Semiconductor Particles Research Articles

Dispersion of Hydrophilic "Hedgehog" Microparticles in Liquid CO2 Mixtures.

Liquid and supercritical CO2 are nontoxic and nonflammable reaction media with pressure-variable physical properties. These states of CO2 also have high solubility limits for gas and liquid hydrocarbons, making them good candidates for "green" hydrophobic solvents in sustainable chemical technologies. However, the dispersion of hydrophilic colloidal nanoscale and microscale particles in CO2 is challenging due to the tendency of polar particles to aggregate in nonpolar media, limiting their available surface area and catalytic efficiencies. Here we show that native hydrophilic semiconductor particles can be effectively dispersed in a liquid CO2 mixture with acetonitrile (ACN) without additional chemical or mechanical dispersion techniques. Using surface corrugation as a method to prevent aggregation, we find that geometrically complex particles with a halo of stiff nanoscale spikes disperse and remain suspended longer in liquid CO2 than those without or with less prominent nanoscale corrugation. For the particles of this size and liquid CO2 mixtures, individual particle mass remains a prominent factor determining particle sedimentation rate even in the absence of aggregation. Particle dispersion and structural stability are confirmed using a combination of UV-vis spectroscopy, finite-difference time-domain modeling, and electron microscopy. The necessity of the cosolvent (ACN) indicates that particle behavior in liquid CO2 is vastly different than in traditional liquid-phase solvents and highlights the need for future studies to understand the wetting behavior of hydrophilic particles in high-pressure nonpolar environments.

Photocatalytic Hydrogen Production under Water Vapor Feeding─A Minireview

Recent advances in photocatalytic water splitting in particulate semiconductor systems have been tremendous in terms of efficiency and scalable photoreactor design. In general, photocatalyst powders are immersed in liquid water, leading to higher efficiency than gas-fed water splitting systems. Conducting a gas-phase photocatalytic reaction under water vapor, however, has several advantages versus liquid water, such as easy scalability and suppression of leaching of the catalyst components. Here, we offer a historical overview of photocatalytic water splitting under vapor feeding. Moreover, the principles of water adsorption are reviewed to understand the basic phenomena occurring on the surface of semiconductor powders. The critical role of relative humidity is identified, including water on the surface for ion conductivity, which can close the electric circuit between cathodic and anodic reaction sites. Finally, on the basis of the cross-sectional discussion of reported works in both water vapor splitting and physical property of the adsorbed water layer, how to develop the photocatalytic water vapor splitting system and the perspective of the CO2 and N2 reduction system using water vapor as an electron donor are provided.

Organic quantum dots: An ultrasmall nanoplatform for cancer theranostics.

Tumours are the second leading cause of death globally, generating alterations in biological interactions and, as a result, malfunctioning of crucial genetic traits. Technological advancements have made it possible to identify tumours at the cellular level, making transcriptional gene variations and other genetic variables more easily investigated. Standard chemotherapy is seen as a non-specific treatment that has the potential to destroy healthy cells while also causing systemic toxicity in individuals. As a result, developing new technologies has become a pressing necessity. QDs are semiconductor particles with diameters ranging from 2 to 10 nanometers. QDs have grabbed the interest of many researchers due to their unique characteristics, including compact size, large surface area, surface charges, and precise targeting. QD-based drug carriers are well known among the many nanocarriers. Using QDs as a delivery approach enhances solubility, lengthens retention time, and reduces the harmful effects of loaded medicines. Several varieties of quantum dots used in drug administration are discussed in this article, along with their chemical and physical characteristics and manufacturing methods. Furthermore, it discusses the role of QDs in biological, medicinal, and theranostic applications.

(Invited) Photo-SECM Measurements of Water Splitting at Single Semiconductor Particles

Understanding and improving the properties of photocatalysts can have important implications for energy conversion and storage. Because the activity of heterogeneous catalysts depends strongly on local atomic structures, probing (photo)catalytic reactions at specific local sites is critically important. We have recently reported the use of scanning electrochemical microscopy (SECM) for nanoscale imaging of photoelectrochemical processes at semiconductor surfaces. To illuminate a microscopic portion of the substrate surface facing the SECM probe, a glass-sealed, polished Pt tip simultaneously serves as a nanoelectrode and a light guide. In this paper, we present the results of first nanoscale SECM and photo-SECM experiments with single BiVO4 and SrTiO3 particles. Local mapping of oxygen and hydrogen fluxes produced by water splitting at single semiconductor particles was carried out using chemically modified SECM nanotips.

Bacteria–photocatalyst sheet for sustainable carbon dioxide utilization

The clean conversion of carbon dioxide and water to a single multicarbon product and O2 using sunlight via photocatalysis without the assistance of organic additives or electricity remains an unresolved challenge. Here we report a bio-abiotic hybrid system with the non-photosynthetic, CO2-fixing acetogenic bacterium Sporomusa ovata grown on a scalable and cost-effective photocatalyst sheet consisting of a pair of particulate semiconductors (La and Rh co-doped SrTiO3 (SrTiO3:La,Rh) and Mo-doped BiVO4 (BiVO4:Mo)). The biohybrid effectively produces acetate (CH3COO–) and oxygen (O2) using only sunlight, CO2 and H2O, achieving a solar-to-acetate conversion efficiency of 0.7% at ambient conditions (298 K, 1 atm). The photocatalyst sheet oxidizes water to O2 and provides electrons and hydrogen (H2) to S. ovata for the selective synthesis of CH3COO– from CO2. To demonstrate utility in a closed carbon cycle, the solar-generated acetate was used directly as feedstock in a bioelectrochemical system for electricity generation. These semi-biological approaches thus offer a promising strategy for sustainably and cleanly fixing CO2 and closing the carbon cycle. Conversion of CO2 to fuels or chemicals via artificial photosynthesis usually requires the assistance of organic additives or electricity. Now, a biohybrid system is reported consisting of a photocatalyst sheet and bacteria producing acetate and O2 from CO2 and H2O using sunlight as the sole energy input.

Platinum containing semiconductor nanomaterials based on SnO2 with Pt-additives to analyze concentration of CH4 in air

Nanosized semiconductor gas sensitive materials Pt/SnO2 were obtained by using sol-gel route, and sensors on their base were created. The nanoscale nature of semiconductor particles in Pt/SnO2 materials and aggregation of platinum clusters for the Pt/SnO2 materials with large platinum loading were confirmed by the x-ray diffraction method (XRD) and transmission electron microscopy (TEM) data. It was found that gas sensitive and catalytic properties to methane oxidation depend on the platinum content. The catalytic activity increases with an increase in the amount of introduced Pt, but the response dependence on the platinum content is extremal. The highest response to methane was found to be 9.7 for the sensors based on 1.76 wt.% Pt/SnO2 at operation temperature 325 °C. This inconsistence was explained by the role of Pt–SnO2 interface in the process of the sensor signal formation.

Erratum to: Broadband Signal Amplification Paths for Semiconductor Radiation and Particle Detectors (Review)

Erratum to: Broadband Signal Amplification Paths for Semiconductor Radiation and Particle Detectors (Review)

A Risk Assessment for Utilities to Prevent Transformer OLTC Failures Caused by Silver Sulphide Corrosion

Silver sulphide corrosion is a recently identified failure mechanism of transformer onload tap changers (OLTC). The corrosive sulphur in transformer oil reacts with the silver coated components of OLTC tap selector and forms silver sulphide films. During OLTC operation, the silver sulphide flakes can be detached from the tap selector and mix with the transformer oil. The silver sulphide is a semi conductive material. As a result, the dielectric strength in the transformer oil around the OLTC silver coated contacts or elsewhere in the transformer, wherever the semi conductive particles travel, will be reduced. Eventually, due to either high electric field stress or aged oil with a low dielectric strength, oil breakdown can occur between adjacent contacts. This can cause a catastrophic failure of the OLTC and quite often the tapping winding as well. Since such failures affect the transformer reliability, utilities are interested in methods of detecting and mitigating silver sulphide corrosion on OLTCs. This paper presents a risk assessment criterion to identify the degree of significance of silver sulphide corrosion in transformers using existing diagnostic techniques.

Reduction of depolarization field effect on ferroelectric switching process in semiconductor–relaxor ferroelectric composite

Temperature-dependent dynamic ferroelectric hysteresis of semiconductor–relaxor ferroelectric (0–3) type composite {0.30(ZnO)–0.70[(Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBTO)]} has been investigated using polarization–electric field (P–E) loops, current density–electric field (J–E) curves, and temperature-dependent dielectric permittivity. It is well known that the polarization reversal mechanism can be explained by the concept of ferroelectric domain switching kinetics, which depends strongly on the temperature. The present work ascribes the role of polar nanoregion induced thermal depolarization field on the temperature-dependent ferroelectric hysteresis loop along with polarization reversal mechanism. The present composite exhibits unique ferroelectric switching behavior above the thermal depolarization temperature (∼100 °C), which is observed in P–E and J–E loops. The depolarization field-induced pinched P–E loops of a BNBTO solid solution above Td (∼100 °C) have been significantly overcome by the incorporation of semiconductor (ZnO) particles, which extensively described the underlying mechanism in the present context. In addition, the temperature-dependent polarization reversal mechanism displays unique two-stage processes [low-T (<100 °C) and high-T (>100 °C)] for the minor loops (∼30 and 40 kV) and saturated loops (∼45 kV) as described by the electric field–temperature phase diagram. The present results may provide a distinct way to Bi0.5Na0.5TiO3-based solid solutions for high-temperature piezoelectric applications.

Photocharging of Semiconductor Materials: Database, Quantitative Data Analysis, and Application in Organic Synthesis

AbstractPhotocharging or photodoping is a process in which electrons are accumulated in a semiconductor upon bandgap excitation followed by quenching of the photogenerated holes by reductants. In semiconductors with excess of electrons, negative charge is compensated by cations, of which the most ubiquitous is H+. Photocharging of semiconductors has been studied since 1980s both from a fundamental perspective and application—as source of electrons and protons for reduction of organic compounds in the dark, solar‐to‐electric energy conversion, and recently also in the design of autonomous microswimmers. In this review, experimental data collected over 40 years of research are summarized and quantified. Maximum specific concentration of electrons stored in 1 g of a semiconductor, maximum average number of electrons stored per semiconductor particle, initial rate of photocharging, and initial rate of discharging are calculated for six classes of semiconductor materials, Ti‐, Zn‐, Cd‐, In‐, W‐based and graphitic carbon nitrides. Dependence of these parameters on material specific surface area, particle volume, and other properties is analyzed and trends are derived. A public database of photocharged materials is created to facilitate design of high‐performing materials with photocharging function, their application as rechargeable reductants in organic synthesis and development of devices.

Modeling and simulation of dye-sensitized solar cell: Model verification for different semiconductors and dyes

In this article, the use of MATLAB/SIMULINK interface to realize a generalized photovoltaic simulation model is introduced. The model was created utilizing the photovoltaic (PV) cell fundamental circuit equations, including the effects of solar radiation and variations in temperature. This modeling approach enables the I–V and P–V curve of PV cells to be understood. It could also be used as a tool to forecast the behavior of any solar PV cell under differing environmental circumstances (e.g., temperature, irradiation conditions). These effects are simultaneously added in real-time. Due to their nonlinear features, they must be modeled to design and simulate the maximum power point of solar cells. This model applies to dye-sensitized solar cells with three different semiconductors, namely, TiO2, ZnO, and SnO2; use N3 dye. According to changes in atmospheric parameter values such as solar radiation, temperature, and operating parameter values like semiconductor type, dye concentration, and particles, the characteristic dimensions of photovoltaic systems such as power supply voltage (PV) and current–voltage (I-V) characteristics are drawn; in the MATLAB/SIMULINK interface observed. The simulation results reveal that these elements and the respective photovoltaic model affect the maximum operating performance of PV modules. The battery made of TiO2 semiconductor and N3 dye showed the greatest consistency with the model battery, followed by the battery made of ZnO, and finally, the battery made of SnO2 with the same dye N3.

Quantum Dots in Peroxidase-like Chemistry and Formamide-Based Hot Spring Synthesis of Nucleobases.

Quantum dots (QDs) are usually seen as artificial semiconductor particles exhibiting optical and electronic properties interesting for nanotechnological applications. However, they may also play a role in prebiotic chemistry. Starting from zinc acetate, cadmium acetate, and mercaptosuccinic acid, we demonstrate the formation of ZnCd QDs upon UV irradiation in prebiotic liquid formamide. We show that ZnCd QDs are able to increase the yield of RNA nucleobase synthesis from formamide up to 300 times, suggesting they might have served as universal catalysts in a primordial milieu. Based on the experimentally observed peroxidase-like activity of ZnCd QDs upon irradiation with visible light, we propose that QDs could be relevant to a broad variety of processes relating to the emergence of terrestrial life.

Broadband Signal Amplification Paths for Semiconductor Radiation and Particle Detectors (Review)

This study is devoted to the development of amplifying paths for plasma diagnostics, a significant part of which use semiconductor detectors as sensors that form low-intensity current signals. One feature of these diagnostics is the oscillographic form of registering sensor signals. In tandem with detectors, broadband transimpedance amplifiers that are based on operational amplifiers are used to amplify and normalize sensor signals. The principles of constructing such amplifying paths are considered taking the factors affecting their final noise and frequency characteristics into account. Practical examples of the construction of amplifying paths of corpuscular and neutron plasma diagnostics, as well as the Thomson-scattering diagnostics, that are used at the plasma installations of the Institute of Nuclear Physics (Siberian Branch, Russian Academy of Sciences) are presented.

Recent advances of hydrogen production through particulate semiconductor photocatalytic overall water splitting

Recent advances of hydrogen production through particulate semiconductor photocatalytic overall water splitting

Size dependence of perovskite-type BaNbO2N particles on sunlight-driven photoelectrochemical water splitting

The size of particulate semiconductors is a critical factor in photoelectrochemical (PEC) water splitting activity because the surface area determined by the particle size establishes the electrochemical reaction sites as well as the resulting photoactivity. Herein we demonstrate the size dependence of perovskite-type BaNbO2N particles, responsive to intensive-visible-light up to 740 nm, on the PEC water splitting activity. The layered perovskite Ba5Nb4O15 particles in different sizes, as a starting oxide for synthesis of BaNbO2N, were synthesized by polymerized complex method, followed by calcination at different temperatures (1073, 1173, 1273, and 1373 K). The size of Ba5Nb4O15 particles was dependent on the calcination temperature so that low-temperature calcination led to smaller BaNbO2N particles. Although the different Ba5Nb4O15 particles experienced nitridation at 1123 K for 13 h, the sizes of the resulting BaNbO2N particles were nearly unchanged from those of the starting oxides. The sizes and Brunauer-Emmett-Teller surface areas of porous BaNbO2N particles largely influenced the PEC water splitting activity. As a result, photoelectrode employing the small BaNbO2N particles, prepared from the calcination at 1173 K, produced the highest photocurrent of 2.20 mA cm−2 at 1.23 VRHE during the sunlight-driven water splitting, showing the size dependence of oxynitride particles on photoactivity. Therefore, findings from this study support that the size reduction of oxynitride particles largely improved the PEC water splitting activity.

Features of the radiative properties of quantum-size particles of narrow-gap semiconductors

For colloidal quantum-size particles (QP) of narrow-gap semiconductors, in contrast to quantum dots of wide-gap CdSe, in QP-PbS there take place an anomalous temperature dependence of the photoluminescence intensity. Also, in the planar microstructure containing QP-InSb, long-wavelength radiation (more than 3 μm) and photoconductivity (over 20 μm) was observed. Under certain conditions, the radiation intensity and photoconductivity demonstrate a resonance maximum. The effects were explained in the model of a one-dimensional quantum oscillator, which energy substantially depends on the effective mass of its quasi-free electron. This leads to competition between the manifestations of long-wave radiation and photoluminescence, and hence, to the anomalous temperature dependence of photoluminescence. It is assumed that QP-InSb in a planar microstructure can be sources and receivers of terahertz radiation, which properties depend on the crystal structure of quantum-sized particles determined by the parameters of their synthesis. Keywords: quantum-dimensional particle, quantum dot, narrow-gap semiconductor, effective mass, Brillouin zone, dimensional quantization, quantum oscillator, photoluminescence, long-wavelength radiation.

Photocatalytic fatigue of the polymer nanocomposites

We discuss the change in mechanical properties of polymeric nanocomposites with photoactive components caused by solar range lighting. Given degradation photoassisted processes are related with the semiconductor nature of component photoactive particles as photocatalysts. Semiconductor particles can be transferred into electron-exited states due to light quanta absorption. One possible way out from these states is through redox electrochemical reactions with neighbor molecules. The redox reactions can produce transformations of polymer structure and composition, decreasing its mechanical strength. The term “photoca-talytic fatigue” denotes a special case of the photo-degradation of polymers resulted only in a change in the strength value of the material. We review not numerous published data on investigations of changes in mechanical properties of polymeric nanocomposite, and mainly in the strength value, arisen from solar range light irradiation. We compare the degradation processes of polymeric nanocomposites containing photoactive components and of the high-cycle fatigue in metals. Likewise, we propose the use of equations of metal high-cycle fatigue curves as a possible approach to mathematical modeling of the processes of polymeric nanocomposites photodegradation. In this, the number of cycles is substitution with exposure time. Especially, the high-cycle fatigue curve equation for the samples with stress concentrations is considered. The experimental parameters of the “photocatalytic fatigue” equation for polymer nanocomposites containing photoactive components are calculated using the Monte Carlo method.

Влияние ионов неодима (III) на фотолюминесценцию сульфидов кадмия и цинка в полиакрилатной матрице

Nanoscale particles ZnS:Nd3+, CdS:Nd3+ and (Zn,Cd)S:Nd3+ were synthesized and doped in a polymerizing methyl methacrylate medium during the production of optically transparent polyacrylate composites of the composition PMMA/ZnS:Nd3+, PMMA/CdS:Nd3+ and PMMA/(Zn,Cd)S:Nd3+. The excitation of photoluminescence (FL) and FL of semiconductor structures in composites is associated with the transition of electrons from the valence band to the conduction band and to the levels of structural defects of semiconductor particles, followed by recombination at these levels. Based on changes in the excitation spectra of FL and FL composites, assumptions are made about the structure of particles, the distribution of Nd3+ ions in it and their effect on photoluminescence.

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Nanoscale particles ZnS:Nd3+, CdS:Nd3+ and (Zn,Cd)S:Nd3+ were synthesized and doped in a polymerizing methyl methacrylate medium during the production of optically transparent polyacrylate composites of the composition PMMA/ZnS:Nd3+, PMMA/CdS:Nd3+ and PMMA/(Zn,Cd)S:Nd3+. The excitation of photoluminescence (FL) and FL of semiconductor structures in composites is associated with the transition of electrons from the valence band to the conduction band and to the levels of structural defects of semiconductor particles, followed by recombination at these levels. Based on changes in the excitation spectra of FL and FL composites, assumptions are made about the structure of particles, the distribution of Nd3+ ions in it and their effect on photoluminescence.

A review on synthesis of quantum dots and their biomedical applications

Quantum Dots (QDs) are ultra-fine nanometer-sized semiconductor particles with a core-shell structure possess both electrical and optical properties. Their unique ability to emit pure, monochromatic light on being exposed to light makes them extremely versatile in their applications. The color of the light emitted directly depends on their size and shape. Smaller QDs emit shorter wavelengths, closer to the violet end of the visible light spectrum (~380-450 nm), while larger QDs emit longer wavelengths i.e in reddish spectrum (~620-750 nm). Owing to their “tunability”, QDs can be exploited in a wide range of fluorescent, photonic, and electrochemical applications. QDs represent elements mainly from Group II-VI (e.g., CdSe) or Group III-V (e.g., InP) with the resultant optical and electronic properties of the quantum dots being somewhere between bulk semiconductor material and individual atoms or molecules. Besides applications in energy and photonics, they are under extensive investigation and development for use in disease diagnosis and therapy, specifically in the area of controlled drug delivery, biosensing and imaging. This review surveys the progress of research explores their properties, synthesis, applications, delivery systems in biology, and their toxicity.