Selenium Alloy Research Articles

A biodegradable Fe–0.6Se alloy with superior strength and effective antibacterial and antitumor capabilities for orthopedic applications

Iron–selenium (Fe–Se) alloys have potential as attractive biodegradable bone–implant materials, given the antitumor properties of Se in cancer prevention and therapy. However, the fabrication of Fe–Se alloys is challenging due to the volatility of elemental Se and the significantly different melting points of Se and Fe. In this study, we successfully fabricated Fe–xSe (x = 0.2, 0.4, 0.6, 0.8, and 1 wt.%) alloys using suction casting, with FeSe compounds as the Se source. The microstructures, tensile properties, corrosion behavior, biocompatibility, antibacterial ability, and antitumor properties of the Fe–Se alloys were evaluated. The microstructures of the Fe–Se alloys were composed of α–Fe and FeSe phases. Among the Fe–Se alloys, Fe–0.6Se showed the best combination of tensile properties, with a yield strength of 1096.5 ± 7.2 MPa, an ultimate tensile strength of 1271.6 ± 6.3 MPa, and a fracture strain of 15.6 ± 3.3 %, and a degradation rate of 56.9 ± 0.4 μm/year. Moreover, the Fe–0.6Se alloy showed superb antibacterial ability against S. aureus, antitumor activity against 143B osteosarcoma cells, and osteogenicity and biocompatibility toward pre–osteoblast MC3T3–E1 cells. In summary, adding 0.2–1.0 wt.% Se to Fe does not affect the growth of healthy cells but effectively inhibits the growth and reproduction of tumor cells, and the Fe–0.6Se alloy is promising for orthopedic applications owing to its unique combination of mechanical and biofunctional properties. Statement of significanceThis work reports on Fe-xSe (x = 0.2, 0.4, 0.6, 0.8, and 1 wt.%) alloys fabricated using suction casting. The microstructures of the Fe–Se alloys were composed of α-Fe and FeSe phases. Among the Fe–Se alloys, the Fe-0.6Se showed the best combination of tensile properties, with a yield strength of 1058.6 ± 3.9 MPa, an ultimate tensile strength of 1134.1 ± 2.9 MPa, and a fracture strain of 16.8 ± 1.5 %, and a degradation rate of 56.9 ± 0.4 μm/year. Moreover, the Fe-0.6Se alloy showed superb antibacterial ability against S. aureus, antitumor activity against 143B osteosarcoma cells, and significant osteogenic ability and biocompatibility toward pre-osteoblast MC3T3-E1 cells. In summary, the Fe-0.6Se alloy is promising for orthopedic applications owing to its unique combination of mechanical and biofunctional properties.

Gas phase alloyed crystalline S–Se dielectrics with high ionic mobility

The advancement of future electronic devices necessitates dielectric materials with enhanced compositional complexity and improved capabilities. We here demonstrate a gas-phase alloying approach that yields ultrathin and crystalline dielectrics with attractive properties for the integration into electronics. A surface-selective deposition process was shown to produce sulfur (S) and selenium (Se) alloys with large-scale uniformity. Through combination of experimental diffraction analysis and materials modeling, we establish the crystallinity of the alloy with a modified lattice structure compared to the host materials. The resulting lattice arrangement endows the alloy dielectric with high ionic mobility as validated by electrochemical impedance spectroscopy. Leveraging this innovative feature, we fabricate memristive devices exhibiting promising performance characteristics. Our findings demonstrate the feasibility of utilizing gas-phase alloying to engineer dielectrics with superior properties and functionality for future device integration.

Thermodynamics of antimony—selenium alloys formation and evaporation

The thermodynamic functions of alloy formation and evaporation were considered for two particular systems — Sb – Sb2Se3 and Sb2Se3 – Se in connection with the presence of congruently melting compound Sb2Se3 in the antimony—selenium system. The calculations are based on the partial vapor pressure values of the components forming the particular systems. The thermodynamic activity of antimony selenide and selenium as the most volatile components in the systems was calculated based on the saturated vapor pressure values of antimony selenide over the Sb – Sb2Se3 and selenium melts over Sb2Se3 – Se liquid alloys determined by the boiling point method (isothermal variant). Similar functions of the low volatile components in the above systems: Sb in the first system and Sb2Se3 in the latter one was calculated by numerical integration of the Gibbs—Duhem equation using the substitution proposed by Darken. The partial pressures of antimony selenide and antimony over Sb – Sb2Se3 and Sb2Se3 – Se melts were approximated by temperature—concentration relationships. The system is distinguished with a positive deviation from ideality due to the presence of a delamination region in the first system. The partial and integral entropies and enthalpies of the formation of liquid alloys were calculated based on the values of component activities found as the ratio of the partial vapor pressure of an element or compound above the solution to the saturated vapor pressure of a pure element or compound. The partial and integral functions of alloy formation are presented in the form of graphical dependences on the selenium amount in the melt. The obtained thermodynamic constants will replenish the physical and chemical data base and will be used to calculate the boundaries of the vapor— liquid equilibrium fields on the diagram of state, allowing to determine the possibility and completeness of distillation separation of molten systems.

Reconfigurability analysis of an all‐dielectric thermal microfluidic‐based metasurface

AbstractMetasurface tuning is performed using different ways for a wide range of applications. This study presents the design of a thermally‐tuned all‐dielectric reconfigurable metasurface. A microfluidic channel, filled with different concentrations of tellurium–selenium (Te‐Se) alloy, is added on the top of the elliptical dielectric resonator (EDR) unit cell of the considered metasurface. The electrical properties of used semiconductor alloy are varied in the range of 400 to 700°C (steps size of 100°C). The impact of thermal tuning on the reflection and transmission characteristics of the designed metasurface is analyzed in the frequency range of 20–30 GHz using COMSOL Multiphysics. Obtained results demonstrated that the realized metasurface exhibits reconfigurable behavior in terms of variations in the reflection and transmission characteristics with a change in either temperature or concentrations of selenium and tellurium. The wider bands with high reflection and low transmission frequency bands are obtained with lower concentrations of selenium and tellurium for all operating temperatures.

The Effect of Fractionation during the Vacuum Deposition of Stabilized Amorphous Selenium Alloy Photoconductors on the Overall Charge Collection Efficiency.

The general fabrication process for stabilized amorphous selenium (a-Se) detectors is vacuum deposition. The evaporant alloy is typically selenium alloyed with 0.3–0.5%As to stabilize it against crystallization. During the evaporation, fractionation leads to the formation of a deposited film that is rich in As near the surface and rich in Se near the substrate. The As content is invariably not uniform across the film thickness. This paper examines the effect of non-uniform As content on the charge collection efficiency (CE). The model for the actual CE calculation is based on the generalized CE equation under small signals; it involves the integration of the reciprocal range-field product (the schubweg) and the photogeneration profile. The data for the model input were extracted from the literature on the dependence of charge carrier drift mobilities and lifetimes on the As content in a-Se1−xAsx alloys to generate the spatial variation of hole and electron ranges across the photoconductor film. This range variation is then used to calculate the actual CE in the integral equation as a function of the applied field. The carrier ranges corresponding to the average composition in the film are also used in the standard CE equation under uniform ranges to examine whether one can simply use the average As content to calculate the CE. The standard equation is also used with ranges from the spatial average and average inverse. Errors are then compared and quantified from the use of various averages. The particular choice for averaging depends on the polarity of the radiation-receiving electrode and the spatial variation of the carrier ranges.

Corrosion Resistance of Sulfur-Selenium Alloy Coatings.

Despite decades of research, metallic corrosion remains a long-standing challenge in many engineering applications. Specifically, designing a material that can resist corrosion both in abiotic as well as biotic environments remains elusive. Here a lightweight sulfur-selenium (S-Se) alloy is designed with high stiffness and ductility that can serve as an excellent corrosion-resistant coating with protection efficiency of ≈99.9% for steel in a wide range of diverse environments. S-Se coated mild steel shows a corrosion rate that is 6-7 orders of magnitude lower than bare metal in abiotic (simulated seawater and sodium sulfate solution) and biotic (sulfate-reducing bacterial medium) environments. The coating is strongly adhesive, mechanically robust, and demonstrates excellent damage/deformation recovery properties, which provide the added advantage of significantly reducing the probability of a defect being generated and sustained in the coating, thus improving its longevity. The high corrosion resistance of the alloy is attributed in diverse environments to its semicrystalline, nonporous, antimicrobial, and viscoelastic nature with superior mechanical performance, enabling it to successfully block a variety of diffusing species.

Correction to: Effect of Aluminum (Al) Concentration on the Thermoelectric Performance of Zinc Aluminum Selenium (ZnAlSe) Alloy

Correction to: Effect of Aluminum (Al) Concentration on the Thermoelectric Performance of Zinc Aluminum Selenium (ZnAlSe) Alloy

Dark current–voltage characteristics of vacuum deposited multilayer amorphous selenium-alloy detectors and the effect of x-ray irradiation

Doped and stabilized amorphous selenium (a-Se) alloys in a multilayer form are currently used as a photoconductor in direct conversion flat panel x-ray imagers in mammography and tomosynthesis. While much progress has been made on the physics of such detectors, there are still unresolved questions on such issues as the principles of operation of the so-called p-i-n detector structure in extinguishing the dark current. The present paper examines dark current transients after the application of a voltage in seven types of a-Se alloy based devices: i-layer, i-n, n-i, i-p, p-i, p-i-n, and n-i-p structures. The substrate was ITO coated glass, the top (radiation receiving) electrode was chromium, and the films were fabricated by vacuum deposition. The nominal device thickness was 200 μm, similar to commercial mammographic detectors. It is shown that n-i, i-n, n-i-p, and p-i-n devices have dark currents less than 1 pA mm−2 at an applied field of 10 V/μm. The dark current in the p-i-n device is the lowest at approximately 0.01 pA mm−2 at an applied field of 10 V μm−1. Experiments have been carried out by subjecting the detector to a staircase voltage-time profile during the voltage application (turn-on) and a staircase voltage ramp-down during the turning-off of the bias voltage. Step-voltage ramp-up and step-voltage ramp-down current transient are typical of expected dark current transient behavior in a semiconductor with traps in which carriers are captured and released from various trap centers in the bandgap. The dark current transients are qualitatively similar to those expected from a capacitor in parallel with a large resistor and both in series with a much smaller resistor. Current transients during charging and discharging experiments were integrated to find how much of the injected charge is released during discharge experiments. It is shown that the majority of this trapped charge is stored in the n-type and p-type blocking layers, near the contacts. The trapped carriers in the i-layer represent a very small portion. The evolution of the dark current upon single and repeated x-ray exposure has also been examined in n-i and p-i-n devices. Right after the cessation of irradiation, there is an excess or residual dark current whose magnitude is roughly ∼20 times higher in p-i-n and about ∼2 times higher in the case of n-i under an exposure of 3.36 R and a mean photon energy of 34.2 keV. The absorbed dose is 1.53 Gy. The excess dark current has a fast decay component with a time constant ∼10 s and a slow component with a time constant ∼100 s. It is shown that the decay in the irradiation induced excess dark current is very similar to the initial dark current. There is no permanent change in the dark current, and within a few hundred seconds, the dark current reaches the same level as that in the unexposed detector. The experimental results in this work highlight the distinct advantages of p-i-n and n-i-type a-Se multilayer structures in x-ray detection applications.

Improved production of 76Br, 77Br and 80mBr via CoSe cyclotron targets and vertical dry distillation

IntroductionThe radioisotopes of bromine are uniquely suitable radiolabels for small molecule theranostic radiopharmaceuticals but are of limited availability due to production challenges. Significantly improved methods were developed for the production and radiochemical isolation of clinical quality 76Br, 77Br, and 80mBr. The radiochemical quality of the radiobromine produced using these methods was tested through the synthesis of a novel 77Br-labeled inhibitor of poly (ADP-ribose) polymerase-1 (PARP-1), a DNA damage response protein. Methods76Br, 77Br, and 80mBr were produced in high radionuclidic purity via the proton irradiation of novel isotopically-enriched Co76Se, Co77Se, and Co80Se intermetallic targets, respectively. Radiobromine was isolated through thermal chromatographic distillation in a vertical furnace assembly. The 77Br-labeled PARP inhibitor was synthesized via copper-mediated aryl boronic ester radiobromination. ResultsCyclotron production yields were 103 ± 10 MBq∙μA−1∙h−1 for 76Br, 88 ± 10 MBq∙μA−1∙h−1 for 80mBr at 16 MeV and 17 ± 1 MBq∙μA−1∙h−1 for 77Br at 13 MeV. Radiobromide isolation yields were 76 ± 11% in a small volume of aqueous solution. The synthesized 77Br-labeled PARP-1 inhibitor had a measured apparent molar activity up to 700 GBq/μmol at end of synthesis. ConclusionsA novel selenium alloy target enabled clinical-scale production of 76Br, 77Br, and 80mBr with high apparent molar activities, which was used to for the production of a new 77Br-labeled inhibitor of PARP-1. Advances in knowledgeNew methods for the cyclotron production and isolation of radiobromine improved the production capacity of 77Br by a factor of three and 76Br by a factor of six compared with previous methods. Implications for patient carePreclinical translational research of 77Br-based Auger electron radiotherapeutics, such as those targeting PARP-1, will require the production of GBq-scale 77Br, which necessitates next-generation, high-yielding, isotopically-enriched cyclotron targets, such as the novel intermetallic Co77Se.

Electron Microscopy of Sulfur Selenium Alloy with High –K Dielectric Properties.

Electron Microscopy of Sulfur Selenium Alloy with High –K Dielectric Properties.

New Earth-Abundant Thin Film Solar Cells Based on Chalcogenides.

At the end of 2017 roughly 1.8% of the worldwide electricity came from solar photovoltaics (PV), which is foreseen to have a key role in all major future energy scenarios with an installed capacity around 5 TW by 2050. Despite silicon solar cells currently rule the PV market, the extremely more versatile thin film-based devices (mainly Cu(In,Ga)Se2 and CdTe ones) have almost matched them in performance and present room for improvement. The low availability of some elements in the present commercially available PV technologies and the recent strong fall of silicon module price below 1 $/Wp focused the attention of the scientific community on cheap earth-abundant materials. In this framework, thin film solar cells based on Cu2ZnSnS4 (CZTS) and the related sulfur selenium alloy Cu2ZnSn(S,Se)4 (CZTSSe) were strongly investigated in the last 10 years. More recently, chalcogenide PV absorbers potentially able to face TW range applications better than CZTS and CZTSSe due to the higher abundance of their constituting elements are getting considerable attention. They are based on both MY2 (where M = Fe, Cu, Sn and Y = S and/or Se) and Cu2XSnY4 (where X = Fe, Mn, Ni, Ba, Co, Cd and Y = S and/or Se) chalcogenides. In this work, an extensive review of emerging earth-abundant thin film solar cells based on both MY2 and Cu2XSnY4 species is given, along with some considerations on the abundance and annual production of their constituting elements.

Enhancement of P3HT organic photodiodes by the addition of a GaSe9 alloy thin layer

We report on gallium–selenium alloy (GaSe9) thin films simultaneously functioning as both blocking layer and active layer on poly(3-hexylthiophene-2, 5-diyl) (P3HT)-based organic photodiodes in order to enhance device performance. In addition to improved transport of the photogenerated charge carriers, GaSe9 films also contribute to light absorption on a different wavelength interval than that of P3HT. Three different devices are compared: ITO/GaSe9/Al, ITO/P3HT/Al and ITO/P3HT/GaSe9/Al, with the last one presenting a lower dark current density (0.90 μA cm−2), higher ON/OFF current ratio (61) and fastest response under AM 1.5 light irradiance. The observed responsivity is 7.3 mA W−1 and is almost linearly dependent on irradiance in the range 0.6–60 W m−2. A maximum external quantum efficiency of 135% and specific detectivity of 16.7 × 1011 Jones at 390 nm incident light wavelength are obtained.

Cu2ZnSnSxO4−x and Cu2ZnSnSxSe4−x: First principles simulations of optimal alloy configurations and their energies

With the aim of exploring oxidation and selenization of the photovoltaic material Cu2ZnSnS4, we used first principles methods to study the structure and stability of Cu2ZnSnSxO4−x and Cu2ZnSnSxSe4−x alloys for 0 ≤ x ≤ 4. Pure Cu2ZnSnO4 was found to have the lowest heat of formation, followed by Cu2ZnSnS4, and finally Cu2ZnSnSe4. This suggests that oxidization is very likely to occur, whereas selenization can only be accomplished under high temperature. For the alloys, the energetically favorable chalcogen configurations are very different for oxygen and selenium. While the energies of the selenium alloys are insensitive to the distribution of S and Se configurations, the lowest energy oxygen alloys have alternating S and O sites in the a–b planes. In considering the heats of formation of the Cu2ZnSnSxO4−x alloys, we find that they are unstable with respect to decomposition into binary oxides and sulfides except for small concentrations of O. Our results also show that it is energetically more favorable to sulfurize Cu2ZnSnSe4 than to selenize Cu2ZnSnS4.

Mechanical synthesis of high purity Cu–In–Se alloy nanopowder as precursor for printed CISe thin film solar cells

Mechanical alloying and ball milling are low cost, up-scalable techniques for the preparation of high purity chalcogenide nanopowders to be used as precursor material for printing thin film solar cells. In this study, high purity copper indium selenium (Cu–In–Se) alloy nanopowders with 20–200nm particle size were synthesized from macroscopic elemental Cu, In and Se powders via mechanical alloying and planetary ball milling. The particle size distribution, morphology, composition, and purity level of the synthesized Cu–In–Se alloy nanopowders were investigated. Thin Cu–In–Se alloy nanopowder ink coatings, deposited on Mo-coated glass substrates by doctor blading, were converted into a CuInSe2 semiconductor film by selenization heat treatment in Se vapor. The CuInSe2 film showed semiconducting band gap around 1eV measured by photoluminescence spectroscopy. CuInSe2 absorber layer based thin film solar cell devices were fabricated to assess their performance. The solar cell device showed a total efficiency of 4.8%, as measured on 0.25cm2 area cell.

Carbon/Ternary Alloy/Carbon Optical Stack on Mylar as an Optical Data Storage Medium to Potentially Replace Magnetic Tape

A novel write-once-read-many (WORM) optical stack on Mylar tape is proposed as a replacement for magnetic tape for archival data storage. This optical tape contains a cosputtered bismuth-tellurium-selenium (BTS) alloy as the write layer sandwiched between thin, protective films of reactively sputtered carbon. The composition and thickness of the BTS layer were confirmed by Rutherford Backscattering (RBS) and atomic force microscopy (AFM), respectively. The C/BTS/C stack on Mylar was written to/marked by 532 nm laser pulses. Under the same conditions, control Mylar films without the optical stack were unaffected. Marks, which showed craters/movement of the write material, were characterized by optical microscopy and AFM. The threshold laser powers for making marks on C/BTS/C stacks with different thicknesses were explored. Higher quality marks were made with a 60× objective compared to a 40× objective in our marking apparatus. The laser writing process was simulated with COMSOL.

Effect of antimony addition on thermal stability and crystallization kinetics of germanium–selenium alloys

Chalcogenide glasses are promising materials for threshold and memory switching. Alloys of Ge19Se81−xSbx (x=0, 4, 8, 12, 16, 17.2, 20) have been prepared by melt quench technique. Differential thermal analysis has been used to characterize samples at different heating rates (α=5, 10, 15, 20K/min). Glass transition temperatures, crystallization temperature, melting temperature, activation energy for glass transition and crystallization have been determined. Thermal stability of alloys has been analyzed in terms of ease by which atomic rearrangements take place and the resistance to devitrification. The correlation between thermal stability and glass forming ability has also been studied.

Optical limiting in hydrogenated amorphous silicon–selenium thin films

Hydrogenated amorphous silicon–selenium alloy thin films grown by capacitively coupled radio-frequency glow-discharge are investigated. Nonlinear absorptive effects are evaluated with the help of open aperture z-scan technique in the 525 to 580 nm spectral range. The nonlinear absorption coefficient is found to be very large and reaching the value of 5.14 × 10 − 3 cm/W at 525 nm. The origin of the optical nonlinearities is studied and found to be due mainly to two photon absorption in the case of pulsed excitation, whereas thermal effects are thought to be dominant when the sample is excited with a continuous wave laser. Optical limiting potentialities of the thin film are experimentally observed and their thresholds are found to be very low.

Studies on excess noise in stabilized amorphous selenium used in X-ray photodetectors

We report investigations of the dependence of 1/f noise on surface condition, alloy composition and the substrate temperature during evaporation in samples of amorphous selenium alloys. The 1/f noise was measured using DC bias currents ranging from 2 to 200nA; the measurements were complicated by the low current levels and highly non-linear I–V relationship of electroded amorphous selenium. The noise power density spectrum varies approximately as 1/fα from 0.5Hz to 1KHz where α ranges from 0.7 to 1.1. A roughened surface produces noise almost two orders of magnitude lower than an as-deposited surface. The dependence of the noise power on Cl concentration was weak but was quite significant for As concentration. The substrate temperature during evaporation of the selenium alloy did not have any effect on 1/f noise for a particular applied voltage, though typically the dark current of a sample deposited at a particular substrate temperature falls sharply when the temperature is increased or decreased. The results stated in this paper have implications for designing the photoconductive layer in the X-ray imaging detectors.

1/f Conductance noise in stabilized amorphous selenium

We report measurements of low-frequency conductance fluctuations in samples of amorphous selenium alloys that find use in direct-conversion, flat-panel X-ray image detectors. The signal-to-noise ratio of these detectors depends in part on the fluctuations in the so-called dark current that flows through the selenium layer; proper modeling of the detector performance requires measurements of this noise signal. The conductance noise was measured for various applied voltages ranging from 400 to 2000V that produced dark currents ranging from 10−9 to 10−6A. The noise power density spectrum varies approximately as 1/fα from 0.5Hz to 1kHz with α in the range from 0.77 to 1.5. The noise spectrum depends on resting time after application of the voltage and on the metal used for the electrodes which implies that the noise is controlled by the metal semiconductor interface. Integration of the noise power density over the measured frequency range yields an rms fluctuation of the dark current that can be as large as 1% of the average value.

Time-of-Flight Study of the Compensation Mechanism in a-Se Alloys

Arsenic is added to amorphous selenium to retard crystallization and to improve its mechanical properties. Arsenic in sufficient quantities acts as a weak hole trap that results in buildup of residual potential when subjected to charge–expose–erase cyclic conditions employed in electrophotography. A halogen, chiefly chlorine, that by itself acts as an electron trap in amorphous selenium is added to arsenic containing selenium to eliminate residual potential when operated in a positive charging mode (hole transport). Some selenium alloys contain 0.33-atom % arsenic and 30-ppm chlorine. Chlorine in excess of that required to compensate arsenic in bulk does not affect hole transport. However, excess chlorine decreases the electron range. When these alloys are employed as photosensitive elements for xeroradiography purposes in which x-rays are bulk absorbed and both hole and electron transports contribute to the sensitivity, the excess chlorine will have the effect of reducing the sensitivity. In this article, compensation of arsenic by chlorine has been explained in terms of structural considerations. These considerations and heat of formation data suggest that approximately 30-ppm chlorine is required to compensate 0.33-atom % arsenic. A technique has been developed to map the excess chlorine profiles. This is based on the principle that if a small electron current is injected into the film from a biased substrate in a time-of-flight setup, the electrons are selectively trapped at these excess chlorine sites. The resulting electric field profiles have been measured and related to the excess chlorine profiles. Experimentally, a film containing 0.33-atom % arsenic and approximately 40-ppm chlorine is ideally compensated, and excess chlorine is observed in films containing more than 40-ppm chlorine.