Chalcogenide Elements Research Articles

Reactivity of N-Heterocyclic Stannylenes: Oxidative Addition of Chalcogen Elements to a Chiral NH-Sn System

The reactivity of the racemic N-heterocyclic stannylene [{MeHCN(tBu)}Sn] (1) with the chalcogenide elements O2, S, Se, and Te has been investigated. In the case of the reaction of 1 with molecular oxygen, the cyclic tristannoxane complex [{MeHCN(tBu)}2Sn(μ-O)]3 (3) was isolated and characterised. NMR studies (1H, 13C, and 119Sn) show the formation of D3- and C2- symmetric assemblies. The reaction of 1 with S, Se, and Te, respectively, yielded the cyclo-distannachalcogenide complexes, [{MeHCN(tBu)}2Sn(μ-E)]3 (4: E = S, 5: E = Se, 6: E = Te), again with multinuclear NMR studies proving the formation of C2- and Cs-symmetric assemblies. Single crystal X-ray diffraction studies have been used to elucidate the molecular structures of the products of oxidative addition, 3, 4, 5, and 6.

CURVA MAESTRA PARA LA CRISTALIZACIÓN DE ALEACIONES AMORFAS SB70TE30

One of the possible uses of chalcogenide glasses is their application in phase change memory devices. The operation of these non-volatile memories is based on the use of an alloy with chalcogenide elements as a sensitive material, taking advantage of the great contrast in electrical resistance between the amorphous and crystalline states. The Sb70Te30(atomic percentage) alloy stands out among the chalcogenide materials with these properties. On the other hand, the knowledge of the microscopic mechanisms of the amorphous alloys crystallization allows microstructural control to optimize properties. At this point, differential scanning calorimetry (DSC) has been widely used for the determination of the thermal stability of amorphous alloys. Previously we have started the study of the crystallization kinetics ofSb70Te30amorphous alloys. In this work, a procedure based on the so-called isokinetic hypothesis has been applied to carry out the kinetic analysis of the calorimetric data of continuous heating. In particular, the so-called master curve of the crystallization kinetics of this alloy is determined.

Prediction of band gap of transition metal sulfide with Janus structure by deep learning atomic feature representation method

With the development of artificial intelligence, machine learning (ML) is more and more widely used in material computing. To apply ML to the prediction of material properties, the first thing to do is to obtain effective material feature representation. In this paper, an atomic feature representation method is used to study a low-dimensional, densely distributed atomic eigenvector, which is applied to the band gap prediction in material design. According to the types and numbers of atoms in the chemical formula of material, the Transformer Encoder is used as a model structure, and a large number of material chemical formula data are trained to extract the features of the training elements. Through the clustering analysis of the atomic feature vectors of the main group elements, it is found that the element features can be used to distinguish the element categories. The Principal Component Analysis of the atomic eigenvector of the main group element shows that the projection of the atomic eigenvector on the first principal component reflects the outermost electron number corresponding to the element. It illustrates the effectiveness of atomic eigenvector extracted by using the transformer model. Subsequently, the atomic feature representation method is used to represent the material characteristics. Three ML methods named Random Forest (RF), Kernel Ridge Regression (KRR) and Support Vector Regression (SVR) are used to predict the band gap of the two-dimensional transition metal chalcogenide compound MXY (M represents transition metal, X and Y refer to the different chalcogenide elements) with Janus structure. The hyperparameters of ML model are determined by searching for parameters. To obtain stable results, the ML model is tested by 5-fold cross-validation. The results obtained from the three ML models show that the average absolute error of the prediction using atomic feature vectors based on deep learning is smaller than that obtained from the traditional Magpie method and the Atom2Vec method. For the atomic eigenvector method proposed in this paper, the prediction accuracy of the KRR model is better than that of the results obtained from the Magpie method and Atom2Vec method. It shows that the atomic feature vector proposed in this paper has a certain correlation between the features, and is a low-dimensional and densely distributed feature vector. Visual analysis and numerical experiments of material property prediction show that the atomic feature representation method based on deep learning extraction proposed in this paper can effectively characterize the material features and can be applied to the tasks of material band gap prediction.

Enhanced thermoelectric performance in n-type Mg3.2Sb1.5Bi0.5 doping with lanthanides at the Mg site

• Gd and Ho have increased the DOS of the valence band near the Fermi level, and the d electrons of Gd and Ho have made extraordinary contributions. • Gd and Ho are effective n-type cation site dopants with higher doping efficiency and better carrier concentration than the anion site dopants chalcogenide elements. • For Mg 3.2 Gd 0.02 Sb 1.5 Bi 0.5 and Mg 3.2 Ho 0.02 Sb 1.5 Bi 0.5 samples, we obtain high zT values of 1.61 and 1.55 at 725 K, respectively. • Gd as well as Ho are an alternative effective n-type doping element for higher thermoelectric performance. Mg-based thermoelectric materials have attracted more and more attention because of their rich composition elements, green environmental protection, and lower price. In recent years, the thermoelectric properties of n-type Mg 3 Sb 2 materials have been optimized by doping chalcogenide elements (S, Se, and Te) at the anionic position. In this work, n-type Mg 3.2 A x Sb 1.5 Bi 0.5 ( A = Gd, Ho; x = 0.01, 0.02, 0.03, and 0.4) samples were prepared by the cation site doping of lanthanide elements (Gd and Ho). The research results show that Gd and Ho doped n-type Mg 3.2 Sb 1.5 Bi 0.5 samples are entirely comparable to the S, Se, and Te doped n-type Mg 3.2 Sb 1.5 Bi 0.5 samples, demonstrating more excellent thermoelectric properties. Doping with lanthanides (Gd and Ho) at the Mg site increases the carrier concentration of the material to 8.161 × 10 19 cm −3 . Doping induces the contribution of more electron, thus obtaining higher conductivity. The maximum zT value of the Mg 3.2 Gd 0.02 Sb 1.5 Bi 0.5 and the Mg 3.2 Ho 0.02 Sb 1.5 Bi 0.5 samples reaches 1.61 and 1.55, respectively. This work theoretically and experimentally demonstrates Gd and Ho are efficient n-type dopants for Mg 3.2 Sb 1.5 Bi 0.5 thermoelectric material.

Chalcogens reduce grain Cd accumulation by enhancing Cd root efflux and upper organ retention in wheat (Triticum aestivum L.)

A seedling-stage sand culture experiment and whole growth period pot experiment were conducted together to investigate the effects of chalcogenide elements (S, Se, Te) on the morphology, photosynthesis, Cd absorption, Cd and mineral nutrient transport, and transporter gene expression of wheat under Cd stress. Compared with S, Se and Te can alleviate wheat Cd toxicity and reduce Cd accumulation more efficiently. Compared with control conditions, S reduced the root Cd concentration by about 20 %, while SeIV and TeIV reduced the root Cd concentration by more than 60 % and the shoot Cd concentration by about 30 %. Chalcogens reduced Cd uptake by increasing root diameter (by about 50 %) and inhibiting lateral root formation under SeIV and TeIV treatments compared to Cd treatment alone. Moreover, chalcogens accelerated Cd efflux by up-regulating TaTM20 , thereby reducing Cd accumulation. Meanwhile, chalcogens enhanced Cd isolation in the cell wall and vacuole, reduced the active Cd proportion by increasing synthesis of chelates, and improved wheat Cd tolerance. Spraying Se and Te increased both the photosynthetic rate and yield, while also improving mineral nutrient contents (including magnesium, calcium, zinc, iron, manganese, copper, and molybdenum contents) in wheat grains. Selenomethionine (SeMet) was more effective in reducing upper organ Cd reactivation and inhibiting Cd transport from upper organs to grains, which was able to reduce grain Cd content by 27 % in the 5 mg/kg Cd treatment. Additionally, SeIV and TeIV reduced grain Cd content by 14 % and 16 %, respectively; while SeVI increased Cd content by 11 %. The current study reveals the mechanism by which chalcogens alleviate Cd toxicity and reduce grain Cd accumulation, which provides valuable insights for safe wheat production despite Cd soil contamination. • Se and Te alleviate Cd toxicity and increase wheat yield. • Chalcogens decrease Cd uptake by increasing root diameter and inhibiting lateral root growth. • Chalcogens reduce Cd accumulation by increasing root Cd efflux. • Increases in PC S -Cd complexes and up-regulation of HMA2 expression promote Cd transport to shoots. • SeMet reduces Cd transport to grains by reducing Cd reactivation in stem, leaf, and glume tissues.

Prediction of antiferromagnetic metal-rich chalcogenide monolayers M2X (M = Ti, Zr, Hf and X = S, Se, Te) with high Néel temperature

We predict by first-principles calculations a new kind of binary metal-rich chalcogenide monolayers M2X (M = Ti, Zr, Hf and X = S, Se, Te), anti-structure of transition metal dichalcogenides, and study their stability, electronic structures and magnetic properties. This system is an intrinsic two-dimensional antiferromagnetic semiconductor. The magnetic ground state can be expressed as ferromagnetic ordering in a M atomic layer with antiferromagnetic coupling between two M atomic layers. The intralayer ferromagnetic ordering originates from the intralayer ferromagnetic d-px / py-d super-exchange interaction and the interlayer antiferromagnetism comes from the interlayer d-pz-d antiferromagnetic coupling through chalcogenide elements. The monolayers have large perpendicular magnetic anisotropic energy and can be up to 2000 μeV/cell for Hf2X. The anisotropy energy decreases by one order of magnitude when the metal atom M changes from Hf to Ti. In addition, the calculated Néel temperature can reach or even exceed the room temperature. Our findings suggest that the M2X may have potential application in the fields of spintronics, and will promote further theoretical and experimental study of the compounds with the anti-structure of transition metal dichalcogenides.

Extended Short-Wavelength Infrared Photoluminescence and Photocurrent of Nonstoichiometric Silver Telluride Colloidal Nanocrystals.

Demands on nontoxic nanomaterials in the short-wavelength infrared (SWIR) have rapidly grown over the past decade. Here, we present the nonstoichiometric silver chalcogenide nanocrystals of AgxTe (x > 2) and Ag2Te/Ag2S CQDs with a tunable bandgap across the SWIR region. When the atomic percent of the metal and chalcogenide elements are varied, the emission frequency of the excitonic peak is successfully extended to 2.7 μm. Surprisingly, the AgxTe CQD film responds to the SWIR light with a responsivity of 2.1 A/W at 78 K. Also, the Ag2S shell growth over the Ag2Te core enhances not only the emission intensity but also the structural rigidity, preventing crystal morphology deformation under the electron beam. The origin of the enhancement in the emission intensity and air stability of AgxTe and Ag2Te/Ag2S CQDs is carefully investigated by X-ray photoelectron spectroscopy (XPS). The optical properties and infrared photocurrent of AgxTe CQDs will provide new opportunities for solution-based SWIR applications.

Design of all-normal dispersion with Ge11.5As24Se64.5/Ge20Sb15Se65 chalcogenide PCF pumped at 1300 nm for supercontinuum generation

Supercontinuum spectrum generation is a process in which laser beam in femtoseconds and high power (kilowatts) is converted into a broad-spectrum beam of light after passing through a specific environment. Of course, achieving this range comes with many limitations. In this paper, photonic crystal fibers are used as a substrate for input pulse due to the ability to control dispersion and loss, and creating single-mode operating conditions. One of the main factors for the formation of supercontinuum spectra of injection pulses is maintaining the nonlinear performance of this type of fiber by controlling the effective mode area and also using chalcogenides (nonlinear coefficients about 100 times higher than silica) in their structure. In the proposed structure, a photonic crystal fiber with silica base element and air cavities with hexagonal structure with the center of Ge11.5As24Se64.5 chalcogenide element have been used to provide the nonlinear property of the structure. Also, in this structure, a ring of Ge20Sb15Se65 chalcogenide elements has been used to reduce the effective mode region and create a flat dispersion curve at a wavelength of 1300 nm (second telecommunication window). The input pulse power is 10 kW and its width is 50 femtoseconds, which has caused the range of the supercontinuum from 800 to 1900 nm. This structure can be used to provide the required wavelengths as a carrier in a wavelength division multiplexing.

PLATINUM METAL MINERALIZATION OF THE SOUTH URALS MAGMATIC COMPLEXES: GEOLOGICAL AND GEODYNAMIC CHARACTERISTICS OF FORMATIONS, PROBLEMS OF THEIR GENESIS, AND PROSPECTS

In the South Urals, we have identified and investigated two platinum-bearing formations – ophiolite chromitebearing complexes, and the Khudolaz differentiated mafic-ultramafic complex with sulfide Cu-Ni mineralization. The ophiolite chromite-bearing complexes include fragments of the upper mantle and lower crust of the Paleouralian Ocean, which were induced by collision onto the edge of the East European platform. The origin of the Khudolaz complex is related a mantle plume activity. Here, we review and compare the main features of platinum-metal mineralization (PMM) in these two formations.The article presents the results of mineralogical and geochemical studies of PMM associated with chromite and sulfide Cu-Ni ores. In association with chromitites, two types of PMM are distinguished: (1) predominating refractory platinoids in chromitites of the mantle unit of the section, and (2) predominating platinum and palladium in chromitites of the transitional wehrlite-clinopyroxenite complex. Compositions of platinum group minerals (PGM) and relations between their elements and host minerals suggest that the minerals of the ophiolite chromite-bearing complexes are of a restite origin, while the Khudolaz complex results from a combination of magmatic processes and solid-phase redistribution of material. Palladium (michenerite, froodite, merenskyite, borovskite, sudburyite) and platinum (sperrylite, moncheite) minerals are found in magmatic sulfide ores of the Khudolaz complex, which were subjected to hydrothermal metasomatization. Texture observations using electron microscope and optical (reflected light) images, as well as LA ICP MS analyses of sulfides suggest late- and post-magmatic crystallization of PMM in three phases: (1) immiscible metalloid or highly fractionated residual sulfide melts trapped in sulfides; (2) segregation of isomorphic impurities of platinum group elements (PGE) and chalcogenide elements from sulfide solid solutions; and (3) interaction of hydrothermal fluids with soluble sulfides.Prospective for PMM are extended bodies of disseminated chromitites in marginal dunites of the Kraka and Nurali massifs, and wehrlite-clinopyroxenite complexes of the same massifs containing PGE (above 500 ppb). In the Khudolaz complex, promising PMM bodies are low-metasomatized parts of sulfide ore bodies (1 ppm of ΣPGE and above) located in the largest massifs, Severny Buskun and Zapadny Karasaz. Exocontact zones of these intrusions are also promising for PMM.

Wet chemical assisted synthesis of self assembled tellurium nanostructures with enhanced stability

Tellurium (Te), a chalcogenide element, and its compounds are essential in the development of energy harvesting applications. Here, we reported successfully synthesized Te nanoparticles (NPs) at room temperature (RT) and 120 °C by wet chemical method, employing potassium tellurite (K2TeO3) and bulk Te powder as source with hydrazine hydrate (HH) as reducing agent. We found that protic solvent supports better reaction than aprotic solvents at RT. X-ray diffraction (XRD) displays enhanced peaks corresponds to hexagonal phase of Te. Raman spectra depicted the presence of intense peaks at 122 and 142 cm−1 attributed to A1 and E2 bond-stretching mode, respectively. Field emission scanning electron microscopy (FESEM) revealed the formation of nanorods, nanoplates or rice-like structures. The presented work has prospective use for many applications like thermoelectric, solar cells etc.

Growth and Electrical Characteristics of PE-ALD Germanium Sulfide for 3D Cross-Point Memory

The 3D cross-point memory, known to contain chalcogenide material-based ovonic threshold switching (OTS) selector, is bringing new changes to the memory hierarchy of DRAM and NAND flash memory. The cross-point memory of current planar 3D structures, meanwhile, is already expected to limit scaling in terms of number of critical masks and normalized cost, so it is necessary to prepare a vertical 3D structures [1]. Atomic layer deposition (ALD) process, which is essential to realize vertical 3D structures, has been mostly studied for phase change materials (PCM) based on GeSbTe but OTS selector research is still in its early stage. So, we have studied plasma enhanced-ALD (PE-ALD) of germanium sulfide (GeS) films containing sulfur chalcogenide element with higher optical bandgap than Te and Se for low off current OTS selector for larger array implementation [2] [3]. The PE-ALD of GeS amorphous chalcogenide films was synthesized using commercially available GeCl4 precursor with H2S plasma reactant. The Ge1S2 film was identified quantitative composition and impurities through AES depth profile analysis, and excellent thermal stability up to 600 ℃ was studied by In-situ high temperature X-ray diffraction (HT-XRD). And PE-ALD Ge1S2 has confirmed the superior step coverage in the vertical 3D structure through FIB-TEM compared to chemical vapor deposited GeS film. In addition, the devices of the 50 nm bottom electrode contact size using PE-ALD Ge1S2 films demonstrated OTS characteristic with of remarkable high threshold field 3.0 MV/cm, and low normalized off-current of 25 nA at half threshold voltage. The achievement of PE-ALD research on simple binary Ge1S2 amorphous chalcogenide will contribute to development the future 3D cross-point memory scaling.AcknowledgmentsThis paper was result of the research project supported by SK Hynix Inc.Reference[1] T. Kim and S. Lee, “Evolution of Phase-Change Memory for the Storage-Class Memory and Beyond,” IEEE Trans. Electron Devices, vol. 1, pp. 1–13, 2020.[2] C. C. Wu, C. H. Ho, J. Y. Wu, S. L. Lin, and Y. S. Huang, “Characterization of Ge(Se1-xSx)2 series layered crystals grown by vertical Bridgman method,” J. Cryst. Growth, vol. 281, no. 2–4, pp. 377–383, Aug. 2005.[3] J. W. Park et al., “Optical properties of pseudobinary GeTe, Ge2 Sb2 Te5, GeSb2 Te4, GeSb4 Te7, and Sb2 Te3 from ellipsometry and density functional theory,” Phys. Rev. B - Condens. Matter Mater. Phys., vol. 80, no. 11, Sep. 2009.

Interlayer Trions in 2D Transition-Metal Dichalcogenide Heterostructures

A dimensionally confined dielectric constant and reduced dielectric screening lead to two-dimensional transition-metal dichalcogenides (TMDs). The confined dielectric constant triggers a strong Coulomb interaction and high exciton binding energies between TMD heterostructures. Here we show a highly efficient interlayer charged exciton or trion formation and its generation sites are present in materials at room temperature. Two different transition metals (Mo, W) and chalcogenide (S, Se) elements were investigated in two different heterostructure combinations (MoS2—WS2 and MoSe2—WS2). Room temperature photoluminescence measurements demonstrate a highly efficient trion formation between and close to the heterostructure interfaces. This study highlights an effective band alignment, strong photoexciting Coulomb interaction, and formation of interlayer trions with different recombination energies. This investigation suggests the possibility of utilizing interlayer trions in promising optoelectronic devices in the future.

Hücre Başına Çoklu Bit Media Geliştirmek İçin Nano Ölçekli Yarı İletken Bir Aygıtın Sonlu Eleman Modellemesi

Generally, a semiconductor device using chalcogenide elements as a fundamental components is considered as a potentially revelation technology for future ultra-high density data storage technology. These kind of device having high contrast between 0 and 1 logic states brought out the possible application of the idea of multiple logic levels in a single bit in an effort to boost data storage density. The potential stabilization of resistance levels in between the logic states enables storage of several data in a single cell (such as 00, 01, 10, 11 levels). I report on investigation of the role of the current injection and material selection in stabilizing middle resistance states within a nanoscale semiconductor cell for fabrication of a multiple-bit-per-cell through 3D finite element modeling. First, to visualize the complex nature of the switching dynamics, 3D finite element simulations were carried out in cell with two active layers Ge2Sb2Te5/Ge2Sb2Te5 (GST/GST) alloys incorporating phase change kinetics, electrical, thermal and percolation. Simulation was constructed by using an iterative approach with coupled differential equations, which are all as a function of temperature, as well as Seebeck coefficient to account for thermoelectric effect. The complex nature of switching dynamics appears highly sensitive to the exact programming voltage and material properties. The model suggests that the physical origin of the formation of stable middle states unexpectedly in circular top contact devices is mainly due to anisotropic heating during the application of a programming current pulse. The model successfully predicts the required programing conditions and the importantce of material selection for such mixed-phase levels, which can be used to optimize memory cells for future ultra-high-density data storage applications.

Redox responsive paclitaxel dimer for programmed drug release and selectively killing cancer cells

Redox stimulus responsive drug delivery systems have been widely investigated and proved to be promising prospects for efficient cancer therapy due to the abnormal high level of reactive oxygen species and glutathione in tumor microenvironment. Herein, three paclitaxel dimers (named as PTX2-R, R = S, Se and Te) bridged with alkyl sulfide, selenide or telluride are synthesized. These dimers can self-assemble into stable uniform nanoparticles (named as PTX2-R NPs, R = S, Se and Te) with impressively high drug loading. As expected, sulfur/selenium/tellurium bonds exhibit different redox responsiveness, thereby affecting the drug release and cytotoxicity. Of note, tellurium bridged paclitaxel dimer shows ultra-sensitivity to hydrogen peroxide, which rapidly cleaves into two paclitaxel under the subsequent dithiothreitol stimulation. Our findings provide deep insight into the redox sensitivity of chalcogenide elements and offer the rational design strategies to biologically redox condition for programmed drug release.

Conspicuous interatomic bonding in chalcogenide crystals and implications on electronic, optical, and elastic properties

Chalcogenide crystals are a unique class of materials very different from semiconductors or metallic alloys. They also have many practical applications, especially in relation to their optical properties. However, the fundamental understanding of their electronic structure and physical properties is rather scattered and incomplete. We present a detailed study using first-principles calculations on the electronic structure, interatomic bonding, and optical and mechanical properties for 32 chalcogenide crystals. They consist of 22 binary (AnBm) and 10 ternary (AnA′Bm) crystals with A = Ag, As, Cu, Ge, Sb, Sn, Cd, Zn; A′ = In, Ge, Sn; and B = S, Se, Te with n = 1, 2, 4 and m = 1, 2, 3, 4, 9. We use the novel concept of total bond order density as a single quantum mechanical metric to characterize the internal cohesion of these crystals and correlate them with the calculated properties, especially the mechanical properties. Based on this large database, we are able to identify some new and conspicuous observations to reach some useful conclusions related to the chemical composition of the chalcogenide compounds and their complex interatomic interactions. Specific examples from crystals and their unique properties in relation to the elements A and A′ and chalcogenide element B (S, Se, and Te) are discussed and highlighted. Finally, generalization of the observed trends and empirical rules can be extended to much larger classes of ternary and quaternary chalcogenide crystals and glasses so far unexplored.

Recent Developments and Future Challenges in Designing Rechargeable Potassium-Sulfur and Potassium-Selenium Batteries

The use of chalcogenide elements, such as sulfur (S) and selenium (Se), as cathode materials in rechargeable lithium (Li) and sodium (Na) batteries has been extensively investigated. Similar to Li and Na systems, rechargeable potassium–sulfur (K–S) and potassium–selenium (K–Se) batteries have recently attracted substantial interest because of the abundance of K and low associated costs. However, K–S and K–Se battery technologies are in their infancy because K possesses overactive chemical properties compared to Li and Na and the electrochemical mechanisms of such batteries are not fully understood. This paper summarizes current research trends and challenges with regard to K–S and K–Se batteries and reviews the associated fundamental science, key technological developments, and scientific challenges to evaluate the potential use of these batteries and finally determine effective pathways for their practical development.

Anion-dependent Hot Carrier Dynamics in Chalcogenide Perovskites SrSnX3 (X = S, Se)

The hot carrier relaxation dynamics in inorganic perovskites SrSnS3 and SrSnSe3 has been investigated using nonadiabatic molecular dynamics simulation. The results indicate that the hot carrier relaxation dynamics strongly depends on the chalcogenide element. It is found that the hot electrons and hot holes have a fast relaxation time in SrSnS3 than SrSnSe3 with the similar excess energy due to the strong nonadiabatic couplings. Moreover, the hot holes hold a dramatic faster decay time than hot electrons for both of the two systems because of the large density of states and the smaller energy level differences in the valence band. Generally, our findings here show that the hot carrier relaxation time in chalcogenide perovskites SrSnS3 and SrSnSe3 is longer than the organic–inorganic perovskites, indicating the present chalcogenide perovskites are promising candidates for solar cell applications.

Chemical, structural and magnetic properties of the Fe/Sb2Te3 interface

Abstract Interfacing topological insulators (TI) with ferromagnetic (FM) layers is a promising route towards the next generation of ultra-low power spintronic devices based on charge-to-spin current conversion. Here, we present the Fe/Sb2Te3 interface structure, its chemical composition and magnetic properties. Thin films (30 nm) of the topological insulator Sb2Te3 were synthesized by Metal Organic Chemical Vapor Deposition (MOCVD) at room temperature on Si/SiO2 substrates, then capped with a 54Fe(10 nm)/57Fe(1 nm) bilayer by Pulsed Laser Deposition (PLD) to allow interface-sensitive Conversion Electron Mossbauer Spectroscopy (CEMS). X-ray diffraction (XRD) showed the polycrystalline nature of both the Fe and Sb2Te3 layers. X-ray reflectivity (XRR) identified a non-trivial layered structure with the presence of an intermixed layer at the Fe/Sb2Te3 interface. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) confirmed the partial elemental interdiffusion between the Fe and Sb2Te3 layers. Interface-sensitive CEMS evidenced that about a half of the 1-nm-thick 57Fe layer in contact with Sb2Te3 coordinates ferromagnetically, whereas the remaining paramagnetic fraction preferentially bonds with Te. The Fe/Sb2Te3 system was shown to have a far from sharp interface, exhibiting a marked chemical reactivity already at room temperature. The tendency of Fe to preferentially bond with the chalcogenide element of topological insulators has been previously observed for the interface with Bi2Se3 and Bi2Te3, thus suggesting a possible universal behavior at the interface between Fe and chalcogenide-based TI.

Structural and Optical Properties of Nickel Sulfoselenide (NiSSe) Thin Film for Photoelectrochemical Applications

The transition metal, nickel is a favourable material to create combination with chalcogenides elements (S, Se and Te) to become either binary or ternary transition metal chalcogenide such NiSe2, NiSe, NiS2 and Ni3Se. Throughout some observation from the previous research regarding the synthesis of ternary transition metal chalcogenide thin film for photoelectrochemical application, the combination of nickel with two chalcogenide elements; S and Se are rarely found due to the nature of selenium and sulphur. In this work, NiSSe thin film is being synthesis onto indium tin oxide (ITO) glass substrates using electrodeposition technique and the structural and optical properties of the films are studied. The resulted thin films are characterized using X-ray diffraction analysis and scanning electron microscope to determine the crystallographic and morphological properties. Optical are also being analysed for their bandgap values in other to determine the suitability of NiSSe thin film for photoelectrochemical properties. Results proved that nickel sulfoselenide thin films are polycrystalline in nature with a good uniformity. The intersection point for the optical analysis gave the direct bandgap. Well-adherent and dark-coloured thin films are derived from the cathodically electrodeposition by using potential in the reduction region. Experimental results proved NiSSe thin films are capable to be used in photoelectrochemical cell application.

Elastic, electronic and optical properties of the two-dimensional PtX2 (X = S, Se, and Te) monolayer

Through hybrid functional calculations, we study the elastic, electronic and optical properties of the two-dimensional (2D) PtX2 (X = S, Se and Te) monolayer. The lattice constants increases and the band gap values decrease monotonously with increasing atomic number of chalcogenide elements. The tensile strain can reduce the band gaps and affect optical properties of 2D PtX2 monolayers. Also, the indirect band structures are kept under considered strain range. Our results show that about −3% of compressive strain can induce semiconductor-to-metal transition. Moreover, the in-plane stiffness are 81 N/m for PtS2, 64 N/m for PtSe2, and 40 N/m for PtTe2, which are smaller than that of 2D MoX2 monolayers.