Resistance Rw Research Articles

Multiscale Electrical Response Assessment of Metal Nanowire Transparent Electrodes: A Computational Strategy

Transparent electrodes made of random distributions of metal nanowires (NWs) are appealing for optoelectronic devices, solar cells, light emitting diodes, and transparent heaters. While these electrodes are comparable to thin films in terms of electrical conductivity and transparency, their network structure allows limiting the amount of conductive material and makes them suitable for low-cost solution-based deposition methods, contributing to an overall costs reduction. Despite these advantages, an even material utilization at different length scales is difficult to achieve. The homogeneous distribution of electric current (electrical homogeneity) is indeed not guaranteed in nanowire electrodes but is crucial for the stability of the electrode and actually desirable in most applications. Despite the relevance of this feature, it is common practice to perform qualitative assessments at the electrode scale, overlooking local effects. To address this issue, we have developed a computational strategy to aid in the design of nanowire electrodes with improved electrical homogeneity.We present a computational approach that allows an objective, quantitative, and systematic assessment of the electrical homogeneity. The approach enables a multiscale comparison of electrodes with different NW content and material properties. Nanowire electrodes are modeled as two-dimensional networks of stick and junction resistors (with resistance Rw and Rj, respectively) to simulate the electric conduction process. Electrodes are discretized into regular grids of squares and the electrical power of the network contained in each square is computed. The mismatch between the areal power density of the entire electrode and that of the squares provides a quantitative electrical homogeneity evaluation. Repeating the analysis with squares of different size yields an evaluation that spans across length scales. A scalar indicator, coined the homogeneity index, summarizes the results of the multiscale evaluation.Parametric studies are performed by varying nanowire content and nanowire-to-junction resistance ratio Rw/Rj. We show that electrical homogeneity improves as i) NW density increases, and ii) junction resistance reduces. The ideal condition of negligible junction resistance (Rw >> Rj) leads to the best-case scenario and guarantees the highest rate of improvement of electrical homogeneity with NW content. Nevertheless, we observe that under condition Rw ≈ Rj the response of the system approaches the response of a system meeting the ideal condition Rw >> Rj (15% difference at most in terms of homogeneity index). We therefore conclude that reducing the junction resistance excessively (with the aim of achieving Rw/Rj > 1) may not always be a worthwhile strategy, as it results in only a marginal improvement in terms of electrical homogeneity.The proposed strategy is employed to assess the electrical homogeneity of silver nanowire electrodes through the analysis of scanning electron microscopy images. Our results agree with the outcomes of the experimental assessment performed on the same electrodes.

Quantitative electrical homogeneity assessment of nanowire transparent electrodes.

The homogeneous distribution of electric current (electrical homogeneity) is not guaranteed in nanowire electrodes but is crucial for the stability of the electrode and actually desirable in most applications. Despite the relevance of this feature, it is common practice to perform qualitative assessments at the electrode scale, thus masking local effects. To address this issue, we have developed a computational strategy to aid in the design of nanowire electrodes with improved electrical homogeneity. Nanowire electrodes are modeled as two-dimensional networks of stick and junction resistors (with resistance Rw and Rj, respectively) to simulate the electric conduction process. Electrodes are discretized into regular grids of squares and the electrical power of the network contained in each square is computed. The mismatch between the areal power density of the entire electrode and that of the squares provides a quantitative electrical homogeneity evaluation. Repeating the analysis with squares of different size yields an evaluation that spans across length scales. A scalar indicator, coined the homogeneity index, summarizes the results of the multiscale evaluation. The proposed strategy is employed to assess the electrical homogeneity of silver nanowire electrodes through the analysis of scanning electron microscopy images. Our results agree with the outcomes of the experimental assessment performed on the same electrodes. Parametric studies are performed by varying nanowire content and nanowire-to-junction resistance ratio Rw/Rj. We observe that a significant reduction of contact resistance is not necessary to ensure a high degree of homogeneity. The ideal condition of negligible junction resistance (Rw ≫ Rj) leads to the best-case scenario, a situation which is closely approached if Rw ≈ Rj (15% difference at the most in terms of homogeneity index).

Modification of river bus catamaran to reduce total resistance by Centerbulb

Ship resistance consists of many components, it can be approximated that the total resistance when the ship is moving uniformly in still water consists of the following main components: frictional resistance RF, residual resistance RR. In the residual resistance RR, the component of pressure resistance RP occupies a large proportion and is expressed through the energy loss due to wave generation, symbolizing wave generating resistance is RW. At large Froude numbers, the wave generating resistance RW accounts for more than 70% of the total resistance value of RT and is a high-order function of the ship's speed (n > 3, n - order of the resistance function), whereas RF is approximately the first-order function of ship speed. Such reasoning proves that the total resistance characteristic RT of a ship is determined by the component characteristic of resistance RW. In this study, we present the results obtained on reducing the RW wave generating resistance of a catamaran by adding a Centerbulb-shaped auxiliary bow. The idea that comes from the theory of ship waves is that of a phased oscillation, the period of which is known from observing the wave profile of the prototype ship at some unfavorable Froude number. Then calculate the independent Centerbulb wave simulation to consider the possibility of partial destructive interference of the whole ship wave and convert the whole ship wave profile to the form of large wavelength and small wave height as announced by Newman and Newman [1], [2].

Temperature effects in contacts between a metal and a semiconductor nanowire near the degenerate doping

We have investigated the nonlinear conductance in diffusion-doped Si:GaAs nanowires contacted by patterned metal films in a wide range of temperatures T. The wire resistance RW and the zero bias resistance RC, dominated by the contacts, exhibit very different responses to temperature changes. While RW shows almost no dependence on T, RC varies by several orders of magnitude as the devices are cooled from room temperature to T = 5 K. We develop a model that employs a sharp donor level very low in the GaAs conduction band and show that our observations are consistent with the model predictions. We then demonstrate that such measurements can be used to estimate carrier properties in nanostructured semiconductors and obtain an estimate for ND, the doping density in our samples. We also discuss the effects of surface states and dielectric confinement on carrier density in semiconductor nanowires.

Domain wall motion in a nanoconstriction of Gd

We report the observation of a DC-current driven magnetic domain wall (DW) motion in an artificially created nanoconstriction (size ∼ 300 nm) in a microstrip of 4f ferromagnet Gd (film thickness, 40 nm), where beyond a critical current density, a sharp reduction in the resistance is observed which gives the DW resistance RW. This is similar to that seen in nanoconstrictions made in conventional 3d ferromagnets such as Ni and its alloys. The effect is most prominent at 100 K or below and becomes smaller as the temperature increases, and it vanishes as T→TC. The value of RW was used in conjunction with the measured anisotropic magnetoresistance to find the domain wall thickness (δ) and the anisotropy energy (EA) of the Gd film. The observation of this phenomenon in 4f metal Gd, which is distinct from itinerant conventional 3d transition metals, extends the phenomena to rare-earth ferromagnets. A low ferromagnetic transition temperature of Gd also allows us to study the phenomena and the evolution of δ and EA as a function of temperature.

Impedimetric Measurements for Monitoring Avidin-Biotin Interaction on Self-Assembled Monolayer

Avidin-biotin has been controllable immobilized on the surface of gold electrodes using mercaptopropionic acid as self-assembled monolayer. Electrochemical impedance spectroscopy (EIS) was employed to investigate the changes that appear at the electrode surface in the presence of a redox mediator, K3[Fe(CN)6]. An electrical model more complex than that in other studies was used to interpret the EIS measurements (Randles circuit). This model is very useful because it takes into consideration both the transfer of electrons at the electrode/electrolyte interface and the diffusion of redox species through the double layer. The model allowed us to determine some important parameters like solution resistance Rsol, charge-transfer resistance Rct, double-layer capacitance Cdl, Warburg resistance RW, and the diffusion time constant τ. The EIS results proved that immobilization of avidin-biotin increased the charge-transfer resistance Rct, due to the insulating character of these molecules.

Water and Air Permeability for Polyester Fabrics

The water permeability was studied in comparison with the air permeability for a series of polyester fabrics. The experimental apparatus for the water permeability measurement is composed of a vertical cylinder at the bottom of which a specimen is attached. The water filled in the cylinder flows by its weight through the specimen. The water flow was measured as a function of time in the water pressure range from about 6.63 to 2.22 kPa. The water pressure drop by the specimen, obtained after correcting the water pressure drop inherent to the apparatus, changed in proportion to the water flow rate. The proportional coefficient of the pressure drop against the flow rate was defined as the water permeation resistance Rw. The air flowresistance Ra was measured by separate experiments. The water flow resistance Rw was proportional to the flow resistance of air Ra, and the flow resistance ratio Rw/Ra was 71.1. According to the Darcy's law the flow resistance ratio Rw/Ra equals the ratio of the water viscosity ηw to the air viscosity na. The value of the viscosity ratio nw / na , which is calculated with the viscosity values of 1.00 mPa*s for water and 18.1 uPa*s for air, is 55.2. This value of viscosity ratio nw / na agrees reasonably with the value of flow resistance ratio Rw/Ra obtained experimentally.

Equation of motion of domain walls and equivalent circuits in soft ferromagnetic materials

The equation of motion for ferromagnetic domain walls is compared with initial permeability measurements of Co-based soft ferromagnetic amorphous ribbons at frequencies in the range 100 Hz–13 MHz. The analysis of these results by complex permeability methods leads to an equivalent circuit formed by a parallel RL arrangement in series with a small resistance RW due to resistance of the measurement coil. This equivalent circuit, however, cannot model the irreversible magnetization behavior for fields higher than the pinning (or propagation) field. It is shown that the equation of motion is also consistent only with the reversible magnetization mechanism, if the displacement term, x, represents instead the bulging of the pinned wall. The correlations between the terms in the equation of motion and the elements of the equivalent circuit are established.

Characteristics and Operation of Xenon Filled Linear Flashlamps

Following a discussion of flashtube impedance and its dependence upon discharge current, the relation between current magnitude, initial charge voltage, circuit constants, and lamp dimensions is derived for lamps operating in pulse forming networks of cascaded LC pisections. The resulting equation, I=0.27(d/l)23(C/L)13V43, has been experimentally verified by data from flashtubes having arc lengths ranging between 7.6 and 91.5 cm. When, as is often the case, a flashtube is operated in series with a single inductor, the current pulse is not rectangular and the assumption of constant discharge resistance used in the multisection line study is invalid. A more precise analysis has been carried out with the aid of a digital computer in which the differential equation for a series RLC circuit is solved with the nonlinear condition R=Rw+R(i). Inclusion of wiring resistance Rw permits further extension of the solution's applicability and the results are found to agree well with experiment.