Junctions In Array Research Articles

Bistable States of Quantum Dot Array Junctions for High-Density Memory

We demonstrate that two-dimensional (2D) arrays of coupled quantum dots (QDs) with six-fold degenerate p orbitals (including spin degeneracy) can display bistable states, suitable for application in high-density memory device with low power consumption. Due to the inter-dot overlap of px,y orbitals in these QD arrays, two dimensional conduction bands can be formed in the x–y plane, while the pz orbitals remain localized in the x–y plane such that the coupling between pz orbitals located at different dots can be neglected. We model such systems by taking into account the on-site repulsive Coulomb interactions (U) between electrons in any of the three p orbitals, which also lead to a coupling between the localized pz orbitals with the 2D conduction bands formed by px/py orbitals. The Green's function method within an extended Anderson model is used to calculate the tunneling current through the QDs. We find that bistable tunneling current can exist for such systems due to the interplay of the on-site Coulomb interactions between the pz orbitals and the delocalized nature of conduction band states derived from the hybridization of px/py orbitals. This bistable current depends critically on the strength of U, the band width, and the ratio of the left and right tunneling rates. The behavior of the electrical bistability can be sustained when the 2D QD array reduces to a one-dimensional (1D) QD array, indicating the feasibility for high-density packing of these bistable nanoscale structures.

Synchronization in stacked array of the Josephson junctions in Bi 2Sr 2CaCu 2O 8+δ

Intrinsic stacked array of Josephson junctions will find potential application as voltage standard or HTSC Josephson spectral detector if internal Josephson oscillations in different layers can be synchronized under electromagnetic radiation. In our experiments we studied synchronization is stacked array of Josephson oscillations contained up to 2500 junctions in Bi 2Sr 2CaCu 2O 8+δ. Phase locking of the internal Josephson oscillation in array to externally applied microwave radiation was manifested by observation of the collective Shapiro steps. Synchronization of all junctions in array was possible in the vortex glass state in high magnetic fields and vortex liquid state on the B– T c-axis vortex phase diagram in frequency range 80–140 GHz. In those regions damping is significantly enhanced and hysteresis on I– V characteristics collapsed. Observations deny major opinion that intrinsic Josephson junctions in Bi 2Sr 2CaCu 2O 8+δ are always underdamped. We interpret our results as a reflecting the pancake vortex disorder and fluctuations in CuO 2 layers.

Individually addressable crystalline conducting polymer nanowires in a microelectrodesensor array

An efficient, site-specific and scalable approach has been developed to produce high-qualityand individually addressable conducting polymer nanowire electrode junctions (CPNEJs)in a parallel-oriented array. Polypyrrole and PEDOT conducting polymer nanowires(CPNWs) with uniform diameters (ca. 60–150 nm) were introduced into the desiredelectrode junctions in a precise manner by performing a three-step constant-currentelectrochemical process at a low current density and a low concentration of monomers. Alow scan rate, cyclic voltammetric method was also employed and gave similar results.These CPNEJ arrays function as a miniaturized sensor for the parallel and real-timedetection of gas and organic vapour. The electrochemical approaches utilizedallow the conducting polymer chains to self-organize in the CPNWs to form novelpolycrystalline structures, observed by high resolution TEM. The weak diffraction rings at4.88 Å and 4.60 Å were observed for PEDOT and polypyrrole CPNWs, respectively.

Metrological Study of YBCO Josephson Junction Arrays Integrated in a Fabry-Perot Resonator

The application of high temperature superconductor Josephson junctions to voltage metrology is promising for many reasons, beyond the evident advantage of simplified cryogenics and reduced costs of the apparatus. Owing to their intrinsic non-hysteretic behavior, arrays of shunted bicrystal YBCO junctions are particularly interesting for the realization of an AC voltage standard with quantum accuracy. Moreover, shunted bicrystal YBCO junctions arrays are advantageous because of the reduced area of the junctions, the wide range of characteristic voltages, and large critical currents. However, some specific problems arise, like possible effects related to the higher operating temperature. Furthermore, fabrication technology sets tight constraints on the design of structures for the distribution of microwave currents along the array junctions. We investigated the step properties under millimeter wave irradiation at frequencies about 75 GHz of HTS junction and arrays prepared on bicrystal substrates having grain boundaries. High sensitivity techniques were adopted to evaluate the step flatness at nV level and assess the accuracy of the step voltage. A new method that makes use of an open resonator, was implemented to irradiate the array, providing synchronization of a large number of junctions.

Reversible Formation of Molecular Junctions in 2D Nanoparticle Arrays

Advanced MaterialsVolume 18, Issue 21 p. 2803-2803 CorrectionFree Access Reversible Formation of Molecular Junctions in 2D Nanoparticle Arrays This article corrects the following: Reversible Formation of Molecular Junctions in 2D Nanoparticle Arrays J. Liao, L. Bernard, M. Langer, C. Schönenberger, M. Calame, Volume 18Issue 18Advanced Materials pages: 2444-2447 First Published online: September 12, 2006 J. Liao, J. Liao Institut für Physik, Universität Basel, Klingelbergstrasse 82, 4056 Basel, SwitzerlandSearch for more papers by this authorL. Bernard, L. Bernard Institut für Physik, Universität Basel, Klingelbergstrasse 82, 4056 Basel, SwitzerlandSearch for more papers by this authorM. Langer, M. Langer Departement Chemie, Universität Basel, St. Johanns-Ring 19, 4056 Basel, SwitzerlandSearch for more papers by this authorC. Schönenberger, C. Schönenberger Institut für Physik, Universität Basel, Klingelbergstrasse 82, 4056 Basel, SwitzerlandSearch for more papers by this authorM. Calame, M. Calame michel.calame@unibas.ch Institut für Physik, Universität Basel, Klingelbergstrasse 82, 4056 Basel, SwitzerlandSearch for more papers by this author J. Liao, J. Liao Institut für Physik, Universität Basel, Klingelbergstrasse 82, 4056 Basel, SwitzerlandSearch for more papers by this authorL. Bernard, L. Bernard Institut für Physik, Universität Basel, Klingelbergstrasse 82, 4056 Basel, SwitzerlandSearch for more papers by this authorM. Langer, M. Langer Departement Chemie, Universität Basel, St. Johanns-Ring 19, 4056 Basel, SwitzerlandSearch for more papers by this authorC. Schönenberger, C. Schönenberger Institut für Physik, Universität Basel, Klingelbergstrasse 82, 4056 Basel, SwitzerlandSearch for more papers by this authorM. Calame, M. Calame michel.calame@unibas.ch Institut für Physik, Universität Basel, Klingelbergstrasse 82, 4056 Basel, SwitzerlandSearch for more papers by this author First published: 30 October 2006 https://doi.org/10.1002/adma.200690086Citations: 7AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume18, Issue21November, 2006Pages 2803-2803 RelatedInformation

Reversible Formation of Molecular Junctions in 2D Nanoparticle Arrays

ual junctions into functional electronic circuits remains a demanding task, requiring innovative approaches in fabrication philosophy and circuit structure. [12,13] We show here that an approach combining the self-assembly [14] and microcontact printing [15] of ligand-protected metallic nanoparticles, followed by an in situ ligand-exchange reaction, [16] allows the preparation of stable 2D networks of molecular junctions. [17] A significant decrease in resistance (up to three orders of magnitude) after the exchange of alkanethiol ligands with conjugated, double-ended organic wires (thiolated oligo(phenylene ethynylene), OPE) confirms a proper interlinking of neighboring nanoparticles. We also demonstrate that the formation of the molecular junctions is reversible, making nanoparticle networks a promising platform for the development of molecular electronic circuits. The flexibility of this approach lets us envisage the realization of more complex networks, for instance, by intermixing ensembles of bimodal nanoparticles [18] of different materials. Both experimental and theoretical evidence shows that the electronic properties of molecular junctions are not only dictated by the molecules contacted but also depend on the anchoring groups and the electrodes forming the junction. [3,11] The use of nanometer-sized metallic colloids as electrodes appears, therefore, as an elegant solution to build molecular junctions with well-defined geometry and electronic properties. Recent results on colloid dimers interlinked by a conjugated molecule demonstrate the validity of this approach. [19] The demonstration here of the fabrication of reversible 2D networks of hybrid metallic colloid organic-molecule junctions opens new possibilities for the realization of molecular circuits.

Detection, Stimulation, and Inhibition of Neuronal Signals with High-Density Nanowire Transistor Arrays

We report electrical properties of hybrid structures consisting of arrays of nanowire field-effect transistors integrated with the individual axons and dendrites of live mammalian neurons, where each nanoscale junction can be used for spatially resolved, highly sensitive detection, stimulation, and/or inhibition of neuronal signal propagation. Arrays of nanowire-neuron junctions enable simultaneous measurement of the rate, amplitude, and shape of signals propagating along individual axons and dendrites. The configuration of nanowire-axon junctions in arrays, as both inputs and outputs, makes possible controlled studies of partial to complete inhibition of signal propagation by both local electrical and chemical stimuli. In addition, nanowire-axon junction arrays were integrated and tested at a level of at least 50 "artificial synapses" per neuron.

Submicron-sized magnetic tunnel junctions in field programmable logic gate arrays

We experimentally demonstrate the feasibility of reprogrammable logic gate arrays with lateral dimensions down to 10×10μm2. The gates are based on magnetic tunnel junctions which are elliptically patterned by e-beam lithography with sizes down to 200×100nm2. The junctions are realized with different tunneling systems and are investigated magnetically and electrically, where the magnetization reversal of the junctions’ soft magnetic layer is done via currents in conducting lines. The switching currents could be reduced by a factor of about 2 by introducing an additional NiFe layer on top of the lines. Thus it is possible to use these gate arrays within a highly integrated environment.

Superconducting Quantum Interference Filters Consisting of Josephson Junctions With Unconventional Current-Phase Relation

Superconducting quantum interference filters (SQIFs) are parallel or serial Josephson junction arrays with a unique DC voltage output around vanishing magnetic field B = 0. Certain features of the voltage output also depend on the current-phase relation of the individual junctions in the array. Taking into account the first two harmonics I/sub c1/ and I/sub c2/ of the supercurrent we investigate the DC voltage output of the array. In particular we describe a characteristic magnetic field asymmetry of the voltage output. Applications of the theory include the design of SQIFs with novel flux to voltage transfer functions using high-T/sub c/ superconductors on bi- or tri-crystal substrates.

Planar thin film YBa2Cu3O7−δ Josephson junction pairs and arrays via nanolithography and ion damage

We have fabricated in-plane high-Tc Josephson junction pairs and series arrays using our established nanolithography and ion damage process. Junctions in a pair showed nearly identical electrical properties. The ten-junction array exhibited current–voltage characteristics that can be described by the resistively shunted junction model at 78K. Flat giant Shapiro steps were observed in both cases. We believe that the ion-damaged high-Tc superconducting Josephson junction is a good candidate to form large numbers of junctions in series arrays that can function above 77K for quantum voltage standards and other applications.

Electrochemically Fabricated Polyaniline Nanoframework Electrode Junctions that Function as Resistive Sensors

In this paper, we demonstrate a template-free, site-specific, and scalable electrochemical method for the fabrication of individually addressable polyaniline nanoframework electrode junctions in a parallel-oriented array. These polyaniline nanoframeworks, which are composed of numerous intercrossing polyaniline nanowires that have uniform diameters ranging from 40 to 80 nm, can be used for the chemical sensing of HCl and NH_3 gases and ethanol vapor and for sensing the pH of aqueous NaCl solutions.

The oscillation linewidth and noise characteristics of a parallel superconducting quantuminterference filter

The basic requirements providing the unique properties of a superconducting quantuminterference filter (SQIF) are discussed. The results of a numerical simulation of theoscillation linewidth for a parallel SQIF are reported and compared with those for aconventional parallel array and single Josephson junction.

Electrochemically Fabricated Conducting Polymer Nanoframework Electrode Junctions That Function as Resistive Sensors

ABSTRACTWe have demonstrated a template-free, site-specific, and scalable electrochemical method for the fabrication of individually addressable conducting polymer nanoframework electrode junctions in a parallel-oriented array. These conducting polymer nanoframeworks, which are composed of numerous intercrossing conducting polymer nanowires that have uniform diameters ranging from 40 to 150 nm, can be used for the chemical sensing of HCl and NH3 gases and organic vapors and for sensing pH values of aqueous solutions.

Magnetic switching and magnetoresistance in nanoscale spin tunnel junctions

Co/AlO x / Co magnetic tunnel junctions in both multijunction arrays and double-tunnel junction geometries have been studied. The junctions exhibit magnetoresistance (MR) and change their resistance by ∼10% depending on the relative magnetic orientation of the tunnel junction electrodes. MR measurements show a strong dependence on the device geometry. We find that it is necessary to form tunnel junctions with electrode width ∼70 nm for the magnetic switching at the tunnel junction to be clean and single domain like.

Nonperiodic flux to voltage conversion of series arrays of dc superconducting quantum interference devices

We present a theoretical study on the voltage response function 〈V〉 of series arrays of dc superconducting quantum interference devices (SQUIDs) for which the elementary dc SQUID loops vary in size and, possibly, in orientation. If the distribution of the array loop sizes is chosen according to an arithmetic relation, 〈V〉 is not a Φ0-periodic function of the strength of external magnetic field B. For arithmetic arrays the periodicity of 〈V〉 is controlled by the geometry of the array alone and does not depend on spreads in the array junction parameters. If small fluctuations are added to the loop size distribution, 〈V〉 becomes a unique function around a global minimum at B=0 without possessing significant additional minima for finite B. This filter property does not apply for conventional SQUIDs and series arrays of identical or nearly identical SQUID loops. Applications of arithmetic series arrays include the design of current amplifiers and novel quantum interference filters, which possess large voltage swing and low noise level. In particular, quantum interference filters should provide a rather simple and extremely sensitive measurement of the absolute strength of magnetic fields.

Two-dimensional Josephson junction network architectures for maximum microwave radiation emission

We have investigated experimentally a novel type of self-synchronizing two-dimensional Josephson junction array based on special symmetry breaking network architectures. The measurements confirm the theoretical prediction that in such Josephson networks the Josephson oscillators mutually synchronize into a coherent in-phase state and that such arrays are capable of emitting maximum coherent microwave power in the entire theoretically expected frequency range. The DC biased oscillator array operates coherently even without a reinjection of the generated microwave by an external load or by a resonator cavity. The selector network possesses a much higher tolerance against imperfections, perturbations and load parameter variations than conventional regular two-dimensional or one-dimensional arrays. The experimental sample has been fabricated in an industrial process using Nb-technology, in effect providing relatively large spreads in the array junction parameters. The measured frequency range goes from 85 GHz up to 380 GHz with a maximum microwave power of 0.16 /spl mu/W matched to a coupled load for an array with only 100 active Nb-AlO/sub x/-Nb junctions.

On and off-chip detection of radiation from HTS Josephson junction arrays

We have investigated the mutual phase interaction between a single detector junction and a phase-locked three-junction array of high-T/sub c/ Josephson junctions. The YBCO Josephson junctions were fabricated on a MgO bicrystal substrate. In the array junction structure, the dc bias current was fed to the junction array having parallel geometry with each pair of junctions shunted by a superconducting coplanar microstrip superconducting loop. The configuration of bias leads was a series connection of interlocking dc SQUIDs geometry which enables all junctions to oscillate at the same frequency. We measured the radiation power of a Josephson-junction array using an off-chip coupled to a radiometer and on-chip coupled to a single junction from centimeter- to millimeter-wave ranges. Clear self-induced Shapiro steps were observed in the current-voltage curves of the detector junction. The power transfered to the single detector junction was estimated from the modulation of Shapiro step height. The maximum detected power level was about 7 nW at frequency 150-250 GHz. The Josephson oscillation power excited the resonant mode coupled to the coplanar microstrip loops.

Highly sensitive magnetometers based on YBa2Cu3O7 Josephson junction arrays

The dependence of the critical current of a Josephson junction on the magnetic flux in the junction area can be used for the sensitive detection of external magnetic fields. In contrast to superconducting quantum interference devices, also the measurement of absolute magnetic fields is possible. To increase the transfer function ∂V/∂B, we use serial arrays of up to 105 Josephson junctions between flux-concentrating areas on 24° SrTiO3 bicrystal substrates. We investigate the scaling properties of the critical current Ic, the normal state resistance Rn and the flux density noise SB in dependence on the number of Josephson junctions in the serial array. By the use of a magnetic field modulation scheme, the 1/f noise from critical current fluctuations in the junctions can be suppressed. At 77 K, we achieve a white noise level of SB=1.2 pT/Hz for a 105-junction array.

Coupling of Josephson Radiation to Voltage Standard Arrays

We coupled the radiation emitted by arrays of Josephson junctions oscillators to detector arrays of small Josephson junctions. The number of junctions in the detector array ranges up to 1536, which is typical for a 1V standard array operation. Evidence is presented that both uniform coupling of the emitted radiation over all the small junctions arrays and coherent emission of the Josephson oscillators can be achieved. PACS numbers: 74.50. + r, 74.40. + k.

Spatially resolved detection of phase locking in Josephson junction arrays

Abstract Two-dimensional arrays of shunted Nb/AlOx/Nb Josephson junctions have been investigated. Shapiro steps in the current–voltage ( I – V ) curve of an on-chip detector junction can be used to sense mutual phase locking of the array junctions. By scanning the array with a low-power electron beam, the phase locked junctions remain locked, whereas the unlocked junctions generate a beam-induced additional voltage drop along the array. In regions of the array’s bias current where pronounced Shapiro steps occur in the detector’s I – V curve, practically no array junction generates a beam-induced voltage signal, thus indicating complete mutual locking. For other bias currents of the array with less than maximum detected power, some of the junctions generate beam-induced signals, and can be identified as being non-locked. Our investigations allow a detailed and spatially resolved analysis of mutual phase locking in arrays of Josephson junctions. Moreover, the results obtained with autonomous arrays are compared to experiments performed with injection locked arrays.