Superconducting properties of iron chalcogenide thin films

Abstract

Iron chalcogenides, binary FeSe, FeTe and ternary FeTe_xSe_1?x, FeTe_xS_1?x and FeTe:O_x, are the simplest compounds amongst the recently discovered iron-based superconductors. Thin films of iron chalcogenides present many attractive features that are covered in this review, such as: (i) easy fabrication and epitaxial growth on common single-crystal substrates; (ii) strong enhancement of superconducting transition temperature with respect to the bulk parent compounds (in FeTe_0.5Se_0.5, zero-resistance transition temperature T_c0^bulk = 13.5 K, but T_c0^film = 19 K on LaAlO₃ substrate); (iii) high critical current density (J_c ～ 0.5 ×10⁶ A cm² at 4.2 K and 0 T for FeTe_0.5Se_0.5 film deposited on CaF₂, and similar values on flexible metallic substrates (Hastelloy tapes buffered by ion-beam assisted deposition) with a weak dependence on magnetic field; (iv) high upper critical field (～50 T for FeTe_0.5Se_0.5, B_c2(0), with a low anisotropy, γ ～ 2). These highlights explain why thin films of iron chalcogenides have been widely studied in recent years and are considered as promising materials for applications requiring high magnetic fields (20–50 T) and low temperatures (2–10 K).     

Effect of cathodic hydrogen-charging current density on the hydrogen diffusivity in nanostructured bainitic steels

ABSTRACT

The effect of cathodic hydrogen-charging current on the effective hydrogen diffusivity in nanostructured bainitic steels produced at transformation temperatures 200°C (BS200) and 350°C (BS350) was investigated and compared to that of mild steel. The effective hydrogen diffusivity at 10?mA?cm^?2 was the lowest for BS200, followed by BS350 and mild steel, due to the finer microstructure and higher dislocation density in the bainitic ferrite of BS200. Increase in the hydrogen-charging current density, i.e. 20 and 30?mA?cm^?2, increased the effective hydrogen diffusivity of mild steel by 37 and 135%, and BS350 by 49 and 150%, respectively. For BS200, the increase was not significant (2%) at 20?mA?cm^?2, but increased by 34% at 30?mA?cm^?2.

This paper is part of a thematic issue on Hydrogen in Metallic Alloys     

Improvement of thickness and uniformity of isotopically enriched C targets on backings by the HIVIPP method

We have made enriched ¹²C targets to accurately measure the cross-section of the ¹²C(α,γ)¹⁶O reaction, which is very important in nuclear astrophysics. Isotopically enriched ¹²C targets for studying this small cross-section, especially for use with an intense pulsed α beam was desired to meet the following requirements: (1) use of impurity-free enriched ¹²C, (2) stability for a long time measurement and (3) uniform thickness in the range 200–300 μg/cm². To meet these experimental requirements, isotopically enriched amorphous ¹²C powder was converted into graphite powder in an electric furnace at a temperature of 3000 K and subsequently the graphite powder was deposited on a thick Au backing via the HIVIPP method. Targets thus prepared could be made thicker than 200 μg/cm². They had a good uniformity and a very high stability against irradiation with high intensity ion beams.     

Transport properties of Nd1.85Ce0.15 δ single crystals: The narrow-band model

The anisotropy of the resistivity and thermoelectric power (TEP)S of Nd_1.85Ce_0.15CuO_4?δ single crystal (T _c =17 K) has been investigated. In the temperature rangeT _c <T<300 K the ratioρ _c/ρ_ab≈10⁴ and the dependencesρ _ab (T) andρ _c (T) change from quadratic to linear atT～200 K. The dependencesS _ab (T) andS _c (T) reach a maximum atT>T _c and then decrease almost linearly with increasing temperature, changing sign from positive to negative nearT～ 150 K. The features of the resistivity and TEP temperature dependences (the lawρ∝T ² changing toρ∝T, the change in the sign of S with temperature, and the low TEP anisotropy at largeρ anisotropy) have been interpreted in the framework of the narrow-band model.     

Super short-range magnetic orderings in a multiferroic relaxor ceramic 0.41Bi(Ni1/2Zr1/2)O3–0.59PbTiO3

Here, we report a multiferroic relaxor material 0.41Bi(Ni_1/2Zr_1/2)O₃–0.59PbTiO₃, which exhibits a large piezoelectric coefficient (d₃₃, 391 pC/N), high remnant polarization (P_r, 52.3 μC/cm²) and a high electrical freezing temperature (T_f, 498 K). The electric-field-induced transition from a cubic-like phase to a tetragonal phase was confirmed by the XRD patterns and first-cycle bipolar electrostrain loop. The magnetization and magnetic field relationship changes from nonlinear to linear when cooled from 300 to 2 K. The unusual trend in magnetic behavior could be interpreted as the transitions between the super short-range orderings. Furthermore, the maximum value of magnetization shows a 14% decrease at 300 K after electrical poling.

Graphical abstract

     

Infrared laser (λ=3.2 μm) based on broken-gap type II heterojunctions with improved temperature characteristics

Laser structures based on broken-gap type II p-GaInAsSb/n-InGaAsSb heterojunctions in the active region are proposed and studied. Lasing at 3.2–3.4 μm has been obtained in the temperature range 77–195 K with a threshold current density of 400 A/cm² at 77 K and a characteristic temperature T₀=47 K. Pis’ma Zh. Tekh. Fiz. 23, 55–60 (February 26, 1997)     

Superconductivity in transparent zinc-doped In2O3 films having low carrier density

Abstract

Thin polycrystalline zinc-doped indium oxide (In₂O₃–ZnO) films were prepared by post-annealing amorphous films with various weight concentrations x of ZnO in the range 0x 0.06. We have studied the dependences of the resistivity ρ and Hall coefficient on temperature T and magnetic field H in the range 0.5T 300 K, H6 Tfor 350 nm films annealed in air. Films with 0x0.03 show the superconducting resistive transition. The transition temperature T_c is below 3.3 K and the carrier density n is about 10²⁵–10²⁶ m^?3. The annealed In₂O₃–ZnO films were examined by transmission electron microscopy and x-ray diffraction analysis revealing that the crystallinity of the films depends on the annealing time. We studied the upper critical magnetic field H_c2 (T) for the film with x = 0.01. From the slope of dH_c2 /dT, we obtain the coherence length ξ (0) ≈ 10 nm at T = 0 K and a coefficient of electronic heat capacity that is small compared with those of other oxide materials.     

Combined effect of substrate temperature and laser energy density on laser ablated BiFeO3 thin films

Bismuth ferrite (BiFeO₃) thin films were prepared on Pt(111)/Ti/SiO₂/Si substrates by laser ablation deposition at various substrate temperature (T _sub) and laser energy density (D _L). The combined effect of T _sub and D _L on crystalline phase, preferential orientation and surface morphology of the films were investigated. The microstructure and morphology of the films showed a strong dependence on T _sub and D _L simultaneously. BiFeO₃ thin films with single phase could be prepared at T _sub-D _L of 893 K?1 J/cm², 943 K?2 J/cm² and 963 K?3 J/cm², respectively. Film deposited at T _sub = 963 K and D _L = 3 J/cm² exhibited better ferroelectric property due to the combination of high (111) preferential orientation, dense surface morphology and less Fe²⁺ content.     

Investigation of electrons localized above solid hydrogen by means of the cyclotron resonance method

The magnetoresistance and cyclotron resonance of a two-dimensional sheet of electrons localized above liquid and solid hydrogen surfaces are investigated at the frequency of 20 GHz. It is found that the effective electron mass relevant to the motion along the surface is close to the free electron mass. The electron mean free path is determined by collisions with defects of the solid hydrogen surface. For 5?T?12 K the electron mobility was ～8×10⁴/T cm²/V sec, with 20% accuracy, for all the specimens investigated. ForT?5 K the mobility follows the law \(\mu \propto 1/\sqrt {{\text{W}}_{\text{e}} } \) , wherew _e is the mean electron energy. The numerical values of the electron mobilities for different specimens differ by factors up to five, and forT?1 K they fall within within the range 2×10⁴ to 10⁵ cm²/V sec. The experimental results indicate that the solid hydrogen surface has a terrace structure with flat sections about 10^?5 cm in size. During the investigation of electrons localized above a saturated helium film wetting the solid hydrogen, we observed a shift of the resonance to weaker magnetic fields, which amounts to ～100% at a pressing field of ～10³ V/cm. It is shown that this shift can be explained by the terrace structure of the substrate.     

Investigation of Electric Discharge in Gas of Superhigh Density with Preliminary Adiabatic Compression

A powerful electric discharge in high-density hydrogen is investigated in a two-stage facility. The initial experimental conditions are as follows: the energy stored in a capacitive storage, 140–300 kJ; the discharge current, 90–220 kA; the current rise rate dI/dt 10⁸ A/s; the charging voltage, 4.0–6.0 kV. The maximal concentration of hydrogen molecules n, achieved after adiabatic compression of gas (immediately before the discharge), is 3.3 × 10²² cm^–3. The electrical parameters of the discharge and the gas pressure are measured in the experiments. The temperature, the concentration of charged particles, and the discharge channel radius are calculated using the results of these measurements. The estimates reveal that, under the given initial conditions, the arc channel temperature is (1.3–1.8) × 10⁵ K, the concentration of charged particles is (0.7–1.2) × 10²⁰ cm^–3, and the channel radius is 0.14–0.20 cm.     

Anomalous temperature dependence ofD andT 2 for dilute solutions of3He in solid4He

Results of measurements of the spin diffusion coefficientD and NMR relaxation timesT ₁,T ₂, and T_1p are presented for a range of fractional³He concentrations 1 × 10^–4x ₃2.5 × 10^–3 in solid⁴He at molar volumes 19.85V _m21.0 cm³ and temperatures 0.4<T<2 K in both hcp and bcc phases. We observe a minimumD(T) atx ₃=5×10^–4, which is interpreted in terms of a transition from coherent impuriton motion to thermally activated diffusion. ForT<0.8 K, (lnD)/(lnV _m)=60±8. TheT ₂ measurements show a minimum as a function of temperature forx ₃10^–3. TheT ₂ (T) andT ₁ (T) results yield values for activation energy and tunneling frequency of vacancies in these dilute solutions. Forx ₃=5×10^–4 andT 0.5 K,T ₂ (V _m) is anomalous.T ₁ measurements at the same concentration indicate there is an important contribution to the spectral density of dipole field fluctuations in the kHz region.Financial support provided for apparatus, materials, and a research studentship (ARA) by the Science Research Council.     

Adsorption of nitrogen,argon, and neon on sintered copper and of neon on argon-coated sintered copper at low temperatures

The results of measurements of adsorption isotherms are given for nitrogen, argon, and neon on bare sintered copper and on sintered copper covered with a monolayer of argon. The temperatures employed where 77.3 K for the N₂ and argon, and 17.26, 20.22, 22.64, 25.71, and 27.00 K for the neon, and the pressure range was from 0.25 to 200 Torr. The sintered copper specimen was of mass 170 g, made with powder (Alcan Metal Powders, Inc., Druid Copper, grade MD60), which had an average particle size of 2 × 2 × 0.5 µ. The sintering was done at 650°C for 0.5 h. The bare surface area in m²/g, of the sintered copper specimen was found from the N₂ adsorption isotherms at 77.3 K. This gave =0.41 m²/g, based on a molecular area of N₂ of 13.8 Ų (solid N₂). The N₂ and argon isotherms on the bare sintered copper at 77.3 K yielded values of the monolayer coverage ofV _m =0.11 cm³(STP)/g for N₂ andV _m =0.11 cm³(STP)/g for argon. The neon results showed that at any given pressure and temperature the mass of neon adsorbed was less when the adsorption was on argon-coated copper than on bare copper. Calculations were made of the isosteric heat of adsorptionQ _st for neon, and the results are presented graphically as functions of the coverage. For neon adsorption on the bare copper,Q _st /R had a maximum value of about 390 K at a coverage of about 0.2 cm³(STP)/m², and it decreased to about 275 K at 0.5 cm³(STP)/m². For neon on the argon-coated copper,Q _st /R had a maximum value of about 320 K- at the lowest coverages and fell to about 245 K at 0.5 cm³(STP)/m². The shape of theQ _st /R curve vs. coverage for neon indicated that the argoncoated copper was more homogeneous from an adsorptive point of view than the bare copper. TheQ _st /R vs. coverage curves allowed an assessment to be made of the monolayer coveragesV _m , which were 0.38 cm³(STP)/m² for neon on the bare sintered copper and 0.34 cm ³ (STP)/m ² on the argon monolayer coated on the sintered copper. This indicated that the effective area for adsorption on the argon monolayer was 0.37 m ² /g, which was 10% less than that for the bare copper. In addition, theQ _st /R values at monolayer coverage were found to be 306 K on the bare copper and 275 K on the argon monolayer.Work supported by a contract with the Department of Defense (Themis Program) and with the Office of Naval Research and by a grant from the National Science Foundation.     

Effect of K substitution on Structural,Electrical and Magnetic Properties of Bi-2212 system

In this work, the effect of K in the Bi₂Sr₂Ca_1?xK_xCu₂O_8+y superconductor with x = 0.0, 0.05, 0.075, and 0.1, has been investigated. The samples were prepared by a polymer solution technique using polyethyleneimine, PEI. The effects of K substitution have been investigated by electrical resistivity (ρ?T), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, and magnetic characterizations. SEM and XRD results have shown that the Bi-(2212) phase is the major one independently of the K concentration. Moreover, the microstructure of samples is improved with K-concentration up to x = 0.075. From electrical resistivity measurements we have found that Tc is slightly higher than 91 K for K-concentrations up to 0.075, and then it decreases for higher doping for about 0.5 K. Moreover, this trend is maintained in the magnetic measurements in which the hysteresis loops are increased until 0.075 K-concentrations. The maximum calculated Jc, using Bean’s model, has been found at around 4.5 10⁶ A/cm² at 10 K and ~1,000 Oe for the 0.05 K doped samples.     

Supersolidity and the Thermodynamics of Solid Helium

The specific heat of solid helium in the temperature range below about 1.2 K has been found to contain a term varying as T ⁷, in addition to the usual T ³ contribution always found in a crystalline dielectric solid. It has been proposed by Anderson, Brinkman and Huse, (Science 310, 1164 (2005)) that the existence of this T ⁷ term supports their theory of supersolidity. However, in this paper we show that corrections to the phonon specific heat arising from phonon dispersion are much larger than expected based on simple order of magnitude estimates and, as a consequence, it is very unlikely that the existence of this T ⁷ term can be considered as evidence for supersolidity.      

Effect of microporation on passive and iontophoretic delivery of diclofenac sodium

Abstract

Skin pretreatment with a microneedle roller (microporation (MP)) appears a simple and inexpensive technique to increase transdermal delivery of topically applied drug products. This study investigates the effect of MP on the passive and iontophoretic delivery of diclofenac (DCF) by quantifying dermis and plasma levels of DCF in a rabbit model. New Zealand albino female rabbits received either: (i) a topical application of 4?g of Voltaren® 1% gel with or without pretreatment with a microroller (0.5?mm needle length; density 23 microneedles per cm² area) or (ii) a DCF solution (40?mg/2.5?mL) via iontophoresis (IOMED transQ^E medium size patch), with or without microroller pretreatment. A 300?µA/cm² cathodic current was applied for 20?min for a total of 80 mA. DCF concentrations were monitored in dermis with microdialysis sampling every 20?min for 5?h. Plasma samples were collected over the same period. In the passive delivery studies, microroller pretreatment increased C_max by 1.5- and 2.0-fold in skin and plasma, respectively, and AUC by 1.5- and 2.4-fold in skin and plasma, respectively. In the iontophoresis delivery studies, microporation increased C_max by 2.0-fold both in skin and in plasma, and AUC by 1.1- and 1.8-fold in skin and plasma, respectively. In conclusion, microneedle pretreatment increased significantly the systemic exposure of DCF from either passive or iontophoretic delivery, whereas the effect in skin was less pronounced.     

Intradermal and follicular delivery of adapalene liposomes

Abstract

Background: Adapalene is a widely used topical anti-acne drug; however, it has many side effects. Liposomal drug delivery can play a major role by targeting delivery to pilosebaceous units, reducing side effects and offering better patient compliance.

Objective: To prepare and evaluate adapalene-encapsulated liposomes for their physiochemical and skin permeation properties.

Methods: A liposomal formulation of adapalene was prepared by the film hydration method and characterized for shape, size, polydispersity index (PDI), encapsulation efficiency and thermal behavior by techniques such as Zetasizer®, differential scanning calorimetry and transmission electron microscopy. Stability of the liposomes was evaluated for three months at different storage conditions. In vitro skin permeation studies and confocal laser microscopy were performed to evaluate adapalene permeation in pig ear skin and hair follicles.

Results: The optimized process and formulation parameters resulted in homogeneous population of liposomes with a diameter of 86.66?±?3.5?nm in diameter and encapsulation efficiency of 97.01?±?1.84% w/w. In vitro permeation studies indicated liposomal formulation delivered more drug (6.72?±?0.83?μg/cm²) in hair follicles than gel (3.33?±?0.26?μg/cm²) and drug solution (1.62?±?0.054?μg/cm²). Drug concentration delivered to the skin layers was also enhanced compared to other two formulations. Confocal microscopy images confirmed drug penetration in the hair follicles when delivered using the liposomal formulation.

Conclusion: Adapalene was efficiently encapsulated in liposomes and led to enhanced delivery in hair follicles, the desired target site for acne.     

Hydriding kinetics of the La1.5Ni0.5Mg17–H system prepared by mechanical alloying

In the study of reaction kinetics between hydrogen and hydriding alloys, what is the most important is to obtain intrinsic kinetic data. The hydriding kinetics of 0.5 g La_1.5Ni_0.5Mg₁₇ sample in the two-phase (-) region was investigated as a function of temperature and pressure in the ranges 553–573 K and 0.256–0.992 MPa H₂ respectively. Mathematical analyses of the time-dependent hydrogen absorption curves indicate agreement with Jander diffusion model, [1 – (1 – )^1/3]² = k(T, P)t, which suggests that the rate-controlling step for hydrogen absorption is three-dimensional diffusion. An apparent activation energy for such diffusion process of 83 ± 1 kJ/mol H₂ has been obtained from the absorption data.     

Field-ion microscopy of deformation effects near the surface in ion-implanted metals (Ir)

Field-ion microscopy is used to determine the deformation due to ion implantation (E=20 keV, D=10¹⁸ ions/cm², j=300 μA/cm²) near the surface in pure iridium. The effect is manifested as a high density of various types of defects in the near-surface volume (∼50 nm from the irradiated surface) of the material. Pis’ma Zh. Tekh. Fiz. 25, 60–64 (March 26, 1999)     

Influence of working gas pressure on the properties of thin films of high-temperature superconductors obtained by magnetron sputtering

The surface morphology, composition, microstructure, and electrical properties of thin films of YBa₂Cu₃O_7−x high-temperature superconductors, obtained by inverted magnetron sputtering, have been studied as a function of the pressure of the working gas mixture and results are presented. The main parameters of the magnetron discharge plasma near the substrate were determined by analyzing the characteristics of Langmuir probes. Changes in the properties of the films are considered to be caused by bombardment of the growing film with plasma ions accelerated in the floating potential field of the substrate. Films obtained at a pressure of 28 Pa and substrate temperature of 630 °C had a superconducting transition end temperature T _c ,off=89 K and a critical current density j _c =2 MA/cm² (at 77 K) and were free from secondary phase particles larger than 10 nm. Pis’ma Zh. Tekh. Fiz. 24, 80–85 (February 26, 1998)     

High-pressure,high-temperature study of GeS2 and GeSe2

Phase transitions of the GeX₂ (X = S, Se) dichalcogenides have been studied at pressures of up to p ? 8 GPa and temperatures from 675 to 1375 K, and portions of their p-T phase diagrams have been constructed using our and previous experimental data. The crystal structure of the GeS₂-III phase has been refined by the Rietveld method (HgI₂ structure, P4₂/nmc, a = 3.46906(2) Å, c = 10.9745(1) Å, Z = 2, D _x = 3.438 g/cm³, R = 0.06). GeSe₂-III crystals have been grown for the first time at p ? 7 GPa in the temperature range 875–1275 K. The unit-cell parameters of GeSe₂-III (hex) are a = 6.468 ± 0.004 Å and c = 24.49 ± 0.10 Å (D _meas = 5.16 g/cm³, D _x = 5.18 g/cm³, Z = 12).