Se Atoms Research Articles

Synthesis of novel alkynyl imidazopyridinyl selenides: copper-catalyzed tandem selenation of selenium with 2-arylimidazo[1,2-a]pyridines and terminal alkynes.

Alkynyl selenides have attracted considerable research interest recently, owing to their applications in the biological and pharmaceutical fields. The Cu-catalyzed tandem reaction for the synthesis of novel alkynyl imidazopyridinyl selenides is presented. A one-pot synthesis route afforded alkynyl imidazopyridinyl selenides in moderate to good yields. This was achieved by a two-step reaction between terminal alkynes and diimidazopyridinyl diselenides, generated from imidazo[1,2-a]pyridines and Se powder, using 10 mol % of CuI and 1,10-phenanthroline as the catalytic system under aerobic conditions. The C(sp2)–Se and C(sp)–Se bond-formation reaction can be performed in one-pot by using inexpensive and easy to handle Se powder as the Se source. The reaction proceeded with terminal alkynes having various substitutions, such as aryl, vinyl, and alkyl groups. The obtained alkynyl imidazopyridinyl selenide was found to undergo nucleophilic substitution reaction on Se atom using organolithium reagents and 1,3-dipolar azide–alkyne cycloaddition based on the alkyne moiety.

Doping effects on electronic structures and current-voltage characteristics of GR/InSe/GR selectors

The graphene(GR)/InSe/GR selector was designed based on the rectifying effect of the Schottky barrier at the GR/InSe heterostructure interface. The selector performance was improved by doping groups I–VII A elements, and the effects were studied by first-principles calculations. The band structure results showed that InSe retained p-type semiconductor characteristics only when Se atoms were substitutionally doped by groups IV A (C, Si, Ge) and VI A (O, S) elements. The band gap of the GR/InSe heterostructure doped with group IV A (C, Si, Ge) elements became narrower, and the conductivity became stronger. The band structures of the GR/InSe heterostructures doped with group VI A (O, S) elements were hardly changed. From the plane average electrostatic potential and the charge density difference, it is observed that doping of group IV A (C, Si, Ge) elements reduced the height and width of the Schottky barrier at the interface and enhanced the built-in electric field strength of the heterostructures. Finally, the current-voltage (I-V) curves show that compared with the undoped GR/InSe/GR selector, the on-state current (Ion) and nonlinearity (NL) coefficient of selectors doped with group IVA (C, Si, Ge) elements increased, and the threshold voltage (Vth) and off-state current (Ioff) decreased. It can better suppress the influence of the leakage current on the RRAM, which is important for the development of high-performance and low-power selectors.

Adsorption and sensing performances of Rh-embedded PtSe2 monolayer upon CO and HCHO in dry-type reactors: A first-principles study

Based on the first-principles method, we theoretically analyze the Rh-embedded PtSe2 (Rh-PtSe2) monolayer as a potential gas sensor in this paper, for detection of CO and HCHO in the dry-type reactor to evaluate its operation status. The Rh-embedding behavior is performed by substituting a Se atom at the topmost Se layer of the pristine PtSe2 monolayer, and we find that the Rh atom can be stably and energy-favorably embedded in the PtSe2 monolayer with the formation energy (Eform) of −0.53 eV. Chemisorption is identified for the CO and HCHO system, with the adsorption energy (Ead) as −1.89 and −1.05 eV, respectively. The electronic property analysis reveals that the Rh-PtSe2 monolayer can be a promising resistance-type sensor or a field-effect transistor sensor for detection of two gas species, with good sensing response or selectivity. This theoretical work can pave the way to further investigate the sensing application of Rh-PtSe2 monolayer upon toxic gases in the dry-type reactors, and related experimental research can verify our findings and to confirm that Rh-PtSe2 monolayer is a promising sensing candidate to evaluate the operation status of the dry-type reactors in the power system.

Dispersible CdS1−xSex solid-solution nanocrystal photocatalysts: Photoinduced self-transformation synthesis and enhanced hydrogen-evolution activity

Modulating the electronic structure of Cadmium sulfide (CdS) by non-metallic elements to produce solid-solution photocatalysts serves as a potential route to improve its performance of photocatalytic hydrogen (H2) evolution. However, exploring an effective synthetic route of CdS-based solid solution is still a great challenge. Herein, the CdS1−xSex solid-solution nanocrystals were successfully synthesized by an accessible photoinduced self-transformation route, including the direct formation of dispersible CdS1−x(SeS)x and the in situ self-transformation of selenosulfide ((SeS)2−) to Se2− by photoexcited electrons. The prepared CdS1−xSex solid-solution photocatalysts possess a small crystallite size of ca. 5 nm and their bandgaps can be easily tuned in a wide range of 1.84–2.28 eV by tailoring the mole ratio of Se/S. The resultant CdS0.90Se0.10 solid-solution photocatalyst realizes the highest H2-production tempo of 94.6 μmol·h−1, which is 1.6 folds higher than that of CdS. The experimental and theoretical studies supported that the incorporation of Se atoms could not only narrow the bandgap value to reinforce visible-light absorption, but also tune its electronic structure to optimize interfacial H2-evolution dynamics, thus achieving an efficient photocatalytic H2-production rate of the dispersible CdS1−xSex solid solution. This study may deliver advanced inspirations for optimizing the electronic structure of photocatalysts towards sustainable H2 production.

First-principles calculations of magnetic and optical properties of (Mn, Mo) co-doped SnSe2

In this paper, based on density functional theory GGA + U method, the electronic structure, magnetic and optical properties of single Mn, single Mo and (Mn, Mo) co-doped SnSe2 are studied. The calculation results show that the doping of single Mn and single Mo can make the intrinsic SnSe2 magnetic. In addition, five different (Mn, Mo) co-doped configurations are calculated and the ∆E of the stable ferromagnetic configuration is about −227.6 meV. The stable ferromagnetic configuration is caused by the strong hybridization of the d-p orbitals of Mn, Mo and Se atoms and the formation a Mn:3d-Se:4p-Mo:4d coupling chain. And the absorption intensity of SnSe2 system in visible light is improved by the introduction of doped atoms. Our study shows that introducing appropriate dopants is a feasible method to improve the magnetic and optical properties of intrinsic SnSe2 base.

Laser fluence dependence of stoichiometry and superconductivity of iron chalcogenide superconducting films on metal tapes

Iron chalcogenide Fe(Se,Te) films with thicknesses of 150 nm were deposited on CeO2-buffered metal tapes via pulsed laser deposition using various laser fluences. The film crystallinity and stoichiometry improved upon increasing the laser fluence. This was explained by the ablation threshold that the superconducting performance was better at higher laser fluences and was attributed to the joint contribution of higher Te contents, better texture, and strengthened in-plane strain. In addition, the pinning mechanism was studied by analyzing the in-field performance characteristics of the Fe(Se,Te) films. The dominant pinning center remained point pinning and was independent of the magnetic field direction and temperature. A collective pinning theory-based analysis showed that the vortex pinning behavior in the Fe(Se,Te) film varied from δl pinning to δTc pinning as the temperature approached the critical temperature. This was related to film superconductivity inhomogeneity, which was driven by unreacted Se and Te atoms.

Impact of local atomic arrangements on ovonic threshold switching of amorphous Ge-As-Se thin films

Amorphous Ge-As-Se film features a good ovonic threshold switching (OTS) performance. However, both endurance of OTS operation and crystallization temperature become dramatically deteriorated at specific compositions. We employ EXAFS technique to elucidate local atomic environments in cosputter-deposited amorphous (Ge50Se50)x-(Ge30As70)1-x films. At low Se contents, Se atoms are preferentially bonded to Ge atoms, and therefore Ge-Se fraction is conspicuously higher than As-Se counterpart. A covalent network structure typical of amorphous chalcogenides is supposed to form. At high Se contents, however, As-Se pair starts to abruptly increase at the expense of As-Ge fraction. Now verified in these high-Se compositions is appearance of molecular units composed of As and Se atoms, i.e., As4Se4 and/or As4Se3. The sudden deterioration is attributed to presence of the molecular units which lower connectivity of the covalent network via introducing inhomogeneity in a medium-range scale. The present finding exemplifies impact of local atomic arrangements on OTS phenomenon.

Post-growth Fe deposition on the superconductivity of monolayer FeSe films on SrTiO3−δ

The superconductivity in bulk FeSe depends sensitively on the stoichiometry, ditto for the monolayer FeSe films grown on $\mathrm{SrTi}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ and other substrates. To tune the stoichiometry, we deposit Fe onto monolayer FeSe films after epitaxial growth. Using in situ low-temperature scanning tunneling microscopy/spectroscopy, we find that the postdeposited Fe atoms incorporate into monolayer films and combine with excess Se to form FeSe, with an upper coverage limit of \ensuremath{\sim}0.4 unit-cell. Consequently, the superconducting gap concentrates in 10 to 12 meV. The work demonstrates a simple method for stoichiometry tuning and improving the spatial uniformity of monolayer FeSe films. Compared with the gap of \ensuremath{\sim}15 to 20 meV for the annealed films, the smaller superconducting gap indicates weakened FeSe-${\mathrm{TiO}}_{2}$ coupling due to interfacial Se atom substitution.

Investigation of structural, optoelectronic and thermoelectric properties of GaCuX2 (X = S, Se and Te) chalcopyrites semiconductors using the accurate mBJ approach

Ternary chalcopyrites have recently been the focus of scientists due to their optoelectronic and thermoelectric application as solar energy converters, nonlinear optical devices and detectors. In the present study, we used the first principle calculations based on the density functional theory (DFT) to explore the structural, optoelectronic and thermoelectric properties of GaCuX2 (X = S, Se and Te). The electronic band structure, density of states and optical properties were investigated using the modified Becke Johnson (TB-mBJ) approximation. These materials were discovered to be direct band gap semiconductors in this study, which agrees well with previously reported results. When compared to GaCuS2 and GaCuTe2, GaCuSe2 has a smaller gap value, due to the lower chemical bonding nature of Ga and Se atoms. The density of states of these three ternary chalcopyrites, as well as their optical properties including dielectric functions, optical conductivity and absorption coefficient have also been examined and discussed in details. The maximum reflectivity occurs at 13.5 eV, which exists in the ultra-violet region, showing that investigated materials can be employed to shield high frequency ultraviolet radiations. The calculated maximum refractive index static value varies from 1.5 to 5.5 eV, predicting that the materials under consideration can be used in a vast range of optoelectronic applications, especially in the visible range. GaCuS2 shows high refraction among these compounds. Finally, the thermoelectric properties of these materials, such as the Seebeck coefficient, the power factor and figure of merit, are analyzed using the semi-classical Boltzmann theory as executed in the BoltzTraP code. The high Seebeck coefficient and figure of merit values reveal that these systems belong to a new class of high-efficiency thermoelectric materials (TE) for high-temperature application fields. These findings are likely to open up new route for researchers looking into the potential areas of application of these compounds in thermoelectric and optoelectronic devices.

Consecutive hybrid mechanism boosting Na+ storage performance of dual-confined SnSe2 in N, Se-doping double-walled hollow carbon spheres

Rationally designed hierarchical structures and heteroatomic doping of carbon are effective strategies to enhance the stability and electrical conductivity of materials. Herein, SnSe2 flakes were generated in the double-walled hollow carbon spheres (DWHCSs), in which N and Se atoms were doped in the carbon walls, to construct SnSe2@N, Se-DWHCSs by confined growth and in-situ derivatization. The N and Se-doped DWHCSs can effectively limit the size increase of SnSe2, promote ion diffusion kinetics, and buffer volume expansion, which can be proved by electron microscope observation and density functional theory calculation. Consequently, the SnSe2@N, Se-DWHCSs as an anode material for sodium ion batteries (SIBs) demonstrated a distinguished reversible capacity of 322.8 mAh g−1 at 5 A g−1 after 1000 cycles and a superior rate ability of 235.3 mAh g−1 at an ultrahigh rate of 15 A g−1. Furthermore, the structure evolution and electrochemical reaction processes of SnSe2@N, Se-DWHCSs in SIBs were analyzed by ex-situ methods, which confirmed the consecutive hybrid mechanism and the phase transition process.

Low-energy Se ion implantation in MoS2 monolayers

In this work, we study ultra-low energy implantation into MoS2 monolayers to evaluate the potential of the technique in two-dimensional materials technology. We use 80Se+ ions at the energy of 20 eV and with fluences up to 5.0·1014 cm−2. Raman spectra of the implanted films show that the implanted ions are predominantly incorporated at the sulfur sites and MoS2−2xSe2x alloys are formed, indicating high ion retention rates, in agreement with the predictions of molecular dynamics simulations of Se ion irradiation on MoS2 monolayers. We found that the ion retention rate is improved when implantation is performed at an elevated temperature of the target monolayers. Photoluminescence spectra reveal the presence of defects, which are mostly removed by post-implantation annealing at 200 °C, suggesting that, in addition to the Se atoms in the substitutional positions, weakly bound Se adatoms are the most common defects introduced by implantation at this ion energy.

Defective Nature of CdSe Quantum Dots Embedded in Inorganic Matrices

Quantum dots (QDs) embedded in inorganic matrices have been extensively studied for their potential applications in lighting, displays, and solar cells. While a significant amount of research studies focused on their experimental fabrication, the origin of their relatively low photoluminescence quantum yield has not been investigated yet, although it severely hinders practical applications. In this study, we use time-dependent density functional theory (TDDFT) to pinpoint the nature of excited states of CdSe QDs embedded in various inorganic matrices. The formation of undercoordinated Se atoms and nonbridging oxygen atoms at the QD/glass interface is responsible for the localization of a hole wave function, leading to the formation of low-energy excited states with weak oscillator strength. These states provide pathways for nonradiative processes and compete with radiative emission. The photoluminescence performance is predicted for CdSe QDs in different matrices and validated by experiments. The results of this study have significant implications for understanding the underlying photophysics of CdSe QDs embedded in inorganic matrices that would facilitate the fabrication of highly luminescent glasses.

Abstract 5451: New organoselenium compounds with cytotoxic activity in vitro and in vivo towards colon cancer

Abstract Colon cancer is currently the third most common diagnosed cancer and the second leading cause of cancer death worldwide. The inclusion of a selenium atom (Se) in organic molecules has been shown to be a valid approximation in the design of novel chemotherapeutic agents with antitumoral activity. On the other hand, non-steroidal anti-inflammatory drugs (NSAIDs) have gained interest in recent years in terms of their chemopreventive and chemotherapeutic use for cancer treatment whether they are evaluated alone, as a combination therapy, or in the form of structurally modified analogs. Considering these findings, we have designed five novel NSAID derivatives containing Se in their structure. The cytotoxicity and selectivity of the new compounds were evaluated in a panel of 10 cancer cell lines including breast, prostate, lung, and colon cancer, and in two non-malignant cell lines. Compound 5 was the most cytotoxic derivative with IC50 values below 10 µM in all the cancer cell lines tested, and it was also the most selectively toxic towards cancer cells while sparing the non-malignant cell lines. The efficacy of compound 5 in vivo was assessed in a subcutaneous colon cancer xenograft mouse model and it showed a significant inhibition of the tumor growth. Taken together, this work supports that the novel Se-NSAID combination provides a feasible frame to develop new agents with potent antitumoral properties Citation Format: Sandra Ramos-Inza, Cesar Aliaga, Asif Raza, Ignacio Encío, Arun Sharma, Carmen Sanmartín, Daniel Plano. New organoselenium compounds with cytotoxic activity in vitro and in vivo towards colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5451.

Abstract 5450: New se-nsaid hybrid molecules as potent and selective cytotoxic agents against breast cancer cells

Abstract Breast cancer is currently the most frequently diagnosed cancer and one of the leading causes of mortality among women worldwide. The introduction of a selenium atom (Se) in the structure of organic molecules has been demonstrated to be a valid approach in the design of novel chemotherapeutic agents with several biological effects, including antitumoral activity. In addition, several epidemiological, preclinical, and clinical studies support the chemopreventive and chemotherapeutic potential use of non-steroidal anti-inflammatory drugs (NSAIDs).On the basis of these findings, and taking into account the results of previous studies by our research group, we have developed a new series of twenty-five NSAID analogs bearing Se in the form of selenoesters modulated with different functional groups. The new compounds were tested in four cancer cell lines (HTB-54, DU-145, HT-29 and MCF-7) and two non-malignant cells (184B5 and BEAS-2B). The cytotoxicity of the five most potent and selective molecules was further studied in other cancer cell lines as well. Compounds 4a and 4d stood out as the most selective compounds with a selectivity index at least 5-fold higher in breast cancer cells. Compound 4d showed IC50 values below 10 µM and was found to be more potent than 4a in almost every cell line tested. Additionally, 4d effectively induced apoptosis in triple negative (MDA-MB-231) and estrogen receptor-positive (MCF-7) breast cancer cell lines. Taken together, this study supports the design of new derivatives containing Se as potential anticancer agents. Citation Format: Sandra Ramos-Inza, Ignacio Encío, Asif Raza, Arun Sharma, Carmen Sanmartín, Daniel Plano. New se-nsaid hybrid molecules as potent and selective cytotoxic agents against breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5450.

Density-functional theory study of magnetic and electronic properties of KFe2Se2 under pressure

The magnetic properties and electronic structures of KFe2Se2 under pressure were studied by first principles calculations. Five different states of KFe2Se2 were considered, and the ground state of collinear antiferromagnetic state was determined. The calculated results showed when the pressure was increased to 0.36 GPa, the connection between Fe atom and Se atom was strengthened and the magnetic moment was reduced to 0 µB. A gap appeared in the density of states between −4 eV and −3 eV, and the Fermi surface was greatly reconstructed. The electronic structures of KFe2Se2 under 0.36 GPa were similar to that of nonmagnetic KFe2Se2, while the stability of the system was not changed obviously. The results indicate that the evolution at the critical pressure 0.36 GPa was worthy of further study for KFe2Se2.

Intelligent Bi2Se3@Cu2−xSe heterostructures with enhanced photoabsorption and photoconversion efficiency for tri-modal imaging guided combinatorial cancer therapy by near-infrared Ⅱ light

A novel nanoplatform that supports multimodal imaging has been designed for deep tumor therapy. In this study, Bi2Se3@Cu2−xSe heterojunction nanocomposites with tunable spectral absorption, effective electron–hole separation and high photothermal conversion efficiency were prepared for the combination therapy of phototherapy (PT), chemodynamic therapy (CDT) and radiotherapy (RT). By adjusting the doping ratio, the heterojunction nanoparticles show obvious tunable ability of local surface plasmon resonance and the ability to promote electron-hole separation with significantly enhanced reactive oxygen species production capacity. The band structure and charge density difference calculated by density functional theory further reveal that the change of band gap and the decrease of free carriers can regulate the spectral absorption of nanomaterials and promote electron-hole separation. In addition, the photothermal conversion properties of low carrier density semiconductors are related to their inherent deep level defects. The formation of heterojunctions making the Se atoms deviate from the Bi2Se3 lattice, resulting in more deep level defects and stronger photothermal conversion properties. Meanwhile, this nanoplatform presented features similar to catalase activities and glutathione (GSH) consumption characteristics, which was capable of effectively alleviate the tumor-specific hypoxia environment to enhance the efficacy of O2-dependent photodynamic therapy (PDT) and radiotherapy (RT) and depletion GSH to prevent the reduction of therapeutic efficacy due to the clearance of reactive oxygen species. In addition to therapeutic enhancement, heterojunction nanomaterials have excellent nuclear magnetic resonance imaging (MRI), infrared thermal imaging (IR) and computed tomography (CT) properties due to their significant paramagnetism and excellent photothermal conversion and X-ray attenuation capacities. In conclusion, our findings provide a new strategy for designing multi-function and efficient nanoplatform to treat tumor.

How arsenic makes amorphous GeSe a robust chalcogenide glass for advanced memory integration

The 3D integration technology in semiconductor fabrication requires a key component, the ovonic threshold switching (OTS) selector, to suppress the current leakage. The As doped amorphous (a-) GeSe glass is a commercialized OTS material in 3D phase-change memory, but the understanding of such a doping mechanism is still inadequate. Here we systematically explore the effect of As doping on the structural, bonding, and dynamics properties of a-GeAsSe using ab initio molecular dynamics simulations. The results reveal that As atoms form strong bonds with both Ge and Se atoms. The distorted octahedral structures and the 5-fold rings linked by atoms are increased. All of these structural features lead to a more disordered configuration. Moreover, As atoms have notably slowed down the atomic mobility, rendering a-GeAsSe a high stability. Our studies offer insightful understanding of As-doping in OTS materials, paving the way for the design and application of advanced selector devices.

A theoretical study of the valence tautomerism of 1H-pyrazolium-4-olates (X = O) and related compounds (X = S, Se, NH): relative stabilities, protonation effects, and tautomerization barriers

The valence isomerism of a series of heterocyclic mesomeric betaines (HMBs) belonging to class 5, called pseudo-semi-conjugated HMBs, has been studied theoretically both the neutral and the protonated species. These HMBs are 1H-pyrazol-2-ium-4-olates and related compounds where the oxygen atom has been replaced by S, Se atoms, and an NH group. The main conclusion of the present work is that the ring/open valence tautomerism is possible both for neutral and protonated although it has never been observed experimentally.

Effects of implantation temperature and annealing on structural evolution and migration of Se into glassy carbon

The use of glassy carbon (GC) as a future nuclear waste storage material depends on its capability to retain all radioactive fission products found in spent nuclear fuels. Selenium (79Se) is found in trace amounts in uranium ores, spent, and reprocessed nuclear fuel. This work investigates the effects of implantation temperature and annealing on the structural evolution and migration of Se implanted GC. To achieve these objectives, 150 keV Se+ was implanted into GC samples separately at room temperature (RT) and 200 °C to a fluence of 1 × 1016 cm−2. Some of the as-implanted samples were annealed at 1000, 1100 and 1200 °C for 5h and characterised by transmission electron microscopy (TEM), Raman spectroscopy, and secondary ion mass spectrometry (SIMS). Both TEM and Raman spectroscopy showed that implantation caused defects in the GC structures, with more defects in the RT as-implanted sample. Annealing caused the healing of both sample types but retained some radiation damage. No migration of Se atoms was observed in the RT and 200 °C as-implanted samples. However, a different migration behaviour was seen after annealing the RT and 200 °C samples up to 1200 °C, attributed to the trapping and de-trapping of Se atoms in different amounts of defect induced by implantation.

Improving the electrochemical activity of PdSe2 by constructing P/T structural interfaces

Palladium diselenide (PdSe2) is acknowledged as a potential electrocatalyst for hydrogen evolution reaction (HER), but its large-scale basal plane is catalytically inert, which enormously limits its application in electrochemical efficiency. Here we employ the phase interface in PdSe2 to activate sites on the basal plane and improve the HER activity. Five P/T interface structures in PdSe2 are constructed and optimized by density functional theory (DFT) calculations. The interface boundaries consist of triangle, pentagonal and hexagonal rings with the formation of more Se-Se bonds. The structural stability and HER activity for these interface structures are evaluated, and the optimal sites for HER are confirmed, which are mostly located on Se atoms. Our proposed strategy proves the formation of interface in PdSe2 could successfully enhance its HER performance and could be also applicable to the other two-dimensional materials.