Reduction In Electrical Resistance Research Articles

Room-temperature stress reduction in welded joints through electropulsing

Conventional residual stress mitigation techniques involve long processing times at high temperatures and/or mechanical loading to build plastic compressive stress below the surface. In this study, we present a new residual stress mitigation methodology at near ambient temperature in less than a minute. This is demonstrated on a welded joint of 316 L stainless steel, where low-frequency DC current pulses are shown to recrystallize the specimen and reduce residual stress. We present experimental evidence of ∼30 % reduction in electrical resistance, which corresponded to ∼40 % decrease in both microhardness and residual stress, measured by the X-ray diffraction tests. Similar improvement was qualitatively observed through significant decrease in the low-angle grain boundary density, which also reflects the decrease of the residual stress. The technique can be applied to relieve residual stress in conditions difficult for the conventional processing, such as locations with extreme space constraints or objects that cannot be heat treated.

Reduction in electrical resistivity of bismuth selenide single crystal via Sn and Te co-doping

The structural and thermoelectric transport properties of melt-grown Bi2Se3 single crystals are systematically investigated with the co-doping of Sn and Te in the temperature range 10–400 K. The powder X-ray diffraction and high-resolution X-ray diffraction studies confirm the hexagonal crystal structure with R3‾m space group. Images of the field emission scanning electron microscopy have shown crack-free smooth surface morphological features. Energy dispersive analysis of X-ray authorizes the chemical composition of elements in the samples. The degenerate semiconducting nature is observed in the entire series of samples with 6.8 times reduction in electrical resistivity for (Bi0.96Sn0.04)2Se2.7Te0.3 compared to the pristine Bi2Se3. The maximum ZT value of ∼0.32 is obtained for Bi2Se2.7Te0.3 single crystal at 400 K, about 7.4 times larger than that of Bi2Se3.

Eco‐Friendly and Particle‐Free Copper Ionic Aqueous Precursor for In Situ Low Temperature Photothermal Synthesizing and Patterning of Highly Conductive Copper Microstructures on Flexible Substrate

Liquid precursor‐based laser‐induced reductive patterning techniques enable fast and economical fabrication of flexible electronics. Herein, an eco‐friendly and particle‐free copper ionic solution for laser‐induced reductive patterning of copper microlines on a low glass transition temperature and transparent flexible substrate is successfully developed. The solvent used is water and the reducing agent is l‐ascorbic acid. A continuous wave 640 nm laser is used as the heat source to initiate the reductive reaction and to deposit copper microlines on the substrate surface. The resistivity of the copper microlines fabricated with optimized laser parameters is remarkably low at 4.7 μΩ cm. To further improve the electrical conductivity and to enhance mechanical durability, the fabricated microlines are annealed using the same laser after the copper ionic liquid precursor is removed. The microstructures and mechanical robustness of the copper microlines, as well as the adhesion between the copper microlines and the substrate, are investigated by cyclic bending test, pull‐off test and scanning electron microscope analyses. Up to 39% reduction of electrical resistance and up to 77% enhancement of mechanical durability after a 1000 cycle bending test can be achieved by laser postprocessing.

A Comparison Study of Electrical Resistivity, Vickers Hardness, and Microstructures of Alloy 625 Prior and Posterior to Rolling

Electrical resistivity and Vickers hardness of Alloy 625 due to cold rolling were measured, and, discussed with the microstructural change obtained using electron backscattered diffraction and X-ray diffraction. Both increase in dislocation density and grain subdivision due to rolling was observed. Although the electrical resistivity of the normal pure metals increases with increasing the rolling reduction, that of Alloy 625 initially decreased with increasing the rolling reduction of 70％. Then, the electrical resistivity slightly increased with increasing the rolling reduction of 80％. Up to the rolling reduction of 70％, the reduction of electrical resistivity is associated with K effect, which is the destroy of the short-range ordered domain due to the plastic deformation. On the other hand, Vickers hardness increased with increasing the rolling reduction. It was associated with the contribution of grain refinement, dislocation, solid solution, and sort-range order strengthening.

Printed Chemiresistive In2O3 Nanoparticle-Based Sensors with ppb Detection of H2S Gas for Food Packaging

Cost-effective and disposable smart sensing technologies capable of monitoring packaged foods’ degradation are necessary for human health and the growing processed-food industry. Herein, highly sensitive and selective hydrogen sulfide (H2S) gas sensors were fabricated from solution-printed nanocomposites comprising indium oxide nanoparticles (In2O3 NPs), graphite flakes (Gt), polystyrene (PS), and copper acetate monohydrate (CuAc). The standard In2O3 NP-based sensor (SS, without CuAc) showed H2S detection ≈100 ppb under ambient conditions. The presence of CuAc resulted in a highly sensitive nanocomposite layer enabling the detection of lower than 100 ppb (<100 ppb) concentrations of H2S gas levels, far superior to the standard In2O3 NP-based nanocomposite. Adding CuAc to the In2O3 NP-based nanocomposite as a modifying additive leads to copper sulfide (CuS) formation owing to its reaction with H2S gas. CuS significantly enhances the nanocomposite layer’s conductivity and H2S reactions on the sensors’ surface, resulting in a substantial reduction in electrical resistance for sensors. The modified In2O3 NP-based sensor presents remarkable enhancement in their selectivity toward H2S gas detection when evaluated against various hazardous vapors. Furthermore, the modified In2O3 NP-based sensors possess good anti-humid property under highly humid conditions (≈80% relative humidity).

Entropy-Induced Multivalley Band Structures Improve Thermoelectric Performance in p-Cu7P(SxSe1-x)6 Argyrodites.

Searching for novel low-cost and eco-friendly materials for energy conversion is a good way to provide widespread utilization of thermoelectric technologies. Herein, we report the thermal behavior, phase equilibria data, and thermoelectric properties for the promising argyrodite-based Cu7P(SxSe1-x)6 thermoelectrics. Alloying of Cu7PSe6 with Cu7PS6 provides a continuous solid solution over the whole compositional range, as shown in the proposed phase diagram for the Cu7PS6-Cu7PSe6 system. As a member of liquid-like materials, the investigated Cu7P(SxSe1-x)6 solid solutions possess a dramatically low lattice thermal conductivity, as low as ∼0.2-0.3 W m-1 K-1, over the entire temperature range. Engineering the configurational entropy of the material by introducing more elements stabilizes the thermoelectrically beneficial high-symmetry γ-phase and promotes the multivalley electronic structure of the valence band. As a result, a remarkable improvement of the Seebeck coefficient and a reduction of electrical resistivity were observed for the investigated alloys. The combined effect of the extremely low lattice thermal conductivity and enhanced power factor leads to the significant enhancement of the thermoelectric figure of merit ZT up to ∼0.75 at 673 K for the Cu7P(SxSe1-x)6 (x = 0.5) sample with the highest configurational entropy, which is around twice higher compared with the pure selenide and almost four times higher than sulfide. This work not only demonstrates the large potential of Cu7P(SxSe1-x)6 materials for energy conversion but also promotes sulfide argyrodites as earth-abundant and environmentally friendly materials for energy conversion.

Reduction in electrical resistivity and enhancing the thermoelectric power factor of β-FeSi2 bulk materials by Se doping

Se-doped FeSi2 (FeSi2−xSex, x = 0, 0.01, 0.03 and 0.05) bulk samples were fabricated by the hot-pressing method. Temperature dependence of electrical resistivity and the Seebeck coefficient were investigated from 365 to 762 K. X-ray diffraction (XRD) results detected the crystalline and impurity phases of β-FeSi2. Field emission scanning electron microscopy (FESEM) images revealed finer crystal grains after Se doping in FeSi2. Electrical resistivity decreased while the Seebeck coefficient increased at higher temperatures. Low electrical resistivity of 40.1 μΩ m at 762 K was obtained for FeSi1.95Se0.05, lower than β-FeSi2 (154 μΩ m). The Seebeck coefficient and power factor values were 65.3 μV K−1 and 15.3 μW m−1 K−2 at 762 K, respectively for FeSi1.97Se0.03 and higher than undoped FeSi2. Results suggested Se doping as a promising technique to enhance the power factor of β-FeSi2 bulk materials.

Electroplating of Aerosol Jet‐Printed Silver Inks

Aerosol jet printing of silver inks is a promising approach for 3D printing of electronics, particularly for obtaining very complex circuits with high‐resolution conductive pads and traces. Common silver inks are however not competitive with traditional bulk metal conductors, requiring sintering at high temperatures as well as having significant porosity that can result in early failure. Herein, the possibility of using electroplating to deposit bulk metal copper on aerosol jetted inks is investigated, and more than an order of magnitude reduction in electrical resistivity is shown. The plating rate, resistivity, and adhesion are characterized, along with the morphology of the resulting deposits. This approach is then shown to allow high‐strength soldering to the electroplated metal traces, demonstrating the capability of this technology for integration of soldered surface mount components with aerosol jet‐printed electronics.

Electrical Resistance Reduction Induced with CO2 Laser Single Line Scan of Polyimide.

We conducted a laser parameter study on CO2 laser induced electrical conductivity on a polyimide film. The induced electrical conductivity was found to occur dominantly at the center of the scanning line instead of uniformly across the whole line width. MicroRaman examination revealed that the conductivity was mainly a result of the multi-layers (4–5) of graphene structure induced at the laser irradiation line center. The graphene morphology at the line center appeared as thin wall porous structures together with nano level fiber structures. With sufficient energy dose per unit length and laser power, this surface modification for electrical conductivity was independent of laser pulse frequency but was instead determined by the average laser power. High electrical conductivity could be achieved by a single scan of laser beam at a sufficiently high-power level. To achieve high conductivity, it was not efficient nor effective to utilize a laser at low power but compensating it with a slower scanning speed or having multiple scans. The electrical resistance over a 10 mm scanned length decreased significantly from a few hundred Ohms to 30 Ohms when energy dose per unit length increased from 0.16 J/mm to 1.0 J/mm, i.e., the laser power increased from 5.0 W to 24 W with corresponding power density of 3.44 × 10 W/cm2 to 16.54 W/cm2 respectively at a speed of 12.5 mm/s for a single pass scan. In contrast, power below 5 W at speeds exceeding 22.5 mm/s resulted in a non-conductive open loop.

Effect of Refractory Tantalum Metal Filling on the Microstructure and Thermoelectric Properties of Co4Sb12 Skutterudites.

We report a systematic investigation of the microstructure and thermoelectric properties of refractory element-filled nanostructured Co4Sb12 skutterudites. The refractory tantalum (Ta) metal-filled Co4Sb12 samples (TaxCo4Sb12 (x = 0, 0.4, 0.6, and 0.8)) are synthesized using a solid-state synthesis route. All the samples are composed of a single skutterudite phase. Meanwhile, nanometer-sized equiaxed grains are present in the Ta0.2Co4Sb12 and Ta0.4Co4Sb12 samples, and bimodal distributions of equiaxed grains and elongated grains are observed in Ta0.6Co4Sb12 and Ta0.8Co4Sb12 samples. The dominant carrier type changes from electrons (n-type) to holes (p-type) with an increase in Ta concentration in the samples. The power factor of the Ta0.6Co4Sb12 sample is increased to 2.12 mW/mK2 at 623 K due to the 10-fold reduction in electrical resistivity. The lowest lattice thermal conductivity observed for Ta0.6Co4Sb12 indicates the rattling action of Ta atoms and grain boundary scattering. Rietveld refinement of XRD data and the analysis of lattice thermal conductivity data using the Debye model confirm that Ta occupies at the voids as well as the Co site. The figure of merit (ZT) of ∼0.4 is obtained in the Ta0.6Co4Sb12 sample, which is comparable to single metal-filled p-type skutterudites reported to date. The thermoelectric properties of the refractory Ta metal-filled skutterudites might be useful to achieve both n-type and p-type thermoelectric legs using a single filler atom and could be one of replacements of the rare earth-filled skutterudites with improved thermoelectric properties.

Shrinkage Limit Studies from Moisture Content: Electrical Resistivity Relationships of Soils

At the shrinkage limit, the soil is just fully saturated. Shrinkage limit of soils can be perceived as a point of inflection in either direction. While decreasing the water content, from its liquid state to the solid state, a point of inflection is reached (shrinkage limit) when further reduction in water content will not cause a reduction in the volume of the soil mass. While increasing the water content, from a partially saturated state to a fully saturated state and beyond, the electrical resistivity reduces, and from the point of shrinkage limit onwards, there is no further appreciable reduction in electrical resistivity. Earlier studies have proven that shrinkage limit is not governed by plasticity characteristics of the soil. Shrinkage limit is primarily a result of the packing phenomenon governed by the grain size distribution of the soil. This research investigates the relationship between moisture contents and electrical resistivity of well compacted/packed soils. It is shown that electrical resistivity measurements (ER–moisture content profile) of a well packed soil, in an electrical resistivity box, can be a useful tool for predicting the shrinkage limit of the soil. A very good agreement is obtained between Shrinkage limit assessed from standard shrinkage limit test and resistivity–water content profile. The assessment is proven to be valid for contaminated soils too, where in the Atterberg limits get altered.

Tertiary alkyl halides as growth activator and inhibitor for novel atomic layer deposition of low resistive titanium nitride

A novel atomic layer deposition (ALD) that utilizes tertiary alkyl (tert-alkyl) halides as both growth activator and inhibitor is introduced and demonstrated for the deposition of a low resistive TiN film using TiCl4 and NH3. Among the alkyl halides, tert-butyl iodide is identified as a suitable material for both growth inhibition and growth activation without any incorporation of C impurity in the film. The electrical resistivity values of TiN thin films in activator-type and inhibitor-type ALD were significantly improved by 55% and 49%, respectively. The mechanism of the reduction in electrical resistivity is elucidated by means of theoretical approach and characterizations of TiN films. For activator-type ALD, tert-butyl iodide induces in situ ligand exchange with an adsorbed Ti precursor to form Ti–I bonds, leading to an increase in the reactivity with a NH3 reactant. For inhibitor-type ALD, the improvement of film conformality in a high aspect ratio (&amp;gt;22:1) substrate is exhibited. This study demonstrates that the effectiveness on the use of tert-alkyl halides in ALD deposition can serve as an important guideline for future studies of the growth activator and growth inhibitor to improve film properties, making the method widely applicable.

Achieving brittle-intermetallic-free and high-conductivity aluminum/copper joints using nickel-phosphorus coatings

Mechanical degradation due to brittle intermetallic compounds (IMCs) formed at the faying interface is a predominant deficiency in dissimilar metal joints. In copper/aluminum (Cu/Al) joints, additional defects (such as partially-bonded interfaces, porosity and cracks) lead to further weakened strength and lowered electrical conductivity. In this study, nickel‑phosphorus (Ni-P) coatings are deposited on Al to address these issues. With the aid of Ni-P coatings, the detrimental Cu-Al IMC is eliminated, a donut-shaped weld with a partially-bonded interface is evolved into an hourglass-shaped weld with a fully-bonded interface, while the porosity and cracks are inhibited. Numerical simulations indicate that, during the welding without Ni-P coating, the Al oxide aggravates the inhomogeneity of heat generation at the Cu/Al interface, promoting the formation of donut-shaped weld and defects. Microstructural characterization suggests that the Ni-P coatings obstruct the Cu-Al interdiffusion which results in CuAl2-free interfaces, while the amorphous Ni-P convert into eutectic microstructure composed of nanocrystalline Ni and fine Ni3P grains through a solid-state transformation. Using the Ni-P coatings, joints gain an improvement of 140% in lap-shear peak load and a 25-fold increase in lap-shear maximum elongation, as well as an 84% reduction in electrical resistance.

A Post-Treatment Method to Enhance the Property of Aerosol Jet Printed Electric Circuit on 3D Printed Substrate.

Aerosol jet printing of electronic devices is increasingly attracting interest in recent years. However, low capability and high resistance are still limitations of the printed electronic devices. In this paper, we introduce a novel post-treatment method to achieve a high-performance electric circuit. The electric circuit was printed with aerosol jet printing method on an ULTEM substrate. The ULTEM substrate was fabricated by the Fused Deposition Modelling method. After post-treatment, the electrical resistance of the printed electric circuit was changed from 236 mΩ to 47 mΩ and the electric property was enhanced. It was found that the reduction of electric resistance was caused by surface property changes. Different surface analysis methods including scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS) were used to understand the effectiveness of the proposed method. The results showed that the microsurface structure remained the same original structure before and after treatment. It was found that the surface carbon concentration was significantly increased after treatment. Detailed analysis showed that the C-C bond increased obviously after treatment. The change of electrical resistance was found to be limited to the material’s surface. After polishing, the circuit resistance was changed back to its original value. As the electric circuit is the basic element of electric devices, the proposed method enables the fabrication of high performance devices such as capacitors, strain gauge, and other sensors, which has potential applications in many areas such as industrial, aerospace, and military usage.

Photoelectric properties of highly conductive samarium-doped cadmium telluride thin films for photovoltaic applications

Cadmium telluride (CdTe) is one of the most important materials for photovoltaic applications. CdTe-based solar cells have significantly high light-to-current conversion efficiency. However, further improvement of the efficiency is affected by two major problems: high electrical resistivity of CdTe and the difficulty to form ohmic contacts with this material. Extrinsic doping has been employed to rectify these problems; in particular, samarium is a rare-earth element that is characterized by its excellent electrical conductivity, high valence, and low oxidation affinity. In this work, thermally evaporated samarium-doped CdTe thin films were deposited with a samarium concentration of 0–6.2 at%. After doping, there were drastic changes in the photoelectric properties of the films, as demonstrated by: (i) conversion of CdTe from p- to n-type material, (ii) reduction of electrical resistivity by eight orders achieving the lowest value of 7.6 × 10−2 Ω⋅cm, (iii) formation of ohmic contacts to CdTe, and (iv) reduction of the optical bandgap, which enhanced the absorption of solar radiation.

Reduction of electrical resistance on suspended glassy carbon nanofibers by localized thermal annealing

Glassy carbon nanofibers (CNF) can be fabricated with relative ease through electrospinning of a polymeric ink—a carbon precursor—followed by a pyrolysis step. These fibers have found applications in fields as diverse as electrochemical sensing, nanoelectronics and energy storage. A critical step for using this type of carbon fibers in such applications is to thermally anneal them. Annealing reduces the variations in electrical resistance inherent to this type of disordered non-graphitizing carbon. In this work, the thermal annealing process was done by exploiting the local Joule heating experienced by the fibers upon application of a voltage. The effect of this annealing process on the CNFs was studied, finding that more than half of the fibers experience a reduction above 90% in their electrical resistance. This decrease was found to be related to the volume of the fibers, with the lesser-volume CNFs experiencing a much more significant reduction in their resistance (thus, indicating a larger graphitization level). The preliminary results presented in this work can serve as the basis for a detailed study on the effect that extreme temperatures have on glassy carbon nanofibers.

Effect of Injection Molding Conditions on Crystalline Structure and Electrical Resistivity of PP/MWCNT Nanocomposites.

Polypropylene (PP) / multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by melt-mixing and used to manufacture samples by injection molding. The effect of processing conditions on the crystallinity and electrical resistivity was studied. Accordingly, samples were produced varying the mold temperature and injection rate, and the DC electrical resistivity was measured. The morphology of MWCNT clusters was studied by optical and electron microscopy, while X-ray diffraction was used to study the role of the crystalline structure of PP. As a result, an anisotropic electrical behavior induced by the process was observed, which is further influenced by the injection molding processing condition. It was demonstrated that a reduction of electrical resistivity can be obtained by increasing mold temperature and injection rate, which was associated to the formation of the γ-phase and the related inter-cluster morphology of the MWCNT conductive network.

Enhanced Thermoelectric Performance of Novel Reaction Condition-Induced Bi2S3-Bi Nanocomposites.

This is the first report on the enhanced thermoelectric (TE) properties of novel reaction-temperature (TRe) and duration-induced Bi2S3-Bi nanocomposites synthesized using a facile one-step polyol method. They are well characterized as nanorod composites of orthorhombic Bi2S3 and rhombohedral Bi phases in which the latter coats the former forming Bi2S3-Bi core-shell-like structures along with independent Bi nanoparticles. A very significant observation is the systematic reduction in electrical resistivity ρ with a whopping 7 orders of magnitude (∼107) with just reaction temperature and duration increase, revealing a promising approach for the reduction of ρ of this highly resistive chalcogenide and hence resolving the earlier obstacles for its thermoelectric application potentials in the past few decades. Most astonishingly, a TE power factor at 300 K of the highest Bi content nanocomposite pellet, made at 27 °C using ∼900 MPa pressure, is 3 orders of magnitude greater than that of hot-pressed Bi2S3. Its highest ZT at 325 K of 0.006 is over twice of that of similarly prepared CuS or Ag2S-based nanocomposites. A significantly improved TE performance potential near 300 K is demonstrated for these toxic-free and rare-earth element-free TE nanocomposites, making the present synthesis method as a pioneering approach for developing enhanced thermoelectric properties of Bi2S3-based materials without extra sintering steps.

Field monitoring of preferential infiltration in loess using time-lapse electrical resistivity tomography

The effect of preferential flow (PF) in loess is of direct interest as flood irrigation is commonly found in loess regions where precipitation is scarce. This study was to assess the applicability of time-lapse electrical resistivity tomography (ERT) data on monitoring infiltration in loess and to analyze the effects of preexisting preferential path on infiltration process at a localized scale. An in situ single-ring infiltrometer (SRI) test was conducted above a preexisting near-surface crack under a constant influx (10 cm water head for 8h), and the test was monitored by the means of 2-D time-lapse ERT and validated by an exploratory trench. The ERT results observed some increasing uncertainties in the electrical resistivity in part due to daily temperature variation; however, they showed that the infiltration process under the presence of preferential path can be effectively monitored by time-lapse ERT with a combination of unit electrode spacing (UES). The test results showed a high relative reduction of electrical resistivity (>80%) due to matrix flow (MF) and PF within 0–0.5h of the test, and followed by a transformation of preferential flow to a more matrix-dominated unsaturated flow, i.e. preferential-to-matrix flow (PMF), with continuous downward progression into the deeper subsurface (greater than 1.2 m) while MF stagnated at the near-surface (about 0.4 m). The results suggested that the presence of even a near-surface preferential path significantly accelerate the infiltration into the deeper loess by the means of PMF, as compared to observed slow infiltration of pure matrix flow in previous studies.

Electrical resistivity reduction and spatial homogenization of Ga-doped ZnO film by Zn layer insertion

Ga-doped ZnO (GZO) films inserted with a Zn layer were deposited at room temperature by a sputtering method to decrease carrier-compensating defects. The Zn-inserted GZO films showed a resistivity decrease resulting from an increase in carrier density. The carrier density further increased by thermal annealing and showed a maximum at around 400ºC. The formation of a SiO2 capping layer on the film surfaces enhanced the carrier density at temperatures higher than 400ºC, resulting in a lowered resistivity to 3.3 × 10−4 Ωcm for a 200-nm-thick film. In addition, resistivity degradation that was induced at the erosion position in the sputtering deposition process disappeared. The increase in carrier density, decrease in resistivity, and homogenization of the electrical property indicate that carrier-compensating crystalline defects such as the zinc vacancy induced in Ga-doped ZnO films during the deposition process are decreased by the Zn enrichment.