Blockade Voltage Research Articles

Cooper-Pair Tunneling in Small Josephson Junction Arrays Under Radio-Frequency Irradiation

The influence of radio frequency microwaves on the Coulomb blockade characteristics in small Josephson junctions was studied using a one-dimensional array of ten small Al tunnel junctions in the frequency range from 1 MHz to 1000 MHz. Coulomb blockade voltage ($V_{\rm th}$) is diminished with increasing microwave power ($V_{\rm ac}$), where the $V_{\rm th}$-$V_{\rm ac}$ plots for varied frequencies fall on a single curve. We observed and theoretically analyzed a magnetic field $dependent$ renormalization of the applied microwave power, in addition to a magnetic-field $independent$ renormalization effect explained using an effective circuit approach of the array. Due to its high sensitivity to microwave power, the array is well-suited for on-chip detection applications in low temperature environments.

Charge control of blockade of Cooper pair tunneling in highly disordered TiN nanowires in an inductive environment

A central problem in understanding the superconductor-insulator transition in disordered superconductors is that the properties of grains and intergrain medium cannot be independently studied. Here we demonstrate an approach to the study of strongly disordered superconducting films by relying on the stochastic nature of the disorder probed by electrostatic gating in a restricted geometry. Charge tuning and magnetotransport measurements in quasihomogeneous TiN nanowires embedded in a superinductor environment allow us to classify different devices and distinguish between spontaneously formed Coulomb islands (with typical blockade voltage in the mV range) and homogeneous wires showing behavior indicative of coherent quantum phase slips (with significantly smaller blockade voltage).

Simultaneous arrayed formation of single-electron transistors using electromigration in series-connected nanogaps

A field-emission-induced electromigration method (activation) is reported for integrating single-electron transistors operating at T = 298 K. The field emission currents between the two opposite electrodes of each series-connected nanogap are tuned to accumulate Ni atoms within the gaps. For ten series-connected nanogaps, the resistance (VD/ID), obtained using the current-voltage (ID-VD) properties of these nanogaps during the activation procedure, is observed to decrease on activation. As a result, island structures are formed within the gaps, and the nanogap-based single-electron transistors can be integrated, when atom migration occurs at the tip of each nanogap electrode. After activating the ten series-connected nanogaps with a preset current, IS = 1 nA, current suppression (representative of coulomb blockade) is not observed in the fabricated devices. On the other hand, coulomb blockade, which depicts the charging and discharging of the nanoislands, can be observed at room temperature, after activation with a preset current, IS = 150 nA. Furthermore, the modulation properties of the coulomb blockade voltage by the gate voltage are also determined at room temperature. These results experimentally demonstrate the arrayed formation of ten single-electron transistors operating at room temperature, constituting a significant step toward the practical realization of single-electron-transistor-based systems.

Sequential reduction of the silicon single-electron transistor structure to atomic scale

Here we present an original CMOS compatible fabrication method of a single-electron transistor structure with extremely small islands, formed by solitary phosphorus dopants in the silicon nanobridge. Its key feature is the controllable size reduction of the nanobridge in sequential cycles of low energy isotropic reactive ion etching that results in a decreased number of active charge centers (dopants) in the nanobridge from hundreds to a single one. Electron transport through the individual phosphorous dopants in the silicon lattice was studied. The final transistor structure demonstrates a Coulomb blockade voltage of ∼30 mV and nanobridge size estimated as . Analysis of current stability diagrams shows that electron transport in samples after the final etching stage had a single-electron nature and was carried through three phosphorus atoms. The fabrication method of the demonstrated structure allows it to be modified further by various impurities in additional etching and implantation cycles.

Bloch Oscillation in a One-Dimensional Array of Small Josephson Junctions

A distinct Bloch nose was demonstrated in the current–voltage characteristics of a one-dimensional array of 20 small Josephson junctions. Arrays of direct-current superconducting quantum interference device (dc-SQUID) structures were used as leads to the array of junctions, and the environmental impedance was tuned with a magnetic field. The observed Bloch nose had a negative differential resistance of its magnitude of as large as 14.3 MΩ, a blockade voltage of 0.36 mV, and a decrease in voltage of 0.21 mV due to the Bloch oscillation, all of which are larger than those obtained in a single junction by more than one order. The observed Bloch oscillation was quantitatively described on the basis of the Bloch oscillation of each single junction in combination with the charge soliton model in a long array. Unexpected constant-current spikes, whose origin lay in the dc-SQUID in the leads, were also observed to be superposed on the current–voltage characteristics when the Coulomb blockade appeared.

Clinical Use of Buprenorphine for Anesthesia and Pain Management in Japan

Buprenorphine (BUP) is a classic analgesic drug, and recent studies have reported a new, unique pharmacological profile of it. BUP can be used in patients with renal dysfunction and failure, and these patients can receive the same dose of BUP administered to those with normal renal function. BUP may have a local anestheticlike effect to blockade voltage gated Na+ channels; it can be used as a local anesthetic peripheral nerve block adjuvant to prolong analgesia. BUP is useful for postoperative pain relief in patients with severe liver dysfunction in Japan. However, the prolonged metabolism of BUP and occurrence of delayed emergence from anesthesia may occur in these patients. Moreover, in Japan, the transdermal buprenorphine patch (TBP) is used for the reducing intractable chronic non-cancer pain such as low back pain or pain caused by osteoarthritis not opioid addiction.

"Size-Independent" Single-Electron Tunneling.

Incorporating single-electron tunneling (SET) of metallic nanoparticles (NPs) into modern electronic devices offers great promise to enable new properties; however, it is technically very challenging due to the necessity to integrate ultrasmall (<10 nm) particles into the devices. The nanosize requirements are intrinsic for NPs to exhibit quantum or SET behaviors, for example, 10 nm or smaller, at room temperature. This work represents the first observation of SET that defies the well-known size restriction. Using polycrystalline Au NPs synthesized via our newly developed solid-state glycine matrices method, a Coulomb Blockade was observed for particles as large as tens of nanometers, and the blockade voltage exhibited little dependence on the size of the NPs. These observations are counterintuitive at first glance. Further investigations reveal that each observed SET arises from the ultrasmall single crystalline grain(s) within the polycrystal NP, which is (are) sufficiently isolated from the nearest neighbor grains. This work demonstrates the concept and feasibility to overcome orthodox spatial confinement requirements to achieve quantum effects.

Conformational electroresistance and hysteresis in nanoclusters.

The existence of multiple thermodynamically stable isomer states is one of the most fundamental properties of small clusters. This work shows that the conformational dependence of the Coulomb charging energy of a nanocluster leads to a giant electroresistance, where charging induced conformational distortion changes the blockade voltage. The intricate interplay between charging and conformation change is demonstrated in a nanocluster Zn3O4 by combining a first-principles calculation with a temperature-dependent transport model. The predicted hysteretic Coulomb blockade staircase in the current-voltage curve adds another dimension to the rich phenomena of tunneling electroresistance. The new mechanism provides a better controlled and repeatable platform to study conformational electroresistance.

Control Parameters for Fabrication of Single-Electron Transistors Using Field-Emission-Induced Electromigration

We report a simple method for the control of electrical characteristics of planar-type metal-based single-electron transistors (SETs) using field-emission-induced electromigration. The advantages of this method are as follows: (1) the fabrication of SETs is achieved by only passing a field emission current through a nanogap and (2) the charging energy of SETs can be controlled by adjusting the magnitude of the applied current during the procedure. In order to better control the electrical properties of the SETs, we investigate the relation between control parameters of the method and electrical characteristics of the SETs. When the field-emission-induced electromigration with the preset current of 500 nA was applied to the nanogaps, current-voltage characteristics of the nanogaps displayed the suppression of electrical current at low-bias voltages known as Coulomb blockade at 16 K. In addition, Coulomb blockade voltage was clearly modulated by the gate voltage periodically at 16 K, resulting in the formation of single island in the SETs by the field-emission-induced electromigration. Furthermore, as the preset current was increased, the charging energy of the SETs was decreased with decreasing the initial gap separation of the nanogaps. These results imply that the electrical characteristics of the SETs are controllable by the preset current of the method and the initial gap separation of the nanogaps. Field-emission-induced electromigration procedure allows us to simply control electrical characteristics of planar-type metal-based SETs.

Single-Charge Transistor Based on the Charge-Phase Duality of a Superconducting Nanowire Circuit

We propose a transistorlike circuit including two serially connected segments of a narrow superconducting nanowire joint by a wider segment with a capacitively coupled gate in between. This circuit is made of amorphous NbSi film and embedded in a network of on-chip Cr microresistors ensuring a sufficiently high external electromagnetic impedance. Assuming a virtual regime of quantum phase slips (QPS) in two narrow segments of the wire, leading to quantum interference of voltages on these segments, this circuit is dual to the dc SQUID. Our samples demonstrated appreciable Coulomb blockade voltage (analog of critical current of the SQUIDs) and periodic modulation of this blockade by an electrostatic gate (analog of flux modulation in the SQUIDs). The model of this QPS transistor is discussed.

Mechanisms of intrinsic force in small human airways

We quantified the magnitude and investigated mechanisms regulating intrinsic force (IF) in human airway smooth muscle (hASM). IF was identified by reducing extracellular calcium (Ca2+) concentration to nominally zero in freshly isolated isometrically mounted 2mm human bronchi. Our results show: (1) the magnitude of IF is ∼50% of the maximal total force elicited by acetylcholine (10(-5) M) and is epithelial independent, (2) IF can also be revealed by β-adrenergic activation (isoproterenol), non-specific cationic channel blockade (La3+) or L-type voltage gated Ca2+ channel blockade (nifedipine), (3) atropine, indomethacin, AA-861, or pyrilamine did not affect IF, (4) IF was reduced by the intracellular Ca2+ ([Ca2+]i) chelating agent BAPTA-AM, (5) ω-conotoxin had no effect on IF. In studies in cultured hASM cells nominally zero Ca2+ buffer and BAPTA-AM reduced [Ca2+]i but isoproterenol and nifedipine did not. Taken together these results indicate that rapid reduction of [Ca2+]i reveals a permissive relationship between extracellular Ca2+, [Ca2+]i and IF. However IF can be dissipated by mechanisms effecting Ca2+ sensitivity. We speculate that an increase of IF, a fundamental property of ASM, could be related to human airway clinical hyperresponsiveness and must be accounted for in in vitro studies of hASM.

The Diversity of Mechanisms of Blockade of Ion Channels as a Pathway to the Design of New Pharmacological Agents

Impairments to glutamatergic synaptic transmission are seen in many pathological CNS states. Excess glutamate actions, inducing persistent depolarization of neurons and massive calcium influx, can lead to cell death. Despite the obvious importance of developing antiglutamate agents as neuroprotectors, the only one of the ionotropic glutamate receptor antagonists which has been introduced into practice is memantine. One of the causes of the multiple side effects occurring when glutamate receptor antagonists are used is that these pharmacological agents inhibit the whole of the receptor pool, both those receptors involved in pathological processes and those performing normal physiological functions. One possible approach to overcoming this problem consists of developing pharmacological agents whose actions are enhanced in potential pathological states, such as high-frequency stimulation of receptors, high glutamate concentrations, decreases in neuron membrane potential, etc. The efficacies of many types of antagonists, such as channel blockers, depends on the membrane potential and the nature of receptor activation. The present article provides a discussion of some of the characteristics of the mechanisms of blockade of glutamate receptor ion channels from the point of view of the potential to create neuroprotective agents. In particular, blockers with different interactions with channel gate structures and different types of blockade voltage dependence are compared, with analysis of the characteristics of the actions of blockers able to penetrate channels to enter cells. We suggest that only detailed study of the mechanisms of action of antagonists on glutamate receptors can bring us towards the ability to predict the results of using blockers in vivo on the basis of data obtained in vitro.

Integration of Single-Electron Transistors Using Field-Emission-Induced Electromigration

A novel technique for the integration of planar-type single-electron transistors (SETs) composed of nanogaps is presented. This technique is based on the electromigration procedure, which is caused by a field emission current. The technique is called "activation." By applying the activation to the nanogaps, SETs can be easily obtained. Furthermore, the charging energy of the SETs can be controlled by adjusting the magnitude of the applied current during the activation process. The integration of two SETs was achieved by passing a field emission current through two series-connected initial nanogaps. The current-voltage (I(D)-V(D)) curves of the simultaneously activated devices exhibited clear electrical-current suppression at a low-bias voltage at 16 K, which is known as the Coulomb blockade. The Coulomb blockade voltage of each device was also obviously modulated by the gate voltage. In addition, the two SETs, which were integrated by the activation procedure, exhibited similar electrical properties, and their charging energy decreased uniformly with increasing the preset current during the activation. These results indicate that the activation procedure allows the simple and easy integration of planar-type SETs.

Field-emission-induced electromigration method for the integration of single-electron transistors

We report a simple and easy method for the integration of planar-type single-electron transistors (SETs). This method is based on electromigration induced by a field emission current, which is so-called “activation”. The integration of two SETs was achieved by performing the activation to the series-connected initial nanogaps. In both simultaneously activated devices, current–voltage (ID–VD) curves displayed Coulomb blockade properties, and Coulomb blockade voltage was also obviously modulated by the gate voltage at 16K. Moreover, the charging energy of both SETs was well controlled by the preset current in the activation.

Fabrication of Single-Electron Transistors Using Field-Emission-Induced Electromigration

We report a novel technique for the fabrication of planar-type Ni-based single-electron transistors (SETs) using electromigration method induced by field emission current. The method is so-called "activation" and is demonstrated using arrow-shaped Ni nanogap electrodes with initial gap separations of 21-68 nm. Using the activation method, we are easily able to obtain the SETs by Fowler-Nordheim (F-N) field emission current passing through the nanogap electrodes. The F-N field emission current plays an important role in triggering the migration of Ni atoms. The nanogap is narrowed because of the transfer of Ni atoms from source to drain electrode. In the activation procedure, we defined the magnitude of a preset current Is and monitored the current I between the nanogap electrodes by applying voltage V. When the current I reached a preset current Is, we stopped the voltage V. As a result, the tunnel resistance of the nanogaps was decreased from the order of 100 T(omega) to 100 k(omega) with increasing the preset current Is from 1 nA to 150 microA. Especially, the devices formed by the activation with the preset current from 100 nA to 1.5 microA exhibited Coulomb blockade phenomena at room temperature. Coulomb blockade voltage of the devices was clearly modulated by the gate voltage quasi-periodically, resulting in the formation of multiple tunnel junctions of the SETs at room temperature. By increasing the preset current from 100 nA to 1.5 microA in the activation scheme, the charging energy of the SETs at room temperature was decreased, ranging from 1030 meV to 320 meV. Therefore, it is found that the charging energy and the number of islands of the SETs are controllable by the preset current during the activation. These results clearly imply that the activation procedure allows us to easily and simply fabricate planar-type Ni-based SETs operating at room temperature.

Enhanced conductance blockade due to Pauli exclusion in tunnel junctions with half-metallic electrodes

A defect-state mediated conductance blockade effect has been studied in magnetic tunnel junctions consisting of La 0.7Sr 0.3MnO 3 (LSMO) electrodes and a SrTiO 3 (STO) barrier. The blockade threshold is an order of magnitude greater than the Coulomb charging energy estimated from the conductance oscillations at low temperature. The blockade voltage decreases with the increase of the temperature or the magnetic field, whereas the Coulomb charging energy washes out at higher temperature but it does not show strong dependence on magnetic field. An explanation is offered in terms of the spin blockade effect due to the combination of the discrete Coulomb charging on the defect state in STO and the half-metallicity of the LSMO electrodes. The result sheds new light on the half-metallic nature of LSMO.

Single Electron Transistor-Based Gas Sensing With Tungsten Nanoparticles at Room Temperature

Single electron transistor (SET)-based gas sensors utilizing tungsten nanoparticles as conducting islands and operating at room temperature have been fabricated. Electrical characterization showed a strong correlation between the drain current of the SET device and the concentration of gas. The reversible exposure to gas resulted in reduction of both the Coulomb blockade voltage and the drain current. The reduction in the drain current shows an oscillatory behavior, with the variation on the gate bias. The sensitivity of the gas sensor can be tuned by controlling the charge on the gate electrode. Relaxation times of 400 ms for a concentration of 36% of gas in were achieved. Although the SET sensor has not been demonstrated with sensitivities in the few tens of ppm compared with existing technologies, the response is very fast and the sensitivity can be tuned by modulating the gate bias. The sensor demonstrates the possibility of gas sensing using SET devices as sensitive electrometers. The sensitivity of the SET gas sensor is higher at lower concentrations.

Influence of Linker Molecules on Charge Transport through Self-Assembled Single-Nanoparticle Devices

We investigate electrical characteristics of single-electron electrode/nanoisland/electrode devices formed by alkanedithiol assisted self-assembly. Contrary to predictions of the orthodox model for double tunnel junction devices, we find a significant ( approximately fivefold) discrepancy in single-electron charging energies determined by Coulomb blockade (CB) voltage thresholds in current-voltage measurements versus those determined by an Arrhenius analysis of conductance in the CB region. The energies do, however, scale with particle sizes, consistent with single-electron charging phenomena. We propose that the discrepancy is caused by a multibarrier junction potential that leads to a voltage divider effect. Temperature and voltage dependent conductance measurements performed outside the blockade region are consistent with this picture. We simulated our data using a suitably modified orthodox model.

Control of the electromagnetic environment for single Josephson junctions using arrays of dc SQUIDs

We have measured the current–voltage characteristics of small-capacitance single Josephson junctions at low temperatures T ≤ 0.04 K, where the strength of the coupling between the single junction and the electromagnetic environment was controlled with one-dimensional arrays of dc SQUIDs. When the zero-bias resistance of the SQUID arrays is much higher than the quantum resistance h/e2 ≈ 26 kΩ, a transition to a clear Coulomb blockade of Cooper-pair tunnelling is induced in the single junction. The measured blockade voltage agrees with the theoretical prediction.

Design Optimization of Coulomb Blockade Devices

We investigate the design of a Coulomb blockade device consisting of a rectangular array of quantum dots or ultrasmall metallic islands with regard to its stability against geometric size disorder and offset charges. To simulate the device operation we perform a statistical analysis of the Coulomb blockade voltage which results in practical design rules.