Rectification Factor Research Articles

Single-step electrochemical functionalization of double-walled carbon nanotube (DWCNT) membranes and the demonstration of ionic rectification

Carbon nanotube (CNT) membranes allow the mimicking of natural ion channels for applications in drug delivery and chemical separation. Double-walled carbon nanotube membranes were simply functionalized with dye in a single step instead of the previous two-step functionalization. Non-faradic electrochemical impedance spectra indicated that the functionalized gatekeeper by single-step modification can be actuated to mimic the protein channel under bias. This functional chemistry was proven by a highly efficient ion rectification, wherein the highest experimental rectification factor of ferricyanide was up to 14.4. One-step functionalization by electrooxidation of amine provides a simple and promising functionalization chemistry for the application of CNT membranes.

Switchable Electric Field Induced Diode Effect in Nanostructured Porous Silicon

Unidirectional current flow (diode-like behavior) is observed in Al/Nanostructured Porous Silicon/Al structures (Al/SP/Al) after applying a forming electric field $(E)$ for a long time. We found that rectifying characteristics depend on the direction of $E$ . The forward direction coincides with the direction of $E$ . The diode direction switches when $E$ is inverted. The rectification factor passes from 200 to 26 from one direction to the other, the effect is reversible and can be repeated several times.

Hybrid photodiodes based on 6,13-bis(triisopropylsilylethynyl) pentacene:poly[2-methoxy-5-(2-ethyl) hexoxy-phenylenevinylene]/p-silicon

6,13-Bis(triisopropylsilylethynyl) pentacene (TIPS) and poly[2-methoxy-5-(2-ethyl) hexoxy-phenylenevinylene] (MEH-PPV) blends with different ratios were deposited onto a p-type silicon (p-Si) single crystal wafer using spin coating technique. The dark current–voltage characteristics of the fabricated diodes were studied at room temperature. This study was carried out to predict the best blend composite to obtain a qualified diode for use in potential application. The obtained results suggest that the diode with 10:4 ratio between TIPS and MEH-PPV has the highest values for both the rectification factor (r=1.7×103) and the ratio between shunt resistance, Rsh, and series resistance, Rs, (Rsh/Rs=1.23×104) among the investigated diodes. Accordingly, the capacitance–voltage–frequency and conductance–voltage–frequency measurements were carried out for this diode in the frequency range between 10kHz and 1MHz at room temperature. Moreover, the I–V characteristics of such a diode were studied under different illumination intensities (P=20:100mW/cm2). The obtained results show a highly optoelectric response; i.e., the diode can be operated as a heterojunction photodiode.

Thermal rectification features: a study starting from local assumptions

In the present work, addressing the investigation of thermal rectification in asymmetric models (in particular, graded systems), we generalize a previously developed approach based on the features of the local thermal conductivities. We study the behavior of the predicted rectification as the gradient of temperature into the system increases, and, considering a small chain, we give indications of a big rectification factor in very asymmetric models, a result which makes these graded materials genuine candidates for the construction of thermal diodes. Moreover, our results allow us to understand the details which determine the direction of the bigger heat flow.

Resistance of In2О3–p-InSe photoconverter to different types of irradiation

The article presents the results of irradiation of In 2 O 3 –p-InSe photoconverters by braking γ-quanta, high-energy electrons and gamma-neutrons. In particular, their electrical and photoelectrical parameters were analyzed. The latest were compared to the similar parameters of test solar IТО–SiO 2 – n -Si element . For the initial doses, depending on the type of irradiation, the major changes consisted in: - the improvement of the rectification factor K at 10-100% and the monochromatic volt-watt sensitivity S U at 18-44%; - the maintenance or increase of voltage of idle running U хх ; - the increase of the short-circuit current J кз at 7% ( under the action of gamma-neutrons and electrons) and the monochromatic ampere-watt sensitivity of S I at 11-28% ( under the action of γ-quanta and electrons). In other cases, the listed parameters have been experiencing the minimal decline (up to 5%). The imperfection coefficient ВАХ n has remained constant or has even slightly improved (under the action of gamma-neutron). With further radiation, it was fixed: values ​​ U хх , J кз , S U and S I were saved in case of γ-quanta; U хх and S U increased under the action of electrons, K value was significantly improved and U хх was unchanged in case of gamma neutrons. The decline of the rest of the parameters was in the range 2-12%. The specific changes in the spectral contours of photoresponse were not detected (except the irradiation by electrons). The possible mechanisms of radiation damages were discussed. In case of γ- and electron radiation, this is the generation of point defects - Frenkel pairs, in case of neutron radiation - formation of vacancy and internodal clusters. At the same time, the used doses and types of radiation have caused severe damage of IТО–SiO 2 –n-Si structure

Asymmetric wave propagation through nonlinear PT-symmetric oligomers

In the present paper, we consider nonlinear PT-symmetric dimers and trimers (more generally, oligomers) embedded within a linear Schrödinger lattice. We examine the stationary states of such chains in the form of plane waves, and analytically compute their reflection and transmission coefficients through the nonlinear PT symmetric oligomer, as well as the corresponding rectification factors which clearly illustrate the asymmetry between left and right propagation in such systems. We examine not only the existence but also the dynamical stability of the plane wave states and interestingly find them to be unstable except in the vicinity of the linear limit. Lastly, we generalize our numerical considerations to the more physically relevant case of Gaussian initial wavepackets and confirm that the asymmetry in the transmission properties persists in the case of such wavepackets, as well. The role of potential asymmetries in the nonlinearity or in the gain/loss pattern is also considered.This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Quantum physics with non-Hermitian operators’.

Sign Reversal of Junction Magnetoresistance in p-La0.7Ca0.3MnO3/SiO2/n-Si Heterostructure: A Possibility in Spintronics Application

We have fabricated a p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure, consisting of a p-type manganite (La0.7Ca0.3MnO3) and n-type Si with a interfacial layer of SiO2 with typical thickness of about 9 nm using pulsed laser deposition technique. The junction exhibits rectifying behavior over the temperature range of 10-300 K with rectification factor 52 at room temperature. Investigation on the electrical properties of p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure exhibits nonlinear J-V characteristics in a wide temperature range. A crossover from negative to positive junction magnetoresistance (JMR) is observed in p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure in current perpendicular to film plane (CPP) geometry. The temperature dependent sign of junction magnetoresistance of the heterojunction has been investigated carefully in details. It is found that the junction exhibits the positive junction magnetoresistance when the temperature is greater than the ferromagnetic to paramagnetic transition temperature (Tc) of the top highly spin-polarized half-metallic ferromagnetic La0.7Ca0.3MnO3 manganite film layer. The relation between junction magnetoresistance and external magnetic field is found to be of (delta rho/rho approximately equal alphaHbeta) type having both alpha and beta temperature dependent. We attribute the emergence of negative JMR at lower temperature (< Tc) and positive JMR at higher temperature (> Tc) to the quantum mechanical tunneling transport mechanism across the heterojunction. Our results might be very useful to fabricate artificial devices using the manganite-based heterojunction grown on single crystalline n-Si (100) in spintronics device applications.

Molecular Architecture and Electrical Properties in Evaporated Films of Cobalt Phthalocyanine

Thin films of cobalt phthalocyanine (CoPc) were deposited onto solid substrates through physical vapor deposition (PVD) by thermal evaporation up to 60 nm thick to determine their molecular architecture and electrical properties. The growth was monitored using UV-Vis absorption spectroscopy, revealing a linear increase for absorbance versus thickness. PVD films were found in the crystalline alpha phase and with the CoPc molecules forming ca. 45 degrees in relation to the substrate surface. The film surface was fairly homogeneous at the micro and nanoscales, with the roughness at ca. 3 nm. DC and AC electrical measurements were carried out for devices built with distinct structures. Perpendicular contact was established by depositing 60 nm CoPc PVD films between indium tin oxide (ITO) and Al, forming a sandwich-type structure (ITO/CoPc/Al). The current versus DC voltage curve indicated a Schottky diode behavior with a rectification factor of 4.2. The AC conductivity at low frequencies increased about 2 orders of magnitude (10(-9) to 10(-7) S/m) with increasing DC bias (0 to 5 V) and the dielectric constant at 1 kHz was 3.45. The parallel contact was obtained by depositing 120 nm CoPc PVD film onto interdigitated electrodes, forming an IDE-structured device. The latter presented a DC conductivity of 5.5 x 10(-10) S/m while the AC conductivity varied from 10(-9) to 10(-1) S/m between 1 Hz and 1 MHz, respectively, presenting no dependence on DC bias. As proof-of-principle, the IDE-structured device was applied as gas sensor for trifluoroacetic acid (TFA).

Optical and current transport properties of CuO/ZnO nanocoral p–n heterostructure hydrothermally synthesized at low temperature

We demonstrate the synthesis and investigate the electrical and optical characteristics of ‘nanocorals’ (NCs) composed of CuO/ZnO grown at low temperature through the hydrothermal approach. High-density CuO nanostructures (NSs) were selectively grown on ZnO nanorods (NRs). The synthesized NCs were used to fabricate p–n heterojunctions that were investigated by the current density–voltage (J–V) and the capacitance–voltage (C–V) techniques. It was found that the NC heterojunctions exhibit a well-defined diode behavior with a threshold voltage of about 1.52 V and relatively high rectification factor of ∼760. The detailed forward J–V characteristics revealed that the current transport is controlled by an ohmic behavior for V≤0.15 V, whereas at moderate voltages 1.46≤V<1.5 the current follows a J α exp(βV) relationship. At higher voltages (≥1.5 V) the current follows the relation J α V2, indicating that the space-charge-limited current mechanism is the dominant current transport. The C–V measurement indicated that the NC diode has an abrupt junction. The grown CuO/ZnO NCs exhibited a broad light absorption range that is covering the UV and the entire visible parts of the spectrum.

NiO cathodic electrochemical deposition from an aprotic ionic liquid: Building metal oxide n–p heterojunctions

NiO thin films have been successfully deposited by cathodic electrochemical deposition in N-butyl-N-methylpyrrolidinium bis(trifloromethanesulfonyl)imide room temperature ionic liquid (IL), giving an unambiguous proof of concept of the metal oxide electrodeposition in aprotic ILs without metal hydroxide formation as an intermediate phase. The electrochemical phenomena involved in the deposition process have been analyzed by cyclic voltammetry, pointing out that the electrochemical reduction of Ni2+ may be quenched in oxygenated IL electrolytes. The physico-chemical properties of the obtained NiO thin films have been characterized by electron scanning and atomic force microscopies, X-ray diffraction and Fourier transform infrared X-ray photo-electron spectroscopies. By taking advantage of the present electrodeposition route, ZnO/NiO heterostructures have been built. The current density-voltage characteristic of the resulting device exhibits clear rectifying behavior, with a rectification factor of 3×103 at V=±1V. This result anticipates a significant potential of the present electrochemical route in the metal oxide electronics.

Thermal rectification in thickness-asymmetric graphene nanoribbons

Thermal rectification in thickness asymmetric graphene nanoribbons connecting single-layer with multi-layer graphene is investigated by using classical nonequilibrium molecular dynamics. It is reported that the graphene nanoribbons with thickness-asymmetry have a good thermal rectification. The thermal rectification factor depends on temperature as well as the thickness-ratio of the two-segment. Our results provide a direct evidence that the thermal rectifier can be achieved in a nanostructure crossing two- and three-dimension.

Studies on device properties of an n-AgIn5Se8/p-Si heterojunction diode

In this study, polycrystalline thin films of ternary AgIn5Se8 compounds with n-type conductivity were deposited on p-type Si substrates from the powder of a Ag3In5Se9 single crystal by a thermal evaporation technique. Transport and photo-transport properties of the In/n-AgIn5Se8/p-Si/Al sandwich structure were investigated by analyzing temperature-dependent dc current–voltage (I–V), and photo-response measurements carried out in the temperature range of 200–360 K. In order to obtain the series resistance (Rs) and shunt resistance (Rsh) values, the parasitic resistance (Rp = ∂V/∂I) was analyzed for forward and reverse voltages. Devices showed very good diode behavior with the rectification factor of about 104 at 1.0 V in dark. The ideality factor n and the barrier height ϕb values of the heterojunction diode were determined by performing different I–V plots. A space charge limited current method was used to determine the conduction mechanism at a high bias region. Spectral photo-response analyses showed a shifting of the band edge to the lower energies with increasing temperature.

First-Principles Study of Rectification in Bis-2-(5-ethynylthienyl)ethyne Molecular Junctions

Using density functional theory (DFT) combined with the first-principles nonequilibrium Green's function (NEGF), we investigated the electron-transport properties and rectifying behaviors of several molecular junctions based on the bis-2-(5-ethynylthienyl)ethyne (BETE) molecule. To examine the roles of different rectification factors, asymmetric electrode-molecule contacts and donor-acceptor substituent groups were introduced into the BETE-based molecular junction. The asymmetric current-voltage characteristics were obtained for the molecular junctions containing asymmetric contacts and donor-acceptor groups. In our models, the computed rectification ratios show that the mode of electrode-molecule contacts plays a crucial role in rectification and that the rectifying effect is not enhanced significantly by introducing the additional donor-acceptor components for the molecular rectifier with asymmetric electrode-molecule contacts. The current-voltage characteristics and rectifying behaviors are discussed in terms of transmission spectra, molecular projected self-consistent Hamiltonian (MPSH) states, and energy levels of MPSH states.

The Role of MS and MIS Devices in Characterization of Electrodeposited ZnO:Ga Films

Thin films of ZnO were electrodeposited on flexible stainless steel (SS) substrate from a Ga-containing solution. The films morphology, structure, and photoluminescence properties are briefly discussed. For the electrical characterization of the films, metal–semiconductor (MS), and metal–insulator–semiconductor (MIS) devices of type and were fabricated and their parameters were determined by the means of current–voltage and capacitance–voltage measurements. Devices with a reasonably good built-in potential, barrier height, and rectification factor were achieved, and the concentration of donors, , in the films was evaluated. Results revealed that increases from by annealing the films in oxygen at . Furthermore, it was observed that the hydrogen peroxide treatment of the films lowers the value by a factor of 10–100 and yields a large electron mobility.

Interface state density of free-standing GaN Schottky diodes

Schottky diodes were fabricated on the HVPE-grown, free-standing gallium nitride (GaN) layers of n- and p-types. Both contacts (ohmic and Schottky) were deposited on the top surface using Al/Ti and Pd/Ti/Au, respectively. The Schottky diode fabricated on n-GaN exhibited double barriers with values of 0.9 and 0.6 eV and better performance in the rectification factor together with reverse and forward currents with an ideality factor of 1.8. The barrier height for the p-GaN Schottky diode is 0.6 eV with an ideality factor of 4.16. From the capacitance–voltage (C–V) measurement, the net doping concentration of n-GaN is 4 × 1017 cm−3, resulting in a lower reverse breakdown of around −12 V. The interface state density (NSS) as a function of EC−ESS is found to be in the range 4.23 × 1012–3.87 × 1011 eV−1 cm−2 (below the conduction band) from Ec-0.90 to EC-0.99. Possible reasons responsible for the low barrier height and high ideality factor have been addressed.

Nonadiabatic corrections to the velocity of a Brownian motor with a complex potential profile

A number of laws have been established that govern the motion of a Brownian particle in a periodic potential profile for the adiabatically fast (with the time τ0) and adiabatically slow variations in its shape. The average velocity of a particle has been calculated including a nonadiabatic contribution depending on τ0 and the characteristic times of the system, which are determined by the characteristic features of the potential profile. It has been shown that the nonadiabatic correction to the velocity is proportional to τ 0 2 for a smooth potential profile and to τ0 for a hopping movement in a potential containing barriers and wells, and this correction limits the large values of the rectification factor of motion for a high-performance motor operation mode.

Structural, optical, and electrical properties of n‐ZnO/p‐GaAs heterojunction

Abstractn‐ZnO film grown by electrodeposition (ECD) on p‐GaAs substrate was characterized by structural, optical, and electrical techniques. X‐ray diffraction (XRD) measurement clearly showed formation of ZnO thin film with a strong c‐axis (0002) preferential orientation. Photoluminescence (PL) measurements showed that the grown film has a strong and narrow ultraviolet (UV) emission indicating high‐quality ZnO thin film. Current–voltage (I–V) measurement of n‐ZnO/p‐GaAs heterojunction shows diode‐like rectifying characteristics with an almost five‐order rectification factor and a turn‐on voltage of 2 V.

Achieving a Stable Time Response in Polymeric Radiation Sensors under Charge Injection by X-rays

Existing inorganic materials for radiation sensors suffer from several drawbacks, including their inability to cover large curved areas, lack of tissue-equivalence, toxicity, and mechanical inflexibility. As an alternative to inorganics, poly(triarylamine) (PTAA) diodes have been evaluated for their suitability for detecting radiation via the direct creation of X-ray induced photocurrents. A single layer of PTAA is deposited on indium tin oxide (ITO) substrates, with top electrodes selected from Al, Au, Ni, and Pd. The choice of metal electrode has a pronounced effect on the performance of the device; there is a direct correlation between the diode rectification factor and the metal-PTAA barrier height. A diode with an Al contact shows the highest quality of rectifying junction, and it produces a high X-ray photocurrent (several nA) that is stable during continuous exposure to 50 kV Mo Kalpha X-radiation over long time scales, combined with a high signal-to-noise ratio with fast response times of less than 0.25 s. Diodes with a low band gap, 'Ohmic' contact, such as ITO/PTAA/Au, show a slow transient response. This result can be explained by the build-up of space charge at the metal-PTAA interface, caused by a high level of charge injection due to X-ray-induced carriers. These data provide new insights into the optimum selection of metals for Schottky contacts on organic materials, with wider applications in light sensors and photovoltaic devices.

Customer Care Management Model for Service Industry

Purpose – This paper describes a model for Customer care management in an automotive service industry. Design/ methodology/approach – Customer care management (CCM) model is developed using TQM techniques, Quality Function Deployment (QFD) and Six Sigma. The matrix structure in QFD is used to transform customer complaints into Critical-to-Quality (CTQ) parameters. By using Six Sigma DMAIC approach, the customer complaint parameters are analyzed for improvement. Findings – The application of CCM model in an automobile service industry has determined that the workload planning is the chronic problem for customer complaint. Further analysis through this model leads to restructuring of existing workload planning practice through a set of algorithms. Research limitations/impli- cations – CCM model lacks to accommodate the effect of relationship between rectification factors. Also competitor technical contemplation is not possible in this model. Originality/value – Customer is the focal point and early response to their complaint is the key to success of every business. This paper has developed a structured complaint management practice which warrants the timely response to customer complaints and speedy resolution for survival in today’s customer driven market.

Electroosmotic Flow Can Generate Ion Current Rectification in Nano- and Micropores

This paper introduces a strategy for generating ion current rectification through nano- and micropores. This method generates ion current rectification by electroosmotic-driven flow of liquids of varying viscosity (and hence varying conductance) into or out of the narrowest constriction of a pore. The magnitude of current rectification was described by a rectification factor, R(f), which is defined by the ratio of the current measured at a positive voltage divided by the current measured at a negative voltage. This method achieved rectification factors in the range of 5-15 using pores with diameters ranging from 10 nm to 2.2 microm. These R(f) values are similar to the rectification factors reported in other nanopore-based methods that did not employ segmented surface charges. Interestingly, this work showed that in cylindrical nanopores with diameters of 10 nm and a length of at least 275 nm, electroosmotic flow was present and could generate ion current rectification. Unlike previous methods for generating ion current rectification that require nanopores with diameters comparable to the Debye length, this work demonstrated ion current rectification in micropores with diameters 500 times larger than the Debye length. Thus this method extends the concept of fluidic diodes to the micropore range. Several experiments designed to alter or remove electroosmotic flow through the pore demonstrated that electroosmotic flow was required for the mode of ion current rectification reported here. Consequently, the magnitude of current rectification could be used to indicate the presence of electroosmotic flow and the breakdown of electroosmotic flow with decreasing ionic strength and hence increasing electric double layer overlap inside nanopores.