Loss Of Hg Research Articles

Structural quality of Hg1-xCdxTe: Equilibrium point defects.

The Phillips--Van Vechten dielectric theory for estimating enthalpies of defect formation and defect concentrations is applied to CdTe and narrow-gap ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Te (${\mathrm{Hg}}_{0.8}$${\mathrm{Cd}}_{0.2}$Te). It is found that favorable ionization levels in CdTe lead to large charged native defect densities (\ensuremath{\sim}${10}^{18}$/${\mathrm{cm}}^{3}$; \ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}${10}^{17}$/${\mathrm{cm}}^{3}$ net at 1365 K), which can condense into extended defects, such as dislocations and Te inclusions at lower temperatures. Intentional incorporation of small amounts of impurities or use of substitutional alloys, such as ${\mathrm{Cd}}_{0.96}$${\mathrm{Zn}}_{0.04}$Te, has often been suggested as a means of improving the quality of CdTe crystals, and addition of Zn or Mn has also been suggested as a means of reducing cation-vacancy concentrations in Hg-rich ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Te. It is shown that equilibrium concentrations of native point defects are not reduced substantially by adding small amounts of other elements either to CdTe or to Hg-rich ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Te, although macroscopic and nonequilibrium phenomena, such as formation of dislocations, may be significantly affected. Increasing metallicity upon addition of Hg to the alloy and the volatility of elemental Hg lead to preferential loss of Hg from ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Te, which must be balanced, in equilibrium, by a larger proportion of Hg in the external phase. The observed strong p-type character of ${\mathrm{Hg}}_{0.8}$${\mathrm{Cd}}_{0.2}$Te, in contrast to the strongly compensated character of CdTe at high temperature, results both from this and from highly favorable cation-vacancy ionization levels.

Surface characterization of Hg0.7Cd0.3Te native oxides

Ultraviolet photoelectron spectroscopy (UPS), x-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (ELS) were used to characterize the surfaces of Hg0.7Cd0.3Te native oxide films grown by air exposure, ozone treatment, oxygen plasma, and electrochemical anodization. The surfaces of the air-grown, plasma-grown, and anodically grown native oxides were found to all be relatively rich in Cd, while the ozone oxide was rich in Hg. Two ELS absorption edges were detected at ∼2.1 and ∼3.6 eV and are attributed to an oxide trap state and the fundamental band gap of the oxide, respectively. Changes in the ELS and XPS spectra following prolonged electron beam exposure resulted from a loss of Hg from the oxide and incomplete bonding of Te in the oxide. The electron beam induced changes were much more dramatic in the ozone oxide spectrum than for any of the other samples studied. XPS analysis of the interface of an air-grown native oxide which was subsequently covered with a thin layer of photochemical SiO2 demonstrated that the air-grown native oxide was partially, but not completely, reduced by chemical reaction with SiH4 during the deposition of SiO2. A generic energy band diagram of the native oxide Hg0.7Cd0.3Te interface is constructed and discussed in terms of its implications for the passivation of Hg1−xCdxTe surfaces.

Surface and interface properties of Hg1−xMnxSe

Synchrotron radiation photoemission studies of Hg1−xMnxSe single crystals for x≤0.15 show the cleaved semiconductor surfaces to be stable in ultrahigh vacuum with no loss of Hg or change in surface stoichiometry oberved with time. Comparison with results for HgSe samples points out a well defined Mn-derived emission feature centered 4.1 eV below the Fermi level EF with a full width at half maximum (FWHM) of 1.1 eV. Analysis of the photoemission cross section demonstrates that the corresponding states have dominant Mn 3d character and are therefore responsible for the semiconductor magnetotransport and magneto-optical properties. Preliminary studies of Hg1−xMnxSe–Al interface formation show that the semiconductor surface is depleted of both Hg and Mn upon metal deposition, while an Al–Se reacted phase is established as the true microscopic interface at the Hg1−xMnxSe–Al junction.

Hg loss rate limitation in HgCdTe thermal processing

The problem of Hg loss from HgCdTe is investigated for rapid thermal processing of device quality material. Outdiffusion of Hg from HgCdTe is characterized by fitting calculated diffusion profiles to measurements by Rutherford backscattering spectrometry (RBS). Fitting parameters used are diffusion length 2(Dt)1/2, and ratio of surface transfer rate to diffusion rate ht/(Dt)1/2. The results of these calculations include an estimation of diffusion coefficient D, surface transfer rate h, Hg concentration profile C(x,t), Hg flux F(t), and total Hg lost Q(t). Measurements were taken over a temperature range of 300 to 400 °C and for Cd compositions of 0.23 and 0.4. Surface transfer rate is found to have a strong dependence on surface preparation and diffusion coefficient is observed to change significantly under large Hg loss conditions. A vacancy pair diffusion mechanism is suggested. This work is intended to aid in establishing guidelines for device fabrication processes.

Mercury emissions from a modified in-situ oil shale retort

Gaseous Hg emissions were measured during the processing of a large modified in-situ oil shale retort (4×10 4 m 3) in Colorado. A continuous, on-line, gas monitor based upon the principal of Zeeman atomic absorption spectroscopy was the primary analytical method. The on-line monitor technique was shown to be well suited for this application and compared favorably with an independent reference method which collects gaseous Hg by Au-amalgamation. Forty-two hours of on-line data were obtained over a 35-day period during the latter half of the retort burn. Hg emission rates in g day −1 were calculated from Hg concentration and offgas flow rate data. The predicted total gaseous Hg mass emission for the retort was 4 kg. Extrapolation of the data to a hypothetical modified in-situ oil shale facility with a daily production of 8× 10 61 (5 × 10 4 bbl) of oil results in a projected emission rate of ≈ 8 kg day −1. This estimated value is higher than Hg emission rates recorded for coal fired power plants. Emission rates were found to be highly variable both within and between days. Factors which may limit Hg emissions from a modified in-situ retort are discussed. Adsorption losses to unretorted shale at the bottom of a retort are suggested as a major sink for Hg. Losses of Hg to the extensive offgas plumbing system may also be substantial.

Humic acid as a preservative for trace mercury(II) solutions stored in polyolefin containers

Humic acid prevents significant loss of trace Hg(II) from aqueous solutions stored in commercial polyolefin containers, thus permitting their use for storing natural water samples prior to mercury determination. At a level of 50 mg/L, humic acid reduces losses from 1 ng/mL Hg(II) solutions over 15 days to less than 10%. Humic acid suppresses mercury loss better than do preservatives based on HNO/sub 3/ and oxidants, and it is simple to use. It is insensitive to pH between pH 3 and pH 9 and to levels of Ca, Mg, and Fe(III) above those found in most natural waters, and it is equally effective in commercial containers fabricated from a number of polyolefins. 8 figures, 3 tables.

Annealing of Hg1−xCdxTe: Hg loss rates and annealing of ion implantation damage

An important problem in processing the infrared detector material Hg1−xCdxTe is avoiding undue mercury loss. Here we quantify that loss and apply the information to the annealing of ion implanted Hg1−xCdxTe. We thus extend the work of Takita et al. on Hg loss in HgTe to the ternary Hg1−xCdxTe. The Hg loss is generated with a thermal-pulse annealing system and measured by Rutherford backscattering spectrometry (RBS). The loss rate is studied as a function of temperature, composition, and surface preparation (chemimechanical and contactless polishing). For each set of conditions the data is fit to an Arrhenius equation N⧠ /t=A exp(−ΔE/kT) and the fitting parameters A and ΔE are determined. ΔE ranges from 1.0 to 2.5 eV and A varies from 1023 to 1036 atoms/cm2 s. Channeling RBS was also used to study the effect of thermal pulse annealing on boron implanted material. The rate of change of the minimum yield (χmin) with depth, which can be related to certain types of damage, was consistent with the calculated implant damage profile. A 260 °C 8 s anneal restored the crystal quality to better than the as-received material, as observed by channeling.

Relation between the electronic states and structural properties of Hg1−xCdxTe

Physical reasons are presented for the coherent potential approximation (CPA) calculation method’s abillity to predict little band gap bowing or alloy scattering, while at the same time predicting large deviation from virtual crystal behavior in other energy ranges. Accurate treatment of structural properties requires that calculations be doubly self-consistent: a density functional method plus CPA is needed. Experimental values of bond energies are greater than those predicted by simple theories. Weakened HgTe bonds in alloys help to explain the loss of Hg when the materials undergo surface treatments.

Uptake and binding of cadmium and mercury to metallothionein in rat hepatocyte primary cultures.

The administration of inorganic Cd and Hg in vivo has been shown to result in markedly different metal concentrations in rat liver. Primary cultures of rat hepatocytes were utilized to gain insight into the dispositional differences between these chemically similar metals. Hepatocyte monolayer cultures were exposed to several concentrations of Cd or Hg (3, 10 and 30mum) in serum-containing medium for 30min. The cells were then washed and incubated in fresh medium for the remainder of the experiment. Hepatocytes exposed to Cd accumulated significantly more metal than hepatocytes exposed to equimolar concentrations of Hg. In cells exposed to 3mum-Cd there was an initial loss of Cd from the hepatocytes when placed in fresh medium, followed by a gradual re-uptake of metal, concomitant with increased binding to metallothionein. In hepatocytes exposed to 3 and 10mum-Cd, 87 and 77% of the intracellular Cd was bound to metallothionein within 24h. Loss of Hg from hepatocytes pulsed with 30mum-Hg was also observed upon the addition of fresh medium and continued for the duration of the experiment. No time-dependent increase in Hg binding to metallothionein was observed. A maximum of about 10% of the intracellular Hg was found associated with metallothionein in hepatocytes exposed to 30mum-Hg. Studies utilizing [(35)S]cysteine incorporation indicated significant increases in the amount of metallothionein synthesized in hepatocytes exposed to 3 and 10mum-Cd (300% of control value) and 30mum-Hg (150% of control value) 24h after metal pulsing. Time-course studies revealed a 6-12h lag in metallothionein synthesis, followed by a significant elevation in [(35)S]cysteine incorporation into metallothionein between 12 and 24h. These studies suggest that (a) isolated hepatocytes differentiate between Cd and Hg and preferentially accumulate the former, and (b) Cd strongly stimulates the induction of, and preferentially binds to, metallothionein, whereas Hg induces weakly, and does not preferentially bind to, metallothionein.

Oxidation of Hg1−xCdxTe studied with surface sensitive techniques

We report the use of surface sensitive electron spectroscopies to monitor the initial steps of formation of a native oxide on atomically clean cleaved Hgl-xCdxTe single crystal surfaces in ultrahigh vacuum (UHV). Here the oxide is formed by oxygen excited by the presence of an operating ion gauge. During the reaction, the composition of the surface region of the substrate was found to change, with a net loss of Hg from the surface. Parallel studies of the compositions of thick anodic oxides using sputter profiling techniques showed only small amounts of Hg in the anodic oxides.

Room temperature stability of cleaved Hg1−xCdxTe

X‐ray and ultraviolet photoemission spectroscopy (XPS and UPS) at 21.2 eV have been used to determine the stability against Hg evaporation of cleaved (110) surfaces of p‐Hg1−xCdxTe (x = 0.2, 0.31, 0.39) in vacuum at room temperature. No evidence of Hg loss was obtained for periods of observation from five to twenty hours. However, oxygen excited by an ionization gauge and Ne ion sputtering both produced preferential loss of Hg.

Stability of an atomically clean Hg 1− xCd xTe surface in vacuum and under O 2 exposure

We report studies of the stability of single crystal surfaces of Hg 1- x Cd x Te with respect to loss of Hg. Ultraviolet photoemission spectroscopy (UPS) and X-ray-induced photoemission (XPS) were used to monitor the electronic structure and atomic composition of a cleaved surface under ultrahigh vacuum (UHV) ( p ≅ 5 x 10 -10 Torr) and under oxygen exposures. These experiments showed the surface to be remarkably stable in UHV for extended periods of time at room temperature. However, changes in the surface concentrations can be induced during exposure to excited oxygen or during ion bombardment. The importance and relevance of these findings to the question of the stability of the material are discussed.

Thermal Pulse Annealing of Hg1−xCdxTe

ABSTRACTThermal pulse annealing has been used to modify the near surface of Hg1−xCdxTe. Using anneals of approximately 260°C for seven seconds, the crystal quality of epitaxial HgCdTe surfaces can be improved as observed by MeV He+ ion channeling. Similar anneals have also been used to repair the damage resulting from a 250 keV, 101511 B/cm2 implant into HgCdTe held at LN2. For higher temperatures and/or longer anneals, surface Hg loss is observed. Rutherford Backscattering measurements are used to measure this loss. The resulting loss rate data is described by No= A exp (−ΔE/kT) where A and ΔE depend on the material composition with A = 1029, ΔE = 1.8 eV and A = 1036, ΔE = 2.6 eV for x = 0.23 and 0.4, respectively.

Characterization of Mercury in a Riverwash Soil

AbstractThe extent of cinnabar (α‐HgS) degradation in a riverwash soil polluted by Hg mining waste was evaluated by determination of persistent α‐HgS and Hg liberated from the mineral. The soil was sequentially extracted to determine soluble, exchangeable, manganese‐oxide‐associated, and free iron‐oxide‐associated Hg. DTPA, 0.5N NaHCO3, and 0.5N and 1.0N HCl were used to determine available, weakly organic‐bound, and strongly adsorbed Hg, respectively. Particle size and density separations using tetrabromoethane and Clerici's solution were employed to determine Hg in < 1.8, 1.8–2.9, > 2.9, < 4.0, and > 4.0 g cm−3 fractions of clay, silt, and sand separates. A thermal fractionation of the soil was used to measure Hg loss at temperatures from 25 to 450°C.Only traces of Hg were recovered by the chemical extractants, implying that very little existed in an adsorbed or easily soluble state. More than 90% of the Hg was recovered in the > 4.0 g cm−3 fraction. This, along with thermal fractionation and x‐ray diffraction data, indicated that this Hg remained primarily in the α‐HgS form. Loss of Hg in the tetrabromoethane separations and at low temperatures during the thermal fractionation suggested that Hg in both the colloidal and lighter fractions was organically bound.

The distribution of mercury in the sediments of the plym estuary

Surface sediment samples collected in the Plym Estuary have been analysed for Fe, Mn, Hg, clay content and organic carbon. Statistical analysis of the data showed that Fe, Mn, clay and organic carbon concentrations all correlate well with each other. The Hg concentrations, which were in the range 18–2610 ng/g, had no strong correlations with any other sedimentary variable. A cluster analysis of the samples revealed the existence of three geochemical facies. Cluster facies P was located upstream and had sediments that were poorly sorted with Hg concentrations above those normally found in the rocks and soils of the catchment area. Cluster facies Q, further downstream, consisted of increased levels of Fe, Mn, clay and organic matter which suggested that estuarine precipitation processes were an important factor. The Hg concentration only increased by 16% and the results indicated a possible loss of Hg to Plymouth Sound. Cluster facies R consisted of sediments that were polluted. The analyses are discussed in terms of the sources and sinks of Hg within the estuary.

Liquidus isotherms, solidus lines and LPE growth in the Te-rich corner of the Hg-Cd-Te system

Liquidus isotherms for the Hg1−xCdxTe primary phase field in the Te-rich corner of the Hg-Cd-Te ternary system have been determined for temperatures from 425 to 600‡C by a modified direct observational technique. These isotherms were used to help establish conditions for the open-tube liquid phase epitaxial growth of Hg1−xCdxTe layers on CdTe1−ySey substrates. Layers with x ranging from 0.1 to 0.8 have been grown from Te-rich HgCdTe solutions under flowing H2 by means of a horizontal slider technique that prevents loss of Hg from the solutions by evaporation. Growth temperatures and times of 450–550‡C and 0.25–10 min, respectively, have been used. The growth solution equilibration time is typically 1 h at 550‡C. Source wafers, supercooled solutions, and (111)-oriented substrates were employed in growing the highest quality layers, which were between 3 and 15 Μm thick. Electron microprobe analysis was used to determine x for the epitaxial layers, and the resulting data, along with the liquidus isotherms, were used to obtain solidus lines. In addition to EMP data, optical transmission results are given.

The in vivo effects of maleate on the cation-distribution in rat kidney metallothionein sub-fractions after induction by cadmium and/or mercury

The metallothionein fractions, isolated by gel filtration from the kidneys of rats that have been dosed with Cd 2+, Hg 2+ or Cd 2+ followed by Hg 2+, yield very different elution profiles on ion-exchange chromatography. The metallothionein from Cd 2+-treated animals is resolved into the isomethallothioneins I and II and a minor, less negatively-charged species (B), which contains Cd 2+ and copper, but little Zn 2+. The corresponding fraction from the kidneys of rats dosed with Hg 2+ yields five components, all of which contain Hg 2+, Zn 2+ and Cu, but in different ratios. Three of these compounds correspond in their elution characteristics from DE-cellulose with the above-mentioned isometallothioneins I and II and fraction B. The last of these, which also is rich in Cu, is the major Hg 2+-binding component. The distribution of Hg 2+ and of other cations between these five sub-fractions, but not the number of sub-fractions, is altered by Cd 2+-pretreatment of the animals. Treatment of Cd 2+-dosed rats with sodium maleate has no significant effect on the distribution of cations (Cd 2+, Zn 2+ and copper) amongst the renal metallothionein subfractions. The same treatment, applied to animals dosed with either Hg 2+ only, or Cd 2+ followed by Hg 2+, causes the elimination of 70–75% of the Hg 2+ from the metallothionein fraction. Loss occurs from all subfractions, but is greatest in subfraction B, which also loses copper. Whilst it is possible that Hg 2+ may induce metallothionein and other metalloproteins in the kidney, Hg 2+ appears to bind to both isometallothioneins I and II, when these are induced by Cd 2+-pretreatment. The loss of Hg 2+, but not of Cd 2+, from these metalloproteins after treatment with sodium maleate may be related to differences in the relative binding affinities of the two cations for thionein and other cellular proteins.

Sirosorb: a collector for use in the determination of mercury in geochemical samples

Sirosorb is a low cost, high efficiency gold collector for mercury vapor for use in mineral exploration programs. The collector is prepared by depositing gold onto a gas chromatography diatomite support. Sirosorb can be employed to collect mercury from soil gas or water samples. It can also be used to selectively collect mercury from gas streams containing substances which interfere with mercury analyses. When dosed with known amounts of mercury vapor, Sirosorb provides a convenient calibration standard for field use. If Sirosorb is stored in a closed tube, Hg loss is negligible at temperatures up to 100°C.

Simple Glaucoma before the Age of 30 Years

'Juvenile glaucoma' is a meaningless term which should not be used. Glaucoma in young subjects can be hydrophthalmus, secondary or simple glaucoma. In this paper, early simple glaucoma is described in 15 patients (8 males, 7 females) below the age of 30 years, starting in some subjects already at 8 years of age. Inheritance was dominant in 6 patients. Anticipation could be shown in 2 pedigrees through 4 and 5 generations, respectively. The course of the disease was severe in 8 patients, with intraocular pressures over 40 mm Hg and/or heavy functional loss. There were usually no subjective symptoms. The chamber angles were gonioscopically normal in all patients. Miotics were effective but did not normalize the intraocular pressure. Surgical treatment is discussed.

Correlation of polynuclear aromatic hydrocarbons with environmental components in sediment from Hirakata bay, Japan.

Polymiclear aromatic hydrocarbons (PAH) including fluoranthene, pyrene, 1,2-benzanthracene, chrysene, 3,4-benzpyrene (1,2-benzpyrene) and 1,12-benzperylene, were identified in sediments from Hirakata Bay. Their concentrations were proved to be in the range from several hundred µg/kg to several mg/kg of dry samples.Significant positive correlations were statistically found between total amount of PAH and Pb, Hg, Cd, Cu, Zn and ignition loss in bay sediment. In addition, significant positive correlations were statistically found between ignition loss and the content of clay as well as the sum of (clay+silt) contents for both river and bay sediments.