Longer Wires Research Articles

First-principles study of the variation of electron transport in a single molecular junction with the length of the molecular wire

We report a first-principles study of quantum transport in a prototype two-terminal device consisting of a molecular nanowire acting as an inter-connect between two gold electrodes. The wire is composed of a series of bicyclo[1.1.1]pentane (BCP) cage-units. The length of the wire $(L)$ is increased by sequentially increasing the number of BCP cage units in the wire from 1 to 3. A two terminal model device is made out of each of the three wires. A parameter free, nonequilibrium Green's function approach, in which the bias effect is explicitly included within a many body framework, is used to calculate the current-voltage characteristics of each of the devices. In the low bias regime that is considered in our study, the molecular devices are found to exhibit Ohmic behavior with resistances of 0.12, 1.4, and $6.5\text{ }\ensuremath{\mu}\ensuremath{\Omega}$ for the wires containing one, two, and three cages respectively. Thus the conductance value, ${G}_{c}$, which is the reciprocal of resistance, decreases as ${e}^{\ensuremath{-}\ensuremath{\beta}L}$ with a decay constant $(\ensuremath{\beta})$ of $0.59\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$. This observed variation of conductance with the length of the wire is in excellent agreement with the earlier reported exponential decay feature of the electron transfer rate predicted from the electron transfer coupling matrix values obtained using the two-state Marcus-Hush model and the Koopman's theorem approximation. The downright suppression of the computed electrical current for a bias up to 0.4 V in the longest wire can be exploited in designing a three terminal molecular transistor; this molecular wire could potentially be used as a throttle to avoid leakage gate current.

Design of High-Throughput Fully Parallel LDPC Decoders Based on Wire Partitioning

We present a method to design high-throughput fully parallel low-density parity-check (LDPC) decoders. With our method, a decoder's longest wires are divided into several short wires with pipeline registers. Log-likelihood ratio messages transmitted along with these pipelined paths are thus sent over multiple clock cycles, and the decoder's critical path delay can be reduced while maintaining comparable bit error rate performance. The number of registers inserted into paths is estimated by using wiring information extracted from initial placement and routing information with a conventional LDPC decoder, and thus only necessary registers are inserted. Also, by inserting an even number of registers into the longer wires, two different codewords can be simultaneously decoded, which improves the throughput at a small penalty in area. We present our design flow as well as post-layout simulation results for several versions of a length-1024, (3,6)-regular LDPC code. Using our technique, we achieve a maximum uncoded throughput of 13.21 Gb/s with an energy consumption of 0.098 nJ per uncoded bit at E b/N0 = 5 dB. This represents a 28% increase in throughput, a 30% decrease in energy per bit, and a 1.6% increase in core area with respect to a conventional parallel LDPC decoder, using a 90-nm CMOS technology.

A New Genetic Variant of MDX Mice: Study of the Phenotype

Genetic selection in a colony of mdx mice (suffering from X-chromosome-linked muscular dystrophy) resulted in generation of their new genetic variant. In this new variant, the genetic, biochemical, and histological markers of muscular dystrophy are combined with signs of oculocutaneous albinism (skin and fur depigmentation), transillumination of the iris, sharply reduced pigmentation of the retinal epithelium, and increase of the eyeball refraction). Two sensorimotor tests (negative geotaxis and wire back down hanging) detected other phenotypical characteristics of albino mdx mice carrying, in addition to the mutation in the dystrophin gene exon 23 (intrinsic of the "classical" black mdx mice), an extra mutation responsible for pigmentation disorders. Slow geotaxis, despite longer wire back down hanging capacity, was regarded as aggravation of the neurological dysfunction in albino mdx mice in comparison with black mdx mice.

An 11 nm Molecular Wire that Switches Electrochemically between an Insulating and a Fully Conjugated Conducting State

[structure: see text] Molecular wires consisting of oligothiophenes and oligothiophenylethynes, ranging in length from 2 to 11 nm, are synthesized and examined by spectroscopy and electrochemistry. UV spectroscopy shows that the longest wires are not fully conjugated, but twisted. However, cyclic voltammetry indicates that their monocations are now flattened and conjugated over the entire length range. In appropriate systems, the wires will link to two electrodes across a nanoscale gap and conduct current.

Optimization of Critical Currents in<tex>$rm MgB_2$</tex>Wires and Coils

We present an analysis of the effect of SiC doping and heat treatments, including hot isostatic pressing (HIPing), on the microstructure, magnetization and transport properties of MgB/sub 2/ wires and coils prepared by the powder in tube (PIT) method. The HIPed wires have higher critical current densities (J/sub c/) than the annealed wires, especially at high temperatures and magnetic fields, and higher irreversibility field. The improvements are due to the reduction of porosity and to a high density of structural defects, which are the likely source of vortex pinning. We demonstrate that the high-quality properties mentioned above can be retained in longer wires. At 25 K our champion 6-layer coil, made with 25 meters of wire, was able to generate a field of 1 T at self-field. We were able to achieve even higher J/sub c/'s in another coil by combining the addition of SiC and HIPing. We also observed a larger upper critical field due to the SiC doping, which drives the sample to the dirty limit.

Magnetic nanowires in hexagonally ordered pores of alumina

Acid-anodized aluminum forms amorphous alumina with long and columnar nanopores with approximately hexagonal ordering ("alumite"). Excellent hexagonal ordering of these nanopores has been achieved by 24 hours of anodization, but with restricted domain size (2-4 /spl mu/m/sup 2/), which can be increased to 100 /spl mu/m/sup 2/ with longer anodization. We have deposited Fe in disordered pores and Co in ordered pores; we can control the average length and diameter of these nanowires, but there is still a distribution of nanowire lengths. Previously, we described Fe nanowires with diameters down to 11 nm in disordered pores. Here we focus on longer (770 nm) and shorter (64 nm) Co nanowires with diameters of 25 nm in ordered pores with 100 nm pore-to-pore separation. The longer wires have an easy axis out-of-plane, with squareness >0.9, coercivity=1900 Oe, and a fluctuation field of 5.3 Oe. The shorter wires are more isotropic, with lower coercivities (/spl ap/1300 Oe) and larger fluctuation fields /spl ap/8.4 Oe.

Conditions for Fabrication of Highly Conductive Wires by Electron-Beam-Induced Deposition

Conductive wires were fabricated by electron-beam-induced deposition (EBID) using WF6 gas. It was difficult to fabricate highly conductive wires with good reproducibility unless samples were cleaned before EBID. Contamination appears to reduce the conductivity of the wires. O2 plasma cleaning of samples before EBID seems to reduce contamination growth; however, it is not effective for regions in the vicinity of Au patterns. We found that by combining annealing at 300°C and O2 plasma cleaning, highly conductive wires could be fabricated with relatively good reproducibility in such regions. A linear relation was found between wire conductance and linedose at lindoses of more than 70 µC/cm. The change in deposition yield estimated from the conductance was about 12% when the gas flux was halved. Wires with a length of less than 40 nm were less conductive than longer wires because of a shortage in gas supply.

Reciprocal-Space and Real-Space Analyses of Compositional Modulation in InAs/AlAs Short-Period Superlattices

AbstractThe microstructure of lateral composition modulation in InAs/AlAs superlattices grown by MBE on InP is examined. The use of x-ray diffraction, TEM, AFM, and STEM to characterize the modulations is discussed. Combining the information from these techniques gives increased insight into the phenomenon and how to manipulate it. Diffraction measures the intensity of modulation and its wavelength, and is used to identify growth conditions giving strong modulation. The TEM and STEM analyses indicate that local compositions are modulated by as much as 0.38 InAs mole fraction. Plan-view images show that modulated structures consists of short (≳0.2 μm) In-rich wires with a 2D organization in a (001) growth plane. However, growth on miscut substrates can produce a single modulation along the miscut direction with much longer wires (≲0.4 μm), as desired for potential applications. Photoluminescence studies demonstrate that the modulation has large effects on the bandgap energy of the superlattice.

Reduction of quantized conductance at low temperatures observed in 2 to 10 μm-long quantum wires

We observe a small but definite decrease in quantized conductance at low temperatures in 2 to 10 μm-long single-mode quantum wires. The temperature dependence is stronger in the longer wires. The conductance of the 2 μm-long wire is nearly constant below a critical temperature, at which the thermal length becomes longer than the wire length, while that of the 5 and 10 μm-long wires decreases fairly monotonically with decreasing temperature. We will discuss the effect of mutual Coulomb interaction that is responsible for the change in quantized conductance observed as a function of temperature and wire length.

Flipping Modules to Minimize Maximum Wire Length

We show that obtaining the optimal orientations of modules to minimize the length of the longest wire is NP-hard. If each module is permitted only two possible orientations, this can be done in linear time. When all four orientations are permissible and wires are restricted to connect modules whose separation is bounded by some constant, the problem also can be solved in linear time.

Optimal joining of compacted cells

Three algorithms to join two compacted cells by using a combination of stretching and river routing are developed. Each of these obtains the minimum area joining. One algorithm obtains a minimum area joining that also minimizes the length of the longest wire. Another obtains a minimum area joining that has the least possible total wire length. The simplest of the algorithms guarantees only a minimum are joining. All algorithms have a low-order polynomial complexity. Experimental results indicate that the algorithms obtain joinings that are significantly superior to those obtained using the heuristic of G. Cheng and A. Despain (1989). >

Conductance Fluctuations in GaAs/AlGaAs Narrow Wires in Quasi-Ballistic Regime

Conductance Fluctuations due to the quantum interference of electrons have been studied in GaAs/AlGaAs narrow wires in the quasi-ballistic transport regime. Narrow channels of length 2 µm and 6 µm were confined by metallic split gates formed by electron beam lithography and a lift off technique. In the shorter wire, the amplitude of the fluctuations first increased as a function of increasing width, and finally approached to the constant value of e2/h. On the other hand, it was almost independent on channel width in the longer wire, as expected for the universal conductance mechanism in the diffusive transport regime. We suspect that the non universal width dependence in the shorter wire might result from averaging among the individual transmission channels, caused by the small number of scattering events.

Studies on Pool Boiling Heat Transfer. 6th Report. Critical Heat Flux on Vertical Wires.

Critical heat flux (CHF) on vertical wires was measured for water and ethanol under atmospheric pressure. The diameter of wires ranged from 0.3mm to 3mm and their length from 4mm to 200mm. For shorter wires, CHF occurred at the top and increased with decreasing length, while for longer wires, CHF occurred in a lower region of the wires and did not vary with diameter. A physical model for CHF on vertical wires was constructed based on a CHF mechanism, in which CHF is caused by the dry-out of liquid macrolayers formed on a heating surface. In the model it is assumed that coalesced bubbles moving upward along a wire have a liquid macrolayer on their bottom, and the motion of the coalesced bubbles is determined by the balance of force between buoyancy and drag. CHF on the longer wires occured where coalesced bubbles begin a zig-zag or spiral motion. The predicted CHF and the location of CHF were compared with experimental data and fairly good agreement was obtained.

Placement of the processors of a hypercube

The authors formalize the problem of minimizing the length of the longest interprocessor wire as the problem of embedding the processors of a hypercube onto a rectangular mesh, so as to minimize the length of longest wire. Where neighboring nodes of the mesh are taken as being at unit distance from one another, and where wires are constrained to be laid out as horizontal and vertical wires, the length of the wire joining nodes u and v of the mesh equals the graph-theoretic distance between u and v. The problem of minimizing delays due to interprocessor communication is then modeled as the problem of embedding the vertices of a hypercube onto the nodes of a mesh, so as to minimize dilation. Two embeddings which achieve dilations that (for large n) are within 26% of the lower bound for square meshes and within 12% for meshes with aspect ratio 2 are presented. >

Processor networks and interconnection networks without long wires (extended abstract)

One processor network that is especially attractive for parallel processing is the Butterfly network. A very closely related interconnection network is the Bidelta (or Omega) network. It is well known how to lay out these networks with minimal area, but these layouts use long wires. We show how to lay them out with optimal area and short wires. We also introduce the Mesh-Connected Cycles network, which has optimal area (in the sense of AT 2 ) for a broad range of running times when executing "ascend-descend" algorithms. The length of its longest wire is nearly optimal, and its layout area has very modest constants.

Length-Dependent Resistance of Thin Wires

The electrical properties of wires with cross-sectional areas of order 1 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}11}$ ${\mathrm{cm}}^{2}$ and lengths as small as 0.2 \ensuremath{\mu}m have been studied. At temperatures below about 10 K, the resistance of the wires increases with decreasing temperature, as found in previous studies of much longer wires. For wires shorter than about 5 \ensuremath{\mu}m, the resistance rise decreases as the length of the wire is decreased. From these results a characteristic length scale of approximately 0.2 \ensuremath{\mu}m at 1.5 K is found, in good agreement with the current theory.

Radar waveform synthesis method--A new radar detection scheme

A new scheme for radar detection and discrimination, the radar waveform synthesis method, is investigated. This scheme consists of synthesizing the waveform of an incident radar signal which excites the target in such a way that the return radar signal from the target contains only a single natural resonance mode of the target. When the synthesized incident radar signal for a known preselected target is applied to a wrong target, the return radar signal will be significantly different from that of a natural mode of resonance, thus the wrong target can be sensitively discriminated. A simple geometry of a thin wire illuminated by a radar signal at normal incidence has been studied. The induced current on the target and the backscattered field from the target are obtained in terms of natural resonance modes. The required waveforms for the incident radar signal for exciting return radar signals which contain various single natural mode of resonance are obtained. When an incident radar signal synthesized to excite a natural resonance mode of a thin wire is applied to a slightly shorter or longer thin wire, the return radar signal from the wrong target is shown to be significantly different from that of a pure natural mode of resonance.

Modification of scattering of waves by central loading

The problem of the scattering of a plane wave by a long, thin, perfectly conducting wire is studied. The scatterer is loaded at its center by a lumped element. The effects of the loading on the scattering of waves are investigated. Numerical results are obtained for the case of normal incidence. The results show that for relatively short wires, the back-scattering cross sections may be modified effectively by central loading, while for longer wires, the modification is rather difficult to achieve. To nullify the back-scattering cross section completely, it is necessary to use active loading if kh > 3.6. A physical explanation is also presented.

Fundamental Study on Electrohydraulic Forming

There were many studies on electrohydraulic forming in which the relationship between the deformation of metallic meterial and the stored electrical energy was investigated. It is necessary for us, however, to explain the correlation between the deformation resistance for each of these metals and the pressure pulse in order to analyze the deformation characteristic of metals. The experiments were carried out by means of pressure gage (BaTiO8) on deformation pressure and pressure pulse which were directly related to the deformation, and further, the shock wave energy was calculated. The efficiency of these apparatus was discussed. The clearance between the electrodes creating pressure was short-circuited with several kinds of fine wire, and the influences of the diameters and lengths of wires were presented. Also in the case when there existed water only between the electrodes, the influences of electrode diameters and clearances were presented. It is found from experimental results that cases where the clearance between the electrodes was short-circuited with a fine wire are superior to the case where water was the only pressure source between the electrodes, and the aluminum wire which had a low boiling point metal was effective. The rise time of pressure pulse is about 5μsec and its duration is about 15μsec. Such shapes of pressure pulse do not change up to 1000 joule charged energy. Shorter wires are better than longer wires as pressure sources, while the diameter of wires creating the largest pressure is limited by characteristic of apparatus and the charged energy.

Fundamental Study on Electrohydraulic Forming

There were many studies on electrohydraulic forming in which the relationship between the deformation of a special metal and the stored electrical energy was investigated. However, it is necessary for us to explain the correlation between the deformation resistance for each of these metals and the pressures in order to analyze the deformation characteristic of metals. The experiments were carried out by means of pressure gage (BaTiO3) on deformation pressures and pressure waves which are directly related to the deformation, and further, the shock wave energies were calculated. The efficiency of these apparatuses is mentioned. The clearance between the electrodes creating pressure is short-circuited with several kinds of fine wire, and the influences of the diameters and lengths of the wires are presented. Also in case there exists water only between the electrodes, the influences of electrod diameters and clearances are presented. It is found from experimental results that such cases where the clearance between the electrodes is short-circuited with a fine wire are superior to the case where water is the only pressure source between the electrodes, and that the aluminum wire which has a low boiling point metal is effective. The rise time of pressure wave is about 5μs and its duration is about 15μs. Such forms of pressure wave does not change up to 1 000 joule stored electrical energy. Shorter wires are better than longer wires as pressure sources, however the diameter of wires creating the largest pressure is limited by characteristic of apparatus and the stored electrical energy.