Three-dimensional Wires Research Articles

Free-standing porous carbon foam as the ultralight and flexible supercapacitor electrode

Highly flexible carbon foam with double-layer structure and hierarchical pores is synthesized based on Co-ZIF-L supported on carbonized melamine sponge (MS). Due to the special leaf-like structure of Co-ZIF-L, the uniform in-situ growth of ZIF-L onto carbonized MS makes the three-dimensional carbon wires dendriform-like, which after carbonization and KOH activation, sufficient micro- and mesopores are created resulting from Co-ZIF-L particles and gaps among them. Such hierarchical pore structure significantly improves the specific capacities (238 F/g at 1 A/g compared to that of 92 F/g for carbonized pristine MS). Moreover, due to the excellent mechanical properties inheriting from MS, the obtained sample can be used directly as a flexible electrode and remains high electrochemical performance under different bending states (the capacitance remains 99% and 96.1% respectively when bent at 90° and 180°). When using such foam as all-solid-state supercapacitors, it shows high specific capacity (149 F/g at 5 mV/s), high stability in high operation voltage window (0–1.8 V) and excellent flexibility, which makes such material a potential candidate for high-performance supercapacitors in modern portable and wearable devices.

Enhancement of discrete changes in resistance in engineered VO2 heterointerface nanowall wire

The nanoconfinement effect in three-dimensional (3D) space was investigated for strongly correlated VO2. Three-dimensional VO2 nanowall wires (nws) with an engineered heterointerface were grown on the side-surface of 3D patterned MgO. A 100-nm-wide VO2 nw 2 µm in length and 100 nm in height showed multistep changes in resistance during the insulator–metal transition owing to confinement of 150 insulator and metal domains in the nw. We showed that further confinement along the longitudinal direction of a nanowall using a nanogap electrode, that is, a reduction of the number of domains to 10, led to much steeper step changes.

High resolution structural characterisation of laser-induced defect clusters inside diamond

Laser writing with ultrashort pulses provides a potential route for the manufacture of three-dimensional wires, waveguides, and defects within diamond. We present a transmission electron microscopy study of the intrinsic structure of the laser modifications and reveal a complex distribution of defects. Electron energy loss spectroscopy indicates that the majority of the irradiated region remains as sp3 bonded diamond. Electrically conductive paths are attributed to the formation of multiple nano-scale, sp2-bonded graphitic wires and a network of strain-relieving micro-cracks.

Three-Dimensional Wiring for Extensible Quantum Computing: The Quantum Socket

Quantum computing architectures are on the verge of scalability, a key requirement for the implementation of a universal quantum computer. The next stage in this quest is the realization of quantum error correction codes, which will mitigate the impact of faulty quantum information on a quantum computer. Architectures with ten or more quantum bits (qubits) have been realized using trapped ions and superconducting circuits. While these implementations are potentially scalable, true scalability will require systems engineering to combine quantum and classical hardware. One technology demanding imminent efforts is the realization of a suitable wiring method for the control and measurement of a large number of qubits. In this work, we introduce an interconnect solution for solid-state qubits: The quantum socket. The quantum socket fully exploits the third dimension to connect classical electronics to qubits with higher density and better performance than two-dimensional methods based on wire bonding. The quantum socket is based on spring-mounted micro wires the three-dimensional wires that push directly on a micro-fabricated chip, making electrical contact. A small wire cross section (~1 mmm), nearly non-magnetic components, and functionality at low temperatures make the quantum socket ideal to operate solid-state qubits. The wires have a coaxial geometry and operate over a frequency range from DC to 8 GHz, with a contact resistance of ~150 mohm, an impedance mismatch of ~10 ohm, and minimal crosstalk. As a proof of principle, we fabricated and used a quantum socket to measure superconducting resonators at a temperature of ~10 mK.

Formation of Nanoporous Electrode on Aligned CNT Films Using Dealloying

Eco-power systems and recyclable energy are in high demand in low-carbon societies for practical applications of power devices. In these power-device fields, there is a requirement for the development of electronic packages for the radiation of heat. Carbon nanotubes (CNTs) have high thermal conductivities, large electron mean free paths, and large maximum current densities, as compared to metals. For these reasons, the application of CNTs in semiconductor packaging and three-dimensional wires is expected. It is reported that CNTs that have high densities and are well aligned are formed by the surface decomposition of SiC, which is the substrate of the power transistor [1]. However, the contact resistance between the CNTs and the electronic circuit is high. On the other hand, metal nanoparticles have been known to possess various properties that are not present in the bulk and are expected to have applications in various fields such as electronics and biotechnology. Metal nanoparticles have achieved low melting points and high chemical reactivity. Lower temperatures for some processes are expected when using nanosized particles. Au is applied in micro/nano electrochemical systems and in biotechnology applications because it exhibits superior stability and conductivity over other metals. Dealloying is the method used to construct a nanoporous structure by the selective etching of the poor metal from a bimetal consisting of a noble metal and a base metal. We have attempted to form nanoporous structures of Au–Ag films using the electrochemical method and a low-temperature dealloying process [2]. We tried to form metal nanoparticles of Au–Ag on the CNTs to get good contact resistance by dealloying. The purpose of this study is to clarify the initial growth mechanism of the electrodeposited films and nanoporous structures on the aligned CNT films, and to propose an electrode structure with good thermal-emission characteristics.

Spin-orbit interaction in InSb nanowires

We use magnetoconductance measurements in dual-gated InSb nanowire devices together with a theoretical analysis of weak antilocalization to accurately extract spin-orbit strength. In particular, we show that magnetoconductance in our three-dimensional wires is very different compared to wires in two-dimensional electron gases. We obtain a large Rashba spin-orbit strength of $0.5 -1\,\text{eV\r{A}}$ corresponding to a spin-orbit energy of $0.25-1\,\text{meV}$. These values underline the potential of InSb nanowires in the study of Majorana fermions in hybrid semiconductor-superconductor devices.

Individually Addressable Suspended Conducting-Polymer Wires in a Chemiresistive Gas Sensor

An effective method is described for producing poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) arched microwires, which are used as transducers in chemiresistive gas sensors. Three-dimensional arched wires with diameters of 0.8, 1.2, 2.5, and 10 μm are individually fabricated by using a simple, inexpensive fountain-pen lithography technique. The wires show superior stretchable behavior under omnidirectional strain of ca. 120%. A gas sensor assembled with the PEDOT:PSS arched wires exhibits linear responses to the concentrations of different vapor gases, such as ethanol, acetone, and methanol, at room temperature. The signal-to-noise ratio in the sensing response, which influences the detection limit, is enhanced by increasing the number of wires with a larger surface-to-volume ratio in parallel to increasing the signal level and diminishing the baseline noise in the wire transducers.

The influence of oxygen on the growth of silver on Cu(110)

The influence of the (2 × 1)O reconstruction on the growth of Ag on a Cu(110) surface was studied by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). On the bare Cu(110) surface, Stranski–Krastanov growth of silver is observed at sample temperatures between 277 K and 500 K: The formation of a Ag wetting layer is followed by the growth of three-dimensional Ag wires. In contrast, on the oxygen-precovered Cu(110) surface, the growth of silver depends heavily on the substrate temperature. Upon Ag deposition at room temperature, a homogeneous, polycrystalline Ag layer is observed, whereas at 500 K, three-dimensional wires separated by (2 × 1)O reconstructed areas are formed. The behavior of a deposited Ag layer upon annealing is also influenced greatly by the presence of oxygen. On the bare surface, annealing does not change the Ag wetting layer and gives rise to Ostwald ripening of the Ag wires. On the oxygen-precovered surface, however, the initial polycrystalline Aglayer first transforms into Ag wires at around 500 K. Above this temperature, the depletion of the (2 × 1)O reconstructed areas due to Ag-induced O desorption is balanced by the formation of a Ag wetting layer. On both, the bare and the oxygen-precovered Cu(110) surface, the deposited silver diffuses into the Cu bulk at temperatures above 700 K.

Spin-reorientation transitions in cobalt nanowires: Role of the microstructure and finite-size effects

We present self-consistent electronic structure calculations in order to analyze the magnetocrystalline anisotropy energy as well as the local spin ${S}_{\ensuremath{\delta}}(i)$ and orbital ${L}_{\ensuremath{\delta}}(i)$ magnetic moments for finite-length Co nanowires. We consider monatomic chains, as well as single-crystal and polycrystalline nanowires, assuming two directions of magnetization $\ensuremath{\delta}$ oriented along $(\ensuremath{\delta}=x)$ and perpendicular $(\ensuremath{\delta}=z)$ to the wire axis. The single-crystal wires are cylindrical fragments of the fcc lattice grown along the (111) direction, while the polycrystalline structures are characterized by the presence of various fcc and hcp grains. We obtain that the Co chains are defined by a highly stable magnetization direction oriented along the chain axis. However, when three-dimensional wires are considered, we found a strong influence of the local atomic environment on the determination of the easy axis. In fact, we observe strong oscillations of the low energy orientation of the magnetization between the parallel and perpendicular directions as the length of the wire increases or when the geometrical details of the wire caps are modified. In contrast, in the polycrystalline structures, we found that the electronic perturbation introduced by the presence of internal interfaces is more localized in nature. Actually, no spin reorientation transitions are found for different microstructures; however, reduced energy differences (compared to uniform single-crystal wires with approximately the same length) between the parallel and perpendicular directions are obtained. Finally, the existence of internal interfaces can induce appreciable perturbations in the density of states around the Fermi energy and, as a consequence, they are expected to modify the number of conduction channels as well as the transport properties of the wires.

Effects of effective mass discontinuity on the conductance of three-dimensional quantum wires

We calculate the conductance of three-dimensional semiconductor quantum wires considering different effective masses in the contacts and in the channel. We show that, with respect to the case with equal masses in the channel and in the contacts, the amplitude of the conductance oscillations increases if the electron effective mass in the channel is larger and decreases if it is smaller than in the contacts. Effects on the density of probability are also shown. These effects of the effective mass discontinuity are explained in terms of kinetic confinement and transmission coefficient modulation.

Fully Quantum Mechanical Simulations of Gated Silicon Quantum Wire Structures: Investigating the Effects of Changing Wire Cross-Section on Transport

We present transport simulations of three-dimensional (3D) silicon quantum wires in which electron-phonon scattering is incorporated via local modifications to the potential encountered by the electron waves. Computing resistance as a function of wire length, we find that the effects of dissipation essentially take hold immediately, and are apparent right from the point at which the wire is long enough to act as a true waveguide.

Thermopower of three-dimensional quantum wires and constrictions

The thermopower of asymmetrical quantum wires and constrictions in an arbitrarilydirected magnetic field is investigated. An analytic expression convenient for analysing thethermopower is obtained. The oscillations in the thermopower are studied. It is shown thatthe thermopower as a function of a magnetic field can undergo Aharonov–Bohm andShubnikov–de Haas oscillations.

Shape effects on scattering in three-dimensional quantum wires

We study the effects of the shape of the cross section of a three-dimensional quantum wire on electron scattering from a single point defect in the wire. The confinement of electrons is modeled by both hard- and soft-wall potentials. We find that as the degree of anisotropy of the cross section of the wire is increased intersubband electron scattering is enhanced and intrasubband transmission is suppressed making it appear as though the defect has stronger impact on electron scattering for asymmetric cross sections. Also, increasing the anisotropy of the cross section results in a decrease of the values of the conductance. Furthermore, for the soft-wall confinement the conductance as a function of Fermi energy rises faster than the conductance for the hard-wall confinement. We use the Lippmann–Schwinger equation of scattering theory in order to calculate analytically the transmission coefficients.

Magnetic properties of nanostructured wires deposited on the side edge of patterned thin film

In the present study, magnetic nanowires with various cross-sectional dimensions have been fabricated by evaporating a magnetic material on the side edges of the patterned nonmagnetic thin film. The method allows the lengths of the two short axes to be defined precisely by controlling the thickness of the oxide (Wx) and magnetic material (Wy). The MFM images of the produced Co wires (2 μm length) with dimensions of Wx=Wy=200 nm and Wx=Wy=50 nm present the single domain configuration. The MFM and magnetoresistance (MR) measurement demonstrate that the longitudinal magnetization switching field increases with the decrease of Wx and Wy, which becomes 1.3 kOe for wires with Wx=Wy=50 nm. The profile of the MR hysteresis suggests that considerable coherent rotation takes place before the irreversible longitudinal switching. Transverse saturation fields larger than 6 kOe were measured in the orthogonal two short axis directions, which confirms the successful fabrication of three-dimensional wires with comparable cross-sectional dimensions.

Force, charge, and conductance of an ideal metallic nanowire

The conducting and mechanical properties of a metallic nanowire formed at the junction between two macroscopic metallic electrodes are investigated. Both two- and three-dimensional wires with a W(ide)-N(arrow)-W(ide) geometry are modelled in the free-electron approximation with hard-wall boundary conditions. Tunneling and quantum-size effects are treated exactly using the scattering matrix formalism. Oscillations of order E_F/lambda_F in the tensile force are found when the wire is stretched to the breaking point, which are synchronized with quantized jumps in the conductance. The force and conductance are shown to be essentially independent of the width of the wide sections (electrodes). The exact results are compared with an adiabatic approximation; the later is found to overestimate the effects of tunneling, but still gives qualitatively reasonable results for nanowires of length L>>lambda_F, even for this abrupt geometry. In addition to the force and conductance, the net charge of the nanowire is calculated and the effects of screening are included within linear response theory. Mesoscopic charge fluctuations of order e are predicted which are strongly correlated with the mesoscopic force fluctuations. The local density of states at the Fermi energy exhibits nontrivial behavior which is correlated with fine structure in the force and conductance, showing the importance of treating the whole wire as a mesoscopic system rather than treating only the narrow part.

Nonlinear magnetoconductance of nanowires

Quantum magnetoconductance properties of three-dimensional nanowires are studied in the nonlinear (finite-voltage) regime. In the absence of a magnetic field a finite applied voltage leads to the appearance of new plateaus in the differential conductance of the wires, as well as shifts in the locations of the conductance steps. For wires that are symmetric with respect to the plane of the narrowest cross section the new plateaus are characterized by heights that are integer multiples of ${e}^{2}/h.$ When placed in a longitudinal magnetic field the conductance as a function of the field strength, and, in particular, magnetic-field-induced switching between quantized conductance levels, can be similarly affected by an applied-finite voltage. This indicates possible experimental control of quantum transport in three-dimensional wires by external fields.

Reflection and Transmission Coefficients for Two- and Three-Dimensional Quantum Wires

The problem of a quantum wire connected smoothly on both sides to leads of variable cross section is studied. A method for solving this problem in terms of a set of nonlinear first order matrix differential equations for the variable reflection amplitude is discussed. The reflection coefficient obtained in this way is directly related to the conductivity, and is calculated as a function of the energy of the ballistic electrons. This formulation can be applied to three-dimensional as well as two dimensional quantum wires. For two specific cases the reflection coefficient is obtained as a function of the wave number of the incident electron, and the contribution of quantum tunneling to the transmission in each case is demonstrated. Also a model with a dissipative force is introduced and its effect on the transmission of the electrons is investigated.

Surface processes and phase diagrams in MBE growth of [formula omitted] heterostuctures

The recent results of development and application of MBE methods for direct growth (self-organization or spontaneous formation) of the heterostructures Ge x Si 1−x Si are discussed. The heterostructures involve nanoobjects confined in two- or three-dimensional quantum-sized boxes or wires. The influence of substrate temperature, film composition and thickness on the structure and the surface morphology of the growing film were studied. Particular attention was paid to the surface structure evolution of Ge x Si 1− x heteroepitaxial films growing on Si(111)7 × 7 and Si(001)2 × 1 substrates over a wide range of concentrations x and growth temperatures. The quantum-sized islands can be self-organized after achievement of the critical thickness of the pseudomorphic layer; the critical thickness can be calculated in terms of the Frank-van der Merwe theory (when the Stranski-Krastanov growth mechanism is achieved). It was shown that with respect to the electronic properties, such films demonstrate the behavior of quantum boxes in which a zero-dimensional electron (hole) gas is localized. A number of heteroepitaxial structures with Ge quantum boxes in a tunnel-thin Si layers are grown by MBE and investigated.

Bound states in three-dimensional quantum wires

We have studied two different cylindrical waveguides with variable cross sections as models for quantum wires. By expanding the total wavefuction in terms of the Bessel function we have obtained an infinite set of coupled equations for the partial wave amplitude. In our models, bound states are present only in the lowest partial wave. For a simple bulge we have obtained the lowest eigenvalues, and for periodic waveguide we have found the width of the energy band.

Calculation of the residual resistivity of three-dimensional quantum wires.

Calculation of the residual resistivity of three-dimensional quantum wires.