Residual Te Research Articles

Metalloid Te‐Doped Fe‐Based Catalysts Applied for Electrochemical Water Oxidation

AbstractMetal telluride nanocatalysts have been widely used in the catalytic reactions. However, there are few examples of electrocatalytic water oxidation with metal telluride as catalysts, especially Fe‐based telluride, to the best of our knowledge, has not yet been reported. In this work, the Te‐doped Fe‐based catalysts (FeTex) with crystalline and amorphous nanosheet structures have been successfully synthesized by chemical vapor deposition (CVD) as well as electrodeposition (ED) on the iron foam (IF), where the latter exhibited more remarkable electrocatalytic performance towards the oxygen evolution reaction (OER) in the alkaline electrolyte, requiring the overpotential (η) of only 264.4 mV to reach a current density of 10 mA cm−2 with a Tafel slope of 54.2 mV dec−1. The electrochemical study confirmed that the residual Te in ED‐FeTex does play a role in promoting the catalytic activity for the electrocatalytic water oxidation.

Formation of Dense Pore Structure by Te Addition in Bi0.5Sb1.5Te3: An Approach to Minimize Lattice Thermal Conductivity

We herein report the electronic and thermal transport properties of p‐type Bi0.5Sb1.5Te3 polycrystalline bulks with dense pore structure. Dense pore structure was fabricated by vaporization of residual Te during the pressureless annealing of spark plasma sintered bulks of Te coated Bi0.5Sb1.5Te3 powders. The lattice thermal conductivity was effectively reduced to the value of 0.35 W m−1 K−1 at 300 K mainly due to the phonon scattering by pores, while the power factor was not significantly affected. An enhanced ZT of 1.24 at 300 K was obtained in spark plasma sintered and annealed bulks of 3 wt.% Te coated Bi0.5Sb1.5Te3 by these synergetic effects.

Electronic Structure of Te/Sb/Ge and Sb/Te/Ge Multi Layer Films Using Photoelectron Spectroscopy

Te/Sb/Ge and Sb/Te/Ge multilayer films with an atomically controlled interface were synthesized using effusion cell and e-beam techniques. The layers interacted during the deposition, resulting in films composed of Sb-Te+Sb-Sb/Ge and Sb/Sb-Te/Ge-Te/Ge respectively. Atomic diffusion and chemical reactions in films during the annealing process were investigated by photoemission spectroscopy. In the case of Te/Sb/Ge, Ge diffused into the Sb-Te region released Sb in Sb-Te bonds and interacted with residual Te, resulting in a change in valence band line shape, which was similar to that of a Ge(1)Sb(2)Te(4) crystalline phase. The Ge-Sb-Te alloy underwent a stoichiometric change during the process, resulting in a 1.2:2:4 ratio, consistent with the most stable stoichiometry value calculated by ab initio density-functional theory. The experimental results strongly suggest that the most stable structure is generated through a reaction process involving the minimization of total energy. In addition, Ge in the Sb/Te/Ge film diffused into Sb-Te region by thermal energy. However, Ge was not able to diffuse to the near surface because Sb atoms of the high concentration at the surface were easily segregated and hindered the diffusion of other elements.

CMB Temperature Polarization Correlation and Primordial Gravitational Waves: WMAP5

we continue our study of the CMB temperature polarization (TE) cross-correlation as a source of information about primordial gravitational waves (PGWs). In a previous paper, we considered two methods for detecting PGWs using the TE cross-correlation. The first method is the zero multipole method, where we find the multipole,ℓ0, where the TE cross-correlation power spectrum,CℓTE, first changes sign. The second method Wiener filters the CMB TE data to remove the density perturbation contribution to the TE power spectrum. We then use statistical tests to determine if there is a detection of negative residual TE correlation and hence a detection of primordial gravitational waves, the only source of negative TE correlation at these superhorizon scales. In this paper, we will apply these tests to the WMAP 5-year data. We find that the TE power spectrum consistent withr< 2.0 at 95% confidence with no additional assumptions about the PGWs. If we assume that the PGWs are generated by inflation, then we getr< 1.0 at 95% confidence.

Surface properties of passivated

We have investigated the properties of surfaces after passivation with various treatments, either by electrochemical processes or by immersion in chemical baths. From the C(V) characteristics of metal-insulator-semiconductor structures, we have determined the density of fixed interface charges deduced from the flat-band voltage. The density of slow traps is obtained from the width of the anticlockwise hysteresis and the energy distribution of fast interface states is reported for all passivation processes. The treatment by immersion in bromine-methanol solution including a small amount of S gives the best interface properties. The energy distribution of fast interface states then presents a broad U-shape with a minimum lower than . The surface roughness as measured by atomic force microscopy is notably reduced after this treatment and the x-ray photoelectron spectroscopy of the samples so obtained reveals the presence of a residual Te layer on the surface.

Surface passivation of HgCdTe by CdZnTe and its characteristics

In this paper, we report the results of capacitance-voltage measurements conducted on several metal-insulator semiconductor (MIS) capacitors in which HgCdTe surfaces are treated with various surface etching and oxidation processes. CdZnTe passivation layers were deposited on HgCdTe surfaces by thermal evaporation after the surfaces were etched with 0.5−2.0% bromine in methanol solution, or thin oxide layers (tox ∼ few ten A) were grown on the surfaces, in order to investigate effects of the surface treatments on the electrical properties of the surfaces, as determined from capacitance-voltage (C-V) measurements at 80K and 1 MHz. A negative flat band voltage has been observed for MIS capacitors fabricated after etching of HgCdTe surfaces with bromine in methanol solutions, which is reported to make the surface Te-rich. It is inferred that residual Te on the surface is a positive charge, Te4+. C-V characteristics for MIS capacitors fabricated on oxide surfaces grown by air-exposure and electrolytic process have shown large hysteresis effects, from which it is inferred that imperfect and electrically active oxide compounds and HgTe particles near the surface become slow interface states.

Biochemistry of tellurium

Tellurium (Te) demonstrates properties similar to those of elements known to be toxic to humans, and has applications in industrial processes, which are rapidly growing in importance and scale. It is relevant, therefore, to consider the tellurium physiology, toxicity, and methods for monitoring the element in biological and environmental specimens. Animal studies suggest that up to 25% of orally administered tellurium is absorbed in the gut. There is a biphasic elimination from the circulation with loss of about 50% within a short period, t1/2 = 0.81 d, and slower elimination of the residual Te, t1/2 = 12.9 d. Following a single ip, injection the largest proportion is in the kidney and bone, but with repeated oral administration, Te is found in the heart > > kidney, spleen, bone, and lung. Formation of dimethyl telluride is a characteristic feature of exposure, and gives a pungent garlic-like odor to breath, excreta, and the viscera. The main target sites for Te toxicity are the kidney, nervous system, skin, and the fetus (hydrocephalus). Te can be reliable measured in different specimens by several analytical techniques. Recent work has employed hydride generation atomic absorption spectrometry. Topics for further investigation are proposed.

Nondestructive analysis of Hg1−xCdxTe (x=0.00, 0.20, 0.29, and 1.00) by spectroscopic ellipsometry. II. Substrate, oxide, and interface properties

Properties of Hg1−x CdxTe substrates, their electrochemically grown anodic oxides, and their interfaces are studied under as-grown conditions using the nondestructive analytic capabilities of spectroscopic ellipsometry to avoid ambiguities arising from destructive analytic techniques. Pseudodielectric functions that are the most accurate representations of the intrinsic bulk responses that we are able to achieve are given for each of the materials studied. The dielectric functions of the oxides are calculated from (tan ψ, cos Δ) data in a three-phase model. These oxides are uniform with sharp interfaces at both substrate and ambient. Residual Te layers of thicknesses of the order of 6%–8% of the initial oxide thicknesses are found on the Hg-containing substrates after their native oxides are stripped with HCl. Four-phase model calculations show that these Te layers are not present (±2 Å) in the as-grown condition for the Hg-containing materials and therefore cannot be invoked to explain leakage in integrated-circuit devices. However, a small residual amorphous (a-Te) layer ∼1.5 Å thick between the semiconductor and electrochemically grown anodic oxide is seen for CdTe. The optical data show the oxide on CdTe to be predominantly the tellurite CdTeO3. The composition of the oxide on HgTe cannot be identified uniquely, but it probably contains a substantial fraction of TeO2. A residual absorption tail below the fundamental edge on all oxides is consistent with the presence of ∼3%–4% a-Te in the oxides. The oxides on the alloys can be represented as physical mixtures of those of the endpoints, suggesting an oxidation mechanism and a structure consisting of TeO2 and some Hg tellurites captured in a relatively insoluble matrix of CdTeO3. After correcting for residual Te overlayers, all substrate dielectric functions for a given material are found to be identical to within 1% regardless of sample history, placing upper limits of less than 2% for cationic or anionic outdiffusion in these materials. A similar consistency of broadening parameters implies that the actual limits may be much lower. The properties of the Hg1−x CdxTe compounds studied in this work vary smoothly with x and show no chemical or physical anomalies.