Dilute Metal Research Articles

Temperature-dependent transport properties of graphene decorated by alkali metal adatoms (Li, K)

We report the electrical transport properties of graphene for dilute alkali metal decoration (n ∼ 2 × 1012 cm−2) at cryogenic temperatures. Upon deposition of K and Li atoms at T = 20 K, graphene devices are doped with electrons, and the charge carrier mobility is decreased. As temperature is increased, the number of electrons donated to the graphene and the number of charged scatterers are reduced, and the mobility of the metal decorated graphene is increased. This differs from the typical temperature-dependent transport in undecorated graphene, where the mobility decreases with increasing temperature. To investigate the kinetic behavior of adatoms on graphene, we estimate the hopping time of the Li and K adatoms on graphene based on the migration barrier in the low concentration regime of the metal adatoms by Density Functional Theory calculations. The calculations reveal that these adatoms are mobile even at cryogenic temperatures and become more mobile with increasing temperature, allowing for cluster formation of adatoms. This indicates that the dominant factor in the electron transport on warming is a cluster formation.

Enhanced Removal of Dissolved Hg(II), Cd(II), and Au(III) from Water by Bacillus subtilis Bacterial Biomass Containing an Elevated Concentration of Sulfhydryl Sites.

In this study, the sorption of Hg(II), Cd(II), and Au(III) onto Bacillus subtilis biomass with an elevated concentration of sulfhydryl sites, induced by adding excess glucose to the growth medium (termed 'High Sulfhydryl Bacillus subtilis' or HSBS) was compared to that onto B. subtilis biomass with a low concentration of sulfhydryl sites (termed 'Low Sulfhydryl Bacillus subtilis' or LSBS) and to sorption onto a commercially available cation exchange resin. Our results show that HSBS exhibits sorption capacities for the three studied metals that are two to five times greater than the sorption capacities of LSBS for these metals. After blocking the bacterial cell envelope sulfhydryl sites using a qBBr treatment, the sorption of the metals onto HSBS was significantly inhibited, indicating that the enhanced sorption onto HSBS was mainly due to the elevated concentration of sulfhydryl sites on the bacteria. A direct comparison of the removal capacity of the HSBS and that of the cation exchange resin for the three metals demonstrates that HSBS, compared to this commercially available resin, exhibits superior sorption capacity and selectivity for the removal of Hg(II), Cd(II), and Au(III), especially in systems with dilute metal concentrations. These results suggest that bacterial sulfhydryl sites control the sorption behavior of these three metals, and therefore biomass with induced high concentrations of sulfhydryl sites represents a promising and low cost biosorbent for the effective removal and recovery of chalcophile heavy metals from aqueous media.

57Fe CEMS study on dilute metal ions codoped SnO2 thin films prepared by spray pyrolysis

Dilute Mn-Fe, Co-Fe and V-Fe codoped tin oxide films prepared by spray pyrolysis were characterized by 57Fe conversion electron Mossbauer spectrometry (CEMS) at room temperature (RT) and at 20 K. Two kinds of paramagnetic Fe3+ species were detected at RT; one doublet 1 (D1) with IS = 0.36–0.37 mm/s, QS = 0.69–0.75 mm/s and LW = 0.32–0.40 mm/s, and another doublet 2 (D2) with IS = 0.31–0.35 mm/s QS = 1.16–1.25 mm/s and LW = 0.46–0.52 mm/s. CEMS at 20 K provided more distinguished doublets than at RT. It is found that especially D2 with relatively small IS and large QS values are influenced by other metal ions codoped in SnO2 matrix, whereas D1 with relatively large IS and small QS has the parameters close to the models of Fe-VO1 and Fe-2VO1-Fe models (Nomura et al. Phys. Rev. B 75, 184411 2007; Mudarra Navarro et al. J. Phys. Chem. C 119, 5596–5603 2015).

Electronic structure and magnetic moment of dilute transition metal impurities in semi-metallic CaB6

Employing the all electron augmented plane wave+local orbital (APW+lo) method based on the density function theory (DFT), we have performed ab-initio calculations of electronic structure and magnetic properties of transition metal impurities doped in semi-metallic CaB6 host. Here, we present our results on the density of states (DOS), local magnetic moment and hyperfine field of 3d (Sc–Ni), 4d (Y–Pd) and 5d (La–Pt) in CaB6. Our results reveal strong localization of impurity d electrons yielding high local moments for most of the transition metal atoms, including the 5d atoms Ta, Re, Os and Ir. The results presented here would be useful towards a comprehensive understanding of the origin of weak ferromagnetism observed in CaB6. We believe that besides B or B6 vacancies which have been argued to be the main source of magnetism in CaB6, the local moments associated with different transition metal impurities can interact via conduction electron polarization and give rise to the weak ferromagnetism observed in this material.

Electronic, magnetic properties of transition metal doped Tl2S: First-principles study

In this paper, the structural, electric and magnetic properties of transition metal (TM) doped monolayer Tl2S are investigated by means of first-principles methods The results show that all the considered TM atoms are strongly bonded to the Tl vacancy site. The magnetic moment, the dilute magnetic semiconductor and metal characteristics are varied depending on the specific TM atoms. The TM doped Tl2S (TM-Tl2S) (from Sc to Ni) systems have fractional magnetic moments changing from 0.539μB to 4.479μB. However, Cu- and Zn-Tl2S systems exit the nonmagnetic ground states. The spin polarized metallic states are achieved by Sc, Ti, V, Mn and Fe doping, while spin polarized semiconducting states are realized by Cr, Co and Ni doping. The charge transfer, the total magnetic moment and the band gap obtained with PBE method are less than the values obtained by PBE+U, which suggests that the Hubbard U plays an important role in TM-Tl2S systems. In the case of two same types of TM atoms doped Tl2S systems, there exist AFM in Sc-, V-, Mn-Tl2S systems and FM only in Ti-Tl2S system. Interestingly, the Cr-, Fe-, Co-, Ni-Tl2S systems manifest paramagnetic. These findings may provide a new route for exploring two-dimensional diluted magnetic semiconductors experimentally and theoretically.

Dispersion of gold and other metals by trees, gravels and soils near Boddington Gold Deposit, Western Australia

South west Western Australia is host to some of the world's largest mineral deposits including bauxite, Ta and Au. The giant Boddington Gold Mine exploits one such deposit and is located in forested areas south east of Perth. Exploration for Au in this area has concentrated on sampling surficial Fe-rich lateritic residuum and its degradation products and was how Boddington was originally discovered; it has a multi-element signature. Despite its location in forest there has been little biogeochemistry undertaken in this area or consideration of whether trees (including eucalypts) are agents of dispersion of metals in this terrain. Eucalyptus trees have been shown to be responsible for forming anomalies above gold deposits in semi-arid areas of Australia and the location of Boddington in a humid environment provided an important comparison in which to investigate this possibility.The Golden Triangle Au prospect near Boddington Gold Deposit is located on the flank of a small lateritic hill. Limited shallow drilling has identified sub-economic mineralisation with some metre composite cuttings grading >1ppm Au. A selection of different trees and shrubs, organic soil and ferruginous pisoliths were collected over a surface traverse of 800m at 50m intervals from across the prospect. Samples were analysed for major elements, Au and several pathfinder metals. Additional foliage samples were collected from the same trees over mineralisation and background to test for sample heterogeneity.Golden Triangle vegetation samples were generally anomalous in Au and pathfinder elements (e.g. Ag, Bi, W and Sn). For example, Banksia and Macrozamia had elemental anomalies in Bi and Ag located directly above or down slope of mineralisation although for Eucalyptus the anomaly over mineralisation itself was poorly defined. Topsoil containing organic matter overlying the ferruginous pisoliths was particularly anomalous in Au (mean of 47ppb against of background of <5ppb). Pathfinder element anomalies were present in all sample media (soil, vegetation and pisoliths) although the specific elements and tenor of the anomaly varied between sample media.The results demonstrate a biotic (plant) influence on the dispersion of metallic elements at Golden Triangle prospect. This process of dispersion may serve to not only disperse and dilute metals in the regolith but potentially create a larger exploration target to detect the presence of the mineralisation. The anomalous metal content of the pisoliths themselves may be due to an earlier biotic mechanism of metal mobilisation from the deeper regolith or be solely a result of inorganic processes as previously thought. The sampling of deep-rooted trees and soil beneath them may assist in the discovery of mineral deposits in areas where there is transported material or leached regolith.

Emptying Dirac valleys in bismuth using high magnetic fields

The Fermi surface of elemental bismuth consists of three small rotationally equivalent electron pockets, offering a valley degree of freedom to charge carriers. A relatively small magnetic field can confine electrons to their lowest Landau level. This is the quantum limit attained in other dilute metals upon application of sufficiently strong magnetic field. Here we report on the observation of another threshold magnetic field never encountered before in any other solid. Above this field, Bempty, one or two valleys become totally empty. Drying up a Fermi sea by magnetic field in the Brillouin zone leads to a manyfold enhancement in electric conductance. We trace the origin of the large drop in magnetoresistance across Bempty to transfer of carriers between valleys with highly anisotropic mobilities. The non-interacting picture of electrons with field-dependent mobility explains most results but the Coulomb interaction may play a role in shaping the fine details.

Recovery of gold from industrial wastewater by extracellular proteins obtained from a thermophilic bacterium Tepidimonas fonticaldi AT-A2

Biosorption has emerged as a promising alternative approach for treating wastewater with dilute metal contents in a green and cost effective way. In this study, extracellular proteins of an isolated thermophilic bacterium (Tepidimonas fonticaldi AT-A2) were used as biosorbent to recover precious metal (i.e., Au) from wastewater. The Au (III) adsorption capacity on the T. fonticaldi AT-A2 proteins was the highest when the pH was set at about 4.0–5.0. The adsorption capacity increased with increasing temperature from 15 to 70°C. Adsorption isotherm studies show that both Langmuir and Freundrich models could describe the adsorption equilibrium. The maximum adsorption capacity of Au (III) at 50°C and pH 5 could reach 9.7mg Au/mg protein. The protein-based biosorbent was also used for the recovery of Au from a wastewater containing 15mg/L of Au, achieving a high adsorption capacity of 1.45mg Au/mg protein and a removal efficiency of 71%.

Purification of a dilute platinum group metals process stream using waste yeast biomass immobilized on plaster of Paris

Purification of a dilute platinum group metals process stream using waste yeast biomass immobilized on plaster of Paris

Self-Terminated Electrodeposition of Ni, Co, and Fe Ultrathin Films

Self-terminated Fe-group metal (Ni, Co, Fe) electrodeposition occurs at potentials negative of the onset of water reduction where OH– generation leads to the formation of a blocking hydroxide monolayer. Quenching of metal deposition is accompanied by an increase in dissipative energy loss in microbalance experiments attributed to increased hydrogen bonding to the adjacent double layer. Pulse deposition at −1.5 VSSCE in 5 mmol/L (NiCl2, CoCl2, FeSO4) – 0.1 mol/L NaCl pH 3.0 electrolytes yields fully coalesced ultrathin films of Ni, Co, Fe, or alloys thereof, on Au. The film thickness is controlled by the nucleation, growth, and termination dynamics constrained by the electrochemical cell time constant. Precipitation of bulk Ni(OH)2 and related phases is minimized by using short deposition times and dilute metal cation concentrations to limit supersaturation. The rapid deposition of smooth, compact ultrathin Fe, Co, and Ni films should facilitate mechanistic and durability studies of Fe-group metal catalysi...

Transition-Metal Mixing and Redox Potentials in Lix(M1–yM′y)PO4 (M, M′ = Mn, Fe, Ni) Olivine Materials from First-Principles Calculations

The performance of olivine cathode materials can be improved using core/shell structures such as LiMnPO4/LiFePO4 and LiMnPO4/LiNiPO4. We use density functional theory to calculate the energetics, phase stability, and voltages of transition-metal mixing for a series of olivine phosphate materials. For LiMn1–yFeyPO4, LiFe1–yNiyPO4, and LiMn1–yNiyPO4, we find phase-separating tendencies with (mean-field) maximum miscibility gap temperatures of 120, 320, and 760 K respectively. At room temperature, we find that Mn is completely miscible in LiFePO4, whereas Mn solubility in LiNiPO4 is just 0.3%. Therefore, we suggest that core/shell LiMnPO4/LiNiPO4 particles could be more effective at containing Mn in the particle core and limiting Mn dissolution into the electrolyte relative to LiMnPO4/LiFePO4 particles. We calculate shifts in redox potentials for dilute transition metals, M, substituted into LixM′PO4 host materials. Unmixed LixMnPO4 exhibits a redox potential of 4.0 V, but we find that dilute Mn in a LiNiPO4...

Bloch states in light transport through a perforated metal

Light transport in a metal with two-dimensional hole arrays is considered. Analytical expressions for a transmission coefficient in periodic, isolated and disordered cases are derived, assuming the existence of waveguide modes transverse tunneling in a two-dimensional plane perpendicular to the traveling direction of light. The one-dimensional case of periodic holes, due to its simplicity, is investigated in detail. In the dilute metal regime, when metal fraction is small, our numerical study of the transmission coefficient of the central diffracted wave indicates the existence of a minimum which is completely independent of an incident wavelength. Further increasing of the metal fraction leads to the unusual monotonic increasing of the central-diffracted-wave transmission. The role of the surface plasmons is discussed.

On mobility of electrons in a shallow Fermi sea over a rough seafloor

Several doped semiconductors, in contrast to heavily-doped silicon and germanium, host extremely mobile carriers, which give rise to quantum oscillations detectable in relatively low magnetic fields. The small Fermi energy in these dilute metals quantifies the depth of the Fermi sea. When the carrier density exceeds a threshold, accessible thanks to the long Bohr radius of the parent insulator, the local seafloor is carved by distant dopants. In such conditions, with a random distribution of dopants, the probability of finding an island or a trench depends on on the effective Bohr radius, and the carrier density, n. This picture yields an expression for electron mobility with a random distribution of dopants: , in reasonable agreement with the magnitude and concentration dependence of the low-temperature mobility in three dilute metals whose insulating parents are a wide-gap (SrTiO3), a narrow-gap (PbTe) and a ‘zero’-gap (TlBiSSe) semiconductor.

Structural, magnetic and optical properties of a dilute magnetic semiconductor based on Ce1−xCoxO2 thin film grown on LaAlO3

The enhancement of the room temperature ferromagnetism and optical properties of the dilute magnetic metal oxides is a crucial clue to construct spin-based optoelectronic devices. In this work, Ce1−xCoxO2 (0.01≤x≤0.15) thin films were prepared via ethylene glycol modified sol–gel spin coating technique on the LaAlO3 (001) substrate to enhance their room temperature ferromagnetism and optical properties. The structures, magnetic and optical properties of the prepared films were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, SQUID magnetometer, X-ray photoelectron spectroscopy and UV–vis spectrophotometer. The results demonstrated that a single phase cubic structure was formed, implying the substitution of Co ions into the Ce ions sites. The prepared films showed room temperature ferromagnetism with saturation magnetic moment of 1.09μB/Co was achieved for 5at.% Co-doped CeO2. This film exhibited high optical transparency of 85% and low optical band energy gap of 3.39eV. The improved magnetic and optical properties are argued to the increase of the density of the oxygen vacancies into the cerium oxide crystal structure due to the incorporation of Co ions.

Removal of heavy metal ions from dilute aqueous solutions by polymer–surfactant aggregates: A novel effluent treatment process

A novel treatment process for effluent streams that employs polymer–surfactant complexation and flocculation has been developed and applied to remove dilute heavy metal ions, such as Cr(III), Zn(II) and Cd(II), from aqueous solutions. This process uses cationic polymers, such as poly diallyldimethylammonium chloride (PolyDADMAC) or poly ethylenimine (PEI), as a back-bone structure onto which anionic surfactants, such as sodium dodecyl sulphate (SDS), can form micelle-like aggregates. The resulting structures, called polymer–surfactant aggregates (PSAs), have the ability to remove heavy metal ions from solution, and to form larger flocculated aggregates through a process of intermolecular association. The flocculated aggregates can then be separated from the effluent stream through a settling or coarse filtration step. In the work presented here, it is shown that 99% of 11.2ppm Cd(II) was removed under optimum dosage using 40ppm PEI and 0.5mM SDS. Surface tension measurement results indicate that the removal of heavy metal ions occurs by the PSAs when the surfactant concentration is well below the critical micellar concentration. The results show that this process is effective for heavy metal ion removal at a pH range from 6 to 9, and is also effective in the presence of organic contaminants (acetone, ethanol and phenol) and in the presence of NaCl. Such a PSA complexation and flocculation process thus has potential application for the efficient removal of dilute heavy metal ions during process effluent water treatment.

Quantum Oscillations, Thermoelectric Coefficients, and the Fermi Surface of Semimetallic WTe2.

We present a study of angle-resolved quantum oscillations of electric and thermoelectric transport coefficients in semimetallic WTe2, which has the particularity of displaying a large B(2) magnetoresistance. The Fermi surface consists of two pairs of electronlike and holelike pockets of equal volumes in a "Russian doll" structure. The carrier density, Fermi energy, mobility, and the mean-free path of the system are quantified. An additional frequency is observed above a threshold field and attributed to the magnetic breakdown across two orbits. In contrast to all other dilute metals, the Nernst signal remains linear in the magnetic field even in the high-field (ωcτ≫1) regime. Surprisingly, none of the pockets extend across the c axis of the first Brillouin zone, making the system a three-dimensional metal with moderate anisotropy in Fermi velocity, yet a large anisotropy in the mean-free path.

Local and systemic metal ion release occurs intraoperatively during correction and instrumented spinal fusion for scoliosis.

Study designProspective pilot study.ObjectivesThe aim of this study was to measure titanium, niobium and aluminium levels in various intraoperative and postoperative samples to determine patterns of metal ion release that occur within the first month following instrumented spinal fusion.Summary of background dataRaised serum metal ion levels are reported following instrumented spinal fusion in adolescent idiopathic scoliosis. The exact topological origin and chronology of metal ion release remains conjectural. Recent literature suggests an immediate rise in serum metal levels within the first postoperative week.MethodsTitanium, niobium and aluminium levels were measured before, during and after surgery in serum and local intraoperative fluid samples obtained from two pediatric patients undergoing posterior correction and instrumentation for scoliosis.ResultsMeasurable metal ion levels were detected in all local samples obtained from wound irrigation fluid, cell saver blood, and fluid that immersed metal universal reduction screw tabs. Postoperative serum metal ion levels were elevated compared to baseline preoperative levels. In general, metal ion levels were considerably higher in the intraoperative fluid samples compared to those observed in the serum levels.ConclusionOur findings of contextually high metal ion concentrations in intraoperative and early postoperative samples provide further empirical support of a ‘putting-in’ phenomenon of metal ion release following instrumented spinal fusion. This challenges existing beliefs that metal ion release occurs during an intermediate ‘wearing-in’ phase. We recommend thorough irrigation of the operative site prior to wound closure to dilute and remove intraoperative metal ion debris. Possibilities of filtering trace metal ions from cell saver content may be considered.

Interplay between antiferrodistortive, ferroelectric, and superconducting instabilities inSr1−xCaxTiO3−δ

$\phantom{\rule{4.pt}{0ex}}{\text{SrTiO}}_{3}$ undergoes a cubic-to-tetragonal phase transition at 105 K. This antiferrodistortive transition is believed to be in competition with incipient ferroelectricity. Substituting strontium by isovalent calcium induces a ferroelectric order. Introducing mobile electrons to the system by chemical nonisovalent doping, on the other hand, leads to the emergence of a dilute metal with a superconducting ground state. The link between superconductivity and the other two instabilities is a question gathering momentum in the context of a popular paradigm linking unconventional superconductors and quantum critical points. We present a set of specific-heat, neutron-scattering, dielectric-permittivity, and polarization measurements on $\phantom{\rule{4.pt}{0ex}}{\text{Sr}}_{1\ensuremath{-}x}\phantom{\rule{4.pt}{0ex}}{\text{Ca}}_{x}\phantom{\rule{4.pt}{0ex}}{\text{TiO}}_{3}$ $(0&lt;x&lt;0.009)$ and a study of low-temperature electric conductivity in $\phantom{\rule{4.pt}{0ex}}{\text{Sr}}_{0.9978}\phantom{\rule{4.pt}{0ex}}{\text{Ca}}_{0.0022}\phantom{\rule{4.pt}{0ex}}{\text{TiO}}_{3\ensuremath{-}\ensuremath{\delta}}$. Calcium substitution was found to enhance the transition temperature for both antiferrodistortive and ferroelectric transitions. Moreover, we find that $\phantom{\rule{4.pt}{0ex}}{\text{Sr}}_{0.9978}\phantom{\rule{4.pt}{0ex}}{\text{Ca}}_{0.0022}\phantom{\rule{4.pt}{0ex}}{\text{TiO}}_{3\ensuremath{-}\ensuremath{\delta}}$ has a superconducting ground state. The critical temperature in this rare case of a superconductor with a ferroelectric parent is slightly lower than in $\phantom{\rule{4.pt}{0ex}}{\text{SrTiO}}_{3\ensuremath{-}\ensuremath{\delta}}$ of comparable carrier concentration. A three-dimensional phase diagram for $\phantom{\rule{4.pt}{0ex}}{\text{Sr}}_{1\ensuremath{-}x}\phantom{\rule{4.pt}{0ex}}{\text{Ca}}_{x}\phantom{\rule{4.pt}{0ex}}{\text{TiO}}_{3\ensuremath{-}\ensuremath{\delta}}$ tracking the three transition temperatures as a function of $x$ and $\ensuremath{\delta}$ results from this study, in which ferroelectric and superconducting ground states are not immediate neighbors.

Magnetic Properties and Oxygen Defects of Dilute Metal Doped Tin Oxide Based Semiconductor

Magnetic Properties and Oxygen Defects of Dilute Metal Doped Tin Oxide Based Semiconductor

Expanding Effective-Medium Theory to Optical Diamagnetic Responses in Magnetoplasmonic Colloids

The authors present an effective-medium theory of the optical diamagnetic response of very dilute metal colloids. These dispersions of ferromagnetic metal clusters in diamagnetic hosts show a large, linear response under an applied magnetic field, which is of interest for emerging applications in sensing, integrated optical communications, and magneto-optical current transformers and transducers. This theory could be further extended to describe e.g., metal inclusions in polymers or glasses.