Diode-like Structures Research Articles

Guided fractures in graphene mechanical diode-like structures.

The concept of a diode is usually applied to electronic and thermal devices but very rarely for mechanical ones. A recently proposed fracture rectification effect in polymer-based structures with triangular void defects has motivated us to test these ideas at the nanoscale using graphene membranes. Using fully-atomistic reactive molecular dynamics simulations we showed that robust rectification-like effects exist. The fracture can be 'guided' to more easily propagate along one specific direction than its opposite. We also observed that there is an optimal value for the spacing between each void for the rectification effect.

Directional shock diode behavior through the interaction of geometric voids in engineered polymer assemblies

With the advent of additive manufacturing (AM) techniques, a new class of shockwave mitigation and structural supports has been realized through the hierarchical assembly of polymer materials. To date, there have been a limited number of studies investigating the role of structure on shockwave localization and whether AM offers a means to tailor shockwave behavior. Of particular interest is whether the mesoscopic structure can be tailored to achieve shockwave properties in one direction of impact vs the other. Here, we illustrate directional response in engineered polymer foams. In situ time-resolved x-ray phase contrast imaging at the Advanced Photon Source was used to characterize these diode-like structures. This work offers a breakthrough in materials technology for the development of protective structures that require augmentation of shock in one direction while diminishing transmission in the opposite direction.

Hybrids of Nickel-histidine Functionalized Graphene Quantum Dots: Fabrication and Non-enzymatic Glucose Sensing

In this work, a method of in-situ recombination of Ni2+ with histidine functionalized graphene quantum dots (His-GQDs) was constructed a three-dimensional network porous structure. The collected precipitate complex precursor was oxidized and the NiO-His-GODs were obtained. The NiO-His-GQDs compound was subjected to high-temperature thermal reduction by inert gas to form Ni-His-GQDs. On the one hand, the intimate contact between Ni nanoparticles and His-GQD greatly shortens the gap between the two complexes, resulting in faster electron migration speed; On the other hand, the conductive (Ni)/semiconductor (His-GQDs) catalytic interface can produce Stokes diode-like structures, accelerate the migration rate of holes carriers in the semiconductor, and exhibit good electrocatalytic activity. A Ni-His-GQDs modified electrode as non-enzymatic glucose electrochemical sensor was shown good electrocatalytic activity and anti-interference property. The concentration of glucose was detected by amperometric analysis, and showed a good linear relation in the concentration range of 5.0 × 10-6∼2.0 × 10-3 M. The detection limit (S/N = 3) is 1.7 × 10−6 M. In addition, interference of sodium chloride (NaCl), uric acid (UA), dopamine (DA) and ascorbic acid (AA) was less than 5.0 % in the same conditions indicating that the hybrids modified electrode sensor could be used for the sensitive and selective detection of glucose.

Ion-Liquid Based Supercapacitors with Inner Gate Diode-Like Separators

In order to minimize unintentional discharge, supercapacitors are interfaced with a membrane that separates the anode from the cathode—this membrane is called the separator. We focus here on separators, which are structured as electronic diode-like. We call an electrically structured separator “the gate”. Through experiments, it was demonstrated that ionic liquid-filled supercapacitors, which were interfaced with gated separators exhibited a substantial capacitance (C) increase and reduction in the equivalent series resistance (ESR) compared to cells with ordinary separators. These two attributes help to increase the energy, which is stored in a cell, since for a given cell’s voltage, the dissipated energy on the cell, UR = V2/4(ESR) and the stored energy, UC = CV2/2, would increase. These were indeed ionic diodes since the order of the diode layout mattered—the diode-like structures exhibited maximum capacitance when their p-side faced the auxiliary electrode.

Investigation of Traps in Thin-Film Organic Semiconductors Using Differential Analysis of Steady-State Current–Voltage Characteristics

A study of traps in thin organic semiconductor films is described through the analysis of their impact on current voltage ( ${J}-{V}$ ) characteristics of two terminal diode-like structures. The ${J}-{V}$ characteristics follow a power law whose exponent exhibits voltage dependence as a result of change in trap occupancy with applied voltage. A method of analysis of ${J}-{V}$ characteristics using the product of differential resistance and current is described which enables different unique regions of device characteristics to be visually delineated and facilitates extraction of threshold voltage, marking onset of trap-filled regime. Simulation results are presented to validate and highlight the usefulness of the proposed concepts and techniques. The experimental results obtained with polymers P3HT, blend of P3HT with phenyl C61 butyric acid methyl ester, and small molecule pentacene organic semiconductor are used to illustrate the insight offered by the proposed method. Both simulation and experimental results indicate that analysis based on double-log plots may lead to large overestimation of voltage marking onset of trap-filled regime.

Supramolecular Organization-Electrical Properties Relation in Nanometric Organic Films

The need to improve the performance of electronic devices based on organic materials has been at the center of structure–property relation research, where the main objective is to develop low cost and flexible electronic components in large-scale. Important contributions to the performance of such devices have been made based on studies of the supramolecular organization of small organic molecules, primarily those with π-conjugated systems. Here we examine the relationship of supramolecular organization and the electrical properties of a substituted perylene tetracarboxylic diimido in nanometric films fabricated by physical vapor deposition (PVD). The morphology of the thin solid films is probed with optical and electron microscopy and the supramolecular characterization includes vibrational and electronic spectroscopies. The electrical properties are studied using AC and DC measurements with interdigitated electrodes and diode-like structures. A higher conductivity is observed when measured with the diod...

Multiple Diode-Like Conduction in Resistive Switching SiO<italic><sub>x</sub></italic>-Based MIM Devices

Filamentary conduction in resistive switching metal- insulator-metal devices is often modeled from the circuital viewpoint using diode-like structures with series resistances. We show in this letter which arrangement of diodes and resistances is compatible with experimental multilevel set and reset I-V characteristics in electroformed TiN/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /TiN structures. The proposed model is based on the solution of the generalized diode equation corresponding to N diodes arranged in parallel with a single series resistance. The model is simple yet accurate and it is able to capture the essential features exhibited by the I-V curves in the low and high bias regimes, revealing that a single equation can deal with both the low and high resistance states. An exact expression for the differential conductance suitable for small-signal analysis and circuit simulators is also provided.

Electrically tunable electron spin lifetimes in GaAs(111)B quantum wells

We investigate the electric tunability of the electron spin lifetime in GaAs(111) quantum wells (QWs) inserted in biased p-i-n and n-i-p diode-like structures. Due to the specific symmetry of these QWs, the Rashba contribution to the spin-orbit magnetic field induced by the applied bias is parallel to the intrinsic Dresselhaus contribution for all directions of the electron wavevector. In particular, the voltage applied to the diode, which controls the amplitude of the Rashba contribution, can be adjusted to attenuate the resulting spin-orbit field, thus strongly suppressing spin dephasing due to the Dyakonov-Perel relaxation mechanism for all spin orientations. Spin lifetimes from below 100 ps at an electric field of −20 kV/cm to values exceeding 4 ns at +8 kV/cm have been measured in 25 nm thick multiple QWs at a temperature of 20 K.

Conduction mechanisms in porous Si LEDs

Abstract Diode-like structures were prepared from p- and n-type Si, in which porous Si layers were sandwiched between the crystalline Si and the evaporated Al top contact. The current–voltage characteristics were investigated in that bias polarity, at which electroluminescence occurs. It was found that the characteristics follow the Fowler–Nordheim tunneling process for both type of devices. The tunneling occurs through the heterojunction barrier at the crystalline-porous interface. The leakage current experienced at low biases in the p-type structure is attributed to trap-assisted tunneling; its saturation character was pointed out by low-frequency noise measurements.

Low resistance high reflectance contacts to p-GaN using oxidized Ni/Au and Al or Ag

We report on a high reflectance low resistance multilayer contact to p-GaN composed of a thin oxidized Ni/Au bilayer overcoated with a thick Al or Ag layer and then capped by Ni/Au. Measurements on 500 μm diameter light emitting diode-like test structures show an operating voltage below 4 V at 20 mA that is comparable to identical devices fabricated with a conventional Ni/Au contact. Back surface light emission is about 70% greater than that from devices with the Ni/Au contact due to lower light absorption by the Al or Ag. Performance for both Al and Ag based contacts is stable at temperatures of up to around 100 °C.