Minimum Resistivity Research Articles

Phase diagram of infinite layer praseodymium nickelate Pr1−xSrxNiO2 thin films

We report the phase diagram of infinite layer Pr$_{1-x}$Sr$_{x}$NiO$_2$ thin films synthesized via topotactic reduction from the perovskite precursor phase using CaH$_2$. Based on the electrical transport properties, we find a doping-dependent superconducting dome extending between $x$ = 0.12 and 0.28, with a maximum superconducting transition temperature $T_{\rm{c}}$ of 14 K at $x$ = 0.18, bounded by weakly insulating behavior on both sides. In contrast to the narrower dome observed in Nd$_{1-x}$Sr$_{x}$NiO$_2$, a local $T_{\rm{c}}$ suppression near $x$ = 0.2 was not observed for the Pr$_{1-x}$Sr$_{x}$NiO$_2$ system. Normal state Hall effect measurements indicate mixed carrier contributions of both electrons and holes, and show a sign change in the Hall coefficient as functions of temperature and $x$, quite similar to that in Nd$_{1-x}$Sr$_{x}$NiO$_2$. Also similar is the observation of a minimum in the normal state resistivity associated with the superconducting compositions. These findings indicate an infinite layer nickelate phase diagram that is relatively insensitive to the rare-earth element, but suggest that disorder arising from the variations of the ionic radii on the rare-earth site affects the superconducting dome.

Electrical properties of electrically conductive adhesives from epoxy and silver-coated copper powders after sintering and thermal aging

In order to enhance the oxidation resistance of a copper substrate, silver films were deposited by three-times electroless plating onto pure copper powders. Silver-coated copper (Ag/Cu) powders were introduced into electrically conductive adhesives (ECAs) as conductive fillers. The electrical conductivity of the ECAs can be increased by the inclusion of conductive fillers into the insulating resin matrix. The structures of the Ag/Cu powders and ECAs were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), respectively. The morphology investigation showed that the silver coatings were compact and continuous. It was found that the ECAs can be solidified through chemical sintering in air at 150 °C for 30min. The minimum volume resistivity was shown to reach2×10-4Ω•cm, suggesting excellent electrical conductivity, which makes us believe that the silver films have excellent oxidation resistance and could be broadly applied in the preparation of ECAs.

Electron–electron interaction dominated resistivity minimum in quasi-continuous Ag nanocluster films

Electronic transport in metal nanoclusters has great significance due to a variety of tunable parameters such as size, dimensionality, and cluster-distribution. Here, we report on the resistivity behavior of randomly distributed quasi-continuous Ag nanocluster films of varying cluster coverage on the substrate. This was achieved by changing the deposition time of clusters on the substrate. The Ag nanoclusters which were about 15 nm in size were deposited on thermally oxidized silicon substrates. As the deposition time reduced, clusters were distributed randomly with less coverage on the surface, resulting in a resistivity minimum at low temperatures. The temperature at which resistivity minimum occurs increases as the deposition time decreases. The resistivity at temperatures above 45 K was found to fit with a modified Bloch–Gruneisen equation which includes interaction of electrons due to structural disorder. However, the obtained Debye temperatures were found to decrease in comparison with the bulk values, which is ascribed to the softening of phonon modes in these structures. The emergence of the resistivity minimum could be explained through disorder effects in electron–electron interaction dominated quantum corrections, as shown in the Altshuler–Aronov model. A T1/2 temperature dependence of resistivity at low temperatures, as predicted by this model, was observed in our system, showing the applicability of this model.

Unconventional Hall response in the quantum limit of HfTe5

Interacting electrons confined to their lowest Landau level in a high magnetic field can form a variety of correlated states, some of which manifest themselves in a Hall effect. Although such states have been predicted to occur in three-dimensional semimetals, a corresponding Hall response has not yet been experimentally observed. Here, we report the observation of an unconventional Hall response in the quantum limit of the bulk semimetal HfTe5, adjacent to the three-dimensional quantum Hall effect of a single electron band at low magnetic fields. The additional plateau-like feature in the Hall conductivity of the lowest Landau level is accompanied by a Shubnikov-de Haas minimum in the longitudinal electrical resistivity and its magnitude relates as 3/5 to the height of the last plateau of the three-dimensional quantum Hall effect. Our findings are consistent with strong electron-electron interactions, stabilizing an unconventional variant of the Hall effect in a three-dimensional material in the quantum limit.

A methodology to characterize a sanitary landfill combining, through a numerical approach, a geoelectrical survey with methane point-source concentrations

Among the different natural sources of drinking water, aquifers are the most exposed to the environmental pressures posed by old landfills. Conventional monitoring methods to follow up the migration of leachate into groundwater and the generation of biogases in landfills are costly, time-consuming, and only provide a partial picture of these complex systems. Alternatively, we present the results of a non-invasive and cost-effective methodology applied to a non-engineered (i.e., no gas or liquid recovery systems) closed landfill in southern Ontario. The study combines, through a numerical approach, data from a direct current (DC) resistivity and an Induced Polarization (IP) survey, with measurements of methane concentrations taken over the landfill. We used a Dipole–Dipole array along four regional Lines of approximately 300 meters each, cutting crosswise and throughout the strike of the site. The interpretation of the inverted resistivity and IP data allowed us to recognize and describe some hydrogeological features that went unnoticed by using conventional monitoring techniques. We also applied a hybrid algorithm that incorporates fuzzy logic to neural networks (ANFIS) for causal variable forecasting of surface methane concentrations, using geoelectrical proxies of leachate accumulation as antecedent parameters (i.e. minimum resistivity and their corresponding IP values). The ANFIS provided a statistically significant inference of the main tendencies of methane concentrations along the surveyed Lines. Some coarse inferences appear to be locally associated with IP bright spots of anomalous metal ion content. Overall, a better inference seems to be hampered by the uncertainties involved in the generation of biogas and its upward flow through the soil cover. These results substantiate the feasibility of employing surface methane concentration data as a first diagnostic test to characterize the areal extent of the leachate plume underground.

Role of plasma parameters on the characteristics properties of flexible transparent ITO films deposited by 3D facing and planar facing magnetron sources

A rectangular closed and hollow three-dimensionally confined large area magnetron source (3-DCLAMS) and a conventional moderate area facing target magnetron source (FTMS) have been used to study the plasma characteristics using different diagnostics at different working pressures. Flexible indium tin oxide (ITO) films deposited at similar operating conditions using these sources were characterized by numerous standard analyses to study their film properties. The 3-DCLAMS with high discharge current at a low-discharge voltage is capable of generating high plasma density, which assists a high ion flux and energy density on the substrate that is necessary for the high growth rate deposition of highly conductive crystalline ITO films with smooth surface morphology. Utilizing suitable plasma characteristics, highly conductive and transparent ITO films of 30 nm with the minimum resistivity ρ ∼ 4.1 × 10−4 Ω cm and ∼9.3 × 10−4 Ω cm and average transmittance T ∼ 84% and 82%, respectively, were deposited in the 3-DCLAMS and the FTMS system. The presented result shows that the 3-DCLAMS system could be useful for making high-quality, flexible ITO films at a very high deposition rate of ∼250 nm/min.

Realization of highly conducting and transparent SnO2 thin films by optimizing F/Sn molar ratio for electrochemical applications

In the present work, fluorine-doped and undoped tin oxide thin films were deposited on microscopic glass substrate by nebulized spray pyrolysis technique at a constant substrate temperature of 350 °C. The influence of fluorine doping on the physical properties of tin oxide has been investigated by depositing the films by varying the F/Sn precursor molar ratio. The structural, morphological, chemical, optical and electrical properties of the films were characterized by X-ray diffractometer, transmission electron microscope, selected area electron diffraction, field emission scanning electron microscope, X-ray photoelectron spectroscopy, ultraviolet visible near infrared spectroscopy, and Hall effect measurements. The results suggest that deposited films are well adhered and uniformly deposited on the substrate. The structural analysis exhibit that the films are highly polycrystalline, crystallized in tetragonal structure with preferred orientations perpendicular to (200), (211) and (110) planes, and without any secondary phases. Optical transmittance greater than 75% in the visible region is obtained with an optical bandgap energy lying in the range 3.98 – 4.07 eV. Minimum resistivity, for optimized fluorine doped on tin oxide thin films, was in the range of 9.002×10−4 Ω-cm at room temperature. Hall Effect measurements show that the fluorine-doped films are degenerate semiconductors with n-type electrical conductivity. The analysis results show that device quality, highly transparent and stable fluorine doped tin oxide thin films which are having least resistivity values for the minimum doping concentration of 6.1% of fluorine can be prepared by nebulizer spray pyrolysis technique.

B-site acceptor doped AgNbO3 lead-free antiferroelectric ceramics: The role of dopant on microstructure and breakdown strength

B-site aliovalent modification of AgNbO3 with a nominal composition of Ag(Nb1-xMx)O3-x/2 (x = 0.01, M = Ti, Zr and Hf) was prepared. The effects of dopants on microstructure, dielectric, ferroelectric and conduction properties were investigated. The results indicate that the introduction of acceptor dopant does not lead to grain coarsening. Zr4+ and Hf4+ doping are beneficial to stabilize the antiferroelectric phase of AgNbO3. Among all the samples, Ti4+ doped AgNbO3 has the minimum resistivity while Hf4+ doped AgNbO3 has the maximum resistivity, therefore, Hf4+ doped AgNbO3 has high BDS. The XPS results indicate that the conduction behaviour is associated with the concentration of oxygen vacancies. This work hints that acceptor dopant is also effective on the microstructure control and chemical modification of AgNbO3-based ceramics.

Size Effects on Charge Transport Mechanisms and Magnetotransport Properties of Pr0.67Sr0.33MnO3 Nanoparticles

This paper covers a detailed study of the sintering temperature (TS) effect on the electrical and magnetotransport properties of Pr0.67Sr0.33MnO3 nanoparticles prepared by sol–gel method. The temperature dependence of resistivity displays a metal–insulator transition with increasing temperature. The electrical resistivity is strongly affected by particle size. The resistivity minimum at low temperature is associated to electron–electron coulombic interactions. Magnetotransport analysis was carried out using a phenomenological percolation model for all our samples. The obtained results indicate that a percolation model is not suitable for samples presenting high magnetic disorder. The magnetoresistance (MR) can be modulated by particle size effect. We have recorded considerable MR values (−MR(T) = 34% at 10 K for a 1T field when TS = 850°C, −MR(T) = 33% at 290 K for a 2T field when TS = 1000°C and −MR(H) = 33% at 5 K for a 1T field when TS = 700°C). The considerable MR values indicate the possibility of using these samples for several technological applications.

Effect of Hf doping content on the structure, optical and electrical properties of flexible HfxZn1-xO thin films by sol-gel method

Transparent and conducting HfxZn1-xO thin films with nominal Hf doping concentration (x = 0–7%) were successfully synthesized on flexible polyimide (PI) substrates by the sol-gel spin coating method. All films showed hexagonal wurtzite structure of ZnO with preferred orientation of c-axis after air and vacuum annealing. The minimum resistivity reached to as low as 6.3 × 10-2 Ω cm after annealed in vacuum atmosphere with 3% Hf content. The carrier concentration increased from 1018 cm-3 to 1019 cm-3, while Hall mobility decreased from 23 cm2v-1s-1 to 3 cm2v-1s-1 with increasing Hf concentration. According to the SEM and XPS analysis, for x = 0–3%, grain boundary scattering was the major factor of mobility, while for x = 5–7%, besides the grain boundary scattering, ionized impurity and natural scattering also play a crucial role in the variation of mobility. The minimum resistivity was due to the competition of increasing carrier concentration and decreasing mobility.

Use of GIS-AHP tools for potable groundwater potential zone investigations—a case study in Vairavanpatti rural area, Tamil Nadu, India

Vairavanpatti is a rural area in the district of Sivagangai, Tamil Nadu, India, prone to water deficiency. Azimuthal square array for vertical electrical sounding (VES) techniques were used to delineate the geoelectrical layers at five different locations. Groundwater samples were collected in 15 locations and analyzed for pH, EC, TDS, TH, T-Alk, Ca, Cl, SO4, Fe, and SiO2 levels. The minimum and maximum apparent resistivity values recorded in location 5 with 37.6 Ωm and location 4 with 1150.7 Ωm. Most of the quality parameters exceeds the WHO (2008) and BIS (2012) guideline values except pH and SO4. Iso-resistivity maps for apparent resistivity values suggest at 10-m intervals a total depth of 80 m. The iso-resistivity maps and spatial distribution maps were reclassified with respect to their desired values based on WHO (2008) and BIS (2012) guidelines for drinking water. Analytical hierarchy processes (AHPs) were used to assign the weights for each reclassified layers. The relative importance of layers for potable groundwater and potential zone were identified, in which the consistency ratio is kept as below 0.1. The result shows that the 23% groundwater of northern part is not suitable for drinking purposes. In the overall study area, 51.33% of the southwest, southeast, and central parts possess potable groundwater with moderate potential. In northern part, 22.42% have non-potable and moderate potential while 13.38% of the northeastern part contains good potential of potable groundwater. All other categories are 12.21% of potable and poor potential, 0.5% of non-potable with good potential, and 0.16% of non-potable with poor potential of groundwater in the study area. Rainwater harvesting and artificial recharge must be implemented in these areas to improve the potential and quality of groundwater. It is understood that AHP-enabled GIS can be used effectively in the identification of potable and potential groundwater zone in any complex regions.

Co-sputtered tantalum-doped tin oxide thin films for transparent conducting applications

A transparent conducting material combines high electrical conductivity with high optical transparency. Such materials are actively sought for their applications in optoelectronic devices and consumer electronics. Undoped tin oxide is a wide-bandgap semiconductor that is optically transparent in the visible range but lacks the electrical conductivity necessary for its function as a transparent conductor. In this study, conductive tin oxide thin films were obtained through extrinsic doping with tantalum, which is considered one of the best dopants due to its oxidation state and smaller ionic radius than that of tin. The films were deposited by co-sputtering; radio-frequency sputtering was applied to tin oxide, and then variable-power direct-current sputtering was applied to tantalum to achieve films with tantalum concentrations in the range of 2.6–15.5 at%. The resulting films were highly transparent, with a bandgap in the range of 4.1–4.2 eV and a minimum electrical resistivity of 2.44 × 10−3 Ω cm, corresponding to a Hall mobility of 8.62 cm2/V⋅s. The suitability of these films as transparent conductors was evaluated.

Gallium-doped zinc oxide films with diverse nanomorphologies grown via sol–gel united spin coating technique

Some gallium-doped zinc oxide nanofilms (GZONFs) with diverse morphologies were produced on the p-type Si (100) substrate by the sol–gel united spin coating. The thermally annealed nanofilms were characterized using different techniques to determine the influence of various Ga contents (0–5%) on their structures, morphologies, optical and electrical characteristics. The XRD patterns of the as-prepared nanofilms displayed the existence of the single-phase polycrystalline particles with varying sizes (55–36 nm). The band gap values of these GZONFs were ranged from 3.227–3.269 eV. The nanofilm produced with 1% of Ga exhibited the minimal electrical resistivity ≈ 4.6429 × 10–3 Ω cm, highest carrier density ≈ 1.37648 × 1020 cm−3 and Hall mobility ≈ 9.779 cm2/V s. It was shown that the overall properties of the proposed GZONFs can be customized by adjusting the concentration of Ga doping.

Supercritical Hydrothermal Synthesis of Polyacrylic Acid-Capped Copper Nanoparticles and Their Feasibility as Conductive Nanoinks

Polyacrylic acid (PAA) applied as surface modifier of zero-valent copper nanoparticles (CuNPs) for electronic printing inks has great potential to replace presently used polymers, because of its favorable technical, environmental and biodegradability characteristics. Continuous synthesis (400°C, 30 MPa) of nanoparticles in supercritical water with short reaction times (1.1 s) was used to form PAA-surface-modified zero-valent (34–46 nm) CuNPs. CuNP particle sizes decreased with an increase in PAA molecular mass (5000, 250,000) and were stable as dispersions in methanol and 1-propanol, respectively. The resistivity of conductive films prepared with CuNPs decreased with an increase in heating temperature. The minimum resistivity of the PAA-modified CuNPs was 1.4 × 10−5 Ω cm at 320°C (PAA25000) and 4.2 × 10−4 Ω cm at 350°C (PAA5000), demonstrating the feasibility of PAA as a dispersant and surface modifier for CuNPs. Polyacrylic acid is thus effective as a surface modifier for zero-valent metal nanoparticles and expands the possible applications in sustainable printed electronics.

Effect of bismuth doping on the structural, magnetic, electrical, and thermopower behavior of lanthanum silver manganites

The structural, magnetic, electrical, and thermoelectric behaviors of lanthanum silver manganite and lanthanum bismuth silver manganite were thoroughly studied in the present work. Two polycrystalline samples, viz., La0.835Ag0.165MnO3 (LAMO) and La0.67Bi0.165Ag0.165MnO3 (LBAMO) possessing almost constant ratio of Mn3+/Mn4+ were synthesized using the wet chemical method. Phase formation was identified from powder X-ray diffraction and it has been confirmed through the structural analysis of which samples crystallize into rhombohedral symmetry with R-3C space group. Apparent changes at phase transition temperature were observed in temperature-dependent resistivity, magnetization and thermoelectric power behavior for bismuth-doped samples. In addition, an enhanced magnetoresistance was observed in LBAMO samples and is attributed to the presence of both ferromagnetic and anti-ferromagnetic states. The temperature-dependent resistivity data in the temperature range (50–300 K) were analyzed using the phase separation model. Spin-dependent scattering and electron–electron interactions were considered to explain the resistivity minimum in the low temperature region (T < 50 K). The Seebeck coefficient is positive and enhances around the transition temperature by substituting bismuth into LAMO. The high-temperature thermoelectric power data were explained in the framework of small polaron hopping mechanism while magnon drag effect dominates in the low temperature region.

An Extended Approach on Power Conversion Efficiency Enhancement Through Deposition of ZnS-Al2S3 Blends on Silicon Solar Cells

Transparent zinc sulfide (ZnS)-aluminium sulfide (Al2S3) composite thin-films are deposited on silicon solar cells through radio frequency (RF) sputtering method at room temperature to investigate the structural, optical, electrical, and thermal characteristics. X-ray diffraction analysis reveals the presence of the powder sample (ZnS-Al2S3) and its average crystallite size is 15.83 nm. The minimum electrical resistivity (ρ), maximum hall mobility (μ), and carrier concentration (N) of ZnS-Al2S3 nano-layer coated solar cells are measured to be 2.98 × 10−3 Ω cm, 14.89 cm2 V−1 s−1 and 24.88 × 1020 cm−3 respectively. For a time period of 25 min, ZnS-Al2S3 nano-layer sputter coating produces the maximum power conversion efficiencies (PCE) of 19.38% and 21%, obtained at open and controlled atmospheric conditions, respectively. The influence of operating temperature at both these open and controlled atmospheric conditions for ZnS-Al2S3 nano-layer coated silicon solar cells is observed. The ZnS-Al2S3 composite demonstrates the properties of a desirable anti-reflection coating material for enhancing the PCE of solar cells.

Fractional quantum Hall effect at ν=2+4/9

Motivated by two independent experiments revealing a resistance minimum at the Landau level (LL) filling factor $\nu=2+4/9$, characteristic of the fractional quantum Hall effect (FQHE) and suggesting electron condensation into a yet unknown quantum liquid, we propose that this state likely belongs in a parton sequence, put forth recently to understand the emergence of FQHE at $\nu=2+6/13$. While the $\nu=2+4/9$ state proposed here directly follows three simpler parton states, all known to occur in the second LL, it is topologically distinct from the Jain composite fermion (CF) state which occurs at the same $\nu=4/9$ filling of the lowest LL. We predict experimentally measurable properties of the $4/9$ parton state that can reveal its underlying topological structure and definitively distinguish it from the $4/9$ Jain CF state.

Measuring current effect on low-temperature resistivity of n-type Bi1.9Lu0.1Te3 compound: Probing the changing in conductivity mechanism under weak electric field

The measuring current effect on low-temperature resistivity of Bi1.9Lu0.1Te3 has been analyzed. Values of currents correspond to weak electric fields with strength of several V·m−1. Temperature behavior of the resistivity is connected to two mechanisms. High-temperature mechanism (above 35 K) is due to acoustic phonon scattering. For this mechanism, the resistivity is growing with both increasing temperature and increasing current (positive current effect). Low-temperature mechanism (below 35 K) results in appearance of resistivity minimum at low temperatures. Below the minimum, the resistivity is growing with decreasing temperature. This feature is originated from contribution from variable-range hopping conductivity. With increasing current, the resistivity is falling (negative current effect). Crossover from positive to negative current effect on the resistivity occurs with decreasing temperature. Positive effect is originated from saturation of drift velocity of electrons under electric field. Negative effect is due to activation of hopping conductivity via electric field.

A new phenomenological model to describe root-soil interactions based on percolation theory

In his paper on net primary productivity of terrestrial communities predicted from climatological data, Rosenzweig (1968) argued that variability in productivity is well accounted for by (evapo)-transpiration, and that water from transpiration is, on global scales, the most variable component in the photosynthesis reaction. The goal of this paper is to investigate whether variability in plant growth on local scales and within species is primarily related to transpiration under several scenarios including different terrain curvature, slope aspect, soil characteristics, and climate ranges. We test the hypothesis that this relationship exists because root growth into the surface soil layers (0–2 m) tends to follow paths with minima in resistance, which in turn maximizes water flow and nutrient delivery rates that regulate growth. The set of all connected paths with individual pore-to-pore flow resistances less than a critical, percolating, value forms a cluster with mass fractal dimensionality, df. We propose that roots follow paths through the 2D percolation cluster, defining the set of all optimal flow paths, making the 2D value of df from percolation relevant to root fractal dimensionality. The tortuosity of such optimal paths as defined in percolation theory should then relate root length to root radial extent, linking the parameters of root tortuosity and plant productivity. Our analysis of large data sets across species implies that root radial extent and tree height are both proportional to cumulative transpiration until trees approached maximum height, and their growth rates are proportional to the transpiration rate, not to the moisture content. Local variations in tree height as functions of the variables investigated appear generally consistent with deduced variations in transpiration. Here this correlation is investigated more closely in the context of studies addressing individual tree species.

Realizing Mechanically Robust and Electrically Conductive Wood via Vacuum Pressure Impregnation.

Wood is highly regarded as the most sustainable resource that is widely used in structural applications. To extend its practicality in electrically conductive applications, it is necessary to confer electrical conductivity to the insulating wood. The most common strategy is to derive carbonized wood powder via an annealing process. Even though these carbonized wood powders are electrically conductive, they lost the ancestry characteristic of wood, that is, excellent mechanical properties. As such, it is of great importance to realize the concept of conductive wood while at the same time maintaining or even enhancing its mechanical properties further. By leveraging on the naturally formed transportation channels found in trees, conductive particles can be aligned along these ordered channels. To substitute active transport in living plants, a vacuum pressure impregnation process was used to infiltrate these conductive particles into the transportation channels. As a result, Cu/wood composite, denoted as Cu-SW, exhibited a minimum volume resistivity of 1.366 × 103 Ω cm, which was lower than those of conventional semiconductors. High Cu loading of ∼43.1 volume % of the final product, Cu-SW, was achieved with such technique, which clearly indicates the ability to achieve deep penetration of Cu nanoparticles into the bulk wood. Furthermore, an encouraging mechanical properties improvement of ∼50% was recorded for Cu-SW as compared to the wood matrix. With the enhancement in both conductivity and mechanical properties, Cu-SW could be used in load-bearing application that requires electrical conduction.