Dependent Resistance Change Research Articles

Bending, electroadhesion and sensing performances of single compliant electrode dielectric elastomer actuator based on SEBS gel

Dielectric elastomer actuators (DEAs) have great potential for application in soft robotics due to their ability to undergo substantial deformations, rapid response times, and high energy density when subjected to external electrical stimuli. However, the application of DEAs in the field of soft grippers is limited by their restricted direct electro-bending capability, output force, self-sensing capacity, and pre-stretching requirement. In this study, we fabricated a single compliant electrode DEA (SCE-DEA) which was made by sandwiching a compliant electrode between two layers of poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS)/white mineral oil (WO) dielectric elastomer films. The SCE-SEBS/WO was demonstrated to have the capacities of bending, sensing, and electroadhesion (EA). The SCE-SEBS/WO can be used in various soft actuator modes, such as the unipolar EA actuator, soft gripper, and soft vibrator. The grabbing mechanism of SCE-SEBS/WO-based soft grippers with opposite bipolar configuration is caused by electric field induced bending of SEC-SEBS/WO and subsequent electrostatic attraction between both SEC-SEBS/WO. The SEC-SEBS/WO based soft grippers have rapid response detachment, and ability to grasp various types of objects. Three-layer stacked SCE-SEBS/WO-60 (with 60 wt% of WO) exhibited 531 mN cm−2 of EA stress on the paper at 3.0 kV applied voltage, and the soft gripper made by four SCE-SEBS/WO-60 can successfully grab wood blocks weighing 162.4 g at 5 kV applied voltage. The sensing capacity of SCE-SEBS/WO based soft gripper was based on the bending strain dependent resistance changes of the compliant electrode. Our results provide new insights into the fabrication of DEA based soft grippers.

Designing dynamic metal-coordinated hydrophobically associated mechanically robust and stretchable hydrogels for versatile, multifunctional applications in strain sensing, actuation and flexible supercapacitors

Combining the synergistic effect of dynamic metal–ligand cross-linking and hydrophobic association along with low density chemical cross-linking, we have developed a mechanically robust and stretchable hydrogel that was synthesized by micellar copolymerization of acrylamide (AM), maleic acid (MA) and butyl acrylate monomer. With optimized composition, this hydrogel showed ∼ 3 MPa tensile strength & ∼ 60 MPa compressive strength. The hydrogel is stretchable ∼ 7 times of its original length. These hydrogel materials are flexible and can be folded, bent, and twisted due to their high toughness (∼10 MJ m−3) and low elastic modulus (0.56 MPa). Because of the dynamic nature of metal–ligand interaction and hydrophobic association, the hydrogel showed high energy dissipation under tensile deformation and quick recovery of the dissipated energy after repeated loading and unloading. This hydrogel showed pH responsive mechanical properties. At lower pH, the mechanical strength and elastic modulus of the hydrogel deteriorated due to the dissociation of metal–ligand interaction. This concept was further used for demonstrating shape memory effect in these materials. Utilizing the colorimetric change in presence of Fe3+ and H+, the hydrogel can be used for data encryption-decryption technology. Combining with a thermoresponsive hydrogel (Poly (N-Isopropyl acrylamide)) layer, our hydrogel showed excellent thermoresponsive reversible actuation effect. Furthermore, because of its high ionic conductivity and strain dependent resistance change, the hydrogel can be used as a flexible strain sensor and as a compressible electrolyte in flexible supercapacitor devices.

Oxygen-Sensitive Layered MoTe2 Channels for Environmental Detection.

The oxygen (O2)-dependent resistance change of multilayered molybdenum ditelluride (MoTe2) channels was characterized. A variation of the channel resistance could reproducibly determine relative O2 content (denoted as the O2 index). We found that Joule heating in a layered MoTe2 field-effect transistor caused the O2 index to decrease drastically from 100 to 12.1% in back gate modulation. Furthermore, Joule heating caused effective O2 desorption from the MoTe2 surface and repeatable O2 detection by multilayered MoTe2 channels was realized. This work not only explored the influence of O2 on the electrical properties of multilayered MoTe2 channels but also revealed that MoTe2 channels are promising for sensing O2 in an environmental condition.

Influence of MoS2 quantum dots size on the properties of memristor devices

In this report we successful synthesized MoS2 QDs with different size using 1-Dodecanethiol as sulfur source by one pot method. The X-ray diffraction pattern confirmed the formation of hexagonal MoS2, whereas the transmission electron microscopic analysis established the growth of zero dimension morphology MoS2 QDs with the reaction temperature. The Fourier transforms infrared spectroscopy and X-ray photoelectron spectroscopy proved that the surfaces of MoS2 QDs were coated by thiol and 2H phase MoS2 were formed. Generally, memristor devices have two states (ON state and OFF state) at the same voltage due to voltage dependent resistance change, which properties can be used for storing information. In this paper, a memristor devices with ITO/PEDOT:PSS /MoS2& PVA/Al structure was prepared and the influence of MoS2 QDs size on the electrical properties of as-prepared devices was investigated. The results indicated that the properties of memristor based on MoS2 QDs can be modulated by the technology parameters of MoS2 QDs.

Design of spin-injection-layer in all-in-plane spin-torque-oscillator for microwave assisted magnetic recording

Abstract A new type of spin-torque-oscillator (STO), all-in-plane STO, is introduced for microwave assisted magnetic recording (MAMR) that consist of a spin-injection-layer (SIL) and a field-generating-layer (FGL) with an effective in-plane easy axis due to the shape anisotropy separated with a metallic spacer. In this device, electrons are injected from SIL to FGL while the magnetization of the SIL and FGL is saturated to the out-of-plane by the external magnetic field of ∼1.0 T. Micromagnetic simulations showed that the magnetization direction of SIL can be switched to the opposite direction to that of the applied external magnetic field by the use of spin-transfer-torque. This results in a larger spin accumulation in FGL and its oscillation with a large cone angle at a low bias current density. We designed SIL to reduce the critical current density, Jc, required for the magnetization switching of SIL. Materials with a smaller saturation magnetization in SIL reduce Jc. Smaller spin polarization of SIL leads to a larger spin accumulation in SIL with an opposite direction to the magnetization, resulting in a reduction of Jc. This enables magnetization switching of SIL in small Jc followed by oscillation of FGL with frequency above 20 GHz with a large out-of-plane oscillation cone angle of 45–50°. The validity of this finding was studied experimentally by developing STO with two SIL materials, Co2Fe(Al0.5Si0.5) Heusler alloy and Fe67Co33, the former has the B2 crystal structure with a large spin polarization and the latter has the A2 crystal structure with a smaller spin polarization. The magnetization configuration of SIL and FGL in STO with a diameter of ∼60 nm is investigated experimentally based on the field dependent resistance change and the oscillation behavior is discussed based on the micromagnetic simulations.

Humidity sensing properties of fluorine doped zinc oxide thin films

In this study, the effect of fluorine (F) doping on the humidity sensing properties of F doped zinc oxide structures was investigated. Undoped zinc oxide (ZnO) and F doped zinc oxide (FZO) nanoparticles were synthesized by sol gel method. The synthesized nanoparticles were coated on glass substrates by dip coating method. In the coating process, the glass substrates were immersed in undoped ZnO and FZO solutions and withdrawn at a rate of 25 cm/s at room temperature. Then, the thin film coated glasses are annealed in a square furnace at 500 °C for 1 h. Structural analyzes of the produced thin films were performed using X-ray diffraction and scanning electron microscopy. The thin film nanostructures were placed in the homemade system in order to investigate the humidity sensing characteristics such as relative humidity dependent resistance change, sensitivity, hysteresis, stability, response and recovery times and reproducibility. As a result, it is predicted that the FZO structures can be used in the humidity sensing applications and it is determined that the optimal F additive amount for application is 2 mol%.

A self-consistent spin-diffusion model for micromagnetics.

We propose a three-dimensional micromagnetic model that dynamically solves the Landau-Lifshitz-Gilbert equation coupled to the full spin-diffusion equation. In contrast to previous methods, we solve for the magnetization dynamics and the electric potential in a self-consistent fashion. This treatment allows for an accurate description of magnetization dependent resistance changes. Moreover, the presented algorithm describes both spin accumulation due to smooth magnetization transitions and due to material interfaces as in multilayer structures. The model and its finite-element implementation are validated by current driven motion of a magnetic vortex structure. In a second experiment, the resistivity of a magnetic multilayer structure in dependence of the tilting angle of the magnetization in the different layers is investigated. Both examples show good agreement with reference simulations and experiments respectively.

UV–VIS sensor system based on SnO2 nanowires

We demonstrate the application of low density SnO2 nanowire mats in a complete UV–VIS sensor system. Ultra long nanowires were grown the first time on ‘black silicon’ substrates by high temperature condensation, yielding high quantity and quality. Compared to other metal oxides like ZnO, fast response times of under 1s and recovery times of 10s at room temperature were observed. Wavelength and power dependent resistance changes are determined. High sensitivity is achieved for UV radiation below 400nm which already gives a response S=1−Ron/Roff to be about 92% at 2.7mW/cm2.

A highly sensitive, label-free gene sensor based on a single conducting polymer nanowire

A prerequisite for exploiting sensing devices based on semiconductor nanowires is ultra-sensitive and selective direct electrical detection of biological and chemical species. Here, we constructed a transducer based on copolymer of poly(3,4,-ethylenedioxythiophene) (PEDOT) and carboxylic group functionalised PEDOT single nanowire in between gold electrodes, followed by covalent attachment of amino-modified probe oligonucleotide. The target ODNs specific to Homo sapiens Breast and ovarian cancer cells were detected at femtomolar concentration and incorporation of negative controls (non-complementary ODN) were clearly discriminated by the sensor. The ex situ measurements were performed by using two terminal device setup and the changes in the interface of the nanowire associated with the association or dissociation of ODNs were measured as change in resistance. In addition, in situ measurements were performed by utilizing scanning ion conductance microscopy to measure the change in resistance of probe modified nanowire upon addition of different concentration of target ODNs in presence of relevant buffer. The constructed, nano sensor showed highly sensitive concentration dependent resistance change.

Effect of Anisotropy Influences on the Angle Dependent Resistance Changes in IrMn Spin-Valves

Giant magneto-resistance (GMR) effect in a spin-valve has a uni-directional or cosine dependence when rotated in an applied magnetic field; however, anisotropy effects cause deviations from this cosine dependence. The influence of uniaxial anisotropy in the free layer and Anisotropic Magneto-Resistance (AMR) were studied on the angle dependent resistance changes in IrMn spin-valves. The uniaxial anisotropy component was analyzed by changing the anisotropy axis from parallel to perpendicular to the bias direction in different sample sets. The deviation due to AMR was determined by changing the current direction from parallel to perpendicular to the bias direction in separate rotation measurements. The results indicated that the uniaxial anisotropy had no influence on the angle dependent resistance change while AMR added a cosine-squared resistance signal to the overall resistance change. A discrepancy between experiment and theory of the AMR influence was seen with use of a simple simulation. Ferromagnetic interlayer coupling is identified as a possible cause for this difference between theory and experiment.

The Transmission Properties of Quantum Dots at High Magnetic Fields

We have fabricated quantum dot structures in GaAs/AlGaAs heterostructures using metallic surface gates defined by electron beam lithography and lift-off. Electrical transport measurements were performed on the dots at low temperatures (10 mK-1.5 K) and in magnetic fields of up to 8 T. Here we discuss the experimental characteristics of the devices, which include the observation of time dependent resistance changes at fixed gate voltage as well as a hysteresis in the resistance as the gate voltage is swept in different directions. These results demonstrate the influence of the dynamical nature of individual defects, charged states, or impurities, on the device behaviour. The corresponding magnetoresistance was found to show resonant peaks on the quantum Hall plateaus. Once the magnetoresistance exceeded the quantum resistance (h/e2), however, periodic oscillations were observed in the magnetoresistance. We discuss these observations with respect to the scattering between different edge states, as well as Coulomb blockade effects, in high magnetic fields.

Changes in AC and DC Resistance in Aluminum Interconnection under Electromigration Condition.

Small-signal AC resistance and DC resistance of evaporated pure Al interconnection were measured under the DC current stress which envokes electromigration. AC resistance weakly depends on frequency and increases as the frequency is lowered. This is compared with the fluctuation phenomenon in thin metal films which has been observed in flicker noise studies. Time dependent resistance change can be analized by the model of nucleation and growth of the voids in a metal film. Observed drop and preceding oscillaion in resistance can be interpreted as the evidence of the condensation of void nuclei and their phase transition into a macroscopic void.

Time dependent resistance changes in a narrow AlGaAs-GaAs wire

We have observed time dependent resistance changes in a narrow wire of AlGaAs-GaAs double hetero structure at low temperatures. There are two types of temporal changes of the resistance. Universal conductance fluctuations are also observed in the same wire. We ascribe the observed time-dependence to defect states in the hetero-interface.