Minimum Resistivity Research Articles

Effects of electron irradiation during the growth of ITO films by an using RF sputtering system

We perform electron irradiation during the radio-frequency (RF) sputtering process to realize the growth of a transparent oxide thin film, indium tin oxide (ITO), to achieve a high transparency and a low resistivity. Using an electron gun attached to the sputtering system, we simultaneously accelerate a large number of electrons onto the substrate along with the sputtered ITO atoms by using a negative bias of up to 1.5 kV. As the electron-beam voltage increased, the preferred orientation of the ITO film changed from the (222) plane to the (400) plane, and the film showed a flake-type surface morphology. Sputtered ITO atoms in the electron-assisted sputtering (EAS) process showed sufficient mobility because of the kinetic effect of continuous electron irradiation without the need for an additional substrate heating process. The ITO films grown using the EAS process had a minimum resistivity value of 1.46×10−4 Ωcm under an electron irradiation condition of 1.5 kV and showed a transmittance of 95% at 550 nm.

Full range optical and electrical properties of Zn-doped SnO2 and oxide/metal/oxide multilayer thin films deposited on flexible PET substrate

As a potential replacement of indium-tin oxide (ITO), Zn-doped SnO2/Ag/Zn-doped SnO2 multilayer transparent conducting electrodes were prepared on the flexible poly ethylene terephthalate (PET) substrates by RF sputtering at room temperature. To find the optimized composition of Zn-doped SnO2 thin film, which will have higher conductivity and transmittance as compared to the undoped SnO2 thin film, an off-axis Continuous Composition Spread (CCS) sputtering method was used. Zn-doped SnO2 thin films have lower resistivity than undoped SnO2 thin films due to excess oxygen vacancies (Vo) and/or zin interstitials (Zni) in thin films. The minimum resistivity of thin film was 0.13 Ω cm at optimized 2.43 wt% Zn-doping. Zn-doped SnO2/Ag/Zn-doped SnO2 multilayer thin films were prepared using the optimized composition deposited by an on-axis RF sputter. The multilayer TCO film has the resistivity ∼5.33 × 10−5 Ω cm and the average transmittance >85% in the 550 nm wavelength region.

Optimization of hierarchical structure and nanoscale-enabled plasmonic refraction for window electrodes in photovoltaics.

An ideal network window electrode for photovoltaic applications should provide an optimal surface coverage, a uniform current density into and/or from a substrate, and a minimum of the overall resistance for a given shading ratio. Here we show that metallic networks with quasi-fractal structure provides a near-perfect practical realization of such an ideal electrode. We find that a leaf venation network, which possesses key characteristics of the optimal structure, indeed outperforms other networks. We further show that elements of hierarchal topology, rather than details of the branching geometry, are of primary importance in optimizing the networks, and demonstrate this experimentally on five model artificial hierarchical networks of varied levels of complexity. In addition to these structural effects, networks containing nanowires are shown to acquire transparency exceeding the geometric constraint due to the plasmonic refraction.

Resistivity minimum in granular composites and thin metallic films

We analyze the temperature dependence of conductivity in thick granular ferromagnetic compounds NiSiO2 and in thin weakly coupled films of Fe, Ni and Py in vicinity of metal-insulator transition. Development of resistivity minimum followed by a logarithmic variation of conductivity at lower temperatures is attributed to granular structure of compounds and thin films fabricated by conventional deposition techniques. Resistivity minimum is identified as a transition between temperature dependent intra-granular metallic conductance and thermally activated inter-granular tunneling.

Effect of the carbon nanotube size dispersity on the electrical properties and pressure sensing of the polymer composites

Two different-diameter carbon nanotubes (CNTs), i.e., CNT-1 (diameter = 10–30 nm, length = 5–15 μm) and CNT-2 (diameter = 20–40 nm, length = 5–15 μm), were mixed in various relative concentrations to obtain series of hybrids with wider diameter disparity, which were subsequently melt blended with a polypropylene-based thermoplastic elastomer to fabricate their respective polymer composites. By changing the relative concentrations of CNTs in a polydisperse mixture, we were able to tune the percolation characteristics and the pressure–resistance sensitivity of the polymer composites. Percolation threshold, percolation window, and the minimum achievable resistivity value of the composites were found to be the function of relative concentration of CNTs in the polydisperse system. An important finding of this study is that percolation characteristics of composites with polydisperse system of CNTs prepared by mixing of two different CNTs with different relative concentrations can be explained by model of hybrid fillers. These findings may open a new pathway to design the conductive polymer composites with controlled electrical and sensing properties for various applications.

Influence of vacuum and Ar/CdS atmospheres-rapid thermal annealing (RTA) on the properties of Cd2SnO4 thin films obtained by sol-gel technique

Transparent conducting oxides are electrical conductive materials with low absorption of light. In recent years, considerable attention has been paid to ternary oxides such as CdIn2O4, Zn2SnO4, ZnGa2O4, and Cd2SnO4. In present work, Cd2SnO4 thin films were deposited via dip-coating; dipping solution was synthesized by sol-gel technique from the mixture of CdO and SnO2 precursor solutions. The films were obtained with 7 layers (~260nm) on Corning glass substrates. Each coating was deposited at a withdrawal speed of 2cm/min, dried at 100°C for 1h, and then sintered at 550°C for 1h in air. The films were subjected to rapid thermal annealing (RTA) treatments at an annealing temperature of 600°C for 5s, under two different atmospheres: vacuum and Ar/CdS (varying Ar pressure inside the chamber from 50 to 200Torr). X-Ray diffraction patterns showed that all the annealed films were constituted mainly by Cd2SnO4 crystals with a very low presence of CdSnO3. All the films showed a high optical transmittance (above 80%) in the UV–Vis region. A slight decrease of transmittance occurs in the near infrared region for RTA films, but it is not as pronounced as the one observed when these films are treated using conventional annealing. The minimum resistivity value obtained was 2.87×10−3Ωcm (1.1×102Ω/□) corresponding to RTA films in vacuum. Electrical and optical properties of the films analyzed in present study make them attractive as electrodes for solar cells, with the advantage of requiring very short annealing times.

Synergistic effects of Mo and F doping on the quality factor of ZnO thin films prepared by a fully automated home-made nebulizer spray technique

Transparent conducting oxide films of undoped, Mo doped, Mo+F co-doped ZnO were deposited using a facile homemade nebulizer spray pyrolysis technique. The effects of Mo and F doping on the structural, optical, electrical and surface morphological properties were investigated using XRD, UV-vis-NIR spectroscopy, I–V and Hall probe techniques, FESEM and AFM, and XPS, respectively. The XRD analysis confirms that all the films are well crystallized with hexagonal wurtzite structure. All the synthesized samples exhibit high transmittance (above 85%) in the visible region. The current-voltage (I–V) characteristics show the ohmic conduction nature of the films. The Hall probe measurements show that the synergistic effects of Mo and F doping cause desirable improvements in the quality factor of the ZnO films. A minimum resistivity of 5.12×10−3Ωcm with remarkably higher values of mobility and carrier concentration is achieved for Mo (2 at.%)+F (15 at.%) co-doped ZnO films. A considerable variation in the intensity of deep level emission caused by Mo and F doping is observed in the photoluminescence (PL) studies. The presence of the constituent elements in the samples is confirmed by XPS analysis.

Fabrication of 10 µm-scale conductive Cu patterns by selective laser sintering of Cu complex ink

A Cu complex ink was synthesized using copper formate as a precursor and its potential for laser patterning was investigated. The Cu ink was spin-coated onto a substrate and the coated film was space-selectively sintered using a nanosecond-pulsed ultraviolet laser. The unexposed Cu ink could be removed from the film by rinsing it with the dispersing agent used to synthesize the ink, disclosing a conductive Cu pattern. A minimum resistivity of 8.46×10−5Ωcm was obtained for the Cu lines with 10–20µm widths. The feasibility of this method for metallization was demonstrated by fabricating a complex Cu electric circuit on an indium tin oxide-coated glass substrate. The selective laser sintering approach provides a simple, cost-effective alternative to conventional lithography for the production of electrode or metallization patterns.

Corrosion behaviour of steel CSN 422707.9 in concentrated synthetic bentonite pore water

Abstract Concentrating of pore bentonite water as a result of water evaporation at the hot container surface is expected when the bentonite cover of the permanent nuclear waste container is being gradually saturated. The study assesses the influence of an extent of the pore water enrichment by chloride and sulphate ions up to a multiple of a hundred of their equilibrium concentration. An increase of concentration of these ions does not imply an increase of the electrolyte aggressivity automatically. A minimum of corrosion resistance was observed at triplicate concentration at all temperatures, 40, 70 and 90°C. Even more significant impact on corrosion behaviour was recognized for composition of anoxic atmosphere above the electrolyte. Contrary to nitrogen, the mixture of nitrogen and carbon dioxide remarkably elevates the electrolyte’s corrosion aggressivity.

Formation of the low-resistivity compound Cu3Ge by low-temperature treatment in an atomic hydrogen flux

The systematic features of the formation of the low-resistivity compound Cu3Ge by low-temperature treatment of a Cu/Ge two-layer system in an atomic hydrogen flux are studied. The Cu/Ge two-layer system is deposited onto an i-GaAs substrate. Treatment of the Cu/Ge/i-GaAs system, in which the layer thicknesses are, correspondingly, 122 and 78 nm, in atomic hydrogen with a flux density of 1015 at cm2 s–1 for 2.5–10 min at room temperature induces the interdiffusion of Cu and Ge, with the formation of a polycrystalline film containing the stoichiometric Cu3Ge phase. The film consists of vertically oriented grains 100–150 nm in size and exhibits a minimum resistivity of 4.5 µΩ cm. Variations in the time of treatment of the Cu/Ge/i-GaAs samples in atomic hydrogen affect the Cu and Ge depth distribution, the phase composition of the films, and their resistivity. Experimental observation of the synthesis of the Cu3Ge compound at room temperature suggests that treatment in atomic hydrogen has a stimulating effect on both the diffusion of Cu and Ge and the chemical reaction of Cu3Ge-compound formation. These processes can be activated by the energy released upon the recombination of hydrogen atoms adsorbed at the surface of the Cu/Ge/i-GaAs sample.

Aging effect of the precursor solution on the structural, morphological, optical and electrical properties of ternary CdZnO thin films suited for optoelectronic applications

Precursor solution aging effect on the physical properties of ternary CdZnO thin films is reported in this paper. Nanostructured CdZnO thin films were fabricated on glass substrates by spray technique using perfume atomizer from fresh precursor solution and from solutions with different aging periods (1, 2, 3 and 4days). XRD studies confirm the polycrystalline nature of the films. All the films exhibit cubic crystal structure with a strong (1 1 1) preferential orientation irrespective of aging period of the starting solution. The CdZnO film prepared from 3days aged solution possess a high crystallite size value of 38.72nm and low strain and dislocation density values of 0.89×10−3 and 0.667×1015lines/m2 respectively which supports for its enhanced crystallinity. Cauliflower shaped nanostrucutres are observed for all the films from the SEM images and the CdZnO film prepared from 3days aged precursor solution exhibit better surface morphology. Optical band gap decreased with increase in aging period of the starting solution which was attributed to quantum confinement effect. Electrical resistivity of the CdZnO films decreased with aging period and the film coated from 3days aged solution exhibited a minimum resistivity of 0.056×10−2Ωcm.

Controllable growth of vertically aligned Bi-doped TiO2 nanorod arrays for all-oxide solid-state DSSCs

In this study, vertically aligned Bi-doped TiO2 nanorod arrays as photoanodes were successfully grown on the fluorine-doped tin oxide by hydrothermal method. Structural analysis showed that bismuth was successfully incorporated into the TiO2 lattice at low concentration, but at higher concentration, phase segregation of Bi2O3 in the TiO2 matrix was occurred. TiO2 nanorods with 3 % bismuth concentration had minimum electrical resistivity. As the solid-state electrolyte, Mg-doped CuCrO2 nanoparticles with p-type conductivity were synthesized by sol–gel method. The fabricated all-oxide solid-state dye-sensitized solar cells with Bi-doped TiO2 nanorods displayed better photovoltaic performance due to the presence of Bi. The improved cell performance was correlated with the higher dye loading, slower charge recombination rate and the higher electrical conductivity of the photoanodes. After mechanical pressing, the all-oxide solid-state DSSC exhibited enhanced photovoltaic performance due to the formation of the large neck between adjacent nanoparticles by mechanical sintering. The open-circuit photovoltage decay measurement of the devices and electrical conductivity of the nanoparticles before and after pressing revealed that the mechanical pressing technique reduces charge recombination rate and facilitates electron transport through the interconnected nanoparticles.

Electrical and Structural Properties of Aluminium Doped tin Oxide Codoped with Sulphur for Solar Energy

Thin films of Tin Oxide co-doped with 28 atomic percentages of Aluminium (i.e. 28 at% Al) and varied concentration of Sulphur were prepared on 1mm thick, 1cm by 1cm glass substrates at 470 0C by Spray Pyrolysis technique. Films were produced from 2.0M solution of hydrous Tin Chloride dissolved in Ethanol with 38% Hydrochloric acid concentration, 1.5M aqueous Aluminium chloride and 2.0M aqueous solution of Ammonium Sulphide. The effects of Sulphur concentration on structural and electrical properties of transparent Tin Oxide thin films were investigated in the atomic percentage of Sulphur content ranging from zero to fifty (i.e. 0at%S -50at%S) with a fixed 28at%Al content. Polycrystalline structures without any second phases were observed with preferential orientations along the (110), (101), (200) and (211) planes. The average grain size as determined from the (110) peaks lay in the range 19.2 nm-47.7nm. The minimum resistivity was found to be 1.15x10-3Ωcm for the Tin Oxide films doped with 32 at% Al content and 9.59x10-3Ωcm for Tin Oxide films co-doped with 28 at% Al and 20 at% S content. It was observed that Aluminium doping lowered the grain size significantly but doping to optimum level of 32 at% Al content increases electrical conductivity of tin oxide. When Sulphur was intentionally introduced in the crystal structure of 28 at% Al doped Tin Oxide, the electrical conductivity decreased appreciably and the grain size increased.

Significant Enhancement in the Conductivity of Al-Doped Zinc Oxide thin Films for TCO Application

Nanostructured Al-doped Zinc oxide (ZnO) thin films were deposited on glass substrate by chemical bath deposition (CBD) using aqueous zinc nitrate solution and subjected for different characterizations. Effect of Al[Formula: see text] substitution on the properties of ZnO annealed at 400[Formula: see text]C was studied by XRD and UV-Vis for structural studies, SEM and TEM for surface morphology and DC four probe resistivity measurements for electrical properties. Al[Formula: see text] substitution does not influence the morphology and well-known peaks related to wurtzite structure of ZnO. Electron microscopy (SEM and TEM) confirms rod shaped Al-doped ZnO nanocrystals with average width of 50[Formula: see text]nm. The optical band gap determined by UV–Visible spectroscopy was found to be in the range 3.37[Formula: see text]eV to 3.44[Formula: see text]eV. An EPR spectrum of AZO reveals peak at [Formula: see text] is due to shallow donors Zn interstitial. The DC electrical resistivity measurements of Al-doped ZnO show a minimum resistivity of [Formula: see text]-cm. Therefore, these samples have potential use in n-type window layer in optoelectronic devices, organic solar cells, photonic crystals, photo-detectors, light emitting diodes (LEDs), gas sensors and chemical sensors.

Mapping coalmine goaf using transient electromagnetic method and high density resistivity method in Ordos City, China

The research about subsurface characteristics by using transient electromagnetic method (TEM) and high density resistivity method (HDRM) were already conducted in Ordos. The objective of this research is to detect coalmine goaf areas based on rock resistivity. The data processing using wavelet transform, three point smoothing, RES2DINV and Maxwell processing software to obtain 2D resistivity structure. The results showed that the layers with maximum resistivity values (30–33 Ω m on Line 1, 30–31 Ω m on Line 2, 32–40 Ω m on Line 3) are founded at station 1–7, and 14–20 on Line 1,13–18 on Line 2, and 8–13 and 16–20 on Line 3 which is predicted as goaf layer, and the minimum resistivity values (20–26 Ω m of TEM, 45–75 Ω m of HDRM) at the other layers. This resistivity difference was caused by the geology and characteristics of the study area which is located close by the cleugh with rich coal, so the goaf area distinguishable with aquifer layer and coal seam. The results were also significant accidents and serious destruction of ecological environment.

Microstructure and Electrical Properties of AZO/Graphene Nanosheets Fabricated by Spark Plasma Sintering.

In this study we report on the sintering behavior, microstructure and electrical properties of Al-doped ZnO ceramics containing 0–0.2 wt. % graphene sheets (AZO-GNSs) and processed using spark plasma sintering (SPS). Our results show that the addition of <0.25 wt. % GNSs enhances both the relative density and the electrical resistivity of AZO ceramics. In terms of the microstructure, the GNSs are distributed at grain boundaries. In addition, the GNSs are also present between ZnO and secondary phases (e.g., ZnAl2O4) and likely contribute to the measured enhancement of Hall mobility (up to 105.1 cm2·V−1·s−1) in these AZO ceramics. The minimum resistivity of the AZO-GNS composite ceramics is 3.1 × 10−4 Ω·cm which compares favorably to the value of AZO ceramics which typically have a resistivity of 1.7 × 10−3 Ω·cm.

Defect mediated room temperature ferromagnetism and resistance minima study in epitaxial ZnGa0.002Al0.02O transparent conducting oxide films

We report on the micro-structural, transport, optical and magnetic properties in ZnGa0.002Al0.02O (AGZO) films grown by pulsed laser deposition under different growth conditions. AGZO films grown at substrate temperatures of 600 °C show metal-like behavior with a resistivity minima at lower temperatures, whereas films grown at 300 °C and ambient oxygen partial pressure of 1 mTorr show metallic nature with resistivity values on the order of 100 µΩ · cm at room temperature. The most interesting features are the concomitant occurrence of high temperature resistivity minima and room temperature ferromagnetism with a saturation magnetic moment of 1000 A m−1 and with coercivity in the range 100–240 Oe. The temperature dependent resistivity data has been interpreted in the light of quantum corrections to conductivity in disordered systems, suggesting that the e–e interactions is the dominant mechanism in the weak-localization (WL) limit in the case of films showing resisitivity minima. The simultaneous ferromagnetic ordering coupled with the enhancements in electrical conductivity in AGZO system should have their origin in native point defects in the form of oxygen and zinc vacancies and interstitials and their complexes. We propose that formation of oxygen vacancy–zinc interstitial defect complex (VO–IZn) is responsible for the enhancement in n-type conductivity, and zinc vacancies (VZn) for the observed room temperature ferromagnetism.

Smart Cement Piezoresistivity Characterization with Sodium Metasilicate under Temperature and Curing Environments for Oil Well–Cementing

AbstractThe smart cement behavior with 0.3% sodium metasilicate (SMS) at 80°C (176°F) under two different environments was investigated in this study. The smart cement was made using the class H oil well cement and 0.1% conductive filler to make it a bulk chemo-piezoresistive material with highly sensing property. The smart cement was cured in air and also submerged in water-saturated sand at 80°C up to 28 days. The smart cement initial resistivity (ρo) decreased from 0.97 to 0.87 Ω·m with 0.3% SMS, a 10% decrease. Similarly the minimum resistivity (ρmin) decreased from 0.81 to 0.72 Ω·m with 0.3% SMS, an 11% decrease, which is an indication of the chemo-resistivity of the smart cement. The resistivity changes were higher than the unit weight changes in the smart material. The resistivity of the smart material oven cured in saturated sand at 80°C was 55 to 75% less than the resistivity of the material cured at 80°C after curing for one, seven, and 28 days. The material resistivity with 0.3% SMS cured in ...

Integrating gamma log and conventional electrical logs to improve identification of fracture zones in hard rocks for hydrofracturing: a case study from Ghana

Hydrofracturing of low-yielding boreholes in hard rocks is a widely used technique in Africa for improvement of yield, thus making them qualified for installation of a hand-pump for domestic water supply. However, the success rate of the hydrofracturing campaigns seems not to be that high as generally claimed by contractors. One reason amongst others might be that the selection of zones for hydrofracturing in the individual borehole is based on pre-hydrofracturing investigation using conventional electrical logs only. Thereby, the zones selected are the occurring resistivity minima interpreted as weak zones with some fracturing. However, resistivity minima can also be caused solely by lithological reasons, which then in most cases could have been seen on a gamma log as corresponding increased gamma radiation. The advantages of using gamma logging in combination with conventional electrical logging technique for prediction of fractured zones in basement rocks is illustrated by investigations of three low-yielding boreholes located in different geological environments in crystalline basement rocks in Ghana.

Engineering of electronic and optical properties of PbS thin films via Cu doping

Copper-doped PbS polycrystalline thin films were deposited by chemical bath deposition by adding small amount of Cu (ysolution = [Cu2+]/[Pb2+]) between 0.5 and 2 at%. The composition, structure, morphology, optical and electrical properties of the films were investigated by means of X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS), UV–visible–near infrared (UV–Vis–NIR) spectrophotometry and Hall effect measurements. The XRD studies showed that the undoped films have PbS face centered cubic structure with (111) preferential orientation, while preferential orientation changes to (200) plane with increasing Cu doping concentration. The AFM and SEM measurements indicated that the film surfaces consisted of nanosized grains with pyramidal shape. Optical band gap was blue shifted from 0.72 eV to 1.69 eV with the increase in Cu doping concentration. The film obtained with the [Cu2+]/[Pb2+] ratio equal to 1.5 at% Cu showed the minimum resistivity of 0.16 Ω cm at room temperature and optimum value of optical band gap close to 1.5 eV. 1.5 at% Cu-doped PbS thin films exhibit the best optical and electrical properties, suitable for solar cells applications.