Presence Of Sb Research Articles

1.31 μm GaAs-based heterojunction p– i– n photodetectors using InGaAsNSb as the intrinsic layer grown by molecular beam epitaxy

GaAs-based double-heterojunction p– i– n photodetectors using In z Ga 1− z As 1− x− y N x Sb y in the i-layer are fabricated for the first time using the solid source molecular beam epitaxy growth method. A peak responsivity of ∼ 0.29 A/W, corresponding to quantum efficiencies (QE) of 38% is attained from the best p– i– n device between 0.9 and 1.1 μm. The dark current is ∼ 70 nA at a reverse bias of 2 V and the cutoff wavelength reaches ∼ 1.4 μm. The surfactant effect generated by the presence of Sb in this material allows thick high quality dilute nitride material growth. A Sb-free p– i– n device consisting of InGaAsN/GaAs is also fabricated to compare the device performance with the InGaAsNSb/GaAs p– i– n devices.

The characterization of the V species and the identification of the promoting effect of dopants in V/Ti/O catalysts for o-xylene oxidation

The present work deals with the study of the role of promoters in TiO 2-supported vanadium oxide, catalyst for the oxidation of o-xylene to phthalic anhydride. Two different series of catalysts were prepared, the first one consisting of undoped samples having different vanadium oxide content, and the second one of samples having 7 wt.% V 2O 5 and variable amounts of Sb and Cs as promoters. All the samples were characterized by means of Raman spectroscopy, X-ray diffraction and thermal-programmed reduction and oxidation, in order to define a method for the quantification of the different V species (i.e., isolated vanadium, dispersed polyvanadate and bulk vanadium oxide) that develop on TiO 2 support in the presence of promoters. It was found that polyvanadate and bulk vanadium oxide spontaneously release molecular oxygen at 600–650 °C, whereas the isolated V is not susceptible of self-reduction. The latter species is predominant in samples having low vanadium oxide loading (≤2 wt.% V 2O 5, with TiO 2 surface area 22.5 m 2/g), and possesses the highest intrinsic activity in o-xylene conversion. The presence of Sb, a promoter of activity, increases the dispersion of the most active species and also hinders its segregation in the reaction environment. These promoting effects are more pronounced when both Cs and Sb are present.

Structure of InAs/GaAs quantum dots grown with Sb surfactant

InAs quantum dots in GaAs, grown under the presence of Sb by metalorganic chemical vapor deposition, were studied with cross-sectional scanning tunneling microscopy. Large flat quantum dots with a truncated pyramidal shape, base lengths between 15 and 30 nm, heights of 1–3 nm, and a rather pure InAs stoichiometry were found for the case of an Sb supply during the InAs deposition. If Sb is already supplied during GaAs stabilization prior to InAs deposition, the dots become even larger and tend to get intermixed with Ga, but remain coherently strained with a reversed cone-like In distribution. Regarding the quantum dot growth Sb acts as surfactant, whereas an incorporation of individual Sb atoms was observed in the wetting layer.

Photoluminescence properties of Te doped AlGaAsSb alloys

A detailed study of the photoluminescence properties in undoped and Te-doped AlGaAsSb alloys lattice matched to InP is presented. Photoluminescent temperature and excitation intensity dependences are employed to discuss the origin of the dominant transition and the influence of the presence of Al and Te on the fluctuation of the electrostatic potential in the epitaxial layers. The behavior of PL dominant transitions is associated with the quasi-donor-acceptor-pair (QDAP) model at a low temperature interval. The temperature dependence of photoluminescence intensities showed characteristics similar to those observed for amorphous semiconductors and disordered superlattices. The presence of two V elements, or the presence of Sb in the ternary and quaternary (III)-III-V-V alloys, causes a reduction in photoluminescence intensity temperature dependence, when compared to (III)-III-III-V alloys.

Surfactant effect of Sb on GaN growth

Periodic, self-consistent, gradient-corrected (PW91-GGA), density functional theory (DFT) calculations are used to investigate the role of Sb as surfactant during GaN growth. The adsorption and diffusion of Ga, Sb, and N on GaN(0 0 0 1) and GaN( 1 1 2 ¯ 0 ) single crystal surfaces is studied. We find that N has a much higher diffusion barrier than Ga and Sb on these surfaces. An approximate phase diagram for Sb-induced surface reconstructions of GaN(0 0 0 1) is constructed. Our findings suggest that N transport on GaN is facilitated by the formation of an SbN intermediate, which diffuses easier than N on the GaN surface. We show that this SbN formation-mediated surfactant action of Sb is much more pronounced on the Ga-terminated GaN(0 0 0 1) than on the GaN( 1 1 2 ¯ 0 ) facet. The insights derived from the DFT studies are used to explain the experimentally observed increased diffusion length of N, decreased surface roughness, and the change in the preferential sidewall facet from ( 1 1 ¯ 0 1 ) to ( 1 1 2 ¯ 0 ) during lateral epitaxial overgrowth in the presence of Sb.

Determination of pentavalent antimony in antileishmaniotic drugs using an automated system for liquid–liquid extraction with on-line detection

An automated system for liquid–liquid extraction flow analysis (LLE-FA) for the determination of Sb(V) in antileishmanial drugs is presented. The method is based on extraction in a 5 mL glass extraction chamber of an ion pair formed between hexachloroantimoniate anion and rhodamine B cation into toluene. The detection system consists of a green light emitting diode (LED) and a photodiode. The system is controlled by a microcomputer using a program written in Visual Basic 3.0. The extraction process was optimized and the following experimental parameters were established: sample loop of 150 μL; reagent loop of 900 μL; stirring time of 100 s; phase separation time of 80 s; volumetric ratio of 1:1 (aqueous/organic). The method was in-house validated for the determination of Sb(V) in meglumine antimoniate. The following performance criteria were obtained: linearity of 0.9989, linear range of 7.0 × 10 −5 to 7.2 × 10 −4 mol Sb(V) L −1, sensitivity of 1.61 × 10 6 ± 2 arbitrary units L mol −1 ( P < 0.05), intra-assay precision of 3.5% ( n = 5; 4.1 × 10 −4 mol L −1 Sb(V). Whereas the method is selective in the presence of Sb(III), As(III) and Pb(II) at concentrations up to one tenth of the concentration of Sb(V), As(V) interferes. The accuracy of the method was evaluated through comparison of results obtained from analyses of pharmaceutical formulations by the proposed LLE-FA method with those obtained by inductively coupled plasma optic emission spectrometry (ICP OES) and differential pulse polarography for total antimony and Sb(III), respectively. The proposed method presented an analytical frequency of eight analysis per hour and is suitable for Sb(V) determination in the quality control of drugs employed for the treatment of leishmaniasis.

GaAs-based heterojunction p-i-n photodetectors using pentanary InGaAsNSb as the intrinsic layer

GaAs-based double-heterojunction p-i-n photodetectors using In/sub z/Ga/sub 1-z/As/sub 1-x-y/N/sub x/Sb/sub y/ in the i layer is fabricated for the first time using the solid source molecular beam epitaxy growth method. The surfactant effect generated by the presence of Sb in this material allows thick high-quality dilute nitride material growth. A peak responsivity of /spl sim/0.29 A/W, corresponding to quantum efficiencies of 38% is attained between 0.9 and 1.1 /spl mu/m from the best p-i-n device. The cutoff wavelength reaches /spl sim/1.4 /spl mu/m and the dark current is /spl sim/0.43 mA/cm/sup 2/ at a reverse bias of 2 V. A Sb-free p-i-n device consisting of InGaAsN-GaAs is also fabricated to compare the device performance with the InGaAsNSb-GaAs p-i-n devices.

Threshold behavior of the formation of nanometer islands in a Ge/Si(100) system in the presence of Sb

Atomic-force microscopy is used to study the behavior of an array of Ge islands formed by molecular-beam epitaxy on an Si (100) surface in the presence of an antimony flux incident on the surface. It is shown that, as the Sb flux increases to a certain critical level, the surface density of the islands increases; however, if this critical level is exceeded, nucleation of the islands is suppressed and mesoscopic small-height clusters are observed on the surface. This effect is explained qualitatively in the context of a kinetic model of the islands’ formation in heteroepitaxial systems mismatched with respect to their lattice parameters.

Nonequivalence of the Nucleotide Binding Domains of the ArsA ATPase

The arsRDABC operon of Escherichia coli plasmid R773 encodes the ArsAB pump that catalyzes extrusion of the metalloids As(III) and Sb(III), conferring metalloid resistance. The catalytic subunit, ArsA, is an ATPase with two homologous halves, A1 and A2, connected by a short linker. Each half contains a nucleotide binding domain. The overall rate of ATP hydrolysis is slow in the absence of metalloid and is accelerated by metalloid binding. The results of photolabeling of ArsA with the ATP analogue 8-azidoadenosine 5'-[alpha-(32)P]-triphosphate at 4 degrees C indicate that metalloid stimulation correlates with a >10-fold increase in affinity for nucleotide. To investigate the relative contributions of the two nucleotide binding domains to catalysis, a thrombin site was introduced in the linker. This allowed discrimination between incorporation of labeled nucleotides into the two halves of ArsA. The results indicate that both the A1 and A2 nucleotide binding domains bind and hydrolyze trinucleotide, even in the absence of metalloid. Sb(III) increases the affinity of the A1 nucleotide binding domain to a greater extent than the A2 nucleotide binding domain. The ATP analogue labeled with (32)P at the gamma position was used to measure hydrolysis of trinucleotide at 37 degrees C. Under these catalytic conditions, both nucleotide binding domains hydrolyze ATP, but hydrolysis in A1 is stimulated to a greater degree by Sb(III) than A2. These results suggest that the two homologous halves of the ArsA may be functionally nonequivalent.

EFFECT OF CERTAIN SURFACTANTS ON Co CEMENTATION USING Zn DUST IN THE PRESENCE OF BOTH Cu AND Sb

The effect of surfactants nonylphenolpolyethylene glycol (D1), dinaphthylmethane-4,4′- disulphonic acid (D2) and polyethylene glycol with a molecular weight 400 (D3) added separately or as a mixture (D1+D2+D3) on Co-Zn dust cementation kinetics and morphology of obtained deposits was investigated in the presence of both Cu and Sb. The rate constant obtained in the presence of Cu and Sb was 3 to 5 times lower than that found in the presence of Cu and up to 3 times higher than that in the presence of Sb. This indicates a high inhibition effect of Sb on Co cementation. D1, D3 and D1+D2+D3 inhibit Co and Sb cementation. The highest effect was obtained in presence of D1. A decrease in the Sb concentration from 200 to 35 mg dm-3 at a constant Cu concentration increased Co cementation rate by up to 3 times despite the presence of D1+D2+D3. An increase of Sb concentration substantially decreased the crystallite size and deposit porosity.On a investigué l’effet des agents surfactants nonylphénolpolyéthylène de glycol (D1), acide bisulfonique binaphthylméthane-4,4′ (D2) et glycol polyéthylénique avec poids moléculaire de 400 (D3), ajoutés séparément ou en un mélange (D1+D2+D3), sur la cinétique de cémentation de la poussière de Co-Zn et sur la morphologie des dépôts obtenus, tant en présence de Cu que de Sb. La constante cinétique obtenue en présence de Cu et de Sb était 3 à 5 fois plus basse que celle trouvée en présence de Cu et jusqu’à 3 fois plus élevée que celle en présence de Sb. Ceci indique un effet important d’inhibition du Sb sur la cémentation du Co. D1, D3 et D1+D2+D3 inhibent la cémentation du Co et du Sb. On a obtenu l’effet le plus important en présence de D1. Une diminution de la concentration de Sb de 200 à 35 mg dm-3 à une concentration constante de Cu augmentait le taux de cémentation du Co jusqu’à 3 fois en dépit de la présence de D1+D2+D3. Une augmentation de la concentration de Sb diminuait substantiellement la taille de cristallite et la porosité du dépôt.

GaInAs/GaAs quantum-well growth assisted by Sb surfactant: Toward 1.3 μm emission

The growth of highly strained GaInAs quantum wells on GaAs is investigated in the presence of Sb. Sb appears as an adequate isoelectronic surfactant: the lateral relaxation of strain is shown to be significantly delayed in comparison with a Sb-free growth. This effect is used to extend the emission wavelength of GaInAs quantum wells. We obtained a 9-nm-thick Ga0.59In0.41As0.986Sb0.008 quantum wells with smooth interfaces, emitting at 1.27 μm at room temperature.

Quantitative kinetic determination of Sb(V) and Sb(III) by spectrophotometric H-point standard addition method

The H-point standard addition method (HPSAM) was applied to kinetic data for simultaneous determination of Sb(V) and Sb(III) and also selectively determines Sb(V) in the presence of Sb(III). The method is based on the differences between rate of complexation of pyrogallol red with Sb(V) and Sb(III) at pH=2. Sb(V) can be determined in the range of 0.3–2.0 μg ml −1 with satisfactory accuracy and precision in the presence of excess Sb(III). Good selectivity was obtained over the variety of metal ions. The proposed method was used for determination of Sb(V) and Sb(III) in river and spring water samples.

Arsenic sensing and resistance system in the cyanobacterium Synechocystis sp. strain PCC 6803.

Arsenic is one of the most important global environmental pollutants. Here we show that the cyanobacterium Synechocystis sp. strain PCC 6803 contains an arsenic and antimony resistance operon consisting of three genes: arsB, encoding a putative arsenite and antimonite carrier, arsH, encoding a protein of unknown function, and arsC, encoding a putative arsenate reductase. While arsB mutant strains were sensitive to arsenite, arsenate, and antimonite, arsC mutants were sensitive only to arsenate. The arsH mutant strain showed no obvious phenotype under the conditions tested. In vivo the arsBHC operon was derepressed by oxyanions of arsenic and antimony (oxidation state, +3) and, to a lesser extent, by bismuth (oxidation state, +3) and arsenate (oxidation state, +5). In the absence of these effectors, the operon was repressed by a transcription repressor of the ArsR/SmtB family, encoded by an unlinked gene termed arsR. Thus, arsR null mutants showed constitutive derepression of the arsBHC operon. Expression of the arsR gene was not altered by the presence of arsenic or antimony compounds. Purified recombinant ArsR protein binds to the arsBHC promoter-operator region in the absence of metals and dissociates from the DNA in the presence of Sb(III) or As(III) but not in the presence of As(V), suggesting that trivalent metalloids are the true inducers of the system. DNase I footprinting experiments indicate that ArsR binds to two 17-bp direct repeats, with each one consisting of two inverted repeats, in the region from nucleotides -34 to + 17 of the arsBHC promoter-operator.

Spectroscopic ellipsometry study of a self-organized Ge dot layer

We report on the determination of the dielectric function of a Ge dot layer obtained by epitaxial growth on Si(001) in the presence of Sb as surfactant and capped by Si. After growth, spectroscopic ellipsometry reveals a SiGe alloy containing Ge rich regions. After etching the Si cap, the dielectric function of the Ge rich regions exhibits critical points located at 2.92, 3.65, and 4.25 eV. It is shown that this dielectric function does not correspond either to an alloy or to bulk Ge, and is affected by confinement.

Effect of antimony(III) on the electrocrystallisation of zinc from sulphate solutions containing SLS

A detailed investigation has been carried out to determine the effect of antimony(III) on the electrocrystallisation of zinc from sulphate solutions containing sodium lauryl sulphate (SLS). The results indicated that addition of Sb(III) at trace level to the electrolysis bath without sodium lauryl sulphate decreased the current efficiency (CE) and deteriorated the quality of the zinc electrodeposits. However, its addition to the bath containing sodium lauryl sulphate increased the current efficiency and also improved the surface morphology of the zinc electrodeposits. There was no trace of antimony found in any of the deposits. Cathodic polarisation curves were traced and analysed to determine the kinetic parameters, exchange current density, Tafel slopes and transfer coefficients so as to elucidate the nature of the electrode reactions. Presence of Sb(III) alone in the electrolyte depolarised the cathode and SLS alone polarised it; however, presence of both gave a balanced condition suitable for zinc electrowinning.

Electrochemical Sensors for the Stripping Voltammetric Determination of Antimony(III)

The conditions of the modification of a glassy-carbon electrode with various polyphenols were studied by multicyclic voltammetry over a wide range of pH. The state of the electrode surface was additionally monitored by measuring cyclic voltammograms of ferrocyanide ions in the presence of a phosphate buffer solution (pH 7.0). It was found that the electrooxidation of all the studied polyphenols at the electrode surface resulted in the formation of a water-insoluble film which is capable of accumulating antimony(III) from aqueous solutions. The surface concentration of chemically active cites was of the order n × 10–9 M/cm2. The electrochemical sensors thus prepared were found to be suitable for the selective determination of antimony(III) by adsorption stripping voltammetry. The maximum signals of antimony(III) were obtained at electrodes modified with pyrocatechol and pyrogallol upon metal deposition from acetate buffer solutions (pH 4.5). The detected peak areas S (μA · s) were directly proportional to the deposition time td (min) and the concentration of antimony(III). The analytical range was 10–250 μg/L at td = 5.0 min, and the detection limit was 6 μg/L. It was found that a sensor based on a pyrogallol film can selectively determine antimony(III) in the presence of Sb(V), Cu(II), and Pb(II), and can be used for the analysis of natural water.

Oxidation of o-Xylene to Phthalic Anhydride on Sb-V/ZrO2 Catalysts

Zirconia-supported and bulk-mixed vanadiumantimonium oxide catalysts were used for the oxidation of o-xylene to phthalic anhydride. X-ray diffraction, Raman spectroscopy and photoelectron spectroscopy were used for characterization. It was found that vanadium promotes the transition of tetragonal to monoclinic zirconia. The simultaneous presence of Sb and V on zirconia at low coverage led to a preferential interaction of individual V and Sb oxides with the zirconia surface rather than the formation of a binary Sb-V oxide, while at higher Sb-V contents the formation of SbVO4 took place. Sb-V/ZrO2 catalysts showed high activity for o-xylene conversion and better selectivity to phthalic anhydride as compared to V/ZrO2 catalysts. However, their selectivity to phthalic anhydride was poor in comparison to a V/TiO2 commercial catalyst. The improved selectivity of the Sb-containing catalysts is attributed to the blocking of non-effective surface sites of ZrO2, the decrease of the total amount of acid sites and the formation of surface V-O-Sb-O-V structures.

The addition of Sb as a surfactant to GaN growth by metal organic vapor phase epitaxy

The role and effect of the isoelectronic center Sb on the structure and properties of GaN epilayers have been investigated. The gas phase Sb concentration was varied by changing the triethyl antimony/trimethyl gallium mole ratio over a wide range of concentrations while keeping other growth parameters constant. The Sb addition slightly improved the optical and structural properties of GaN epilayer at a low level of Sb incorporation, especially for the films grown under a high group V/III ratio conditions. The addition of Sb resulted in changes in GaN surface morphology, which was further explored by the lateral epitaxy overgrowth (LEO) technique through the changes in the growth rates and the facet formation. The presence of Sb in the gas phase greatly enhanced the lateral overgrowth rate and altered the formation of the dominant facets. Vertical facets to the LEO growth appeared with the addition of Sb under conditions that normally produced sloped sidewalls. While Sb altered the growth facet present during LEO, only a small amount of Sb was incorporated into the GaN, suggesting that Sb acts as a surfactant during the GaN metal organic vapor phase epitaxy growth. Sb addition produces surface conditions characteristic of a Ga-rich surface stoichiometry indicating both a possible change in the reactivity of NH3 and/or enhanced surface diffusion of Ga adatom species in the presence of Sb.

Sb-surfactant mediated growth of Ge nanostructures

This paper reports the AFM and HREM study of the Sb surfactant mediated growth of Ge on Si(0 0 1). We show that very dense self-organised Ge dots of small lateral dimensions can be grown by using a sub-monolayer coverage of Sb on Si(0 0 1) in the transient growth regime between 2D nucleation and step flow. The dramatic Ge growth change induced by Sb is attributed to both kinetic and thermodynamic effects. Indeed, HREM observations evidence mainly two phenomena: the close-packing of ultra-small Ge islands indicating a lower surface diffusion in presence of Sb and a mono-modal island shape and size that strongly differs from the bimodal islands ‘huts’ and ‘domes’ commonly observed without Sb. Morphological and microstructural features of Ge islands formed with and without Sb are studied and the differences between facets and aspect ratio are exhibited. Moreover, at lower growth temperature (in the 2D nucleation regime, T g⩽350 °C), a delay to 3D island nucleation is observed and defect free 2D flat layers can be grown up to thicknesses of ∼18 Å. At higher growth temperature, (in pure step flow at T g∼750 °C) large, well separated ‘dome’ islands partially relaxed by dislocation nucleation on their edges are obtained. Such islands are very similar to those obtained without Sb coverage. The complete desorption of Sb on Ge rich surface at T>720 °C explains this result. This study which improves the understanding on the formation of ultra-small dense islands is very promising for the fabrication of quantum devices that require highly homogeneous islands of small lateral sizes and of MOSFET heterostructures with strained SiGe n-channel which require flat Ge rich layers with abrupt interfaces.

Antimonite regulation of the ATPase activity of ArsA, the catalytic subunit of the arsenical pump.

The ArsA ATPase is the catalytic subunit of the pump protein, coupling the hydrolysis of ATP to the movement of arsenicals and antimonials through the membrane-spanning ArsB protein. Previously, we have shown the binding and hydrolysis of MgATP to ArsA to be a multi-step process in which the rate-limiting step is an isomerization between different conformational forms of ArsA. This isomerization occurs after product release, at the end of the ATPase reaction, and involves the return of the ArsA to its original conformation, which can then bind MgATP. ArsA possesses an allosteric site for antimonite [Sb(III)], the binding of which elevates the steady-state ATPase activity. We have used a transient kinetics approach to investigate the kinetics of ternary complex formation that lead to an enhancement in the ATPase activity. These studies revealed that ArsA exists in at least two conformational forms that differ in their ligand binding affinities, and that ATP favours one form and Sb(III) the other. Ternary complex formation is rate-limited by a slow transition between these conformational forms, leading to a lag in attaining maximal steady-state activity. Sb(III) enhances the steady-state ATPase activity by inducing rapid product release, allowing ArsA to adopt a conformation that can bind MgATP for the next catalytic cycle. In the presence of Sb(III), ArsA avoids the rate-limiting isomerization at the end of the ATPase reaction and ATP hydrolysis becomes rate-limiting for the reaction. The binding of Sb(III) probably results in more effective pumping of the substrates from the cell by enhancing the rate of efflux.