Amorphous Selenium Research Articles

Physicochemical stability of lichenan (Usnea longissima) decorated-selenium nanoparticles for cancer chemoprevention

The biological activity of amorphous selenium nanoparticles (SeNPs) was limited by their poor stability and rapid spontaneous phase transformation. Herein, we prepared amorphous SeNPs by decorating them with lichenan (LC), a natural random coil conformation polysaccharide, through C–O⋯Se bonds or O–H⋯Se bonds. The synthesized amorphous spherical LC-SeNPs maintained their amorphous phase and zero valence state after being stored for 60 days at 4 °C. This stability can be also maintained under different heating treatment temperatures (37, 55, 75, and 95 °C), pH conditions (pH 3–10), and ionic strength (10–200 mM). Furthermore, LC-SeNPs displayed potential anticancer efficacy based on their ROS-triggered selenium release property and variable redox potential in the ROS model. The underlying antiproliferative mechanism was related to cell cycle arrest, intracellular redox imbalance, and mitochondrial dysfunction. This work provides a promising strategy for using LC-SeNPs in diet supplements or cancer chemoprevention.

Formation of Red Elemental Selenium from Seleniferous Oxyanions: Deoxygenation by a Homogeneous Iron Catalyst.

Seleniferous oxyanions are groundwater contaminants from both anthropogenic and natural sources, while pure amorphous selenium nanoparticles have a variety of industrial applications. Biology can achieve the multicomponent 6 e-/8 H+ reduction of selenate to amorphous selenium using multiple metalloenzymes, like selenate and selenite reductase. Inspired by biology, we developed a new homogeneous system that can generate pure elemental selenium with no caustic waste. The stoichiometric reductions of selenate, selenite, and selenium dioxide with an iron(II) complex produced an iron(III)-oxo and red elemental selenium, the latter of which has been characterized by a variety of spectroscopic techniques. The catalytic reduction of SeO42- and SeO32- directly to amorphous Se and isolated as Se=PPh3 is reported with a turnover number of 12 and 7, respectively.

Amorphous selenium inhibits oxidative stress injury of neurons in vascular dementia rats by activating NMDAR pathway

Vascular dementia (VD) is one of the most common causes of dementia, taking account for about 20% of all cases. Although studies have found that selenium supplementation can improve the cognitive ability of Alzheimer's patients, there is currently no research on the cognitive impairment caused by VD. This study aimed to investigate the role and mechanism of Amorphous selenium nanodots (A SeNDs) in the prevention of VD. The bilateral common carotid artery occlusion (BCCAO) method was used to establish a VD model. The neuroprotective effect of A SeNDs was evaluated by Morris water maze, Transcranial Doppler TCD, hematoxylin–eosin (HE) staining, Neuron-specific nuclear protein (Neu N) staining and Golgi staining. Detect the expression levels of oxidative stress and Calcium-calmodulin dependent protein kinase II (CaMK II), N-methyl-D-aspartate receptor subunit NR2A, and postsynaptic dense protein 95 (PSD95). Finally, measure the concentration of calcium ions in neuronal cells. The results showed that A SeNDs could significantly improve the learning and memory ability of VD rats, restore the posterior arterial blood flow of the brain, improve the neuronal morphology and dendritic remodeling of pyramidal cells in hippocampal CA1 area, reduce the level of oxidative stress in VD rats, increase the expression of NR2A, PSD95, CaMK II proteins and reduce intracellular calcium ion concentration, but the addition of selective NR2A antagonist NVP-AAMO77 eliminated these benefits. It suggests that A SeNDs may improve cognitive dysfunction in vascular dementia rats by regulating the NMDAR pathway.

The influence of mercury vapor on the electrical resistance of chalcogenide amorphous films

Using the planar structures "Ni layer - chalcogenide amorphous film - Ni layer" and "graphite probe - chalcogenide amorphous film graphite probe" samples, the influence of mercury vapor on the electrical resistance of amorphous films of the Se-Te, Se-Sb and Se-As systems was investigated. It was established that exposure of samples in mercury vapor leads to a decrease in their electrical resistance by 4-7 orders of magnitude. As the temperature and mercury concentration increase, the transition time from a high-resistance state to a low-resistance state decreases. When introducing Te, Sb, and As into amorphous selenium and increasing their concentration in the composition of the films, the transition time increases, and the value of the change in resistance decreases. It was established that the change in resistance is mainly determined by the change in surface conductivity of chalcogenide films. A decrease in the electrical resistance of selenium-containing amorphous films modified with mercury is caused by the formation of HgSe crystalline inclusions in their matrix.

Non-Markovian Hole Excess Noise in Avalanche Amorphous Selenium Thin Films.

Enhancing the signal-to-noise ratio in avalanche photodiodes by utilizing impact ionization gain requires materials exhibiting low excess noise factors. Amorphous selenium (a-Se) as a wide bandgap at ∼2.1 eV, a solid-state avalanche layer, demonstrates single-carrier hole impact ionization gain and manifests ultralow thermal generation rates. A comprehensive study of the history dependent and non-Markovian nature of hot hole transport in a-Se was modeled using a Monte Carlo (MC) random walk of single hole free flights, interrupted by instantaneous phonon, disorder, hole-dipole, and impact-ionization scattering interactions. The hole excess noise factors were simulated for 0.1-15 μm a-Se thin-films as a function of mean avalanche gain. The hole excess noise factors in a-Se decreases with an increase in electric field, impact ionization gain, and device thickness. The history dependent nature of branching of holes is explained using a Gaussian avalanche threshold distance distribution and the dead space distance, which increases determinism in the stochastic impact ionization process. An ultralow non-Markovian excess noise factor of ∼1 was simulated for 100 nm a-Se thin films corresponding to avalanche gains of 1000. Future detector designs can utilize the nonlocal/non-Markovian nature of the hole avalanche in a-Se, to enable a true solid-state photomultiplier with noiseless gain.

Performance Evaluation of an Amorphous Selenium Photodetector at High Fields for Application Integration

Performance Evaluation of an Amorphous Selenium Photodetector at High Fields for Application Integration

Revealing the Electrochemistry of All-Solid-State Li-SeS2 Battery via Transmission Electron Microscopy

Li-SeS2 batteries balance the opposing and complimentary qualities of Li-S and Li-Se batteries by having a high specific capacity and high electrical conductivity. However, there is still a lack of knowledge regarding the electrochemical characteristics of Li-SeS2 all-solid-state batteries (ASSB). Herein, transmission electron microscopy (TEM) is used to reveal the electrochemistry of a Li-SeS2 battery. It is discovered that, without the Polyethylene glycol (PEG), amorphous SeS2 in Li-SeS2 ASSB change into crystalline selenium and a small amount of sulfur. The continuous loss of sulfur from the active material may be related to the failure of the cell at 15 cycles and the severe instability of the Coulombic efficiency. It was found that the PEG coating selenium disulfide graphene composite (PEG@rGO-SeS2) cathode maintained a specific capacity of 258 mAh g−1 and a stable Coulombic efficiency of about 97% after 50 cycles. TEM analysis shows that the charging product remains as a granular amorphous selenium disulfide with a constant Se/S ratio during cycling. The PEG-protected selenium disulfide can effectively limit the loss of elemental sulfur and regulate the reaction mechanism of the Li-SeS2 batteries.

Study of linear and non-linear optoelectronic properties of thermally grown thin films of amorphous selenium doped with graphene, multiwalled carbon nanotubes, and silver nanoparticles

The present research covers the impact of doping of different nano-materials [Graphene, Multiwalled Carbon Nanotubes (MWCNTs), and Silver nanoparticles (Ag: NPs)] on the optoelectronic properties of selenium glass. For this, we have prepared the amorphous thin films (ATFs) of pure selenium and nano-additives doped Se and the systematic optical characterization of ATFs of as-prepared samples has been done. We have examined the optical characteristics of prepared ATFs by collecting the experimental spectral data of reflection/transmission in the range of 400 nm to 2500 nm. Knowing the spectral variation of the dispersion parameters, we have calculated the values of the optical band gap Egopt and Urbach tail Ee. The indirect optical transition is found in the present samples that are confirmed by the transition power factor m. The values of real component (i.e., ε') and imaginary components (i.e., ε″) of the dielectric constant and its value in the high-frequency range (i.e., ε∞), as well as single-oscillator dispersion parameters, are also determined. The value of infinite dielectric constant (ε∞) of ATF of parent selenium (ε∞ = 2.65) is increased significantly after the doping of graphene (ε∞ = 3.82), MWCNT (ε∞ = 4.37), and Ag: NPs (ε∞ = 6.19). Further, we have investigated the dependence of tan δ (dissipation factor), τ (relaxation time), optical/electrical conductivities, and volume/surface energy loss functions on photon energy hν. The nonlinear properties of the samples are discussed in terms of their susceptibility and nonlinear refractive index.

Tuning Amorphous Selenium Composition with Tellurium to Improve Quantum Efficiency at Long Wavelengths and High Applied Fields.

Amorphous selenium (a-Se) is a large-area compatible photoconductor that has received significant attention toward the development of UV and X-ray detectors for a wide range of applications in medical imaging, life science, high-energy physics, and nuclear radiation detection. A subset of applications require detection of photons with spectral coverage from UV to infrared wavelengths. In this work, we present a systematic study utilizing density functional theory simulations and experimental studies to investigate optical and electrical properties of a-Se alloyed with tellurium (Te). We report hole and electron mobilities and conversion efficiencies for a-Se1-xTex (x = 0, 0.03, 0.05, 0.08) devices as a function of applied field, along with band gaps and comparisons to previous studies. For the first time, these values are reported at high electric field (>10 V/μm), demonstrating recovery of quantum efficiency in Se-Te alloys. A comparison to the Onsager model for a-Se demonstrates the strong field dependence in the thermalization length and expands on the role of defect states in device performance.

Early crystallization of amorphous selenium under high pressure studied by synchrotron XRD method

The amorphous selenium (a-Se) was studied via x-ray diffraction (XRD) under pressures ranging from ambient pressure up to 30 GPa at room temperature to study its high-pressure behavior. Two compressional experiments on a-Se samples, with and without heat treatment, respectively, were conducted. Contrary to the previous reports that a-Se crystallized abruptly at around 12 GPa, in this work we report an early partially crystallized state at 4.9 GPa before completing the crystallization at around 9.5 GPa based on in-situ high pressure XRD measurements on the a-Se with 70 °C heat treatment. In comparison, crystallization pressure on another a-Se sample without thermal treatment history was observed to be 12.7 GPa, consistent with the previously reported crystallization pressure. Thus, it is proposed in this work that prior heat treatment of a-Se can result in an earlier crystallization under high pressure, which helps to understand the possible mechanism caused by the previous controversial reports on pressure induced crystallization behavior in a-Se.

High spatial resolution direct conversion amorphous selenium X-ray detectors with monolithically integrated CMOS readout

Recent progress in the field of micron-scale spatial resolution direct conversion X-ray detectors for high-energy synchrotron light sources serve applications ranging from nondestructive and noninvasive microscopy techniques which provide insight into the structure and morphology of crystals, to medical diagnostic measurement devices. Amorphous selenium (a-Se) as a wide-bandgap thermally evaporated photoconductor exhibits ultra-low thermal generation rates for dark carriers and has been extensively used in X-ray medical imaging. Being an amorphous material, it can further be deposited over large areas at room temperatures and at substantially lower costs as compared to crystalline semiconductors. To address the demands for a high-energy and high spatial resolution X-ray detector for synchrotron light source applications, we have thermally evaporated a-Se on a Mixed-Mode Pixel Array Detector (MM-PAD) Application Specific Integrated Circuit (ASIC). The ASIC format consists of 128 × 128 square pixels each 150 μm on a side. A 200 μm a-Se layer was directly deposited on the ASIC followed by a metal top electrode. The completed detector assembly was tested with 45 kV Ag and 23 kV Cu X-ray tube sources. The detector fabrication, performances, Modulation Transfer Function (MTF) measurements, and simulations are reported.

Effect of graphite on the power density of selenium doped polyaniline ink based hybrid screen-printed flexible thermoelectric generator

Enhancement in the thermoelectric performance of inorganic/organic hybrid composites and the need for low-cost, flexible thermoelectric generators have motivated this work. The thermoelectric effect on the addition of amorphous polyaniline, crystalline selenium, and layer-structured graphite, with different concentrations on the thermoelectric properties of selenium-doped polyaniline, is reported. Tuning of microstrain, dislocation density, and carrier concentration has improved the Seebeck coefficient by 39.10% and electrical conductivity by 60.22%. The maximum power output and power factor exhibited by the hybrid device are 1.89 nW and 0.42 nW/m2K2 at a temperature difference of 100 °C. Replacing 90 wt% of Selenium-doped polyaniline with graphite resulted in a power density of 0.65 mW/m2 under external load conditions.

Effective Coupling of Amorphous Selenium Phosphide with High‐Conductivity Graphene as Resilient High‐Capacity Anode for Sodium‐Ion Batteries

AbstractIt is of great importance to develop high‐capacity electrodes for sodium‐ion batteries (SIBs) using low‐cost and abundant materials, so as to deliver a sustainable technology as alternative to the established lithium‐ion batteries (LIBs). Here, a facile ball milling process to fabricate high‐capacity SIB anode is devised, with large amount of amorphous SeP being loaded in a well‐connected framework of high‐conductivity crystalline graphene (HCG). The HCG substrate enables fast transportation of Na ions and electrons, while accommodating huge volumetric changes of the active anode matter of SeP. The strong glass forming ability of NaxSeP helps prevent crystallization of all stable compounds but ultrafine nanocrystals of Na2Se and Na3P. Thus, the optimized anode delivers excellent rate performance with high specific capacities being achieved (855 mAh g−1 at 0.2 A g−1 and 345 mAh g−1 at 5 A g−1). More importantly, remarkable cycling stability is realized to maintain a steady capacity of 732 mAh g−1 over 500 cycles, when the SeP in the SeP@HCG still remains 86% of its theoretical capacity. A high areal capacity of 2.77 mAh is achieved at a very high loading of 4.1 mg cm−2 anode composite.

Recent Development of Halide Perovskite Materials and Devices for Ionizing Radiation Detection.

Ionizing radiation such as X-rays and γ-rays has been extensively studied and used in various fields such as medical imaging, radiographic nondestructive testing, nuclear defense, homeland security, and scientific research. Therefore, the detection of such high-energy radiation with high-sensitivity and low-cost-based materials and devices is highly important and desirable. Halide perovskites have emerged as promising candidates for radiation detection due to the large light absorption coefficient, large resistivity, low leakage current, high mobility, and simplicity in synthesis and processing as compared with commercial silicon (Si) and amorphous selenium (a-Se). In this review, we provide an extensive overview of current progress in terms of materials development and corresponding device architectures for radiation detection. We discuss the properties of a plethora of reported compounds involving organic-inorganic hybrid, all-inorganic, all-organic perovskite and antiperovskite structures, as well as the continuous breakthroughs in device architectures, performance, and environmental stability. We focus on the critical advancements of the field in the past few years and we provide valuable insight for the development of next-generation materials and devices for radiation detection and imaging applications.

Preparation of solution-processed thin films of As-S-Se system from As40S60 solution modified by amorphous selenium

This work presents the possibility of As-S-Se chalcogenide glass thin film preparation from a solution of commercially available As40S60 glass by modification of the solution composition with elemental selenium. We studied the dissolution of elemental selenium in n-butylamine and ethylenediamine based chalcogenide glass solutions.Samples of four compositions ranging from 0% selenium content (pure As40S60) to 30% selenium content (As28S42Se30) were prepared by spin-coating in specular optical quality with low surface roughness (below 1 nm). Structure, refractive index, optical band gap, organic residua content, and chemical resistance were studied in dependence on the annealing temperature. The structure was studied using Raman spectroscopy, and the data suggest incorporation of selenium into the glass structure already in the solution, which resulted in an increased refractive index and reduced optical band gap of deposited thin films. Due to chalcogen over-stoichiometry, modified thin films have lower organic residua content.

Processing Gray Selenium in Phosphonium-Based Ionic Liquids.

The dissolution of gray selenium in tetraalkylphosphonium acetate ionic liquids was investigated by UV-vis, NMR, and Raman spectroscopy as well as quantum chemical calculations and electrochemical methods. Acetate anions and tetraalkylphosphonium cations facilitate the formation and stabilization of oligoselenides Sen2- and cationic Se species in the ionic liquid phase. Chemical exchange of selenium atoms was demonstrated by variable-temperature 77Se NMR experiments. Additionally, uncharged cycloselenium molecules exist at high selenium concentrations. Upon dilution with ethanol, amorphous red selenium precipitates from the solution. Moreover, crystalline Se1-xTex solid solutions precipitate when elemental tellurium is added to the mixture as confirmed by powder X-ray diffraction and Raman spectroscopy.

Facile preparation of fully amorphous bulk PbO-Ga2O3 system for direct photon-charge conversion X-ray detector with low dark current and high photocurrent

An amorphous state makes the material free of interface and ensures the overall uniformity of the material and device, to the benefit of large-area electronic devices, such as amorphous silicon and indium gallium zinc oxide display devices and amorphous selenium flat panel detectors. Elements with high atomic number endow the PbO-Ga2O3 system materials with high X-ray absorption coefficients, and wide band gap leading to a low dark current and high signal-to-noise ratio. These advantages are in line with the criteria for a practical X-ray detector development. Herein, the direct photon-charge conversion X-ray detectors based on fully amorphous bulk PbO-Ga2O3 system [(PbO)x(Ga2O3)1-x (x = 0.698, 0.747, 0.761, 0.789)] was fabricated by using high-temperature melt quenching method. Under a fixed electric field of 100 V/mm and X-ray irradiation dose rate of 0.57 μGy ms−1, the dark current as low as 1.1 pA mm−2, photocurrent up to 1600 pA mm−2, signal-to-noise ratio up to 800, comparable sensitivity as 2.02 μC Gy−1 cm−2 of the as fabricated X-ray detector were obtained. All the results suggest that amorphous bulk PbO-Ga2O3 system materials are potential candidates for developing of direct photon-charge conversion X-ray detectors.

Development of a novel, windowless, amorphous selenium based photodetector for use in liquid noble detectors

Detection of the vacuum ultraviolet (VUV) scintillation light produced by liquid noble elements is a central challenge in order to fully exploit the available timing, topological, and calorimetric information in detectors leveraging these media. In this paper, we characterize a novel, windowless amorphous selenium based photodetector with direct sensitivity to VUV light. We present here the manufacturing and experimental setup used to operate this detector at low transport electric fields (2.7–5.2 V/μm) and across a wide range of temperatures (77 K–290 K). This work shows that the first proof-of-principle windowless amorphous selenium device is robust under cryogenic conditions, responsive to VUV light at cryogenic temperatures, and preserves argon purity. These findings motivate a continued exploration of amorphous selenium devices for simultaneous detection of scintillation light and ionization charge in noble element detectors.

Управляемый синтез текстурированной пленки CuSe(006) вакуумно-термической обработкой пленочной структуры Se/Cu

A nanocomposite film consisting of crystalline CuSe and amorphous selenium (a-Se) was obtained by vacuum-thermal deposition. It has been shown for the first time that thermal heating of a CuSe/a-Se nanocomposite film in vacuum can transform it into a textured CuSe(006) film. It has been established that at a temperature of 438 K, CuSe crystallites grow intensively in the (006) crystallographic plane. Using the X-ray diffraction analysis method and the technique for measuring the electrical resistance of the CuSe/a-Se composite film, the phase transformation temperatures at which monoclinic Se8, trigonal t-Se, orthorhombic CuSe2, and hexagonal CuSe are formed.

Vertical Architecture Solution-Processed Quantum Dot Photodetectors with Amorphous Selenium Hole Transport Layer

Colloidal quantum dots (CQDs) provide wide spectral tunability and high absorption coefficients owing to quantum confinement and large oscillator strengths, which along with solution processability, allow a facile, low-cost, and room-temperature deposition technique for the fabrication of photonic devices. However, many solution-processed CQD photodetector devices demonstrate low specific-detectivity and slow temporal response. To achieve improved photodetector characteristics, limiting carrier recombination and enhancing photogenerated carrier separation are crucial. In this study, we develop and present an alternate vertical-stack photodetector wherein we use a solution-processed quantum dot photoconversion layer coupled to an amorphous selenium (a-Se) wide-bandgap charge transport layer that is capable of exhibiting single-carrier hole impact ionization and is compatible with active-matrix readout circuitry. This a-Se chalcogenide transport layer enables the fabrication of high-performance and reliable solution-processed quantum dot photodetectors, with enhanced charge extraction capabilities, high specific detectivity (D* ∼ 0.5–5 × 1012 Jones), fast 3 dB electrical bandwidth (3 dB BW ∼ 22 MHz), low dark current density (JD ∼ 5–10 pA/cm2), low noise current (in ∼ 20–25 fW/Hz1/2), and high linear dynamic range (LDR ∼ 130–150 dB) across the measured visible electromagnetic spectrum (∼405–656 nm).