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Sample records for nanotunneling junction-based hyperspectal

  1. Nanotunneling Junction-based Hyperspectal Polarimetric Photodetector and Detection Method

    NASA Technical Reports Server (NTRS)

    Son, Kyung-ah (Inventor); Moon, Jeongsun J. (Inventor); Chattopadhyay, Goutam (Inventor); Liao, Anna (Inventor); Ting, David (Inventor)

    2009-01-01

    A photodetector, detector array, and method of operation thereof in which nanojunctions are formed by crossing layers of nanowires. The crossing nanowires are separated by a few nm thick electrical barrier layer which allows tunneling. Each nanojunction is coupled to a slot antenna for efficient and frequency-selective coupling to photo signals. The nanojunctions formed at the intersection of the crossing wires defines a vertical tunneling diode that rectifies the AC signal from a coupled antenna and generates a DC signal suitable for reforming a video image. The nanojunction sensor allows multi/hyper spectral imaging of radiation within a spectral band ranging from terahertz to visible light, and including infrared (IR) radiation. This new detection approach also offers unprecedented speed, sensitivity and fidelity at room temperature.

  2. Carbon nanotunnels form from single-walled carbon nanotubes interacting with a diamond (100)-(2 X 1) surface.

    SciTech Connect

    Horner, D. A.; Sternberg, M.; Zapol, P.; Curtiss, L. A.

    2011-08-01

    A quantum chemical study of the interaction of (5,5), (7,7), (9,9) and (8,0) single-walled carbon nanotubes with a clean (100)-(2 x 1) diamond surface is reported. Stable structures with covalent bonds at the interface were found for carbon nanotubes oriented parallel or perpendicular to the dimer rows on the reconstructed (100) surface. The binding energy of the most stable (5,5) nanotube-diamond structure is 1.7 eV/{angstrom}, and is attributed to strong covalent bonds formed between the carbon nanotube and the diamond surface. The structure of the nanotube is distorted by adsorption on the surface such that it adopts a tunnel-like geometry. Two other nanotunnel geometries were found for the (5,5) nanotube, with binding energies of 1.39 and 1.09 eV/{angstrom}. In the most stable (5,5) nanotube-diamond structure the interaction between the nanotube and the diamond surface produces a 0.6 eV band gap near the Fermi level, but the metallic character of the nanotube is maintained in the two other, less strongly bound nanotunnel structures. No charge transfer occurs between the diamond surface and the nanotunnels in any of the three orientations. Binding energies decrease with increases in tube diameter, to the extent that one of the three nanotunnel structures is not formed by (9,9) carbon nanotubes.

  3. Junction-based field emission structure for field emission display

    DOEpatents

    Dinh, Long N.; Balooch, Mehdi; McLean, II, William; Schildbach, Marcus A.

    2002-01-01

    A junction-based field emission display, wherein the junctions are formed by depositing a semiconducting or dielectric, low work function, negative electron affinity (NEA) silicon-based compound film (SBCF) onto a metal or n-type semiconductor substrate. The SBCF can be doped to become a p-type semiconductor. A small forward bias voltage is applied across the junction so that electron transport is from the substrate into the SBCF region. Upon entering into this NEA region, many electrons are released into the vacuum level above the SBCF surface and accelerated toward a positively biased phosphor screen anode, hence lighting up the phosphor screen for display. To turn off, simply switch off the applied potential across the SBCF/substrate. May be used for field emission flat panel displays.

  4. Effect of sound on gap-junction-based intercellular signaling: Calcium waves under acoustic irradiation

    NASA Astrophysics Data System (ADS)

    Deymier, P. A.; Swinteck, N.; Runge, K.; Deymier-Black, A.; Hoying, J. B.

    2015-11-01

    We present a previously unrecognized effect of sound waves on gap-junction-based intercellular signaling such as in biological tissues composed of endothelial cells. We suggest that sound irradiation may, through temporal and spatial modulation of cell-to-cell conductance, create intercellular calcium waves with unidirectional signal propagation associated with nonconventional topologies. Nonreciprocity in calcium wave propagation induced by sound wave irradiation is demonstrated in the case of a linear and a nonlinear reaction-diffusion model. This demonstration should be applicable to other types of gap-junction-based intercellular signals, and it is thought that it should be of help in interpreting a broad range of biological phenomena associated with the beneficial therapeutic effects of sound irradiation and possibly the harmful effects of sound waves on health.

  5. Decoherence and mode hopping in a magnetic tunnel junction based spin torque oscillator.

    PubMed

    Muduli, P K; Heinonen, O G; Akerman, Johan

    2012-05-18

    We discuss the coherence of magnetic oscillations in a magnetic tunnel junction based spin torque oscillator as a function of the external field angle. Time-frequency analysis shows mode hopping between distinct oscillator modes, which arises from linear and nonlinear couplings in the Landau-Lifshitz-Gilbert equation, analogous to mode hopping observed in semiconductor ring lasers. These couplings and, therefore, mode hopping are minimized near the current threshold for the antiparallel alignment of free-layer with reference layer magnetization. Away from the antiparallel alignment, mode hopping limits oscillator coherence. PMID:23003182

  6. Paramagnetic molecule induced strong antiferromagnetic exchange coupling on a magnetic tunnel junction based molecular spintronics device

    NASA Astrophysics Data System (ADS)

    Tyagi, Pawan; Baker, Collin; D'Angelo, Christopher

    2015-07-01

    This paper reports our Monte Carlo (MC) studies aiming to explain the experimentally observed paramagnetic molecule induced antiferromagnetic coupling between ferromagnetic (FM) electrodes. Recently developed magnetic tunnel junction based molecular spintronics devices (MTJMSDs) were prepared by chemically bonding the paramagnetic molecules between the FM electrodes along the tunnel junction’s perimeter. These MTJMSDs exhibited molecule-induced strong antiferromagnetic coupling. We simulated the 3D atomic model analogous to the MTJMSD and studied the effect of molecule’s magnetic couplings with the two FM electrodes. Simulations show that when a molecule established ferromagnetic coupling with one electrode and antiferromagnetic coupling with the other electrode, then theoretical results effectively explained the experimental findings. Our studies suggest that in order to align MTJMSDs’ electrodes antiparallel to each other, the exchange coupling strength between a molecule and FM electrodes should be ˜50% of the interatomic exchange coupling for the FM electrodes.

  7. Paramagnetic molecule induced strong antiferromagnetic exchange coupling on a magnetic tunnel junction based molecular spintronics device.

    PubMed

    Tyagi, Pawan; Baker, Collin; D'Angelo, Christopher

    2015-07-31

    This paper reports our Monte Carlo (MC) studies aiming to explain the experimentally observed paramagnetic molecule induced antiferromagnetic coupling between ferromagnetic (FM) electrodes. Recently developed magnetic tunnel junction based molecular spintronics devices (MTJMSDs) were prepared by chemically bonding the paramagnetic molecules between the FM electrodes along the tunnel junction's perimeter. These MTJMSDs exhibited molecule-induced strong antiferromagnetic coupling. We simulated the 3D atomic model analogous to the MTJMSD and studied the effect of molecule's magnetic couplings with the two FM electrodes. Simulations show that when a molecule established ferromagnetic coupling with one electrode and antiferromagnetic coupling with the other electrode, then theoretical results effectively explained the experimental findings. Our studies suggest that in order to align MTJMSDs' electrodes antiparallel to each other, the exchange coupling strength between a molecule and FM electrodes should be ∼50% of the interatomic exchange coupling for the FM electrodes. PMID:26159362

  8. Mode-hopping mechanism generating colored noise in a magnetic tunnel junction based spin torque oscillator

    SciTech Connect

    Sharma, Raghav; Dürrenfeld, P.; Iacocca, E.; Heinonen, O. G.; Åkerman, J.; Muduli, P. K.

    2014-09-29

    The frequency noise spectrum of a magnetic tunnel junction based spin torque oscillator is examined where multiple modes and mode-hopping events are observed. The frequency noise spectrum is found to consist of both white noise and 1/f frequency noise. We find a systematic and similar dependence of both white noise and 1/f frequency noise on bias current and the relative angle between the reference and free layers, which changes the effective damping and hence the mode-hopping behavior in this system. The frequency at which the 1/f frequency noise changes to white noise increases as the free layer is aligned away from the anti-parallel orientation w.r.t the reference layer. These results indicate that the origin of 1/f frequency noise is related to mode-hopping, which produces both white noise as well as 1/f frequency noise similar to the case of ring lasers.

  9. Programmable Schottky Junctions Based on Ferroelectric Gated MoS2 Transistors

    NASA Astrophysics Data System (ADS)

    Xiao, Zhiyong; Song, Jingfeng; Drcharme, Stephen; Hong, Xia

    We report a programmable Schottky junction based on MoS2 field effect transistors with a SiO2 back gate and a ferroelectric copolymer poly(vinylidene-fluoride-trifluorethylene) (PVDF) top gate. We fabricated mechanically exfoliated single layer MoS2 flakes into two point devices via e-beam lithography, and deposited on the top of the devices ~20 nm PVDF thin films. The polarization of the PVDF layer is controlled locally by conducting atomic force microscopy. The devices exhibit linear ID-VD characteristics when the ferroelectric gate is uniformly polarized in one direction. We then polarized the gate into two domains with opposite polarization directions, and observed that the ID-VD characteristics of the MoS2 channel can be modulated between linear and rectified behaviors depending on the back gate voltage. The nonlinear ID-VD relation emerges when half of the channel is in the semiconductor phase while the other half is in the metallic phase, and it can be well described by the thermionic emission model with a Schottky barrier of ~0.5 eV. The Schottky junction can be erased by re-write the entire channel in the uniform polarization state. Our study facilitates the development of programmable, multifunctional nanoelectronics based on layered 2D TMDs..

  10. CMOS Interface Circuits for Spin Tunneling Junction Based Magnetic Random Access Memories

    SciTech Connect

    Ganesh Saripalli

    2002-12-31

    Magneto resistive memories (MRAM) are non-volatile memories which use magnetic instead of electrical structures to store data. These memories, apart from being non-volatile, offer a possibility to achieve densities better than DRAMs and speeds faster than SRAMs. MRAMs could potentially replace all computer memory RAM technologies in use today, leading to future applications like instan-on computers and longer battery life for pervasive devices. Such rapid development was made possible due to the recent discovery of large magnetoresistance in Spin tunneling junction devices. Spin tunneling junctions (STJ) are composite structures consisting of a thin insulating layer sandwiched between two magnetic layers. This thesis research is targeted towards these spin tunneling junction based Magnetic memories. In any memory, some kind of an interface circuit is needed to read the logic states. In this thesis, four such circuits are proposed and designed for Magnetic memories (MRAM). These circuits interface to the Spin tunneling junctions and act as sense amplifiers to read their magnetic states. The physical structure and functional characteristics of these circuits are discussed in this thesis. Mismatch effects on the circuits and proper design techniques are also presented. To demonstrate the functionality of these interface structures, test circuits were designed and fabricated in TSMC 0.35{micro} CMOS process. Also circuits to characterize the process mismatches were fabricated and tested. These results were then used in Matlab programs to aid in design process and to predict interface circuit's yields.

  11. High efficiency single Ag nanowire/p-GaN substrate Schottky junction-based ultraviolet light emitting diodes

    SciTech Connect

    Wu, Y.; Li, X.; Xu, P.; Wang, Y.; Shen, X.; Liu, X.; Yang, Q.; Hasan, T.

    2015-02-02

    We report a high efficiency single Ag nanowire (NW)/p-GaN substrate Schottky junction-based ultraviolet light emitting diode (UV-LED). The device demonstrates deep UV free exciton electroluminescence at 362.5 nm. The dominant emission, detectable at ultralow (<1 μA) forward current, does not exhibit any shifts when the forward current is increased. External quantum efficiency (EQE) as high as 0.9% is achieved at 25 μA current at room temperature. Experiments and simulation analysis show that devices fabricated with thinner Ag NWs have higher EQE. However, for very thin Ag NWs (diameter < 250 nm), this trend breaks down due to heat accumulation in the NWs. Our simple device architecture offers a potentially cost-effective scheme to fabricate high efficiency Schottky junction-based UV-LEDs.

  12. Targeting Ilmenite on the Moon Using M3 Hyperspectal Imagery

    NASA Astrophysics Data System (ADS)

    Standart, D. L.; Hurtado, J. M.

    2013-12-01

    In-situ resource utilization (ISRU) will be a key technology in sustained human exploration of the solar system. The lunar surface hosts a variety of potentially exploitable resources. For example, KREEP (potassium, rare earth elements, phosphorus) material on the Moon is shown to be relatively rich in ilmenite (FeTiO3 ) and other useful materials. By targeting areas with anomalously high Th signatures, as seen by Lunar Prospector gamma ray spectroscopy (LP-GRS), we have mapped areas with the highest concentrations of ilmenite-rich material on the nearside of the Moon. To map Th, we employ a continuum slope band depth (CSBD) technique that takes advantage of the fact that the visible-infrared reflectance spectrum of ilmenite exhibits low reflectance and a flat continuum slope. As a result, the spectra of materials bearing ilmenite will also have a lower reflectance and a flattened continuum slope. These effects may also obscure spectral absorption features indicative of other minerals, such as pyroxene, within the host rock. We use the results of the CSBD analysis to construct ilmenite classification maps that can be compared to Lunar Reconnaissance Orbiter (LRO) Wide Angle Camera (WAC) ultraviolet/visible-infrared composite imagery. The LRO-WAC and M3 images together provide strong evidence for the presence of high concentrations of ilmenite, which can then be related to the distribution of associated KREEP material. The sites of interest for analyzing ilmenite and Th in this study include Gruithuisen Domes (including the Federov feature), Hansteen Alpha, Lassell Crater, and the Compton Belkovich Thorium Anomaly (CBTA). Each of these sites is also geologically interesting because they contain what are interpreted to be non-mare silicic volcanic features.

  13. Model of a tunneling current in a p-n junction based on armchair graphene nanoribbons - an Airy function approach and a transfer matrix method

    SciTech Connect

    Suhendi, Endi; Syariati, Rifki; Noor, Fatimah A.; Khairurrijal; Kurniasih, Neny

    2014-03-24

    We modeled a tunneling current in a p-n junction based on armchair graphene nanoribbons (AGNRs) by using an Airy function approach (AFA) and a transfer matrix method (TMM). We used β-type AGNRs, in which its band gap energy and electron effective mass depends on its width as given by the extended Huckel theory. It was shown that the tunneling currents evaluated by employing the AFA are the same as those obtained under the TMM. Moreover, the calculated tunneling current was proportional to the voltage bias and inversely with temperature.

  14. Molecular tunnel junctions based on π-conjugated oligoacene thiols and dithiols between Ag, Au, and Pt contacts: effect of surface linking group and metal work function.

    PubMed

    Kim, BongSoo; Choi, Seong Ho; Zhu, X-Y; Frisbie, C Daniel

    2011-12-14

    The tunneling resistance and electronic structure of metal-molecule-metal junctions based on oligoacene (benzene, naphthalene, anthracene, and tetracene) thiol and dithiol molecules were measured and correlated using conducting probe atomic force microscopy (CP-AFM) in conjunction with ultraviolet photoelectron spectroscopy (UPS). Nanoscopic tunnel junctions (~10 nm(2)) were formed by contacting oligoacene self-assembled monolayers (SAMs) on flat Ag, Au, or Pt substrates with metalized AFM tips (Ag, Au, or Pt). The low bias (<0.2 V) junction resistance (R) increased exponentially with molecular length (s), i.e., R = R(0) exp(βs), where R(0) is the contact resistance and β is the tunneling attenuation factor. The R(0) values for oligoacene dithiols were 2 orders of magnitude less than those of oligoacene thiols. Likewise, the β value was 0.5 per ring (0.2 Å(-1)) for the dithiol series and 1.0 per ring (0.5 Å(-1)) for the monothiol series, demonstrating that β is not simply a characteristic of the molecular backbone but is strongly affected by the number of chemical (metal-S) contacts. R(0) decreased strongly as the contact work function (Φ) increased for both monothiol and dithiol junctions, whereas β was independent of Φ within error. This divergent behavior was explained in terms of the metal-S bond dipoles and the electronic structure of the junction; namely, β is independent of contact type because of weak Fermi level pinning (UPS revealed E(F) - E(HOMO) varied only weakly with Φ), but R(0) varies strongly with contact type because of the strong metal-S bond dipoles that are responsible for the Fermi level pinning. A previously published triple barrier model for molecular junctions was invoked to rationalize these results in which R(0) is determined by the contact barriers, which are proportional to the size of the interfacial bond dipoles, and β is determined by the bridge barrier, E(F) - E(HOMO). Current-voltage (I-V) characteristics obtained over

  15. USING HYPERSPECTAL IMAGERY AND SPECTRAL UNMIXING TECHNIQUES FOR MAPPING GRAIN SORGHUM YIELD VARIABILITY

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Vegetation indices derived from remotely sensed imagery are commonly used to estimate crop yields. Spectral unmixing techniques provide an alternative approach to quantifying crop canopy abundance within each pixel and have the potential for mapping crop yield variability. The objective of this stud...

  16. Tunnel junction based memristors as artificial synapses

    PubMed Central

    Thomas, Andy; Niehörster, Stefan; Fabretti, Savio; Shepheard, Norman; Kuschel, Olga; Küpper, Karsten; Wollschläger, Joachim; Krzysteczko, Patryk; Chicca, Elisabetta

    2015-01-01

    We prepared magnesia, tantalum oxide, and barium titanate based tunnel junction structures and investigated their memristive properties. The low amplitudes of the resistance change in these types of junctions are the major obstacle for their use. Here, we increased the amplitude of the resistance change from 10% up to 100%. Utilizing the memristive properties, we looked into the use of the junction structures as artificial synapses. We observed analogs of long-term potentiation, long-term depression and spike-time dependent plasticity in these simple two terminal devices. Finally, we suggest a possible pathway of these devices toward their integration in neuromorphic systems for storing analog synaptic weights and supporting the implementation of biologically plausible learning mechanisms. PMID:26217173

  17. Magnetic tunnel junction based spintronic logic devices

    NASA Astrophysics Data System (ADS)

    Lyle, Andrew Paul

    The International Technology Roadmap for Semiconductors (ITRS) predicts that complimentary metal oxide semiconductor (CMOS) based technologies will hit their last generation on or near the 16 nm node, which we expect to reach by the year 2025. Thus future advances in computational power will not be realized from ever-shrinking device sizes, but rather by 'outside the box' designs and new physics, including molecular or DNA based computation, organics, magnonics, or spintronic. This dissertation investigates magnetic logic devices for post-CMOS computation. Three different architectures were studied, each relying on a different magnetic mechanism to compute logic functions. Each design has it benefits and challenges that must be overcome. This dissertation focuses on pushing each design from the drawing board to a realistic logic technology. The first logic architecture is based on electrically connected magnetic tunnel junctions (MTJs) that allow direct communication between elements without intermediate sensing amplifiers. Two and three input logic gates, which consist of two and three MTJs connected in parallel, respectively were fabricated and are compared. The direct communication is realized by electrically connecting the output in series with the input and applying voltage across the series connections. The logic gates rely on the fact that a change in resistance at the input modulates the voltage that is needed to supply the critical current for spin transfer torque switching the output. The change in resistance at the input resulted in a voltage margin of 50--200 mV and 250--300 mV for the closest input states for the three and two input designs, respectively. The two input logic gate realizes the AND, NAND, NOR, and OR logic functions. The three input logic function realizes the Majority, AND, NAND, NOR, and OR logic operations. The second logic architecture utilizes magnetostatically coupled nanomagnets to compute logic functions, which is the basis of Magnetic Quantum Cellular Automata (MQCA). MQCA has the potential to be thousands of times more energy efficient than CMOS technology. While interesting, these systems are academic unless they can be interfaced into current technologies. This dissertation pushed past a major hurdle by experimentally demonstrating a spintronic input/output (I/O) interface for the magnetostatically coupled nanomagnets by incorporating MTJs. This spintronic interface allows individual nanomagnets to be programmed using spin transfer torque and read using magneto resistance structure. Additionally the spintronic interface allows statistical data on the reliability of the magnetic coupling utilized for data propagation to be easily measured. The integration of spintronics and MQCA for an electrical interface to achieve a magnetic logic device with low power creates a competitive post-CMOS logic device. The final logic architecture that was studied used MTJs to compute logic functions and magnetic domain walls to communicate between gates. Simulations were used to optimize the design of this architecture. Spin transfer torque was used to compute logic function at each MTJ gate and was used to drive the domain walls. The design demonstrated that multiple nanochannels could be connected to each MTJ to realize fan-out from the logic gates. As a result this logic scheme eliminates the need for intermediate reads and conversions to pass information from one logic gate to another.

  18. Magnetic tunnel junction based spintronic logic and memory devices

    NASA Astrophysics Data System (ADS)

    Yao, Xiaofeng

    2011-12-01

    The development of semiconductor devices is limited by the high power consumption and further physical dimension reduction. Spintronic devices, especially the magnetic tunnel junction (MTJ) based devices, have advantages of non-volatility, reconfigurable capability, fast-switching speed, small-dimension, and compatibility to semiconductor devices, which is a promising candidate for future logic and memory devices. However, the previously proposed MTJ logic devices have been operated independently and therefore are limited to only basic logic operations. Consequently, the MTJ device has only been used as ancillary device in the circuit, rather than the main computation component. In this thesis, study has been done on both spintronic logic and memory devices. In the first part, systematic study has been performed on MTJ based logic devices in order to expand the functionalities and properties of MTJ devices. Basic logic cell with three-input has been designed and simulated. Nano-magnetic-channel has been proposed, which is the first design to realize the communication between the MTJ logic cells. With basic logic unit as a building block, a spintronic logic circuit has been designed with MTJ as the dominant component. HSPICE simulation has been done for this spintronic logic circuit, which acts as an Arithmetic Logic Unit. In the spintronic memory device part, study has been focused on the fundamental study on the current induced switching in MTJ devices with hybrid free layer. With hybrid free layer, magnetic non-uniformity is introduced along the current direction, which induces extra spin torque component. Unique current-induced switching has been observed and studied in the hybrid free layer MTJ. Adiabatic spin torque, which is introduced by spatial non-uniform magnetization in the hybrid free layer, plays an important role for the unique switching. By tuning the bias field, single-polar current switching was achieved in this hybrid MTJ device, which gives the potential application of unidirectional switching in the spintronic memory devices.

  19. Supercurrent reversal in Josephson junctions based on bilayer graphene flakes

    NASA Astrophysics Data System (ADS)

    Rameshti, Babak Zare; Zareyan, Malek; Moghaddam, Ali G.

    2015-08-01

    We investigate the Josephson effect in a bilayer graphene flake contacted by two monolayer sheets deposited by superconducting electrodes. It is found that when the electrodes are attached to the different layers of the bilayer, the Josephson current is in a π state, if the bilayer region is undoped and there is no vertical bias. Applying doping or bias to the junction reveals π -0 transitions which can be controlled by varying the temperature and the junction length. The supercurrent reversal here is very different from the ferromagnetic Josephson junctions where the spin degree of freedom plays the key role. We argue that the scattering processes accompanied by layer and sublattice index change give rise to the scattering phases, the effect of which varies with doping and bias. Such scattering phases are responsible for the π -0 transitions. On the other hand, if both of the electrodes are coupled to the same layer of the flake or the flake has AA stacking instead of common AB, the junction will be always in 0 state since the layer or sublattice index is not changed.

  20. Large magnetocapacitance effect in magnetic tunnel junctions based on Debye-Fröhlich model

    SciTech Connect

    Kaiju, Hideo Takei, Masashi; Misawa, Takahiro; Nishii, Junji; Nagahama, Taro; Xiao, Gang

    2015-09-28

    The frequency dependence of tunneling magnetocapacitance (TMC) in magnetic tunnel junctions (MTJs) is investigated theoretically and experimentally. According to the calculation based on Debye-Fröhlich model combined with Julliere formula, the TMC ratio strongly depends on the frequency and it has the maximum peak at a specific frequency. The calculated frequency dependence of TMC is in good agreement with the experimental results obtained in MgO-based MTJs with a tunneling magnetoresistance (TMR) ratio of 108%, which exhibit a large TMC ratio of 155% at room temperature. This calculation also predicts that the TMC ratio can be as large as about 1000% for a spin polarization of 87%, while the TMR ratio is 623% for the same spin polarization. These theoretical and experimental findings provide a deeper understanding on AC spin-dependent transport in the MTJs and will open up wider opportunities for device applications, such as highly sensitive magnetic sensors and impedance-tunable devices.

  1. Microwave holography using a magnetic tunnel junction based spintronic microwave sensor

    NASA Astrophysics Data System (ADS)

    Fu, L.; Gui, Y. S.; Bai, L. H.; Guo, H.; Abou-Rachid, H.; Hu, C.-M.

    2015-06-01

    In this work, a spintronic sensor based microwave holographic imaging system is developed, demonstrating the feasibility of microwave holographic imaging applications using a spintronic microwave sensor. The high sensitivity of the microwave phase measurement allows the coherent imaging of the target reconstructed in noise environments. Adapting the broadband measurement, not only the shape but also the distance of target can be determined, which implies that a three-dimensional imaging is achievable using a spintronic device.

  2. A dispersion-engineered Josephson junction-based travelling wave parametric amplifier with low loss dielectric

    NASA Astrophysics Data System (ADS)

    Mutus, J.; White, T.; Hoi, I.-C.; Barends, R.; Campbell, B.; Chen, Y.; Chen, Z.; Chiaro, B.; Fowler, A.; Dunsworth, A.; Jeffrey, E.; Kelly, J.; Megrant, A.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Quintana, C.; Sank, D.; Vainsencher, A.; Wenner, J.; Gao, J.; Chaudhuri, S.; Cleland, A. N.; Martinis, J. M.

    2015-03-01

    Travelling wave parametric amplifiers (TWPAs) promise wide-band performance with high saturation power for amplifying microwave frequency signals. Designing a TWPA requires a careful balance of many parameters in order to approach quantum-limited noise performance with sufficient gain and saturation power. We present a design based on an LC-ladder transmission line of Josephson junctions and parallel plate capacitors using low-loss amorphous silicon dielectric. Crucially, we have inserted λ / 4 resonators at regular intervals along the transmission line in order maintain the phase matching condition between pump, signal and idler in order to increase gain. The design and performance of the device will be presented, demonstrating high-gain, wide bandwidth and high dynamic range.

  3. A novel approach for accurate identification of splice junctions based on hybrid algorithms.

    PubMed

    Mandal, Indrajit

    2015-01-01

    The precise prediction of splice junctions as 'exon-intron' or 'intron-exon' boundaries in a given DNA sequence is an important task in Bioinformatics. The main challenge is to determine the splice sites in the coding region. Due to the intrinsic complexity and the uncertainty in gene sequence, the adoption of data mining methods is increasingly becoming popular. There are various methods developed on different strategies in this direction. This article focuses on the construction of new hybrid machine learning ensembles that solve the splice junction task more effectively. A novel supervised feature reduction technique is developed using entropy-based fuzzy rough set theory optimized by greedy hill-climbing algorithm. The average prediction accuracy achieved is above 98% with 95% confidence interval. The performance of the proposed methods is evaluated using various metrics to establish the statistical significance of the results. The experiments are conducted using various schemes with human DNA sequence data. The obtained results are highly promising as compared with the state-of-the-art approaches in literature. PMID:25203504

  4. RKKY interaction in P-N junction based on surface states of 3D topological insulator

    NASA Astrophysics Data System (ADS)

    Zhang, Shuhui; Yang, Wen; Chang, Kai

    The RKKY interaction mediated by conduction electrons supplies a mechanism to realize the long-range coupling of localized spins which is desired for the spin devices. Here, we examine the controllability of RKKY interaction in P-N junction (PNJ) based on surface states of 3D topological insulator (3DTI). In this study, through quantum way but not usual classical analogy to light propagation, the intuitive picture for electron waves across the interface of PNJ is obtained, e.g., Klein tunneling, negative refraction and focusing. Moreover, we perform the numerical calculations for all kinds of RKKY interaction including the Heisenberg, Ising, and Dzyaloshinskii-Moriya terms. We find the focusing of surface states leads to the local augmentation of RKKY interaction. Most importantly, a dimension transition occurs, i.e., the decay rate of RKKY interaction from the deserved 1/R 2 to 1/ R . In addition, the quadratic gate-dependence of RKKY interaction is also beneficial to the application of 3DTI PNJ in the fields of spintronics and quantum computation. This work was supported by the MOST (Grant No. 2015CB921503, and No. 2014CB848700) and NSFC (Grant No. 11434010, No. 11274036, No. 11322542, and No. 11504018).

  5. Parametric excitation in a magnetic tunnel junction-based spin torque oscillator

    SciTech Connect

    Dürrenfeld, P.; Iacocca, E.; Åkerman, J.; Muduli, P. K.

    2014-02-03

    Using microwave current injection at room temperature, we demonstrate parametric excitation of a magnetic tunnel junction (MTJ)-based spin-torque oscillator (STO). Parametric excitation is observed for currents below the auto-oscillation threshold, when the microwave current frequency f{sub e} is twice the STO free-running frequency f{sub 0}. Above threshold, the MTJ becomes parametrically synchronized. In the synchronized state, the STO exhibits an integrated power up to 5 times higher and a linewidth reduction of two orders of magnitude, compared to free-running conditions. We also show that the parametric synchronization favors single mode oscillations in the case of multimode excitation.

  6. Magnetic Tunnel Junction-Based On-Chip Microwave Phase and Spectrum Analyzer

    NASA Technical Reports Server (NTRS)

    Fan, Xin; Chen, Yunpeng; Xie, Yunsong; Kolodzey, James; Wilson, Jeffrey D.; Simons, Rainee N.; Xiao, John Q.

    2014-01-01

    A magnetic tunnel junction (MTJ)-based microwave detector is proposed and investigated. When the MTJ is excited by microwave magnetic fields, the relative angle between the free layer and pinned layer alternates, giving rise to an average resistance change. By measuring the average resistance change, the MTJ can be utilized as a microwave power sensor. Due to the nature of ferromagnetic resonance, the frequency of an incident microwave is directly determined. In addition, by integrating a mixer circuit, the MTJ-based microwave detector can also determine the relative phase between two microwave signals. Thus, the MTJ-based microwave detector can be used as an on-chip microwave phase and spectrum analyzer.

  7. Magnetic Tunnel Junction-Based On-Chip Microwave Phase and Spectrum Analyzer

    NASA Technical Reports Server (NTRS)

    Fan, Xin; Chen, Yunpeng; Xie, Yunsong; Kolodzey, James; Wilson, Jeffrey D.; Simons, Rainee N.; Xiao, John Q.

    2014-01-01

    A magnetic tunnel junction (MTJ)-based microwave detector is proposed and investigated. When the MTJ is excited by microwave magnetic fields, the relative angle between the free layer and pinned layer alternates, giving rise to an average resistance change. By measuring the average resistance change, the MTJ can be utilized as a microwave power sensor. Due to the nature of ferromagnetic resonance, the frequency of an incident microwave is directly determined. In addition, by integrating a mixer circuit, the MTJ-based microwave detector can also determine the relative phase between two microwave signals. Thus, the MTJbased microwave detector can be used as an on-chip microwave phase and spectrum analyzer.

  8. Electronic transport properties of molecular junctions based on the direct binding of aromatic ring to electrodes

    NASA Astrophysics Data System (ADS)

    Lan, Tran Nguyen

    2014-01-01

    We have used the non-equilibrium Green's function in combination with the density functional theory to investigate the quantum transport properties of the molecular junctions including a terminated benzene ring directly coupled to surface of metal electrodes (physisorption). The other side of molecule was connected to electrode via thiolate bond (chemisorption). Two different electrodes have been studied, namely Cu and Al. Rectification and negative differential resistance behavior have been observed. We found that the electron transport mechanism is affected by the nature of benzene-electrode coupling. In other words, the transport mechanism depends on the nature of metallic electrode. Changing from sp- to sd-metallic electrode, the molecular junction changes from the Schottky to p-n junction-like diode. The transmission spectra, projected density of state, molecular projected self-consistent Hamiltonian, transmission eigenchannel, and Muliken population have been analyzed for explanation of electronic transport properties. Understanding the transport mechanism in junction having direct coupling of π-conjugate to electrode will be useful to design the future molecular devices.

  9. A Single-Material Logical Junction Based on 2D Crystal PdS2.

    PubMed

    Ghorbani-Asl, Mahdi; Kuc, Agnieszka; Miró, Pere; Heine, Thomas

    2016-02-01

    A single-material logical junction with negligible contact resistance is designed by exploiting quantum-confinement effects in 1T PdS2 . The metallic bilayer serves as electrodes for the semiconducting channel monolayer, avoiding contact resistance. Heat dissipation is then governed by tunnel loss, which becomes negligible at channel lengths larger than 2.45 nm. This value marks the integration limit for a conventional 2D transistor. PMID:26632273

  10. Normal metal tunnel junction-based superconducting quantum interference proximity transistor

    SciTech Connect

    D'Ambrosio, Sophie Meissner, Martin; Blanc, Christophe; Ronzani, Alberto; Giazotto, Francesco

    2015-09-14

    We report the fabrication and characterization of an alternative design for a superconducting quantum interference proximity transistor (SQUIPT) based on a normal metal (N) probe. The absence of direct Josephson coupling between the proximized metal nanowire and the N probe allows us to observe the full modulation of the wire density of states around zero voltage and current via the application of an external magnetic field. This results into a drastic suppression of power dissipation which can be as low as a few ∼10{sup −17} W. In this context, the interferometer allows an improvement of up to four orders of magnitude with respect to earlier SQUIPT designs and makes it ideal for extra-low power cryogenic applications. In addition, the N-SQUIPT has been recently predicted to be the enabling candidate for the implementation of coherent caloritronic devices based on proximity effect.

  11. Design and simulation of an electrically pumped Schottky-junction-based plasmonic amplifier.

    PubMed

    Livani, Abdolber Mallah; Kaatuzian, Hassan

    2015-03-20

    We have investigated an amplifier which operates on surface plasmon polaritons (SPPs). A semiconductor is considered instead of dielectric since its interface with metal can support transverse-magnetic-polarized SPP propagation. A T-shaped cross section for the analyzed waveguide is considered. Metal-semiconductor interface conditions in particular can be regarded as a Schottky junction that has the capability of being pumped electrically. So compensation of propagation loss imposed by metal is possible and beyond that, amplification occurs. This configuration has advantages such as a simple fabrication process and compact size. This scheme has been implemented previously in 3.16, 1.7, and 0.8 μm for increasing the propagation length of the SPP but here, the free-space wavelength of 1.55 μm is considered for designing a plasmonic amplifier. This wavelength is selected because this is the most used wavelength in fiber-optic telecommunications due to its ultralow attenuation in silica. However, designing such an amplifier with too many effects that arise in a Schottky junction may be an extremely difficult process. So simplification, which regards essential effects and ignores nonimportant ones, is included. In this work, gold is considered as the metal and n+-doped In0.53Ga0.47As as the semiconductor to form a Schottky junction. The semiconductor has a doping concentration of 1×1018  cm-3. In forward bias of 1.25 V, the gain coefficient of the SPP mode is estimated up to 337  cm-1 which corresponds to 14.62 dB power gain for a 100 μm long amplifier. PMID:25968496

  12. Magnetic tunnel junction based eddy current testing probe for detection of surface defects

    NASA Astrophysics Data System (ADS)

    Cardoso, F. A.; Rosado, L.; Ferreira, R.; Paz, E.; Cardoso, S.; Ramos, P. M.; Piedade, M.; Freitas, P. P.

    2014-05-01

    In recent years, magnetoresistive sensors have been applied to a large spectrum of applications from biomedical devices to industrial devices. Their high sensitivity and high spatial resolution are of special interest for eddy current based non-destructive testing. In this particular application, giant magnetoresistive sensors have been recently used for detecting surface and buried defects. Nevertheless, although very promising, magnetic tunnel junctions (MTJs) are still barely used in this application. In this work, two sensors with 6 and 10 MTJs in series were successfully fabricated, characterized, and tested on an aluminum mock-up including defects 100 μm wide and with a depth ranging from 0.2 to 1 mm. The sensors including 6 MTJ in series showed sensitivities of 50.8 mV/mT, while the sensor with 10 MTJ in series showed a sensitivity of 84.5 mV/mT. Due to its high sensitivity the latter was able to detect the smallest defect with a signal to noise ratio of 50, which seems promising for more challenging applications.

  13. Magnetic field resistant quantum interferences in Josephson junctions based on bismuth nanowires

    NASA Astrophysics Data System (ADS)

    Li, Chuan; Kasumov, A.; Murani, Anil; Sengupta, Shamashis; Fortuna, F.; Napolskii, K.; Koshkodaev, D.; Tsirlina, G.; Kasumov, Y.; Khodos, I.; Deblock, R.; Ferrier, M.; Guéron, S.; Bouchiat, H.

    2014-12-01

    We investigate proximity-induced superconductivity in micrometer-long bismuth nanowires connected to superconducting electrodes with a high critical field. At low temperature we measure a supercurrent that persists in magnetic fields as high as the critical field of the electrodes (above 11 T). The critical current is also strongly modulated by the magnetic field. In certain samples we find regular, rapid SQUID-like periodic oscillations occurring up to high fields. Other samples exhibit less periodic but full modulations of the critical current on Tesla field scales, with field-caused extinctions of the supercurrent. These findings indicate the existence of low dimensionality, phase coherent, interfering conducting regions through the samples, with a subtle interplay between orbital and spin contributions. We relate these surprising results to the electronic properties of the surface states of bismuth, strong Rashba spin-orbit coupling, large effective g factors, and their effect on the induced pair correlations. In particular, we emphasize the possible contribution of topological edge states of specific facets of the nanowires.

  14. Polarity-tunable magnetic tunnel junctions based on ferromagnetism at oxide heterointerfaces

    NASA Astrophysics Data System (ADS)

    Ngo, Thach D. N.; Chang, Jung-Won; Lee, Kyujoon; Han, Seungju; Lee, Joon Sung; Kim, Young Heon; Jung, Myung-Hwa; Doh, Yong-Joo; Choi, Mahn-Soo; Song, Jonghyun; Kim, Jinhee

    2015-08-01

    Complex oxide systems have attracted considerable attention because of their fascinating properties, including the magnetic ordering at the conducting interface between two band insulators, such as LaAlO3 and SrTiO3. However, the manipulation of the spin degree of freedom at the LaAlO3/SrTiO3 heterointerface has remained elusive. Here, we have fabricated hybrid magnetic tunnel junctions consisting of Co and LaAlO3/SrTiO3 ferromagnets with the insertion of a Ti layer in between, which clearly exhibit magnetic switching and the tunnelling magnetoresistance effect below 10 K. The magnitude and sign of the tunnelling magnetoresistance are strongly dependent on the direction of the rotational magnetic field parallel to the LaAlO3/SrTiO3 plane, which is attributed to a strong Rashba-type spin-orbit coupling in the LaAlO3/SrTiO3 heterostructure. Our study provides a further support for the existence of the macroscopic ferromagnetism at LaAlO3/SrTiO3 heterointerfaces and opens a novel route to realize interfacial spintronics devices.

  15. Single-Molecule Break Junctions Based on a Perylene-Diimide Cyano-Functionalized (PDI8-CN2) Derivative

    NASA Astrophysics Data System (ADS)

    Frisenda, Riccardo; Parlato, Loredana; Barra, Mario; van der Zant, Herre S. J.; Cassinese, Antonio

    2015-07-01

    In this letter, we report the single-molecule conductance properties of a cyano-functionalized perylene-diimide derivative (PDI8-CN2) investigated with gold nano-electrodes. This molecule is of large interest for the fabrication of high-performance and air-stable n-type organic field-effect transistors. Low-bias experiments performed on mechanically controllable break junctions reveal the presence of two different values of the single-molecule conductance, which differ by about two orders of magnitudes. Up to date, this feature was never observed for other perylene-diimide compounds having alternative chemical moieties attached to the basic aromatic core. Theoretical calculations suggest that the highest single-molecule conductance value here observed, comprised between 10-2 and 10-3 G0, is related to a charge transport path directly linking the two cyano groups.

  16. Contact resistance in metal-molecule-metal junctions based on aliphatic SAMs: effects of surface linker and metal work function.

    PubMed

    Beebe, Jeremy M; Engelkes, Vincent B; Miller, Larry L; Frisbie, C Daniel

    2002-09-25

    Using conducting probe atomic force microscopy (CP-AFM), we have formed molecular tunnel junctions consisting of alkanethiols and alkane isonitrile self-assembled monolayers sandwiched between gold, platinum, silver, and palladium contacts. We have measured the resistance of these junctions at low bias (dV/dI |V=0) as a function of alkane chain length. Extrapolation to zero chain length gives the contact resistance, R0 . R0 is strongly dependent on the type of metal used for the contacts and decreases with increasing metal work function; that is, R0,Ag > R0,Au > R0,Pd > R0,Pt. R0 is approximately 10% smaller for Au junctions with isonitrile versus thiol surface linkers. We conclude that the Fermi level of the junction lies much closer to the HOMO than to the LUMO. PMID:12236731

  17. Wafer-scale arrayed p-n junctions based on few-layer epitaxial GaTe

    NASA Astrophysics Data System (ADS)

    Yuan, Xiang; Tang, Lei; Hu, Weida; Xiu, Faxian

    2015-03-01

    Two dimensional (2D) materials have showed appealing applications in electronics and optoelectronics. Gapless graphene presents ultra-broadband and fast photoresponse while the 2D semiconducting MoS2 and GaTe exhibit highly sensitive and tunable responsivity to the visible light. However, the device yield and its repeatability call for a further improvement of 2D materials to render large-scale uniformity. Here we report a layer-by-layer growth of the wafer-scale GaTe by molecular beam epitaxy. To develop the arrayed p-n junctions, the few-layer GaTe was grew on three-inch Si wafers. The resultant diodes reveal good rectifying characteristics and photoresponse with maximum photodetection responsivity of 2.74 A/W and photovoltaic external quantum efficiency up to 62%. The photocurrent reaches saturation very fast within 22 μs and shows no sign of device degradation after 1.37 million cycles of operation. Most strikingly, such high performance has been achieved across the entire wafer, making the volume production of devices accessible. Finally, several photo-images was acquired by using these photodiodes with a reasonable contrast and resolution, demonstrating for the first time the potential for these 2D technology coming into the real life.

  18. Analysis and simulation of nonlinearity and effects of spontaneous emission in Schottky-junction-based plasmonic amplifiers.

    PubMed

    Livani, Abdolber Mallah; Kaatuzian, Hassan

    2015-07-01

    An amplifier that operates on surface plasmon polaritons has been analyzed and simulated. Nonlinearity behavior and the spontaneous emission effects of the plasmonic amplifier are investigated in this paper. A rate equations approach has been used in which parameters are derived from simulation results of the plasmonic amplifier (Silvaco/ATLAS). Details on the method of this derivation are included, which were not previously reported. Rate equations are solved numerically by MATLAB codes. These codes verify the Silvaco results. The plasmonic amplifier operates on surface plasmons with a free-space wavelength of 1550 nm. Results show that, even without the effect of spontaneous emission, gain of the plasmonic amplifier saturates in high input levels. Saturation power, which can be used for comparing nonlinearity of different amplifiers, is 2.1 dBm for this amplifier. Amplified spontaneous emission reduces the gain of the amplifiers, which is long. There is an optimum value for the length of the amplifier. For the amplifier of this work, the optimum length for the small signal condition is 265 μm. PMID:26193159

  19. Magnetic Tunnel Junctions Based on CrO2/SnO2 Epitaxial Bilayers

    SciTech Connect

    Miao, G. X.; LeClair, P.; Gupta, A.; Varela del Arco, Maria; Pennycook, Stephen J

    2006-01-01

    Magnetic tunnel junctions (MTJs) were fabricated using thin films of the half-metallic ferromagnet CrO2, employing semiconducting SnO2 tunnel barriers. Heteroepitaxial CrO2/SnO2 bilayers were grown on (100)-TiO2 substrates via chemical vapor deposition under atmospheric conditions. X-ray diffraction and transmission electron microscopy were used to confirm heteroepitaxy. A polycrystalline cobalt film forms the top magnetic electrode, yielding CrO2(001)/SnO2(001)/Co structures after patterning. Tunneling magnetoresistances (TMR) up to +14% at 5 K were observed. The sign of the TMR reverses for barrier thicknesses < 1nm, attributed to tunneling being dominated by Co-3d states at low thicknesses, and Co-4s states at larger thicknesses.

  20. Carrier Polarity Control in α-MoTe2 Schottky Junctions Based on Weak Fermi-Level Pinning.

    PubMed

    Nakaharai, Shu; Yamamoto, Mahito; Ueno, Keiji; Tsukagoshi, Kazuhito

    2016-06-15

    The polarity of the charge carriers injected through Schottky junctions of α-phase molybdenum ditelluride (α-MoTe2) and various metals was characterized. We found that the Fermi-level pinning in the metal/α-MoTe2 Schottky junction is so weak that the polarity of the carriers (electron or hole) injected from the junction can be controlled by the work function of the metals, in contrast to other transition metal dichalcogenides such as MoS2. From the estimation of the Schottky barrier heights, we obtained p-type carrier (hole) injection from a Pt/α-MoTe2 junction with a Schottky barrier height of 40 meV at the valence band edge. n-Type carrier (electron) injection from Ti/α-MoTe2 and Ni/α-MoTe2 junctions was also observed with Schottky barrier heights of 50 and 100 meV, respectively, at the conduction band edge. In addition, enhanced ambipolarity was demonstrated in a Pt-Ti hybrid contact with a unique structure specially designed for polarity-reversible transistors, in which Pt and Ti electrodes were placed in parallel for injecting both electrons and holes. PMID:27203118

  1. Magnetization reversal and enhanced tunnel magnetoresistance ratio in perpendicular magnetic tunnel junctions based on exchange spring electrodes

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Yin, Xiaolu; Le Roy, D.; Jiang, Jun; Wei, H. X.; Liou, S. H.; Han, X. F.

    2013-04-01

    The [Co/Pt]n multilayer based perpendicular magnetic tunnel junction stacks with wedged Co60Fe20B20 insertions up to 2 nm, and corresponding perpendicular magnetic tunnel junctions were magnetically and electrically investigated. The focus is on the influence of CoFeB insertions in the free and reference electrodes on the overall junction magnetization reversal and magnetoresistance response. The exchange spring behavior was revealed as the Co60Fe20B20 spins canting towards the in-plane direction in the [Co/Pt]n/Co60Fe20B20 hard/soft perpendicular magnetic electrodes. The broad range thickness of wedged Co60Fe20B20 insertion enables to reveal the critical transition, in particular, from rigid coupling to exchange spring coupling. With the help of 375°C annealing under 10 kOe magnetic field, the recovery from distinct multi-domain structure to nearly single domain structure was distinctly observed in the unpatterned perpendicular magnetic tunnel junction (p-MTJ) films with CoFeB thickness tCFB≥1.5 nm. Meanwhile, for the corresponding patterned perpendicular magnetic tunnel junctions with AlOx barrier, the tunnel magnetoresistance (TMR) ratio exhibited an intense enhancement over 100%. The TMR results and spin configurations were illustrated using an exchange spring model in both magnetic electrodes. The presented study shows the benefit of using exchange spring magnetic electrodes in perpendicular magnetic tunnel junction on their performance.

  2. Spin-dependent transport properties of hetero-junction based on zigzag graphene nanoribbons with edge hydrogenation and oxidation

    NASA Astrophysics Data System (ADS)

    Cui, Li-ling; Long, Meng-qiu; Zhang, Xiao-jiao; Li, Xin-mei; Zhang, Dan; Yang, Bing-chu

    2016-02-01

    Using the non-equilibrium Green's function method and the spin-polarized density functional theory, we investigate the magnetism and spin resolved transport properties of hetero-structures based on zigzag graphene nanoribbons (ZGNRs) with edge hydrogenation (H) and oxidation (O). It is found that a perfect spin filtering effect can be realized on O-ZGNR-H/H-ZGNR-H in both parallel and anti-parallel spin configurations. Interestingly, an excellent dual spin filtering behavior can be obtained on O-ZGNR-H/H2-ZGNR-H, which is independent of the width of the nanoribbon. Our results indicate that the hetero-structure holds promise for spintronic devices in future.

  3. Investigation of TiO{sub x} barriers for their use in hybrid Josephson and tunneling junctions based on pnictide thin films

    SciTech Connect

    Döring, S. Monecke, M.; Schmidt, S.; Schmidl, F.; Tympel, V.; Seidel, P.; Engelmann, J.; Kurth, F.; Iida, K.; Holzapfel, B.; Haindl, S.; Mönch, I.

    2014-02-28

    We tested oxidized titanium layers as barriers for hybrid Josephson junctions with high I{sub c}R{sub n}-products and for the preparation of junctions for tunneling spectroscopy. For that we firstly prepared junctions with conventional superconductor electrodes, such as lead and niobium, respectively. By tuning the barrier thickness, we were able to change the junction's behavior from a Josephson junction to tunnel-like behavior applicable for quasi-particle spectroscopy. Subsequently, we transferred the technology to junctions using Co-doped BaFe{sub 2}As{sub 2} thin films prepared by pulsed laser deposition as base electrode and evaporated Pb as counter electrode. For barriers with a thickness of 1.5 nm, we observe clear Josephson effects with I{sub c}R{sub n}≈90 μV at 4.2 K. These junctions behave SNS'-like (SNS: superconductor-normal conductor-superconductor) and are dominated by Andreev reflection transport mechanism. For junctions with barrier thickness of 2.0 nm and higher, no Josephson but SIS'- (SIS: superconductor-insulator-superconductor) or SINS'-like (SINS: superconductor-normal conductor-insulator-superconductor) behavior with a tunnel-like conductance spectrum was observed.

  4. Magnetic-tunnel-junction based low-energy nonvolatile flip-flop using an area-efficient self-terminated write driver

    NASA Astrophysics Data System (ADS)

    Suzuki, Daisuke; Hanyu, Takahiro

    2015-05-01

    A nonvolatile flip-flop (NV-FF) that makes it possible to minimize the backup energy before power-off is proposed. The use of a self-terminated write driver with continuous voltage monitoring enables automatic write-current termination to be performed immediately after the desired data are written, resulting in great energy saving. Moreover, by utilizing single-ended circuitry together with a symmetrical write current path structure, both a nonvolatile storage function and self-termination are compactly embedded in the NV-FF without performance degradation. As a result, the backup energy is reduced by 83% compared to that of the average of conventional magnetic tunnel junction (MTJ)-based NV-FFs with no self-termination. It is also demonstrated that total transistor counts are reduced by 43% compared to a conventional MTJ-based NV-FF with self-termination.

  5. New type of magnetic tunnel junction based on spin filtering through a reduced symmetry oxide: FeCo|Mg3B2O6|FeCo.

    PubMed

    Stewart, Derek A

    2010-01-01

    Magnetic tunnel junctions with high-tunneling magnetoresistance values such as Fe|MgO|Fe capitalize on spin filtering in the oxide region based on the band symmetry of incident electrons. However, these structures rely on magnetic leads and oxide regions of the same cubic symmetry class. A new magnetic tunnel junction (FeCo|Mg(3)B(2)O(6)|FeCo) is presented that uses a reduced symmetry oxide region (orthorhombic) to provide spin filtering between the two cubic magnetic leads. Complex band structure analysis of Mg(3)B(2)O(6) based on density functional calculations shows that significant spin filtering could occur in this system. This new type of magnetic tunnel junction may have been fabricated already and can explain recent experimental studies of rf-sputtered FeCoB|MgO|FeCoB junctions where there is significant B diffusion into the MgO region. PMID:20017563

  6. Effect of an interface Mg insertion layer on the reliability of a magnetic tunnel junction based on a Co2FeAl full-Heusler alloy

    NASA Astrophysics Data System (ADS)

    Lee, Jung-Min; Kil, Gyu Hyun; Lee, Gae Hun; Choi, Chul Min; Song, Yun-Heub; Sukegawa, Hiroaki; Mitani, Seiji

    2014-04-01

    The reliability of a magnetic tunnel junction (MTJ) based on a Co2FeAl (CFA) full-Heusler alloy with a MgO tunnel barrier was evaluated. In particular, the effect of a Mg insertion layer under the MgO was investigated in view of resistance drift by using various voltage stress tests. We compared the resistance change during constant voltage stress (CVS) and confirmed a trap/detrap phenomenon during the interval stress test for samples with and without a Mg insertion layer. The MTJ with a Mg insertion layer showed a relatively small resistance change for the CVS test and a reduced trap/detrap phenomenon for the interval stress test compared to the sample without a Mg insertion layer. This is understood to be caused by the improved crystallinity at the bottom of the CFA/MgO interface due to the Mg insertion layer, which provides a smaller number of trap site during the stress test. As a result, the interface condition of the MgO layer is very important for the reliability of a MTJ using a full-Heusler alloy, and the the insert of a Mg layer at the MgO interface is expected to be an effective method for enhancing the reliability of a MTJ.

  7. Magnetic Tunnel Junction Based Long-Term Short-Term Stochastic Synapse for a Spiking Neural Network with On-Chip STDP Learning.

    PubMed

    Srinivasan, Gopalakrishnan; Sengupta, Abhronil; Roy, Kaushik

    2016-01-01

    Spiking Neural Networks (SNNs) have emerged as a powerful neuromorphic computing paradigm to carry out classification and recognition tasks. Nevertheless, the general purpose computing platforms and the custom hardware architectures implemented using standard CMOS technology, have been unable to rival the power efficiency of the human brain. Hence, there is a need for novel nanoelectronic devices that can efficiently model the neurons and synapses constituting an SNN. In this work, we propose a heterostructure composed of a Magnetic Tunnel Junction (MTJ) and a heavy metal as a stochastic binary synapse. Synaptic plasticity is achieved by the stochastic switching of the MTJ conductance states, based on the temporal correlation between the spiking activities of the interconnecting neurons. Additionally, we present a significance driven long-term short-term stochastic synapse comprising two unique binary synaptic elements, in order to improve the synaptic learning efficiency. We demonstrate the efficacy of the proposed synaptic configurations and the stochastic learning algorithm on an SNN trained to classify handwritten digits from the MNIST dataset, using a device to system-level simulation framework. The power efficiency of the proposed neuromorphic system stems from the ultra-low programming energy of the spintronic synapses. PMID:27405788

  8. Magnetic tunnel junction based on Mn2-xCo2xNi1-xO4 Mixed valent manganite spinels

    NASA Astrophysics Data System (ADS)

    Wu, Jing; Huang, Zhiming; Chu, Junhao

    2013-03-01

    Mn2-xCo2xNi1-xO4 (0 <=x <=1) (MCNO), developing basically from the prototype of Mn3O4, which are spinel-structure mixed-valent manganites and electrical and magnetic properties are closely linked with interactions among spin, orbit and lattice. The electrical conduction mechanism in MCNO is small polarons hopping between localized Mn3 + and Mn4 + octahedral sites. As we known, the magnetic orders of spinel-structure transition metal oxide are commonly ferrimagnetic with antiferromagnetic exchange between tetrahedral and octahedral sites. The conductive electron i.e. eg orbital electron hopping between octahedral Mn3+ and Mn4+ sites tends to be totally spin polarized due to the strong ferromagnetic couple between octahedral sites. Vice versa, the hopping electron enhanced the ferromagnetic couple between Mn3+ and Mn4+ sites by RKKY indirect exchange interaction. This feature of MCNO is very potential for developing MTJ due to the totally spin polarized conductive electrons. MTJs based on MCNO have been constructed by Magnetron Sputtering method. The performance of these MTJs is under studying at present. Supported by NNFS (Grant No. 11204336, 61275111) and SNFS (Grant No.11ZR1442400 and 12ZR1452200).

  9. Observation of large low field magnetoresistance in ramp-edge tunneling junctions based on doped manganite ferromagnetic electrodes and a SrTiO{sub 3} insulator

    SciTech Connect

    Kwon, C.; Jia, Q.X.; Fan, Y.; Hundley, M.F.; Reagor, D.W.; Hawley, M.E.; Peterson, D.E.

    1998-07-01

    The authors report the fabrication of ferromagnet-insulator-ferromagnet junction devices using a ramp-edge geometry based on (La{sub 0.7}Sr{sub 0.3})MnO{sub 3} ferromagnetic electrodes and a SrTiO{sub 3} insulator. The multilayer thin films were deposited using pulsed laser deposition and the devices were patterned using photolithography and ion milling. As expected from the spin-dependent tunneling, the junction magnetoresistance depends on the relative orientation of the magnetization in the electrodes. The maximum junction magnetoresistance (JMR) of 30% is observed below 300 Oe at low temperatures (T < 100 K).

  10. Magnetic Tunnel Junction Based Long-Term Short-Term Stochastic Synapse for a Spiking Neural Network with On-Chip STDP Learning

    NASA Astrophysics Data System (ADS)

    Srinivasan, Gopalakrishnan; Sengupta, Abhronil; Roy, Kaushik

    2016-07-01

    Spiking Neural Networks (SNNs) have emerged as a powerful neuromorphic computing paradigm to carry out classification and recognition tasks. Nevertheless, the general purpose computing platforms and the custom hardware architectures implemented using standard CMOS technology, have been unable to rival the power efficiency of the human brain. Hence, there is a need for novel nanoelectronic devices that can efficiently model the neurons and synapses constituting an SNN. In this work, we propose a heterostructure composed of a Magnetic Tunnel Junction (MTJ) and a heavy metal as a stochastic binary synapse. Synaptic plasticity is achieved by the stochastic switching of the MTJ conductance states, based on the temporal correlation between the spiking activities of the interconnecting neurons. Additionally, we present a significance driven long-term short-term stochastic synapse comprising two unique binary synaptic elements, in order to improve the synaptic learning efficiency. We demonstrate the efficacy of the proposed synaptic configurations and the stochastic learning algorithm on an SNN trained to classify handwritten digits from the MNIST dataset, using a device to system-level simulation framework. The power efficiency of the proposed neuromorphic system stems from the ultra-low programming energy of the spintronic synapses.

  11. Modular Nuclease-Responsive DNA Three-Way Junction-Based Dynamic Assembly of a DNA Device and Its Sensing Application.

    PubMed

    Zhu, Jing; Wang, Lei; Xu, Xiaowen; Wei, Haiping; Jiang, Wei

    2016-04-01

    Here, we explored a modular strategy for rational design of nuclease-responsive three-way junctions (TWJs) and fabricated a dynamic DNA device in a "plug-and-play" fashion. First, inactivated TWJs were designed, which contained three functional domains: the inaccessible toehold and branch migration domains, the specific sites of nucleases, and the auxiliary complementary sequence. The actions of different nucleases on their specific sites in TWJs caused the close proximity of the same toehold and branch migration domains, resulting in the activation of the TWJs and the formation of a universal trigger for the subsequent dynamic assembly. Second, two hairpins (H1 and H2) were introduced, which could coexist in a metastable state, initially to act as the components for the dynamic assembly. Once the trigger initiated the opening of H1 via TWJs-driven strand displacement, the cascade hybridization of hairpins immediately switched on, resulting in the formation of the concatemers of H1/H2 complex appending numerous integrated G-quadruplexes, which were used to obtain label-free signal readout. The inherent modularity of this design allowed us to fabricate a flexible DNA dynamic device and detect multiple nucleases through altering the recognition pattern slightly. Taking uracil-DNA glycosylase and CpG methyltransferase M.SssI as models, we successfully realized the butt joint between the uracil-DNA glycosylase and M.SssI recognition events and the dynamic assembly process. Furthermore, we achieved ultrasensitive assay of nuclease activity and the inhibitor screening. The DNA device proposed here will offer an adaptive and flexible tool for clinical diagnosis and anticancer drug discovery. PMID:26943244

  12. On the conditions for enhanced transport through molecular junctions based on metal centres ligated by pairs of pyridazino-derived ligands

    SciTech Connect

    Ding, Bei; Washington, Victoria; Dunietz, Barry D

    2010-10-10

    Transport properties of a Ni bis-η{sup 2} complex ligated by a pair of bi-pyridazino derivative are considered. This complex provides the opportunity to avoid perpendicular alignment of the ligand π planes. We study the effects of π-bonding and of intramolecular hydrogen bonding between the ligands as mediated by the metal centre on electron transport. The complicated effect of the electronic structure equilibration with the electrodes on the transport is discussed. The analysis at the electronic structure level provides guidelines to design a molecular bridge that is based on metal complexation with effective electronic transport.

  13. Magnetic Tunnel Junction Based Long-Term Short-Term Stochastic Synapse for a Spiking Neural Network with On-Chip STDP Learning

    PubMed Central

    Srinivasan, Gopalakrishnan; Sengupta, Abhronil; Roy, Kaushik

    2016-01-01

    Spiking Neural Networks (SNNs) have emerged as a powerful neuromorphic computing paradigm to carry out classification and recognition tasks. Nevertheless, the general purpose computing platforms and the custom hardware architectures implemented using standard CMOS technology, have been unable to rival the power efficiency of the human brain. Hence, there is a need for novel nanoelectronic devices that can efficiently model the neurons and synapses constituting an SNN. In this work, we propose a heterostructure composed of a Magnetic Tunnel Junction (MTJ) and a heavy metal as a stochastic binary synapse. Synaptic plasticity is achieved by the stochastic switching of the MTJ conductance states, based on the temporal correlation between the spiking activities of the interconnecting neurons. Additionally, we present a significance driven long-term short-term stochastic synapse comprising two unique binary synaptic elements, in order to improve the synaptic learning efficiency. We demonstrate the efficacy of the proposed synaptic configurations and the stochastic learning algorithm on an SNN trained to classify handwritten digits from the MNIST dataset, using a device to system-level simulation framework. The power efficiency of the proposed neuromorphic system stems from the ultra-low programming energy of the spintronic synapses. PMID:27405788

  14. Peach maturity/quality assessment using hyperspectral imaging-based spatially-resolved technique

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The objective of this research was to measure the absorption and reduced scattering coefficients of peaches, using a hyperspectral imaging-based spatially-resolved method, for their maturity/quality assessment. A newly developed optical property measuring instrument was used for acquiring hyperspect...

  15. A 600-µW ultra-low-power associative processor for image pattern recognition employing magnetic tunnel junction-based nonvolatile memories with autonomic intelligent power-gating scheme

    NASA Astrophysics Data System (ADS)

    Ma, Yitao; Miura, Sadahiko; Honjo, Hiroaki; Ikeda, Shoji; Hanyu, Takahiro; Ohno, Hideo; Endoh, Tetsuo

    2016-04-01

    A novel associative processor using magnetic tunnel junction (MTJ)-based nonvolatile memories has been proposed and fabricated under a 90 nm CMOS/70 nm perpendicular-MTJ (p-MTJ) hybrid process for achieving the exceptionally low-power performance of image pattern recognition. A four-transistor 2-MTJ (4T-2MTJ) spin transfer torque magnetoresistive random access memory was adopted to completely eliminate the standby power. A self-directed intelligent power-gating (IPG) scheme specialized for this associative processor is employed to optimize the operation power by only autonomously activating currently accessed memory cells. The operations of a prototype chip at 20 MHz are demonstrated by measurement. The proposed processor can successfully carry out single texture pattern matching within 6.5 µs using 128-dimension bag-of-feature patterns, and the measured average operation power of the entire processor core is only 600 µW. Compared with the twin chip designed with 6T static random access memory, 91.2% power reductions are achieved. More than 88.0% power reductions are obtained compared with the latest associative memories. The further power performance analysis is discussed in detail, which verifies the special superiority of the proposed processor in power consumption for large-capacity memory-based VLSI systems.

  16. Continuously-tuned tunneling behaviors of ferroelectric tunnel junctions based on BaTiO{sub 3}/La{sub 0.67}Sr{sub 0.33}MnO{sub 3} heterostructure

    SciTech Connect

    Ou, Xin; Xu, Bo Yin, Qiaonan; Xia, Yidong; Yin, Jiang; Liu, Zhiguo; Gong, Changjie; Lan, Xuexin

    2014-05-15

    In this work, we fabricate BaTiO{sub 3}/La{sub 0.67}Sr{sub 0.33}MnO{sub 3} (BTO/LSMO) ferroelectric tunnel junction on (001) SrTiO{sub 3} substrate by pulsed laser deposition method. Combining piezoresponse force and conductive-tip atomic force microscopy, we demonstrate robust and reproducible polarization-controlled tunneling behaviors with the resulting tunneling electroresistance value reaching about 10{sup 2} in ultrathin BTO films (∼1.2 nm) at room temperature. Moreover, local poling areas with different conductivity are finally achieved by controlling the relative proportion of upward and downward domains, and different poling areas exhibit stable transport properties.

  17. Nanofabrication of highly ordered, tunable metallic mesostructures via quasi-hard-templating of lyotropic liquid crystals

    PubMed Central

    Zhang, Xinyi; Lu, Wei; Dai, Jiyan; Bourgeois, Laure; Yao, Jianfeng; Wang, Huanting; Friend, James R.; Zhao, Dongyuan; MacFarlane, Douglas R.

    2014-01-01

    The synthesis of metal frameworks perforated with nanotunnels is a challenge because metals have high surface energies that favor low surface area structures; traditional liquid-crystal templating techniques cannot achieve the synthetic control required. We report a synthetic strategy to fabricate metal nanomaterials with highly ordered, tunable mesostructures in confined systems based on a new quasi-hard-templating liquid-crystals mechanism. The resulting platinum nanowires exhibit long range two-dimensional hexagonally ordered mesopore structures. In addition, single crystalline hexagonal mesoporous platinum nanowires with dominant {110} facets have been synthesized. Finally, we demonstrate that the mesostructures of metal nanomaterials can be tuned from hexagonal to lamellar mesostructures. PMID:25502015

  18. Energetics and electronic structure of tubular Si vacancies filled with carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Kochi, Taketo; Okada, Susumu

    2016-05-01

    We studied the energetics and electronic structure of tubular Si vacancies incorporating a carbon nanotube (CNT), using first-principles total-energy calculations based on the density functional theory. Our calculations show that the incorporated CNT into a Si nanotunnel acts as an atom-thickness liner providing the electrostatically flat nanoscale space inside them by shielding the dangling bond states of tubular Si vacancies. The incorporation of the CNT into the tubular Si vacancies is exothermic with an energy gain up to 7.4 eV/nm depending on the diameters of the vacancy and encapsulated CNT. The electronic states of the vacancy substantially hybridize with those of the CNT, leading to the complex electronic energy band near the Fermi level.

  19. Multifractal analysis of satellite images. (Polish Title: Multifraktalna analiza zobrazowan satelitarnych)

    NASA Astrophysics Data System (ADS)

    Wawrzaszek, A.; Krupiński, M.; Drzewiecki, W.; Aleksandrowicz, S.

    2015-12-01

    Research presented in this paper is focused on the efficiency assessment of multifractal description as a tool for Image Information Mining. Large datasets of very high spatial resolution satellite images (WorldView-2 and EROS-A) have been analysed. The results have confirmed the superiority of multifractals as global image descriptors in comparison to monofractals. Moreover, their usefulness in image classification by using decision trees classifiers was confirmed, also in comparison with textural features. Filtration process preceding fractal and multifractal features estimations was also proved to improve classification results. Additionally, airborne hyperspectral data have been initially analysed. Fractal dimension shows high potential for the description of hyperspectral data. To summarise all conducted tests indicate the usefulness of multifractal formalism in various aspects of remote sensing. Prepared methodology can be further developed and used for more specific tasks, for example in change detection or in the description of hyperspectal data complexity.

  20. Correlation analysis of simulated MODIS vegetation indices and the red edge and rice agricultural parameter

    NASA Astrophysics Data System (ADS)

    Cheng, Qian; Wu, Xiuju

    2007-10-01

    In this study, Hyperspectral data of two variety of rice (common rice and hybrid rice) in whole growing stage during 2002 and 2003 was measured using the ASD FieldSpec UV/VNIR Spectroradiometer with resolution of 3 nm, and the LAI and leaf chlorophyll content of rice agricultural parameter were obtained. Analyses of the correlation between rice agricultural parameter, and hyperspectal data, normalized difference vegetation index (NDVI), enhanced vegetation index (EVI) and the red-edge position (REP) were studied. Results showed that a strong non-linear correlation was found between the rice LAI of two varieties and REP. The REP, EVI and NDVI were well related with LAI for the common rice, but the REP and EVI were more sensitive than the NDVI to rice LAI for the hybrid rice because of different body for two variety rice.

  1. Design of nanoporous materials with optimal sorption capacity

    NASA Astrophysics Data System (ADS)

    Zhang, Xuan; Urita, Koki; Moriguchi, Isamu; Tartakovsky, Daniel M.

    2015-06-01

    Modern technological advances have enabled one to manufacture nanoporous materials with a prescribed pore structure. This raises a possibility of using controllable pore-scale parameters (e.g., pore size and connectivity) to design materials with desired macroscopic properties (e.g., diffusion coefficient and adsorption capacity). By relating these two scales, the homogenization theory (or other upscaling techniques) provides a means of guiding the experimental design. To demonstrate this approach, we consider a class of nanoporous materials whose pore space consists of nanotunnels interconnected by nanotube bridges. Such hierarchical nanoporous carbons with mesopores and micropores have shown high specific electric double layer capacitances and high rate capability in an organic electrolyte. We express the anisotropic diffusion coefficient and adsorption coefficient of such materials in terms of the tunnels' properties (pore radius and inter-pore throat width) and their connectivity (spacing between the adjacent tunnels and nanotube-bridge density). Our analysis is applicable for solutes that undergo a non-equilibrium Langmuir adsorption reaction on the surfaces of fluid-filled pores, but other homogeneous and heterogeneous reactions can be handled in a similar fashion. The presented results can be used to guide the design of nanoporous materials with optimal permeability and sorption capacity.

  2. Theory of back-surface-field solar cells

    NASA Technical Reports Server (NTRS)

    Vonroos, O.

    1979-01-01

    Report describes simple concise theory of back-surface-field (BSF) solar cells (npp + junctions) based on Shockley's depletion-layer approximation and cites superiority of two-junction devices over conventional unijunction cells.

  3. Research on method of geometry and spectral calibration of pushbroom dispersive hyperspectral imager

    NASA Astrophysics Data System (ADS)

    He, Zhiping; Shu, Rong; Wang, Jianyu

    2012-11-01

    Development and application of airborne and aerospace hyperspectral imager press for high precision geometry and spectral calibration of pixels of image cube. The research of geometry and spectral calibration of pushbroom hyperspectral imager, its target is giving the coordinate of angle field of view and center wavelength of each detect unit in focal plane detector of hyperspectral imager, and achieves the high precision, full field of view, full channel geometry and spectral calibration. It is importance for imaging quantitative and deep application of hyperspectal imager. The paper takes the geometry and spectral calibration of pushbroom dispersive hyperspectral imager as case study, and research on the constitution and analysis of imaging mathematical model. Aimed especially at grating-dispersive hyperspectral imaging, the specialty of the imaging mode and dispersive method has been concretely analyzed. Based on the analysis, the theory and feasible method of geometry and spectral calibration of dispersive hyperspectral imager is set up. The key technique has been solved is As follows: 1). the imaging mathematical model and feasible method of geometry and spectral calibration for full pixels of image cube has been set up, the feasibility of the calibration method has been analyzed. 2). the engineering model and method of the geometry and spectral calibration of pushbroom dispersive hyperspectral imager has been set up and the calibration equipment has been constructed, and the calibration precision has been analyzed.

  4. Hyperspectral-LIDAR system and data product integration for terrestrial applications

    NASA Astrophysics Data System (ADS)

    Corp, Lawrence A.; Cheng, Yen-Ben; Middleton, Elizabeth M.; Parker, Geoffrey G.; Huemmrich, K. Fred; Campbell, Petya K. E.

    2009-08-01

    This manuscript details the development and validation of a unique forward thinking instrument and methodology for monitoring terrestrial carbon dynamics through synthesis of existing hyperspectal sensing and Light Detection and Ranging (LIDAR) technologies. This technology demonstration is directly applicable to linking target mission concepts identified as scientific priorities in the National Research Council (NRC, 2007) Earth Science Decadal Survey; namely, DESDynI and HyspIRI. The primary components of the Hyperspec-LIDAR system are the ruggedized imaging spectrometer and a small footprint LIDAR system. The system is mounted on a heavy duty motorized pan-tilt unit programmed to support both push-broom style hyperspectral imaging and 3-D canopy LIDAR structural profiling. The integrated Hyperspec-LIDAR sensor system yields a hypserspectral data cube with up to 800 bands covering the spectral range of 400 to 1000 nm and a 3-D scanning LIDAR system accurately measuring the vertical distribution of intercepted surfaces within a range of 150 m with an accuracy of 15 mm. Preliminary field tests of the Hyperspec-LIDAR sensor system were conducted at a mature deciduous mixed forest tower site located at the Smithsonian Environmental Research Center in Edgewater, MD. The goal of this research is to produce integrated science and data products from ground observations that will support satellite-based hybrid spectral/structural profile linked through appropriate models to monitor Net Ecosystem Exchange and related parameters such as ecosystem Light Use Efficiency.

  5. Standoff aircraft IR characterization with ABB dual-band hyper spectral imager

    NASA Astrophysics Data System (ADS)

    Prel, Florent; Moreau, Louis; Lantagne, Stéphane; Bullis, Ritchie D.; Roy, Claude; Vallières, Christian; Levesque, Luc

    2012-09-01

    Remote sensing infrared characterization of rapidly evolving events generally involves the combination of a spectro-radiometer and infrared camera(s) as separated instruments. Time synchronization, spatial coregistration, consistent radiometric calibration and managing several systems are important challenges to overcome; they complicate the target infrared characterization data processing and increase the sources of errors affecting the final radiometric accuracy. MR-i is a dual-band Hyperspectal imaging spectro-radiometer, that combines two 256 x 256 pixels infrared cameras and an infrared spectro-radiometer into one single instrument. This field instrument generates spectral datacubes in the MWIR and LWIR. It is designed to acquire the spectral signatures of rapidly evolving events. The design is modular. The spectrometer has two output ports configured with two simultaneously operated cameras to either widen the spectral coverage or to increase the dynamic range of the measured amplitudes. Various telescope options are available for the input port. Recent platform developments and field trial measurements performances will be presented for a system configuration dedicated to the characterization of airborne targets.

  6. Classifier Fusion of Hyperspectral and LIDAR Remote Sensing Data for Improvement of Land Cover Classifcation

    NASA Astrophysics Data System (ADS)

    Bigdeli, B.; Samadzadegan, F.; Reinartz, P.

    2013-09-01

    The interest in the joint use of remote sensing data from multiple sensors has been remarkably increased for classification applications. This is because a combined use is supposed to improve the results of classification tasks compared to single-data use. This paper addressed using of combination of hyperspectral and Light Detection And Ranging (LIDAR) data in classification field. This paper presents a new method based on the definition of a Multiple Classifier System on Hyperspectral and LIDAR data. In the first step, the proposed method applied some feature extraction strategies on LIDAR data to produce more information in this data set. After that in second step, Support Vector Machine (SVM) applied as a supervised classification strategy on LIDAR data and hyperspectal data separately. In third and final step of proposed method, a classifier fusion method used to fuse the classification results on hypersepctral and LIDAR data. For comparative purposes, results of classifier fusion compared to the results of single SVM classifiers on Hyperspectral and LIDAR data. Finally, the results obtained by the proposed classifier fusion system approach leads to higher classification accuracies compared to the single classifiers on hyperspectral and LIDAR data.

  7. The Narrow Band AOTF Based Hyperspectral Microscopic Imaging on the Rat Skin Stratum Configuration

    NASA Astrophysics Data System (ADS)

    Zhang, C.; Wang, H.; Huang, J.; Gao, Q.

    2014-08-01

    A noncollinear acousto-optic tunable filter (AOTF) was designed with a comprehensive treatment of the properties of TeO2 as an acoustooptic (A-O) material. The results of optical testing validated that it predicted the performance of the designed AOTF. The bandwidth of the AOTF was very narrow in the visible light range. The high spectral resolution of AOTF was useful in practical applications to the hyperspectral imaging. The experimentally observed spectral pattern of the diffracted light was nearly the same as the theoretical result. The measured tuning relationship between the diffracted central optical wavelength and acoustic frequency was in accordance with the theoretical prediction. It demonstrates the accuracy of our design theory. Furthermore, by selecting the AOTF as the spectroscopic element, a hyperspectral microscopic imaging system was designed. The hyperspectral microscopic images of the rat skin tissue under the different optical center wavelength were acquired. The experimental results indicated that the imaging performance was satisfactory. The stratums of the rat skin can be clearly distinguished. The inner details of the epidermis and the corium can be shown on the hyperspectral microscopic images. Some differences also can be found by the comparison of the hyperspectal images under the different optical wavelengths. The study indicated the applicability and the advantage of our system on biomedicine area.

  8. Time-temperature evolution of microtextures and contained fluids in a plutonic alkali feldspar during heating

    NASA Astrophysics Data System (ADS)

    Parsons, Ian; Fitz Gerald, John D.; Lee, James K. W.; Ivanic, Tim; Golla-Schindler, Ute

    2010-08-01

    Microtextural changes brought about by heating alkali feldspar crystals from the Shap granite, northern England, at atmospheric pressure, have been studied using transmission and scanning electron microscopy. A typical unheated phenocryst from Shap is composed of about 70 vol% of tweed orthoclase with strain-controlled coherent or semicoherent micro- and crypto-perthitic albite lamellae, with maximum lamellar thicknesses <1 μm. Semicoherent lamellae are encircled by nanotunnel loops in two orientations and cut by pull-apart cracks. The average bulk composition of this microtexture is Ab27.6Or71.8An0.6. The remaining 30 vol% is deuterically coarsened, microporous patch and vein perthite composed of incoherent subgrains of oligoclase, albite and irregular microcline. The largest subgrains are ~3 μm in diameter. Heating times in the laboratory were 12 to 6,792 h and T from 300°C into the melting interval at 1,100°C. Most samples were annealed at constant T but two were heated to simulate an 40Ar/39Ar step-heating schedule. Homogenisation of strain-controlled lamellae by Na↔K inter-diffusion was rapid, so that in all run products at >700°C, and after >48 h at 700°C, all such regions were essentially compositionally homogeneous, as indicated by X-ray analyses at fine scale in the transmission electron microscope. Changes in lamellar thickness with time at different T point to an activation energy of ~350 kJmol-1. A lamella which homogenised after 6,800 h at 600°C, therefore, would have required only 0.6 s to do so in the melting interval at 1,100°C. Subgrains in patch perthite homogenised more slowly than coherent lamellae and chemical gradients in patches persisted for >5,000 h at 700°C. Homogenisation T is in agreement with experimentally determined solvi for coherent ordered intergrowths, when a 50-100°C increase in T for An1 is applied. Homogenisation of lamellae appears to proceed in an unexpected manner: two smooth interfaces, microstructurally sharp

  9. Photoresponse enhancement in graphene/silicon infrared detector by controlling photocarrier collection

    NASA Astrophysics Data System (ADS)

    Tang, Xin; Zhang, Hengkai; Tang, Xiaobing; Lai, King W. C.

    2016-07-01

    Graphene/silicon junction based photodetectors have attracted great interest due to their superior characteristics like large photosensitive area, fast photocarrier collection and low dark current. Currently, the weak optical absorption and short photocarrier lifetime of graphene remain major limitations for detection of infrared light with wavelengths above 1.2 μm. Here, we elucidate the mechanism of photocarrier transport in graphene/silicon junction based photodetector and propose a theoretical model to study the design and effect of finger-electrode structures on the photocurrent in graphene. We demonstrate that the top finger-like electrode in graphene/silicon photodetector can be designed to enhance the photocarrier collection efficiency in graphene by reducing the average transport distance of photocarriers. Therefore, the photoresponsivity of the graphene/silicon junction based photodetector can be increased. Our results have successfully demonstrated that by optimizing the design of finger electrodes, 4 times enhancement of photocurrents in graphene can be obtained at room temperature.

  10. Ferroelectric-semiconductor photovoltaics: Non-PN junction solar cells

    NASA Astrophysics Data System (ADS)

    Liu, Fude; Wang, Wentao; Wang, Lei; Yang, Guandong

    2014-03-01

    Traditional positive-negative (PN) junction based solar cells have many limitations. Herein, we introduce ferroelectric-semiconductor solar cells that use the bound surface charges of the ferroelectric for achieving charge separation in the semiconductor. The feasibility of the new concept cells was verified both experimentally and theoretically in detail. The new cells are unique in that free charge carriers and fixed charge carriers are physically separated from each other. The feature allows us to go beyond traditional junction-based structures and have more freedom in material selection, device design, and fabrication.

  11. Suspended InAs nanowire Josephson junctions assembled via dielectrophoresis

    NASA Astrophysics Data System (ADS)

    Montemurro, D.; Stornaiuolo, D.; Massarotti, D.; Ercolani, D.; Sorba, L.; Beltram, F.; Tafuri, F.; Roddaro, S.

    2015-09-01

    We present a novel technique for the realization of suspended Josephson junctions based on InAs semiconductor nanowires. The devices are assembled using a technique of drop-casting guided by dielectrophoresis, which allows one to finely align the nanostructures on top of the electrodes. The proposed architecture removes the interaction between the nanowire and the substrate which is known to influence disorder and the orientation of the Rashba vector. The relevance of this approach in view of the implementation of hybrid Josephson junctions based on semiconducting nanowires coupled with high-temperature superconductors is discussed.

  12. Suspended InAs nanowire Josephson junctions assembled via dielectrophoresis.

    PubMed

    Montemurro, D; Stornaiuolo, D; Massarotti, D; Ercolani, D; Sorba, L; Beltram, F; Tafuri, F; Roddaro, S

    2015-09-25

    We present a novel technique for the realization of suspended Josephson junctions based on InAs semiconductor nanowires. The devices are assembled using a technique of drop-casting guided by dielectrophoresis, which allows one to finely align the nanostructures on top of the electrodes. The proposed architecture removes the interaction between the nanowire and the substrate which is known to influence disorder and the orientation of the Rashba vector. The relevance of this approach in view of the implementation of hybrid Josephson junctions based on semiconducting nanowires coupled with high-temperature superconductors is discussed. PMID:26335273

  13. Server-side Filtering and Aggregation within a Distributed Environment

    NASA Astrophysics Data System (ADS)

    Currey, J. C.; Bartle, A.

    2015-12-01

    Intercalibration, validation, and data mining use cases require more efficient access to the massive volumes of observation data distributed across multiple agency data centers. The traditional paradigm of downloading large volumes of data to a centralized server or desktop computer for analysis is no longer viable. More analysis should be performed within the host data centers using server-side functions. Many comparative analysis tasks require far less than 1% of the available observation data. The Multi-Instrument Intercalibration (MIIC) Framework provides web services to find, match, filter, and aggregate multi-instrument observation data. Matching measurements from separate spacecraft in time, location, wavelength, and viewing geometry is a difficult task especially when data are distributed across multiple agency data centers. Event prediction services identify near coincident measurements with matched viewing geometries near orbit crossings using complex orbit propagation and spherical geometry calculations. The number and duration of event opportunities depend on orbit inclinations, altitude differences, and requested viewing conditions (e.g., day/night). Event observation information is passed to remote server-side functions to retrieve matched data. Data may be gridded, spatially convolved onto instantaneous field-of-views, or spectrally resampled or convolved. Narrowband instruments are routinely compared to hyperspectal instruments such as AIRS and CRIS using relative spectral response (RSR) functions. Spectral convolution within server-side functions significantly reduces the amount of hyperspectral data needed by the client. This combination of intelligent selection and server-side processing significantly reduces network traffic and data to process on local servers. OPeNDAP is a mature networking middleware already deployed at many of the Earth science data centers. Custom OPeNDAP server-side functions that provide filtering, histogram analysis (1D

  14. Qubit readout with a directional parametric amplifier

    NASA Astrophysics Data System (ADS)

    Sliwa, K. M.; Abdo, B.; Narla, A.; Shankar, S.; Hatridge, M.; Frunzio, L.; Schoelkopf, R. J.; Devoret, M. H.

    2014-03-01

    Josephson junction based quantum limited parametric amplifiers play an essential role in superconducting qubit measurements. These measurements necessitate circulators and isolators between the amplifier and qubit to add directionality and/or isolation. Unfortunately, this extra hardware limits both quantum measurement efficiency and experimental scalability. Here we present a quantum-limited Josephson-junction-based directional amplifier (JDA) based on a novel coupling between two nominally identical Josephson parametric converters (JPCs). The device achieves a forward gain of 11 dB with a 15 MHz dynamical bandwidth, but higher gains are possible at the expense of bandwidth. We also present measurements of a transmon qubit made with the JDA, and show minimal measurement back-action despite the absence of any isolator or circulator before the amplifier. These results provide a first step toward realizing on-chip integration of qubits and parametric amplifiers. Work supported by: IARPA, ARO, and NSF.

  15. Quantum memory with millisecond coherence in circuit QED

    NASA Astrophysics Data System (ADS)

    Reagor, Matthew; Pfaff, Wolfgang; Axline, Christopher; Heeres, Reinier W.; Ofek, Nissim; Sliwa, Katrina; Holland, Eric; Wang, Chen; Blumoff, Jacob; Chou, Kevin; Hatridge, Michael J.; Frunzio, Luigi; Devoret, Michel H.; Jiang, Liang; Schoelkopf, Robert J.

    2016-07-01

    Significant advances in coherence render superconducting quantum circuits a viable platform for fault-tolerant quantum computing. To further extend capabilities, highly coherent quantum systems could act as quantum memories for these circuits. A useful quantum memory must be rapidly addressable by Josephson-junction-based artificial atoms, while maintaining superior coherence. We demonstrate a superconducting microwave cavity architecture that is highly robust against major sources of loss that are encountered in the engineering of circuit QED systems. The architecture allows for storage of quantum superpositions in a resonator on the millisecond scale, while strong coupling between the resonator and a transmon qubit enables control, encoding, and readout at MHz rates. This extends the maximum available coherence time attainable in superconducting circuits by almost an order of magnitude compared to earlier hardware. Our design is an ideal platform for studying coherent quantum optics and marks an important step towards hardware-efficient quantum computing in Josephson-junction-based quantum circuits.

  16. Automated position control of a surface array relative to a liquid microjunction surface sampler

    DOEpatents

    Van Berkel, Gary J.; Kertesz, Vilmos; Ford, Michael James

    2007-11-13

    A system and method utilizes an image analysis approach for controlling the probe-to-surface distance of a liquid junction-based surface sampling system for use with mass spectrometric detection. Such an approach enables a hands-free formation of the liquid microjunction used to sample solution composition from the surface and for re-optimization, as necessary, of the microjunction thickness during a surface scan to achieve a fully automated surface sampling system.

  17. Hyper-Cam automated calibration method for continuous hyperspectral imaging measurements

    NASA Astrophysics Data System (ADS)

    Gagnon, Jean-Philippe; Habte, Zewdu; George, Jacks; Farley, Vincent; Tremblay, Pierre; Chamberland, Martin; Romano, Joao; Rosario, Dalton

    2010-04-01

    COTS hyperspectal sensors that allows for full autonomous data collection capability for the user. The accuracy of the automatic calibration was characterized and is presented in this paper.

  18. Challenges in collecting hyperspectral imagery of coastal waters using Unmanned Aerial Vehicles (UAVs)

    NASA Astrophysics Data System (ADS)

    English, D. C.; Herwitz, S.; Hu, C.; Carlson, P. R., Jr.; Muller-Karger, F. E.; Yates, K. K.; Ramsewak, D.

    2013-12-01

    Airborne multi-band remote sensing is an important tool for many aquatic applications; and the increased spectral information from hyperspectral sensors may increase the utility of coastal surveys. Recent technological advances allow Unmanned Aerial Vehicles (UAVs) to be used as alternatives or complements to manned aircraft or in situ observing platforms, and promise significant advantages for field studies. These include the ability to conduct programmed flight plans, prolonged and coordinated surveys, and agile flight operations under difficult conditions such as measurements made at low altitudes. Hyperspectral imagery collected from UAVs should allow the increased differentiation of water column or shallow benthic communities at relatively small spatial scales. However, the analysis of hyperspectral imagery from airborne platforms over shallow coastal waters differs from that used for terrestrial or oligotrophic ocean color imagery, and the operational constraints and considerations for the collection of such imagery from autonomous platforms also differ from terrestrial surveys using manned aircraft. Multispectral and hyperspectral imagery of shallow seagrass and coral environments in the Florida Keys were collected with various sensor systems mounted on manned and unmanned aircrafts in May 2012, October 2012, and May 2013. The imaging systems deployed on UAVs included NovaSol's Selectable Hyperspectral Airborne Remote-sensing Kit (SHARK), a Tetracam multispectral imaging system, and the Sunflower hyperspectal imager from Galileo Group, Inc. The UAVs carrying these systems were Xtreme Aerial Concepts' Vision-II Rotorcraft UAV, MLB Company's Bat-4 UAV, and NASA's SIERRA UAV, respectively. Additionally, the Galileo Group's manned aircraft also surveyed the areas with their AISA Eagle hyperspectral imaging system. For both manned and autonomous flights, cloud cover and sun glint (solar and viewing angles) were dominant constraints on retrieval of quantitatively

  19. Water consumption information and other hydrologic retrievals from the proposed NASA HyspIRI mission

    NASA Astrophysics Data System (ADS)

    Allen, R. G.; Anderson, M. C.; Hook, S. J.

    2010-12-01

    soil water extraction by roots or by surface evaporation. The combination of energy balance, ET and other thermally based information with the hyperspectal VSWIR will complement retrievals of other hydrologic related information from other satellites.

  20. Potential Application of Novel Hyperspectral LIDAR for Monitoring Crops Nitrogen Stress

    NASA Astrophysics Data System (ADS)

    Shi, Shuo; Gong, Wei; Du, Lin; Sun, Jia; Yang, Jian

    2016-06-01

    Precision agriculture has always been the research hotspot around the world. And the optimization of nitrogen fertilization for crops is the core concerns. It is not only to improve the productivity of crops but also to avoid the environmental risks caused by over-fertilization. Therefore, accurate estimation of nitrogen status is crucial for determining an nitrogen recommendation. Remote sensing techniques have been widely used to monitor crops for years, and they could offer estimations for stress status diagnosis through obtaining vertical structure parameters and spectral reflectance properties of crops. As an active remote sensing technology, lidar is particularly attractive for 3-dimensional information at a high point density. It has unique edges in obtaining vertical structure parameters of crops. However, capability of spectral reflectance properties is what the current lidar technology lacks because of single wavelength detection. To solve this problem, the concept of novel hyperspectral lidar (HSL), which combines the advantages of hyperspectal reflectance with high 3-dimensional capability of lidar, was proposed in our study. The design of instrument was described in detail. A broadband laser pulse was emitted and reflectance spectrum with 32 channels could be detected. Furthermore, the experiment was carried out by the novel HSL system to testify the potential application for monitoring nitrogen stress. Rice under different levels of nitrogen fertilization in central China were selected as the object of study, and four levels of nitrogen fertilization (N1-N4) were divided. With the detection of novel lidar system, high precision structure parameters of crops could be provided. Meanwhile, spectral reflectance properties in 32 wavebands were also obtained. The high precision structure parameters could be used to evaluate the stress status of crops. And abundant spectral information in 32 wavebands could improve the capacity of lidar system significantly

  1. Stacking fault induced tunnel barrier in platelet graphite nanofiber

    SciTech Connect

    Lan, Yann-Wen E-mail: ywlan@phys.sinica.edu.tw; Chang, Yuan-Chih; Chang, Chia-Seng; Chen, Chii-Dong E-mail: ywlan@phys.sinica.edu.tw; Chang, Wen-Hao; Li, Yuan-Yao

    2014-09-08

    A correlation study using image inspection and electrical characterization of platelet graphite nanofiber devices is conducted. Close transmission electron microscopy and diffraction pattern inspection reveal layers with inflection angles appearing in otherwise perfectly stacked graphene platelets, separating nanofibers into two domains. Electrical measurement gives a stability diagram consisting of alternating small-large Coulomb blockade diamonds, suggesting that there are two charging islands coupled together through a tunnel junction. Based on these two findings, we propose that a stacking fault can behave as a tunnel barrier for conducting electrons and is responsible for the observed double-island single electron transistor characteristics.

  2. Engineering ferroelectric tunnel junctions through potential profile shaping

    SciTech Connect

    Boyn, S.; Garcia, V. Fusil, S.; Carrétéro, C.; Garcia, K.; Collin, S.; Deranlot, C.; Bibes, M.; Barthélémy, A.

    2015-06-01

    We explore the influence of the top electrode materials (W, Co, Ni, Ir) on the electronic band profile in ferroelectric tunnel junctions based on super-tetragonal BiFeO{sub 3}. Large variations of the transport properties are observed at room temperature. In particular, the analysis of current vs. voltage curves by a direct tunneling model indicates that the metal/ferroelectric interfacial barrier height increases with the top-electrode work function. While larger metal work functions result in larger OFF/ON ratios, they also produce a large internal electric field which results in large and potentially destructive switching voltages.

  3. Stacking fault induced tunnel barrier in platelet graphite nanofiber

    NASA Astrophysics Data System (ADS)

    Lan, Yann-Wen; Chang, Wen-Hao; Li, Yuan-Yao; Chang, Yuan-Chih; Chang, Chia-Seng; Chen, Chii-Dong

    2014-09-01

    A correlation study using image inspection and electrical characterization of platelet graphite nanofiber devices is conducted. Close transmission electron microscopy and diffraction pattern inspection reveal layers with inflection angles appearing in otherwise perfectly stacked graphene platelets, separating nanofibers into two domains. Electrical measurement gives a stability diagram consisting of alternating small-large Coulomb blockade diamonds, suggesting that there are two charging islands coupled together through a tunnel junction. Based on these two findings, we propose that a stacking fault can behave as a tunnel barrier for conducting electrons and is responsible for the observed double-island single electron transistor characteristics.

  4. Solar cells made by laser-induced diffusion directly from phosphine gas

    SciTech Connect

    Turner, G.B.; Tarrant, D.; Pollock, G.; Pressley, R.; Press, R.

    1981-12-15

    A new method for making p-n junctions based on immersion in a transparent dopant gas followed by irradiation with a pulsed laser is presented. An alexandrite laser was used, operating at 0.73 ..mu..m where photolysis of the dopant gas PH/sub 3/ does not occur. Multiple pulses of 2.2--2.7 J/cm/sup 2/ were used to make Si solar cells with total area efficiencies up to 8.6% without benefit of antireflection coatings.

  5. Electroluminescent Devices Using RE-Doped III-Nitrides

    NASA Astrophysics Data System (ADS)

    Wakahara, Akihiro

    The III-nitride semiconductors doped with RE atoms appear to be excellent materials for thin film optical device applications. The spectral coverage extends from UV to infrared and thus light-emitting devices suitable for full-color displays, solid-state lasers, and optical telecommunication fields are expected. This chapter reviews the current status of electrically pumped light-emitting devices based on RE-doped GaN, such as AC- and/or DC-biased electroluminescent (EL) devices and `p-n' junction based light-emitting diodes. The different excitation mechanisms are reviewed.

  6. Electroluminescent Devices Using RE-Doped III-Nitrides

    NASA Astrophysics Data System (ADS)

    Wakahara, Akihiro

    The III-nitride semiconductors doped with RE atoms appear to be excellent materials for thin film optical device applications. The spectral coverage extends from UV to infrared and thus light-emitting devices suitable for full-color displays, solid-state lasers, and optical telecommunication fields are expected. This chapter reviews the current status of electrically pumped light-emitting devices based on RE-doped GaN, such as AC- and/or DC-biased electroluminescent (EL) devices and 'p-n' junction based light-emitting diodes. The different excitation mechanisms are reviewed.

  7. Gap-engineered quasiparticle traps in the fluxonium artificial atom

    NASA Astrophysics Data System (ADS)

    Serniak, K.; de Lange, G.; Vool, U.; Hays, M.; Burkhart, L. D.; Gao, Y. Y.; Wang, C.; Sliwa, K. M.; Pop, I. M.; Frunzio, L.; Glazman, L. I.; Schoelkopf, R. J.; Devoret, M. H.

    Recent experiments have shown that the density of quasiparticles in superconducting quantum circuits exceeds the expected thermal density. In Josephson junction based superconducting qubits, these non-equilibrium quasiparticles can tunnel through the junctions of the circuit, causing decoherence. Quasiparticle traps aim to reduce the density of quasiparticles near the junctions, and therefore the rate of energy loss and dephasing due to tunneling events. These traps must be designed to not introduce any additional losses in the qubit. In this talk we will discuss recent progress in the design and implementation of quasiparticle traps in the fluxonium artificial atom. Work supported by ARO, ONR, YINQE, and the European Union.

  8. Determination of Na acceptor level in Na+ ion-implanted ZnO single crystal

    NASA Astrophysics Data System (ADS)

    Wang, Zheng; Liu, Huibin; He, Haiping; Huang, Jingyun; Chen, Lingxiang; Ye, Zhizhen

    2015-03-01

    Ion implantation was used to dope Na acceptor into ZnO single crystals. With three mixed implantation energies, uniform depth distribution of Na ion in the surface region (~300 nm) of ZnO bulk crystals is achieved. Via post-implantation annealing, a donor-acceptor pair recombination band is identified in the low-temperature photoluminescence spectra, from which the energy level of Na-related acceptor in single crystalline ZnO is estimated to be 300 meV. A p-n junction based on this ZnO-Na layer shows rectifying characteristics, confirming the p-type conductivity.

  9. Nonintrusive Measurement Of Temperature Of LED Junction

    NASA Technical Reports Server (NTRS)

    Leidecker, Henning; Powers, Charles

    1991-01-01

    Temperature inferred from spectrum of emitted light. Method of determining temperature of junction based on two relevant characteristics of LED. Gap between valence and conduction electron-energy bands in LED material decreases with increasing temperature, causing wavelength of emitted photon to increase with temperature. Other, as temperature increases, non-radiative processes dissipate more of input electrical energy as heat and less as photons in band-gap wavelenth region; optical and quantum efficiencies decrease with increasing temperature. In principal, either characteristic alone used to determine temperature. However, desirable to use both to obtain indication of uncertainty.

  10. Enhancement of spin-torque diode sensitivity in a magnetic tunnel junction by parametric synchronization

    NASA Astrophysics Data System (ADS)

    Tiwari, Dhananjay; Sisodia, Naveen; Sharma, Raghav; Dürrenfeld, P.; Åkerman, J.; Muduli, P. K.

    2016-02-01

    We demonstrate enhanced radio frequency (RF) detection sensitivity in a magnetic tunnel junction based spin torque oscillator (STO) using parametric synchronization. The parametric synchronization is observed above the auto-oscillation threshold of the STO and enhances the RF sensitivity at 2f0, where f0 is the auto-oscillation frequency. The maximum RF sensitivity for parametric synchronization at 2 f0≃9 GHz is 16 mV/mW, while the maximum RF sensitivity at f0≃4.5 GHz without parametric synchronization is 12 mV/mW. Macrospin simulations corroborate the experimental results.

  11. Enhanced Magnetoresistance in Molecular Junctions by Geometrical Optimization of Spin-Selective Orbital Hybridization.

    PubMed

    Rakhmilevitch, David; Sarkar, Soumyajit; Bitton, Ora; Kronik, Leeor; Tal, Oren

    2016-03-01

    Molecular junctions based on ferromagnetic electrodes allow the study of electronic spin transport near the limit of spintronics miniaturization. However, these junctions reveal moderate magnetoresistance that is sensitive to the orbital structure at their ferromagnet-molecule interfaces. The key structural parameters that should be controlled in order to gain high magnetoresistance have not been established, despite their importance for efficient manipulation of spin transport at the nanoscale. Here, we show that single-molecule junctions based on nickel electrodes and benzene molecules can yield a significant anisotropic magnetoresistance of up to ∼200% near the conductance quantum G0. The measured magnetoresistance is mechanically tuned by changing the distance between the electrodes, revealing a nonmonotonic response to junction elongation. These findings are ascribed with the aid of first-principles calculations to variations in the metal-molecule orientation that can be adjusted to obtain highly spin-selective orbital hybridization. Our results demonstrate the important role of geometrical considerations in determining the spin transport properties of metal-molecule interfaces. PMID:26926769

  12. Morphology-tunable assembly of periodically aligned Si nanowire and radial pn junction arrays for solar cell applications

    NASA Astrophysics Data System (ADS)

    Li, Xiaocheng; Liang, Kun; Tay, Beng Kang; Teo, Edwin H. T.

    2012-06-01

    Large-area periodically aligned Si nanowire (PASiNW) arrays have been fabricated on Si substrates via a templated catalytic chemical etching process. The diameter, length, packing density, and even the shape of Si nanowires (SiNWs) could be precisely controlled and tuned. A local coupling redox mechanism involving the reduction of H2O2 on silver particles and the dissolution of Si is responsible for formation of SiNWs. With the as-prepared SiNWs as templates, three kinds of PASiNW radial pn junction structures were fabricated on Si substrates via a solid-state phosphorous diffusion strategy and their applications in solar cells were also explored. The PASiNW radial pn junction-based solar cell with big diameter and interspace shows the highest power conversion efficiency (PCE) of 4.10% among the three kinds of devices. Further optimization, including surface passivation and electrode contact, is still needed for the higher efficiency PASiNW radial pn junction-based solar cells in the future.

  13. Channel waveguides and y-junctions in x-cut single-crystal lithium niobate thin film.

    PubMed

    Cai, Lutong; Kong, Ruirui; Wang, Yiwen; Hu, Hui

    2015-11-01

    Proton exchanged channel waveguides in x-cut single-crystal lithium niobate thin film could avoid optical leakage loss which existed in the z-cut case. Indicated by simulations, the mechanism and condition of the optical leakage loss were studied. The light energy in the exchanged layer and the mode sizes were calculated to optimize the parameters for fabrication. By a very short time (3 minutes) proton exchange process without anneal, the channel waveguide with 2 μm width and 0.16 μm exchanged depth in the x-cut lithium niobate thin film had a propagation loss as low as 0.2 dB/cm at 1.55 μm. Furthermore, the Y-junctions based on the low-loss waveguide were designed and fabricated. For a Y-junction based on the 3 μm wide channel waveguide with 8000 μm bending radius, the total transmission could reach 85% ~90% and the splitting ratio maintained at a stable level around 1:1. The total length was smaller than 1 mm, much shorter than the conventional Ti-diffused and proton exchanged Y-junctions in bulk lithium niobate. PMID:26561191

  14. Energetic initiators with narrow firing thresholds using Al/CuO Schottky junctions

    NASA Astrophysics Data System (ADS)

    Wang, Feng; Zhu, Peng; Li, Jie; Hu, Bo; Shen, Ruiqi; Ye, Yinghua

    2016-07-01

    We designed and prepared Schottky-junction-based Al/CuO energetic initiators with narrow firing thresholds according to Schottky barrier theory. Using various characterization methods, we preliminarily investigated the electrical breakdown property, withstand strike current ability, and multiple-firing performance of the energetic initiators. The breakdown voltage of the Al/CuO Schottky junction was ~8 V; and electrical breakdown in the initiators occurred one by one rather than simultaneously. The withstand strike current ability of the initiator mainly depended on the heat capacity of its ceramic plug when the electrical stimulus is more than ~8 V, its breakdown voltage. The ceramic plug can absorb heat from the initiator chip, letting the initiator withstand a constant current of 0.5 A for 20 s. More importantly, the initiators might be able to withstand hard electromagnetic interference by coupling the multiple-firing performance with an out-of-line slider in the explosive train. This knowledge of the characteristics of Schottky-junction-based Al/CuO energetic initiators will help in preparing highly insensitive, efficient initiating explosive devices for weapon systems.

  15. Long-range spin current driven by superconducting phase difference in a josephson junction with double layer ferromagnets.

    PubMed

    Hikino, S; Yunoki, S

    2013-06-01

    We theoretically study spin current through ferromagnet (F) in a Josephson junction composed of s-wave superconductors and two layers of ferromagnets. Using quasiclassical theory, we show that the long-range spin current can be driven by the superconducting phase difference without a voltage drop. The origin of this spin current is due to spin-triplet Cooper pairs (STCs) formed by electrons of equal spin, which are induced by the proximity effect inside the F. We find that the spin current carried by the STCs exhibits long-range propagation in the F even where the Josephson charge current is practically zero. We also show that this spin current persists over a remarkably longer distance than the ordinary spin current carried by spin polarized conduction electrons in the F. Our results thus indicate the promising potential of Josephson junctions based on multilayer ferromagnets for spintronics applications with long-range propagating spin current. PMID:25167525

  16. Electrodeposited CulnSe2 Thin Film Junctions

    NASA Technical Reports Server (NTRS)

    Raffaelle, R. P.; Mantovani, J. G.; Bailey, S. G.; Hepp, A. F.; Gordon, E. M.; Haraway, R.

    1998-01-01

    We have investigated thin films and junctions based on copper indium diselenide (CIS) which have been grown by electrochemical deposition. CIS is a leading candidate for use in polycrystalline thin film photovoltaic solar cells. Electrodeposition is a cost-effective method for producing thin-film CIS. We have produced both p and n type CIS thin films from the same aqueous solution by simply varying the deposition potential. A CIS pn junction was deposited using a step-function potential. Stoichiometry of the single layer films was determined by energy dispersive spectroscopy. Carrier densities of these films increased with deviation from stoichiometry, as determined by the capacitance versus voltage dependence of Schottky contacts. Optical bandgaps for the single layer films as determined by transmission spectroscopy were also found to increase with deviation from stoichiometry. Rectifying current versus voltage characteristics were demonstrated for the Schottky barriers and for the pn junction.

  17. Electrodeposited CuInSe2 Thin Film Junctions

    NASA Technical Reports Server (NTRS)

    Raffaelle, R. P.; Mantovani, J. G.; Bailey, S. G.; Hepp, A. F.; Gordon, E. M.; Haraway, R.

    1997-01-01

    We have investigated thin films and junctions based on copper indium diselenide (CIS) which have been grown by electrochemical deposition. CIS is a leading candidate for use in polycrystalline thin film photovoltaic solar cells. Electrodeposition is a cost-effective method for producing thin-film CIS. We have produced both p and n type CIS thin films from the same aqueous solution by simply varying the deposition potential. A CIS pn junction was deposited using a step-function potential. Stoichiometry of the single layer films was determined by energy dispersive spectroscopy. Carrier densities of these films increased with deviation from stoichiometry, as determined by the capacitance versus voltage dependence of Schottky contacts. Optical bandgaps for the single layer films as determined by transmission spectroscopy were also found to increase with deviation from stoichiometry. Rectifying current versus voltage characteristics were demonstrated for the Schottky barriers and for the pn junction.

  18. Frequency control of a spin-torque oscillator using magnetostrictive anisotropy

    NASA Astrophysics Data System (ADS)

    Park, Min Gyu Albert; Baek, Seung-heon Chris; Park, Byong-Guk; Lee, Seok-Hee

    2016-01-01

    We report the working principle of a spin-torque oscillator, of which the frequency is efficiently controlled by manipulating the magnetostrictive anisotropy. To justify the scheme, we simulate a conventional magnetic-tunnel junction-based oscillator which is fabricated on a piezoelectric material. By applying mechanical stress to a free layer using a piezoelectric material, the oscillation frequency can be controlled to ensure a broad tuning range without a significant reduction of the dynamic resistance variation. Such controllability, which appears in the absence of an external magnetic field, will not only enable the integration of spin-torque oscillators and conventional complimentary metal-oxide semiconductor technology but will also broaden the applicability of spin-torque oscillators.

  19. Dual Control of Giant Field-like Spin Torque in Spin Filter Tunnel Junctions

    PubMed Central

    Tang, Y. -H.; Chu, F. -C.; Kioussis, Nicholas

    2015-01-01

    We predict a giant field-like spin torque, , in spin-filter (SF) barrier tunnel junctions in sharp contrast to existing junctions based on nonmagnetic passive barriers. We demonstrate that has linear bias behavior, is independent of the SF thickness, and has odd parity with respect to the SF’s exchange splitting. Thus, it can be selectively controlled via external bias or external magnetic field which gives rise to sign reversal of via magnetic field switching. The underlying mechanism is the interlayer exchange coupling between the noncollinear magnetizations of the SF and free ferromagnetic electrode via the nonmagnetic insulating (I) spacer giving rise to giant spin-dependent reflection at the SF/I interface. These findings suggest that the proposed field-like-spin-torque MRAM may provide promising dual functionalities for both ‘reading’ and ‘writing’ processes which require lower critical current densities and faster writing and reading speeds. PMID:26095146

  20. Dual Control of Giant Field-like Spin Torque in Spin Filter Tunnel Junctions.

    PubMed

    Tang, Y-H; Chu, F-C; Kioussis, Nicholas

    2015-01-01

    We predict a giant field-like spin torque, T[symbol in text], in spin-filter (SF) barrier tunnel junctions in sharp contrast to existing junctions based on nonmagnetic passive barriers. We demonstrate that has linear bias behavior, is independent of the SF thickness, and has odd parity with respect to the SF's exchange splitting. Thus, it can be selectively controlled via external bias or external magnetic field which gives rise to sign reversal of T[symbol in text] via magnetic field switching. The underlying mechanism is the interlayer exchange coupling between the noncollinear magnetizations of the SF and free ferromagnetic electrode via the nonmagnetic insulating (I) spacer giving rise to giant spin-dependent reflection at the SF/I interface. These findings suggest that the proposed field-like-spin-torque MRAM may provide promising dual functionalities for both 'reading' and 'writing' processes which require lower critical current densities and faster writing and reading speeds. PMID:26095146

  1. Low-field Switching Four-state Nonvolatile Memory Based on Multiferroic Tunnel Junctions

    PubMed Central

    Yau, H. M.; Yan, Z. B.; Chan, N. Y.; Au, K.; Wong, C. M.; Leung, C. W.; Zhang, F.Y.; Gao, X. S.; Dai, J. Y.

    2015-01-01

    Multiferroic tunneling junction based four-state non-volatile memories are very promising for future memory industry since this kind of memories hold the advantages of not only the higher density by scaling down memory cell but also the function of magnetically written and electrically reading. In this work, we demonstrate a success of this four-state memory in a material system of NiFe/BaTiO3/La0.7Sr0.3MnO3 with improved memory characteristics such as lower switching field and larger tunneling magnetoresistance (TMR). Ferroelectric switching induced resistive change memory with OFF/ON ratio of 16 and 0.3% TMR effect have been achieved in this multiferroic tunneling structure. PMID:26239505

  2. Monolithic integration of enhancement-mode vertical driving transistorson a standard InGaN/GaN light emitting diode structure

    NASA Astrophysics Data System (ADS)

    Lu, Xing; Liu, Chao; Jiang, Huaxing; Zou, Xinbo; Zhang, Anping; Lau, Kei May

    2016-08-01

    In this letter, monolithic integration of InGaN/GaN light emitting diodes (LEDs) with vertical metal-oxide-semiconductor field effect transistor (VMOSFET) drivers have been proposed and demonstrated. The VMOSFET was achieved by simply regrowing a p- and n-GaN bilayer on top of a standard LED structure. After fabrication, the VMOSFET is connected with the LED through the conductive n-GaN layer, with no need of extra metal interconnections. The junction-based VMOSFET is inherently an enhancement-mode (E-mode) device with a threshold voltage of 1.6 V. By controlling the gate bias of the VMOSFET, the light intensity emitted from the integrated VMOSFET-LED device could be well modulated, which shows great potential for various applications, including solid-state lighting, micro-displays, and visible light communications.

  3. A quasi-classical mapping approach to vibrationally coupled electron transport in molecular junctions

    SciTech Connect

    Li, Bin; Miller, William H.; Wilner, Eli Y.; Thoss, Michael

    2014-03-14

    We develop a classical mapping approach suitable to describe vibrationally coupled charge transport in molecular junctions based on the Cartesian mapping for many-electron systems [B. Li and W. H. Miller, J. Chem. Phys. 137, 154107 (2012)]. To properly describe vibrational quantum effects in the transport characteristics, we introduce a simple transformation rewriting the Hamiltonian in terms of occupation numbers and use a binning function to facilitate quantization. The approach provides accurate results for the nonequilibrium Holstein model for a range of bias voltages, vibrational frequencies, and temperatures. It also captures the hallmarks of vibrational quantum effects apparent in step-like structure in the current-voltage characteristics at low temperatures as well as the phenomenon of Franck-Condon blockade.

  4. Josephson ϕ0-junction in nanowire quantum dots

    NASA Astrophysics Data System (ADS)

    Szombati, D. B.; Nadj-Perge, S.; Car, D.; Plissard, S. R.; Bakkers, E. P. A. M.; Kouwenhoven, L. P.

    2016-06-01

    The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier. This current is driven by a superconducting phase difference ϕ between the leads. In the presence of chiral and time-reversal symmetry of the Cooper pair tunnelling process, the current is strictly zero when ϕ vanishes. Only if these underlying symmetries are broken can the supercurrent for ϕ = 0 be finite. This corresponds to a ground state of the junction being offset by a phase ϕ0, different from 0 or π. Here, we report such a Josephson ϕ0-junction based on a nanowire quantum dot. We use a quantum interferometer device to investigate phase offsets and demonstrate that ϕ0 can be controlled by electrostatic gating. Our results may have far-reaching implications for superconducting flux- and phase-defined quantum bits as well as for exploring topological superconductivity in quantum dot systems.

  5. Normal Metal Quasiparticle Traps in 3D-Transmon Qubits

    NASA Astrophysics Data System (ADS)

    Burkhart, Luke D.; Gao, Yvonne Y.; Wang, Chen; Serniak, Kyle; de Lange, Gijs; Chu, Yiwen; Vool, Uri; Frunzio, Luigi; Devoret, Michel H.; Catelani, Gianluigi; Glazman, Leonid I.; Schoelkopf, Robert J.

    Quasiparticles are a known source of decoherence in Josephson-junction based superconducting qubits. While equilibrium quasiparticles should not be present in devices operated at dilution refrigeration temperatures well below the superconducting energy gap, non-thermal quasiparticles have been observed in many different superconducting qubits, including 3D-transmons and fluxonium qubits. Vortices induced by applied magnetic fields have been shown to improve non-equilibrium quasiparticle decay rates and improve coherence times by creating regions of the superconductor with vanishing energy gap, which act as quasiparticle traps. We aim to further mitigate quasiparticle-induced limits on coherence by engineering strong trapping via the introduction of normal metal to the superconducting qubit. In this talk, we present recent results regarding normal metal quasiparticle traps in 3D-transmon qubits. Work supported by ARO, A*STAR.

  6. Optical switching of electric charge transfer pathways in porphyrin: a light-controlled nanoscale current router.

    PubMed

    Thanopulos, Ioannis; Paspalakis, Emmanuel; Yannopapas, Vassilios

    2008-11-01

    We introduce a novel molecular junction based on a thiol-functionalized porphyrin derivative with two almost energetically degenerate equilibrium configurations. We show that each equilibrium structure defines a pathway of maximal electric charge transfer through the molecular junction and that these two conduction pathways are spatially orthogonal. We further demonstrate computationally how to switch between the two equilibrium structures of the compound by coherent light. The optical switching mechanism is presented in the relevant configuration subspace of the compound, and the corresponding potential and electric dipole surfaces are obtained by ab initio methods. The laser-induced isomerization takes place in two steps in tandem, while each step is induced by a two-photon process. The effect of metallic electrodes on the electromagnetic irradiation driving the optical switching is also investigated. Our study demonstrates the potential for using thiol-functionalized porphyrin derivatives for the development of a light-controlled nanoscale current router. PMID:21832723

  7. Cavity QED Based on Collective Magnetic Dipole Coupling: Spin Ensembles as Hybrid Two-Level Systems

    NASA Astrophysics Data System (ADS)

    Imamoǧlu, Atac

    2009-02-01

    We analyze the magnetic dipole coupling of an ensemble of spins to a superconducting microwave stripline structure, incorporating a Josephson junction based transmon qubit. We show that this system is described by an embedded Jaynes-Cummings model: in the strong coupling regime, collective spin-wave excitations of the ensemble of spins pick up the nonlinearity of the cavity mode, such that the two lowest eigenstates of the coupled spin wave-microwave cavity-Josephson junction system define a hybrid two-level system. The proposal described here enables new avenues for nonlinear optics using optical photons coupled to spin ensembles via Raman transitions. The possibility of strong coupling cavity QED with magnetic dipole transitions also opens up the possibility of extending quantum information processing protocols to spins in silicon or graphene, without the need for single-spin confinement.

  8. Multiple Resonators as a Multi-Channel Bus for Coupling Josephson Junction Qubits

    NASA Astrophysics Data System (ADS)

    Thrailkill, Zechariah; Lambert, Joseph; Ramos, Roberto

    2010-03-01

    Josephson junction-based qubits have been shown to be promising components for a future quantum computer. A network of these superconducting qubits will require quantum information to be stored in and transferred among them. Resonators made of superconducting metal strips are useful elements for this purpose because they have long coherence times and can dispersively couple qubits. We explore the use of multiple resonators with different resonant frequencies to couple qubits. We find that an array of resonators with different frequencies can be individually addressed to store and retrieve information, while coupling qubits dispersively. We show that a control qubit can be used to effectively isolate an active qubit from an array of resonators so that it can function within the same frequency range used by the resonators.

  9. Theoretical Study of Midwave Infrared HgCdTe nBn Detectors Operating at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Akhavan, Nima Dehdashti; Jolley, Gregory; Umana-Membreno, Gilberto A.; Antoszewski, Jarek; Faraone, Lorenzo

    2015-09-01

    We report a theoretical study of mercury cadmium telluride (HgCdTe) unipolar n-type/barrier/ n-type (nBn) detectors for midwave infrared (MWIR) applications at elevated temperatures. The results obtained indicate that the composition, doping, and thickness of the barrier layer in MWIR HgCdTe nBn detectors can be optimized to yield performance levels comparable with those of ideal HgCdTe p- n photodiodes. It is also shown that introduction of an additional barrier at the back contact layer of the detector structure (nBnn+) leads to substantial suppression of the Auger generation-recombination (GR) mechanism; this results in an order-of-magnitude reduction in the dark current level compared with conventional nBn or p- n junction-based detectors, thus enabling background-limited detector operation above 200 K.

  10. Direct observation of large quantum interference effect in anthraquinone solid-state junctions.

    PubMed

    Rabache, Vincent; Chaste, Julien; Petit, Philippe; Della Rocca, Maria Luisa; Martin, Pascal; Lacroix, Jean-Christophe; McCreery, Richard L; Lafarge, Philippe

    2013-07-17

    Quantum interference in cross-conjugated molecules embedded in solid-state devices was investigated by direct current-voltage and differential conductance transport measurements of anthraquinone (AQ)-based large area planar junctions. A thin film of AQ was grafted covalently on the junction base electrode by diazonium electroreduction, while the counter electrode was directly evaporated on top of the molecular layer. Our technique provides direct evidence of a large quantum interference effect in multiple CMOS compatible planar junctions. The quantum interference is manifested by a pronounced dip in the differential conductance close to zero voltage bias. The experimental signature is well developed at low temperature (4 K), showing a large amplitude dip with a minimum >2 orders of magnitude lower than the conductance at higher bias and is still clearly evident at room temperature. A temperature analysis of the conductance curves revealed that electron-phonon coupling is the principal decoherence mechanism causing large conductance oscillations at low temperature. PMID:23805821

  11. 35% magnetocurrent with spin transport through Si

    NASA Astrophysics Data System (ADS)

    Huang, Biqin; Zhao, Lai; Monsma, Douwe J.; Appelbaum, Ian

    2007-07-01

    Efficient injection of spin-polarized electrons into the conduction band of silicon is limited by the formation of a silicide at the ferromagnetic metal (FM)/silicon interface. In the present work, this "magnetically dead" silicide (where strong spin scattering significantly reduces injected spin polarization) is eliminated by moving the FM in the spin injector from the tunnel junction base anode to the emitter cathode and away from the silicon surface. This results in over an order-of-magnitude increase in spin injection efficiency, from a previously reported magnetocurrent ratio of ≈2% to ≈35% and an estimated spin polarization in Si from ≈1% to at least ≈15%. The injector tunnel junction bias dependence of this spin transport signal is also measured, demonstrating the importance of low bias voltage to preserve high injected spin polarization.

  12. On-chip molecular electronic plasmon sources based on self-assembled monolayer tunnel junctions

    NASA Astrophysics Data System (ADS)

    Du, Wei; Wang, Tao; Chu, Hong-Son; Wu, Lin; Liu, Rongrong; Sun, Song; Phua, Wee Kee; Wang, Lejia; Tomczak, Nikodem; Nijhuis, Christian A.

    2016-04-01

    Molecular electronic control over plasmons offers a promising route for on-chip integrated molecular plasmonic devices for information processing and computing. To move beyond the currently available technologies and to miniaturize plasmonic devices, molecular electronic plasmon sources are required. Here, we report on-chip molecular electronic plasmon sources consisting of tunnel junctions based on self-assembled monolayers sandwiched between two metallic electrodes that excite localized plasmons, and surface plasmon polaritons, with tunnelling electrons. The plasmons originate from single, diffraction-limited spots within the junctions, follow power-law distributed photon statistics, and have well-defined polarization orientations. The structure of the self-assembled monolayer and the applied bias influence the observed polarization. We also show molecular electronic control of the plasmon intensity by changing the chemical structure of the molecules and by bias-selective excitation of plasmons using molecular diodes.

  13. Current rectification in a single molecule diode: the role of electrode coupling

    NASA Astrophysics Data System (ADS)

    Sherif, Siya; Rubio-Bollinger, Gabino; Pinilla-Cienfuegos, Elena; Coronado, Eugenio; Cuevas, Juan Carlos; Agraït, Nicolás

    2015-07-01

    We demonstrate large rectification ratios (\\gt 100) in single-molecule junctions based on a metal-oxide cluster (polyoxometalate), using a scanning tunneling microscope (STM) both at ambient conditions and at low temperature. These rectification ratios are the largest ever observed in a single-molecule junction, and in addition these junctions sustain current densities larger than 105 A cm-2. By following the variation of the I-V characteristics with tip-molecule separation we demonstrate unambiguously that rectification is due to asymmetric coupling to the electrodes of a molecule with an asymmetric level structure. This mechanism can be implemented in other type of molecular junctions using both organic and inorganic molecules and provides a simple strategy for the rational design of molecular diodes.

  14. The interplay between the Aharonov-Bohm interference and parity selective tunneling in graphene nanoribbon rings.

    PubMed

    Nguyen, V Hung; Niquet, Y-M; Dollfus, P

    2014-05-21

    We report on a numerical study of the Aharonov-Bohm (AB) effect and parity selective tunneling in pn junctions based on rectangular graphene rings where the contacts and ring arms are all made of zigzag nanoribbons. We find that when applying a magnetic field to the ring, the AB interference can reverse the parity symmetry of incoming waves and hence can strongly modulate the parity selective transmission through the system. Therefore, the transmission between two states of different parity exhibits the AB oscillations with a π-phase shift, compared to the case of states of the same parity. On this basis, it is shown that interesting effects, such as giant (both positive and negative) magnetoresistance and strong negative differential conductance, can be achieved in this structure. Our study thus presents a new property of the AB interference in graphene nanorings, which could be helpful for further understanding the transport properties of graphene mesoscopic systems. PMID:24785639

  15. Results of Resonant Activation and Macroscopic Quantum Tunneling Experiments in Magnesium Diboride Thin Film Josephson Junctions

    NASA Astrophysics Data System (ADS)

    Ramos, Roberto; Carabello, Steve; Lambert, Joseph; Mlack, Jerome; Dai, Wenqing; Shen, Yi.; Li, Qi; Cunnane, Daniel; Zhuang, C. G.; Chen, Ke; Xi, X. X.

    2012-02-01

    The Josephson junction is an experimental testbed widely used to study resonant activation and macroscopic quantum tunneling. These phenomena have been observed in junctions based on conventional low-temperature superconductors such as Nb and Al, and even in high-Tc, intrinsic superconductors. We report results of superconducting-to normal state switching experiments below 1 K using MgB2-based Josephson heterojunctions with Pb and Nb counter-electrodes. Measurements were made with and without RF excitation. With microwaves, we see evidence of a resonant peak, in addition to the primary escape (from ground state) peak -- consistent with resonant activation. We also observe features suggestive of macroscopic quantum tunneling including peaks in the escape rate enhancements and an ``elbow'' in the graph of calculated escape temperatures Tesc versus sample temperature.

  16. Facial synthesis of SnO2 nanoparticle film for efficient fiber-shaped dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Peng, Ming; Cai, Xin; Fu, Yongping; Yu, Xiao; Liu, Suqi; Deng, Bing; Hany, Kafafy; Zou, Dechun

    2014-02-01

    SnO2 nanoparticle film is directly prepared by in situ thermal calcining isopropanol solution of tin tetraisopropoxide, and is used to construct the SnO2-TiO2 junction on titanium wire substrate. The titanium wire supported SnO2-TiO2 junction is further applied to fiber-shaped dye-sensitized solar cells (FDSCs). High efficiency of 5.8% (Normal Model) and 12.4% (Diffuse Model) are achieved. Our results indicate that Jsc enhancement derived by SnO2-TiO2 junction and the recombination shielding effect of the compact TiO2 film could synergistically contribute to high efficiencies. This study offers a novel and alternative strategy for achieving efficient SnO2-TiO2 junction based solar cells in a facile, scalable and cost-effective way.

  17. Castleman disease of the mesentery as the great mimic: Incidental finding of one case and the literature review.

    PubMed

    Lv, Ang; Hao, Chunyi; Qian, Honggang; Leng, Jiahua; Liu, Wendy

    2015-06-01

    Castleman disease is an uncommon benign lymphoproliferative disorder characterized by hyperplasia of lymphoid follicles. More commonly described in the mediastinum, its occurrence in the mesentery is exceedingly rare, which is easily to be ignored in differential diagnosis when an abdominal mass is found. We report the case of an asymptomatic 71-year-old woman with a homogenous and hypervascular mass at the inner side of duodenojejunal junction. Based on the clinical suspicion of a gastrointestinal stromal tumor, a surgical resection was performed. Final diagnosis of the mass was hyaline vascular variant of Castleman disease. Here, we summarize the clinicopathological and radiological features of this disease by literature review, which may be helpful to bring awareness of this entity and improve the clinical decision making when similar scenarios are encountered. PMID:26166374

  18. Modulation-mediated unlocking of a parametrically phase-locked spin torque oscillator

    SciTech Connect

    Dürrenfeld, P.; Iacocca, E.; Åkerman, J.; Muduli, P. K.

    2014-12-22

    Modulation of an oscillator is crucial for its application in communication devices. While the output power and linewidth of single magnetic tunnel junction-based spin-torque oscillators (MTJ-STO) are not yet adequate for practical uses, the synchronization of such devices can overcome these limitations. Here, we investigate the modulation behavior of a parametrically synchronized MTJ-STO and show experimentally that modulation of the synchronized state preserves synchronization as long as the modulation frequency, f{sub mod}, is above a characteristic frequency, f{sub unlock}. The unlocking frequency increases with the modulation amplitude in agreement with analytical estimates and numerical simulations. These phenomena are described as a non-resonant unlocking mechanism, whose characteristics are directly related to inherent parameters of the oscillator.

  19. Skyrmion based microwave detectors and harvesting

    SciTech Connect

    Finocchio, G.; Giordano, A.; Ricci, M.; Burrascano, P.; Tomasello, R.; Lanuzza, M.; Puliafito, V.; Azzerboni, B.; Carpentieri, M.

    2015-12-28

    Magnetic skyrmions are topologically protected states that are very promising for the design of the next generation of ultra-low-power electronic devices. In this letter, we propose a magnetic tunnel junction based spin-transfer torque diode with a magnetic skyrmion as ground state and a perpendicular polarizer patterned as nano-contact for a local injection of the current. The key result is the possibility to achieve sensitivities (i.e., detection voltage over input microwave power) larger than 2000 V/W for optimized contact diameters. We also pointed out that large enough voltage controlled magnetocrystalline anisotropy could significantly improve the sensitivity. Our results can be very useful for the identification of a class of spin-torque diodes with a non-uniform ground state and to understand the fundamental physics of the skyrmion dynamical properties.

  20. Current rectification in a single molecule diode: the role of electrode coupling.

    PubMed

    Sherif, Siya; Rubio-Bollinger, Gabino; Pinilla-Cienfuegos, Elena; Coronado, Eugenio; Cuevas, Juan Carlos; Agraït, Nicolás

    2015-07-24

    We demonstrate large rectification ratios (> 100) in single-molecule junctions based on a metal-oxide cluster (polyoxometalate), using a scanning tunneling microscope (STM) both at ambient conditions and at low temperature. These rectification ratios are the largest ever observed in a single-molecule junction, and in addition these junctions sustain current densities larger than 10(5) A cm(-2). By following the variation of the I-V characteristics with tip-molecule separation we demonstrate unambiguously that rectification is due to asymmetric coupling to the electrodes of a molecule with an asymmetric level structure. This mechanism can be implemented in other type of molecular junctions using both organic and inorganic molecules and provides a simple strategy for the rational design of molecular diodes. PMID:26133791

  1. Dilute Group III-V nitride intermediate band solar cells with contact blocking layers

    DOEpatents

    Walukiewicz, Wladyslaw; Yu, Kin Man

    2012-07-31

    An intermediate band solar cell (IBSC) is provided including a p-n junction based on dilute III-V nitride materials and a pair of contact blocking layers positioned on opposite surfaces of the p-n junction for electrically isolating the intermediate band of the p-n junction by blocking the charge transport in the intermediate band without affecting the electron and hole collection efficiency of the p-n junction, thereby increasing open circuit voltage (V.sub.OC) of the IBSC and increasing the photocurrent by utilizing the intermediate band to absorb photons with energy below the band gap of the absorber layers of the IBSC. Hence, the overall power conversion efficiency of a IBSC will be much higher than an conventional single junction solar cell. The p-n junction absorber layers of the IBSC may further have compositionally graded nitrogen concentrations to provide an electric field for more efficient charge collection.

  2. Dilute group III-V nitride intermediate band solar cells with contact blocking layers

    DOEpatents

    Walukiewicz, Wladyslaw; Yu, Kin Man

    2015-02-24

    An intermediate band solar cell (IBSC) is provided including a p-n junction based on dilute III-V nitride materials and a pair of contact blocking layers positioned on opposite surfaces of the p-n junction for electrically isolating the intermediate band of the p-n junction by blocking the charge transport in the intermediate band without affecting the electron and hole collection efficiency of the p-n junction, thereby increasing open circuit voltage (V.sub.OC) of the IBSC and increasing the photocurrent by utilizing the intermediate band to absorb photons with energy below the band gap of the absorber layers of the IBSC. Hence, the overall power conversion efficiency of a IBSC will be much higher than an conventional single junction solar cell. The p-n junction absorber layers of the IBSC may further have compositionally graded nitrogen concentrations to provide an electric field for more efficient charge collection.

  3. Enhancement of Spin-transfer torque switching via resonant tunneling

    SciTech Connect

    Chatterji, Niladri; Tulapurkar, Ashwin A.; Muralidharan, Bhaskaran

    2014-12-08

    We propose the use of resonant tunneling as a route to enhance the spin-transfer torque switching characteristics of magnetic tunnel junctions. The proposed device structure is a resonant tunneling magnetic tunnel junction based on a MgO-semiconductor heterostructure sandwiched between a fixed magnet and a free magnet. Using the non-equilibrium Green's function formalism coupled self consistently with the Landau-Lifshitz-Gilbert-Slonczewski equation, we demonstrate enhanced tunnel magneto-resistance characteristics as well as lower switching voltages in comparison with traditional trilayer devices. Two device designs based on MgO based heterostructures are presented, where the physics of resonant tunneling leads to an enhanced spin transfer torque thereby reducing the critical switching voltage by up to 44%. It is envisioned that the proof-of-concept presented here may lead to practical device designs via rigorous materials and interface studies.

  4. Single Molecule Junctions: Probing Contact Chemistry and Fundamental Circuit Laws

    SciTech Connect

    Hybertsen M. S.

    2013-04-11

    By exploiting selective link chemistry, formation of single molecule junctions with reproducible conductance has become established. Systematic studies reveal the structure-conductance relationships for diverse molecules. I will draw on experiments from my collaborators at Columbia University, atomic-scale calculations and theory to describe progress in two areas. First, I will describe a novel route to form single molecule junctions, based on SnMe3 terminated molecules, in which gold directly bonds to carbon in the molecule backbone resulting in near ideal contact resistance [1]. Second, comparison of the conductance of junctions formed with molecular species containing either one backbone or two backbones in parallel allows demonstration of the role of quantum interference in the conductance superposition law at the molecular scale [2].

  5. Dual Control of Giant Field-like Spin Torque in Spin Filter Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Tang, Y.-H.; Chu, F.-C.; Kioussis, Nicholas

    2015-06-01

    We predict a giant field-like spin torque, , in spin-filter (SF) barrier tunnel junctions in sharp contrast to existing junctions based on nonmagnetic passive barriers. We demonstrate that has linear bias behavior, is independent of the SF thickness, and has odd parity with respect to the SF’s exchange splitting. Thus, it can be selectively controlled via external bias or external magnetic field which gives rise to sign reversal of via magnetic field switching. The underlying mechanism is the interlayer exchange coupling between the noncollinear magnetizations of the SF and free ferromagnetic electrode via the nonmagnetic insulating (I) spacer giving rise to giant spin-dependent reflection at the SF/I interface. These findings suggest that the proposed field-like-spin-torque MRAM may provide promising dual functionalities for both ‘reading’ and ‘writing’ processes which require lower critical current densities and faster writing and reading speeds.

  6. Tunnel electroresistance through organic ferroelectrics

    PubMed Central

    Tian, B. B.; Wang, J. L.; Fusil, S.; Liu, Y.; Zhao, X. L.; Sun, S.; Shen, H.; Lin, T.; Sun, J. L.; Duan, C. G.; Bibes, M.; Barthélémy, A.; Dkhil, B.; Garcia, V.; Meng, X. J.; Chu, J. H.

    2016-01-01

    Organic electronics is emerging for large-area applications such as photovoltaic cells, rollable displays or electronic paper. Its future development and integration will require a simple, low-power organic memory, that can be written, erased and readout electrically. Here we demonstrate a non-volatile memory in which the ferroelectric polarisation state of an organic tunnel barrier encodes the stored information and sets the readout tunnel current. We use high-sensitivity piezoresponse force microscopy to show that films as thin as one or two layers of ferroelectric poly(vinylidene fluoride) remain switchable with low voltages. Submicron junctions based on these films display tunnel electroresistance reaching 1,000% at room temperature that is driven by ferroelectric switching and explained by electrostatic effects in a direct tunnelling regime. Our findings provide a path to develop low-cost, large-scale arrays of organic ferroelectric tunnel junctions on silicon or flexible substrates. PMID:27143121

  7. Quantifying the relative molecular orbital alignment for molecular junctions with similar chemical linkage to electrodes

    NASA Astrophysics Data System (ADS)

    Bâldea, Ioan

    2014-11-01

    Estimating the relative alignment between the frontier molecular orbitals (MOs) that dominates the charge transport through single-molecule junctions represents a challenge for theory. This requires approaches beyond the widely employed framework provided by the density functional theory, wherein the Kohn-Sham ‘orbitals’ are treated as if they were real MOs, which is not the case. In this paper, we report results obtained by means of quantum chemical calculations, including the equation-of-motion coupled-cluster singles and doubles, which is the state-of-the-art of quantum chemistry for medium-size molecules like those considered here. These theoretical results are validated against data on the MO energy offset relative to the electrodes’ Fermi energy extracted from experiments for junctions based on 4,4’-bipyridine and 1,4-dicyanobenzene.

  8. Enhanced surface photovoltage response of ZnO nanorod based inorganic/organic hybrid junctions by constructing embedded bulk composite structures

    NASA Astrophysics Data System (ADS)

    Kang, Dawei; Liu, Aimin; Bian, Jiming; Hu, Zengquan; Liu, Yiting; Qiao, Fen

    2013-02-01

    Two kinds of inorganic/organic hybrid junctions based on ZnO nanorods (NRs), i.e. two-layer planar heterojunction and embedded bulk composite structures, were fabricated on ITO glass substrates. Surface photovoltage (SPV) methods based on a Kelvin probe and a lock-in amplifier were respectively utilized to study the photogenerated charges at the surface and the interface in the ZnO-based hybrid junctions. Results indicate that the lock-in SPV response of the bulk composite structure is much higher than its planar counterpart in terms of intensity and spectral range. Therefore, ZnO NR/PF (poly(9,9-di-n-octylfluorenyl-2,7-diyl)) embedded bulk composite structures are more suitable and preferred for photovoltaic application.

  9. Tunnel electroresistance through organic ferroelectrics.

    PubMed

    Tian, B B; Wang, J L; Fusil, S; Liu, Y; Zhao, X L; Sun, S; Shen, H; Lin, T; Sun, J L; Duan, C G; Bibes, M; Barthélémy, A; Dkhil, B; Garcia, V; Meng, X J; Chu, J H

    2016-01-01

    Organic electronics is emerging for large-area applications such as photovoltaic cells, rollable displays or electronic paper. Its future development and integration will require a simple, low-power organic memory, that can be written, erased and readout electrically. Here we demonstrate a non-volatile memory in which the ferroelectric polarisation state of an organic tunnel barrier encodes the stored information and sets the readout tunnel current. We use high-sensitivity piezoresponse force microscopy to show that films as thin as one or two layers of ferroelectric poly(vinylidene fluoride) remain switchable with low voltages. Submicron junctions based on these films display tunnel electroresistance reaching 1,000% at room temperature that is driven by ferroelectric switching and explained by electrostatic effects in a direct tunnelling regime. Our findings provide a path to develop low-cost, large-scale arrays of organic ferroelectric tunnel junctions on silicon or flexible substrates. PMID:27143121

  10. Tunnel electroresistance through organic ferroelectrics

    NASA Astrophysics Data System (ADS)

    Tian, B. B.; Wang, J. L.; Fusil, S.; Liu, Y.; Zhao, X. L.; Sun, S.; Shen, H.; Lin, T.; Sun, J. L.; Duan, C. G.; Bibes, M.; Barthélémy, A.; Dkhil, B.; Garcia, V.; Meng, X. J.; Chu, J. H.

    2016-05-01

    Organic electronics is emerging for large-area applications such as photovoltaic cells, rollable displays or electronic paper. Its future development and integration will require a simple, low-power organic memory, that can be written, erased and readout electrically. Here we demonstrate a non-volatile memory in which the ferroelectric polarisation state of an organic tunnel barrier encodes the stored information and sets the readout tunnel current. We use high-sensitivity piezoresponse force microscopy to show that films as thin as one or two layers of ferroelectric poly(vinylidene fluoride) remain switchable with low voltages. Submicron junctions based on these films display tunnel electroresistance reaching 1,000% at room temperature that is driven by ferroelectric switching and explained by electrostatic effects in a direct tunnelling regime. Our findings provide a path to develop low-cost, large-scale arrays of organic ferroelectric tunnel junctions on silicon or flexible substrates.

  11. Low-field Switching Four-state Nonvolatile Memory Based on Multiferroic Tunnel Junctions.

    PubMed

    Yau, H M; Yan, Z B; Chan, N Y; Au, K; Wong, C M; Leung, C W; Zhang, F Y; Gao, X S; Dai, J Y

    2015-01-01

    Multiferroic tunneling junction based four-state non-volatile memories are very promising for future memory industry since this kind of memories hold the advantages of not only the higher density by scaling down memory cell but also the function of magnetically written and electrically reading. In this work, we demonstrate a success of this four-state memory in a material system of NiFe/BaTiO3/La0.7Sr0.3MnO3 with improved memory characteristics such as lower switching field and larger tunneling magnetoresistance (TMR). Ferroelectric switching induced resistive change memory with OFF/ON ratio of 16 and 0.3% TMR effect have been achieved in this multiferroic tunneling structure. PMID:26239505

  12. Thermoelectricity at the molecular scale: a large Seebeck effect in endohedral metallofullerenes

    NASA Astrophysics Data System (ADS)

    Lee, See Kei; Buerkle, Marius; Yamada, Ryo; Asai, Yoshihiro; Tada, Hirokazu

    2015-12-01

    Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C82, Gd@C82, and Ce@C82. We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C82 and Ce@C82 junctions. The conductance, on the other hand, remains comparable for all three systems. The power factor determined for the Gd@C82 based junction is so far the highest obtained for a single-molecule device. Although the encapsulated metal atom does not directly contribute to the transport, we show that the observed enhancement of the thermopower for Gd@C82 and Ce@C82 is elucidated by the substantial changes in the electronic- and geometrical structure of the fullerene molecule induced by the encapsulated metal atom.Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C82, Gd@C82, and Ce@C82. We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C82 and Ce@C82 junctions. The conductance, on the other hand

  13. Electrostatically tunable lateral MoTe2 p-n junction for use in high-performance optoelectronics

    NASA Astrophysics Data System (ADS)

    Wang, Zhenxing; Wang, Feng; Yin, Lei; Huang, Yun; Xu, Kai; Wang, Fengmei; Zhan, Xueying; He, Jun

    2016-07-01

    Because of their ultimate thickness, layered structure and high flexibility, pn junctions based on layered two-dimensional semiconductors have been attracting increasing attention recently. In this study, for the first time, we fabricated lateral pn junctions (LPNJs) based on ultrathin MoTe2 by introducing two separated electrostatic back gates, and investigated their electronic and photovoltaic performance. Pn, np, nn, and pp junctions can be easily realized by modulating the conductive channel type using gate voltages with different polarities. Strong rectification effects were observed in the pn and np junctions and the rectification ratio reached ~5 × 104. Importantly, we find a unique phenomenon that the parameters for MoTe2 LPNJs experience abrupt changes during the transition from p to n or n to p. Furthermore, a high performance photovoltaic device with a filling factor of above 51% and electrical conversion efficiency (η) of around 0.5% is achieved. Our findings are of importance to comprehensively understand the electronic and optoelectronic properties of MoTe2 and may further open up novel electronic and optoelectronic device applications.Because of their ultimate thickness, layered structure and high flexibility, pn junctions based on layered two-dimensional semiconductors have been attracting increasing attention recently. In this study, for the first time, we fabricated lateral pn junctions (LPNJs) based on ultrathin MoTe2 by introducing two separated electrostatic back gates, and investigated their electronic and photovoltaic performance. Pn, np, nn, and pp junctions can be easily realized by modulating the conductive channel type using gate voltages with different polarities. Strong rectification effects were observed in the pn and np junctions and the rectification ratio reached ~5 × 104. Importantly, we find a unique phenomenon that the parameters for MoTe2 LPNJs experience abrupt changes during the transition from p to n or n to p. Furthermore

  14. Lateral graphene p-n junctions formed by the graphene/MoS2 hybrid interface

    NASA Astrophysics Data System (ADS)

    Meng, Jie; Song, Hua-Ding; Li, Cai-Zhen; Jin, Yibo; Tang, Lei; Liu, Dameng; Liao, Zhi-Min; Xiu, Faxian; Yu, Da-Peng

    2015-07-01

    Graphene/two-dimensional (2D) semiconductor heterostructures have been demonstrated to possess many advantages for electronic and optoelectronic devices. However, there are few reports about the utilization of a 2D semiconductor monolayer to tune the properties of graphene. Here, we report the fabrication and characterization of graphene p-n junctions based on graphene/MoS2 hybrid interfaces. Monolayered graphene across the monolayered MoS2 boundary is divided into n-type regions on the MoS2 and p-type regions on the SiO2 substrate. Such van der Waals heterostructure based graphene p-n junctions show good photoelectric properties. The photocurrent modulation of such devices by a single back gate is also demonstrated for the first time, which shows that the graphene on and off MoS2 regions have different responses to the gate voltage. Our results suggest that the atomic thin hybrid structure can remarkably extend the device applications.Graphene/two-dimensional (2D) semiconductor heterostructures have been demonstrated to possess many advantages for electronic and optoelectronic devices. However, there are few reports about the utilization of a 2D semiconductor monolayer to tune the properties of graphene. Here, we report the fabrication and characterization of graphene p-n junctions based on graphene/MoS2 hybrid interfaces. Monolayered graphene across the monolayered MoS2 boundary is divided into n-type regions on the MoS2 and p-type regions on the SiO2 substrate. Such van der Waals heterostructure based graphene p-n junctions show good photoelectric properties. The photocurrent modulation of such devices by a single back gate is also demonstrated for the first time, which shows that the graphene on and off MoS2 regions have different responses to the gate voltage. Our results suggest that the atomic thin hybrid structure can remarkably extend the device applications. Electronic supplementary information (ESI) available: More details on device fabrication, control

  15. Uncovering a law of corresponding states for electron tunneling in molecular junctions

    NASA Astrophysics Data System (ADS)

    Bâldea, Ioan; Xie, Zuoti; Frisbie, C. Daniel

    2015-06-01

    Laws of corresponding states known so far demonstrate that certain macroscopic systems can be described in a universal manner in terms of reduced quantities, which eliminate specific substance properties. To quantitatively describe real systems, all these laws of corresponding states contain numerical factors adjusted empirically. Here, we report a law of corresponding states deduced analytically for charge transport via tunneling in molecular junctions, which we validate against current-voltage measurements for conducting probe atomic force microscope junctions based on benchmark molecular series (oligophenylenedithiols and alkanedithiols) and electrodes (silver, gold, and platinum), as well as against transport data for scanning tunneling microscope junctions. Two salient features distinguish the present law of corresponding states from all those known previously. First, it is expressed by a universal curve free of empirical parameters. Second, it demonstrates that a universal behavior is not necessarily affected by strong stochastic fluctuations often observed in molecular electronics. An important and encouraging message of this finding is that transport behavior across different molecular platforms can be similar and extraordinarily reproducible.Laws of corresponding states known so far demonstrate that certain macroscopic systems can be described in a universal manner in terms of reduced quantities, which eliminate specific substance properties. To quantitatively describe real systems, all these laws of corresponding states contain numerical factors adjusted empirically. Here, we report a law of corresponding states deduced analytically for charge transport via tunneling in molecular junctions, which we validate against current-voltage measurements for conducting probe atomic force microscope junctions based on benchmark molecular series (oligophenylenedithiols and alkanedithiols) and electrodes (silver, gold, and platinum), as well as against transport data

  16. Graphene oxide as a p-dopant and an anti-reflection coating layer, in graphene/silicon solar cells

    NASA Astrophysics Data System (ADS)

    Yavuz, S.; Kuru, C.; Choi, D.; Kargar, A.; Jin, S.; Bandaru, P. R.

    2016-03-01

    It is shown that coating graphene-silicon (Gr/Si) Schottky junction based solar cells with graphene oxide (GO) improves the power conversion efficiency (PCE) of the cells, while demonstrating unprecedented device stability. The PCE has been shown to be increased to 10.6% (at incident radiation of 100 mW cm-2) for the Gr/Si solar cell with an optimal GO coating thickness compared to 3.6% for a bare/uncoated Gr/Si solar cell. The p-doping of graphene by the GO, which also serves as an antireflection coating (ARC) has been shown to be a main contributing factor to the enhanced PCE. A simple spin coating process has been used to apply GO with thickness commensurate with an anti-refection coating (ARC) and indicates the suitability of the developed methodology for large-scale solar cell assembly.It is shown that coating graphene-silicon (Gr/Si) Schottky junction based solar cells with graphene oxide (GO) improves the power conversion efficiency (PCE) of the cells, while demonstrating unprecedented device stability. The PCE has been shown to be increased to 10.6% (at incident radiation of 100 mW cm-2) for the Gr/Si solar cell with an optimal GO coating thickness compared to 3.6% for a bare/uncoated Gr/Si solar cell. The p-doping of graphene by the GO, which also serves as an antireflection coating (ARC) has been shown to be a main contributing factor to the enhanced PCE. A simple spin coating process has been used to apply GO with thickness commensurate with an anti-refection coating (ARC) and indicates the suitability of the developed methodology for large-scale solar cell assembly. Electronic supplementary information (ESI) available: (i) Experimental methods, (ii) optical images of devices with and without graphene oxide (GO), (iii) comparison of the power conversion efficiency (PCE) due to the GO coating and nitric acid doping, (iv) specular and diffuse reflectance measurements, (v) stability data of pristine graphene/silicon (Gr/Si) solar cells. See DOI: 10.1039/c5

  17. Electrochemical metallization switching with a platinum group metal in different oxides

    NASA Astrophysics Data System (ADS)

    Wang, Zhongrui; Jiang, Hao; Hyung Jang, Moon; Lin, Peng; Ribbe, Alexander; Xia, Qiangfei; Yang, J. Joshua

    2016-07-01

    In a normal electrochemical metallization (ECM) switch, electrochemically active metals, such as Ag and Cu are used to provide mobile ions for the conducting filament. In both ECM and valence change memory (VCM) devices, platinum group metals, such as Pt and Pd, are typically used as the counter electrode and assumed to be chemically and physically inert. In this study, we explore whether the so-called inert metal itself can form a conducting filament and result in repeatable resistance switching. Pd and different oxide host matrices are used for this purpose. We have observed that the transport of oxygen anions dominates over Pd metal cations in ALD deposited AlOx and HfOx. However, in sputtered SiOx, Pd cation transport was revealed, accompanied by the formation of nano-crystalline Pd filament(s) in the junctions. Based on these observations, memristors with reversible and repeatable switching were obtained by using Pd doped SiOx as the switching material.In a normal electrochemical metallization (ECM) switch, electrochemically active metals, such as Ag and Cu are used to provide mobile ions for the conducting filament. In both ECM and valence change memory (VCM) devices, platinum group metals, such as Pt and Pd, are typically used as the counter electrode and assumed to be chemically and physically inert. In this study, we explore whether the so-called inert metal itself can form a conducting filament and result in repeatable resistance switching. Pd and different oxide host matrices are used for this purpose. We have observed that the transport of oxygen anions dominates over Pd metal cations in ALD deposited AlOx and HfOx. However, in sputtered SiOx, Pd cation transport was revealed, accompanied by the formation of nano-crystalline Pd filament(s) in the junctions. Based on these observations, memristors with reversible and repeatable switching were obtained by using Pd doped SiOx as the switching material. Electronic supplementary information (ESI) available

  18. Asymmetric angular dependence of spin-transfer torques in CoFe/Mg-B-O/CoFe magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Tang, Ling; Xu, Zhi-Jun; Zuo, Xian-Jun; Yang, Ze-Jin; Gao, Qing-He; Linghu, Rong-Feng; Guo, Yun-Dong

    2016-04-01

    Using a first-principles noncollinear wave-function-matching method, we studied the spin-transfer torques (STTs) in CoFe/Mg-B-O/CoFe(001) magnetic tunnel junctions (MTJs), where three different types of B-doped MgO in the spacer are considered, including B atoms replacing Mg atoms (Mg3BO4), B atoms replacing O atoms (Mg4BO3), and B atoms occupying interstitial positions (Mg4BO4) in MgO. A strong asymmetric angular dependence of STT can be obtained both in ballistic CoFe/Mg3BO4 and CoFe/Mg4BO4 based MTJs, whereas a nearly symmetric STT curve is observed in the junctions based on CoFe/Mg4BO3. Furthermore, the asymmetry of the angular dependence of STT can be suppressed significantly by the disorder of B distribution. Such skewness of STTs in the CoFe/Mg-B-O/CoFe MTJs could be attributed to the interfacial resonance states induced by the B diffusion into MgO spacer.

  19. Conductance saturation in a series of highly transmitting molecular junctions

    NASA Astrophysics Data System (ADS)

    Yelin, T.; Korytár, R.; Sukenik, N.; Vardimon, R.; Kumar, B.; Nuckolls, C.; Evers, F.; Tal, O.

    2016-04-01

    Revealing the mechanisms of electronic transport through metal-molecule interfaces is of central importance for a variety of molecule-based devices. A key method for understanding these mechanisms is based on the study of conductance versus molecule length in molecular junctions. However, previous works focused on transport governed either by coherent tunnelling or hopping, both at low conductance. Here, we study the upper limit of conductance across metal-molecule-metal interfaces. Using highly conducting single-molecule junctions based on oligoacenes with increasing length, we find that the conductance saturates at an upper limit where it is independent of molecule length. With the aid of two prototype systems, in which the molecules are contacted by either Ag or Pt electrodes, we find two different possible origins for conductance saturation. The results are explained by an intuitive model, backed by ab initio calculations. Our findings shed light on the mechanisms that constrain the conductance of metal-molecule interfaces at the high-transmission limit.

  20. Transport properties of the H2O@C60-dimer-based junction.

    PubMed

    Zhu, Chengbo; Wang, Xiaolin

    2015-09-23

    Theoretical predictions play an important role in finding potential applications in molecular electronics. Fullerenes have a number of potential applications, and the charge flow from a single C60 molecule to another becomes more versatile and more interesting after doping. Here, we report the conductance of two H2O@C60 molecules in series order and how the number of encapsulated water molecules influences the transport properties of the junction. Encapsulating an H2O molecule into one of the C60 cages increases the conductance of the dimer. Negative differential resistance is found in the dimer systems, and its peak-to-valley current ratio depends on the number of encapsulated H2O molecules. The conductance of the C60 dimer and the H2O@C60 dimer is two orders of magnitude smaller than that of the C60 monomer. Furthermore, we demonstrate that the conductance of the molecular junctions based on the H2O@C60 dimer can be tuned by moving the encapsulated H2O molecules. The conductance is H2O-position dependent. Our findings indicate that H2O@C60 can be used as a building block in C60-based molecular electronic devices and sensors. PMID:26325223

  1. Transport properties of the H2O@C60-dimer-based junction

    NASA Astrophysics Data System (ADS)

    Zhu, Chengbo; Wang, Xiaolin

    2015-09-01

    Theoretical predictions play an important role in finding potential applications in molecular electronics. Fullerenes have a number of potential applications, and the charge flow from a single C60 molecule to another becomes more versatile and more interesting after doping. Here, we report the conductance of two H2O@C60 molecules in series order and how the number of encapsulated water molecules influences the transport properties of the junction. Encapsulating an H2O molecule into one of the C60 cages increases the conductance of the dimer. Negative differential resistance is found in the dimer systems, and its peak-to-valley current ratio depends on the number of encapsulated H2O molecules. The conductance of the C60 dimer and the H2O@C60 dimer is two orders of magnitude smaller than that of the C60 monomer. Furthermore, we demonstrate that the conductance of the molecular junctions based on the H2O@C60 dimer can be tuned by moving the encapsulated H2O molecules. The conductance is H2O-position dependent. Our findings indicate that H2O@C60 can be used as a building block in C60-based molecular electronic devices and sensors.

  2. Coherent-state storage and retrieval between superconducting cavities using parametric frequency conversion

    SciTech Connect

    Sirois, A. J.; Castellanos-Beltran, M. A.; DeFeo, M. P.; Ranzani, L.; Lecocq, F.; Simmonds, R. W.; Teufel, J. D.; Aumentado, J.

    2015-04-27

    In superconducting quantum information, machined aluminum superconducting cavities have proven to be a well-controlled, low-dissipation electromagnetic environment for quantum circuits such as qubits. They can possess large internal quality factors, Q{sub int} > 10{sup 8}, and present the possibility of storing quantum information for times far exceeding those of microfabricated circuits. However, in order to be useful as a storage element, these cavities require a fast “read/write” mechanism—in other words, they require tunable coupling between other systems of interest such as other cavity modes and qubits, as well as any associated readout hardware. In this work, we demonstrate these qualities in a simple dual cavity architecture in which a low-Q “readout” mode is parametrically coupled to a high-Q “storage” mode, allowing us to store and retrieve classical information. Specifically, we employ a flux-driven Josephson junction-based coupling scheme to controllably swap coherent states between two cavities, demonstrating full, sequenced control over the coupling rates between modes.

  3. Josephson current in a normal-metal nanowire coupled to a superconductor/ferromagnet/superconductor junction

    NASA Astrophysics Data System (ADS)

    Ebisu, Hiromi; Lu, Bo; Taguchi, Katsuhisa; Golubov, Alexander A.; Tanaka, Yukio

    2016-01-01

    We consider a superconducting nanowire proximity coupled to a superconductor/ferromagnet/superconductor (S/F/S) junction, where the magnetization penetrates into a superconducting segment in a nanowire decaying as ˜exp[-∣n/∣ ξ ] , where n is the site index and the ξ is the decay length. We tune chemical potential and spin-orbit coupling so that the topological superconducting regime hosting the Majorana fermion is realized for long ξ . We find that when ξ becomes shorter, zero energy state at the interface between a superconductor and a ferromagnet splits into two states at nonzero energy. Accordingly, the behavior of the Josephson current is drastically changed due to this "zero mode-nonzero mode crossover." By tuning the model parameters, we find an almost second-harmonic current-phase relation sin2 φ , where φ is the phase difference of the junction. Based on the analysis of Andreev bound state (ABS), we clarify that the current-phase relation is determined by coupling of the states within the energy gap. We find that the emergence of crossing points of ABS is a key ingredient to generate sin2 φ dependence in the current-phase relation. We further study both the energy and φ dependence of pair amplitudes in the ferromagnetic region. For large ξ , an odd-frequency spin-triplet s -wave component is dominant. The magnitude of the odd-frequency pair amplitude is enhanced at the energy level of ABS.

  4. Thermoelectricity at the molecular scale: a large Seebeck effect in endohedral metallofullerenes.

    PubMed

    Lee, See Kei; Buerkle, Marius; Yamada, Ryo; Asai, Yoshihiro; Tada, Hirokazu

    2015-12-28

    Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C(82), Gd@C(82), and Ce@C(82). We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C(82) and Ce@C(82) junctions. The conductance, on the other hand, remains comparable for all three systems. The power factor determined for the Gd@C(82) based junction is so far the highest obtained for a single-molecule device. Although the encapsulated metal atom does not directly contribute to the transport, we show that the observed enhancement of the thermopower for Gd@C(82) and Ce@C(82) is elucidated by the substantial changes in the electronic- and geometrical structure of the fullerene molecule induced by the encapsulated metal atom. PMID:26583505

  5. Correlation of anomalous write error rates and ferromagnetic resonance spectrum in spin-transfer-torque-magnetic-random-access-memory devices containing in-plane free layers

    SciTech Connect

    Evarts, Eric R.; Rippard, William H.; Pufall, Matthew R.; Heindl, Ranko

    2014-05-26

    In a small fraction of magnetic-tunnel-junction-based magnetic random-access memory devices with in-plane free layers, the write-error rates (WERs) are higher than expected on the basis of the macrospin or quasi-uniform magnetization reversal models. In devices with increased WERs, the product of effective resistance and area, tunneling magnetoresistance, and coercivity do not deviate from typical device properties. However, the field-swept, spin-torque, ferromagnetic resonance (FS-ST-FMR) spectra with an applied DC bias current deviate significantly for such devices. With a DC bias of 300 mV (producing 9.9 × 10{sup 6} A/cm{sup 2}) or greater, these anomalous devices show an increase in the fraction of the power present in FS-ST-FMR modes corresponding to higher-order excitations of the free-layer magnetization. As much as 70% of the power is contained in higher-order modes compared to ≈20% in typical devices. Additionally, a shift in the uniform-mode resonant field that is correlated with the magnitude of the WER anomaly is detected at DC biases greater than 300 mV. These differences in the anomalous devices indicate a change in the micromagnetic resonant mode structure at high applied bias.

  6. Optically Induced PN Junction Diode and Photovoltaic Response on Ambipolar MoSe2 Field-effect Transistor

    NASA Astrophysics Data System (ADS)

    Pradhan, Nihar; Lu, Zhengguang; Rhodes, Daniel; Terrones, Mauricio; Smirnov, Dmitry; Balicas, Luis

    2015-03-01

    Transition metal dichalcogenides (TMDs) have emerged as an attractive material for electronic and optoelectronic devices due to their sizable band gap, flexibility and reduced dimensionality, which makes them promising candidates for applications in translucent optoelectronics components, such as solar cells and light emitting diodes. Here, we present an optically induced diode like response and concomitant photovoltaic effect in few-atomic layers molybdenum diselenide (MoSe2) field-effect transistors. Compared to recently reported PN junctions based on TMDs, ambipolar MoSe2 shows nearly ideal diode rectification under illumination, with a sizable photovoltaic efficiency. The observed light induced diode response under fixed gate voltage, yields a maximum open circuit voltage 0.28V and short circuit current 230nA at 30uW incident laser power. The sense of current rectification can be altered by changing the polarity of the applied gate voltage (Vbg) . At Vbg = 0V the highest electrical power obtained is 175pW corresponding to a maximum photovoltaic efficiency of 0.01%. These values increased to 11nW and 0.05% under a Vbg = -7.5V. At an excitation voltage 1V we observed maximum photocurrent responsivity surpassing 100mA/W with corresponding external quantum efficiency ~ 30%.

  7. Epitaxial growth of ultrathin MgO layers on Fe3O4(0 0 1) films

    NASA Astrophysics Data System (ADS)

    Nordmann, T.; Kuschel, O.; Wollschläger, J.

    2016-09-01

    The initial growth stages of MgO on Fe3O4 films are studied by means of X-ray photoelectron spectroscopy and low energy electron diffraction to clarify stoichiometric and structural properties of these layered structures. This bilayer structure is important to fabricate high quality magnetic tunnel junctions based on Fe3O4 electrodes and MgO tunneling barriers. For this purpose, the deposition temperature of MgO has been varied between 100 °C and 250 °C. Initially, MgO grows layer-by-layer on Fe3O4/MgO(0 0 1) forming a wetting layer. Depending on the growth temperature, after growth of a 2-3 nm thick laminar wetting layer, the MgO films finally start to roughen during growth. Thus the growth of MgO on Fe3O4/MgO(0 0 1) is described by a Stranski-Krastanov growth mode. Diffraction experiments show that the magnetite (√{ 2} ×√{ 2})R45° superstructure is removed already during the initial stages of MgO deposition. Furthermore, these experiments show that MgO films are rougher for growth at low deposition temperatures.

  8. Uncovering a law of corresponding states for electron tunneling in molecular junctions.

    PubMed

    Bâldea, Ioan; Xie, Zuoti; Frisbie, C Daniel

    2015-06-21

    Laws of corresponding states known so far demonstrate that certain macroscopic systems can be described in a universal manner in terms of reduced quantities, which eliminate specific substance properties. To quantitatively describe real systems, all these laws of corresponding states contain numerical factors adjusted empirically. Here, we report a law of corresponding states deduced analytically for charge transport via tunneling in molecular junctions, which we validate against current-voltage measurements for conducting probe atomic force microscope junctions based on benchmark molecular series (oligophenylenedithiols and alkanedithiols) and electrodes (silver, gold, and platinum), as well as against transport data for scanning tunneling microscope junctions. Two salient features distinguish the present law of corresponding states from all those known previously. First, it is expressed by a universal curve free of empirical parameters. Second, it demonstrates that a universal behavior is not necessarily affected by strong stochastic fluctuations often observed in molecular electronics. An important and encouraging message of this finding is that transport behavior across different molecular platforms can be similar and extraordinarily reproducible. PMID:26008991

  9. Very large thermophase in ferromagnetic Josephson junctions.

    PubMed

    Giazotto, F; Heikkilä, T T; Bergeret, F S

    2015-02-13

    The concept of thermophase refers to the appearance of a phase gradient inside a superconductor originating from the presence of an applied temperature bias across it. The resulting supercurrent flow may, in suitable conditions, fully counterbalance the temperature-bias-induced quasiparticle current therefore preventing the formation of any voltage drop, i.e., a thermovoltage, across the superconductor. Yet, the appearance of a thermophase is expected to occur in Josephson-coupled superconductors as well. Here, we theoretically investigate the thermoelectric response of a thermally biased Josephson junction based on a ferromagnetic insulator. In particular, we predict the occurrence of a very large thermophase that can reach π/2 across the contact for suitable temperatures and structure parameters; i.e., the quasiparticle thermal current can reach the critical current. Such a thermophase can be several orders of magnitude larger than that predicted to occur in conventional Josephson tunnel junctions. In order to assess experimentally the predicted very large thermophase, we propose a realistic setup realizable with state-of-the-art nanofabrication techniques and well-established materials, based on a superconducting quantum interference device. This effect could be of strong relevance in several low-temperature applications, for example, for revealing tiny temperature differences generated by coupling the electromagnetic radiation to one of the superconductors forming the junction. PMID:25723238

  10. Carbon Nanotube Sheet as Top Contact Electrode for Nanowires: Highly Versatile and Simple Process.

    PubMed

    Ternon, Céline; Dupas, Florence; Stein, Sergio; Aguirre, Carla; Dhalluin, Florian; Baron, Thierry

    2015-02-01

    In the past years, lots of research works were dedicated to nanowires and their integration into functional devices. However, despite the great potential of such materials, no device based on nanowires has been transferred in all-day-life. In fact, the vertical device integration is slowed down by the difficulty to contact easily the top electrode. With this work, we present a simple, elegant and versatile process for creating a top electrode contact on nanowires: a carbon nanotube sheet is suspended at the top of the nanowire field. The proof of concept is made through the realization of photovoltaic devices composed of an assembly of vertical PN-junctions based on silicon nanowires. For an illumination density of 100 mW . cm-2, our devices exhibit short circuit current density as high as 15 mA . cm-2. Due to the numerous advantages of the carbon nanotube sheets as top electrode, such as transparency, porosity, good mechanical performance and no need to embed nanowires, such simple and elegant technology should definitely find developments in every field of nanotechnology. PMID:26353710

  11. Fabrication-process-induced variations of Nb/Al/AlOx/Nb Josephson junctions in superconductor integrated circuits

    NASA Astrophysics Data System (ADS)

    Tolpygo, Sergey K.; Amparo, Denis

    2010-03-01

    Currently, superconductor digital integrated circuits fabricated at HYPRES, Inc. can operate at clock frequencies approaching 40 GHz. The circuits present multilayered structures containing tens of thousands of Nb/Al/AlOx/Nb Josephson junctions (JJs) of various sizes interconnected by four Nb wiring layers, resistors, and other circuit elements. In order to be fully operational, the integrated circuits should be fabricated such that the critical currents of the JJs are within the tight design margins and the proper relationships between the critical currents of JJs of different sizes are preserved. We present experimental data and discuss mechanisms of process-induced variations of the critical current and energy gap of Nb/Al/AlOx/Nb JJs in integrated circuits. We demonstrate that the Josephson critical current may depend on the type and area of circuit elements connected to the junction, on the circuit pattern, and on the step in the fabrication process at which the connection is made. In particular, we discuss the influence of (a) the junction base electrode connection to the ground plane, (b) the junction counter electrode connection to the ground plane, and (c) the counter electrode connection to the Ti/Au or Ti/Pd/Au contact pads by Nb wiring. We show that the process-induced changes of the properties of Nb/Al/AlOx/Nb junctions are caused by migration of impurity atoms (hydrogen) between the different layers comprising the integrated circuits.

  12. Superfluid qubit systems with ring shaped optical lattices

    PubMed Central

    Amico, Luigi; Aghamalyan, Davit; Auksztol, Filip; Crepaz, Herbert; Dumke, Rainer; Kwek, Leong Chuan

    2014-01-01

    We study an experimentally feasible qubit system employing neutral atomic currents. Our system is based on bosonic cold atoms trapped in ring-shaped optical lattice potentials. The lattice makes the system strictly one dimensional and it provides the infrastructure to realize a tunable ring-ring interaction. Our implementation combines the low decoherence rates of neutral cold atoms systems, overcoming single site addressing, with the robustness of topologically protected solid state Josephson flux qubits. Characteristic fluctuations in the magnetic fields affecting Josephson junction based flux qubits are expected to be minimized employing neutral atoms as flux carriers. By breaking the Galilean invariance we demonstrate how atomic currents through the lattice provide an implementation of a qubit. This is realized either by artificially creating a phase slip in a single ring, or by tunnel coupling of two homogeneous ring lattices. The single qubit infrastructure is experimentally investigated with tailored optical potentials. Indeed, we have experimentally realized scaled ring-lattice potentials that could host, in principle, n ~ 10 of such ring-qubits, arranged in a stack configuration, along the laser beam propagation axis. An experimentally viable scheme of the two-ring-qubit is discussed, as well. Based on our analysis, we provide protocols to initialize, address, and read-out the qubit. PMID:24599096

  13. Improving photovoltaic performance through radiative cooling in both terrestrial and extraterrestrial environments.

    PubMed

    Safi, Taqiyyah S; Munday, Jeremy N

    2015-09-21

    The method of detailed balance, introduced by Shockley and Queisser, is often used to find an upper theoretical limit for the efficiency of semiconductor pn-junction based photovoltaics. Typically the solar cell is assumed to be at an ambient temperature of 300 K. In this paper, we describe and analyze the use of radiative cooling techniques to lower the solar cell temperature below the ambient to surpass the detailed balance limit for a cell in contact with an ideal heat sink. We show that by combining specifically designed radiative cooling structures with solar cells, efficiencies higher than the limiting efficiency achievable at 300 K can be obtained for solar cells in both terrestrial and extraterrestrial environments. We show that our proposed structure yields an efficiency 0.87% higher than a typical PV module at operating temperatures in a terrestrial application. We also demonstrate an efficiency advantage of 0.4-2.6% for solar cells in an extraterrestrial environment in near-earth orbit. PMID:26406742

  14. Near-ultraviolet-sensitive graphene/porous silicon photodetectors.

    PubMed

    Kim, Jungkil; Joo, Soong Sin; Lee, Kyeong Won; Kim, Ju Hwan; Shin, Dong Hee; Kim, Sung; Choi, Suk-Ho

    2014-12-10

    Porous silicon (PSi) is recognized as an attractive building block for photonic devices because of its novel properties including high ratio of surface to volume and high light absorption. We first report near-ultraviolet (UV)-sensitive graphene/PSi photodetectors (PDs) fabricated by utilizing graphene and PSi as a carrier collector and a photoexcitation layer, respectively. Thanks to high light absorption and enlarged energy-band gap of PSi, the responsivity (Ri) and quantum efficiency (QE) of the PDs are markedly enhanced in the near-UV range. The performances of PDs are systemically studied for various porosities of PSi, controlled by varying the electroless-deposition time (td) of Ag nanoparticles for the use of Si etching. Largest gain is obtained at td = 3 s, consistent with the maximal enhancement of Ri and QE in the near UV range, which originates from the well-defined interface at the graphene/PSi junction, as proved by atomic- and electrostatic-force microscopies. Optimized response speed is ∼10 times faster compared to graphene/single-crystalline Si PDs. These and other unique PD characteristics prove to be governed by typical Schottky diode-like transport of charge carriers at the graphene/PSi junctions, based on bias-dependent variations of the band profiles, resulting in novel dark- and photocurrent behaviors. PMID:25384018

  15. Exploring tight junction alteration using double fluorescent probe combination of lanthanide complex with gold nanoclusters.

    PubMed

    Wang, Xinyi; Wang, Na; Yuan, Lan; Li, Na; Wang, Junxia; Yang, Xiaoda

    2016-01-01

    Tight junctions play a key role in restricting or regulating passage of liquids, ions and large solutes through various biological barriers by the paracellular route. Changes in paracellular permeation indicate alteration of the tight junction. However, it is very difficult to obtain the structural change information by measuring paracellular flux based on transepithelial electrical resistance or using fluorescein-labeled dextrans. Here we show that the BSA and GSH stabilized gold nanoclusters exhibit marginal cytotoxicity and pass through the MDCK monolayer exclusively through the paracellular pathway. We propose a double fluorescence probe strategy, the combination of a proven paracellular indicator (europium complex) with fluorescent gold nanoclusters. We calculate changes of structural parameters in tight junctions based on determination of the diffusion coefficients of the probes. Two different types of tight junction openers are used to validate our strategy. Results show that EDTA disrupts tight junction structures and induces large and smooth paracellular pore paths with an average radius of 17 nm, but vanadyl complexes induce paths with the radius of 6 nm. The work suggests that the double fluorescence probe strategy is a useful and convenient approach for in vitro investigation of tight junction structural alternations caused by pharmacological or pathological events. PMID:27574102

  16. Resolving metal-molecule interfaces at single-molecule junctions

    PubMed Central

    Komoto, Yuki; Fujii, Shintaro; Nakamura, Hisao; Tada, Tomofumi; Nishino, Tomoaki; Kiguchi, Manabu

    2016-01-01

    Electronic and structural detail at the electrode-molecule interface have a significant influence on charge transport across molecular junctions. Despite the decisive role of the metal-molecule interface, a complete electronic and structural characterization of the interface remains a challenge. This is in no small part due to current experimental limitations. Here, we present a comprehensive approach to obtain a detailed description of the metal-molecule interface in single-molecule junctions, based on current-voltage (I-V) measurements. Contrary to conventional conductance studies, this I-V approach provides a correlated statistical description of both, the degree of electronic coupling across the metal-molecule interface, and the energy alignment between the conduction orbital and the Fermi level of the electrode. This exhaustive statistical approach was employed to study single-molecule junctions of 1,4-benzenediamine (BDA), 1,4-butanediamine (C4DA), and 1,4-benzenedithiol (BDT). A single interfacial configuration was observed for both BDA and C4DA junctions, while three different interfacial arrangements were resolved for BDT. This multiplicity is due to different molecular adsorption sites on the Au surface namely on-top, hollow, and bridge. Furthermore, C4DA junctions present a fluctuating I-V curve arising from the greater conformational freedom of the saturated alkyl chain, in sharp contrast with the rigid aromatic backbone of both BDA and BDT. PMID:27221947

  17. Spin-Orbit Coupling in Hybrid Semiconductor Structures: From Majorana Fermions to Topological Insulators

    NASA Astrophysics Data System (ADS)

    Scharf, Benedikt

    Hybrid semiconductor structures with strong spin-orbit coupling are responsible for many fascinating phenomena. Topological states in systems of reduced dimensionality, in particular, offer many intriguing possibilities, both for fundamental research as well as for potential applications. In this talk, we describe the importance of the interplay of spin-orbit coupling (SOC) and the sample geometry in realizing exotic Majorana fermions (MFs) in quantum dots and rings and discuss several schemes to detect MFs. An effective SOC from the magnetic textures provided by magnetic tunnel junctions could enable a versatile control of MFs and their adiabatic exchange. We show that in 2D topological insulators (TIs), such as inverted HgTe/CdTe QWs, helical quantum spin Hall (QSH) states persist even at finite magnetic fields below a critical magnetic field above which only quantum Hall (QH) states can be found. We propose magneto-optical absorption measurements to probe the magnetic-field induced transition between the QSH and QH regimes. This measurement scheme is robust against perturbations such as additional SOC due to bulk or structure-inversion asymmetry. Finally, tunnel junctions based on the surfaces of 3D TIs are presented. These junctions can exhibit giant tunneling anomalous Hall (TAH) currents and negative differential TAH conductance, which makes them an attractive and versatile system for spintronic applications.

  18. Physical model of the contact resistivity of metal-graphene junctions

    SciTech Connect

    Chaves, Ferney A. Jiménez, David; Cummings, Aron W.; Roche, Stephan

    2014-04-28

    While graphene-based technology shows great promise for a variety of electronic applications, including radio-frequency devices, the resistance of the metal-graphene contact is a technological bottleneck for the realization of viable graphene electronics. One of the most important factors in determining the resistance of a metal-graphene junction is the contact resistivity. Despite the large number of experimental works that exist in the literature measuring the contact resistivity, a simple model of it is still lacking. In this paper, we present a comprehensive physical model for the contact resistivity of these junctions, based on the Bardeen Transfer Hamiltonian method. This model unveils the role played by different electrical and physical parameters in determining the specific contact resistivity, such as the chemical potential of interaction, the work metal-graphene function difference, and the insulator thickness between the metal and graphene. In addition, our model reveals that the contact resistivity is strongly dependent on the bias voltage across the metal-graphene junction. This model is applicable to a wide variety of graphene-based electronic devices and thus is useful for understanding how to optimize the contact resistance in these systems.

  19. Spin electronic magnetic sensor based on functional oxides for medical imaging

    NASA Astrophysics Data System (ADS)

    Solignac, A.; Kurij, G.; Guerrero, R.; Agnus, G.; Maroutian, T.; Fermon, C.; Pannetier-Lecoeur, M.; Lecoeur, Ph.

    2015-09-01

    To detect magnetic signals coming from the body, in particular those produced by the electrical activity of the heart or of the brain, the development of ultrasensitive sensors is required. In this regard, magnetoresistive sensors, stemming from spin electronics, are very promising devices. For example, tunnel magnetoresistance (TMR) junctions based on MgO tunnel barrier have a high sensitivity. Nevertheless, TMR also often have high level of noise. Full spin polarized materials like manganite La0.67Sr0.33MnO3 (LSMO) are attractive alternative candidates to develop such sensors because LSMO exhibits a very low 1/f noise when grown on single crystals, and a TMR response has been observed with values up to 2000%. This kind of tunnel junctions, when combined with a high Tc superconductor loop, opens up possibilities to develop full oxide structures working at liquid nitrogen temperature and suitable for medical imaging. In this work, we investigated on LSMO-based tunnel junctions the parameters controlling the overall system performances, including not only the TMR ratio, but also the pinning of the reference layer and the noise floor. We especially focused on studying the effects of the quality of the barrier, the interface and the electrode, by playing with materials and growth conditions.

  20. Hybrid pn-junction solar cells based on layers of inorganic nanocrystals and organic semiconductors: optimization of layer thickness by considering the width of the depletion region.

    PubMed

    Saha, Sudip K; Guchhait, Asim; Pal, Amlan J

    2014-03-01

    We report the formation and characterization of hybrid pn-junction solar cells based on a layer of copper diffused silver indium disulfide (AgInS2@Cu) nanoparticles and another layer of copper phthalocyanine (CuPc) molecules. With copper diffusion in the nanocrystals, their optical absorption and hence the activity of the hybrid pn-junction solar cells was extended towards the near-IR region. To decrease the particle-to-particle separation for improved carrier transport through the inorganic layer, we replaced the long-chain ligands of copper-diffused nanocrystals in each monolayer with short-ones. Under illumination, the hybrid pn-junctions yielded a higher short-circuit current as compared to the combined contribution of the Schottky junctions based on the components. A wider depletion region at the interface between the two active layers in the pn-junction device as compared to that of the Schottky junctions has been considered to analyze the results. Capacitance-voltage characteristics under a dark condition supported such a hypothesis. We also determined the width of the depletion region in the two layers separately so that a pn-junction could be formed with a tailored thickness of the two materials. Such a "fully-depleted" device resulted in an improved photovoltaic performance, primarily due to lessening of the internal resistance of the hybrid pn-junction solar cells. PMID:24452695

  1. Lateral graphene p-n junctions formed by the graphene/MoS₂ hybrid interface.

    PubMed

    Meng, Jie; Song, Hua-Ding; Li, Cai-Zhen; Jin, Yibo; Tang, Lei; Liu, Dameng; Liao, Zhi-Min; Xiu, Faxian; Yu, Da-Peng

    2015-07-21

    Graphene/two-dimensional (2D) semiconductor heterostructures have been demonstrated to possess many advantages for electronic and optoelectronic devices. However, there are few reports about the utilization of a 2D semiconductor monolayer to tune the properties of graphene. Here, we report the fabrication and characterization of graphene p-n junctions based on graphene/MoS2 hybrid interfaces. Monolayered graphene across the monolayered MoS2 boundary is divided into n-type regions on the MoS2 and p-type regions on the SiO2 substrate. Such van der Waals heterostructure based graphene p-n junctions show good photoelectric properties. The photocurrent modulation of such devices by a single back gate is also demonstrated for the first time, which shows that the graphene on and off MoS2 regions have different responses to the gate voltage. Our results suggest that the atomic thin hybrid structure can remarkably extend the device applications. PMID:26090791

  2. Tunable GaTe-MoS2 van der Waals p-n Junctions with Novel Optoelectronic Performance.

    PubMed

    Wang, Feng; Wang, Zhenxing; Xu, Kai; Wang, Fengmei; Wang, Qisheng; Huang, Yun; Yin, Lei; He, Jun

    2015-11-11

    P-n junctions based on vertically stacked van der Waals (vdW) materials have attracted a great deal of attention and may open up unforeseen opportunities in electronics and optoelectronics. However, due to the lack of intrinsic p-type vdW materials, most previous studies generally adopted electrical gating, special electrode contacts, or chemical doping methods to realize p-n vdW junctions. GaTe is an intrinsic p-type vdW material with a relatively high charge density, and it has a direct band gap that is independent of thickness. Here, we report the construction of ultrathin and tunable p-GaTe/n-MoS2 vdW heterostructure with high photovoltaic and photodetecting performance. The rectification ratio, external quantum efficiency, and photoresponsivity are as high as 4 × 10(5), 61.68%, and 21.83 AW(-1), respectively. In particular, the detectivity is up to 8.4 × 10(13) Jones, which is even higher than commercial Si, InGaAs photodetectors. This study demonstrates the promising potential of p-GaTe/n-MoS2 heterostructures for next-generation electronic and optoelectronic devices. PMID:26469092

  3. Biological Derived Nanomotors in a ``Domino Fashion''

    NASA Astrophysics Data System (ADS)

    Maksoed, W. H.

    2015-11-01

    For disproportionation of H2 O2 , we also considers an electrokinetic mechanism they appear.So far, the more efficient micro/nanoscale motors are derived from biological systems [2003]. Besides, a control experimenting using 3 stripped Au/Pt/Au rods with catalyzed the composition of H2 O2 , at a similar rate-Walter F Paxton: ``Catalytic Nanomotors,'' JACS, 2004. We also intended to accomaplishes the HCCI quotes from Marcin Frackowiak, dissertation, 2009, just in several characters seems as twin of IGNITION through IceCube document project held since Oct 11, 2001 ever concludes as ``saw none'' so they can be follows the ITER/IFMIF. Refers to S29286 file in UI retrieved: ``magnetic quantum-dot cellular automata which is nonvolatile & lower power consist of nanomagnets. Since they are magnetically coupled, logic can be performed by switching, on the other hand in a DOMINO fashion..'' [A. Klenm: ``Fabrication of Magnetic Tunnel Junction-based Spintronic Devices..,'' convocation, Aug 11-14, 2010]. Acknowledgments devotes to BB Mandelbrot: ``Fractal Geometry: What is it & What Does it do?''.

  4. Understanding the failure mechanisms of microwave bipolar transistors caused by electrostatic discharge

    NASA Astrophysics Data System (ADS)

    Jin, Liu; Yongguang, Chen; Zhiliang, Tan; Jie, Yang; Xijun, Zhang; Zhenxing, Wang

    2011-10-01

    Electrostatic discharge (ESD) phenomena involve both electrical and thermal effects, and a direct electrostatic discharge to an electronic device is one of the most severe threats to component reliability. Therefore, the electrical and thermal stability of multifinger microwave bipolar transistors (BJTs) under ESD conditions has been investigated theoretically and experimentally. 100 samples have been tested for multiple pulses until a failure occurred. Meanwhile, the distributions of electric field, current density and lattice temperature have also been analyzed by use of the two-dimensional device simulation tool Medici. There is a good agreement between the simulated results and failure analysis. In the case of a thermal couple, the avalanche current distribution in the fingers is in general spatially unstable and results in the formation of current crowding effects and crystal defects. The experimental results indicate that a collector-base junction is more sensitive to ESD than an emitter-base junction based on the special device structure. When the ESD level increased to 1.3 kV, the collector-base junction has been burnt out first. The analysis has also demonstrated that ESD failures occur generally by upsetting the breakdown voltage of the dielectric or overheating of the aluminum-silicon eutectic. In addition, fatigue phenomena are observed during ESD testing, with devices that still function after repeated low-intensity ESDs but whose performances have been severely degraded.

  5. Optimization on photoelectric detection based on stacked La{sub 0.9}Sr{sub 0.1}MnO{sub 3-{delta}}/LaAlO{sub 3-{delta}} multijunctions

    SciTech Connect

    Jie Xing; Hui Yinghao; Er Jiaguo; Fang Yang

    2011-08-01

    Three multijunctions consisting of La{sub 0.9}Sr{sub 0.1}MnO{sub 3-{delta}} and LaAlO{sub 3-{delta}} on Si substrate have been fabricated under different oxygen pressures by laser molecular beam epitaxy. They exhibit nonlinear and rectifying current-voltage characteristics and evident photocurrent response to He-Ne laser illumination. Experimental results indicate that the periodically stacked multijunction grown under lower oxygen pressure shows a better rectification behavior and a higher photocurrent. The photovoltaic responsivities of the multijunctions are enhanced greatly at reverse bias and are much higher than that of a similarly grown single p-n junction. Based on the band structure of the multilayers, a possible mechanism of the photovoltaic process was proposed. A high photovoltage responsivity of 168.6 mV/mW has been achieved at - 6 V bias; this demonstrates the potential of the present multijunction configuration for photodetectors operating at room temperature.

  6. Coherent-state storage and retrieval between superconducting cavities using parametric frequency conversion

    NASA Astrophysics Data System (ADS)

    Sirois, A. J.; Castellanos-Beltran, M. A.; DeFeo, M. P.; Ranzani, L.; Lecocq, F.; Simmonds, R. W.; Teufel, J. D.; Aumentado, J.

    2015-04-01

    In superconducting quantum information, machined aluminum superconducting cavities have proven to be a well-controlled, low-dissipation electromagnetic environment for quantum circuits such as qubits. They can possess large internal quality factors, Qint > 108, and present the possibility of storing quantum information for times far exceeding those of microfabricated circuits. However, in order to be useful as a storage element, these cavities require a fast "read/write" mechanism—in other words, they require tunable coupling between other systems of interest such as other cavity modes and qubits, as well as any associated readout hardware. In this work, we demonstrate these qualities in a simple dual cavity architecture in which a low-Q "readout" mode is parametrically coupled to a high-Q "storage" mode, allowing us to store and retrieve classical information. Specifically, we employ a flux-driven Josephson junction-based coupling scheme to controllably swap coherent states between two cavities, demonstrating full, sequenced control over the coupling rates between modes.

  7. Ultrasensitive mechanical crack-based sensor inspired by the spider sensory system

    NASA Astrophysics Data System (ADS)

    Kang, Daeshik; Pikhitsa, Peter V.; Choi, Yong Whan; Lee, Chanseok; Shin, Sung Soo; Piao, Linfeng; Park, Byeonghak; Suh, Kahp-Yang; Kim, Tae-Il; Choi, Mansoo

    2014-12-01

    Recently developed flexible mechanosensors based on inorganic silicon, organic semiconductors, carbon nanotubes, graphene platelets, pressure-sensitive rubber and self-powered devices are highly sensitive and can be applied to human skin. However, the development of a multifunctional sensor satisfying the requirements of ultrahigh mechanosensitivity, flexibility and durability remains a challenge. In nature, spiders sense extremely small variations in mechanical stress using crack-shaped slit organs near their leg joints. Here we demonstrate that sensors based on nanoscale crack junctions and inspired by the geometry of a spider's slit organ can attain ultrahigh sensitivity and serve multiple purposes. The sensors are sensitive to strain (with a gauge factor of over 2,000 in the 0-2 per cent strain range) and vibration (with the ability to detect amplitudes of approximately 10 nanometres). The device is reversible, reproducible, durable and mechanically flexible, and can thus be easily mounted on human skin as an electronic multipixel array. The ultrahigh mechanosensitivity is attributed to the disconnection-reconnection process undergone by the zip-like nanoscale crack junctions under strain or vibration. The proposed theoretical model is consistent with experimental data that we report here. We also demonstrate that sensors based on nanoscale crack junctions are applicable to highly selective speech pattern recognition and the detection of physiological signals. The nanoscale crack junction-based sensory system could be useful in diverse applications requiring ultrahigh displacement sensitivity.

  8. Loss of the Coffin-Lowry syndrome-associated gene RSK2 alters ERK activity, synaptic function and axonal transport in Drosophila motoneurons.

    PubMed

    Beck, Katherina; Ehmann, Nadine; Andlauer, Till F M; Ljaschenko, Dmitrij; Strecker, Katrin; Fischer, Matthias; Kittel, Robert J; Raabe, Thomas

    2015-11-01

    Plastic changes in synaptic properties are considered as fundamental for adaptive behaviors. Extracellular-signal-regulated kinase (ERK)-mediated signaling has been implicated in regulation of synaptic plasticity. Ribosomal S6 kinase 2 (RSK2) acts as a regulator and downstream effector of ERK. In the brain, RSK2 is predominantly expressed in regions required for learning and memory. Loss-of-function mutations in human RSK2 cause Coffin-Lowry syndrome, which is characterized by severe mental retardation and low IQ scores in affected males. Knockout of RSK2 in mice or the RSK ortholog in Drosophila results in a variety of learning and memory defects. However, overall brain structure in these animals is not affected, leaving open the question of the pathophysiological consequences. Using the fly neuromuscular system as a model for excitatory glutamatergic synapses, we show that removal of RSK function causes distinct defects in motoneurons and at the neuromuscular junction. Based on histochemical and electrophysiological analyses, we conclude that RSK is required for normal synaptic morphology and function. Furthermore, loss of RSK function interferes with ERK signaling at different levels. Elevated ERK activity was evident in the somata of motoneurons, whereas decreased ERK activity was observed in axons and the presynapse. In addition, we uncovered a novel function of RSK in anterograde axonal transport. Our results emphasize the importance of fine-tuning ERK activity in neuronal processes underlying higher brain functions. In this context, RSK acts as a modulator of ERK signaling. PMID:26398944

  9. Room-temperature single-electron junction.

    PubMed Central

    Facci, P; Erokhin, V; Carrara, S; Nicolini, C

    1996-01-01

    The design, realization, and test performances of an electronic junction based on single-electron phenomena that works in the air at room temperature are hereby reported. The element consists of an electrochemically etched sharp tungsten stylus over whose tip a nanometer-size crystal was synthesized. Langmuir-Blodgett films of cadmium arachidate were transferred onto the stylus and exposed to a H2S atmosphere to yield CdS nanocrystals (30-50 angstrom in diameter) imbedded into an organic matrix. The stylus, biased with respect to a flat electrode, was brought to the tunnel distance from the film and a constant gap value was maintained by a piezo-electric actuator driven by a feedback circuit fed by the tunneling current. With this set-up, it is possible to measure the behavior of the current flowing through the quantum dot when a bias voltage is applied. Voltage-current characteristics measured in the system displayed single-electron trends such as a Coulomb blockade and Coulomb staircase and revealed capacitance values as small as 10(-19) F. PMID:11607710

  10. Photoelectrochemical oxidation of ibuprofen via Cu2O-doped TiO2 nanotube arrays.

    PubMed

    Sun, Qiannan; Peng, Yen-Ping; Chen, Hanlin; Chang, Ken-Lin; Qiu, Yang-Neng; Lai, Shiau-Wu

    2016-12-01

    A p-n junction based Cu2O-doped TiO2 nanotube arrays (Cu2O-TNAs) were synthesized and used as a working anode in a photoelectrochemical (PEC) system. The results revealed that the Cu2O-TNAs were dominated by the anatase phase and responded significantly to visible light. XPS analyses indicated that with an amount of 24.79% Cu doping into the structure, the band gap of Cu2O-TNAs was greatly reduced. SEM images revealed that the supported TiO2 nanotubes had diameters of approximately 80nm and lengths of about 2.63μm. Upon doping with Cu2O, the TiO2 nanotubes maintained their structural integrity, exhibiting no significant morphological change, favoring PEC applications. Under illumination, the photocurrent from Cu2O/TNAs was 2.4 times larger than that from TNAs, implying that doping with Cu2O significantly improved electron mobility by reducing the rate of recombination of electron-hole pairs. The EIS and Bode plot revealed that the estimated electron lifetimes, τel, of TNAs and Cu2O/TNAs were 6.91 and 26.26ms, respectively. The efficiencies of degradation of Ibuprofen by photoelectrochemical, photocatalytic (PC), electrochemical (EC) and photolytic (P) methods were measured. PMID:27021261

  11. High-Yield Growth and Characterization of ⟨100⟩ InP p-n Diode Nanowires.

    PubMed

    Cavalli, Alessandro; Wang, Jia; Esmaeil Zadeh, Iman; Reimer, Michael E; Verheijen, Marcel A; Soini, Martin; Plissard, Sebastien R; Zwiller, Val; Haverkort, Jos E M; Bakkers, Erik P A M

    2016-05-11

    Semiconductor nanowires are nanoscale structures holding promise in many fields such as optoelectronics, quantum computing, and thermoelectrics. Nanowires are usually grown vertically on (111)-oriented substrates, while (100) is the standard in semiconductor technology. The ability to grow and to control impurity doping of ⟨100⟩ nanowires is crucial for integration. Here, we discuss doping of single-crystalline ⟨100⟩ nanowires, and the structural and optoelectronic properties of p-n junctions based on ⟨100⟩ InP nanowires. We describe a novel approach to achieve low resistance electrical contacts to nanowires via a gradual interface based on p-doped InAsP. As a first demonstration in optoelectronic devices, we realize a single nanowire light emitting diode in a ⟨100⟩-oriented InP nanowire p-n junction. To obtain high vertical yield, which is necessary for future applications, we investigate the effect of the introduction of dopants on the nanowire growth. PMID:27045232

  12. Electrostatically tunable lateral MoTe2 p-n junction for use in high-performance optoelectronics.

    PubMed

    Wang, Zhenxing; Wang, Feng; Yin, Lei; Huang, Yun; Xu, Kai; Wang, Fengmei; Zhan, Xueying; He, Jun

    2016-07-21

    Because of their ultimate thickness, layered structure and high flexibility, pn junctions based on layered two-dimensional semiconductors have been attracting increasing attention recently. In this study, for the first time, we fabricated lateral pn junctions (LPNJs) based on ultrathin MoTe2 by introducing two separated electrostatic back gates, and investigated their electronic and photovoltaic performance. Pn, np, nn, and pp junctions can be easily realized by modulating the conductive channel type using gate voltages with different polarities. Strong rectification effects were observed in the pn and np junctions and the rectification ratio reached ∼5 × 10(4). Importantly, we find a unique phenomenon that the parameters for MoTe2 LPNJs experience abrupt changes during the transition from p to n or n to p. Furthermore, a high performance photovoltaic device with a filling factor of above 51% and electrical conversion efficiency (η) of around 0.5% is achieved. Our findings are of importance to comprehensively understand the electronic and optoelectronic properties of MoTe2 and may further open up novel electronic and optoelectronic device applications. PMID:27335271

  13. Loss of the Coffin-Lowry syndrome-associated gene RSK2 alters ERK activity, synaptic function and axonal transport in Drosophila motoneurons

    PubMed Central

    Beck, Katherina; Ehmann, Nadine; Andlauer, Till F. M.; Ljaschenko, Dmitrij; Strecker, Katrin; Fischer, Matthias; Kittel, Robert J.; Raabe, Thomas

    2015-01-01

    ABSTRACT Plastic changes in synaptic properties are considered as fundamental for adaptive behaviors. Extracellular-signal-regulated kinase (ERK)-mediated signaling has been implicated in regulation of synaptic plasticity. Ribosomal S6 kinase 2 (RSK2) acts as a regulator and downstream effector of ERK. In the brain, RSK2 is predominantly expressed in regions required for learning and memory. Loss-of-function mutations in human RSK2 cause Coffin-Lowry syndrome, which is characterized by severe mental retardation and low IQ scores in affected males. Knockout of RSK2 in mice or the RSK ortholog in Drosophila results in a variety of learning and memory defects. However, overall brain structure in these animals is not affected, leaving open the question of the pathophysiological consequences. Using the fly neuromuscular system as a model for excitatory glutamatergic synapses, we show that removal of RSK function causes distinct defects in motoneurons and at the neuromuscular junction. Based on histochemical and electrophysiological analyses, we conclude that RSK is required for normal synaptic morphology and function. Furthermore, loss of RSK function interferes with ERK signaling at different levels. Elevated ERK activity was evident in the somata of motoneurons, whereas decreased ERK activity was observed in axons and the presynapse. In addition, we uncovered a novel function of RSK in anterograde axonal transport. Our results emphasize the importance of fine-tuning ERK activity in neuronal processes underlying higher brain functions. In this context, RSK acts as a modulator of ERK signaling. PMID:26398944

  14. Remote driven and read MEMS sensors for harsh environments.

    PubMed

    Knobloch, Aaron J; Ahmad, Faisal R; Sexton, Dan W; Vernooy, David W

    2013-01-01

    The utilization of high accuracy sensors in harsh environments has been limited by the temperature constraints of the control electronics that must be co-located with the sensor. Several methods of remote interrogation for resonant sensors are presented in this paper which would allow these sensors to be extended to harsh environments. This work in particular demonstrates for the first time the ability to acoustically drive a silicon comb drive resonator into resonance and electromagnetically couple to the resonator to read its frequency. The performance of this system was studied as a function of standoff distance demonstrating the ability to excite and read the device from 22 cm when limited to drive powers of 30 mW. A feedback architecture was implemented that allowed the resonator to be driven into resonance from broadband noise and a standoff distance of 15 cm was demonstrated. It is emphasized that no junction-based electronic device was required to be co-located with the resonator, opening the door for the use of silicon-based, high accuracy MEMS devices in high temperature wireless applications. PMID:24152935

  15. Dirac electron states formed at the heterointerface between a topological insulator and a conventional semiconductor.

    PubMed

    Yoshimi, R; Tsukazaki, A; Kikutake, K; Checkelsky, J G; Takahashi, K S; Kawasaki, M; Tokura, Y

    2014-03-01

    Topological insulators are a class of semiconductor exhibiting charge-gapped insulating behaviour in the bulk, but hosting a spin-polarized massless Dirac electron state at the surface. The presence of a topologically protected helical edge channel has been verified for the vacuum-facing surface of several topological insulators by means of angle-resolved photoemission spectroscopy and scanning tunnelling microscopy. By performing tunnelling spectroscopy on heterojunction devices composed of p-type topological insulator (Bi1−xSbx)2Te3 and n-type conventional semiconductor InP, we report the observation of such states at the solid-state interface. Under an applied magnetic field, we observe a resonance in the tunnelling conductance through the heterojunction due to the formation of Landau levels of two-dimensional Dirac electrons at the interface. Moreover, resonant tunnelling spectroscopy reveals a systematic dependence of the Fermi velocity and Dirac point energy on the composition x. The successful formation of robust non-trivial edge channels at a solid-state interface is an essential step towards functional junctions based on topological insulators. PMID:24553653

  16. Colorimetric detection of gene transcript by target-induced three-way junction formation.

    PubMed

    Wang, Xuchu; Liu, Weiwei; Yin, Binbin; Yu, Pan; Duan, Xiuzhi; Liao, Zhaoping; Liu, Chunhua; Sang, Yiwen; Zhang, Gong; Chen, Yuhua; Tao, Zhihua

    2016-09-01

    Gene transcript often varies by alternative splicing, which plays different biological role that results in diversity of gene expression. Therefore, a simple and accurate identification of targeted transcript variant is of prime importance to achieve a precise molecular diagnosis. In this work, we presented a three-way junction based system where two split G-quadruplex forming sequences were coupled into two probes. Only upon the introduction of target gene transcript that offering a specific recognizable splicing site did the two probes assembled into three way junction conformation in a devised process, thus providing a functional G-quadruplex conformation that greatly enhanced hemin peroxidation. A notable resolution for gene splicing site detection was achieved. The detection limitation by colorimetric assay was 0.063μM, and this system has been proved to discriminate even in a single base false level around splicing site (about 3 times of single mismatched analyte to gain an equal signal by perfect analyte ). Furthermore, recoveries of 78.1%, 88.1%, 104.6% were obtained with 0.75μM, 0.25μM, 0.083μM of target, respectively, showing a capacity to further exploit a simple equipped device for gene transcript detection. PMID:27343570

  17. Integrated Spintronic Platforms for Biomolecular Recognition Detection

    NASA Astrophysics Data System (ADS)

    Martins, V. C.; Cardoso, F. A.; Loureiro, J.; Mercier, M.; Germano, J.; Cardoso, S.; Ferreira, R.; Fonseca, L. P.; Sousa, L.; Piedade, M. S.; Freitas, P. P.

    2008-06-01

    This paper covers recent developments in magnetoresistive based biochip platforms fabricated at INESC-MN, and their application to the detection and quantification of pathogenic waterborn microorganisms in water samples for human consumption. Such platforms are intended to give response to the increasing concern related to microbial contaminated water sources. The presented results concern the development of biological active DNA chips and protein chips and the demonstration of the detection capability of the present platforms. Two platforms are described, one including spintronic sensors only (spin-valve based or magnetic tunnel junction based), and the other, a fully scalable platform where each probe site consists of a MTJ in series with a thin film diode (TFD). Two microfluidic systems are described, for cell separation and concentration, and finally, the read out and control integrated electronics are described, allowing the realization of bioassays with a portable point of care unit. The present platforms already allow the detection of complementary biomolecular target recognition with 1 pM concentration.

  18. Ultrasensitive mechanical crack-based sensor inspired by the spider sensory system.

    PubMed

    Kang, Daeshik; Pikhitsa, Peter V; Choi, Yong Whan; Lee, Chanseok; Shin, Sung Soo; Piao, Linfeng; Park, Byeonghak; Suh, Kahp-Yang; Kim, Tae-il; Choi, Mansoo

    2014-12-11

    Recently developed flexible mechanosensors based on inorganic silicon, organic semiconductors, carbon nanotubes, graphene platelets, pressure-sensitive rubber and self-powered devices are highly sensitive and can be applied to human skin. However, the development of a multifunctional sensor satisfying the requirements of ultrahigh mechanosensitivity, flexibility and durability remains a challenge. In nature, spiders sense extremely small variations in mechanical stress using crack-shaped slit organs near their leg joints. Here we demonstrate that sensors based on nanoscale crack junctions and inspired by the geometry of a spider's slit organ can attain ultrahigh sensitivity and serve multiple purposes. The sensors are sensitive to strain (with a gauge factor of over 2,000 in the 0-2 per cent strain range) and vibration (with the ability to detect amplitudes of approximately 10 nanometres). The device is reversible, reproducible, durable and mechanically flexible, and can thus be easily mounted on human skin as an electronic multipixel array. The ultrahigh mechanosensitivity is attributed to the disconnection-reconnection process undergone by the zip-like nanoscale crack junctions under strain or vibration. The proposed theoretical model is consistent with experimental data that we report here. We also demonstrate that sensors based on nanoscale crack junctions are applicable to highly selective speech pattern recognition and the detection of physiological signals. The nanoscale crack junction-based sensory system could be useful in diverse applications requiring ultrahigh displacement sensitivity. PMID:25503234

  19. There are four dynamically and functionally distinct populations of E-cadherin in cell junctions

    PubMed Central

    Erami, Zahra; Timpson, Paul; Yao, Wu; Zaidel-Bar, Ronen; Anderson, Kurt I.

    2015-01-01

    ABSTRACT E-cadherin is a trans-membrane tumor suppressor responsible for epithelial cell adhesion. E-cadherin forms adhesive clusters through combined extra-cellular cis- and trans-interactions and intracellular interaction with the actin cytoskeleton. Here we identify four populations of E-cadherin within cell junctions based on the molecular interactions which determine their mobility and adhesive properties. Adhesive and non-adhesive populations of E-cadherin each consist of mobile and immobile fractions. Up to half of the E-cadherin immobilized in cell junctions is non-adhesive. Incorporation of E-cadherin into functional adhesions require all three adhesive interactions, with deletion of any one resulting in loss of effective cell-cell adhesion. Interestingly, the only interaction which could independently slow the diffusion of E-cadherin was the tail-mediated intra-cellular interaction. The adhesive and non-adhesive mobile fractions of E-cadherin can be distinguished by their sensitivity to chemical cross-linking with adhesive clusters. Our data define the size, mobility, and adhesive properties of four distinct populations of E-cadherin within cell junctions, and support association with the actin cytoskeleton as the first step in adhesion formation. PMID:26471767

  20. Modeling and theoretical efficiency of a silicon nanowire based thermoelectric junction with area enhancement

    SciTech Connect

    Seong, M; Sadhu, JS; Ma, J; Ghossoub, MG; Sinha, S

    2012-06-15

    Recent experimental work suggests that individual silicon nanowires with rough surfaces possess a thermoelectric figure of merit as high as 0.6 near room temperature. This paper addresses the possibility of using an array of such nanowires in a thermoelectric junction for generation. Employing a model of frequency dependent phonon boundary scattering, we estimate the effective thermal conductivity of the array and investigate heat flow through the junction. We show that charge transport is largely unaffected by the roughness scales considered. Enhancing the area for heat exchange at an individual 200 mu m x 200 mu m p-n junction yields significant temperature differences across the junction leading to power >0.6 mW and efficiency >1.5% for a junction with effective thermal conductivity <5 W/mK, when the source and sink are at 450 K and 300 K, respectively. We show that relatively short nanowires of similar to 50 mu m length are sufficient for obtaining peak power and reasonable efficiency. This substantially reduces the challenge of engineering low resistivity electrical contacts that critically affect power and efficiency. This paper provides insight into how fundamental transport in relation to bulk heat transfer and charge transport, affects the performance of thermoelectric junctions based on nanostructured materials. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4728189

  1. Exploring tight junction alteration using double fluorescent probe combination of lanthanide complex with gold nanoclusters

    PubMed Central

    Wang, Xinyi; Wang, Na; Yuan, Lan; Li, Na; Wang, Junxia; Yang, Xiaoda

    2016-01-01

    Tight junctions play a key role in restricting or regulating passage of liquids, ions and large solutes through various biological barriers by the paracellular route. Changes in paracellular permeation indicate alteration of the tight junction. However, it is very difficult to obtain the structural change information by measuring paracellular flux based on transepithelial electrical resistance or using fluorescein-labeled dextrans. Here we show that the BSA and GSH stabilized gold nanoclusters exhibit marginal cytotoxicity and pass through the MDCK monolayer exclusively through the paracellular pathway. We propose a double fluorescence probe strategy, the combination of a proven paracellular indicator (europium complex) with fluorescent gold nanoclusters. We calculate changes of structural parameters in tight junctions based on determination of the diffusion coefficients of the probes. Two different types of tight junction openers are used to validate our strategy. Results show that EDTA disrupts tight junction structures and induces large and smooth paracellular pore paths with an average radius of 17 nm, but vanadyl complexes induce paths with the radius of 6 nm. The work suggests that the double fluorescence probe strategy is a useful and convenient approach for in vitro investigation of tight junction structural alternations caused by pharmacological or pathological events. PMID:27574102

  2. Direct detection of spin chemical potential shift through spin filtering effect

    NASA Astrophysics Data System (ADS)

    Miao, Guoxing; Moodera, Jagadeesh

    2010-03-01

    Spin filtering (SF) effect is a unique way to generate highly spin-polarized tunnel currents from nonmagnetic electrodes. Magnetic tunnel junctions based on pure SF effect have been realized recently [1] as a clear demonstration of principle for the spin manipulation through SF effect. The next challenge is the readout of spin information. In this work, we present the direct detection of the spin chemical potential shift in an Al nano cluster sandwiched between two SF EuS tunnel barriers. The spin channels are split by depositing Al directly onto EuS, and the indirect exchange interaction between the Al conduction electrons and the localized Eu 4f electrons gives rise to an effective Zeeman splitting with the strength of a few mV. EuS on the readout side is isolated from the Al clusters with a natural Al2O3 barrier. In a vertical measurement geometry with no transport current, we directly detected the spin dependent voltage levels by aligning the detection SF barrier parallel or antiparallel to the first SF barrier, corresponding to the equilibrium up- and down-spin chemical potentials. A simple analysis treating the barriers as a set of resistors revealed that the observed voltage difference is the actual chemical potential shift modulated by the SF efficiency.[4pt] [1] G.X. Miao, M. Muller, J.S. Moodera,PRL102,076601(2009)

  3. Low Noise SIS Mixer for the Frequency above 1 THz

    NASA Astrophysics Data System (ADS)

    Karpov, Alexander; Miller, D.; Zmuidzinas, J.; Stern, J. A.; Bumble, B.; Leduc, H. G.

    We developed a SIS mixer for the 1.1-1.25 THz band of the heterodyne receiver of Herschel space observatory. Our approach may be used up to 1.6 THz. The quasi-optical SIS mixer has two NbN/AlN/Nb junctions with the critical current 30-50 kA/cm2 and the gap voltage of 3.4 mV. The tuning circuit integrated with SIS junction has the base electrode of Nb and a gold wire layer. This approach simplifies the SIS junction technology, compared to a design using NbTiN base electrode. The junction base electrode and the ground of the tuning micro strip circuit are formed in one step. The frequency of operation of the mixer is well above the gap frequency of Nb, and it behaves here as a normal metal. The resistivity of Nb at the critical temperature of 0.2 mOhm cm is below the resistivity of the best normal metal films. The measured receiver noise temperature is below 600 K.

  4. Remote Driven and Read MEMS Sensors for Harsh Environments

    PubMed Central

    Knobloch, Aaron J.; Ahmad, Faisal R.; Sexton, Dan W.; Vernooy, David W.

    2013-01-01

    The utilization of high accuracy sensors in harsh environments has been limited by the temperature constraints of the control electronics that must be co-located with the sensor. Several methods of remote interrogation for resonant sensors are presented in this paper which would allow these sensors to be extended to harsh environments. This work in particular demonstrates for the first time the ability to acoustically drive a silicon comb drive resonator into resonance and electromagnetically couple to the resonator to read its frequency. The performance of this system was studied as a function of standoff distance demonstrating the ability to excite and read the device from 22 cm when limited to drive powers of 30 mW. A feedback architecture was implemented that allowed the resonator to be driven into resonance from broadband noise and a standoff distance of 15 cm was demonstrated. It is emphasized that no junction-based electronic device was required to be co-located with the resonator, opening the door for the use of silicon-based, high accuracy MEMS devices in high temperature wireless applications. PMID:24152935

  5. Geometric photovoltaics applied to amorphous silicon thin film solar cells

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, Timothy

    Geometrically generalized analytical expressions for device transport are derived from first principles for a photovoltaic junction. Subsequently, conventional planar and unconventional coaxial and hemispherical photovoltaic architectures are applied to detail the device physics of the junction based on their respective geometry. For the conventional planar cell, the one-dimensional transport equations governing carrier dynamics are recovered. For the unconventional coaxial and hemispherical junction designs, new multi-dimensional transport equations are revealed. Physical effects such as carrier generation and recombination are compared for each cell architecture, providing insight as to how non-planar junctions may potentially enable greater energy conversion efficiencies. Numerical simulations are performed for arrays of vertically aligned, nanostructured coaxial and hemispherical amorphous silicon solar cells and results are compared to those from simulations performed for the standard planar junction. Results indicate that fundamental physical changes in the spatial dependence of the energy band profile across the intrinsic region of an amorphous silicon p-i-n junction manifest as an increase in recombination current for non-planar photovoltaic architectures. Despite an increase in recombination current, however, the coaxial architecture still appears to be able to surpass the efficiency predicted for the planar geometry, due to the geometry of the junction leading to a decoupling of optics and electronics.

  6. Partitioning of Holocene kinematics and interaction between the Theistareykir Fissure Swarm and the Husavik-Flatey Fault, North Iceland

    NASA Astrophysics Data System (ADS)

    Tibaldi, A.; Bonali, F. L.; Einarsson, P.; Hjartardóttir, Á. R.; Pasquarè Mariotto, F. A.

    2016-02-01

    Our research is aimed at contributing to the general understanding of how transform-rift junctions work, a topic that can be studied in exceptional detail in North Iceland, where the active transform Husavik-Flatey Fault (HFF) connects with the Gudfinnugja Fault (GF), the westernmost structure of the Theistareykir Fissure Swarm (TFS). We studied in the field: i) offsets along the easternmost HFF, ii) the geometry and kinematics of 649 faults and 1208 tension fractures in the TFS, iii) the interactions among all these structures. The HFF transtensional kinematics is compatible with the GF, which shows different offsets north and south of the junction between these two faults. We suggest the possible prolongation of the HFF beyond the junction, based on: i) the change in offsets and strikes of TFS normal faults, ii) the presence of en-échelon, NNW-SSE-striking normal faults and tension fractures with a slight right-lateral component, iii) the transition of some of the faults into tension fractures north of the prolongation of the HFF, and iv) the decrease in the cumulated offset of all the faults north of the HFF prolongation. We interpret these data as field evidence of the first stages of propagation of the HFF upward or across the TFS: This has clear implications for defining the potential rupture length of the HFF and, hence, for seismic hazard assessment.

  7. Concurrent and Accurate Short Read Mapping on Multicore Processors.

    PubMed

    Martínez, Héctor; Tárraga, Joaquín; Medina, Ignacio; Barrachina, Sergio; Castillo, Maribel; Dopazo, Joaquín; Quintana-Ortí, Enrique S

    2015-01-01

    We introduce a parallel aligner with a work-flow organization for fast and accurate mapping of RNA sequences on servers equipped with multicore processors. Our software, HPG Aligner SA (HPG Aligner SA is an open-source application. The software is available at http://www.opencb.org, exploits a suffix array to rapidly map a large fraction of the RNA fragments (reads), as well as leverages the accuracy of the Smith-Waterman algorithm to deal with conflictive reads. The aligner is enhanced with a careful strategy to detect splice junctions based on an adaptive division of RNA reads into small segments (or seeds), which are then mapped onto a number of candidate alignment locations, providing crucial information for the successful alignment of the complete reads. The experimental results on a platform with Intel multicore technology report the parallel performance of HPG Aligner SA, on RNA reads of 100-400 nucleotides, which excels in execution time/sensitivity to state-of-the-art aligners such as TopHat 2+Bowtie 2, MapSplice, and STAR. PMID:26451814

  8. Resolving metal-molecule interfaces at single-molecule junctions

    NASA Astrophysics Data System (ADS)

    Komoto, Yuki; Fujii, Shintaro; Nakamura, Hisao; Tada, Tomofumi; Nishino, Tomoaki; Kiguchi, Manabu

    2016-05-01

    Electronic and structural detail at the electrode-molecule interface have a significant influence on charge transport across molecular junctions. Despite the decisive role of the metal-molecule interface, a complete electronic and structural characterization of the interface remains a challenge. This is in no small part due to current experimental limitations. Here, we present a comprehensive approach to obtain a detailed description of the metal-molecule interface in single-molecule junctions, based on current-voltage (I-V) measurements. Contrary to conventional conductance studies, this I-V approach provides a correlated statistical description of both, the degree of electronic coupling across the metal-molecule interface, and the energy alignment between the conduction orbital and the Fermi level of the electrode. This exhaustive statistical approach was employed to study single-molecule junctions of 1,4-benzenediamine (BDA), 1,4-butanediamine (C4DA), and 1,4-benzenedithiol (BDT). A single interfacial configuration was observed for both BDA and C4DA junctions, while three different interfacial arrangements were resolved for BDT. This multiplicity is due to different molecular adsorption sites on the Au surface namely on-top, hollow, and bridge. Furthermore, C4DA junctions present a fluctuating I-V curve arising from the greater conformational freedom of the saturated alkyl chain, in sharp contrast with the rigid aromatic backbone of both BDA and BDT.

  9. Theoretical study of the charge transport through C60-based single-molecule junctions

    NASA Astrophysics Data System (ADS)

    Bilan, S.; Zotti, L. A.; Pauly, F.; Cuevas, J. C.

    2012-05-01

    We present a theoretical study of the conductance and thermopower of single-molecule junctions based on C60 and C60-terminated molecules. We first analyze the transport properties of gold-C60-gold junctions and show that these junctions can be highly conductive (with conductances above 0.1G0, where G0=2e2/h is the quantum of conductance). Moreover, we find that the thermopower in these junctions is negative due to the fact that the lowest unoccupied molecular orbital dominates the charge transport, and its magnitude can reach several tens of microvolts per kelvin, depending on the contact geometry. On the other hand, we study the suitability of C60 as an anchoring group in single-molecule junctions. For this purpose, we analyze the transport through several dumbbell derivatives using C60 as anchors, and we compare the results with those obtained with thiol and amine groups. Our results show that the conductance of C60-terminated molecules is rather sensitive to the binding geometry. Moreover, the conductance of the molecules is typically reduced by the presence of the C60 anchors, which in turn makes the junctions more sensitive to the functionalization of the molecular core with appropriate side groups.

  10. There are four dynamically and functionally distinct populations of E-cadherin in cell junctions.

    PubMed

    Erami, Zahra; Timpson, Paul; Yao, Wu; Zaidel-Bar, Ronen; Anderson, Kurt I

    2015-01-01

    E-cadherin is a trans-membrane tumor suppressor responsible for epithelial cell adhesion. E-cadherin forms adhesive clusters through combined extra-cellular cis- and trans-interactions and intracellular interaction with the actin cytoskeleton. Here we identify four populations of E-cadherin within cell junctions based on the molecular interactions which determine their mobility and adhesive properties. Adhesive and non-adhesive populations of E-cadherin each consist of mobile and immobile fractions. Up to half of the E-cadherin immobilized in cell junctions is non-adhesive. Incorporation of E-cadherin into functional adhesions require all three adhesive interactions, with deletion of any one resulting in loss of effective cell-cell adhesion. Interestingly, the only interaction which could independently slow the diffusion of E-cadherin was the tail-mediated intra-cellular interaction. The adhesive and non-adhesive mobile fractions of E-cadherin can be distinguished by their sensitivity to chemical cross-linking with adhesive clusters. Our data define the size, mobility, and adhesive properties of four distinct populations of E-cadherin within cell junctions, and support association with the actin cytoskeleton as the first step in adhesion formation. PMID:26471767

  11. Brain endothelial cells and the glio-vascular complex.

    PubMed

    Wolburg, Hartwig; Noell, Susan; Mack, Andreas; Wolburg-Buchholz, Karen; Fallier-Becker, Petra

    2009-01-01

    We present and discuss the role of endothelial and astroglial cells in managing the blood-brain barrier (BBB) and aspects of pathological alterations in the BBB. The impact of astrocytes, pericytes, and perivascular cells on the induction and maintenance of the gliovascular unit is largely unidentified so far. An understanding of the signaling pathways that lie between these cell types and the endothelium and that possibly are mediated by components of the basal lamina is just beginning to emerge. The metabolism for the maintenance of the endothelial barrier is intimately linked to and dependent on the microenvironment of the brain parenchyma. We report the structure and function of the endothelial cells of brain capillaries by describing structures involved in the regulation of permeability, including transporter systems, caveolae, and tight junctions. There is increasing evidence that caveolae are not only vehicles for endo- and transcytosis, but also important regulators of tight-junction-based permeability. Tight junctions separate the luminal from the abluminal membrane domains of the endothelial cell ("fence function") and control the paracellular pathway ("gate function") thus representing the most significant structure of the BBB. In addition, the extracellular matrix between astrocytes/pericytes and endothelial cells contains numerous molecules with inherent signaling properties that have to be considered if we are to improve our knowledge of the complex and closely regulated BBB. PMID:18633647

  12. Giant piezoresistivity in aligned carbon nanotube nanocomposite: account for nanotube structural distortion at crossed tunnel junctions.

    PubMed

    Gong, S; Zhu, Z H

    2015-01-28

    High piezoresistivity is critical for multifunctional carbon nanotube polymer composites with sensing capability. By developing a new percolation network model, this work reveals theoretically that a giant piezoresistivity in the composites can be potentially achieved by controlled nanotube alignment resulting from field based alignment techniques. The tube-tube and/or tube-matrix interaction in conjunction with the aligned carbon nanotube networks are fully considered in the newly proposed model. The structural distortion of nanotubes is determined self-consistently by minimizing the pseudo-potential energy at crossed-tube junctions based on the Lennard-Jones potential and simulation of coarse grain molecular dynamics. The tunneling transport through crossed-tube junctions is calculated by the Landauer-Büttiker formula with empirical fitting by first-principle calculation. The simulation results also reveal that the piezoresistivity can be further improved by using low carbon nanotube loadings near the percolation threshold, carbon nanotubes with a small aspect ratio, high intrinsic conductivity and polymers with a small Poisson's ratio. This giant piezoresistive effect offers a tremendously promising future, which needs further thorough exploration. PMID:25492244

  13. Dithiocarbamate anchoring in molecular wire junctions: a first principles study.

    PubMed

    Li, Zhenyu; Kosov, Daniel S

    2006-05-25

    Recent experimental realization [J. Am. Chem. Soc., 127 (2005) 7328] of various dithiocarbamate self-assembly on gold surface opens the possibility for use of dithiocarbamate linkers to anchor molecular wires to gold electrodes. In this paper, we explore this hypothesis computationally. We computed the electron transport properties of 4,4'-bipyridine (BP), 4,4'-bipyridinium-1,1'-bis(carbodithioate) (BPBC), 4-(4'-pyridyl)-peridium-1-carbodithioate (BPC) molecule junctions based on the density functional theory and nonequilibrium Green's functions. We demonstrated that the stronger molecule-electrode coupling associated with the conjugated dithiocarbamate linker broadens transmission resonances near the Fermi energy. The broadening effect along with the extension of the pi conjugation from the molecule to the gold electrodes lead to enhanced electrical conductance for BPBC molecule. The conductance enhancement factor is as large as 25 at applied voltage bias 1.0 V. Rectification behavior is predicted for BPC molecular wire junction, which has the asymmetric anchoring groups. PMID:16706444

  14. Experimental Study of Resistive Bistability in Metal Oxide Junctions

    SciTech Connect

    Su, D.; Tan, Z.; Patel, V.; Likharev, K.K.; Zhu, Y.

    2011-05-01

    We have studied resistive bistability (memory) effects in junctions based on metal oxides, with a focus on sample-to-sample reproducibility, which is necessary for the use of such junctions as crosspoint devices of hybrid CMOS/nanoelectronic circuits. Few-nm-thick layers of NbO{sub x}, CuO{sub x} and TiO{sub x} have been formed by thermal and plasma oxidation, at various deposition and oxidation conditions, both with and without rapid thermal post-annealing. The resistive bistability effect has been observed for all these materials, with particularly high endurance (over 10{sup 3} switching cycles) obtained for single-layer TiO{sub 2} junctions, and the best reproducibility reached for multi-layer junctions of the same material. Fabrication optimization has allowed us to improve the OFF/ON resistance ratio to about 10{sup 3}, but the sample-to-sample reproducibility is so far lower than that required for large-scale integration.

  15. Electrochemical metallization switching with a platinum group metal in different oxides.

    PubMed

    Wang, Zhongrui; Jiang, Hao; Hyung Jang, Moon; Lin, Peng; Ribbe, Alexander; Xia, Qiangfei; Yang, J Joshua

    2016-08-01

    In a normal electrochemical metallization (ECM) switch, electrochemically active metals, such as Ag and Cu are used to provide mobile ions for the conducting filament. In both ECM and valence change memory (VCM) devices, platinum group metals, such as Pt and Pd, are typically used as the counter electrode and assumed to be chemically and physically inert. In this study, we explore whether the so-called inert metal itself can form a conducting filament and result in repeatable resistance switching. Pd and different oxide host matrices are used for this purpose. We have observed that the transport of oxygen anions dominates over Pd metal cations in ALD deposited AlOx and HfOx. However, in sputtered SiOx, Pd cation transport was revealed, accompanied by the formation of nano-crystalline Pd filament(s) in the junctions. Based on these observations, memristors with reversible and repeatable switching were obtained by using Pd doped SiOx as the switching material. PMID:27166623

  16. Gate-Free Electrical Breakdown of Metallic Pathways in Single-Walled Carbon Nanotube Crossbar Networks.

    PubMed

    Li, Jinghua; Franklin, Aaron D; Liu, Jie

    2015-09-01

    Aligned single-walled carbon nanotubes (SWNTs) synthesized by the chemical vapor deposition (CVD) method have exceptional potential for next-generation nanoelectronics. However, the coexistence of semiconducting (s-) and metallic (m-) SWNTs remains a considerable challenge since the latter causes significant degradation in device performance. Here we demonstrate a facile and effective approach to selectively break all m-SWNTs by stacking two layers of horizontally aligned SWNTs to form crossbars and applying a voltage to the crossed SWNT arrays. The introduction of SWNT junctions amplifies the disparity in resistance between s- and m-pathways, leading to a complete deactivation of m-SWNTs while minimizing the degradation of the semiconducting counterparts. Unlike previous approaches that required an electrostatic gate to achieve selectivity in electrical breakdown, this junction process is gate-free and opens the way for straightforward integration of thin-film s-SWNT devices. Comparison to electrical breakdown in junction-less SWNT devices without gating shows that this junction-based breakdown method yields more than twice the average on-state current retention in the resultant s-SWNT arrays. Systematic studies show that the on/off ratio can reach as high as 1.4 × 10(6) with a correspondingly high retention of on-state current compared to the initial current value before breakdown. Overall, this method provides important insight into transport at SWNT junctions and a simple route for obtaining pure s-SWNT thin film devices for broad applications. PMID:26263184

  17. Gate-tunable tunneling resistance in graphene/topological insulator vertical junctions

    NASA Astrophysics Data System (ADS)

    Zhang, Liang; Yan, Yuan; Wu, Han-Chun; Liao, Zhi-Min; Yu, Da-Peng

    The emergence of graphene-based vertical heterostructures, especially stacked by various layered materials, opens up new promising possibilities for investigations and applications. The junction based on two famous Dirac materials, graphene and topological insulator, Bi2Se3, can considerably enlarge the family of van der Waals heterostructures, while the experimental approach to obtain controllable interface of these junctions is still a challenge. Here we show the experimental realization of the vertical heterojunction between Bi2Se3 and monolayer graphene. The tunneling-mediated quantum oscillations are identified to arise from several two-dimensional conducting layers. The electrostatic field induced by back gate voltage, as well as the magnetic field, is applied to tailor the available density of states near the Fermi surface. We observe exotic gate-tunable tunneling resistance in high magnetic field, which is attributed to semimetal-quantum Hall insulator transition in the underlying graphene. This work was supported by MOST (Nos. 2013CB934600, 2013CB932602) and NSFC (Nos. 11274014, 11234001).

  18. Characterization of the reliability and uniformity of an anodization-free fabrication process for high-quality Nb/Al-AlOx/Nb Josephson junctions

    NASA Astrophysics Data System (ADS)

    Kempf, S.; Ferring, A.; Fleischmann, A.; Gastaldo, L.; Enss, C.

    2013-06-01

    We have developed a reliable and reproducible fabrication process for high-quality Nb/Al-AlOx/Nb Josephson junctions that completely avoids anodization techniques, that are typically used to define the junction area, to electrically insulate the base electrode as well as the sidewalls of the counter-electrode and to protect the tunnel barrier. Hence, this process is well suited for the fabrication of electrically floating junction-based devices such as non-hysteretic rf-SQUIDs. Josephson junctions of various sizes have been produced and characterized at 4.2 K. We found that our junctions have a high quality, which is confirmed by measured gap voltages Vg and Ic Rn products up to 2.9 and 1.8 mV and on-wafer average values of the resistance ratio Rsg/Rn above 30 in most cases. Here, Rsg and Rn denote the subgap and the normal state resistance of a Josephson junction. Although the uniformity of the properties of the Josephson junctions across a wafer is high, we observe some systematic variations of the critical current density and the gap voltage over an entire wafer. These variations are most likely to be attributed to residual stress in the Nb films as well as the surface roughness of the Nb base electrode.

  19. Analysis of the attainable efficiency of a direct-bandgap betavoltaic element

    NASA Astrophysics Data System (ADS)

    Sachenko, A. V.; Shkrebtii, A. I.; Korkishko, R. M.; Kostylyov, V. P.; Kulish, M. R.; Sokolovskyi, I. O.; Evstigneev, M.

    2015-11-01

    Conversion of energy of beta-particles into electric energy in a p-n junction based on direct-bandgap semiconductors, such as GaAs, is analyzed considering realistic semiconductor system parameters. An expression for the collection coefficient, Q, of the electron-hole pairs generated by beta-electrons is derived taking into account the existence of the dead layer. We show that the collection coefficient of beta-electrons emitted by a 3H-source to a GaAs p-n junction is close to 1 in a broad range of electron lifetimes in the junction, ranging from 10-9to 10-7 s. For the combination 147Pm/GaAs, Q is relatively large (≥slant 0.4) only for quite long lifetimes (about 10-7 s) and large thicknesses (about 100 μm) of GaAs p-n junctions. For realistic lifetimes of minority carriers and their diffusion coefficients, the open-circuit voltage realized due to the irradiation of a GaAs p-n junction by beta-particles is obtained. The attainable beta-conversion efficiency η in the case of a 3H/GaAs combination is found to exceed that of the 147Pm/GaAs combination.

  20. Josephson Effect in SFNS Josephson Junctions

    NASA Astrophysics Data System (ADS)

    Karminskaya, T. Yu.; Kupriyanov, M. Yu.; Golubov, A. A.; Sidorenko, A. S.

    The critical current, I C, of Josephson junctions both in ramp-type (S-FN-S) and in overlap (SNF-FN-FNS, SN-FN-NS, SNF-N-FNS) geometries has been calculated in the frame of linearized Usadel equations (S-superconductor, F-ferromagnetic, N-normal metal). For the ramp-type structures, in which S electrodes contact directly the end walls of FN bilayer, it is shown that I C may exhibit damping oscillations as a function of both the distance L between superconductors and thicknesses d F,N of ferromagnetic and normal layers. The conditions have been determined under which the decay length and period of oscillation of I C(L) at fixed d F are of the order of decay length of superconducting correlations in the N metal, ξN, that is much larger than in F film. In overlap configurations, in which S films are placed on the top of NF bilayer, the studied junctions have complex SNF or SN electrodes (N or NF bilayer are situated under a superconductor). We demonstrate that in these geometries the critical current can exceed that in ramp-type junctions. Based on these results, the choice of the most practically applicable geometry is discussed.

  1. Josephson effect in superconductor/ferromagnet structures with a complex weak-link region

    NASA Astrophysics Data System (ADS)

    Karminskaya, T. Yu.; Golubov, A. A.; Kupriyanov, M. Yu.; Sidorenko, A. S.

    2010-06-01

    The critical currents IC of SNF-FN-FNS, SN-FN-NS, and SNF-N-FNS Josephson junctions (S—superconductor, F—ferromagnetic, N—normal metal) with complex SNF or SN electrodes (N or NF bilayer are situated under a superconductor) are calculated in the framework of linearized Usadel equations for arbitrary overlap length d of SN interface. We demonstrate that in these geometries, in the case of large resistances of SN interfaces, the critical current can exceed that in ramp-type junctions. Based on these results, the choice of the most practically applicable geometry is discussed. We predict that in a certain parameter range there is single 0-π transition with the increase in the overlap length d . This single transition can be realized also in SFN-N-FNS Josephson junctions, where the coherence length in the weak-link region is a real quantity. Further, we predict that in SNF-N-FNS Josephson junctions 0-π transition may take place with increase in distance between superconducting electrodes.

  2. G4-FETs as Universal and Programmable Logic Gates

    NASA Technical Reports Server (NTRS)

    Johnson, Travis; Fijany, Amir; Mojarradi, Mohammad; Vatan, Farrokh; Toomarian, Nikzad; Kolawa, Elizabeth; Cristoloveanu, Sorin; Blalock, Benjamin

    2007-01-01

    An analysis of a patented generic silicon- on-insulator (SOI) electronic device called a G4-FET has revealed that the device could be designed to function as a universal and programmable logic gate. The universality and programmability could be exploited to design logic circuits containing fewer discrete components than are required for conventional transistor-based circuits performing the same logic functions. A G4-FET is a combination of a junction field-effect transistor (JFET) and a metal oxide/semiconductor field-effect transistor (MOSFET) superimposed in a single silicon island and can therefore be regarded as two transistors sharing the same body. A G4-FET can also be regarded as a single transistor having four gates: two side junction-based gates, a top MOS gate, and a back gate activated by biasing of the SOI substrate. Each of these gates can be used to control the conduction characteristics of the transistor; this possibility creates new options for designing analog, radio-frequency, mixed-signal, and digital circuitry. With proper choice of the specific dimensions for the gates, channels, and ancillary features of the generic G4-FET, the device could be made to function as a three-input, one-output logic gate. As illustrated by the truth table in the top part of the figure, the behavior of this logic gate would be the inverse (the NOT) of that of a majority gate. In other words, the device would function as a NOT-majority gate. By simply adding an inverter, one could obtain a majority gate. In contrast, to construct a majority gate in conventional complementary metal oxide/semiconductor (CMOS) circuitry, one would need four three-input AND gates and a four-input OR gate, altogether containing 32 transistors.

  3. ZO-1 and -2 Are Required for TRPV1-Modulated Paracellular Permeability.

    PubMed

    Li, J; Cong, X; Zhang, Y; Xiang, R L; Mei, M; Yang, N Y; Su, Y C; Choi, S; Park, K; Zhang, L W; Wu, L L; Yu, G Y

    2015-12-01

    The tight junction-based paracellular pathway plays an important role in saliva secretion. Zonula occludens (ZO) proteins are submembranous proteins of tight junction complex; however, their function in salivary epithelium is poorly understood. Here, we found that activation of transient receptor potential vanilloid subtype 1 (TRPV1) by capsaicin increased rat saliva secretion both in vivo and ex vivo. Meanwhile, TRPV1 activation enlarged the width of tight junctions between neighboring acinar cells, increased the paracellular flux of 4-kDa fluorescein isothiocyanate (FITC)-dextran in submandibular gland (SMG) tissues, and decreased transepithelial electric resistance (TER) in SMG-C6 cells. ZO-1, -2, and -3 were distributed principally to the apical lateral region of acinar cells in SMG tissues and continuously encircled the peripheries of SMG-C6 cells in the untreated condition. TRPV1 activation obviously diminished ZO-1 and -2 staining, but not ZO-3 or β-catenin, at the cell-cell contacts ex vivo and in vitro. Moreover, in untreated SMG-C6 cells, ZO-1 and -2 single or double knockdown by small interfering RNA (siRNA) increased the paracellular flux of 4-kDa FITC-dextran. In capsaicin-treated cells, ZO-1 and -2 single or double knockdown abolished, whereas their re-expression restored, the capsaicin-induced increase in paracellular permeability. Furthermore, TRPV1 activation increased RhoA activity, and inhibition of either RhoA or Rho kinase (ROCK) abolished the capsaicin-induced TER decrease as well as ZO-1 and -2 redistribution. These results indicate that ZO-1 and -2 play crucial roles in both basal salivary epithelial barrier function and TRPV1-modulated paracellular transport. RhoA-ROCK signaling pathway is responsible for TRPV1-modulated paracellular permeability as well as ZO-1 and -2 redistribution. PMID:26464396

  4. Theory based design and optimization of materials for spintronics applications

    NASA Astrophysics Data System (ADS)

    Xu, Tianyi

    The Spintronics industry has developed rapidly in the past decade. Finding the right material is very important for Spintronics applications, which requires good understanding of the physics behind specific phenomena. In this dissertation, we will focus on two types of perpendicular transport phenomena, the current-perpendicular-to-plane giant-magneto-resistance (CPP-GMR) phenomenon and the tunneling phenomenon in the magnetic tunnel junctions. The Valet-Fert model is a very useful semi-classical approach for understanding the transport and spin-flip process in CPP-GMR. We will present a finite element based implementation for the Valet-Fert model which enables a practical way to calculate the electron transport in real CPP-GMR spin valves. It is very important to find high spin polarized materials for CPP-GMR spin valves. The half-metal, due to its full spin polarization, is of interest. We will propose a rational way to find half-metals based on the gap theorem. Then we will focus on the high-MR TMR phenomenon. The tunneling theory of electron transport in mesoscopic systems will be covered. Then we will calculate the transport properties of certain junctions with the help of Green's function under the Landauer-Buttiker formalism, also known as the scattering formalism. The damping constant determines the switching rate of a device. We can calculate it using a method based on the Extended Huckel Tight-Binding theory (EHTB). The symmetry filtering effect is very helpful for finding materials for TMR junctions. Based upon which, we find a good candidate material, MnAl, for TMR applications.

  5. Hippo pathway elements Co-localize with Occludin: A possible sensor system in pancreatic epithelial cells

    PubMed Central

    Cravo, Ana Santos; Carter, Edward; Erkan, Mert; Harvey, Emma; Furutani-Seiki, Makoto; Mrsny, Randall

    2015-01-01

    External adherens junction-based cell-cell contacts involving E-cadherin interactions function to sense planar cell status and modulate epithelial cell proliferation through Hippo (Hpo) and non-canonical Wnt pathways signaling. We hypothesized these regulatory processes should also be sensitive to a similar cell-cell contact sensor associated with apical-basal polarity events at epithelial surfaces. We used 2 human pancreatic cancer cell lines to explore this hypothesis: one with the capacity to form functional tight junction structures and polarize (HPAFII) and one lacking this capacity (AsPc1). Occludin (Ocln), a tetraspanning protein associated with TJ structures and capable of establishing external cell-cell contacts, was observed to partially co-localize with Hpo elements YAP (c-yes associated protein) and TEAD (TEA-dependent), which function to drive a proliferative transcription program. Treatment with dobutamine, known to affect YAP, was shown to suppress proliferation in an Ocln-dependent manner. Blockade of protein kinase C-zeta (PKC-ζ) diminished transepithelial electrical resistance (TER) of HPAFII monolayers that was not corrected by dobutamine treatment while the loss of TER resulting from inhibition of ROCK1 could be partially recovered. Examination of normal and cancerous human pancreatic biopsies showed that the cellular localization of Ocln, c-Yes, YAP, and TEAD were similar to HPAFII for normal cells and AsPc1 for cancerous cells. Together, these results suggest a link between Hpo and signals emanating from cell-cell contacts involving Ocln that may regulate pancreatic cell proliferation through the coordination of planar cell polarity with apical-basal polarity events. PMID:26451343

  6. The role of ultra-thin SiO2 layers in metal-insulator-semiconductor (MIS) photoelectrochemical devices (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Esposito, Daniel V.

    2015-08-01

    Solid-state junctions based on a metal-insulator-semiconductor (MIS) architecture are of great interest for a number of optoelectronic applications such as photovoltaics, photoelectrochemical cells, and photodetection. One major advantage of the MIS junction compared to the closely related metal-semiconductor junction, or Schottky junction, is that the thin insulating layer (1-3 nm thick) that separates the metal and semiconductor can significantly reduce the density of undesirable interfacial mid-gap states. The reduction in mid-gap states helps "un-pin" the junction, allowing for significantly higher built-in-voltages to be achieved. A second major advantage of the MIS junction is that the thin insulating layer can also protect the underlying semiconductor from corrosion in an electrochemical environment, making the MIS architecture well-suited for application in (photo)electrochemical applications. In this presentation, discontinuous Si-based MIS junctions immersed in electrolyte are explored for use as i.) photoelectrodes for solar-water splitting in photoelectrochemical cells (PECs) and ii.) position-sensitive photodetectors. The development and optimization of MIS photoelectrodes for both of these applications relies heavily on understanding how processing of the thin SiO2 layer impacts the properties of nano- and micro-scale MIS junctions, as well as the interactions of the insulating layer with the electrolyte. In this work, we systematically explore the effects of insulator thickness, synthesis method, and chemical treatment on the photoelectrochemical and electrochemical properties of these MIS devices. It is shown that electrolyte-induced inversion plays a critical role in determining the charge carrier dynamics within the MIS photoelectrodes for both applications.

  7. Reconfigurable Josephson Circulator/Directional Amplifier

    NASA Astrophysics Data System (ADS)

    Sliwa, K. M.; Hatridge, M.; Narla, A.; Shankar, S.; Frunzio, L.; Schoelkopf, R. J.; Devoret, M. H.

    2015-10-01

    Circulators and directional amplifiers are crucial nonreciprocal signal routing and processing components involved in microwave read-out chains for a variety of applications. They are particularly important in the field of superconducting quantum information, where the devices also need to have minimal photon losses to preserve the quantum coherence of signals. Conventional commercial implementations of each device suffer from losses and are built from very different physical principles, which has led to separate strategies for the construction of their quantum-limited versions. However, as recently theoretically, by establishing simultaneous pairwise conversion and/or gain processes between three modes of a Josephson-junction-based superconducting microwave circuit, it is possible to endow the circuit with the functions of either a phase-preserving directional amplifier or a circulator. Here, we experimentally demonstrate these two modes of operation of the same circuit. Furthermore, in the directional amplifier mode, we show that the noise performance is comparable to standard nondirectional superconducting amplifiers, while in the circulator mode, we show that the sense of circulation is fully reversible. Our device is far simpler in both modes of operation than previous proposals and implementations, requiring only three microwave pumps. It offers the advantage of flexibility, as it can dynamically switch between modes of operation as its pump conditions are changed. Moreover, by demonstrating that a single three-wave process yields nonreciprocal devices with reconfigurable functions, our work breaks the ground for the development of future, more complex directional circuits, and has excellent prospects for on-chip integration.

  8. Scanning tunneling microscopy, orbital-mediated tunneling spectroscopy, and ultraviolet photoelectron spectroscopy of metal(II) tetraphenylporphyrins deposited from vapor.

    PubMed

    Scudiero, L; Barlow, D E; Mazur, U; Hipps, K W

    2001-05-01

    Thin films of vapor-deposited Ni(II) and Co(II) complexes of tetraphenylporphyrin (NiTPP and CoTPP) were studied supported on gold and embedded in Al-Al(2)O(3)-MTPP-Pb tunnel diodes, where M = Ni or Co. Thin films deposited onto polycrystalline gold were analyzed by ultraviolet photoelectron spectroscopy (UPS) using He I radiation. Scanning tunneling microscopy (STM) and orbital-mediated tunneling spectroscopy (STM-OMTS) were performed on submonolayer films of CoTPP and NiTPP supported on Au(111). Inelastic electron tunneling spectroscopy (IETS) and OMTS were measured in conventional tunnel diode structures. The highest occupied pi molecular orbital of the porphyrin ring was seen in both STM-OMTS and UPS at about 6.4 eV below the vacuum level. The lowest unoccupied pi molecular orbital of the porphyrin ring was observed by STM-OMTS and by IETS-OMTS to be located near 3.4 eV below the vacuum level. The OMTS spectra of CoTPP had a band near 5.2 eV (below the vacuum level) that was attributed to transient oxidation of the central Co(II) ion. That is, it is due to electron OMT via the half-filled d(z)(2) orbital present in Co(II) of CoTPP. The NiTPP OMTS spectra show no such band, consistent with the known difficulty of oxidation of the Ni(II) ion. The STM-based OMTS allowed these two porphyrin complexes to be easily distinguished. The present work is the first report of the observation of STM-OMTS, tunnel junction OMTS, and UPS of the same compounds. Scanning tunneling microscope-based orbital-mediated tunneling provides more information than UPS or tunnel junction-based OMTS and does so with molecular-scale resolution. PMID:11457159

  9. Demonstration of 10 K Superconducting Electronics in an Infrared Imaging System

    NASA Astrophysics Data System (ADS)

    Ressler, Michael E.

    1997-04-01

    We report the successful operation of a superconducting niobium nitride (NbN) Josephson Junction-based analog-to-digital converter (ADC) in an infrared imaging system. This system is a flexible testbed which will allow the evaluation of a large variety of cryogenic components (e.g. detector arrays, ADC's, etc.), while still following the general architecture of a scientific instrument, permitting us to determine how well the component will perform in the ``real world''. The testbed is currently composed of a Rockwell International HF-16 128x128 pixel Si:As BIB array, a JPL-developed GaAs 16-to-1 analog multiplexer, and a TRW 12-bit, 10 mega-samples per second, NbN ADC. All three components are located inside a pour/fill liquid helium dewar and operated at 10 K. Simple cold optics along with an 8.5 micron filter image objects onto the focal plane. The images are read out at rates up to 600 frames per second; data can either be stored to hard disk at this rate or every 20th frame can be displayed on a monitor providing ``real-time'' video. We describe the layout and operation of the testbed, with particular emphasis on the lessons learned about operating superconducting electronics as merely another component in a system. We also discuss images and other data comparing the performance of the NbN ADC with a commercially available, equal speed and resolution, silicon ADC. Finally, we explore the future of superconducting electronics; potential products as well as their impact on instrument and spacecraft design.

  10. Bipolar resistive switching properties of Ti-CuO/(hexafluoro-hexa-peri-hexabenzocoronene)-Cu hybrid interface device: Influence of electronic nature of organic layer

    SciTech Connect

    Singh, Bharti; Mehta, B. R.; Varandani, Deepak; Govind; Narita, A.; Feng, X.; Muellen, K.

    2013-05-28

    This study reports the change in the structural and junction properties of Ti-CuO-Cu structure on incorporation of a 2-dimensional (2D) organic layer comprising of n-type hexafluoro-hexa-peri-hexabenzocoronene (6F-HBC). A bipolar resistive switching is observed in the device having interface between sputter deposited copper oxide (CuO) and vacuum sublimated 6F-HBC hybrid interface. The CuO/6F-HBC hybrid interface exhibits rectifying I-V characteristics in complete contrast to the ohmic and rectifying characteristics of junctions based on individual 6F-HBC and CuO layers. Large change in resistive switching property from unipolar resistive switching in CuO/HBC to bipolar resistive switching in CuO/6F-HBC interface was observed. At the CuO/6F-HBC interface, C1s peak corresponding to fluorinated carbon is shifted by 0.68 eV towards higher binding energy (BE) side and O1s peak due to non-lattice oxygen is shifted by 0.6 eV towards lower BE, confirming the interaction of O{sup 2-} ion in CuO with fluorinated carbon atoms in 6F-HBC at the hybrid interface. Correlation between conductive atomic force microscopy images and atomic force microscopy topography images, I-V characteristics in conducting, non-conducting, and pristine regions along with x-ray photoelectron spectroscopy results establishes the important role of hybrid interface to determining the resistive switching properties. This study demonstrates that the resistive switching and interface properties of a hybrid device based on inorganic and organic 2D materials can be modified by changing the electronic properties of organic layer by attaching suitable functional groups.

  11. Metamorphic Ga0.76In0.24As/GaAs0.75Sb0.25 tunnel junctions grown on GaAs substrates

    NASA Astrophysics Data System (ADS)

    García, I.; Geisz, J. F.; France, R. M.; Kang, J.; Wei, S.-H.; Ochoa, M.; Friedman, D. J.

    2014-08-01

    Lattice-matched and pseudomorphic tunnel junctions have been developed in the past for application in a variety of semiconductor devices, including heterojunction bipolar transistors, vertical cavity surface-emitting lasers, and multijunction solar cells. However, metamorphic tunnel junctions have received little attention. In 4-junction Ga0.51In0.49P/GaAs/Ga0.76In0.24As/Ga0.47In0.53As inverted-metamorphic solar cells (4J-IMM), a metamorphic tunnel junction is required to series connect the 3rd and 4th junctions. We present a tunnel junction based on a metamorphic Ga0.76In0.24As/GaAs0.75Sb0.25 structure for this purpose. This tunnel junction is grown on a metamorphic Ga0.76In0.24As template on a GaAs substrate. The band offsets in the resulting type-II heterojunction are calculated using the first-principles density functional method to estimate the tunneling barrier height and assess the performance of this tunnel junction against other material systems and compositions. The effect of the metamorphic growth on the performance of the tunnel junctions is analyzed using a set of metamorphic templates with varied surface roughness and threading dislocation density. Although the metamorphic template does influence the tunnel junction performance, all tunnel junctions measured have a peak current density over 200 A/cm2. The tunnel junction on the best template has a peak current density over 1500 A/cm2 and a voltage drop at 15 A/cm2 (corresponding to operation at 1000 suns) lower than 10 mV, which results in a nearly lossless series connection of the 4th junction in the 4J-IMM structure.

  12. CellFIT: A Cellular Force-Inference Toolkit Using Curvilinear Cell Boundaries

    PubMed Central

    Brodland, G. Wayne; Veldhuis, Jim H.; Kim, Steven; Perrone, Matthew; Mashburn, David; Hutson, M. Shane

    2014-01-01

    Mechanical forces play a key role in a wide range of biological processes, from embryogenesis to cancer metastasis, and there is considerable interest in the intuitive question, “Can cellular forces be inferred from cell shapes?” Although several groups have posited affirmative answers to this stimulating question, nagging issues remained regarding equation structure, solution uniqueness and noise sensitivity. Here we show that the mechanical and mathematical factors behind these issues can be resolved by using curved cell edges rather than straight ones. We present a new package of force-inference equations and assessment tools and denote this new package CellFIT, the Cellular Force Inference Toolkit. In this approach, cells in an image are segmented and equilibrium equations are constructed for each triple junction based solely on edge tensions and the limiting angles at which edges approach each junction. The resulting system of tension equations is generally overdetermined. As a result, solutions can be obtained even when a modest number of edges need to be removed from the analysis due to short length, poor definition, image clarity or other factors. Solving these equations yields a set of relative edge tensions whose scaling must be determined from data external to the image. In cases where intracellular pressures are also of interest, Laplace equations are constructed to relate the edge tensions, curvatures and cellular pressure differences. That system is also generally overdetermined and its solution yields a set of pressures whose offset requires reference to the surrounding medium, an open wound, or information external to the image. We show that condition numbers, residual analyses and standard errors can provide confidence information about the inferred forces and pressures. Application of CellFIT to several live and fixed biological tissues reveals considerable force variability within a cell population, significant differences between populations

  13. Efficient G(sup 4)FET-Based Logic Circuits

    NASA Technical Reports Server (NTRS)

    Vatan, Farrokh

    2008-01-01

    A total of 81 optimal logic circuits based on four-gate field-effect transistors (G(sup 4)4FETs) have been designed to implement all Boolean functions of up to three variables. The purpose of this development was to lend credence to the expectation that logic circuits based on G(sup 4)FETs could be more efficient (in the sense that they could contain fewer transistors), relative to functionally equivalent logic circuits based on conventional transistors. A G(sup 4)FET a combination of a junction field-effect transistor (JFET) and a metal oxide/semiconductor field-effect transistor (MOSFET) superimposed in a single silicon island and can therefore be regarded as two transistors sharing the same body. A G(sup 4)FET can also be regarded as a single device having four gates: two side junction-based gates, a top MOS gate, and a back gate activated by biasing of a silicon-on-insulator substrate. Each of these gates can be used to control the conduction characteristics of the transistor; this possibility creates new options for designing analog, radio-frequency, mixed-signal, and digital circuitry. One such option is to design a G(sup 4)FET to function as a three-input NOT-majority gate, which has been shown to be a universal and programmable logic gate. Optimal NOT-majority-gate, G(sup 4)FET-based logic-circuit designs were obtained in a comparative study that also included formulation of functionally equivalent logic circuits based on NOR and NAND gates implemented by use of conventional transistors. In the study, the problem of finding the optimal design for each logic function and each transistor type was solved as an integer-programming optimization problem. Considering all 81 non-equivalent Boolean functions included in the study, it was found that in 63% of the cases, fewer logic gates (and, hence, fewer transistors) would be needed in the G(sup 4)FET-based implementations.

  14. Quantitation of CYP24A1 Enzymatic Activity With a Simple Two-Hybrid System

    PubMed Central

    Mugg, Amy; Legeza, Balazs; Tee, Meng Kian; Damm, Izabella; Long, Roger K.

    2015-01-01

    Context: Mutations of the CYP24A1 gene encoding the 24-hydroxylase (24OHase) that inactivates metabolites of vitamin D can cause hypercalcemia in infants and adults; in vitro assays of 24OHase activity have been difficult. Objective: We sought an alternative assay to characterize a CYP24A1 mutation in a young adult with bilateral nephrolithiasis and hypercalcemia associated with ingestion of excess vitamin D supplements and robust dairy intake for 5 years. Methods: CYP24A1 exons were sequenced from leukocyte DNA. Wild-type and mutant CYP24A1 cDNAs were expressed in JEG-3 cells, and 24OHase activity was assayed by a two-hybrid system. Results: The CYP24A1 missense mutation L409S was found on only one allele; no other mutation was found in exons or in at least 30 bp of each intron/exon junction. Based on assays of endogenous 24OHase activity and of activity from a transiently transfected CYP24A1 cDNA expression vector, JEG-3 cells were chosen over HepG2, Y1, MA10, and NCI-H295A cells for two-hybrid assays of 24OHase activity. The apparent Michaelis constant, Km(app), was 9.0 ± 2.0 nm for CYP24A1 and 8.6 ± 2.2 nm for its mutant; the apparent maximum velocity, Vmax(app), was 0.71 ± 0.055 d−1 for the wild type and 0.22 ± 0.026 d−1 for the mutant. As assessed by Vmax/Km, the L409S mutant has 32% of wild-type activity (P = .0012). Conclusions: The two-hybrid system in JEG-3 cells provides a simple, sensitive, quantitative assay of 24OHase activity. Heterozygous mutation of CYP24A1 may cause hypercalcemia in the setting of excessive vitamin D intake, but it is also possible that the patient had another, unidentified CYP24A1 mutation on the other allele. PMID:25375986

  15. Electronic properties of electrodeposited semiconductor junctions

    NASA Astrophysics Data System (ADS)

    Chatman, Shawn Michael Edward

    This thesis describes the synthesis, structural properties, optical properties, and electronic properties of semiconductor junctions based on electrochemically deposited ZnO and CU2O thin films. The first focus is characterizing the effect of deposition conditions (including applied potential and electrolyte composition) on the fundamental properties of these materials (including carrier concentration, band gap, and microstructure). Subsequent discussion addresses electrical conduction to and through ZnO/substrate junctions as a function of these deposition conditions. Finally, three device applications for these ZnO-based junction are explored: Schottky rectifiers, humidity sensors, and photovoltaic cells. Since electrical conduction to and through heterojunction interfaces is very important for maximizing the functionality of semiconductor devices, this thesis work is an essential step towards increasing the functionality of multi-layer ZnO-based heterojunction devices prepared by electrodeposition. Capacitive Mott-Schottky analyses showed that the carrier concentrations of our ZnO electrodeposits are dependent upon deposition potential, with higher net carrier concentration at more positive potentials. UV/Visible diffuse reflectance data indicates that band gap increases with more positive deposition potentials. Together, these results suggest that hydrogen is the dominant, yet unintentional, Moss-Burstein like dopant in our n-type ZnO. Furthermore, the range of carrier concentrations we can achieve (10 18 -- 1021 cm-3) is comparable to that obtained with intentional doping. This is significant because using deposition potential to change growth rate or morphology will simultaneously change electronic properties. The deposition potential studies evolved into a procedure for selective, one-step production of either ohmic or rectifying (Schottky) ZnO/metal junctions (Chatman et al., Appi.Phys.Lett., 2008, 92, 012103/1-3). Rectifying ratio and soft

  16. Experimental and Theoretical Analysis of Nanotransport in Oligophenylene Dithiol Junctions as a Function of Molecular Length and Contact Work Function.

    PubMed

    Xie, Zuoti; Bâldea, Ioan; Smith, Christopher E; Wu, Yanfei; Frisbie, C Daniel

    2015-08-25

    We report the results of an extensive investigation of metal-molecule-metal tunnel junctions based on oligophenylene dithiols (OPDs) bound to several types of electrodes (M1-S-(C6H4)n-S-M2, with 1 ≤ n ≤ 4 and M1,2 = Ag, Au, Pt) to examine the impact of molecular length (n) and metal work function (Φ) on junction properties. Our investigation includes (1) measurements by scanning Kelvin probe microscopy of electrode work function changes (ΔΦ = ΦSAM - Φ) caused by chemisorption of OPD self-assembled monolayers (SAMs), (2) measurements of junction current-voltage (I-V) characteristics by conducting probe atomic force microscopy in the linear and nonlinear bias ranges, and (3) direct quantitative analysis of the full I-V curves. Further, we employ transition voltage spectroscopy (TVS) to estimate the energetic alignment εh = EF - EHOMO of the dominant molecular orbital (HOMO) relative to the Fermi energy EF of the junction. Where photoelectron spectroscopy data are available, the εh values agree very well with those determined by TVS. Using a single-level model, which we justify via ab initio quantum chemical calculations at post-density functional theory level and additional UV-visible absorption measurements, we are able to quantitatively reproduce the I-V measurements in the whole bias range investigated (∼1.0-1.5 V) and to understand the behavior of εh and Γ (contact coupling strength) extracted from experiment. We find that Fermi level pinning induced by the strong dipole of the metal-S bond causes a significant shift of the HOMO energy of an adsorbed molecule, resulting in εh exhibiting a weak dependence with the work function Φ. Both of these parameters play a key role in determining the tunneling attenuation factor (β) and junction resistance (R). Correlation among Φ, ΔΦ, R, transition voltage (Vt), and εh and accurate simulation provide a remarkably complete picture of tunneling transport in these prototypical molecular junctions. PMID

  17. Geodetic constraints on vertical tectonic deformation in the Coachella and San Bernardino Valleys from InSAR and well level data

    NASA Astrophysics Data System (ADS)

    Wisely, B. A.; Schmidt, D.

    2006-12-01

    We investigate the relationship of InSAR observations and groundwater levels for the Coachella and San Bernardino Valleys, CA. Surface deformation in both valleys is induced by seasonal and long-term changes in groundwater levels such that tectonic signals are largely obscured. Our objective is to identify and remove any seasonal and anthropogenic signals from the InSAR data set at selected sites, thereby revealing the tectonic signal related to interseismic strain accumulation. Interferograms from 1993 to 2000 are produced from ERS1/2. We also present preliminary ENVISAT interferograms from 2003-2006. InSAR and well level data sets are compared to demonstrate where seasonal and long-term signals are induced by groundwater fluctuations. Where data sets are consistent, we invert for the elastic coefficient and vertical tectonic deformation rates at the well locations. We explore the vertical uplift rates within the basins and fault junctions based on simple elastic dislocation models. In the Coachella Valley we observe long-term residual subsidence with a stack of 23 interferograms from 1993-2000, chosen for their minimal atmospheric contamination. Near Indio, a maximum vertical subsidence rate of 9 mm/yr is observed during this seven year period. We produce an InSAR timeseries with the same set of interferograms, in which we observe a maximum annual seasonal oscillation up to 21 mm. Generally, surface elevation inferred from InSAR correlates with groundwater levels. However, we occasionally observe discrepancies in the data sets for several locations. We investigate potential causes for these discrepancies including temporary increase in artificial and natural recharge, aquifer partitioning, and tectonic events. In the San Bernardino Valley, long-term uplift on the order of 4 mm/yr from 1995-2000 is observed with a stack of 30 interferograms. The InSAR timeseries reveals a maximum annual seasonal oscillation for this period up to 10.5 mm. Our investigation of the

  18. Molecular series-tunneling junctions.

    PubMed

    Liao, Kung-Ching; Hsu, Liang-Yan; Bowers, Carleen M; Rabitz, Herschel; Whitesides, George M

    2015-05-13

    Charge transport through junctions consisting of insulating molecular units is a quantum phenomenon that cannot be described adequately by classical circuit laws. This paper explores tunneling current densities in self-assembled monolayer (SAM)-based junctions with the structure Ag(TS)/O2C-R1-R2-H//Ga2O3/EGaIn, where Ag(TS) is template-stripped silver and EGaIn is the eutectic alloy of gallium and indium; R1 and R2 refer to two classes of insulating molecular units-(CH2)n and (C6H4)m-that are connected in series and have different tunneling decay constants in the Simmons equation. These junctions can be analyzed as a form of series-tunneling junctions based on the observation that permuting the order of R1 and R2 in the junction does not alter the overall rate of charge transport. By using the Ag/O2C interface, this system decouples the highest occupied molecular orbital (HOMO, which is localized on the carboxylate group) from strong interactions with the R1 and R2 units. The differences in rates of tunneling are thus determined by the electronic structure of the groups R1 and R2; these differences are not influenced by the order of R1 and R2 in the SAM. In an electrical potential model that rationalizes this observation, R1 and R2 contribute independently to the height of the barrier. This model explicitly assumes that contributions to rates of tunneling from the Ag(TS)/O2C and H//Ga2O3 interfaces are constant across the series examined. The current density of these series-tunneling junctions can be described by J(V) = J0(V) exp(-β1d1 - β2d2), where J(V) is the current density (A/cm(2)) at applied voltage V and βi and di are the parameters describing the attenuation of the tunneling current through a rectangular tunneling barrier, with width d and a height related to the attenuation factor β. PMID:25871745

  19. Parallel-stranded duplex DNA containing blocks of trans purine-purine and purine-pyrimidine base pairs.

    PubMed Central

    Evertsz, E M; Rippe, K; Jovin, T M

    1994-01-01

    A 30 base pair parallel-stranded (ps) duplex ps-L1.L2 composed of two adjoined purine-purine and purine-pyrimidine sequence blocks has been characterized thermodynamically and spectroscopically. The 5'-terminal 15 residues in both strands ('left-half') consisted of the alternating d(GA)7G sequence that forms a ps homoduplex secondary structure stabilized by d(G.G) and d(A.A) base pairs. The 3'-terminal 15 positions of the sequence ('right-half') were combinations of A and T with complementary reverse Watson-Crick d(A.T) base pairing between the two strands. The characteristics of the full length duplex were compared to those of the constituent left and right halves in order to determine the compatibility of the two ps helical forms. The thermal denaturation curves and hyperchromicity profiles of all three duplexes determined by UV absorption spectroscopy were characteristic of ps-DNA, in accordance with previous studies. The thermodynamic properties of the 30 bp duplex corresponded within experimental error to the linear combination of the two 15-mers. Thus, the Tm and delta HvH of ps-L1.L2 in 10 mM MgCl2, derived from analyses according to a statistical mechanical formulation for the helix-coil transition, were 43 degrees C and 569 kJ mol-1, compared to 21 degrees C, 315 kJ mol-1 (ps-F5.F6) and 22 degrees C, 236 kJ mol-1 (ps-GA15). The UV absorption and CD spectra of ps-L1.L2 and the individual 15-mer ps motifs were also compared quantitatively. The sums of the two constituent native spectra (left+right halves) accurately matched that of the 30 bp duplex, with only small deviations in the 195-215 nm (CD) and 220-240 nm (absorption) regions. Based on analysis by native gel electrophoresis, the sequences studied formed duplex structures exclusively; there were no indications of higher order species. Chemical modification with diethyl pyrocarbonate showed no hyperreactivity of the junctional bases, indicating a smooth transition between the two parallel

  20. Fabrication and characterization of all oxidep-n junction diodes

    NASA Astrophysics Data System (ADS)

    Zhuang, Lin

    We have grown ZnO and MgO mixed oxide thin films by pulsed laser deposition. Most other similar work reported in the open literature so far involved preparing wurtzite structured MgxZn1-xO (w-MZO) films on sapphire substrates with x<0.4. We argue that the cubic form of ZnO, including cubic MgxZn1-xO (c-MZO) could be useful as transparent conducting oxide (TCO), n-type or p-type doped semiconducting oxide, wide bandgap UV detector and dilute magnetic semiconductor (DMS) that can be matched with and grown on many other cubic oxides and perovskites to form interesting devices. By the use of single crystal substrate of matched cubic structures, such as MgO and LaAlO3 (LAO), we have demonstrated that cubic Mgx Zn1-xO thin films even with x=0.57, representing maximum reported solubility of Zn in MgO, can be stabilized under normal ambient. High quality homoepitaxially and heteroepitaxially grown c-MZO films on MgO and LAO respectively have also been obtained. MZO is a wide bandgap material. Its absorption band edge shifts deep into UV with increased MgO content. Indium doped c-MZO (In-MZO) thin films show typical n-type semiconducting properties. Electrical conductivity at room temperature as high as 102 S cm-1 has been achieved for samples with In 8 at.% doping. Yet they remain optically transparent over the whole visible spectrum. Thus they become desirable n-type TCO. Li-doped NiO (Li0.15Ni0.85O, LNO), on the other hand, is a p-type conductor with good optical transmittance. We have fabricated a number of optical transparent all-oxide p-n junctions based on p-LNO/n-Nb doped SrTiO3 single crystal substrate, p-LNO/n-ZnO(wurtzite) and p-LNO/n-In-MZO. Their structural qualities have been studied and excellent heteroepitaxial relationships have been demonstrated. The results of our present investigation provide affirmative evidence for using all-oxide to develop p-n diode junction devices. In particular the advantages of utilizing the diversified properties of oxide such

  1. Photoelectrochemical Hydrogen Production - Final Report

    SciTech Connect

    Miller, E.L.; Marsen, B.; Paluselli, D.; Rocheleau, R.

    2004-11-17

    The scope of this photoelectrochemical hydrogen research project is defined by multijunction photoelectrode concepts for solar-powered water splitting, with the goal of efficient, stable, and economic operation. From an initial selection of several planar photoelectrode designs, the Hybrid Photoelectrode (HPE) has been identified as the most promising candidate technology. This photoelectrode consists of a photoelectrochemical (PEC) junction and a solid-state photovoltaic (PV) junction. Immersed in aqueous electrolyte and exposed to sunlight, these two junctions provide the necessary voltage to split water into hydrogen and oxygen gas. The efficiency of the conversion process is determined by the performance of the PEC- and the PV-junctions and on their spectral match. Based on their stability and cost effectiveness, iron oxide (Fe2O3) and tungsten oxide (WO3) films have been studied and developed as candidate semiconductor materials for the PEC junction (photoanode). High-temperature synthesis methods, as reported for some high-performance metal oxides, have been found incompatible with multijunction device fabrication. A low-temperature reactive sputtering process has been developed instead. In the parameter space investigated so far, the optoelectronic properties of WO3 films were superior to those of Fe2O3 films, which showed high recombination of photo-generated carriers. For the PV-junction, amorphous-silicon-based multijunction devices have been studied. Tandem junctions were preferred over triple junctions for better stability and spectral matching with the PEC junction. Based on a tandem a-SiGe/a-SiGe device and a tungsten trioxide film, a prototype hybrid photoelectrode has been demonstrated at 0.7% solar-to-hydrogen (STH) conversion efficiency. The PEC junction performance has been identified as the most critical element for higher-efficiency devices. Research into sputter-deposited tungsten trioxide films has yielded samples with higher photocurrents of

  2. A mathematical formalism for diffusion in crystalline solids incorporating deviations from the Fickian behavior

    NASA Astrophysics Data System (ADS)

    Narayanan, Raghavan S.

    2007-12-01

    incorrect assumption. Finally, a method to design stable triple junctions based on Herring's relation is described and experimental results that demonstrate the occurrence of enhanced diffusion of nickel through triple junctions of copper and diffusion induced triple junction migration are presented.

  3. The Preparation and Properties of Niobium Superconducting Structures Prepared by Electron Beam Evaporation in Uhv

    NASA Astrophysics Data System (ADS)

    Goodchild, Martin S.

    Available from UMI in association with The British Library. This work has achieved the development of a fabrication method for the realisation of superconductor-insulator -superconductor (SIS) junctions based on niobium thin films with an artificial barrier layer. Such devices are likely to have advantages over lead alloy devices because of the enhanced mechanical and chemical stability. A principal objective was to attempt to exploit the offset mask technology developed by Dolan that has been successfully employed by Davies et.al. in the realisation of lead alloy SIS junction heterodyne mixers. In order to transfer this technology to niobium based devices it is essential that an evaporation method is used to allow shadow formation beneath the offset mask. As a result of the chemical reactivity and the low vapour pressure of niobium, a UHV system has been developed which incorporates an electrostatically focussed electron beam evaporation source. This is capable of providing deposition rates of close to 10A/sec. with a source to substrate distance of 120mm. During deposition the system pressure is below 5 times 10 ^{-9} mbar. These process parameters have been recorded, for a number of depositions, on a specially built data acquisition system controlled by a BBC microcomputer. Such recording allows detailed comparison of conditions which helps in the understanding of differences between the superconducting behaviour of various films. A further extremely important aspect of these real time measurements is that it helps to ensure optimum settings of the focus conditions of the electron beam source. The results of the depositions are extremely encouraging with critical temperatures of between 9.1 and 9.3K being achieved. These results compare well with expected values for bulk niobium. An all-metal offset mask technology has been developed to replace the photo-resist technique pioneered by Dolan. This new method is needed because the photo-resist is not compatible

  4. Four-Quadrant Analog Multipliers Using G4-FETs

    NASA Technical Reports Server (NTRS)

    Mojarradi, Mohammad; Blalock, Benjamin; Christoloveanu, Sorin; Chen, Suheng; Akarvardar, Kerem

    2006-01-01

    Theoretical analysis and some experiments have shown that the silicon-on-insulator (SOI) 4-gate transistors known as G4-FETs can be used as building blocks of four-quadrant analog voltage multiplier circuits. Whereas a typical prior analog voltage multiplier contains between six and 10 transistors, it is possible to construct a superior voltage multiplier using only four G4-FETs. A G4-FET is a combination of a junction field-effect transistor (JFET) and a metal oxide/semiconductor field-effect transistor (MOSFET). It can be regarded as a single transistor having four gates, which are parts of a structure that affords high functionality by enabling the utilization of independently biased multiple inputs. The structure of a G4-FET of the type of interest here (see Figure 1) is that of a partially-depleted SOI MOSFET with two independent body contacts, one on each side of the channel. The drain current comprises of majority charge carriers flowing from one body contact to the other that is, what would otherwise be the side body contacts of the SOI MOSFET are used here as the end contacts [the drain (D) and the source (S)] of the G4-FET. What would otherwise be the source and drain of the SOI MOSFET serve, in the G4-FET, as two junction-based extra gates (JG1 and JG2), which are used to squeeze the channel via reverse-biased junctions as in a JFET. The G4-FET also includes a polysilicon top gate (G1), which plays the same role as does the gate in an accumulation-mode MOSFET. The substrate emulates a fourth MOS gate (G2). By making proper choices of G4-FET device parameters in conjunction with bias voltages and currents, one can design a circuit in which two input gate voltages (Vin1,Vin2) control the conduction characteristics of G4-FETs such that the output voltage (Vout) closely approximates a value proportional to the product of the input voltages. Figure 2 depicts two such analog multiplier circuits. In each circuit, there is the following: The input and output

  5. Fabrication, Characterization and Application of Metal-oxide Tunnel Junctions by Anodization

    NASA Astrophysics Data System (ADS)

    Fan, Wenbin

    Metal oxides have become of significant interest due to their wide range of electrical properties showing potential applications to next generation memory and logic devices. Recent advances in oxide growth technology and the discovery of some unique properties of metal oxides have led to a renewed potential for novel device functionality. Electrochemical anodization offers an effective means to produce oxides in terms of cost, convenience and purity. In this dissertation, Reactive Bias Target Ion Beam Deposition (RBTIBD) system and electrochemical anodization have been used to fabricate granular nano-structured metal-oxide lateral junctions based on the transition metals, particularly, vanadium (V) and tantalum (Ta). The electrical transport properties of anodized V and Ta metal-oxide junctions were investigated at various temperatures. The results turned out that these junctions all had very non-linear I-V characteristics indicating tunneling-like behaviors. Anodized Ta junction shown an appreciable non- linear behavior of the temperature-dependent I-V characteristic with a resistance change of nearly two orders of magnitude at T-300K at currents between 0 and 0.1 mA (˜ 1.3x104 A/cm2 or 104 V/cm). The metal-insulator-transition (MIT) was observed in both wire and bulk V junctions at ˜ 80°C. The microstructure of these anodized transition metal films was characterized by Transmission Electron Microscope (TEM), which was consistent with metallic grains embedded in an oxide matrix. Therefore an anodized granular metal film could be treated as a tunnel junction network. Two dominant electron conduction mechanisms were clearly identified by fitting the I(V, T) data of a Ta oxide- metal junction. The first mechanism was a temperature-independent tunneling including F-N and direct tunneling. The second mechanism was the modified temperature-dependent 2-dimentional Mott's variable-range hopping (VRH) model. The classical Simmons' equation was used to quantify the

  6. Point Defects in Two-Dimensional Layered Semiconductors: Physics and Its Applications

    NASA Astrophysics Data System (ADS)

    Suh, Joonki

    thermoelectric materials are thoroughly investigated. Point defects can potentially beat the undesired coupling, often term "thermoelectric Bermuda triangle", among electrical conductivity, thermal conductivity and thermopower. The maximum thermoelectric performance is demonstrated with an intermediate density of defects when they beneficially and multi-functionally act as electron donors, as well as strongly energy-dependent electron and phonon scatterers. Therefore, this is a good example of how fundamental defect physics can be applied for practical devices toward renewable energy technology. Another interesting field of layered nanomaterials is on transition-metal dichalcogenides (TMDs), sensational candidates for 2D semiconductor physics and applications. At the reduced dimensionality of 2D where a far stronger correlation between point defects and charge carriers is expected, it is studied how chalcogen vacancies alter optical properties of monolayer TMDs. A new, sub-bandgap broad emission lines as well as increase in the overall photoluminescence intensity at low temperatures are reported as a result of high quantum efficiency of excitons, i.e., bound electron-hole pairs, localized at defect sites. On electrical transport, both n- and p-type materials are needed to form junctions and support bipolar carrier conduction while typically only one type of doping is stable for a particular TMD. For example, MoS2 is natively n-type, thus the lack of p-type doping hampers the development of charge-splitting p-n junctions of MoS2. To address this issue, we demonstrate stable p-type conduction in MoS2 by substitutional Nb doping up to the degenerate level. Proof-of-concept, van der Waals p-n homo-junctions based on vertically stacked MoS2 layers are also fabricated which enable gate-tuneable current rectification. Various electronic devices fabricated are stable in ambient air even without additional treatment such as capping layer protection, thanks to the substitutionality nature

  7. A possible deep, long-term source for water in the Northern San Andreas Fault system: A ghost of Cascadia subduction past?

    NASA Astrophysics Data System (ADS)

    Kirby, S.; Wang, K.; Brocher, T.

    2002-12-01

    California continental slope (posited as the former position of the trench) and the traces of faults of the SAF system, suggesting that the San Andreas fault system may be positioned above the dehydrating mantle wedge. The total volume of water stored in the wedge is large, estimated to be 0.6 to 1.2 Gm3/m of margin. Its release over time provides a deep source of water, reducing the effective normal stress across this fault system, reducing the resistance to frictional sliding and, in turn, explaining the inferred low regional stresses and the lack of a heat-flow anomaly. The dehydrating wedge may also be a deep source region for serpentinite slivers that occur along the SAF. Numerical modeling in progress involving incorporating the effects of the endothermic dehydration reaction and the advection of heat by upward water migration should give insight into the time evolution of water release and the observed restoration of the Moho south of the triple junction based on seismic surveys.

  8. Supernova-driven interstellar turbulence

    NASA Astrophysics Data System (ADS)

    Joung, M. K. Ryan

    To study how supernova feedback structures the turbulent interstellar medium, we construct 3D models of vertically stratified gas stirred by discrete supernova explosions, including vertical gravitational field and parametrized heating and cooling. The models reproduce many observed characteristics of the Galaxy such as global circulation of gas (i.e., galactic fountain) and the existence of cold dense clouds in the galactic disk. Global quantities of the model such as warm and hot gas filling factors in the midplane, mass fraction of thermally unstable gas, and the averaged vertical density profile are compared directly with existing observations, and shown to be broadly consistent. We find that energy injection occurs over a broad range of scales. There is no single effective driving scale, unlike the usual assumption for idealized models of incompressible turbulence. However, >90% of the total kinetic energy is contained in wavelengths shortward of 200 pc. The shape of the kinetic energy spectrum differs substantially from that of the velocity power spectrum, which implies that the velocity structure varies with the gas density. Velocity structure functions demonstrate that the phenomenological theory proposed by Boldyrev is applicable to the medium. We show that it can be misleading to predict physical properties such as the stellar initial mass junction based on numerical simulations that do not include self-gravity of the gas. Even if all the gas in turbulently Jeans unstable regions in our simulation is assumed to collapse and form stars in local freefall times, the resulting total collapse rate is significantly lower than the value consistent with the input supernova rate. Supernova-driven turbulence inhibits star formation globally rather than triggering it. Feedback from massive stars is perhaps the least understood aspect of the current scenario of large-scale structure formation. Many recent observations on both galactic and cosmological scales require

  9. Point Defects in Two-Dimensional Layered Semiconductors: Physics and Its Applications

    NASA Astrophysics Data System (ADS)

    Suh, Joonki

    thermoelectric materials are thoroughly investigated. Point defects can potentially beat the undesired coupling, often term "thermoelectric Bermuda triangle", among electrical conductivity, thermal conductivity and thermopower. The maximum thermoelectric performance is demonstrated with an intermediate density of defects when they beneficially and multi-functionally act as electron donors, as well as strongly energy-dependent electron and phonon scatterers. Therefore, this is a good example of how fundamental defect physics can be applied for practical devices toward renewable energy technology. Another interesting field of layered nanomaterials is on transition-metal dichalcogenides (TMDs), sensational candidates for 2D semiconductor physics and applications. At the reduced dimensionality of 2D where a far stronger correlation between point defects and charge carriers is expected, it is studied how chalcogen vacancies alter optical properties of monolayer TMDs. A new, sub-bandgap broad emission lines as well as increase in the overall photoluminescence intensity at low temperatures are reported as a result of high quantum efficiency of excitons, i.e., bound electron-hole pairs, localized at defect sites. On electrical transport, both n- and p-type materials are needed to form junctions and support bipolar carrier conduction while typically only one type of doping is stable for a particular TMD. For example, MoS2 is natively n-type, thus the lack of p-type doping hampers the development of charge-splitting p-n junctions of MoS2. To address this issue, we demonstrate stable p-type conduction in MoS2 by substitutional Nb doping up to the degenerate level. Proof-of-concept, van der Waals p-n homo-junctions based on vertically stacked MoS2 layers are also fabricated which enable gate-tuneable current rectification. Various electronic devices fabricated are stable in ambient air even without additional treatment such as capping layer protection, thanks to the substitutionality nature

  10. CONFERENCE SUMMARY: Summary and comment on superconducting analogue electronics research, including materials and fabrication, as presented at ISEC 07

    NASA Astrophysics Data System (ADS)

    Foley, C. P.

    2007-11-01

    -micron Josephson junctions using laser etching (Büttner et al) and the development of passivation layers using amorphous YBCO and SiO2 (Seidel et al) were also presented. Characterization methods using Raman and photo-emission spectroscopy (Kikunaga et al) emerged as fresh approaches. Josephson junction (JJ) research covered the areas of critical current fluctuations where results on Tl-based junctions suggested a 40 times lower δI/Ic, and LTS junctions for voltage standards using a Nb-Si barrier for improved SNS junctions (Kieler et al). Development of MTS junctions based on MgB2 are yet to be realized with the interface barrier appearing to be the limiting factor. HTS Josephson junctions were reviewed by asking the question: `Are all HTS JJs the same?' with a clear `no' as the answer. Research on intrinsic stacked junctions, sub-micron junctions, the manipulation of electronic band structure to increase energy gap and mid-gap states was also presented. Developments in packaging and cooling were not as dominant at this conference as in previous years. However, there was research reported on the importance of non-magnetic structures in packaging, the design of magnetic shielding improvement by using finite element analysis to optimize design (Tanaka et al) and the use of cryocoolers (Vernik et al). SQUID research reported some breakthrough developments with new ideas presented on nano-SQUIDs with the possible detection of a ferritin spin-flip, a successful airborne trial using a rotating gradiometer and the development of a new 4 cm long baseline planar gradiometer, achieving a sensitivity of 35 fT cm-1 Hz-½. Applications in non-destructive evaluation (NDE) covered the use of SQUIDs in the detection of stainless steel foreign objects in food, defects in wire and circuit boards and surface imaging with most developments focusing on potential customer requirements. Biomagnetic applications have continued to be embraced in the use of SQUIDs in MRI (Zotev et al), NMR, MEG

  11. CONFERENCE SUMMARY: Summary and comment on superconducting analogue electronics research, including materials and fabrication, as presented at ISEC 07

    NASA Astrophysics Data System (ADS)

    Foley, C. P.

    2007-11-01

    -micron Josephson junctions using laser etching (Büttner et al) and the development of passivation layers using amorphous YBCO and SiO2 (Seidel et al) were also presented. Characterization methods using Raman and photo-emission spectroscopy (Kikunaga et al) emerged as fresh approaches. Josephson junction (JJ) research covered the areas of critical current fluctuations where results on Tl-based junctions suggested a 40 times lower δI/Ic, and LTS junctions for voltage standards using a Nb-Si barrier for improved SNS junctions (Kieler et al). Development of MTS junctions based on MgB2 are yet to be realized with the interface barrier appearing to be the limiting factor. HTS Josephson junctions were reviewed by asking the question: `Are all HTS JJs the same?' with a clear `no' as the answer. Research on intrinsic stacked junctions, sub-micron junctions, the manipulation of electronic band structure to increase energy gap and mid-gap states was also presented. Developments in packaging and cooling were not as dominant at this conference as in previous years. However, there was research reported on the importance of non-magnetic structures in packaging, the design of magnetic shielding improvement by using finite element analysis to optimize design (Tanaka et al) and the use of cryocoolers (Vernik et al). SQUID research reported some breakthrough developments with new ideas presented on nano-SQUIDs with the possible detection of a ferritin spin-flip, a successful airborne trial using a rotating gradiometer and the development of a new 4 cm long baseline planar gradiometer, achieving a sensitivity of 35 fT cm-1 Hz-½. Applications in non-destructive evaluation (NDE) covered the use of SQUIDs in the detection of stainless steel foreign objects in food, defects in wire and circuit boards and surface imaging with most developments focusing on potential customer requirements. Biomagnetic applications have continued to be embraced in the use of SQUIDs in MRI (Zotev et al), NMR, MEG