SEARCH · Search NASA

Results for “Selenium”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11

All sources NASA NTRS DOE OSTI

DOE OSTI2025

Systematic Bandgap Engineering of a 2D Organic–Inorganic Chalcogenide Semiconductor via Ligand Modification

Hybrid organic–inorganic semiconductors present new opportunities for optoelectronic materials design not available in all-organic or all-inorganic materials. One example is silver phenylselenide (AgSePh) – or “mithrene” – a blue-emitting 2D organic–inorganic semiconductor exhibiting strong optical and electronic anisotropy. Here, we show that the bandgap of mithrene can be systematically tuned by introducing electron-donating and electron-withdrawing groups to the phenyl ligands. We synthesized nine mithrene variants, eight of which formed 2D van der Waals crystals analogous to those of AgSePh. Density functional theory calculations reveal that these 2D mithrene variants are direct-gap or nearly direct gap semiconductors. Furthermore, we identify correlations between the optical gap and three experimental observables – the Hammett constant, 77 Se chemical shift, and selenium partial charge – offering predictive power for bandgap tuning. These findings highlight new opportunities for applying the tools of chemical synthesis to semiconductor materials design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Near Quantitative Removal of Selenate and Sulfate Anions from Wastewaters by Cocrystallization with Chelating Hydrogen-Bonding Guanidinium Ligands

Selenium (Se) has become an environmental contaminant of aquatic ecosystems as a result of human activities, particularly mining, fossil fuel combustion, and agricultural activities. By leveraging the high sulfate concentrations relative to Se oxyanions (i.e., SeO n 2– , n = 3, 4) present in some wastewaters, we have developed an efficient approach to Se-oxyanion removal by cocrystallization with bisiminoguanidinium (BIG) ligands that form crystalline sulfate/selenate solid solutions. The crystallization of the sulfate, selenate and selenite, oxyanions and of sulfate/selenate mixtures with five candidate BIG ligands are reported along with the thermodynamics of crystallization and aqueous solubilities. Oxyanion removal experiments with the top two performing candidate ligands show a near quantitative removal (>99%) of sulfate or selenate from solution. When both sulfate and selenate are present, there is near quantitative removal (>99%) of selenate, down to sub-ppb Se levels, with no discrimination between the two oxyanions during cocrystallization. Reducing the selenate concentrations by 3 orders of magnitude or more relative to sulfate, as found in many wastewaters, led to no measurable loss in Se removal efficiencies. This work offers a simple and effective alternative to selective separation of trace amounts of highly toxic selenate oxyanions from wastewaters, to meet stringent regulatory discharge limits.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

A new generation of direct X-ray detectors for medical and synchrotron imaging applications

Abstract Large-area X-ray imaging is one of the most widely used imaging modalities that spans several scientific and technological fields. Currently, the direct X-ray conversion materials that are being commercially used for large-area (> 8 cm × 4 cm without tiling) flat panel applications, such as amorphous selenium (a-Se), have usable sensitivities of up to only 30 keV. Although there have been many promising candidates (such as polycrystalline HgI 2 and CdTe), none of the semiconductors were able to assuage the requirement for high energy (> 40 keV) large-area X-ray imaging applications due to inadequate cost, manufacturability, and long-term performance metrics. In this study, we successfully demonstrate the potential of the hybrid Methylammonium lead iodide (MAPbI 3 ) perovskite-based semiconductor detectors in satisfying all the requirements for its successful commercialization in synchrotron and medical imaging. This new generation of hybrid detectors demonstrates low dark current under electric fields needed for high sensitivity X-ray imaging applications. The detectors have a linear response to X-ray energy and applied bias, no polarization effects at a moderate bias, and signal stability over long usage durations. Also, these detectors have demonstrated a stable detection response under BNL’s National Synchrotron Light Source II (NSLS-II) 70 keV monochromatic synchrotron beamline.

47 OTHER INSTRUMENTATION↗

DOE OSTI2025

Stacking polymorphism of PtSe 2 : its implication to layer-dependent metal-insulator transitions

Using diffusion Monte Carlo (DMC) and density functional theory (DFT) calculations, we examine the structural stability and interlayer binding properties of PtSe 2 . Our DMC study reveals that AA and AB-r bilayer stacking modes are nearly degenerate, highlighting the significant role of interlayer hybridization in offsetting the energy cost due to larger interlayer separations in the AB-r mode. Additionally, our DMC-benchmarked DFT calculations with the r 2 SCAN+rVV10 functional uncover pronounced stacking polymorphism in few-layer PtSe 2 , driven by degenerate AA and AB-r interfaces, which leads to substantial band gap variations across different stacking configurations. This polymorphism, along with selenium vacancies, influences a layer-dependent metal-insulator transition observed in few-layer PtSe 2 . Our findings emphasize the importance of both van der Waals interactions and interlayer hybridization in determining the phase stability and electronic properties of PtSe 2 , advancing our understanding of its fundamental properties and refining theoretical models for practical applications in nanoelectronic devices.

Electronic materials↗

DOE OSTI2026

Discovery of magnetic-field-tunable density modulations and spin tilting in a layered altermagnet

Altermagnets recently emerged as a new class of magnetic materials, arising from specific spin crystal symmetries. They exhibit a spin-polarized electronic band structure similar to ferromagnets, yet possess zero net magnetization, promising exotic properties. Here we study a layered triangular lattice altermagnet, cobalt-intercalated NbSe 2 using scanning tunneling microscopy and spectroscopy (STM/S). Spectroscopic-imaging STM and spin-polarized STM reveals emergent 2 a 0 tri-directional charge and spin density modulations on the selenium surface. Density functional theory simulations suggest these modulations reflect the underlying cobalt superstructure. We discover that an out-of-plane magnetic field tunes the modulation amplitudes and the electronic density-of-states in a manner dependent on the field direction and strength. This behavior is attributed to the field-induced tilting of cobalt spins, which can have profound implications on the electronic properties of the altermagnet. Our results provide atomic-scale insights to uncover a magnetic-field tunable altermagnetic band structure, highlight the importance of understanding spin canting in altermagnets.

condensed-matter physics↗

DOE OSTI2020

The synthesis of competing phase GeSe and GeSe 2 2D layered materials

We report the synthesis of layered anisotropic semiconductor GeSe and GeSe 2 nanomaterials through low temperature and atmospheric pressure chemical vapor deposition using halide based precursors. The crystal phase is controlled by simply changing selenium vapor pressure.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Design, synthesis and characterization of fused bithiazole- and dithiophene-based low bandgap thienylenevinylene copolymers

The structural rigidity of fused units in the polymer backbone, in addition to the resulting stabilizing effect of the quinoidal structure, and tunable electronic properties have played a key role in promoting highly-ordered π-stacking moieties, exhibiting promising charge carrier mobilities. The electron-deficient thiazole moiety shows high planarity and effective π–π stacking, which leads to the reduction in the energy levels of the highest occupied and lowest unoccupied molecular orbitals (HOMO/LUMO), and ideally enhances the electron charge mobility. Four heterocycle-based monomers BTzS, BTzSe, DTS, and DTG based on fused bithiazole and dithiophene units incorporated with sulfur, selenium, silicon, and germanium as the bridging atoms were synthesized and characterized. Here, the monomers were copolymerized with the electron-rich alkylated thienylenevinylene (TV) unit to afford copolymers P1–P4. The thermal, optical, and electrochemical properties and crystallinity of the copolymers were thoroughly investigated. Extensive OFET device optimization using different solvents and annealing temperatures resulted in the best charge mobility of 0.09 cm2 V –1 s –1 for the electron-deficient bithiazole BTzS copolymer P1 and 0.36 cm2 V –1 s –1 for the DTS copolymer P3.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Isostructural bridging diferrous chalcogenide cores [Fe II (μ-E)Fe II ] (E = O, S, Se, Te) with decreasing antiferromagnetic coupling down the chalcogenide series

Iron compounds containing a bridging oxo or sulfido moiety are ubiquitous in biological systems, but substitution with the heavier chalcogenides selenium and tellurium, however, is much rarer, with only a few examples reported to date. Here we show that treatment of the ferrous starting material [( tBu pyrpyrr 2 )Fe(OEt 2 )] (1-OEt 2 ) ( tBu pyrpyrr 2 = 3,5- t Bu 2 -bis(pyrrolyl)pyridine) with phosphine chalcogenide reagents E = PR 3 results in the neutral phosphine chalcogenide adduct series [( tBu pyrpyrr 2 )Fe(EPR 3 )] (E = O, S, Se; R = Ph; E = Te; R = t Bu) (1-E) without any electron transfer, whereas treatment of the anionic starting material [K] 2 [( tBu pyrpyrr 2 )Fe 2 (μ-N 2 )] (2-N 2 ) with the appropriate chalcogenide transfer source yields cleanly the isostructural ferrous bridging mono-chalcogenide ate complexes [K] 2 [( tBu pyrpyrr 2 )Fe 2 (μ-E)] (2-E) (E = O, S, Se, and Te) having significant deviation in the Fe–E–Fe bridge from linear in the case of E = O to more acute for the heaviest chalcogenide. All bridging chalcogenide complexes were analyzed using a variety of spectroscopic techniques, including 1 H NMR, UV-Vis electronic absorbtion, and 57 Fe Mössbauer. The spin-state and degree of communication between the two ferrous ions were probed via SQUID magnetometry, where it was found that all iron centers were high-spin (S = 2) Fe II , with magnetic exchange coupling between the Fe II ions. Magnetic studies established that antiferromagnetic coupling between the ferrous ions decreases as the identity of the chalcogen is tuned from O to the heaviest congener Te.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Photodoping of graphene with long-lived electrons by interfacing with Janus WSSe

The performance of semiconductor optoelectronic devices depends on efficient photodoping of active materials, where optical excitation generates photocarriers. Despite more than two decades of research, efficient photodoping in graphene remains elusive due to the formation of neutral excitons with ultrashort lifetimes. Here, by interfacing graphene with a Janus WSSe monolayer, we achieve unipolar photodoping of graphene with long-lived carriers. The Janus monolayer was synthesized via selenium implantation of WS 2 monolayers grown by chemical vapor deposition. We fabricated the heterostructure by transferring a mechanically exfoliated graphene monolayer onto the Se-terminated side of WSSe. Through photoluminescence and transient absorption spectroscopy, we demonstrate that photoexcited electrons in WSSe transfer efficiently to graphene, while a portion of the photoexcited holes remains confined in WSSe due to its built-in electric field. This charge separation leads to a net electron population in graphene. These electrons exhibit extended lifetimes due to spatial separation from their recombination partners, offering a promising route to enhancing the performance of graphene-based optoelectronic devices.

Zheng, Ting [Southeast Univ., Nanjing (China); Uni↗

DOE OSTI2025

Computational discovery of a novel double transition metal nitride MXene and its applications as an anchoring and catalytic material in Li–Se batteries

Double transition metal (DTM) nitride MXenes offer enhanced electrical conductivity and tunable catalytic properties compared to conventional carbide-based MXenes. In this study, we employed first-principles density functional theory (DFT) calculations to discover and computationally validate a novel DTM nitride MXene, Nb 2 TiN 2 , derived from its MAX phase precursor and investigated its potential as an anchoring material (AM) for Li–Se batteries. This newly proposed MXene expands the compositional landscape of DTM nitrides and opens new avenues for functional material design. We performed a comprehensive analysis of the thermodynamic and electronic properties of Nb 2 TiAlN 2 , and the MAX phase precursor to Nb 2 TiN 2 to assess its structural stability and exfoliation potential. Exfoliation energy calculations confirmed the feasibility of synthesizing Nb 2 TiN 2 from Nb 2 TiAlN 2 . We then explored the functionalized form, Nb 2 TiN 2 S 2 , evaluating its capability to serve as an effective anchoring material (AM) in Li–Se batteries by analyzing the reaction mechanisms and kinetics of the selenium reduction reaction (SeRR). Our results indicate that Nb 2 TiN 2 S 2 exhibits a strong binding affinity for lithium polyselenides (Li 2 Se n ), effectively suppressing the shuttle effect. Gibbs free energy calculations for the rate-limiting step of the SeRR reveal favorable kinetics and reduced reaction barriers. Overall, this study provides a detailed evaluation of the structural and electronic properties of a newly proposed DTM nitride MXene and its S-functionalized derivative and the catalyzing effect of Nb 2 TiN 2 S 2 in accelerating the reaction kinetics in Li–Se batteries. These findings underscore the potential importance of the further exploration of MXenes to address current challenges in high-performance Li–Se batteries.

25 ENERGY STORAGE↗

DOE OSTI2025

Hydrazine-free precursor for solution-processed all-inorganic Se and Se 1− x Te x photovoltaics

Selenium (Se) has reemerged as a promising absorber material for indoor and tandem photovoltaics (PVs), and its alloys with Te (Se 1−x Te x ) offer a widely tunable bandgap. Solution processing of this materials system offers a route to low-cost fabrication. However, solution processing of Se has, thus far, only used hydrazine, which is an extremely hazardous solvent. In this work, we prepare and isolate propylammonium poly-Se and poly-Se–Te precursors from a safer thiol-amine solvent system. We formulate molecular inks by dissolving the precursor in dimethylformamide (DMF) with a monoethanolamine (EA) additive and process high-quality Se and Se 1−x Te x films with bandgaps ranging from 1.20 eV to 1.86 eV. We fabricate PVs from these films using TiO 2 and MoO 3 charge transport layers (CTLs) to achieve power conversion efficiencies as high as 2.73% for Se and 2.33% for Se 0.7 Te 0.3 under solar simulation. Se devices show excellent stability with no degradation after 1 month in air, enabled by the excellent stability of Se and the use of inorganic CTLs. This work represents an important step towards low-cost solution-phase processing of Se and Se 1−x Te x alloys for PVs and photodetectors with low toxicity and high bandgap tunability.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Bypassing sulfides: comparing the morphology and performance of solution processed Cu(In,Ga)Se 2 films prepared via two selenide molecular precursor routes

Solution-processing of thin-film photovoltaics offers an alternative to vacuum-deposition based approaches. The amine–thiol reactive solvent system has become a focal point for the solution-processing of chalcogenide species, owing to the convenience of precursor preparation and comparatively high performance of prepared devices. Selenide species prepared via the amine–thiol route typically progress through a sulfide intermediate phase, and as such are commonly afflicted with sulfur and carbon impurities along- side the presence of a carbonaceous fine-grained layer. Here, two routes of preparing films directly to a selenide phase are examined; first by the co-dissolution of selenium in an amine–thiol solution and second via the novel use of reactive alkylammonium polyselenides. Lamella are cut from these selenide precursor films and final devices, and STEM-EDX and TEM are used to characterize film morphology and secondary phases. A champion device efficiency of 11.2% is reported for the novel polyselenide route, and clear paths of improvement are identified.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Defect-mediated metastability and carrier lifetimes in polycrystalline (Ag,Cu)(In,Ga)Se 2 absorber materials

Using a combination of optical and electrical measurements, we develop a model for metastable defects in Ag-alloyed Cu(In,Ga)Se 2 , one of the leading thin film photovoltaic materials. By controlling the pre-selenization conditions of the back contact prior to the growth of polycrystalline (Ag,Cu)(In,Ga)Se 2 absorbers and subsequently exposing them to various stresses (light soaking and dark-heat), we explore in this paper the nature and role of metastable defects on the electro-optical and photovoltaic performance of high-efficiency solar cell materials and devices. Positron annihilation spectroscopy indicates that dark-heat exposure results in an increase in the concentration of the selenium–copper divacancy complex (V Se –V Cu ), attributed to depassivation of donor defects. Deep-level optical spectroscopy finds a corresponding increase of a defect at Ev+0.98 eV, and deep-level transient spectroscopy suggests that this increase is accompanied by a decrease in the concentration of mid-bandgap recombination centers. Time-resolved photoluminescence excitation spectroscopy data are consistent with the presence of the V Se –V Cu divacancy complex, which may act as a shallow trap for the minority carriers. Light-soaking experiments are consistent with the V Se –V Cu optical cycle proposed by Lany and Zunger, resulting in the conversion of shallow traps into recombination states that limit the effective minority carrier recombination time (and the associated carrier diffusion length) and an increase in the doping density that limits carrier extraction in photovoltaic devices.

14 SOLAR ENERGY↗

DOE OSTI2020

Impact of UV-induced ozone and low-energy Ar + -ion cleaning on the chemical structure of Cu(In,Ga)(S,Se) 2 absorber surfaces

Dry buffer layer deposition techniques for chalcopyrite (CIGSSe)-based thin-film solar cells lack the surface-cleaning characteristics of the commonly used CdS or Zn(O,S) wet-chemical bath deposition. Here, a UV-induced ozone and/or a low-energy Ar + -ion treatment could provide dry CIGSSe surface cleaning steps. To study the impact of these treatments, the chemical surface structure of a CIGSSe absorber is investigated. For this purpose, a set of surface-sensitive spectroscopic methods, i.e., laboratory-based x-ray photoelectron spectroscopy and x-ray-excited Auger electron spectroscopy, is combined with synchrotron-based soft x-ray emission spectroscopy. After treatment times as short as 15 s, the UV-induced ozone treatment decreases the amount of carbon adsorbates at the CIGSSe surface significantly, while the oxygen content increases. This is accompanied by the oxidation of all absorber surface elements, i.e., indium, selenium, sulfur, and copper. Short (60 s) low-energy Ar + -ion treatments, in contrast, primarily remove oxygen from the surface. Longer treatment times also lead to a removal of carbon, while extremely long treatment times can also lead to additional (likely metallic) Cu phases at the absorber surface as well.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Electronic structure modulation of MoS2 by substitutional Se incorporation and interfacial MoO3 hybridization: Implications of Fermi engineering for electrocatalytic hydrogen evolution and oxygen evolution

The design of earth-abundant electrocatalysts that can facilitate water splitting at low overpotentials, provide high current densities, and enable prolonged operational lifetimes is central to the production of sustainable fuels. The distinctive atomistic and electronic structure characteristics of the edges of MoS2 imbue high reactivity toward the hydrogen evolution reaction. MoS2 is nevertheless characterized by significantly high overpotentials as compared to platinum. Here, we demonstrate that modulation of the electronic structure of MoS2 through interfacial hybridization with MoO3 and alloying of selenium on the anion sublattice allows for systematic lowering of the conduction band edge and raising of the valence band edge, respectively. The former promotes enhanced electrocatalytic activity toward hydrogen evolution, whereas the latter promotes enhanced activity toward the oxygen evolution reaction. Such alloyed heterostructures prepared by sol-gel reactions and hydrothermal selenization expose a high density of edge sites. The alloyed heterostructures exhibit low overpotential, high current density, high turnover frequency, and prolonged operational lifetime. The mechanistic origins of catalytic activity have been established based on electronic structure calculations and x-ray absorption and emission spectroscopy probes of electronic structure, which suggest that interfacial hybridization at the MoO3 interface yields low-lying conduction band states that facilitate hydrogen adsorption. In contrast, shallow Se 4p-derived states give rise to a raised effective valence band maximum, which facilitates adsorption of oxygen intermediates and engenders a low overpotential for the oxygen evolution reaction. The findings illustrate the use of electronic structure modulation through interfacial hybridization and alloying to systematically improve electrocatalytic activity.

Parija, Abhishek↗

DOE OSTI2022

Structural heterogeneity in non-crystalline Te x Se1−x thin films

Rapid crystallization behavior of amorphous TexSe1−x thin films limits the use of these alloys as coatings and in optoelectronic devices. Understanding the short- and medium-range ordering of the amorphous structure and the fundamental physics governing the crystallization of the films is crucial. Although the lack of long range crystalline order restricts the characterization of the amorphous films, electron microscopy offers a way to extract information about the nanoscale ordering. In this paper, the local ordering of amorphous TexSe1−x thin films with x=0.22, 0.61, 0.70, 0.90, and 1 grown by thermal evaporation is investigated using radial distribution function (RDF) and fluctuation electron microscopy (FEM) analysis. RDF results show that the nearest-neighbor distances of selenium (Se) and tellurium (Te) in their crystalline structure are preserved, and their bond lengths increase with the addition of Te. Density functional theory (DFT) calculations predict structures with interatomic distances similar to those measured experimentally. Additionally, fluctuations in atomic coordination are analyzed. Medium range order (MRO) analysis obtained from FEM and DFT calculations suggests that there are at least two populations within the chain network structure, which are close to the Se–Se and Te–Te intrachain distances. For the binary alloy with x > 0.61, TexSe1−x, Te–Te like populations increase and Te fragments might form, suggesting that the glass forming ability decreases rapidly.

Sari, Bengisu (ORCID:0000000244217098)↗

DOE OSTI2021

Selective cysteine-to-selenocysteine changes in a [NiFe]-hydrogenase confirm a special position for catalysis and oxygen tolerance

Significance Substitution of cysteine by selenocysteine is held responsible for the increased performance of many enzymes: The higher activity of [NiFeSe]-hydrogenases compared with their [NiFe] counterparts is often attributed to the Sec replacement of one active-site cysteine ligand. Replacing each of the four active-site cysteine residues in an O 2 -tolerant [NiFe]-hydrogenase by selenocysteine shows that this substitution alone does not overcome the inability to evolve H 2 that is a characteristic of the group 1d hydrogenases. A nonbridging cysteine lying on the direct path between the Ni and an adjacent proton-relaying glutamic acid emerges as being very special: Its substitution by selenocysteine confers extreme tolerance to O 2 but disrupts the proton transfer pathway, providing an example of where sulfur is superior to selenium.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Copper migration and surface oxidation of CuxBi2Se3 in ambient pressure environments

Abstract Chemical modifications such as intercalation can be used to modify surface properties or to further functionalize the surface states of topological insulators (TIs). Using ambient pressure x-ray photoelectron spectroscopy, we report copper migration in C u x B i 2 S e 3 , which occurs on a timescale of hours to days after initial surface cleaving. The increase in near-surface copper proceeds along with the oxidation of the sample surface and large changes in the selenium content. These complex changes are further modeled with core-level spectroscopy simulations, which suggest a composition gradient near the surface which develops with oxygen exposure. Our results shed light on a new phenomenon that must be considered for intercalated TIs—and intercalated materials in general—that surface chemical composition can change when specimens are exposed to ambient conditions.

36 MATERIALS SCIENCE↗