Twisted Nanowires Research Articles

Catalyst- and template-free direct electrodeposition of germanium and germanium–tin alloy nanowires from an ionic liquid

Ge and GeSn alloy nanowires exhibit a widely application potential in the fields of nanoscale electronic and optoelectronic devices, furthermore, they are important candidates for anode materials in the next-generation of lithium-ion batteries. Here, a simple catalyst- and template-free technique is proposed for electrodeposition of SnGe nanowires, Ge and GeSn nanowires from ionic liquid. The addition of 0.01 M GeCl4 to the SnCl2/ionic liquid electrolyte is found to inhibit the fractal growth of Sn and form hair-like nanowires with lengths more than 50 μm, while tree-like fractal structures are formed in the absence of GeCl4. The concentration of GeCl4 in the solution greatly affects the morphology of the deposit. Taper and kinked Ge and GeSn nanowires can be directly electrodeposited from ionic liquid, interweaving of these twisted nanowires produces a microporous structure. This method may not only be limited to the preparation of Sn- and Ge-based nanowires, but also be used to prepare other group IV nanowires.

Stacking Engineered Room Temperature Ferroelectricity in Twisted Germanium Sulfide Nanowires

AbstractGroup‐IV monochalcogenides have emerged with immense potential to be used as ferroelectric materials in recent times. However, in most of them, ferroelectricity is limited by the presence of inversion symmetry in their natural crystal structure. Here, an experimental observation of ferroelectric order at room temperature by introducing Eshelby twist in Germanium sulfide (GeS) nanowires is reported. The twisted nanowires are synthesized by low‐pressure chemical vapor deposition. The existence of room temperature ferroelectricity in a single nanowire is confirmed by electrical measurements, piezoelectric force microscopy, and second harmonic generation spectroscopy. Density functional theory calculations reveal that the twist in the GeS nanowires breaks the inversion symmetry where the inversion symmetry breaking phonon modes get hardened giving rise to ferroelectricity. These results are expected to be useful in making non‐volatile memory devices, flexible electronics, electronic sensors, and neuromorphic computing.

Self-assembling twisted nanowires

Self-assembling twisted nanowires

Benzoate ester as a new species for supramolecular chiral assembly.

In this work, a benzoate ester molecule, dodecamethylnonacosane-2,28-diyl dibenzoate (DMNDB), has been discovered as a new species that aggregates into chiral nano-assemblies. In the tetrahydrofuran (THF)/water system, the benzoate ester, DMNDB, could self-assemble into left-handed twisted nanowires, and the most suitable THF/water volume ratio to obtain uniform twisted nanowires was 3 : 7. The driving forces of assembly and the molecular packing type in assemblies for the twisted nanowires were explored, and a possible assembly mechanism was proposed to understand the generation of chiral assemblies. Interestingly, the left-handed nanowires could cross-link and immobilize the solvent in the isopropanol (iPrOH)/water (2 : 8) system to form chiral gels. When the iPrOH/water ratio was increased to 6 : 4, the left-handed nanowires as structural units were found to evolve to right-handed nanofibers. Accordingly, the intermolecular interactions and the molecular packing type also changed with the solvent ratio. What is more, the xerogel could be obtained by drying the gel and left-handed twisted nanowires could form in the THF/water system again, showing the recyclability of chiral nanoassemblies. Also, these DMNDB chiral nanostructures exhibited potential for application in enantioselective separation by co-assembling with tetra-aniline.

One-dimensional twisted and tubular structures of zinc oxide by semiconductor-catalyzed vapor–liquid–solid synthesis

The exploration of unconventional catalysts for the vapor–liquid–solid synthesis of one-dimensional materials promises to yield new morphologies and functionality. Here, we show, for the model ZnO system, that unusual nanostructures can be produced via a semiconductor (Ge) catalyst. As well as the usual straight nanowires, we describe two other distinct morphologies: twisted nanowires and twisted nanotubes. The twisted nanotubes show large hollow cores and surprisingly high twisting rates, up to 9°/μm, that cannot be easily explained through the Eshelby twist model. A combination of ex situ and in situ transmission electron microscopy measurements suggest that the hollow core results from a competition between growth and etching at the Ge–ZnO interface during synthesis. The twisting rate is consistent with a softening of elastic rigidity. These results indicate that the use of unconventional, nonmetallic catalysts provides opportunities to synthesize unusual oxide nanostructures with potentially useful properties.

Aligned Ni nanowires towards highly stretchable electrode

Easy fabrication of super-stretchable electrodes can pave the way for smart and wearable electronics. Using drop casting unidirectional nickel nanowires with polyurethane matrix, we fabricated a super-stretchable film with high electric conductivity. The as-fabricated film can withstand a 300% tensile strain in the direction perpendicular to nanowires, owing to the transformation of percolating nanowire network from 2D to 3D. In contrast to the decreased film conductivities under large tension in most stretchable electrodes, which usually associate with fractures and irreversible deformations, our film conductivity can increase with the applied strain This probably benefits from the enhanced electrical contacts between twisted nanowires under tension The developed super-stretchable film with unprecedented behavior in this work sheds light on the facile fabrication of super-stretchable electrodes with durable performance

Droplet models of cells

New approach based on catalysed crystal growth allowed synthesizing twisted nanowires of van der Waals materials and finely tune their topology.

Growing twisted nanowires

New approach based on catalysed crystal growth allowed synthesizing twisted nanowires of van der Waals materials and fine tuning of their topology.

Analysis of structural distortion in Eshelby twisted InP nanowires by scanning precession electron diffraction

Transmission electron microscopes (TEM) are widely used in nanotechnology research. However, it is still challenging to characterize nanoscale objects; their small size coupled with dynamical diffraction makes interpreting real- or reciprocal-space data difficult. Scanning precession electron diffraction ((S)PED) represents an invaluable contribution, reducing the dynamical contributions to the diffraction pattern at high spatial resolution. Here a detailed analysis of wurtzite InP nanowires (30–40 nm in diameter) containing a screw dislocation and an associated wire lattice torsion is presented. It has been possible to characterize the dislocation with great detail (Burgers and line vector, handedness). Through careful measurement of the strain field and comparison with dynamical electron diffraction simulations, this was found to be compatible with a Burgers vector modulus equal to one hexagonal lattice cell parameter despite the observed crystal rotation rate being larger (ca. 20%) than that predicted by classical elastic theory for the nominal wire diameter. These findings corroborate the importance of the (S)PED technique for characterizing nanoscale materials.

Generation of twisted nanowires with achiral organic amphiphilic copper complexes.

Drying under solvent atmosphere (DUSA) was investigated as an experimental technique to generate self-assembled nanowires and needles from solutions of organic molecules under controlled conditions. Experimental observations of twisted nanowires are reported. These twisted nanowires were obtained by drying of solutions of achiral molecules under solvent controlled atmospheres: achiral, amphiphilic copper complexes were dissolved in an achiral solvent and these solutions were dried under controlled conditions. Two structurally related copper complexes were investigated. Microscopic investigations of the resulting nanowires revealed, and scanning electron microscopy confirmed: self-assembled twisted ribbons could be selectively obtained from one of these compounds. This behavior could be explained by comparing the ratio of the size of the head group and the overall length of the molecules. The occurrence of chiral filaments and chiral phases of nanosegregated filaments are rare in achiral compounds. The occurance of such twisted filaments is thought to be related to symmetry-breaking during a phase transition from liquid crystalline or lyotropic liquid crystalline phases to a nanosegregated phase. In the reported experiments, the concentration of a solution was gradually increased until crystallization occurred. The results clearly show how DUSA can be applied to investigate the capability of achiral substances to yield twisted filaments. Moreover, the investigated compounds had high-enough charge carrier mobilities, such that the twisted filaments obtained are candidates for self-assembled, intrinsically coiled nano-inductivities.

Diffraction from twisted nanowires: helicity revealed by anisotropy

The helical nature of twisted nanowires is studied by simulated X-ray diffraction. It is shown that this helicity is revealed by the anisotropy, which can be both an elastic anisotropy, through the warping displacement generated by torsion, or a shape anisotropy of the cross section. To support the analytical calculations, based on the kinematic theory of diffraction by helices, atomistic simulations of copper nanowires are performed.

Growth of Eshelby twisted ZnO nanowires through nanoflakes & nanoflowers: A room temperature ammonia sensor

Insight into the controlled growth features of nanowires has been in the prominent spotlight for engineering the material properties. Defect and dislocation induced nanowire growth has been emerging as a robust model by dwindling the conventional growth models. In this context, we have proposed a screw dislocated Eshelby twist origin in cationic assimilated ZnO nanowires synthesized via Successive Ionic Layer Absorption and Reaction (SILAR) technique. The growth of twisted nanowires occurred through a subsequent transformation from nanoflakes to nanoflowers. Presence of twist contours in various zone axis pattern provided strong validation of Eshelby origin in twisted nanowires. The preferential plane orientation of (0 0 0 2) confirmed the twisted growth along c-axis orientation. Presence of screw tail at the twisted end of nanowire confirmed the influence of Peach-Kohler force acted on the screw axis. Active vibrational modes and surface defect states of nanoflowers and nanowires were investigated and reported. Twisted ZnO nanowires showed maximum sensing response of 291 towards 100 ppm of ammonia at room temperature with the lowest detection limit of 5 ppm. The response and recovery times were found to be 39 and 17 s. Influence of grain alignment, grain orientation and potential barrier height on ammonia sensing signatures are reported.

Electrical transport properties of an isolated CdS microrope composed of twisted nanowires.

CdS is one of the important II-VI group semiconductors. In this paper, the electrical transport behavior of an individual CdS microrope composed of twisted nanowires is studied. It is found that the current–voltage (I-V) characteristics show two distinct power law regions from 360 down to 60 K. Space-charge-limited current (SCLC) theory is used to explain these temperature- and electric-field-dependent I-V curves. The I-V data can be well fitted by this theory above 100 K, and the corresponding carrier mobility, trap energy, and trap concentration are also obtained. However, the I-V data exhibit some features of the Coulomb blockade effect below 80 K.

Twisted ultrathin silicon nanowires: A possible torsion electromechanical nanodevice

Nanowires have been considered for a number of applications in nanometrology. In such a context, we have explored the possibility of using ultrathin twisted nanowires as torsion nanobalances to probe forces and torques at molecular level with high precision, a nanoscale system analogous to the Coulomb's torsion balance electrometer. In order to achieve this goal, we performed a first-principles investigation on the structural and electronic properties of twisted silicon nanowires, in their pristine and hydrogenated forms. The results indicated that wires with pentagonal and hexagonal cross-sections are the thinnest stable silicon nanostructures. Additionally, all wires followed a Hooke's law behavior for small twisting deformations. Hydrogenation leads to spontaneous twisting, but with angular spring constants considerably smaller than the ones for the respective pristine forms. We observed considerable changes on the nanowire electronic properties upon twisting, which allows to envision the possibility of correlating the torsional angular deformation with the nanowire electronic transport. This could ultimately allow a direct access to measurements on interatomic forces at molecular level.

Effect of quasibound states on coherent electron transport in twisted nanowires

Quantum transmission spectra of a twisted electron waveguide expose the coupling between traveling and quasi-bound states. Through a direct numerical solution of the open-boundary Schr\"odinger equation we single out the effects of the twist and show how the presence of a localized state leads to a Breit-Wigner or a Fano resonance in the transmission. We also find that the energy of quasi-bound states is increased by the twist, in spite of the constant section area along the waveguide. While the mixing of different transmission channels is expected to reduce the conductance, the shift of localized levels into the traveling-states energy range can reduce their detrimental effects on coherent transport.

New properties of halogen plasma-treated Cu films

Abstract Luminescence activity and structure of halogen plasma-treated Cu films on Si substrate have been investigated. Peculiar photoluminescence signals in the range of 1.6 – 2.0 eV were detected both at low (from 77 to 15 K), and at room temperature. The observed luminescence peaks are not present for stoichiometric CuCl. The exposure of CuCl- and CuBr-containing layers to helium plasma, with UV-illumination, result in the formation of knots of twisted nanowires on the surface of these layers. These wires don't have luminescent activity. The accelerated degradation of luminescence of these samples in air in the presence of light illumination and ozone treatment was studied.

Observation of Metal-Layer Stress on Si Nanowires in Gate-All-Around High- $\kappa$/Metal-Gate Device Structures

This letter reports, for the first time, the observation of mechanical stress from metal-gate layer on the Si nanowires formed by the top-down scheme. High-kappa (HfO2 ~ 5 nm) and metal-gate (TaN ~ 100 nm) are evaluated on Si nanowires having ~5-7 nm diameter. While no significant mechanical effect is observed after high-kappa deposition, the TaN metal layer is found to viciously stretch and twist the straight wires. The wire lengths increase significantly (~3%), which suggests that the Si nanowires are subjected to large tensile strain ( > 4 GPa), assuming that the wires obey Hooke's law with Young's modulus ~150 GPa for bulk Si. Interestingly, the twisted nanowires maintained their physical continuity, as demonstrated by the excellent performance of the fully functional gate-all-around MOSFETs fabricated with the wires as channels.