Minimum Resistivity Research Articles

Epitaxial growth and properties of Nb-doped anatase TiO2 films on LSAT by MOCVD

High quality single crystalline Nb-doped anatase phase TiO2 films with different Nb concentrations were deposited on LSAT (100) substrates by metal organic chemical vapor deposition (MOCVD) at 600 °C. The influences of Nb concentration on the structural, electrical and optical properties of the films have been investigated. The obtained films were single crystalline anatase TiO2 and the epitaxial relationship between the films and the substrates was confirmed as TiO2 (001) || LSAT (100) with TiO2 [010] || LSAT [010]. The resistivity of the films was reduced by almost 8 orders of magnitude after Nb doping and a minimum resistivity of 4.0 × 10−2Ω⋅cm was obtained in 0.6% Nb-doped samples. The films achieved a maximum mobility as high as 13.5 cm2⋅V−1⋅s−1. The carrier concentration was in a range of 9.4 × 1017–1.7 × 1019 cm−3. The optical transmittance of the films in the visible range exceeded 93% and the optical band gap was varied from 3.48 to 3.53 eV.

Enhanced electrical properties of ZnO transparent conducting films prepared by electron beam annealing

Abstract Pure ZnO precursor films were prepared by a sol-gel spin coating method. The films were directly annealed by the electron beam (EB) for 5 min. The structural, optical and electrical properties were investigated by means of SEM, AFM, XRD, UV–vis spectrophotometer and Hall-effect measurement. SEM and AFM studies revealed smooth, dense film microstructure with some holes. The average grain size ranged from 10 nm to 60 nm and the surface RMS roughness of the films is less than 3 nm. X-rays diffraction patterns showed (002) preferential growth in all annealed films. From optical transmittance spectra, the absorption edge of the films was determined to be at ∼380 nm with > 85% transmittance in visible region. ZnO film annealed with beam current 0.7 mA was found to exhibit minimum resistivity value of 1.57 × 10 −2 Ωcm and carrier concentration as high as 6.37 × 10 19 cm −3 , which is 2 ∼ 3 orders better than that of the typical pure ZnO thin films using sol-gel method.

Signatures of the Kondo effect in VSe2

VSe2 is a transition metal dichaclogenide which has a charge- density wave transition that has been well studied. We report on a low-temperature upturn in the resistivity and, at temperatures below this resistivity minimum, an unusual magnetoresistance which is negative at low fields and positive at higher fields, in single crystals of VSe2. The negative magnetoresistance has a parabolic dependence on the magnetic field and shows little angular dependence. The magnetoresistance at temperatures above the resistivity minimum is always positive. We interpret these results as signatures of the Kondo effect in VSe2. An upturn in the susceptibility indicates the presence of interlayer V ions which can provide the localized magnetic moments required for scattering the conduction electrons in the Kondo effect. The low-temperature behaviour of the heat capacity, including a high value of γ, along with a deviation from a Curie-Weiss law observed in the low-temperature magnetic susceptibility, are consistent with the presence of magnetic interactions between the paramagnetic interlayer V ions and a Kondo screening of these V moments.

Preparation of Aluminum doped Zinc Oxide Thin Films on Glass Substrate by Sparking Process and Their Optical and Electrical Properties

Aluminum doped Zinc Oxide (AZO) nanoparticle thin films were deposited on glass substrates by a double tip sparking process. The effect of Al doped ZnO on electrical and optical transmittance properties were studied. The doping ratios of Al into ZnO were 3, 5, 7, 13 and 22 %. SEM images indicated particle size decreased with increasing the Al content after annealing. Raman spectra results of AZO films associated with the hexagonal structure. AZO films have an average transmittance in visible region at 60 %. The energy gap increased with increasing Al content. The minimum resistivity was found at 5 % of Al doping for AZO film.

Comparative studies of the cage systems ThFe2Al10 and UFe2Al10

We have grown single crystals of ThFe2Al10 and used them for the refinement of its crystal structure. From the specific heat data, we determined the phonon components, that is, the Debye and Einstein modes, for Th- and U-based isostructural aluminides. To approximate the Sommerfeld coefficients, we had to include the T3lnT term characteristic of spin-fluctuations originating from the Fe-sublattice. The roughly estimated spin-fluctuation temperature is about 11 K. ThFe2Al10 is a weakly temperature-dependent Pauli-paramagnet. However, at lower temperatures the ferromagnetic correlations are observed, which signals that the system drives to quantum criticality. The distinct minimum in electrical resistivity observed at about 20 K suggests a realization of a nonmagnetic two-channel Kondo-effect in ThFe2Al10, as discussed for ThAsSe [Phys. Rev. Lett. 94, 236603 (2005)], for example. The [ρ(T) – ρmin] versus T curves of ThFe2Al10, determined along the a- and c-axes, were used to subtract the phonon contributions from the corresponding ρ(T)a,c of UFe2Al10. The resulting magnetic part of the average ρm(T)av curve was then analysed in terms of the influence of the crystal field effect on the transport properties. However, to obtain agreement with the experiment, we had to take into account another effect, namely the Kondo-like one. This kind of probe has been applied for the first time in the case of uranium compounds. Based on the magnetoresistivity, we have revealed the anisotropic low-frequency vibrations of the Th atom (located in its [Al16Fe4] cage) interacting with the conduction band, the phenomenon revealed previously in the metallic UB12 [Phil. Mag. B 95, 2343 (2015)]. Furthermore, fully relativistic band structure calculations performed for ThFe2Al10 revealed its metallic-like character with a similarly large contribution of the Fe 3d electrons at the Fermi level as predicted previously for its 5f-electron analogue UFe2Al10. In addition, there are substantial differences between their Fermi surfaces.

Influence of substrate temperature on structural, electrical, and optical properties of transparent conductive hydrogen and vanadium co-doped ZnO films fabricated by radiofrequency magnetron sputtering

In this study, we fabricate hydrogen and vanadium co-doped ZnO (HVZO) films using radio frequency magnetron sputtering from a ceramic target with various substrate temperatures (STs) at a fixed H2 flow rate. The results reveal that the HVZO films exhibit a (002) preferred orientation with the c-axis perpendicular to the substrate, and the morphology changes from small and loose grains to large blocks and then to small grains. A minimum resistivity of 1.15×10−3Ωcm, along with a high average transmittance greater than 80% at a wavelength of 400–1200nm, is obtained at an ST of 150°C. We apply theoretical calculations based on density functional theory to analyze the electronic structure and conduction mechanism. The configuration of HVZO-1, where the optical band gap is widening and the charge carrier predominantly originates from the orbits of V 3d, O 2p, and H 1s, is found to be the most stable.

Cryogenic Fab-on-a-Chip Sticks the Landing.

Using a microelectromechanical systems (MEMS)-based Fab-on-a-Chip, we quench-condense lead thin-films. Suppressing the formation of lead islands makes it possible to grow a homogeneous and continuous film as thin as 2 nm, without the use of an adhesion layer. Thermal cycling from 3 K to as low as 10 K reveals irreversible annealing of the thin-film characteristic of a metastable state. The transition to the stable state is smooth and is completed by cycling the temperature above ∼42 K, where a distinctive resistance minimum is observed. This resistive minimum is accompanied by an unexpected peak in the superconducting transition temperature. After further thermal cycling, the standard metallic/superconductive behavior is established. The MEMS-based approach yields a platform for systematic studies of quench-condensed thin-film materials, making an intriguing parameter space of mesoscopic physics experimentally accessible.

Boosting the photovoltaic performance of Zn2SnO4‐based dye‐sensitized solar cells by Si doping into Zn2SnO4

AbstractIn the present work, Zn2SnO4 nanoparticles were doped with silicon to improve their electrical and optical properties by the conventional solid‐state reaction method. The results showed that the minimum electrical resistivity of about 0.09 Ωcm was obtained for Zn2SnO4 nanoparticles with 3% Si doping. The decrease in the electrical resistivity can be attributed to the insertion of Si+4 atoms into the Zn+2 and/or Sn+4 sites and also the formation of more oxygen vacancies in the Zn2SnO4 lattice. The formation of the more oxygen vacancy defect states in Si‐doped Zn2SnO4 nanoparticles was verified by photoluminescence spectroscopy. The efficiency of a dye‐sensitized solar cell based on 3% Si‐doped Zn2SnO4 was significantly better, by about 81%, compared to that of a cell based on the undoped Zn2SnO4. The enhancement in the efficiency can be ascribed to the facilitation of electron transport throughout a photoelectrode due to increase in the charge carrier concentration which was caused by Si doping.

Enhancing Optical and Electrical Properties of La- and Al-Codoped ZnO Thin Films Prepared by Sol-Gel Method -La Codoping Effect

This work focuses on the fabrication and potential application of the various cation-doped ZnO materials in recent patents and literature and then presents the La codoping effects of Al-doped ZnO films. Films were deposited by a sol-gel route and characterized by various techniques including X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, UV-vis and luminescent spectroscopies, and electrical conduction analysis. The UV-vis. transmittance and band gap increased and then decreased, whereas the resistivity decreased and then slightly increased with the increase in La/Al ratio. The La/Al ratio of 0.0105 led to a maximal transmittance, a widest band gap, and a minimal resistivity. The films also illustrated a near band gap emission and some intrinsic defect-related emissions with varied intensity with La/Al ratio. This work reveal that the electrical and optical properties of the ZnO:Al films can be well enhanced by La codoping. This is significant to the applications of the ZnO:Al materials.

Large magnetoresistance in LaFeO3-substituted SrRuO3 epitaxial thin films

In this work, the magnetotransport properties of epitaxial Sr1-xLaxRu1-xFexO3 (x = 0.05, 0.10, 0.20, and 0.30) thin films grown by pulsed laser deposition on SrTiO3 (001) substrates were investigated. Compared to doping Fe into the Ru4+ site of SrRuO3, doping LaFeO3 into SrRuO3 resulted in an increase in the zero-field resistivity. A larger zero-field resistivity value in magnetic perovskite oxide is, in many cases, favorable for obtaining high magnetoresistance. The films (0.0 ≤ x ≤ 0.10) showed metallic behavior and ferromagnetic ordering, although the resistivity increased and the ferromagnetic transition temperature TC decreased with an increase in x. The thin film with x = 0.20 displayed a clear metal-to-insulator phase transition at low temperature and also displayed a well-defined resistivity minimum. This upturn in the resistivity curve is associated with the large electron-electron interaction present in the material. The magnetoresistance values increased as x increased, and we observed a large negative magnetoresistance (MR = −35%) for the thin film with x = 0.30. The observed high MR values are associated with spin fluctuation of the mobile electronic carriers in the material.

Organic Photovoltaics with Non-Stoichiometric InZnSnO Thin Film Cathodes

Non-stoichiometric indium zinc tin oxide (IZTO) thin films were deposited onto glass substrates at 400 °C by DC magnetron sputtering using non-stoichiometric (In0.5Zn0.25−xSn0.25+xO1.5 and In0.4Zn0.3−xSn0.3+xO1.5, where x = ±0.05) IZTO ceramic targets. After deposition, all of the films were given annealing treatment at 450 °C in argon. The crystallization behavior was examined by X-ray diffraction, while the optical properties were measured by ultraviolet-visible spectroscopy, in which the average transmittance values higher than 80% were observed from all films. The minimum resistivity of approximately 6.3 × 10−4 Ω·cm was observed from the Sn-rich In0.5Zn0.2Sn0.3O1.5 film. The resistivity values of Sn-rich IZTO thin films were a little smaller than those of Zn-rich IZTO films. An OPV cell with the so-called inverted structure was fabricated using various IZTO films deposited under optimized conditions as the cathode electrode. It was found that the solar cell efficiency could reach up to 7.9% which is the same with the OPV cell with conventional ITO film.

Anomalous Hall effect in ion-beam sputtered Co2FeAl full Heusler alloy thin films

Investigations of temperature dependent anomalous Hall effect and longitudinal resistivity in Co2FeAl (CFA) thin films grown on Si(100) at different substrate temperature Ts are reported. The scaling of the anomalous Hall conductivity (AHC) and the associated phenomenological mechanisms (intrinsic and extrinsic) are analyzed vis-à-vis influence of Ts. The intrinsic contribution to AHC is found to be dominating over the extrinsic one. The appearance of a resistivity minimum at low temperature necessitates the inclusion of quantum corrections on account of weak localization and electron-electron scattering effects whose strength reduces with increase in Ts. The study establishes that the optimization of Ts plays an important role in the improvement of atomic ordering which indicates the higher strength of spin-orbit coupling and leads to the dominant intrinsic contribution to AHC in these CFA full Heusler alloy thin films.

Characteristics and dispersity of a two gap capillary discharge applied for long spark gap ignition in air

In this paper, the characteristics and dispersity of a two gap capillary (TGC) discharge applied for long spark gap ignition are studied. Under the same discharge condition, 30 repetitive discharges are done to get a certain number of data samples. Accordingly, the change trend of the characteristics and the dispersity with the charging voltage of C1 are analyzed statistically. The delay of soft capillary discharge is determined by the saturation rate of the magnetic core of the pulse transformer and decreases with the increase in the charging voltage. The main discharge delay decreases from 1.0 kV to 2.0 kV and stops the decreasing trend when the charging voltage increases to 2.5 kV. In contrast, the current amplitude of soft capillary discharge and main discharge increases with charging voltage. Long tail extinction is witnessed at the charging voltage of 1.0 kV and the major cause is the insufficient pressure in the post discharge. The waveform of the capillary arc resistivity is U-like shape and the minimum resistivity decreases with the increase in the charging voltage. Meanwhile, the arc resistivity in the ascending stage is much higher than that in the descending stage with the same value of the discharge current. The energy consumption of the TGC discharge can be mainly divided into four parts and more than 70% of the energy is consumed in main discharge.

Effects of oxygen flow velocity on the sintering properties of ITO targets

Due to the considerable influence of oxygen flow on the resistivity and transmittance of ITO films, the study on the effects of oxygen flow velocity on the sintering properties of ITO targets has a positive role in promoting their use in large output industries. In the work, ITO targets of three sintering conditions were used to reveal the action mechanism of oxygen flow velocity on the phase and elemental composition, micro-morphology, density, mass loss ratio, oxide content, resistivity and elemental chemical states by XRD, BSE, EPMA, SEM, XRF and XPS et al. ITO target sintered under oxygen flow velocity of 10 L/min owns super high relative density of 99.83%, mass loss ratio of 1.417% and the minimum resistivity of 1.583 × 10−4 Ω·cm. It can conclude that the increase of oxygen flow velocity can increase the oxygen pressure within the sintering furnace, which can influence the mass transport mechanism throughout the whole sintering process, improve the density of ITO targets, and decrease the InO formation of the target interior as a result of maintaining the mass content ratio of indium to tin and decreasing the resistivity of ITO targets.

Carbon fabrics coated with nickel film through alkaline electroless plating technique

The nickel-coated carbon fabric with continuous and uniform coating was fabricated at 85°C by a simple electroless plating method. Sodium hypophosphite served as an environmental-friendly reducing agent. The carbon fabric substrate was pre-treated by cleaning, etching, sensitization, and activation processes. It was found that the reaction temperature and amount of reducing agent played important roles for the formation of perfect nickel coating. The carbon fabric covered with a compact and uniform nickel layer possessed the minimum volume resistivity of 5.50×10−3Ω·cm. Such composites can be used as flexible electrode materials, shielding materials and so forth.

Facile synthesis of high antistatic mica-titania@graphene composite pearlescent pigment at room temperature

A facile and rapid method is reported to effectively in synthesizing high performance graphene based mica-titania antistatic pearlescent pigment. Znic powder is firstly introduced to prepare the composite pearlescent pigment as a reduction catalyst. Through a comparative analysis with previous Argon annealing reduction method, it can obviously increase 100–4600 fold antistatic performance of mica-titania pearlescent pigment at room temperature in a short time. The minimum volume resistivity of as-prepared composite pigments is 12 kΩ cm and decreases about 104 times than that without graphene. The composite pearlescent pigment samples also remain the silver white pearlescent effect, as well as that of raw mica-titania pigment. The stability of titanium chemical state and reduced graphene oxide have been proved by Raman and X-ray photoelectron spectroscopy tests. Since the method is efficient, relatively environmental friendly and low cost, it could be expected to satisfy a large-area application of antistatic pearlescent pigment.

Magnetoresistance of Bi2Se3 Whiskers at Low Temperatures

Temperature dependencies of Bi2Se3 whiskers’ resistance with Pd doping concentration of 1´1019 cm-3 where measured in temperature range 4.2 - 300 K. At temperature 5.3 K a sharp drop in the whisker resistance was found. The observed effect is likely connected with contribution of two processes such as the electron localization in the whiskers and transition in superconducting state at temperature 5.3 K, which is likely result from Pd complexes.Transversemagnetoresistance in n-type Bi2Se3 whiskers with Pd doping concentration in the vicinity to themetal-insulator transition (MIT) from metal side of the transition were studied in magnetic field 0 -10 T. For the whiskers a resistance minimum was observed at temperature about 25 K that is connected with Kondo effect.

Fabrication of Conductive Copper Films on Flexible Polymer Substrates by Low-Temperature Sintering of Composite Cu Ink in Air.

The development of a thermal sintering method for Cu-based inks under an air atmosphere could greatly expand their application for printed electronics. However, it is well-known that Cu-based inks cannot produce conductive Cu films when sintered at low temperatures in air because Cu readily oxidizes under such conditions. In this study, we have successfully demonstrated air atmosphere sintering at low temperatures (less than 150 °C) via a simple hot plate heat treatment for producing conductive Cu films on flexible polymer substrates, using a novel Cu-based composite ink with sub-10 nm Cu nanoparticles protected with 1-amino-2-propanol with micrometer-sized Cu particles and submicrometer-sized Cu particles; oxalic acid was also added to prevent the oxidation of the Cu during sintering. The Cu films showed a minimum resistivity of 5.5 × 10-5 Ω·cm when sintered in air at 150 °C for a very short period of 10 s. To the best of our knowledge, this is the first report of sintering of Cu-based inks in air at less than 150 °C. Another novel property of the present Cu-based composite ink is the lowest reported resistivity at 80 °C under N2 flow (5.3 × 10-5 Ω·cm at 80 °C and 8.4 × 10-6 Ω·cm at 120 °C). This fast, efficient, and inexpensive technology for thermal sintering in ambient air using composite inks could be a commercially viable method for fabricating printed electronics on flexible substrates.

Thickness-Dependent Structural, Electrical, and Optical Properties of ZnS Thin Films Deposited by Thermal Evaporation

Zinc sulfide (ZnS) thin films are deposited onto an ultrasonically clean glass substrate, by using the thermal evaporation technique at room temperature. The film thickness was varied in the range from 400 nm to 1300 nm. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive analysis of X-rays (EDAX) are used to characterize the structural properties of films. The electrical and optical properties of films are characterized with a dc two-point probe, the Hall effect, and ultra-violet visible absorption spectra. The XRD spectra indicate that the thin films have polycrystalline nature and possess the cubic structure with (111) preferential orientation. The diffraction patterns are sharpen with increase in the film thickness. Scanning electron microscope data disclose that the films have nanograins approximately 97.89 nm in size. A reduction in the resistivity shows that the films are semiconductors in nature. For a film thickness of 1200 nm, the maximum mobility is 26.03 × 101 cm2/Vs, minimum resistivity is 0.08 × 106 (Ohm·cm), and band gap is 3.26 eV.  The film thickness has been optimized on the basis of the observed properties.

Electroless deposition of pure copper film on carbon fabric substrate using hydrazine as reducing agent

We report on a simple but efficient strategy for the fabrication of conductive copper/carbon fabric composites by electroless plating method. The carbon fabric was firstly treated by cleaning, etching, sensitization, and activation processes. Hydrazine hydrate served as a powerful reducing agent, and all deposition procedure was conducted in alkaline media. It was found that the dosage of sodium hydroxide and reaction time played important roles for the formation of copper coatings with high quality. The composite with continuous and compact copper film on the surface of carbon fabric possessed a minimum volume resistivity of 4.13 × 10−3 Ω cm, and such material would be expected to be used in electromagnetic interference shielding, wave absorbing, and electric sensors.