Trigonal Selenium Research Articles

Generalization of the crystalline optical activity dispersion relations for arbitrary propagation direction of electromagnetic waves

This study suggests an alternative method concerning the derivation of the dispersion relations in crystalline optical activity for the arbitrary propagation direction of the electromagnetic waves. The solution is based on the dipole–dipole interactions between the valence electrons that are represented by the harmonic oscillators. The following theoretical description of the optical activity uses the modified Rosenfeld relations. The rotational strengths of the quantum-mechanical transitions in the normal modes of vibrations are obtained following simple calculations of a sum of two independent components. The specific model of three coupled oscillators, which seems to be sufficient for the description of the optical activity of crystals having space groups of symmetry D34 or D36, is solved as the example and the dispersion relations are derived for the optical rotatory power and circular dichroism. The results are applied on the example of trigonal selenium, for which the optical rotatory power ratio in the direction perpendicular and in the direction parallel to the optic axis is calculated. The calculated relation is compared with a similar relation derived by Chandrasekhar. The validity of both relations is then discussed.

Local structure of Se nanotube investigated by X-ray absorption fine structure spectroscopy

The structures of selenium nanoparticles and nanotubes synthesized by the dismutation of precursor Na2SeSO3 under acidic condition in micellar solution are studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray absorption fine structure spectroscopy (XAFS). Spherical-like nanoparticles contain both amorphous and crystalline parts while, as shown by XRD patterns, nanotubes have the crystal structure of trigonal selenium (t-Se). They display quite different XANES spectral features indicating different local atomic arrangements. Theoretical XANES calculations show that the local structure around Se atom in the nanotubes is similar to a hexangular cylinder. Quantitative extended XAFS (EXAFS) analysis further shows that the average Se–Se bond length for both nanotubes and nanoparticles is 2.35 Å.

Rapid growth of t-Se nanowires in acetone at room temperature and their photoelectrical properties

Trigonal selenium (t-Se) nanowires with uniform sizes were obtained through the conversion from freshly prepared amorphous selenium (a-Se) nanoparticles in acetone at room temperature. The experimental results show that some organic solvents, such as acetone and pyridine can dramatically promote the conversion from a-Se to t-Se, and t-Se with different morphologies like nanowires and microrods can be obtained. Acetone is an appropriate medium for obtaining t-Se nanowires in a short time. The as-prepared t-Se nanowires were characterized and confirmed by means of powder X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The photoelectrical properties of t-Se nanowires were investigated, which shows their potential uses in the fabrication of microdevices or photo-switches.

Synthesis of trigonal selenium nanorods by electrodeposition from an ionic liquid at high temperature

We report on the electrodeposition of trigonal selenium (t-Se) nanorods from 1-ethyl-3-methylimidazolium tetrafluoroborate/chloride ([C 2mim][BF 4]/[C 2mim]Cl) at high temperature (T > 100 °C). It is shown that the Se 4+ precursor salt significantly influences the electrochemical behaviour, as well as the phase, morphology and crystallinity of the Se deposits. Amorphous selenium (a-Se) films are deposited from [C 2mim][BF 4]/[C 2mim]Cl-SeCl 4 whereas high aspect ratio single-crystalline trigonal selenium nanorods are formed from [C 2mim][BF 4]/[C 2mim]Cl-SeO 2. The t-Se nanorods are characterized by XRD, SEM, TEM and Raman spectroscopy and the growth mechanism of the single-crystalline t-Se nanorods from a-Se particles during the electrodeposition process is elucidated. The crystallinity of the t-Se nanorods is improved by increasing the temperature from 100 to 160 °C. Photoelectrochemical measurements performed in the ionic liquid confirm the p-type conductivity of the t-Se nanorods.

Gas Detection of Volatile Organic Compounds Using Trigonal Selenium Nanowires

The conductivity of random networks of trigonal selenium (t-Se) nanowires has been investigated under the presence of various kinds of evaporated organic gases. The conductivity shows a characteristic response for an individual organic gas at room temperature without heating t-Se. These results indicate that recognizable detection of organic gases is possible using simple-to-fabricate t-Se nanowire devices.

Characterization and Growth Mechanism of Selenium Microtubes Synthesized by a Vapor Phase Deposition Route

A simple and rapid vapor deposition route has been developed for the growth of trigonal phase selenium microtubes in a horizontal tubular furnace under argon flow gas. Selenium powder was evaporate...

Lone-pair states as a key to understanding impact ionization in chalcogenidesemiconductors

Impact ionization of holes and domination of p-conductivity in chalcogenide semiconductorsare attributed to a weak electron–phonon interaction inherent to lone-pair states. Thisargument is supported by first-principles calculations of an acoustical deformation potentialin trigonal selenium. Results of the calculations reveal a strong dependence of thedeformation potential on the excess energy of charge carriers. The latter is interpretedusing a simple tight-binding model.

A new hydrothermal route to nano- and microstructures of trigonal selenium exhibiting diverse morphologies

High purity single crystalline trigonal selenium (t-Se) with different morphologies (wires, rods, flowerlike, and hollow spheres) have been synthesized under hydrothermal conditions through simple one-step at lower temperature (120 °C) using in situ generated sulphurous acid as a new reducing agent. It is noted that the experimental parameters such as reaction duration, temperature and surfactants have an effective and important influence on the formation of different morphologies. The phase analysis, purity, morphology and optical properties of the as obtained products have been characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis spectroscopy, respectively. A possible reaction scheme as well as growth mechanism has been proposed for the formation of t-Se nanowires.

Optical absorption spectrum of trigonal selenium under high pressure

Optical absorption spectra of trigonal selenium have been measured at pressure up to 5 GPa using a diamond anvil cell with two kinds of pressure-transmitting media, that is, a mixture of methanol, ethanol and water, and a potassium bromide, to confirm no effects of them. With increasing pressure, the absorption edge shifts to a lower energy and the pressure coefficients of the absorption edge at atmospheric pressure obtained by using both pressure-transmitting media agree with each other. At high pressure, as more clearly observed in the spectra obtained by using a potassium bromide, the edge shifts to a lower energy become moderate near 3 GPa, where an abrupt decrease in intramolecular covalent bond length was observed. This result must be related to the transition of the electronic band structure in trigonal selenium at approximately 3 GPa.

Selenium nanowires and nanotubes synthesized via a facile template-free solution method

Trigonal selenium (t-Se) nanowires and nanotubes were successfully prepared on a large scale via an environment-friendly synthetic process, in which no templates or surfactants were employed. These t-Se nanowires having a width of 70–100 nm and length up to tens of micrometers were synthesized in absolute ethanol at room temperature, while t-Se nanotubes with outer diameter ranging from 180 to 350 nm were obtained at 85 °C in water system. SEM and TEM analyses of the samples obtained at different stages indicated that the formation of these t-Se 1D nanostructures was governed by a “solid-solution-solid” growth process. The amorphous Se (a-Se) nanoparticles were initially generated and then would transform into crystal seeds for the subsequent growth of nanowires or nanotubes. Detailed experiments found that temperature and solvents as well as concentrations of starting materials were crucial to the formation of final morphology.

A New Chemical Approach to the Low-Temperature Growth of Single Crystalline Trigonal Selenium Scrolled Nanotubes and Nanowires

In this paper, we present the formation of high quality trigonal phase selenium (t-Se) scrolled nanotubes and nanowires at 100 degrees C by a simple wet chemical method using of Na2S as new reducing agent and poly(vinylpyrolidone) (PVP) as the stabilizing agent. The Na2S used in this method is not only cheaper and easily available but also easy to handle as compared to many earlier reported inorganic reducing agents e.g., hydrazine hydrate, hydroxyl amine hydrochloride, sodium borohydride, H2O2 etc. The phase purity of the as obtained product is confirmed by X-ray diffraction (XRD), Raman spectroscopy. We have also proposed a possible growth mechanism for the formation of scroll-type nanotubes on the basis of a series of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies of the product obtained at different reaction durations.

Selenium: A Nonprecious Metal Cathode Catalyst for Oxygen Reduction

From voltammetric studies, trigonal phase selenium (t-Se) nanotubes, which are bundles of hexagonally packed helical chains of Se atoms, have been shown by others to be stable in acid and have a double-layer region extending from −0.2 (standard hydrogen electrode) to 0.75 V. This is broader than the to double layer for platinum and presents a potential range that might allow oxygen reduction activity. This paper presents theoretical predictions of oxygen reduction mechanisms on t-Se. Adsorption energies from Gaussian cluster hybrid density functional and Vienna ab initio simulation program density functional calculations are used in the linear Gibbs energy relationship to predict the reversible potentials for the one-electron reduction steps during the four-electron reduction of to water, which ideally occurs at 1.229 V. Adsorption energies for reduction intermediates are calculated using single-chain models. Calculated reversible potentials for the four reduction steps lead to the prediction that the step with the highest overpotential is the reductive elimination of OH(ads) to form water and occurs at about 0.8 V. The overall behavior predicted for t-Se is similar to that of platinum, and it is suggested that t-Se is worthy of trials as a potential oxygen cathode electrocatalyst.

Study on the effect of surfactants on morphologies of trigonal selenium in microfluidic reactor

The influence of the surfactants on the morphologies of trigonal selenium (t-Se) submicrostructures was studied in a two-step microfluidic system, which is composed of a glass microchip for preparing spherical amorphous selenium (a-Se) colloids coupled with a poly(methyl methacrylate) microchip for transferring a-Se into its t-Se seeds under sonication. The selenious acid containing surfactants and hydrazine solutions were delivered through the two-inlets of the glass microfluidic chip. Submicro-rods, -wires as well as -tubes of t-Se were obtained by simply varying the coexisted surfactants. The as-synthesized products were characterized by powder X-ray diffraction (XRD), Raman spectrum, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED).

The selenium based chalcogenide glasses with low content of As and Sb: DSC, StepScan DSC and Raman spectroscopy study

Thermal properties and structure of As x Se 100− x and Sb x Se 100− x glass-forming systems ( x = 0, 1, 2, 4, 8 and 16) were studied by conventional and StepScan DSCs and Raman spectroscopy. Compositional dependence of the glass transition temperature, T g, was determined from reversible part of StepScan DSC records and discussed. The attention was also focused on the crystallization of undercooled melts of these systems. It was found that only selenium crystallizes from undercooled melts of As–Se system and its tendency to crystallize decreases markedly with increasing As content, for arsenic content higher than 4 at.% no crystallization was observed. In the case of Sb–Se system Sb 2Se 3 crystallizes in the first step followed by trigonal selenium crystallization from non-stoichiometric undercooled melt. Sb 2Se 3 crystallizes from incongruent melt with crystallization enthalpy Δ H c(Sb 2Se 3) = −52 ± 2 J/(g of Sb 2Se 3), Johnson–Mehl–Avrami kinetics of crystallization and kinetic exponent close to 3 was found. Raman spectra were measured to obtain basic information on the structure of both glassy systems.

Electronic structure of selenium chains by the SCF-SW-Xα method

SCF—SW-Xα calculations of the electronic structure of a series of selenium aggregates are presented and compared with experiment. It is found that some of the properties of bulk trigonal selenium are approached as the path from Se2 to Se10 is followed. On the basis of charge distributions and energy-level populations the paramagnetic properties of trigonal and amorphous selenium are predicted and the process of growth of selenium chains is discussed.

Synthesis of selenium nanowires morphologically directed by Shinorhizobial oligosaccharides

Shinorhizobial cyclosophoraose (cyclic β-(1→2)-glucan) or succinoglycan monomer (SGM 2), which has one acetyl, pyruvyl, and succinyl group, functions as a morphology-directing agent for the synthesis of pure trigonal selenium nanowires by using ascorbic acid (vitamin C) as the reducing agent. The synthesis was achieved in water at room temperature. Under these experimental conditions, the diameters of the as-prepared Se nanowires were varied in the range of 34–120 nm by cyclosophoraose and of 33–66 nm by SGM 2, in which the nanowires were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. Through this study, we propose that Shinorhizobial cyclic and linear oligosaccharides have morphologically directing functions for the synthesis of single-crystalline selenium nanowires by green chemical methods.

Inorganic and organic templates‐assisted solvothermal synthesis of trigonal selenium microrods

AbstractA facile and environment‐friendly solvothermal method has been developed for the controlled growth of nano‐ and micro‐structured trigonal selenium (t‐Se) by using green templates. And, the morphology of trigonal selenium can be tuned by using different kinds of templates. The as‐obtained products were characterized by X‐ray powder diffraction (XRD) and scanning electron microscope (SEM). Furthermore, the formation mechanism of trigonal selenium nano‐ and microcrystals was rationally suggested. This method will open a new avenue to synthesize other functional inorganic nano‐ and microcrystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Polychloro‐alkanes used as templates in solvothermal synthesis of selenium microrods

AbstractPolychloro‐alkanes, including dichloromethane (CH2Cl2), chloroform (CHCl3) and tetrachloromethane (CCl4), were first introduced to synthesize trigonal selenium (t‐Se) microrods as a new kind of coordinating solvent, which played two important roles in the formation of Se nuclei and templated effect of Se microrods. The possible formation mechanism of t‐Se microrods was proposed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Controlled synthesis of PbSe nanotubes by solvothermal transformation from seleniumnanotubes

PbSe nanotubes were successfully synthesized by a reactive template approach viasolvothermal transformation of trigonal selenium (t-Se) nanotubes in ethyleneglycol. It was revealed that a relatively high reaction temperature (e.g.,200 °C), adequate ascorbic acid, and proper lead source were crucial for preparing PbSenanotubes through shape-preserved transformation of t-Se nanotubes. Moreover, novelSe@PbSe composite nanotubes consisting of Se nanotubes covered with a PbSe sheath wereobtained by shortening the reaction time and subsequent removal of the inner Se nanotubesresulted in the formation of thin-walled PbSe nanotubes (less than 20 nm in wallthickness). On the basis of the experimental observations, a plausible mechanismfor the formation of PbSe nanotubes as well as Se@PbSe composite nanotubeswas proposed. Furthermore, preliminary electrochemical measurements showedthat the prepared PbSe nanotubes exhibited a good electrochemical activity.

Synthesis and Characterization of Selenium−Carbon Nanocables

In this letter, we report the synthesis and characterization of a novel Se-C hybrid nanostructure. X-ray diffraction data indicates a high degree of crystallinity for the nanostructured Se shell. High resolution transmission electron microscopy images show that the Se-C nanostructures consist of coaxial nanocables made of single wall carbon nanotubes, as the core, surrounded by a trigonal Selenium shell. Resonance Raman spectroscopy was used to access the properties of both the carbon nanotubes and selenium. The behavior of the radial breathing mode and the G-band indicates that the Se shell primarily covers semiconducting nanotubes. X-ray photoelectron spectroscopy show that the nanocables have a thin coverage of selenium oxide. We envisage that this system could be used in the fabrication of photonic devices as an interface between electronic and photonic materials.