Zigzag Wires Research Articles

Layer-by-Layer Assemblies of Coordinative Surface-Confined Electroactive Multilayers: Zigzag vs Orthogonal Molecular Wires with Linear vs Molecular Sponge Type of Growth

Surface-anchored coordination-based molecular assemblies (CBMA) are very powerful tools for the design of modern materials. The CBMAs were created using bis-terpyridine–iron coordination chemistry by the alternation of linear or bent bis-terpyridine ligands and Fe(II) metal centers. The coordination of the bent ligand results in the formation of zigzag structures that experience linear growth with each successive deposition step. Interestingly, the deposition of the linear ligand has two distinct steps. During the first four deposition cycles, the thickness and iron uptake (surface coverage) of the multilayer change similarly to ones of the bent ligand based multilayer. However, during the following deposition cycles, the linear ligand based multilayer demonstrates significantly higher growth rate. This unusual behavior might be attributed with the reorganizational transformations leading to a higher organizational level of the assembly. As a result, a part of templating layer molecules, which due to ster...

Geometric Shape Regulation and Noncovalent Synthesis of One-Dimensional Organic Luminescent Nano-/Micro-Materials

Noncovalent synthesis of one-dimensional (1D) organic nano-/micro-materials with controllable geometric shapes or morphologies and special luminescent and electronic properties is one of the greatest challenges in modern chemistry and material science. Control of noncovalent interactions is fundamental for realizing desired 1D structures and crucial for understanding the functions of these interactions. Here, a series of thiophene-fused phenazines composed of a halogen-substituted π-conjugated plate and a pair of flexible side chains is presented, which displays halogen-dependent 1D self-assemblies. Luminescent 1D twisted wires, straight rods, and zigzag wires, respectively, can be generated in sequence when the halogen atoms are varied from the lightest F to the heaviest I. It was demonstrated that halogen-dependent anisotropic noncovalent interactions and mirror-symmetrical crystallization dominated the 1D-assembly behaviors of this class of molecules. The methodology developed in this study provides a potential strategy for constructing 1D organic materials with unique optoelectronic functions.

Transport properties of exchange biased mesoscale wires

The magnetic field dependence of the anisotropic magneto-resistance (AMR) was measured in exchange biased straight and zigzag CoFe wires. The field dependent AMR of the zigzag wires is modeled as a superposition of the AMR of the straight wires. Micromagnetic simulations of the system provided additional information on the magnetization in the straight and zigzag wires.

Shape Control of Periodic Metallic Nanostructures for Transparent Conductive Films

The transmittance limitations of metallic nanomeshes with hexagonally ordered perforations that are typically prepared by conventional nanosphere lithography (NSL) were demonstrated. Specially, the optoelectronic properties of perforated metallic films with continuously varying morphologies, ranging from spherical apertures to egg-shaped apertures, zigzag wires and approximate straight wires to metallic crosswire grids, are investigated, shedding light on the dependence of the optoelectronic properties on subtle changes of the film morphology especially on its periodicity. Further, to exploit both the high transmittance of these nanowires and the low sheet resistance of the nanomesh, we have developed a novel transparent metal electrode composed of two overlapping nanowire arrays via a stepwise ARNSL method. This sophisticated electrode has an increased optoelectronic performance with a sheet resistance of 100 ω sq and an average optical transmittance of 80% and is hopeful to be further improved. The stepwise ARNSL method addresses the challenges of fabricating intercrossed pattern from parallelly aligned conductive wires arrays, which are significant in constructing nanowire devices. These findings provide useful insights in the design and fabrication of unique 2D metallic electrodes for potential high-performance transparent electrode application in the transparent electronics.

The effect of semi-infinite crystalline electrodes on transmission of gold atomic wires using DFT

First principle calculations of the conductance of gold atomic wires containing chain of 3–8 atoms each with 2.39Å bond lengths are presented using density functional theory. Three different configurations of wire/electrodes were used. For zigzag wire with semi-infinite crystalline electrodes, even–odd oscillation is observed which is consistent with the previously reported results. A lower conductance is observed for the chain in semi-infinite crystalline electrodes compared to the chains suspended in wire-like electrode. The calculated transmission spectrum for the straight and zig-zag wires suspended between semi-infinite crystalline electrodes showed suppression of transmission channels due to electron scattering occurring at the electrode-wire interface.

Domain Structure and Magnetoresistance in Co2MnGe Zigzag Structures

We report a clear manifestation of the negative contribution to the magnetoresistance due to domain walls in Co2MnGe-Heusler submicron zigzag wires in which the domain structure, domain size and domain wall density can be well controlled. The magnetic behavior of these systems results from the interplay between the intrinsic magneto-crystalline (K4) anisotropy, growth induced uniaxial (KU = 4.7x103 J/m3) anisotropy and shape anisotropy (KS), as observed by magnetic-force microscopy (MFM) and longitudinal Kerr hysteresis loop measurements. Magnetoresistance measurements were performed by the four-point method under a field applied in the plane of the wires at a temperature of 300K. In these structures, domain wall-creation and annihilation occur in a coherent way. As a result, clear jumps of the resistance are detected during the transition from single-domain- to multi-domain states. At room temperature a value RDW = -2.5 mΩ was obtained; this result is the same order of magnitude as other experimental and theoretical findings. The negative resistive contribution due to the domain wall is also discussed and compared with the existing theoretical models.

Suppression of Parallel Plate Modes in Low Frequency Microstrip Circuit Packages Using Lid of Printed Zigzag Wires

This work deals with the suppression of parallel plate and cavity modes in shielded microstrip circuits operating at the lower microwave frequency range. The suppression is achieved by using a lid made of zigzag wires printed periodically on narrow slices of ungrounded circuit boards, located vertically side by side. This structure is very compact both in periodicity and height, it suppresses cavity modes over about an octave 2:1 bandwidth, and it does not interfere with the packaged microstrip circuit.

Design principle for increasing charge mobility of π-conjugated polymers using regularly localized molecular orbitals

The feasibility of using π-conjugated polymers as next-generation electronic materials is extensively studied; however, their charge mobilities are lower than those of inorganic materials. Here we demonstrate a new design principle for increasing the intramolecular charge mobility of π-conjugated polymers by covering the π-conjugated chain with macrocycles and regularly localizing π-molecular orbitals to realize an ideal orbital alignment for charge hopping. Based on theoretical predictions, insulated wires containing meta-junctioned poly(phenylene–ethynylene) as the backbone units were designed and synthesized. The zigzag wires exhibited higher intramolecular charge mobility than the corresponding linear wires. When the length of the linear region of the zigzag wires was increased to 10 phenylene–ethynylene units, the intramolecular charge mobility increased to 8.5 cm2 V−1 s−1. Theoretical analysis confirmed that this design principle is suitable for obtaining ideal charge mobilities in π-conjugated polymer chains and that it provides the most effective pathways for inter-site hopping processes.

Starting Point of Cluster-Derived Silicon Nanowires

The assembly of medium-sized silicon nanoclusters was simulated to study the starting point of the formation of cluster-derived silicon nanowires (CDSiNWs). Hydrogen-terminated clusters were found repulsing each other and inter-connecting through the hydrogen bonds, thus could not form a stable silicon nanowire (SiNW). Between the pristine silicon clusters without hydrogen saturation, the assembly takes place automatically. An orientation priority in cluster assembly is obtained, as silicon clusters Si29 are more possibly adhered along direction than the other directions. Such an assembly may be the starting point of the SiNW growth along direction. Moreover, it indicates the possibility of silicon tetrapods or zigzag wires formation, besides straight SiNWs.

Electronic and vibrational properties of vanadium-carbide nanowires

We have made an effort to understand the properties of transition metal carbide nanowires (NWs) and studied vanadium-carbide (VC) nanowires as a specific case. Different structures have been considered and their electronic and vibrational properties studied employing density functional theory. The effect of dimensionality is very well brought forth by these NWs, narrow/thinner structures have clear preference for magnetic state with sizeable magnetic moment at the V sites. As the thickness/width increases, the margin decreases and the magnetic moment disappears altogether for structures like square and rectangular NWs. The cohesive energy per atom increases with the increase in lateral dimensions of the NW, and it is about 88% of the bulk value for the rectangular NW, while it is only 50% for the linear chain. All the wires are conducting in nature, with the linear and zigzag wires having half-metallic character. Our calculations show that the V atoms decide the electronic and magnetic properties in these while compressibility, a mechanical property, is governed by the C atoms. The electron localization function beautifully illustrates the closeness of thicker/wider NWs to the bulk. It also reveals that electrons are highly localized around C atoms; however, the amount of charge transferred depends strongly on the structure of wire. The optical properties unfurl the impact of different spatial expanse in the cross section of NW in a nice way, e.g., ε2xx > ε2yy (ε2 is imaginary part of dielectric function) for all those with a larger expanse along X compared to Y and vice-versa. Thicker nanowires seem to be more suitable for optical applications. Site-resolved phonon density of states shows that presence of C atoms is responsible for high frequency branches. The heat capacity variation for various structures closely follows the magnitude of respective phonon density of states.

Characterization of domain wall–based traps for magnetic beads separation

We characterize the magnetic behavior of an array of magnetic bead traps based on domain walls (DWs) formed in zig-zag permalloy wires patterned on a Si substrate. Using magnetic force and magneto-optical Kerr effect microscopy, we study the nucleation and annihilation of DWs for two different wire widths. Through scanning electron microscopy with polarization analysis, we analyze in detail the magnetization configuration of the DWs in the presence of a magnetic bead previously trapped by the DW stray field. Finally, we patterned the magnetic nanostructures directly on a polydimethylsiloxane (PDMS) substrate, and we show that the functionality of the device is completely maintained. These results pave the way to the integration of DW-based devices in a PDMS lab-on-a-chip system for magnetic bead separation.

Magnetic Wire Traps and Programmable Manipulation of Biological Cells

We present a multiplex method, based on microscopic programmable magnetic traps in zigzag wires patterned on a platform, to simultaneously apply directed forces on multiple fluid-borne cells or biologically inert magnetic microparticles or nanoparticles. The gentle tunable forces do not produce damage and retain cell viability. The technique is demonstrated with T-lymphocyte cells remotely manipulated (by a joystick) along desired trajectories on a silicon surface with average speeds up to 20 microm/s.

Ab initiodensity functional calculations of ferromagnetism in low-dimensional nanostructures: From nanowires to nanorods

We present ab initio spin-density functional calculations of the electronic and magnetic properties of Fe and Ni nanostructures with a geometry varying between a straight linear wire and a three-dimensional nanorod. With decreasing tension along the axis of the nanostructure we find a series of transitions first from dimerized to periodic and zigzag wires, then to a planar triangular stripe, and further to a nanorod consisting of a periodic stacking of triangular antiprims. In all nanostructures atoms are in a high-moment state, with magnetic moments of about 3.1muB for Fe and about 1muB for Ni. A transition to a low-spin or nonmagnetic state is initiated at a fixed critical value of the interatomic distance, independent of dimension and coordination number. The analysis of the electronic structure shows that already for the one-dimensional nanostructures the ratio between exchange splitting and magnetic moment is close to the universal value I=Delta/M=1 eV/muB established for bulk itinerant magnets.

First principle study on the possibilities of magnetism in one-dimensional In and Tl atomic wires with the full-potential linearized augmented plane wave method

Using ab initio total energy calculations with the full-potential linearized augmented plane wave method, the possibilities of magnetism in one-dimensional In and Tl wires were explored and their properties as the function of geometric structures were studied. The results suggest that the linear In and Tl wires show magnetization at the equilibrium bond distance with magnetic moments of 0.71 and 0.67 μB/atom, respectively. Allowing ions to relax, the wires were deformed as zigzag structures, but no dimerization occurs. The zigzag wires also exhibit spontaneous magnetization, although the magnetic moments are lower than those of straight wires.

Domain walls, domain wall transformations and structural changes in permalloy nanowires when subjected to current pulses

AbstractWe report the direct transmission electron microscopy observation of spin structure transformations in nanoscale Permalloy zigzag wires due to Joule heating during the injection of current pulses. This heating is sufficient to overcome the energy barriers separating the different metastable domain wall spin structures. Due to the large energy barriers these are stable and observable at room temperature by off‐axis electron holography and Fresnel imaging. The interaction between different domain walls is probed and the main pinning mechanism is determined to be the edge roughness. In addition to transformations, we also report on thermally assisted domain wall hopping between two pinning sites and structural changes that occur when the samples are subjected to even higher current pulses. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure and magnetism in carbon nanotubes including magnetic wire

We have studied the electronic structure of the carbon nanotubes which include Fe atomic wire with using the density functional theory. As the stable geometries, we obtained the straight and zigzag wires, which have ferromagnetic and antiferromagnetic alignments, respectively. The antiferromagnets consists of the two ferromagnetic dimers which couple in antiparallel alignment. We presents the band dispersions and the density of states for the magnetic nanotubes. The electronic structure at the Fermi level consists of the Fe 3d and C 2pπ states, which shows a strong hybridization between them.

Electronic structure and magnetism of Fe wire in carbon nanotubes

We investigated electronic structures of the carbon nanotube (CNT) which includes Fe atoms using the first-principles molecular dynamics. We obtained the two stable geometries in which the Fe atoms form the zigzag and straight wires, respectively. The zigzag wire, showing the ferromagnetic configuration, is more stable than the straight one in the CNT. The latter has a novel antiferromagnetic configuration, which forms an antiparallel alignment of ferromagnetic dimers.

Ab initio study of the structural, electronic and optical properties of ultrathin bismuthnanowires

The energetics, structural, electronic and optical absorption properties of the bismuth nanowiresBin with n = 1, 6 have been investigated using density functional theory (DFT) in the local densityapproximation (LDA) including the spin–orbit coupling (SOI). The inclusion of the SOIappreciably affects all the physical properties of the wires. The stable structures form fourgroups: the planar structures, the caged configurations, the pyramidal structures and thehelical configurations. This finding may be a guide for the construction of atomicconfigurations of the nanowires possessing a larger number of atoms per unit cell. Themost stable wire configurations are the 5-Bi pentagonal, and the 6-Bi hexagonaland 6-Bi triple zigzag wires, which should be seen in the experiments. All thewires are metallic. The behaviour of the electron states of the second categorystructures is quite near to that of a linear chain where the parabolic bands cross theEF, and the number of the channels available for the electric conduction is large.Thus, one should grow the wire structures falling into the second category forachieving high conduction. For the 5-Bi pentagonal and 6-Bi hexagonal cross-sectionalwires, the number of channels available for the electric conduction are ten andtwelve, respectively. The SOI drastically affects the calculated optical absorption,especially in the low energy region. The absorption peaks are different in terms of thenumber and the energy locations for the different wires, and may be used forthe characterization of the structure of a wire. Our analysis of the calculatedelectronic structure and the optical data of all the studied structures supports theoccurrence of the 4-Bi double and/or 6-Bi triple zigzag chains in the samples ofRomanov.

Magnetism of Zr atomic wires

By using the full-potential linearized augmented plane wave method to perform ab initio total energy calculations, we have explored magnetic ordering in one-dimensional Zr wires. The result shows that Zr can form linear, or dimerized, or zigzag wires and the magnetic properties strongly depend on their geometric structures. The linear and zigzag wires exhibit ferromagnetic ground states at the equilibrium bonding distance, while the dimerized wire, despite its higher stability than that of the linear one, exhibits nonmagnetic ground states. The most stable geometry is shown to be the zigzag wire with a magnetic moment of 0.26 μB per atom.

Quantitative study of magnetoresistance in patterned Ni80Fe20 wires

AbstractThe domain wall resistivity of the patterned Ni80Fe20 zigzag wires has been studied as functions of the number of corners and temperature in zigzag wires. The quantitative ratio of domain wall magnetoresistance (MR) is estimated by two methods. One is the discontinuous jump that represent the domain state sweep between two states in MR curve. The other is the angular dependence on the resistance at remanent state. The ratio of domain wall MR increased when domain wall number density over total wire length (DWs/L) changed from 12/73 to 34/73 with film thickness 40 nm at 10–300 K. Especially, the ratio of domain wall MR decreased slightly as the temperature ranged from 10 to 300 K. The anisotropic magnetoresistance (AMR) has been subtracted in the calculation. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)