Contribution To Resistivity Research Articles

Molecular dynamics simulation of shock waves in Fe and Fe–C: Influence of system characteristics

Pressure-induced phase transformation in iron and its alloys is a classic research topic in solid-state physics, material science, and geophysics. The crystal structure of iron undergoes a phase transformation at a hydrostatic pressure of 13 GPa, changing from a body-centered cubic system to a hexagonal close-packed system. Although extensive research has been carried out on the transformation in iron by using molecular dynamics simulations, there is very limited literature that focuses on the contribution of parent phase orientations, system size, and impurities to the phase evolution. In this work, classic molecular dynamics simulations have been employed to investigate the effects of system size, lattice orientation, and impurity concentration on the pressure-induced phase transformation of iron and iron alloys for the first time. Our results show that the lattice orientation has a strong influence on the phase transition behavior, while the influence of carbon is small. The phase transition is slightly delayed with increasing carbon content, whereas the transition pressure increases from [001] to [011] to [111] orientation. The amount of twinning and stacking faults highly depends on the orientation. It is easiest for solitary waves to travel through [111] lattice orientation. The addition of carbon has a slow-down effect on shock velocities, and this effect increases with carbon content and lattice orientation of the samples from [001] to [011] to [111].

Kondo screening cloud scaling: impurity entanglement and magnetization

The screening of an impurity spin in the Kondo model occurs over a characteristic length scale ξ K , that defines the size of the Kondo screening cloud or ‘mist’. The presence of such a length scale in experimental and numerical results is rather subtle. A consistent way to show the presence of the screening cloud is to demonstrate scaling in the spatial correlations in terms of the single variable, r/ξK instead of the correlations depending on r and ξ K separately. Here we study the paradigmatic one channel Kondo model using a spin chain representation, with an impurity spin at one end of the chain coupled with a strength JK′ . Using Fermi liquid theory combined with numerical results, we obtain new high precision estimates of the non-universal terms in the entanglement entropy which leads to a verification of the expected non-integer ground-state degeneracy, g. This then allows us to study the impurity contribution to the entanglement in detail. If the impurity coupling JK′ is varied, a precise determination of ξ K can then be obtained. The length scale, ξ K , is then shown to characterize the scaling of both the uniform and alternating part of a measure of the magnetization of part of an odd length chain.

Intrinsic ferromagnetism in Hg1-xFexSe (0.00012 ≤ x ≤ 0.0013) diluted magnetic semiconductor bulk single crystals at room temperature: Role of hybridization of impurity electronic states

We investigate room-temperature structural properties and spontaneous magnetism in a series of Hg1-xFexSe (0.00012 ≤ x ≤ 0.0013) diluted magnetic semiconductor bulk single crystals grown by the Bridgman method. In order to elucidate the experimentally observed high-temperature magnetism in the studied systems, the dependencies of magnetization on magnetic field strength for the entire sample series were studied. Their detailed analysis revealed impurity contributions typical of ferromagnetic materials, which are described by magnetization curves with the parameters characterizing the spontaneous spin magnetism of the donor conduction electrons of the outer d-shells of the impurity atoms. According to the previously-developed theoretical concept, such a magnetic ordering mechanism stems from the direct exchange coupling of donor conduction electrons due to hybridization of impurity states, rather than from inter-impurity interactions. The results of optical emission spectroscopy and X-ray diffraction analysis confirmed the observed ferromagnetism to be intrinsic and linked directly to the d-electrons of iron impurity atoms.

Dynamics in between Structural and Electrical Properties of as Grown ZnO Thin Films by Thermal ALD

The mechanism behind n-type conductivity of undoped ZnO films are not understood well. One and two dimensional defects (grain boundaries, dislocations), and zero dimensional stoichiometric point defects (vacancies, self-interstitials and impurities) play a crucial role in determining the electrical properties of ZnO. All defect mechanisms are strongly controlled by the growth method and conditions. While it is more straightforward examining the one and two dimensional defects, measuring and unveiling the mechanism behind the zero dimensional point defect contribution and their sole effect on the electrical properties are challenging. This is why there has been controversial discussion of results among experimental and computational works relating physical and chemical properties of ZnO to sustainable electrical properties. In this study, to correlate the dynamics in between structural and electrical properties of ZnO grown by thermal ALD; growth temperature, DEZ and DI water precursor pulse times, DEZ/DI water precursor pulse ratio, and N2 purge time were varied. To obtain growth condition specific structural and electrical properties; XRD, AFM, profilometer, ellipsometry, XPS/CasaXPS, UV-VIS spectrometer, Hall-Effect measurements were utilized. Although, there was no strong correlation for oxygen vacancies, the contribution of hydrogen impurities, zinc interstitials and oxygen vacancies to conductivity was observed at different growth conditions. Lowest resistivity and highest average % transmittance were obtained as 6.8x10-3 ohm.cm and 92% in visible spectrum (380-700 nm), respectively.

Impurity contribution to ultraviolet absorption of saturated fatty acids.

Saturated fatty acids are abundant organic compounds in oceans and sea sprays. Their photochemical reactions induced by solar radiation have recently been found as an abiotic source of volatile organic compounds, which serve as precursors of secondary organic aerosols. However, photoabsorption of wavelengths longer than 250 nanometers in liquid saturated fatty acids remains unexplained, despite being first reported in 1931. Here, we demonstrate that the previously reported absorption of wavelengths longer than 250 nanometers by liquid nonanoic acid [CH3(CH2)7COOH)] originates from traces of impurities (0.1% at most) intrinsically contained in nonanoic acid reagents. Absorption cross sections of nonanoic acid newly obtained here indicate that the upper limit of its photolysis rate is three to five orders of magnitude smaller than those for atmospherically relevant carbonyl compounds.

Impurity-related defect complexes-mediated ferromagnetism and impurity band hopping conduction in a highly compensated Zn-doped SnO2

We reported the ferromagnetism (FM) and electrical transport properties induced by donor-acceptor compensated defect complexes and related impurity bands in highly compensated Zn-doped SnO2 thin films. Various characterizations were used to study the optical, electrical, luminescent, and magnetic properties of SnO2 films with Zn dopants. Comparing with the paramagnetic nature of undoped n-type SnO2, we observed a room temperature d0 FM in the highly compensated and p-type Zn-doped SnO2 films with a low conductivity of ∼10−3 Scm−1, suggesting a strong correlation between ferromagnetism and the donor-acceptor compensation. The coercive field, remanent and saturation magnetization for the Zn-doped SnO2 film at 300 K are 310 Oe, 0.8 emu/cm3, and 2.6 emu/cm3, respectively. A detailed analysis for temperature-dependent resistivity indicates that the electrical conduction behavior of Zn-doped SnO2 at low temperatures follows the variable range hopping mechanism proposed by Mott and confirms that impurity bands occur at the Fermi level. As the concentration of Zn dopants increases, the fitting Mott temperature gradually rises, suggesting the contribution of Zn impurities to form the impurity bands where the carriers are localized. First-principles calculations reveal that the Zn substituting Sn site (ZnSn) defect with a low formation energy is responsible for the transformation of the charge carrier type. Furthermore, the oxygen vacancy (VO) between two nearest-neighbor ZnSn defects can stabilize the ferromagnetic coupling and form Mott's variable range hopping conduction derived from the localized carriers in the compensated impurity bands. Our results are of significance for the better understanding of the physical mechanisms underlying the effects of impurity/defect bands on the magnetic and electrical properties of the SnO2 with Zn dopants.

Giant Second-Order Nonlinear Hall Effect in Twisted Bilayer Graphene.

In the second-order response regime, the Hall voltage can be nonzero without time-reversal symmetry breaking but inversion symmetry breaking. Multiple mechanisms contribute to the nonlinear Hall effect. The disorder-related contributions can enter the NLHE in the leading role, but experimental investigations are scarce, especially the exploration of the contributions from different disorder sources. Here, we report a giant nonlinear response in twisted bilayer graphene, dominated by disorder-induced skew scattering. The magnitude and direction of the second-order nonlinearity can be effectively tuned by the gate voltage. A peak value of the second-order Hall conductivity reaching 8.76 μm SV^{-1} is observed close to the full filling of the moiré band, four order larger than the intrinsic contribution detected in WTe_{2}. The scaling shows that the giant second-order nonlinear Hall effect in twisted bilayer graphene stems from the collaboration of the static (impurities) and dynamic (phonons) disorders. It is mainly determined by the impurity skew scattering at 1.7K. The phonon skew scattering, however, has a much larger coupling coefficient, and becomes comparable to the impurity contribution as the temperature rises. Our observations provide a comprehensive experimental understanding of the disorder-related mechanisms in the nonlinear Hall effect.

Determination of ICH-Q3D Elemental Impurity Leachables in Glass Vials by Inductively Coupled Plasma Mass Spectrometry.

Container closure systems that are used for packaging pharmaceutical products are required to satisfy numerous safety requirements. Maximum permitted limits on the concentrations of numerous toxic elemental impurities that potentially leach from the packaging are one such requirement. The implementation of ICH-Q3D Guideline for Elemental Impurities, in conjunction with the 2018 publication of USP <232> Elemental Impurities-Limits and USP <233> Elemental Impurities-Procedures, requires a critical risk assessment of all container closure systems to evaluate their contribution of certain elemental impurities to the enclosed drug product. ICH-Q3D has established limits for each specific elemental impurity that considers relevant toxicological data and administration route (oral, parenteral, or inhalation) and presents them as permitted daily exposures based on the maximum daily dosage of the final drug product. A study was undertaken to assess the degree of elemental impurity leaching from one type of pharmaceutical glass vial under specific, fixed environmental controls. Multiple buffer systems representing a broad spectrum of possible parenteral drug product formulations were used in the study. Resulting buffer solutions that had been in contact with a single type of glass vial under specific conditions were subsequently analyzed using an inductively coupled plasma mass spectrometry (ICP-MS) method developed and validated specifically for the purpose of quantifying elemental impurity leachables in a variety of parenteral formulations. Results indicated that the degree of elemental impurity leachables imparted by the specific type of glass vial evaluated during this study posed no risk to patient safety, regardless of the drug product buffer formulation. Following this evaluation, the ICP-MS method developed for the determination of elemental impurities leachables has been successfully applied to the assessment of elemental impurities in a number of different biological parenteral drug product formulations currently under development. These data can be leveraged for inclusion in elemental impurities component ICH-Q3D risk assessments to satisfy the container closure system contribution.

Fabrication of enriched 170Yb2O3 thin targets for studying asymmetric fission in sub-lead mass region

Owing to the highly oxidizing and chemically active nature of rare-earth elements, preparation of isotopically enriched thin targets of rare-earth metals has been a challenging task. The successful fabrication of thin films of enriched 170Yb2O3 on carbon backing with areal density in the range 160–200 μg/cm2 and approximately 22μg/cm2, respectively is described here along with the various challenges encountered during the fabrication and new optimized operational parameters. On account of limited availability and high cost of the enriched 170Yb due to its extremely low natural abundance, many iterations were attempted with natural ytterbium to optimize the evaporation setup and its associated parameters. The electron beam physical vapour deposition technique in ultra-high vacuum facility was found suitable for the evaporation and a specially designed cylindrical tantalum crucible was used to further improve the collection efficiency. Optimization trials were carried out with the deposition parameters reported in the literature but a considerably high concentration of tantalum was noticed in the films. This impurity could drastically contaminate the experimental data and needed to be minimized. The present work reports a new set of deposition parameters optimized for the fabrication of thin ytterbium oxide films with the tantalum contamination reduced to indiscernible amounts. The final evaporation of enriched 170Yb2O3 was carried out with a 30 mg of the material that was found to be fully consumed. Various characterization techniques were carried out to ascertain thinness, purity and the elemental composition of the films viz. Rutherford Backscattering Spectroscopy (RBS) and Energy Dispersive X-ray Spectroscopy (EDS). These measurements corroborated the achieved optimization of deposition parameters with negligible contribution of impurities in the films. The purity and stability of the films were further established with a good quality of data obtained after irradiation with 28Si beam.

Determination of ultrahigh molar mass of polyelectrolytes by Taylor dispersion analysis

Taylor dispersion analysis (TDA) was successfully applied to obtain broadly distributed, ultrahigh molar masses of industrial anionic polyacrylamides (IPAMs) up to 25×106g/mol, far beyond the limits of Size Exclusion Chromatography (SEC) (about 7.3×106g/mol for anionic polyacrylamides standards (APAM)). Two protocols of TDA differing in capillary surface and rinsing procedure were employed: (i) bare fused silica capillaries under intensive between-run rinsing with 1M NaOH, and (ii) fused silica capillaries coated with polyelectrolyte multilayers composed of polydiallyldimethylammonium chloride polycation and sodium polystyrenesulfonate polyanion under simple rinsing with background electrolyte. Both cases led to similar results and in agreement with those obtained by static light scattering, the rinsing capillary step being much shorter in the second case (8min instead of 30min). The data processing of the obtained taylorgrams was realized using multiple-Gaussian fitting of the overall taylorgrams, by separating the contribution of low molar mass impurities from the polymeric profiles, and by determining the mean hydrodynamic radii and diffusion coefficients of the polymers. The molar masses of ultra-high molar mass industrial anionic polyacrylamides (IPAM) were derived from the hydrodynamic radii according to logRh versus logMw linear correlation established with APAM standards. Compared to capillary gel electrophoresis for which the size separation was only feasible up to Mw ∼ 10×106g/mol due to field induced polymer aggregation, TDA largely extended the range of accessible molar mass with easy-to-run and time saving assays.

Nonlinear Thermopower Behaviour of N-Type Carbon Nanofibres and Their Melt Mixed Polypropylene Composites.

The temperature dependent electrical conductivity σ (T) and thermopower (Seebeck coefficient) S (T) from 303.15 K (30 °C) to 373.15 K (100 °C) of an as-received commercial n-type vapour grown carbon nanofibre (CNF) powder and its melt-mixed polypropylene (PP) composite with 5 wt.% of CNFs have been analysed. At 30 °C, the σ and S of the CNF powder are ~136 S m−1 and −5.1 μV K−1, respectively, whereas its PP/CNF composite showed lower conductivities and less negative S-values of ~15 S m−1 and −3.4 μV K−1, respectively. The σ (T) of both samples presents a dσ/dT < 0 character described by the 3D variable range hopping (VRH) model. In contrast, their S (T) shows a dS/dT > 0 character, also observed in some doped multiwall carbon nanotube (MWCNT) mats with nonlinear thermopower behaviour, and explained here from the contribution of impurities in the CNF structure such as oxygen and sulphur, which cause sharply varying and localized states at approximately 0.09 eV above their Fermi energy level (EF).

Спонтанный спиновый магнетизм донорных электронов проводимости гибридизированных состояний кристалла, образованных системой примесных атомов 3d-элементов низкой концентрации (&amp;lt;1 at.&amp;#37;)

The given work is devoted to the experimental proof of existing the spontaneous spin polarization of the donor electron system of 3d-transition element impurity atoms of low concentration (&lt;1 at.%) in a mercury selenide crystal. For this purpose there have been measured the dependences of the magnetization on the magnetic field strength. As a result of the analysis of the obtained dependences, there were extracted the impurity contributions, which are described by the magnetization curves typical of the ferromagnets, and by the magnetic parameters conforming to the spontaneous magnetism of the systems under study, which are unambiguously related to the donor conduction electrons of the outer d-shells of impurity atoms. By its nature, according to the developed theoretical concepts, the spontaneous spin polarization manifests itself in exchange interaction, taking place in hybridizing the electronic states of the impurity atom and the conduction band ones of the crystal.

Spontaneous spin magnetism of donor conduction electrons of hybridized states of a crystal formed by a system of 3d-elements impurity atoms of low concentration (&lt;1 at.%)

The given work is devoted to the experimental proof of existing the spontaneous spin polarization of the donor electron system of 3d-transition element impurity atoms of low concentration (&lt;1 at.%) in a mercury selenide crystal. For this purpose there have been measured the dependences of the magnetization on the magnetic field strength at low temperatures (T=5 K). As a result of the analysis of the obtained dependences, there were extracted the impurity contributions, which are described by the magnetization curves typical of the ferromagnets, and by the magnetic parameters conforming to the spontaneous magnetism of the systems under study, which are unambiguously related to the donor conduction electrons of the outer d-shells of impurity atoms. By its nature, according to the developed theoretical concepts, the spontaneous spin polarization manifests itself in exchange interaction, taking place in hybridizing the electronic states of the impurity atom and the conduction band ones of the crystal. Keywords: 3d-impurities of the low concentration, gapless semiconductors, hybridized electronic states, spontaneous spin polarization, low-temperature ferromagnetism

Collisional-radiative non-equilibrium impurity treatment for JOREK simulations

A collisional-radiative non-equilibrium impurity treatment for JOREK 3D nonlinear magneto-hydrodynamic (MHD) simulations has been developed. The impurities are represented by marker-particles flowing along the fluid velocity field lines, while ionizing and recombining independently according to ADAS data and local fluid density and temperature. The non-equilibrium impurity contributions are then projected back to the fluid field for self-consistent time evolution. A 2D test case is used to compare the new non-equilibrium impurity model against previous coronal equilibrium (CE) impurity treatment, as well as to compare the non-equilibrium impurity behavior between the single and the two temperature model. Further, we conduct benchmark with previously published coronal non-equilibrium results by other 3D nonlinear MHD codes such as M3D-C1 and NIMROD. The new non-equilibrium treatment is shown to successfully capture the early phase cooling by weakly ionized impurities which the CE model missed. The benchmarks with M3D-C1 and NIMROD show general agreement in both the integrated quantities and the 2D profile evolution, despite the difference in the atomic model used. The above comparison and benchmark cases demonstrate the capability of the non-equilibrium impurity model for JOREK, paving the way for more sophisticated 3D non-linear massive material injection simulations which have important applications in disruption mitigation studies.

Metallic Impurities in Pharmaceuticals: An Overview

Backgroun:Metallic impurities are the traces of metals that can be found in finished drug products. Description:These metallic impurities in pharmaceutical preparations can enter from formulation ingredients, catalysts, and process equipment, containers and closures. They are not completely removed from the product by practical manufacturing techniques and should be evaluated relative to safetybased limits. They can affect drug efficacy or produce direct toxic effect on the patient. Methods:In this paper, an attempt has been made to review these metallic impurities including potential sources and analytical procedures to quantify these impurities. ICH guideline on these impurities and measures to control impurities has also been discussed in the paper. Results:The implementation of ICH Q3D guideline with the quality risk assessment approach is an important milestone to harmonize control of elements worldwide. Conclusion:This approach allows manufacturers to provide vital information about the contribution of impurities in the drug product.

Regulation of absorption coefficients between multi-photon and free-carrier in PbTe films by deposition temperature

We investigate the effects of deposition temperature on a crystal structure and electrical and optical properties of PbTe thin films sputtered on BaF2 (111). We observe that with the increase in deposition temperature, the grain size increases, and when it reaches 300 °C, the grain size reaches the maximum, and the preferred orientation begins to change. At 400 °C, the lattice mismatch rate decreases from 4.2% to 3.6% due to lattice contraction caused by reevaporation, and the conduction type changes from p-type dominated by a mismatch strain defect to n-type dominated by a Te vacancy. These changes lead to the interplay of various absorption mechanisms. We find that, in addition to the overall absorption coefficient curve significantly changing with deposition temperature, more importantly, the contribution of various internal absorption mechanisms to the below bandgap absorption spectrum does no longer synchronize. Instead, the contribution of an acoustic phonon to free-carrier absorption (FCA) decreases, while the relative contribution of optical phonon, impurity, two-photon absorption (2PA), and three-photon absorption (3PA) increases. This regulation effect reaches its maximum at 300 °C, which of various absorption mechanisms at 300 °C are 6.3, 11.6, 4.4, and 14.7 times higher than that at 20 °C corresponding to an optical phonon, impurity, 2PA, and 3PA processes, respectively. These results indicate that it should be possible to regulate the FCA, 2PA, and 3PA processes by changing the deposition temperature, thus making them suitable for applications in optoelectronic devices.

Gapped magnetic ground state in quantum spin liquid candidate κ-(BEDT-TTF)2Cu2(CN)3.

Geometrical frustration, quantum entanglement, and disorder may prevent long-range ordering of localized spins with strong exchange interactions, resulting in an exotic state of matter. κ-(BEDT-TTF)2Cu2(CN)3 is considered the prime candidate for this elusive quantum spin liquid state, but its ground-state properties remain puzzling. We present a multifrequency electron spin resonance (ESR) study down to millikelvin temperatures, revealing a rapid drop of the spin susceptibility at 6 kelvin. This opening of a spin gap, accompanied by structural modifications, is consistent with the formation of a valence bond solid ground state. We identify an impurity contribution to the ESR response that becomes dominant when the intrinsic spins form singlets. Probing the electrons directly manifests the pivotal role of defects for the low-energy properties of quantum spin systems without magnetic order.

Calculations for the nuclear reaction cross-sections via α-particle induced reactions on 65Cu to produce impurity free 67Ga for medical applications

Diagnostics field is facilitated with advancements enacted in anatomic imaging (cross-sectional modalities). Radionuclide scans (imaging) escorted by 67Ga are extensively beneficial in bone scintigraphy and recognition of prosthetic joint failure. Present work comprises the data concerning 67Ga production via α-particle induced nuclear reactions, TTY (thick target yield) and impurity analysis. Experimental measurements regarding 67Ga production are analyzed through a comparative study performed with calculations of theoretical model codes (TALYS-1.95, EMPIRE-3.2.3 and ALICE-IPPE). A data set of recommended cross-sections was generated and utilized to deduce TTY. The contribution of radionuclidic impurities is canvassed to suggest an energy region to produce impurity free 67Ga for medical applications.

Effect of deviation from stoichiometry on transport and mechanical properties of Bi2Se3 polycrystals

The dependences of electrical conductivity, the Hall coefficient, the Seebeck coefficient, thermoelectric power factor and microhardness of Bi2Se3 polycrystals on the degree of deviation from stoichiometry 59.9–60.0 at. % Se and temperature (77–300 K) were obtained. The samples exhibited n-type conductivity in the studied ranges of compositions and temperatures. The boundaries of the Bi2Se3 homogeneity region were estimated. A non-monotonic behavior of the concentration dependences of the properties in the studied composition range, associated with a change in the phase composition and defect structure under the deviation from stoichiometry, was observed. The calculation of the power coefficient in the temperature dependence of electron mobility showed that in a stoichiometric Bi2Se3, electrons are predominantly scattered by acoustic phonons, and under the deviation from stoichiometry the contribution of impurity scattering increases. Based on the experimental data, the Fermi energy EF was calculated in the approximation of the relaxation time and within the framework of the single-band model with a quadratic dispersion law. The obtained values of EF showed that both in stoichiometric and non- stoichiometric Bi2Se3, the conduction is mainly due to electrons in the lower conduction subband.

Magnetic impurity in a triple-component semimetal

We investigate the effects of a magnetic impurity in a multiband touching fermion system, specifically, a triple-component semimetal with a flat band, which can be realized in a family of transition metal silicides (CoSi family). When the chemical potential coincides with the flat band, it is expected that the impurity response of this system will be very different from that of an ordinary Dirac or Weyl semimetal of which the density of states at the Fermi level vanishes. We first determine the phase diagram within the mean-field approximation. Then, we study the local moment regime by employing two different methods. In the low temperature regime, the Kondo screening is analyzed by the variational wavefunction approach and the impurity contributions to the magnetic susceptibility and heat capacity are obtained, while at higher temperature, we use the equation of motion approach to calculate the occupation number of the impurity site and the impurity magnetic susceptibility. The results are compared and contrasted with those in the usual Fermi liquid and the Dirac/Weyl semimetals.