Se 3d Research Articles

Anomalous band bending in the (K 0.8 Na 0.2) 0.8 Fe 1.8 Se 2 superconductor

Iron dichalcogenides intercalated with alkali metal atoms attract the attention of physicists due to their unusual natural phase separation, in which superconducting clusters are formed at the boundaries of the antiferromagnetic phase. In this work, using photoelectron spectroscopy, we discovered an unusual effect that presumably arises due to this phase separation. We studied the temperature dependences of the photoelectron spectra of Se 3d, Fe 3p and the valence band at temperatures above and below Tc ≈ 27 K of the compound (K0.8Na0.2)0.8Fe1.8Se2 with a unique substitution of alkali metal atoms. A strong temperature dependence of both the valence band and core levels was discovered: we observed a strong broadening of the spectra, which monotonically decreased with increasing sample temperature, while the temperature changes were cyclic. We believe that this broadening is associated with the appearance of space charges in the dielectric matrix, which leads to band bending. Moreover, the shape of the potential arising under the surface of a given compound was reconstructed, and an estimate was obtained for the relative amount of the superconducting phase. The results obtained will help to better understand the physical processes occurring in this compound.

HAXPES reference spectra of bulk Mo and MoSe2 with Cr Kα excitation

Monochromatic Cr Kα radiation (5414.8 eV) was used to acquire high-energy photoelectron spectroscopy (HAXPES) data on pure Mo and bulk MoSe2 compound with special attention paid to binding energy scale correction and quantification. The reported spectra include a survey scan and high-resolution Mo 2s, Mo 2p1/2, Mo 2p3/2, Mo 3d, Mo 3p1/2, Mo 3p3/2, Mo 3s, Mo 4s, Mo4p, Se2s, Se 2p1/2, Se 2p3/2, Se 3s, Se 3p1/2, Se 3p3/2, and Se 3d core-levels. The data will be useful as reference core-level spectra for HAXPES studies on molybdenum and its compounds.

Improving the performance of solution-based CZTSSe absorber by selenization annealing with selenium powder in argon

Due to the low toxicity and abundance of nature, Cu2ZnSn(S,Se)4 (CZTSSe) has been considered as a promising solar cell material. The absorber is the most critical structure in a solar cell, which determines the performance of the cell. Selenium-rich CZTSSe can be formed by replacing S atoms of CZTS with Se. However, the method of adding Se element through H2Se is constrained due to the toxicity of H2Se. The work adopted a method to prepare excellent CZTSSe absorbers without H2Se. The stack structure CZTS precursor films were prepared by solution-based deposition, and CZTSSe absorbers were obtained after selenization annealing at 550 °C with 0.1, 0.2 and 0.3 g of selenium powders in argon, respectively. The obtained CZTSSe absorbers had pure CZTSSe phase, high absorption coefficients and appropriate bandgaps. After annealing with 0.2 g of selenium powder, the holes in the CZTSSe film diminished, and the grain size of absorbers increased from 0.31 µm in the CZTS absorber to 1.17 µm. The peaks of Se 3d for CZTSSe absorber were observed, the lattice spacing of plane (112) increased from 3.10 Å to 3.22 Å, and the work function decreased from 5.31 eV to 5.19 eV. The improved performance of absorber will be of great significance for the efficiency of CZTSSe device.

Mass spectrometry and in situ x-ray photoelectron spectroscopy investigations of organometallic species induced by the etching of germanium, antimony and selenium in a methane-based plasma

Organometallic positive ions were identified in inductively coupled plasmas by means of mass spectrometry during the etching of Ge, Sb, Se materials. A preliminary study was focused on identifying M x H y + (M = Ge, Sb, Se) positive ion clusters during a H2/Ar etching process. The methane addition to the H2/Ar mixture generates CH x reactive neutral species. The latter react with the metalloids within gas phase to form M x C y H z + organometallic ions. In addition, the etching of Sb2Se3 and Ge19.5Sb17.8Se62.7 bulk targets forms mixed products via ion-molecule reactions as evidenced by the presence of SeSbC x H y + ion clusters. Changes in surface composition induced by the newly formed organometallic structures were investigated using in situ x-ray photoelectron spectroscopy. In the case of the Ge and Sb surfaces, (M)–M–C x environments broadened the Ge 2p3/2, Ge 3d, Sb 3d and Sb 4d spectra to higher values of binding energy. For the Se surface, only the hydrogen and methyl bonding could explain the important broadening of the Se 3d core level. It was found that the Ge39Se61 thin film presents an induced (Ge)–Ge–Se entity on the Ge 2p3/2 and Ge 3d core levels.

Chiral Se Nanobrooms with Wavelength and Polarization Sensitive Scattering

AbstractHigh‐index dielectric nanostructures offer strong magnetic and electric resonances in the visible range and low optical losses, stimulating research interest in their use for light manipulation technologies. Lithographic fabrication of dielectric nanostructures, while providing precise control over the pattern dimensions, limits the scalability of this approach for practical applications due to an inefficient fabrication process and limited production quantity. Here, the colloidal synthesis of high‐index chiral dielectric nanostructures with a broom‐like geometry made from trigonal Se is demonstrated. The anisotropic morphology and crystal structure of Se nanobrooms enable both linearly and circularly polarized scattering, as well as spectrum variation along the particle axis, which is, to the authors’ knowledge, the first observation of such behavior from dielectric colloidal nanostructures. To show the versatility of the highly scattering Se NB suspensions, 2D and 3D printing of Se NB inks are demonstrated as a proof of concept. This approach provides a way to manipulate light using aqueous dispersions of high‐index dielectric nanostructures, unlocking their potential to fit in various morphologies and dimensions in 2D and 3D for broad applications.

Characterization of the O-centered vanadium selenoiodides V4OSe8I6·X (X = I2, 3,5-dimethylpyrazole)

O-centered vanadium(IV) selenoiodide V4OSe8I6·3,5-dimethylpyrazole was synthesized in a sealed glass ampoule at moderate temperature 220 °C from the mixture of V, Se, I2, small quantity of water and 3,5-dimethylpyrazole. The X-ray single crystal structure of the compound was solved. The crystal structure includes O-centered tetranuclear complex [V4(μ4-O)(μ-Se2)4(μ-I)2I4] in which vanadium atoms are bridged by diselenide (Se2)2– and iodide I– groups; four terminal iodides coordinate vanadium atoms additionally. Molecules of 3,5-dimethylpyrazole form non-covalent contacts with iodine and selenium atoms of the V4OSe8I6 complexes. Once compounds V4OSe8I6·3,5-dimethylpyrazole and V4OSe8I6·I2 contain similar electroneutral coordination molecular fragment V4OSe8I6, we present here a discussion of spectroscopic properties as well as thermal behavior. Comparing XPS data, both compounds contain vanadium complexes with major V 2p binding energies very similar to each other, and almost equal binding energies in XPS Se 3d and I 3d showing their forms of (Se2–)2 and I–, respectively. Thermolysis character of these compounds revealed higher stability of V4OSe8I6·I2 than V4OSe8I6·3,5-dimethylpyrazole, that indicates a greater stability of the system of non-covalent contacts involving iodine molecules than 3,5-dimethylpyrazole.

Efficient multi-component PL emission tunning in single emissive layer (SEL) by amino-functionalized graphene quantum dots in type-II ZnSe/af-GQDs soft core/shell interface as an efficient phosphor

This research demonstrates first report on successful formation of ZnSe/amino functionalized graphene quantum dots (af-GQDs), type-II core-shell structures. The structures having potential as a single emissive layer (SEL), were synthesized via a facile and eco-friendly hot injection method. We achieved a highly efficient tuning of PL emission spectral components in visible region ranging from (∼458 to 750nm). The functional groups attached with af-GQDs rendered soft shell feature to the structures and the soft core-shell interface significantly passivated the strain-induced defect states and reduced Auger recombination (AR). The PL emission properties of ZnSe/af-GQDs were studied through steady state and temperature dependent photoluminescence (TDPL) spectroscopy within the temperature range (80-300k), using 457nm excitation laser. Three samples including bare ZnSe QDs, bare af-GQDs and ZnSe/af-GQDs core/shell structures were prepared. The steady state PL emission spectra revealed a weak blue and pronounced green, yellow, orange and red emission, whereas the full width half maximum (FWHM) of PL spectra distinctly decreased in ZnSe/af-GQDs. The carrier activation and escape energies of radiative and non-radiative recombination respectively were estimated through Arhenious and Brethelot fitting functions for TDPL measurements. The calculated values clearly indicated a decrease in activation energies and an increase in escape energies in ZnSe/af-GQD X-ray photon spectroscopy (XPS) measurements revealed the presence of Zn 2p and Se (3d) O1s and NIs orbitals of constituent elements including Zn, Se, C, O and N. Tight binding model was applied to estimate the valance and conduction band energies that suggested formation of type-II core-shell band alignment in the structures. The relative PLQY was estimated using comparative method and Rhodamine-B was used as reference and calculated PLQY are 58%, 61% and 83% for ZnSe, af-GQDs and ZnSe/af-GQDs. A mechanism of formation of a soft core-shell interface for ZnSe/af-GQDs is clarified. We suggest that ZnSe-/af-GQDs structures synthesized in this report have a great potential for LEDs and display devices in which multi-color components are of paramount importance, such as white light emission. This report may open a gate way for more and vivid possibilities to apply af-GQDs for optoelectronic devices.

The Effect of Scanning Strategy on Intraoral Scanner's Accuracy.

The purpose of the present study was to examine the impact of scanning strategy on trueness and precision of the impression acquired from an intraoral scanner. Fifteen complete-arch, mandibular, post-orthodontic treatment casts were scanned with a laboratory scanner (Identica SE 3D, Medit) as the gold standard, and with an intraoral scanner (i500 Medit) following three different paths of the scanning head over the arch (scanning strategies A, B, and C). The hand scans were performed twice by one examiner and repeated by a second examiner, resulting in 180 triangular mesh surfaces (digital casts). The meshes were superimposed on the gold standards using the Viewbox 4 software. The closest distances between the meshes were computed and trueness and precision were evaluated using a General Linear Model. An interaction was found among the examiner and strategy. The accuracy of complete-arch impressions was affected by the scanning strategy; the manufacturer’s recommended strategy (A) was statistically significantly better (p < 0.05) than B and C, which were similar. An average accuracy below 50 μm, which is clinically acceptable in most orthodontic procedures, was achieved with all the examined scanning strategies.

Mo-rich rGO–2H–MoSe2 nanocomposites with novel crystal growth plane of (106) for high hydrogen evolution reaction activity

In this study, MoSe2-reduced graphene oxide (rGO) nanocomposites with novel crystal growth plane of (106) of 2H–MoSe2 nanosheets were modified as working electrode for enhancement of hydrogen evolution reaction (HER). Versatile characterizations revealed that rGO as a template evolves the crystal growth of MoSe2 nanosheets to (106) atomic plane while inducing an amorphous type structure at the same time. XPS studies identified the Mo rich structure and the increase of the contribution of Mo6+ oxidation state in rGO-MoSe2 structure with broad full width at half maximum (FWHM) characteristic of Mo 3d peaks and the 0.4–0.6 eV shift of Se 3d to higher binding energies resulting in the defective MoSe2 nanosheets. Polarization measurement studies revealed a small Tafel slope of 49 mV.dec−1, onset potential of 52 mV and low over potential of 271 mV at J = 100 mA cm−2 for HER. In addition, it was found that the weight ratio of MoSe2 and rGO has a critical role in the cyclic stability of the nanocomposite in HER activity.

Электронная структура ультратонких интерфейсов Cs/Bi-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=-

The electronic structure of ultrathin Cs/Bi2Se3 interfaces has been studied by photoelectron spectroscopy using synchrotron radiation. The experiments were carried out in situ in an ultrahigh vacuum with submonolayer Cs coverages on Bi2Se3 samples. It was found that the adsorption of Cs causes changes in the spectra of the core levels of Bi 4f, Bi 5d, and Se 3d. It has been established that Cs atoms are adsorbed predominantly on Bi atoms in the upper surface layer. The states of the valence band are studied for a clean Bi2Se3 surface and for the Cs/Bi2Se3 interface. Near the Fermi level, 2D topological states have been found. Two induced surface states appear in the region of the valence band upon adsorption of Cs.

Electronic structure of ultrathin Cs/Bi-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=- interfaces

The electronic structure of ultrathin Cs/Bi2Se3 interfaces has been studied by photoelectron spectroscopy using synchrotron radiation. The experiments were carried out in situ in ultrahigh vacuum with submonolayer Cs coverages on Bi2Se3 samples. It was found that the adsorption of Cs causes changes in the core level spectra of Bi 4f, Bi 5d, Se 3d. It has been established that Cs atoms are adsorbed predominantly on Bi atoms in the upper surface layer. The states of the valence band were studied for a clean Bi2Se3 surface and for the Cs/Bi2Se3 interface. Near the Fermi level, 2D topological states have been found. Two induced surface states appear in the region of the valence band upon adsorption of Cs. Keywords: topological insulators, electronic structure, ultrathin interfaces, photoelectron spectroscopy.

A novel 2D/2D MoSe2/SnSe heterojunction photocatalyst with large carrier transmission channel shows excellent photoelectrochemical performance

A novel 2D/2D face-to-face MoSe2/SnSe heterojunction photocatalysts have been successfully obtained from SnSe nanosheets and MoSe2 nanoplates. These MoSe2/SnSe heterojunction photocatalysts show well full spectrum absorption. The XPS results demonstrate obvious peaks shift of Sn 3d and Se 3d which reveals a binding was formed between SnSe and MoSe2 and MoSe2/SnSe heterojunction can be also confirmed by the TEM images. Pristine SnSe has a high photocurrent of 8.6 μA/cm2 which is much higher than many other metal sulfides and selenides such as SnS2 (1.5 μA/cm2), In2S3 (1.0 μA/cm2), MnS (1.6 μA/cm2), MoS2 (0.73 μA/cm2), MoSe2 (0.58 μA/cm2), ZnSe (0.94 μA/cm2) and FeSe2 (0.49 μA/cm2) in our previous work. This MoSe2/SnSe heterojunction photocatalyst shows excellent photoelectrochemical performance improvement by 3 times than pristine SnSe under a compositing ratio of 5.0% MoSe2. The photocurrent of the heterojunction photocatalyst can reach 26.2 μA/cm2. The large improvement of photoelectrochemical performance can be ascribed to the 2D/2D face-to-face contact between SnSe nanosheets and MoSe2 nanoplates. There is carriers’ transmission channel between the heterojunction which can improve the separation efficiency. The work develops a potential new energy material.

XPS analysis of ZnS0.4Se0.6 thin films deposited by spray pyrolysis technique

XPS being important study for the analysis of chemical state and composition at the surface level along with the bonding between elements. XPS study was carried out for the optimized spray deposited ZnS0.4Se0.6 thin films, which is a prominent IIVI ternary chalcogenide optoelectronic material. Core spectra of Zn 2p, S 2p, Se 3d, and Se 3p were recorded for the analysis. As sulfur and selenium coexist in the sample, the detailed analysis of XPS is much needed. Analysis is challenging due to overlapping region of Se 3p peak and S 2p peak. Compared to previous reports, in the present sample, relatively lower charging effects were observed. The binding energies reported here could be used as reference for ZnSSe material. The composition of elements in the sample were also calculated, which agrees with the nominal composition.

Charge Transfer Doping of 2D PdSe2 Thin Film and Its Application in Fabrication of Heterostructures

AbstractPalladium diselenide (PdSe2) is an emerging 2D material with exotic optical and electrical properties and widely tunable layer dependent band gap in the infrared regime. The ability to further tune the electronic properties of PdSe2 via doping is of fundamental importance for a wide range of electronic and optoelectronic device applications. Here, surface charge transfer doping of chemical vapor deposition grown p‐type PdSe2 thin film using benzyl viologen (BV) molecules is reported. The electrical transport measurements of the PdSe2 device show an increase in resistance by ≈1700 percent from 2.1 MΩ for the pristine sample to 36.2 MΩ upon BV doping, revealing electrons are transferred from BV molecules to PdSe2 resulting in an n‐doping. Raman characterization shows a red‐shift and broadening of A3g characteristic peak for the doped sample, while X‐ray photoelectron spectroscopy shows a negative shift in Pd 3d and Se 3d binding energies confirming n‐doping by BV. Kelvin force probe microscopy measurements show a ≈0.3 eV decrease in work function for doped PdSe2, consistent with the n‐doping by BV molecules. A selective doping of PdSe2 channel is implemented for the fabrication of lateral heterojunction device which shows good current rectifying behavior with a rectification ratio of up to ≈55.

Ultrathin Metal–Organic Framework Nanosheets-Derived Yolk–Shell Ni 0.85 Se@NC with Rich Se-Vacancies for Enhanced Water Electrolysis

We present a controlled fabrication of selective ultrathin metal–organic framework (MOF) nanosheets as preassembling platforms, yolk–shell structured with a few-layered N-doped carbon (NC) shell-en...

Post-annealing effect on the structural and optical properties of electrophoretically coated 2D-Layered MoSe2

Abstract Temperature dependent changes in the structural, nanomorphological and optical characteristics of the 2D layered molybdenum diselenide (MoSe2), processed by electrophoretic coating (EPC) method, were examined. EPC processed MoSe2 was subjected to Raman spectroscopy confirming distinct active modes of A1g, E 1 1 g and E 2 2 u at 240.9 cm−1, 282.53 cm−1 and 337.7 cm−1, respectively. The in- and out-of plane vibrational modes observed in the Raman spectra were asserted as the 2H–MoSe2 phase which was not affected by the post annealing temperature. X-ray photoelectron spectroscopic measurements confirmed the states of Mo 3d at 228.9 eV and 232.1 eV, and of Se 3d at 54.5 eV and 55.3 eV. Studies on the surface morphology of the EPC processed MoSe2 showed significant changes due to the post-annealing treatment performed at 150 °C, 250 °C and 350 °C in terms of morphology, flake-size distribution and compactness of the film. The samples annealed at 150 °C and 250 °C showed a better optical absorption in the visible and the near infrared spectral regions with dominant characteristic peaks at 691.2 nm and 801.6 nm. Further studies assured that the EPC process yielded good quality and large area MoSe2 films with exotic structural, optical and nanomorphological characteristics that are highly suitable for functional devices.

Molybdenum diselenide thin films grown by atomic layer deposition: An XPS analysis

Molybdenum diselenide (MoSe2) thin films were deposited on annealed titanium foils by atomic layer deposition using suitable precursors. In this paper, a detailed x-ray photoelectron spectroscopy analysis of the MoSe2 film is presented. Survey spectra, Mo 3d, Se 3d, Mo 3p, Se LMM, Se 3p, C 1s, and Se 4s core level along with the valence band spectra were measured. Quantitative analysis indicates a surface composition of MoSe1.8, suggesting a deficiency of selenium on the surface.

Zinc selenide analyzed by XPS

Zinc selenide (ZnSe) was analyzed using x-ray photoelectron spectroscopy (XPS). A small notched rod was fractured in the XPS vacuum system at 6 × 10−4 Pa to create an oxygen-free surface for analysis. Spectral regions for Zn 2p, Zn 3d, Zn LMM, O 1s, C 1s, Se 3d, Se 3p, and Se LMM and valence band regions were acquired. The presence of carbon could not be confirmed due to interferences between C 1s and Se LMM and between C KLL and Zn 3s. It is believed that any carbon present is very low.

Cadmium selenide by XPS

Cadmium selenide was analyzed using x-ray photoelectron spectroscopy. The specimen is a powder purchased from Chemsavers. The sample was fixed to a stainless-steel sample holder with copper 3MTM double-sided adhesive tape. Survey spectra, Cd 3d, Se 3d, O 1s, Cd 3p, Cd MNN, Se LMM, Se 3p, C 1s, and Cd 4d core level along with the valence band spectra were recorded. Results point out a stoichiometry of 0.95 on surface.

2D topological insulator bismuth selenide analyzed by in situ XPS

Bismuth selenide (Bi2Se3), a two-dimensional topological insulator material purchased from Alfa Aesar, was analyzed using in situ x-ray photoelectron spectroscopy (XPS). The XPS spectra obtained from a fresh surface exfoliated in ultrahigh vacuum include a survey scan, high resolution spectra of O 1s, Bi 5d, Se 3d, Bi 4f, Se 3p, Se LMM, C 1s, and the valence band. Quantitative analysis indicates a Se deficient surface composition of Bi2Se2.8, which is consistent with the Fermi level position in the conduction band detected in this work.