Narrow Voltage Range Research Articles

Li +-intercalation electrochemical/electrochromic properties of vanadium pentoxide films by sol electrophoretic deposition

Thin films of orthorhombic V 2O 5 have been prepared by sol electrophoretic deposition (EPD) followed by post-treatment at 500 °C. Their electrochemical and optical performances have been investigated for possible applications in electrochemical/electrochromic devices. Li +-intercalation properties of the films have been explored in two voltage ranges: 0.4 to −1.1 V and 0.4 to −1.6 V versus Ag/Ag +, respectively. High capacities of over 300 mAh/g are acquired in the wider voltage range at a current density of 50 μA/cm 2 and moderate capacities of 140 and 110 mAh/g are obtained in the narrower voltage range at a current density of 25 and 50 μA/cm 2, respectively. Electrochemical measurements have shown that the films demonstrate good cyclability in both voltage ranges. X-ray diffraction, scanning electron microscopy and optical spectra have been used to examine the changes in crystallinity, microstructure, morphology and transmittance of the films during cycling. Films cycled to a deeper voltage of −1.6 V versus Ag/Ag + deliver higher capacity with appreciable morphological change, while films cycled in the narrower voltage range show moderate capacity and maintain the morphology, optical responses and crystalline structure. Voltage range can be optimized in between to acquire both high capacity and stability in structure, electrochemical and optical properties. High Li +-intercalation capacity and good cyclic stability are attributed to the porous structure of V 2O 5 films prepared by EPD.

Low temperature synthesis and electrochemical behavior of LiV 3O 8 cathode

LiV 3O 8 cathode has been synthesized by two simple low temperature methods without involving the melting of V 2O 5 and characterized by X-ray diffraction, scanning electron microscopy (SEM), discharge–charge measurements in lithium cells and differential scanning calorimetry (DSC). While the first method involves the heating of the components in H 2 at 500 °C followed by in N 2 at 600 °C, the second method involves the dispersion of the components in methanol followed by evaporating the solvent and heating at 500 °C in N 2 atmosphere. The samples exhibit a high capacity of around 230 mAh g −1 at 0.5 mA cm −2 and 25 °C in a narrow voltage range of 2–3.5 V with excellent cyclability at −30 to 60 °C. Additionally, the samples exhibit superior safety characteristics compared to the currently used LiCoO 2 cathode as indicated by the absence of exothermic peaks (DSC) up to 450 °C in the charged state.

Comparison of gate and drain current detection of hydrogen at room temperature with AlGaN∕GaN high electron mobility transistors

Pt-gated AlGaN∕GaN high electron mobility transistors can be used as room-temperature hydrogen gas sensors at hydrogen concentrations as low as 100ppm. A comparison of the changes in drain and gate current-voltage (I-V) characteristics with the introduction of 500ppm H2 into the measurement ambient shows that monitoring the change in drain-source current provides a wider gate voltage operation range for maximum detection sensitivity and higher total current change than measuring the change in gate current. However, over a narrow gate voltage range, the relative sensitivity of detection by monitoring the gate current changes is up to an order of magnitude larger than that of drain-source current changes. In both cases, the changes are fully reversible in <2–3min at 25°C upon removal of the hydrogen from the ambient.

The impact of non-uniform channel layer growth on device characteristics in state of the Art Si/SiGe/Si p-metal oxide semiconductor field effect transistors

In this study we have highlighted the effect of non-uniform channel layer growth by the direct correlation of the microstructure and electrical characteristics in state-of-the-art pseudomorphic Si/SiGe p-channel metal oxide semiconductor field effect transistor devices fabricated on Si. Two nominally identical sets of devices from adjacent locations of the same wafer were found to have radically different distributions in gate threshold voltages. Due to the close proximity and narrow gate length of the devices, focused ion beam milling was used to prepare a number of thin cross-sections from each of the two regions for subsequent analysis using transmission electron microscopy. It was found that devices from the region giving a very narrow range of gate threshold voltages exhibited a uniform microstructure in general agreement with the intended growth parameters. However, in the second region, which showed a large spread in the gate threshold voltages, profound anomalies in the microstructure were observed. These anomalies consisted of fluctuations in the quality and thickness of the SiGe strained layers. The non-uniform growth of the strained SiGe layer clearly accounted for the poorly controlled threshold voltages of these devices. The results emphasize the importance of good layer growth uniformity to ensure optimum device yield.

EIS study on the formation of solid electrolyte interface in Li-ion battery

Formation of solid electrolyte interface (SEI) on the surface of graphite in Li/graphite cells was studied using the electrochemical impedance spectroscopy (EIS) technique. Results show that EIS of the cells varies considerably with cell voltage. In particular, resistance ( R sei) of the SEI increases significantly with lithiation and decreases reversibly in the subsequent delithiation in a narrow voltage range between 0.15 and 0.04 V. According to the change of the R sei during the first lithiation process, we might divide the formation of the SEI into two voltage regions: the first region generally occurs above 0.15 V and the second region below 0.15 V. The SEI formed in the first region is less conductive, and that formed in the second region is highly conductive. It is shown that ionic conductivity of the preliminarily formed SEI is greatly affected by the kind of solvents and salts of the electrolyte. We observed that the R sei increases in the order of LiBF 4 > LiSO 3CF 3 > LiBOB > LiPF 6 for salt, and of NMP > EMC > MB for solvent. Addition of vinylene carbonate into the electrolyte results in a significant increase of the R sei.

Electrolyte-Gate a-Si:H Thin Film Transistors

AbstractThis paper presents the fabrication and characterization of electrolyte-gate (EG) hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs). In these devices, the metal gate is replaced by a Pt electrode immersed in an electrolyte. The source-drain current of these devices is modulated by the voltage applied through the Pt electrode. Device characteristics are compared with structurally equivalent top-gate a-Si:H TFTs. The EG devices show higher mobility and smaller subthreshold slope than their counterparts with metal gate and work in a narrower voltage range. EG-TFTs show chemical sensitivity, illustrated by a voltage shift in the transfer curve as a consequence of pH variation. The sensitivity of the devices to pH is different depending on whether the top layer in contact with the electrolyte is SiO2 or SiNx.

Precise formation of nanoscopic dots on polystyrene film using z-lift electrostatic lithography

Z -lift electrostatic lithography on thin (10–50nm) polystyrene (PS) films is discussed. The height of nanostructures can be controlled via mechanically drawing or depressing the cantilever height (z-lift) during the application of a voltage. Since polymer is not removed or crosslinked during structure formation, the features are erasable. Various aspects such as voltage doses, film thickness, z-lift height, and rate are explored. Structure height formation relies mainly on, and is proportional, to the z-lift magnitude; however, only a narrow range of voltages yields structures for any given film thickness. Structures ranging from 0–10nm are produced on a 40nm thick PS film using −36V by varying the z-lift on a 0.1–0.9N∕m cantilever from −20nm to +400nm.

Single-Electron Tunneling with Strong Mechanical Feedback

A harmonic nanomechanical oscillator with a high quality factor weakly coupled to a single-electron tunneling device can provide a strong feedback for electron transport. Strong feedback occurs in a narrow voltage range just above the Coulomb blockade threshold. In this regime, current is strongly modified and current noise is drastically enhanced compared to the Schottky value.

Separation of ions from explosives in differential mobility spectrometry by vapor-modified drift gas.

Differential mobility spectrometry (DMS) of nitro-organic explosives and related compounds exhibited the expected product ions of M- or M x NO2- from atmospheric pressure chemical ionization reactions in purified air at 100 degrees C. Peaks in the differential mobility spectra for these ions were confined to a narrow range of compensation voltages between -1 to +3 V which arose through a low dependence of mobility for the ions in electric fields at E/N values between 0 and 120 Td (1 Td = 10(-17) V cm2). The field dependence of ions, described as an alpha parameter, ranged from -0.005 to 0.02 at a separation field of 100 Td. The alpha parameter could be controlled through the addition of organic vapors into the drift gas and was increased to 0.08-0.24 with 1000 ppm of methylene chloride in the drift gas. This modification of the drift gas resulted in compensation voltages of +3 to +21 V for peaks. The improved separation of peaks was consistent with a model of ion characterization by DeltaK or Kl - Kh, where Kl is the mobility coefficient of ions clustered with vapor neutrals during the low-field portion of the separation field waveform and Kh is for the same core ion when heated and declustered during the high-field portion of waveform.

Influence of the surface tilt angle on the spatially periodic distortions in super-twisted nematic displays

Periodic deformation arising as parallel stripes in super-twisted nematic displays are studied numerically. The role played by a surface tilt angle δ in their appearance and structure is determined. It is found that the stripes exist in a narrow voltage range between two thresholds. The lower threshold at which they arise is practically independent of the tilt angle. The higher threshold at which the homogeneous deformation occurs decreases with δ. For relatively small twist angles (e.g., 180°) the transition to the homogeneously deformed structure is continuous. If the twist angle is high (e.g., 270°) this transition becomes discontinuous. The stripes are eliminated if the tilt angle exceeds some critical value which increases with the twist angle and may be larger than 30°.

Interface states in high-temperature gas sensors based on silicon carbide

Silicon carbide (SiC)-based metal-insulator-semiconductor devices are attractive for gas sensing in automotive exhausts and flue gases. The response of the devices to reducing gases has been assumed to be due to a reduced metal work function at the metal-oxide interface that shifts the flat band capacitance to lower voltages. We have discovered that high temperature (700 K) exposure to hydrogen results not only in the flat-band voltage occurring at a more negative bias than in oxygen, but also in the transition from accumulation (high capacitance) to inversion (low capacitance) occurring over a relatively narrow voltage range. In oxygen, this transition is broadened, indicating the creation of a high density of interface states. We present a model of the hydrogen/oxygen response based on two independent phenomena: a chemically induced shift in the metal-semiconductor work function difference and the passivation/creation of charged states at the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -SiC interface that is much slower than the work function shift. We discuss the effect of these results on sensor design and the choice of operating point.

Peculiar features in the electrical characteristics of CuPc based diodes

We have investigated electrical properties of copper phthalocyanine (CuPc) thin films by means of current–voltage (I–V), capacitance–voltage (C–V) and charge deep-level transient spectroscopy (Q-DLTS) measurements. CuPc films were deposited on indium tin oxide (ITO) via organic molecular beam deposition (OMBD) at room temperature followed by Ag evaporation through a shadow mask, resulting in contacts of different sizes of dots. The measurements were carried out in situ at a pressure below 8×10−10mbar. No noticeable changes of electrical characteristics have been found after storing the devices for a few days under these conditions. Diodes of 330nm CuPc sandwiched between ITO and Ag show very low reverse currents with hysteresis-like characteristics for short delay times, which are the times between two consecutive voltage steps in an I–V measurement. Especially the bias at which current passes through zero is drastically affected by the sweep voltage direction. Almost identical curves in both directions can only be achieved using an extremely long delay time of 100s. It was found that the offset voltages for delay times of 5 and 100s are −0.85 and −0.1V for up-sweep and 0.14 and 0V for down-sweep voltage directions, respectively. This effect is likely due to the presence of deep traps which require a large time constant for charging and discharging in response to a change of the external voltage. The forward current, on the other hand, is virtually not affected, increasing initially over many orders of magnitude in a narrow voltage range and then increasing at a reduced slope. This behaviour is not stable when a high external voltage is applied. Q-DLTS measurements show presence of traps with time constants exceeding 50ms at ambient temperature.

Mechanism of generation of spontaneous miniature outward currents (SMOCs) in retinal amacrine cells.

A subtype of retinal amacrine cells displayed a distinctive array of K+ currents. Spontaneous miniature outward currents (SMOCs) were observed in the narrow voltage range of −60 to −40 mV. Depolarizations above approximately −40 mV were associated with the disappearance of SMOCs and the appearance of transient (Ito) and sustained (Iso) outward K+ currents. Ito appeared at about −40 mV and its apparent magnitude was biphasic with voltage, whereas Iso appeared near −30 mV and increased linearly. SMOCs, Ito, and a component of Iso were Ca2+ dependent. SMOCs were spike shaped, occurred randomly, and had decay times appreciably longer than the time to peak. In the presence of cadmium or cobalt, SMOCs with pharmacologic properties identical to those seen in normal Ringer's could be generated at voltages of −20 mV and above. Their mean amplitude was Nernstian with respect to [K+]ext and they were blocked by tetraethylammonium. SMOCs were inhibited by iberiotoxin, were insensitive to apamin, and eliminated by nominally Ca2+-free solutions, indicative of BK-type Ca2+-activated K+ currents. Dihydropyridine Ca2+ channel antagonists and agonists decreased and increased SMOC frequencies, respectively. Ca2+ permeation through the kainic acid receptor had no effect. Blockade of organelle Ca2+ channels by ryanodine, or intracellular Ca2+ store depletion with caffeine, eradicated SMOCs. Internal Ca2+ chelation with 10 mM BAPTA eliminated SMOCs, whereas 10 mM EGTA had no effect. These results suggest a mechanism whereby Ca2+ influx through L-type Ca2+ channels and its subsequent amplification by Ca2+-induced Ca2+ release via the ryanodine receptor leads to a localized elevation of internal Ca2+. This amplified Ca2+ signal in turn activates BK channels in a discontinuous fashion, resulting in randomly occurring SMOCs.

Anomalous isotope effect in the permeation, retention, and reemission at interaction of energetic hydrogen with niobium

A niobium membrane sample was placed in H or D plasma and electrically biased. Isotope effects for H vs. D in factors of 20, 40, and 40, respectively, were observed in plasma driven permeation, retention, and in the reemission, within a narrow range of bias voltages (40–80 V) at the lowest metal temperature investigated (910 K). The phenomenon occurred at the “superpermeation” of suprathermal hydrogen arising from an oxygen monolayer at the metal surface. The phenomenon is supposed to be caused by dynamics of the oxygen monolayer under the action of ion sputtering and surface segregation of dissolved O. Such and even much stronger isotope effects are also expected on other metals with a similar “real” surface. This isotope effect may be important for D/T-mixture recycling, retention and permeation at its interactions with plasma facing components of fusion reactors as well as for the applications of superpermeable membranes for pumping of hydrogen isotopes and their separation from He.

Influence of Interface States on High Temperature SiC Sensors and Electronics

ABSTRACTSilicon carbide based metal/oxide/semiconductor (MOS) devices are well suited for operation in chemically reactive high temperature ambients. The response of catalytic gate SiC MOS sensors to hydrogen-containing species has been assumed to be due to the formation of a dipole layer at the metal/oxide interface, which gives rise to a voltage translation of the high frequency capacitance voltage (C-V) curve. From in-situ C-V spectroscopy, performed in a controlled gaseous environment, we have discovered that high temperature (800 K) exposure to hydrogen results in (i) a flat band voltage occurring at a more negative bias than in oxygen and (ii) the transition from accumulation to inversion occurring over a relatively narrow voltage range. In oxygen, this transition is broadened indicating the creation of a large number of interface states. We interpret these results as arising from two independent phenomena – a chemically induced shift in the metal/semiconductor work function difference and the passivation/creation of charged states (DIT) at the SiO2/SiC interface. Our results are important for both chemical sensing and electronic applications. MOS capacitance gas sensors typically operate in constant capacitance mode. Since the slope of the C-V curve changes dramatically with gas exposure, we discuss how sensor-to-sensor reproducibility and device response time are influenced by the choice of operating point. For electronic applications understanding the environmentally induced changes in DIT is crucial to designing drift-free MOS devices. Our results are applicable to n-type SiC MOS devices in general, independent of the specifics of sample fabrication.

Photocapacitance effect at low temperatures in a unipolar MIS capacitor with a semiconductor electrode doped with two different acceptor impurities

The photocapacitance effect at low temperatures in a unipolar MIS capacitor with a semiconductor electrode doped with two types of acceptor impurities characterized by different ionization energies E ia (deep-level acceptor) and E ib (shallow-level acceptor) is examined theoretically. It is shown that the photocapacitance response of such a capacitor arises in a relatively narrow range of bias voltages. The maximum of the response at a constant bias depends on the temperature as exp(E ia /kT). An infinite increase in the photocapacitance response is related to the singularity that appears with decreasing temperature in the bias-voltage dependence of the ionized acceptor concentration. The capacitance and photocapacitance characteristics for a structure with a silicon electrode doped with In and B are calculated.

Understanding Solid Electrolyte Interface Film Formation on Graphite Electrodes

Using ac impedance, we studied the formation process of solid electrolyte interface (SEI) film on graphite electrode during initial cycles. Results show that the SEI formation takes place through two major stages. The first stage takes place at voltages above 0.25 V (before lithiation of graphite), during which a loose and highly resistive film is formed. The second stage occurs at a narrow voltage range of 0.25-0.04 V, which proceeds simultaneously with lithiation of graphite electrode. In the second stage, a stable, compact, and highly conductive SEI film is produced. © 2001 The Electrochemical Society. All rights reserved.

Characterization and functional consequences of delayed rectifier current transient in ventricular repolarization.

Although inactivation of the rapidly activating delayed rectifier current (I(Kr)) limits outward current on depolarization, the role of I(Kr) (and recovery from inactivation) during repolarization is uncertain. To characterize I(Kr) during ventricular repolarization (and compare with the inward rectifier current, I(K1)), voltage-clamp waveforms simulating the action potential were applied to canine ventricular, atrial, and Purkinje myocytes. In ventricular myocytes, I(Kr) was minimal at plateau potentials but transiently increased during repolarizing ramps. The I(Kr) transient was unaffected by repolarization rate and maximal after 150-ms depolarizations (+25 mV). Action potential clamps revealed the I(Kr) transient terminating the plateau. Although peak I(Kr) transient density was relatively uniform among myocytes, potentials characterizing the peak transients were widely dispersed. In contrast, peak inward rectifier current (I(K1)) density during repolarization was dispersed, whereas potentials characterizing I(K1) defined a narrower (more negative) voltage range. In summary, rapidly activating I(Kr) provides a delayed voltage-dependent (and functionally time-independent) outward transient during ventricular repolarization, consistent with rapid recovery from inactivation. The heterogeneous voltage dependence of I(Kr) provides a novel means for modulating the contribution of this current during repolarization.

Somatic amplification of distally generated subthreshold EPSPs in rat hippocampal pyramidal neurones.

1. Intracellular recordings from hippocampal CA1 pyramidal neurones revealed that EPSPs evoked by selective stimulation of the isolated afferent input to the distal third of the apical dendrites were relatively insensitive to changes in dendritic membrane potential (Vm) but amplified by depolarizations of the somatic Vm. The amplification was present at potentials depolarized from resting membrane potential (RMP) but was most marked when the EPSPs were close to threshold for action potential generation. The amplification consisted of a uniform component and a variable component which was only present when the EPSPs were threshold straddling. 2. The somatic amplification was caused by an intrinsic membrane current which was blocked by somatic application of tetrodotoxin (TTX, 10 microM), but was insensitive to bath application of NiCl2 (100-200 microM). We therefore suggest that the amplification of the subthreshold EPSP is due primarily to the activation of a non-inactivating Na+ current (INaP). 3. Injection of 4-aminopyridine (4-AP, 25-50 mM) during intradendritic recordings resulted in amplification of the EPSPs in 37% of the dendrites, which was similar to that observed in somatic recordings. However, in the one case in which somatic application of TTX was tested, dendritic amplification was blocked, suggesting that it is a reflection of the somatic amplification. 4. Because the shift to variable amplification was very abrupt and it is present in only a very narrow voltage range close to threshold, we suggest that the variable component is caused by the regenerative activation of INaP. The variability itself is probably due to the simultaneous activation of different outward K+ currents. 5. The present results indicate that the somatic region of CA1 pyramidal neurones can function as a voltage-dependent amplifier of distally evoked EPSPs and that this is due to the activation of a somatic INaP. The presence of this amplifying mechanism will have important functional consequences for the way in which distally generated EPSPs are integrated.

Conditions for the ignition of a transverse discharge with prebreakdown multiplication of electrons in the active media of gas lasers

Conditions for the generation of a stable transverse discharge with prebreakdown ionisation multiplication of electrons in the active media of recombination — collisional He and Ne atomic lasers, a chemical nonchain-reaction HF laser, and an electric-discharge N2 laser were investigated. It was found that a transverse discharge with prebreakdown ionisation multiplication of electrons was ignited in a narrow range of supply voltages applied to mixtures of He and Ne with SF6, F2, and HCl molecules at a pressure p = 5 — 150 kPa and in the SF6 — H2 (p ≤ 2 kPa) and He — N2 — SF6 (p ≤ 50 kPa) mixtures. This discharge was characterised by an increased spatial homogeneity and a low charging voltage (2 — 15 kV). Such a discharge is of interest in the development of electric-discharge atomic He and Ne plasma lasers and also for its employment as a predischarge in volume preionisers of wide-aperture laser oscillators.