside from the fact that present energy sources are insufficient to meet modern-day demands, they also have several unfavorable side effects. In this review, we describe how the catalytic and photocatalytic processes can assist us in solving these problems in a cost-, energy-, and environmentally-conscious way. This article covers the main concepts of nanotechnology and the lingo related to it. The study presents a brief overview of the several categories of nanomaterials that can be utilised to provide a catalytic activity that is both practical and inexpensive. According to projected trends, the study also examines the use of a number of unique approaches to improve the selectivity and sensitivity of metal oxide semiconductors. This study summarises the perspectives and outlook on upcoming developments in the field of metal oxide nanostructure research, as well as a thorough collection of the work done to date to address the challenges and current successes, highlighting the effects of nanotechnology on the environment and society.

Ladungstransferdynamiken in organisch–anorganischen hybriden Heterostrukturen – Einblicke mithilfe von Summenfrequenzspektroskopie

AbstractOrganisch–anorganische Heterostrukturen spielen eine zentrale Rolle in modernen elektronischen und optoelektronischen Anwendungen. Dazu gehören Photodetektoren und Feldeffekttransistoren sowie die Umwandlung von Solarenergie mithilfe von Photoelektroden für Farbstoffsolarzellen, photoelektrochemischen Zellen und organischen Photovoltaiksystemen. Die Leistung solcher Systeme wird zu großen Teilen durch die Dynamik des Ladungstransfers an und zwischen (inneren) Grenzflächen, z. B. zwischen einem Halbleiter mit großer Bandlücke und molekularen Sensibilisatoren und/oder Katalysatoren, bestimmt. Daher ist ein detailliertes Verständnis der Beziehung zwischen Struktur, Dynamik und Funktion solcher funktionalen Grenzflächen notwendig, um mögliche Limitationen der Leistungsfähigkeit dieser Materialien und Systeme auf molekularer Ebene zu erklären. Die Summenfrequenzspektroskopie (SFS) als grenzflächenempfindliche Technik ermöglicht es, spezifische chemische Informationen über Grenzflächen zu erhalten. Wird diese in ein Anregungs‐Abfrage‐Schema integriert, liefert sie neben solchen chemischen Erkenntnissen eine ultraschnelle Zeitauflösung. Dieser Mini‐Review‐Artikel diskutiert die Vorteile und das Potenzial der SFS für die Untersuchung von Ladungstransferdynamiken an Grenzflächen und von strukturellen Veränderungen an inneren Grenzflächen. Es wird ein wichtiger Beitrag dieser einzigartigen spektroskopischen Einblicke in ansonsten unzugängliche Grenzflächen vorgestellt, der, so hoffen wir, neue Wege für ein besseres Verständnis der funktionsbestimmenden Prozesse in komplexen Materialien aufzeigt. Damit sollen Gemeinschaften, die sich dem Design von Materialien und Bauteilen widmen, mit Spektroskopikern zusammengebracht werden.

Charge Transfer Dynamics in Organic-Inorganic Hybrid Heterostructures-Insights by Vibrational-Sum Frequency Generation Spectroscopy.

Organic-inorganic heterostructures play a pivotal role in modern electronic and optoelectronic applications including photodetectors and field effect transistors, as well as in solar energy conversion such as photoelectrodes of dye-sensitized solar cells, photoelectrochemical cells, and in organic photovoltaics. To a large extent, performance of such devices is controlled by charge transfer dynamics at and across (inner) interfaces, e.g., between a wide band gap semiconductor and molecular sensitizers and/or catalysts. Hence, a detailed understanding of the structure-dynamics-function relationship of such functional interfaces is necessary to rationalize possible performance limitations of these materials and devices on a molecular level. Vibrational sum-frequency generation (VSFG) spectroscopy, as an interface-sensitive spectroscopic technique, allows to obtain chemically specific information from interfaces and combines such chemical insights with ultrafast time resolution, when integrated as a spectroscopic probe into a pump-probe scheme. Thus, this minireview discusses the advantages and potential of VSFG spectroscopy for investigating interfacial charge transfer dynamics and structural changes at inner interfaces. A critical perspective of the unique spectroscopic view of otherwise inaccessible interfaces is presented, which we hope opens new opportunities for an improved understanding of function-determining processes in complex materials, and brings together communities who are devoted to designing materials and devices with spectroscopists.

Structure-regulated enhanced Raman scattering on a semiconductor to study temperature-influenced enantioselective identification.

Surface-enhanced Raman scattering (SERS) spectroscopy is an effective technique that can reveal molecular structure and molecular interaction details. Semiconductor-based SERS platforms exhibit multifaceted tunability and unique selectivity to target molecules as well as high spectral reproducibility. However, the detection sensitivity of semiconductors is impeded by inferior SERS enhancement. Herein, a surface and interference co-enhanced Raman scattering (SICERS) platform based on corrugated TiO2 nanotube arrays (c-TiO2 NTs) was developed, and the coupling of structural regulation and photo-induced charge transfer (PICT) effectively optimized the SERS performance of the semiconductor substrate. Due to the regularly oscillating optical properties of the c-TiO2 NTs, well-defined interference patterns were generated and the local electric field was significantly increased, which greatly promoted both the electromagnetic mechanism and PICT processes. The c-TiO2 NTs were subsequently applied as a highly sensitive SICERS substrate to investigate the mechanism of temperature influence on enantioselective identification. This identification process is related to the existence of temperature-sensitive hydrogen bonds and π-π interaction. This work demonstrates a simply prepared, low-cost, and sensitive SERS substrate that enables better investigation into molecular identification.

Influence of Different Pt Functionalization Modes on the Properties of CuO Gas-Sensing Materials.

The functionalization of noble metals is an effective approach to lowering the sensing temperature and improving the sensitivity of metal oxide semiconductor (MOS)-based gas sensors. However, there is a dearth of comparative analyses regarding the differences in sensitization mechanisms between the two functionalization modes of noble metal loading and doping. In this investigation, we synthesized Pt-doped CuO gas-sensing materials using a one-pot hydrothermal method. And for Pt-loaded CuO, Pt was deposited on the synthesized pristine CuO surface by using a dipping method. We found that both functionalization methods can considerably enhance the response and selectivity of CuO toward NO2 at low temperatures. However, we observed that CuO with Pt loading had superior sensing performance at 25 °C, while CuO with Pt doping showed more substantial response changes with an increase in the operating temperature. This is mainly due to the different dominant roles of electron sensitization and chemical sensitization resulting from the different forms of Pt present in different functionalization modes. For Pt doping, electron sensitization is stronger, and for Pt loading, chemical sensitization is stronger. The results of this study present innovative ideas for understanding the optimization of noble metal functionalization for the gas-sensing performance of metal oxide semiconductors.

Large‐Area 2D Perovskite Oxides/Organic Heterojunction Enables Highly‐Sensitive Self‐Powered Photodetector for Ultraviolet Light Communication

AbstractUltraviolet (UV)‐sensitive semiconductors play a key role in converting UV light into electric signals in a UV photodetector. Two‐dimensional (2D) oxide perovskite, as a kind of green and stable semiconductor materials, exhibits excellent UV detection capabilities. However, the non‐dense nanosheet thin film induces alternative shunts in vertical‐structured devices results in high ohmic leakage currents. Large number of oxygen vacancies in 2D oxide perovskite leads to the adsorption / desorption process of oxygen molecules that slows down the device's response speed. Therefore, an inorganic–organic heterojunction that effectively fills up the pinholes in nanosheet films, effectively suppressing the dark current of the device by 100 000 times are designed. Meanwhile, the construction of inorganic–organic heterojunctions can accelerate the charge carriers’ transporting process, resulting in a fast rise / decay response time of 0.7 ms / 8.5 ms. Moreover, the inorganic–organic heterojunction endows the device with excellent self‐powered performance, presenting a high responsivity of 60 mA W−1. This photodetector demonstrates application potential in a UV communication system with a detection angle of 30 degrees and a close‐range communication of 1.2 m.

Total ionising dose multilayer shielding optimisation for nanosatellites on geostationary transfer orbit

The rising number of proposed nanosatellite missions with Commercial Off-The-Shelf electronics to higher orbits necessitates innovative, compact, and lightweight radiation shielding. In this study, several thousand multilayer radiation shielding configurations were simulated against trapped particle spectra predicted for a geostationary transfer orbit to demonstrate how material combinations and layer structures can be selected to minimise the total ionising dose inside nanosatellites with constrained mass budgets. The Geant4 Radiation Analysis for Space (GRAS) application was used to calculate ionising dose deposition behind multilayer shielding. Thousands of planar shielding stacks were procedurally generated and simulated on top of silicon plates representing sensitive semiconductor devices. To allow for comparison between configurations, all shielding stacks had a total mass of 1.5 g/cm2, and shielding performance was evaluated based on the total ionising dose absorbed by the silicon plates. The simulations consistently show that configurations with low-atomic-number (low-Z) materials on top of high-Z materials yield the lowest doses. The two- and three-layer mass allocation optimisations demonstrate the non-linear dependence of ionising dose on mass allocation between materials. Optimised polyethylene-lead shields achieved up to 30% lower ionising doses compared to an equal mass of either of the two materials or up to 50% lower than the same mass of aluminium. Contrary to previous claims about Z-graded shielding, no significant improvements were observed for using more than two different materials, and optimisation of multilayer shields tends to reduce them to two-layer structures. Optimal multilayer radiation shielding depends on various factors and must be tailored to specific radiation environments and mission requirements. The primary contributions of this article are the methods presented for achieving this tailoring using open-source software and parallel computing. The multilayer simulations performed for this work resulted in an extensive dataset for multilayer shielding performance that enabled novel visualisations of the ionising dose dependence on shielding composition based on quantitative results.

Highly Strain-Stable Intrinsically Stretchable Olfactory Sensors for Imperceptible Health Monitoring.

Intrinsically stretchable gas sensors possess outstanding advantages in seamless conformability and high-comfort wearability for real-time detection toward skin/respiration gases, making them promising candidates for health monitoring and non-invasive disease diagnosis and therapy. However, the strain-induced deformation of the sensitive semiconductor layers possibly causes the sensing signal drift, resulting in failure in achievement of the reliable gas detection. Herein, a surprising result that the stretchable organic polymers present a universal strain-insensitive gas sensing property is shown. All the stretchable polymers with different degrees of crystallinity, including indacenodithiophene-benzothiadiazole (PIDTBT), diketo-pyrrolo-pyrrole bithiophene thienothiophene (DPPT-TT) and poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5]thiad-iazolo [3,4-c] pyridine] (PCDTPT), show almost unchanged gas response signals in the different stretching states. This outstanding advantage enables the intrinsically stretchable devices to imperceptibly adhere on human skin and well conform to the versatile deformations such as bending, twisting, and stretching, with the highly strain-stable gas sensing property. The intrinsically stretchable PIDTBT sensor also demonstrates the excellent selectivity toward the skin-emitted trimethylamine (TMA) gas, with a theoretical limit of detection as low as 0.3ppb. The work provides new insights into the preparation of the reliable skin-like gas sensors and highlights the potential applications in the real-time detection of skin gas and respiration gas for non-invasive medical treatment and disease diagnosis.

Surface Modulation of Co3O4 Yolk-Shell Spheres with Tungsten Doping for Superior Acetone Sensitivity.

This study introduces a promising technique to enhance the sensitivity of p-type semiconductors in gas-sensing applications. By utilizing a glycerate-templated synthesis approach, a unique hierarchical W-doped Co3O4 yolk-shell sphere (YSS)-based sensor was developed, exhibiting exceptional sensitivity toward acetone gas. The synthesized YSSs feature a yolk-shell structure with a diameter of approximately 500 nm and a large surface area of 117.46 m2/g, which allows for efficient gas interaction and high sensitivity toward acetone gas. Furthermore, the incorporation of tungsten (W), a non-noble metal, as a dopant significantly enhances the surface activity of Co3O4, leading to a remarkably high response of 16.5 toward 5 ppm acetone, which is substantially higher than that of the pure Co3O4 YSS (2.9). The W-doped Co3O4 YSS also exhibits excellent selectivity to other interfering gases and the ability to detect ultralow concentrations of acetone as low as 10 ppb. The proposed non-noble metal doping strategy presents a practical solution for enhancing the sensitivity and selectivity of p-type semiconductor-based gas sensors. This approach holds great potential for practical gas-sensing applications due to their affordability and abundance, making them a cost-effective and versatile alternative to noble metal-catalyzed sensors.

Covalently grafting porphyrin on SnO2 nanorods for hydrogen evolution and tetracycline hydrochloride removal from real pharmaceutical wastewater with significantly improved efficiency

The sensitization of a wide-gap oxide semiconductor with a strong visible-light-absorbing porphyrin has been evidenced as a promising approach to craft highly efficient photocatalysts towards photocatalytic hydrogen evolution and environmental remediation. However, the practical utilization of porphyrins-sensitized oxide catalysts relies on the integration mode between porphyrins and metal oxide. Herein, a novel high-performance porphyrin-sensitized oxide catalyst is constructed via covalent assembling of copper porphyrin derivative of 5-(4-azidophenyl)-10,15,20-triaminoporphyrin (CuTPP–N3) on SnO2 nanorods by click reaction for the first time. The optimized 10 %CuTPP-N3/SnO2 hybrid demonstrates remarkably enhanced photocatalytic activity in H2 evolution of 658.6 μmol g−1h−1. It is almost 78 times higher than that of pristine SnO2. It also exhibits great potential for eliminating tetracycline hydrochloride (TCH) from various aqueous solutions with high durability under visible-light irradiation. Its removal rates in deionized water, tap water and real pharmaceutical wastewater are 90.5%, 72.2% and 85%, respectively. It is almost 13 times higher than that of pristine SnO2 nanorods in deionized water. The experimental evidence indicates that the highly conjugated linker between CuTPP–N3 and SnO2 plays a critical role for facilitating photoinduced electron transfer ability. This forms an efficient Z-scheme carrier transmission system in the hybrid. Therefore, the present work affords a well-designed molecule-engineered chromophore/oxide hybrid for highly efficient application in hydrogen evolution and environmental remediation.

Solid state pelletizing for the synthesis of new Bi-doped strontium molybdate and its development as a photocatalytic precursor for Rhodamine B degradation

At present, climate change, urbanization and globalization are the main factors that affect water quality, the primary vehicle for the translocation and permanence of emerging pollutants, resulting in a danger to human health and the environment. The scheelite-type compounds have been investigated owing to their interesting photocatalytic properties in water purification trough the removal of different organic and inorganic pollutants. In this article a method solid state for doping of bismuth(III) in systems Sr1−3xBi2xΦxMoO4 with (0 ≤ x ≤ 0.225) were obtained and, likewise its pelletizing process. Subsequently, these new materials were spectroscopically characterized with photocatalytic properties and finally is describe its development as oxidant against Rhodamine B. This work can be used for the synthesis of new Bi-doped strontium molybdates, which the best photochemical properties are chosen and, in turn, it is experimentally shown how can favor its absorption in the visible region. These electronic properties can be used in near studies, for to compressive the role of bismuth(III) in sheelite as photocatalyst and, to implement its use in the degradation of persistent pollutants that affect the world's water resources.•The doping of bismuth(III) for systems Sr1−3xBi2xΦxMoO4 modified the GAP absorption and this catalytic properties using this new solid state method.•The degradation of Rhodamine B for systems Sr1−3xBi2xΦxMoO4 as case study using of this methodology allows multiple applications associated with climate change such as: the degradation of emerging pollutants and the sensitization of semiconductors with solar claims.•The role of bismuth(III) in these systems can be harnessed to design similar materials with photocatalytic properties.

Increasing crystal plane orientation ratio of n-type Bi2WO6 to enhancing surface photovoltage due to higher hole mobility

Enhancing photoelectric sensitivity of semiconductors is meaningful to develop novel photoelectric materials but still challenging for a pristine semiconductor. Here we increase the crystal plane orientation ratio for higher hole mobility to enhance the surface photovoltage of n-type Bi2WO6 depending on the anisotropy of hole mobility. A strategy of hydrothermal synthesis and post-heating is adopted to prepare Bi2WO6. The diffraction peak relative intensity of (200) crystal plane in Bi2WO6 increases with the post-heating temperature from 200 to 400 °C and then decreases. The surface photovoltage of nano-sheet Bi2WO6 is enhanced to the maximum and then decreased with the diffraction peak change of (200) crystal plane. Theory calculation shows the hole effective mass of the crystal with (200) crystal plane is smaller than that of (113), indicating the higher hole mobility in (200) plane which contributes to the enhanced photovoltaic response. The investigation paves a way to enhance the photovoltaic properties of semiconductors by increasing the hole mobility depending on surface photovoltaic technology facilely.

Ultrafine Pt-doped SnO2 mesopore nanofibers-based gas sensor for enhanced acetone sensing

There is still an urgent need to develop a highly sensitive semiconductor oxide sensor capable of detecting trace disease biomarkers within the exhaled breath. Here, we propose an electrospinning technique and annealing process to obtain platinum (Pt) nanoparticles doped ultrafine SnO2 mesopore nanofiber. As a result of the strong synergistic effect between Pt and ultrafine SnO2 mesopore nanofiber structure, the change of oxygen adsorption caused a significant increase in resistance variation. The ultrafine nanofiber structure and one-dimensional interconnection of SnO2 are beneficial to the high gas accessibility and fast recovery. The results indicated that the Pt/SnO2 sensor have a high response value (31.2 for 2 ppm acetone), rapid response-recovery times, an actual detection limit (100 ppb), and satisfactory acetone selectivity. The above results demonstrate that Pt-doped ultrafine SnO2 nanofibers are potentially helpful as non-invasive real-time diabetic diagnosis materials.

Inverse Piezoelectric and Trap Effects With Temperature Dependence in AlGaN/GaN HEMTs Under Narrowband Microwave Pulses

This article aims to study the thermal effect, inverse piezoelectric effect, and trap effect of aluminum gallium nitride (AlGaN)/gallium nitride (GaN) high-electron mobility transistors (HEMTs) with injection of narrowband (NB) microwave pulses where sensitive semiconductor devices are often disturbed or even damaged by intentionally electromagnetic interference. A series of AlGaN/GaN HEMT-based power amplifiers is designed and measured by utilizing an NB microwave system. The thermal analysis is performed by observing the temperature and thermal stress distributions over the structure and the temperature transient response in different dc conditions. Moreover, in the inverse piezoelectric analysis, the elastic energy density of AlGaN is calculated using a simulated vertical electric field and compared with the critical value of the material itself. Lastly, to fully understand these two failure mechanisms above on the device degradation, the influences of traps generated by these two effects above are investigated by analyzing the electron movement, trap behavior, and output drain current.

Accurate Cutting-Force Measurement with Smart Tool Holder in Lathe.

Cutting force in lathe work is closely related to tool wear and affects the turning quality. Direct measurement of the cutting force by measuring the strain of the tool holder is challenging because the tool holder design aims to be highly rigid in order to undertake large cutting forces. Accordingly, the most popular dynamometer designs modify the standard tool holder by decreasing the structural rigidity of the holder, which reduces the machining precision and is not widely accepted. In order to solve the issue of the low stiffness of the dynamometer reducing the machining precision, in this paper, the ultra-low strain on the tool holder was successfully detected by the highly sensitive semiconductor strain gauges (SCSG) adjacent to the blade cutting insert. However, the cutting process would generate much heat, which increases the force measuring area temperature of the tool holder by about 30 °C. As a result, the readout drifted significantly with the temperature changes due to the high temperature coefficient of SCSG. To solve this problem, the temperature on the tool holder was monitored and a BP neural network was proposed to compensate for temperature drift errors. Our methods improved the sensitivity (1.14 × 10-2 mV/N) and the average relative error of the BP neural network prediction (≤1.48%) while maintaining the original stiffness of the tool holder. The smart tool holder developed possesses high natural frequency (≥6 kHz), it is very suitable for dynamic cutting-force measurement. The cutting experiment data in the lathe work show comparable performance with the traditional dynamometers and the resolution of the smart tool holder is 2 N (0.25% of total range).

Semiconductor Gas Sensors for Detecting Chemical Warfare Agents and Their Simulants

On-site detection of chemical warfare agents (CWAs) can be performed by various analytical techniques. Devices using well-established techniques such as ion mobility spectrometry, flame photometry, infrared and Raman spectroscopy or mass spectrometry (usually combined with gas chromatography) are quite complex and expensive to purchase and operate. For this reason, other solutions based on analytical techniques well suited to portable devices are still being sought. Analyzers based on simple semiconductor sensors may be a potential alternative to the currently used CWA field detectors. In sensors of this type, the conductivity of the semiconductor layer changes upon interaction with the analyte. Metal oxides (both in the form of polycrystalline powders and various nanostructures), organic semiconductors, carbon nanostructures, silicon and various composites that are a combination of these materials are used as a semiconductor material. The selectivity of a single oxide sensor can be adjusted to specific analytes within certain limits by using the appropriate semiconductor material and sensitizers. This review presents the current state of knowledge and achievements in the field of semiconductor sensors for CWA detection. The article describes the principles of operation of semiconductor sensors, discusses individual solutions used for CWA detection present in the scientific literature and makes a critical comparison of them. The prospects for the development and practical application of this analytical technique in CWA field analysis are also discussed.

Characterization and photocatalysis of visible light driven Z-scheme Bi2WO6/Bi2MoO6 heterojunction for Rhodamine B degradation

Efficient visible light sensitive semiconductors are instrumental for the effective dye degradation for the decontamination of water. Thus, the novel visible light driven photocatalysts of (1-x)Bi2WO6-xBi2MoO6 (where x = 0.05, 0.10, 0.15 and 0.20 wt%) heterostructures were synthesized using one-pot hydrothermal method. The samples were thoroughly characterized by XRD, FESEM, XPS, UV–vis DRS, FTIR and photoluminescence (PL), respectively to identify phase purity, morphology, oxidation states, optical band gap, vibrational groups and charge recombination. The photodegradation studies carried out on Rhodamine B dye by these heterostructures under visible light displayed that 0.90Bi2WO6/0.10Bi2MoO6 heterostructure exhibited the optimum degradation for 4 hrs than that of Bi2WO6 and Bi2MoO6. The interplay between the optical band gaps and the redox potentials of Bi2WO6 and Bi2MoO6 endowed these heterostructures for the effective charge separation resulting in the active participation for the adequate photodegradation. The results of scavenger’s data affirmed that ∙O2- and h+ radicals played superior role comparably with OH∙ radicals for dye degradation. The charge accumulation via Z-scheme formed between Bi2WO6 and Bi2MoO6 heterojunction causes these heterostructures to exhibit the improved PCA.

Co/Au bimetal synergistically modified SnO2-In2O3 nanocomposite for efficient CO sensing

For improving the sensitivity and selectivity of metal oxide semiconductor (MOS) materials to CO, Co/Au bimetal modified SnO2-In2O3 nanocomposite was prepared to fabricate MOS gas sensors and tested the gas-sensing performance. The results showed that 1 mol%Au decorated 3 mol%Co-doped SnO2-In2O3 nanocomposite (1Au-40ISC0.03O, the mole ratio of Sn0.97Co0.03O2 to In2O3 is 3:1) exhibited the response of 14.01 towards 1000ppm CO at 400 °C, which was about 7.5 and 2.3 times higher than that of pristine SnO2 and 40ISO (the mole ratio of SnO2 to In2O3 is 3:1), respectively. Besides, it showed a rapid response time of 4s and good selectivity towards CO against H2, which was about 12 times higher than that of SnO2. Furthermore, the gas sensing enhancement mechanism was revealed based on the results of XPS, UPS and UV–Vis DRS tests. It was found that the oxygen vacancy content was increased by Co doping modification, bringing about the higher baseline resistance and adsorbed oxygen content. Simultaneously, the Fermi level position of Sn0.97Co0.03O2 (SC0.03O) shifted towards the valence band by 1.08eV, resulting in the increase of potential barrier at the interface between SC0.03O and In2O3. After Au decorating, the Schottky barrier also increased due to the different work function values among Au, SC0.03O and In2O3, which were 4.8, 4.68 and 4.17eV, respectively. It facilitated the oxygen adsorption on SC0.03O and Au, improving the material sensitization. Additionally, electron exchange was greatly improved via the spill-over catalytic effect of Au, accelerating the reaction between oxygen ions and CO, and shortening the response time.