Applied Ac Bias Research Articles

Water Washable and Flexible Light-Emitting Fibers Based on Electrochemiluminescent Gels.

Herein, a new concept of device architecture to fabricate fibrous light-emitting devices is demonstrated based on an electrochemiluminescence (ECL) material for an electronic textile system. A unique feature of this work is that instead of conventional semiconductor materials, such as organics, perovskites, and quantum dots for fibrous light emitting devices, a solid-state ECL electrolyte gel is employed as a light-emitting layer. The solid-state ECL gel is prepared from a precursor solution composed of matrix polymer, ionic liquid, and ECL luminophore. From this, we successfully realize light-emitting fibers through a simple and cost-effective single-step dip-coating method in ambient air, without complicated multistep vacuum processes. The resulting fiber devices reliably operated under applied AC bias of ±2.5 V and showed luminance of 47 cd m-2. More importantly, the light-emitting fibers exhibited outstanding water resistance without any passivation layers, owing to the water immiscible and hydrophobic nature of the ECL gel. In addition, because of their simple structure, the fiber devices can be easily deformed and woven together with commercial knitwear by hand. Therefore, these results suggest a promising strategy for the development of practical fiber displays and contribute to progress in electronic textile technology.

Spiral Waves in a Lattice Array of Josephson Junction Chaotic Oscillators with Flux Effects

Josephson junction devices play a significant role in various physical nonlinear systems because of their complex characteristics. Chaotic phenomenon in various types of Josephson junction devices has been widely reported, but many of those literature studies exempted the analysis into multistability and megastability features of the device. In this work, we investigate the network behaviour using a type of Josephson junction-memristor (JJM) device considering the feedback flux effects while modelling. We have considered both AC- and DC-type external excitation currents, and while considering the AC excitation, the system shows megastability (Ramakrishnan et al. 2020). When analysing the lattice layer network constructed with JJM excited by DC bias current, the network shows a turbulent behaviour thus forming spiral waves. This was not the case when we applied AC bias current for which the network showed a much pattern-like formation confirming localised areas of energy distribution. This energy distribution is due to the homogeneous states of the local nodes which are correlated by the respective periodicity plots. When we apply AC bias current with very low frequency, the network shows small areas of local spirals which are soon dissipated by the inhomogeneous nodes nearby. Thus, we could show that the external bias current plays an important role in the collective performance of the Josephson junction devices.

Design and Experimental Verification of a Liquid Crystal-Based Terahertz Phase Shifter for Reconfigurable Reflectarrays

A liquid crystal (LC)-based double dipole terahertz phase shifter is proposed. The block model is utilized in simulations to analysis the influence of inhomogeneity of the LC substrate. The sensitive parameters of the double dipole are simulated and analyzed. An array consisting of 30 × 30 patch elements is designed and fabricated. Experimental results exhibit that the phase shift is over 360° in the range of 355.8–358.8 GHz at 1 kHz, at an applied AC bias in the 0–50 V range. The phase change at different frequencies of AC bias voltage is also investigated, and the effect of the frequency of AC bias voltage is expressed by the coefficient of the amplitude of the bias voltage.

Synthetic antiferromagnet-based spin Josephson oscillator

Two easy-plane ferromagnetic layers, antiferromagnetically coupled through a thin nonmagnetic metal layer, form the magnetic analog of a Josephson junction. A current driven spin chemical potential drives a 2π precession of the in-plane magnetization of each ferromagnet. The participation of the full magnetic moment in the 2π precession maximizes the giant magnetoresistance and the ac output power. The frequency can be continuously tuned by a dc bias. An applied ac bias results in a time-averaged magnetoresistance with Shapiro-like steps. The multistate mode-locking behavior exhibited by the Shapiro steps may be exploited for applications such as microwave detectors and neuromorphic computing. They may also serve as an experimental signature of spin superfluidity.

Distinctive translational and self-rotational motion of lymphoma cells in an optically induced non-rotational alternating current electric field.

In this paper, the translational motion and self-rotational behaviors of the Raji cells, a type of B-cell lymphoma cell, in an optically induced, non-rotational, electric field have been characterized by utilizing a digitally programmable and optically activated microfluidics chip with the assistance of an externally applied AC bias potential. The crossover frequency spectrum of the Raji cells was studied by observing the different linear translation responses of these cells to the positive and negative optically induced dielectrophoresis force generated by a projected light pattern. This digitally projected spot served as the virtual electrode to generate an axisymmetric and non-uniform electric field. Then, the membrane capacitance of the Raji cells could be directly measured. Furthermore, Raji cells under this condition also exhibited a self-rotation behavior. The repeatable and controlled self-rotation speeds of the Raji cells to the externally applied frequency and voltage were systematically investigated and characterized via computer-vision algorithms. The self-rotational speed of the Raji cells reached a maximum value at 60 kHz and demonstrated a quadratic relationship with respect to the applied voltage. Furthermore, optically projected patterns of four orthogonal electrodes were also employed as the virtual electrodes to manipulate the Raji cells. These results demonstrated that Raji cells located at the center of the four electrode pattern could not be self-rotated. Instead any Raji cells that deviated from this center area would also self-rotate. Most importantly, the Raji cells did not exhibit the self-rotational behavior after translating and rotating with respect to the center of any two adjacent electrodes. The spatial distributions of the electric field generated by the optically projected spot and the pattern of four electrodes were also modeled using a finite element numerical simulation. These simulations validated that the electric field distributions were non-uniform and non-rotational. Hence, the non-uniform electric field must play a key role in the self-rotation of the Raji cells. As a whole, this study elucidates an optoelectric-coupled microfluidics-based mechanism for cellular translation and self-rotation that can be used to extract the dielectric properties of the cells without using conventional metal-based microelectrodes. This technique may provide a simpler method for label-free identification of cancerous cells with many associated clinical applications.

Orientation- and position-controlled alignment of asymmetric silicon microrod on a substrate with asymmetric electrodes

In this paper, we demonstrate the orientation-controlled alignment of asymmetric Si microrods on a glass substrate with an asymmetric pair of electrodes. The Si microrods have the shape of a paddle with a blade and a shaft part, and the pair of electrodes consists of a narrow electrode and a wide electrode. By applying AC bias to the electrodes, the Si microrods suspended in a fluid align in such a way to settle across the electrode pair, and over 80% of the aligned Si microrods have an orientation with the blade and the shaft of the paddle on the wide and the narrow electrodes, respectively. When Si microrods have a shell of dielectric film and its thickness on the top face is thicker than that on the bottom face, 97.8% of the Si microrods are aligned with the top face facing upwards. This technique is useful for orientation-controlled alignment of nano- and microsized devices that have polarity or a distinction between the top and bottom faces.

Manipulation of microparticles and red blood cells using optoelectronic tweezers

We report the development of an optoelectronic tweezers set-up which works by light-induced dielectrophoresis mechanism to manipulate microparticles. We used thermal evaporation technique for coating the organic polymer, titanium oxide phthalocyanine (TiOPc), as a photoconductive layer on ITO-coated glass slide. Compare to the conventional optical tweezers, the technique requires optical power in μW range and provides a manipulation area of a few mm2. The set-up was used to manipulate the polystyrene microspheres and red blood cells (RBCs). The RBCs could be attracted or repelled by varying the frequency of the applied AC bias..

Fabrication and Evaluation of Arrayed Needle-Like TiO<sub>2</sub> Particle – Transparent Resin Composite Films

Needle-like TiO2-resin composite films were fabricated using needle-like TiO2 particle filler and urethane matrix. The needle-like TiO2 particles in the composite film were arrayed completely under the fabrication condition of applying AC bias of 10 volt with 0.1 Hz for 4 hr, and the transmittance of the resulting composite film showed angularly dependence. The needle-like TiO2 particles in the composite were oriented quickly by a larger applying bias. Furthermore, increase of the mixing ratio of TiO2 particles in the composite film caused increasing an angularly dependence of the transmittance of the composites.

Arraying needle-like TiO2 particles in a composite film by applying ac bias and its transmittance anisotropy

In an effort to improve energy-efficient windows, we experimented with a precursor slurry composite by using needle-like TiO2 particles as the filler in a urethane matrix. Applying dc bias to the slurry failed to array the needle-like particles in the composite and to deposit on the film surface because of electrophoretic movement. However, applying ac bias of ±5 V to the precursor slurry composite for 12 h resulted in the needle-like TiO2 particles being arrayed in the composite in a direction normal to the film surface. This resulted in an improvement in the energy efficiency of the material through an angular dependence of transmittance in the visible–near-infrared range.

The AC-Bias Stability of Short Channel a-Si:H TFT

The AC-bias stress was applied at 2um gate length a-Si:H TFT and 4.2um gate length a-Si:H TFT respectively in order to investigate the stability of short channel a-Si:H TFT. The peak voltage of applied AC bias was 7.5 V and the base voltage of it was -7.5 V respectively. The AC bias stress was applied for 100,000 seconds at 60oC. The VTH of short channel a-Si:H TFT was decreased about 0.34V after the AC bias stress while that of long channel a-Si:H TFT was increased about 0.20V. Because the VTH of short channel a-Si:H TFT was less increased than that of long channel a-Si:H TFT during on state period the increase of short channel a-Si:H TFT was compensated more efficiently than that of long channel one at off sate period. Our experimental result showed that the AC stability of short channel a-Si:H TFT was better than that of long channel one.

Dynamic Manipulation by Light and Electric Fields: Micrometer Particles to Microliter Droplets

We demonstrate a new hybrid optoelectric technique that can manipulate objects across several length scales. The technique leverages a variety of different physical mechanisms to achieve the dynamic manipulation of droplets and also the in situ concentration of colloidal particles suspended in the droplets. Various physical mechanisms such as optoelectrowetting, electrothermal flows, and ac electroosmosis are leveraged through different modes of operation of the device. Each operational mode, which is activated through the proper combination of an applied ac bias and the illumination used, is characterized by the ability to manipulate objects on a certain length scale. We also demonstrate that the device lends itself to the active control of microstructure patterns that emerge from a droplet evaporation process.

A 2-D MEMS Scanning Mirror Using Piezoelectric PZT Beam Actuators

A silicon micromirror driven by a piezoelectric Pb(Zr,Ti)O3 beam actuator has been demonstrated for two-dimensional scanning mirror applications. The mirror is micromachined from the device layer of an SOI wafer, while the piezoelectric beam actuator contains multilayers of Pt/Ti/PZT/Pt/Ti/SiO2/Si which is deposited and released from a SOI wafer. A 1x10 PZT arrayed actuator are separately arranged in parallel on a Si beam. Bending mode is measured at 34Hz as while the torsional mode is measured at 197Hz. We demonstrated 2-D raster scanning patterns by applying AC bias of 34Hz on half of the 10 actuators and 197Hz on the other half actuators.

Increase in Intensity of Electrochemiluminescence from Cell Consisting of TiO2 Nanohole Array Film

The increase in the intensity of electrochemiluminescnece (ECL) from cells consisting of titania nanohole array film (T-NHA-AL) is reported. The T-NHA-AL with a thin alumina insulation layer on the edge was prepared by an improved liquid-phase deposition method. The T-NHA-AL was sandwiched between two transparent conductive glasses (F-doped , FTO). The space between these two FTO substrates was filled with a solution of in propylene carbonate. The ECL from the cell was observed by applying ac bias on the FTO glass electrode. The ECL from the cell consisting of the T-NHA-AL was larger than that without T-NHA-AL (the cell with flat FTO glasses). In addition, the ECL intensity from the cell consisting of T-NHA-AL was higher than that consisting of alumina nanohole array (anodically oxidized porous alumina). The increase in the intensity of the ECL from the cell consisting of T-NHA-AL was explained by the electron injection from the large surface of the T-NHA-AL and the confinement of the luminescence species [Ru(I) and Ru(III)] in the restricted area of nanopores in the T-NHA-AL film. If a nanohole array film without the thin layer on the edge (T-NHA) was inserted between these two electrodes, short circuiting occurred through the T-NHA film. It is emphasized that the thin alumina insulation layer at the edge of the T-NHA-AL film is essential to realize an increase in ECL intensity.

Voltage rectification in two-dimensional Josephson junction arrays

We study numerically the directed motion of vortices (antivortices) under an applied ac bias in two-dimensional Josephson junction arrays (JJA) with an asymmetrically modulated periodic vortex pinning potential. We find that the ratchet effect in large 2D JJA can be obtained using the RSJ model for the overdamped vortex dynamics. The rectification effect shows a strong dependence on vortex density as well as an inversion of the vortex flow direction with the ac amplitude, for a wide range of magnetic field around f=1/2 (f being the vortex density). Our results are in good agreement with very recent experiments by D.E. Shalóm and H. Pastoriza [D.E. Shalóm, H. Pastoriza, Phys. Rev. Lett. 94 (2005) 177001].

Influence of carrier freeze-out on SiC Schottky junction admittance

Incomplete impurity ionization is investigated in the case of nitrogen donors and aluminum and boron acceptors in 4H and 6H SiC. We calculate the degree of ionization for these impurities residing on different lattice sites in a broad temperature range and for different impurity concentrations. It is shown that the degree of carrier freeze-out is significant in heavily N-doped 6H SiC and in Al- and B-doped SiC. Using the general Schottky junction admittance model we calculate the temperature and frequency dependencies of the junction admittance in the case when impurity ionization by the applied ac bias is present. It is shown that admittance frequency dispersion may be significant at room temperature in the case of N- and B-doped SiC. Finally, we calculate the Schottky junction capacitance as a function of the applied dc bias and simulate the doping profile, using the capacitance-voltage data. The calculated profile is shown to deviate from the actual impurity concentration profile if the impurity ionization time constant is comparable with the ac bias period, which is so for N-and B-doped SiC with certain values of the impurity activation energy and capture cross-section.

The alternating-current-driven motion of dislocations in a weakly damped Frenkel - Kontorova lattice

By means of numerical simulations, we demonstrate that an alternating-current (ac) field can support stably moving collective nonlinear excitations in the form of dislocations (topological solitons, or kinks) in the Frenkel - Kontorova (FK) lattice with weak friction, as was qualitatively predicted by Bonilla and Malomed (Bonilla L L and Malomed B A 1991 Phys. Rev. B 43 11539). Direct generation of the moving dislocations turns out to be virtually impossible; however, they can be generated initially in the lattice subject to an auxiliary spatial modulation of the on-site potential strength. Gradually relaxing the modulation, we are able to get stable moving dislocations in the uniform FK lattice with periodic boundary conditions, provided that the driving frequency is close to the gap frequency of the linear excitations in the uniform lattice. The excitations that can be generated in this way have a large and noninteger index of commensurability with the lattice (so suggesting that the actual value of the commensurability index is irrational). The simulations reveal two different types of moving dislocation: broad ones, that extend, roughly, to half the full length of the periodic lattice (in that sense, they cannot be called solitons); and localized soliton-like dislocations, that can be found in an excited state, demonstrating strong persistent internal vibrations. The minimum (threshold) amplitude of the driving force necessary to support the travelling excitation is found as a function of the friction coefficient. Its extrapolation suggests that the threshold does not vanish at zero friction, which may be explained by radiation losses. The moving dislocation can be observed experimentally in an array of coupled small Josephson junctions in the form of an inverse Josephson effect, i.e., a direct-current-voltage response to the uniformly applied ac bias current.

Direct comparison of cross-sectional scanning capacitance microscope dopant profile and vertical secondary ion-mass spectroscopy profile

The scanning capacitance microscope (SCM) has been shown to be useful for quantitative 2D dopant profiling near the surface of silicon. An atomic force microscope is used to position a nanometer scale tip at a silicon surface, and local capacitance change is measured as a function of sample bias. A new feedback method has been recently demonstrated in which the magnitude of the ac bias voltage applied to the sample is adjusted to maintain a constant capacitance change as the tip is scanned across the sample surface. The applied ac bias voltage as a function of position is then input into an inversion algorithm to extract the dopant density profile. The new feedback approach allows for the use of a quasi-1D model in the inversion algorithm. Since there are no alternative 2D dopant profiling techniques which are well established at present, evaluation of the quantitative character of 2D SCM measured profiles has been a challenge. To avoid this obstacle, we have developed sample preparation methods which allow direct comparison of lateral SCM measured profiles on cleaved wafers (cross-sectional plane) with vertical secondary ion-mass spectroscopy (SIMS) profiles. The direct comparison of inverted SCM data and SIMS profiles indicates that quantitative 2D dopant profiling can be achieved by the SCM on a nanometer scale.

Atomic ordering of GaInP studied by Kelvin probe force microscopy

The atomic ordering of GaInP has been established and studied by a variety of methods, including transmission electron microscopy, cathodoluminescence, and photoluminescence. In this work, a Kelvin probe force microscope (KPFM) has been employed to image several GaInP samples previously characterized by these established techniques. The results of our study clearly show that the KPFM is capable of distinguishing between ordered and disordered regions in GaInP, and that the KPFM contrast strongly depends on the amplitude of the applied ac bias voltage of the KPFM. The measurements indicate that ordering in GaInP modifies the density and/or lifetime of the surface states.

EL2 deep donor state in semi-insulating GaAs revealed by frequency dependent positron mobility measurements.

Positron mobility measurements carried out on semi-insulating GaAs, using the Doppler shift in annihilation radiation technique, show a sharp transition from a high mobility value \ensuremath{\sim}120 ${\mathrm{cm}}^{2}$ ${\mathrm{V}}^{\ensuremath{-}1}$ ${\mathrm{s}}^{\ensuremath{-}1}$ to a lower value \ensuremath{\sim}45 ${\mathrm{V}}^{\ensuremath{-}1}$ ${\mathrm{s}}^{\ensuremath{-}1}$ just below room temperature. The temperature of the transition is found to be dependent on the frequency of the applied AC bias. We show that this effect is an artifact due to the thermal ionization of the $\mathrm{EL}2$ deep donor state, which in its ionized state forms a positive space charge that causes the positron to experience large electric fields. This observation suggests a new positron annihilation-based deep-level transient technique applicable to semi-insulating materials.

AC bias type magnetoresistive sensor

An AC-bias-type magnetoresistive (MR) sensor which uses a ferromagnetic thin film is proposed to improve offset voltage and hysteresis. It was experimentally confirmed that an MR sensor with an applied AC bias magnetic field can generate an AC output proportional to the external magnetic field (DC magnetic field) which is independent of offset voltage and hysteresis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>