Diameter Of Nanowires Research Articles

Nanowire Tunnel Field Effect Transistors at High Temperature

The aim of this work is to study how the performance of nanowire tunnel field effect transistors (TFETs) is influenced by temperature variation. First of all, simulated energy band diagrams were presented to justify its fundamental working principle and this analysis was compared to experimental data obtained for temperature ranging from 300 to 420 K. This methodology was performed for different nanowire diameters and bias conditions, leading to a deep investigation of parameters such as the ratio of on-state and off-state current (ION/IOFF) and the subthreshold slope (S). Three different transport mechanisms (band-to-band tunneling, Shockley-Read-Hall generation/recombination and trap-assisted tunneling) were highlighted to explain the temperature influence on the drain current. As the final step, subthreshold slope values for each configuration were compared to the room temperature. Therefore, it was observed that larger nanowire diameters and lower temperatures tended to increase ION/IOFF ratio. Meanwhile, it was clear that band-to-band tunneling prevailed for higher gate voltage bias, resulting in a much slighter temperature effect on the drain current.

Condensing of silver nanowire with polyacetylene to the core-shell nanocluster

In this paper, condensing silver nanowire with polyacetylene to the core-shell nanocluster is demonstrated using a molecular dynamic simulation. The simulation results display that the silver nanowire can be condensed by polyacetylene to form a nanocluster and a perfect and stable core-shell configuration is exhibited finally. The thickness of silver nanowire influences the formation of nanocluster. When the nanowire is fine, the structure of nanowire changes to nanocluster induced by polyacetylene. However, when the nanowire is wide enough, the structure of silver nanowire remains unchanged in the whole process. Through the whole process, the van der Waals force plays a significant role in the fabrication of the polyacetylene/silver nanocluster core-shell composite nanostructures. Furthermore, some effect factors such as the length of silver nanowire, the diameter of silver nanowire, the chain number of silver nanowire and the length of polyacetylene are also elaborated. Moreover, the other formed metal nanoclusters (copper, gold, nickel, platinum and iron) which are induced by polyacetylene are also discussed.

Modelling and Measurement of Magnetically Soft Nanowire Arrays for Sensor Applications

Soft magnetic wires and microwires are currently used for the cores of magnetic sensors. Due to their low demagnetization, they contribute to the high sensitivity and the high spatial resolution of fluxgates, Giant Magnetoimpedance (GMI), and inductive sensors. The arrays of nanowires can be prepared by electrodeposition into predefined pores of a nanoporous polycarbonate membrane. While high coercivity arrays with square loops are convenient for information storage and for bistable sensors such as proximity switches, low coercivity cores are needed for linear sensors. We show that coercivity can be controlled by the geometry of the array: increasing the diameter of nanowires (20 µm in length) from 30 nm to 200 nm reduced the coercivity by a factor of 10, while the corresponding decrease in the apparent permeability was only 5-fold. Finite element simulation of nanowire arrays is important for sensor development, but it is computationally demanding. While an array of 2000 wires can be still modelled in 3D, this is impossible for real arrays containing millions of wires. We have developed an equivalent 2D model, which allows us to solve these large arrays with acceptable accuracy. Using this tool, we have shown that as a core of magnetic sensors, nanowires are efficiently employed only together with microcoils with diameter comparable to the nanowire length.

Welding deformations of welded joints between 1D Ag nanowire connectors and 3D substrates: a molecular dynamics study

In order to enrich the understanding of the relationship between 1D and 3D Ag nanomaterials in welding deformation, molecular dynamics simulations were performed to study a common structure of welded joints in Ag nanowire (NW) connectors on Ag substrates. The effects of the overlapping length, welding temperature and NW diameter on welding strength, dislocation and atomic strain were investigated, with the aim of understanding welding deformations of welded joints. With the increase in the overlapping length, welding temperature and NW diameter, the welding strength increases while the increment decreases. Dislocations can be reduced by increasing the overlapping lengths, NW diameters and annealing time. Moreover, the welded joint performance in shear strength could be improved by performing thermal annealing or decreasing NW diameters. The coordination number, residual stress and energy variation have also been analyzed to explain the above phenomenon. This work can provide guidance for the welding of nanomaterials with different dimensions.

Far-field optical imaging of surface plasmons with a subdiffraction limited separation.

When an ultrathin silver nanowire with a diameter less than 100 nm is placed on a photonic band gap structure, surface plasmons can be excited and propagate along two side-walls of the silver nanowire. Although the diameter of the silver nanowire is far below the diffraction limit, two bright lines can be clearly observed at the image plane by a standard wide-field optical microscope. Simulations suggest that the two bright lines in the far-field are caused by the unique phase distribution of plasmons on the two side-walls of the silver nanowire. Combining with the sensing ability of surface plasmons to its environment, the configuration reported in this work is capable of functioning as a sensing platform to monitor environmental changes in the near-field region of this ultrathin nanowire.

Inherent Dipole Layer Formation Driven by Surface Energy at Nonplanar Dielectric Interface

This work investigates the correlation between dipole formation and surface energy at a nonplanar dielectric interface on a Si nanowire (NW) by means of molecular dynamics simulations. According to the atom and charge distribution obtained by simulations, the built-in electric field and potential are calculated at the dielectric interface based on the Poisson equation. It is found that the built-in potential is dependent on the diameter of the Si NW, which is attributed to the dependence of the surface energy difference on the surface curvature of the dielectric heterointerface, driving atom diffusion and leading to a dipole layer at the interface. The impact of the built-in potential on the threshold voltage of a transistor with a multigate configuration is discussed as well.

Study of Wurtzite Crystal Phase Stabilization in Heterostructured Ga(As,P) Nanowires

GaP as well as GaAs has face-centered cubic crystal phase at standard conditions. Despite it, GaP and GaAs nanowires frequently grow in a metastable hexagonal crystal phase called wurtzite. In this work, stable growth of GaP nanowire in the metastable phase is explained by accounting the elastic strain in the nucleus of a new layer. Crystal phase switch in heterostructured Ga(As,P) nanowire caused by heterointerface was studied theoretically and experimentally. Length of wurtzite segment after the switch of crystal phase linearly increases with nanowire diameter. Such dependence can not be explained by only kinetically driven effects. We consider such dependence as an evidence of elastic strain stabilization of the metastable phase in nanowires.

Structural, morphological and magnetic properties of compositionally modulated CoNi nanowires

Ferromagnetic nanowires (NWs) are novel materials that offer unique magnetic properties, as the geometrical dimensions become comparable to key length scales in magnetism, such as the exchange length or the domain wall width. In this work, compositionally modulated Co1−xNix nanowires (diameter 10–15 nm) with high coercivity have been synthesized via a thermal decomposition method. The structural analysis demonstrates that the hexagonal close-packed (hcp) crystal structure and the wire-shape morphology are maintained up to Ni content of x = 0.3. Based on the shape anisotropy and orientation, the aligned Co1−xNix nanowire assemblies show that the coercivity at room temperature decreases from 11.4 to 5.4 kOe with increasing x from 0 to 0.3. The monotonous decrease in coercivity with Ni content is related to the effective magnetic anisotropy and nanowire diameter which are found to be strongly varied with Ni addition. In addition, it is found that the increase of Ni content in the nanowires brings more resistance to oxidation than the pristine Co nanowires. The exchange bias study indicates that the Ni addition leads to lower blocking temperature of the CoNiO grains and consequently the switch-on temperature for the exchange bias field shifts to low temperatures with the increase of Ni content. Further, the exchange bias behavior that is associated with the existence of antiferromagnetic and spin-glass-like states are confirmed by temperature-dependent magnetization measurements.

(Invited) Vertical Gate All Around GeSn/Ge Heterostructure Transistors

In this paper we present our recent research on vertical GeSn/Ge heterojunction gate all around (GAA) nanowire pMOSFETs. The vertical nanowires were fabricated with a diameter as small as 20 nm. Our experimental results demonstrate that scaling of the nanowire diameter improves the device performance in terms of subthreshold swing, drain induced barrier lowering (DIBL) and Ion/Ioff ratio due to the better gate controllability. However, one of the big challenges for vertical nanowire transistors is the nanowire top contact resistance. Due to the very small contact area the nanowire contact resistance dominates the series source/drain resistance. The contact resistance can be lowered by optimized NiGeSn and NiGe contacts. Compared to vertical Ge homojunction nanowire GAA FETs, the utilization of GeSn as source can significantly lower the source/drain resistance. The band engineering of GeSn/Ge heterojunction for device improvement will be discussed in the paper.

1D to 2D Transition in Tellurium Observed by 4D Electron Microscopy.

A new microwave-enhanced synthesis method for the production of tellurium nanostructures is reported-with control over products from the 1D regime (sub-5nm diameter nanowires), to nanoribbons, to the 2D tellurene regime-along with a new methodology for local statistical quantification of the crystallographic parameters of these materials at the nanometer scale. Using a direct electron detector and image-corrected microscope, large and robust 4D scanning transmission electron microscopy datasets for accurate structural analysis are obtained. These datasets allow the adaptation of quantitative techniques originally developed for X-ray diffraction (XRD) refinement analyses to transmission electron microscopy, enabling the first demonstration of sub-picometer accuracy lattice parameter extraction while also obtaining both the size of the coherent crystallite domains and the nanostrain, which is observed to decrease as nanowires transition to tellurene. This new local analysis is commensurate with global powder XRD results, indicating the robustness of both the new synthesis approach and new structural analysis methodology for future scalable production of 2D tellurene and characterization of nanomaterials.

Raman study of germanium nanowires formed by low energy Ag+ ion implantation

Porous Ge layers of nanowires were formed by low energy (30 keV) Ag+ ion implantation of crystalline c-Ge substrate. Different radiation doses resulted in the formation of nanowires with various mean diameters. The obtained layers were studied by Raman spectroscopy using helium-neon and argon exciting lasers at wavelength of 633 and 488 nm respectively. It was demonstrated that implanted amorphous layers were locally crystallized by the lasers. The crystallization thresholds were found to be 3 kW/cm2 for helium-neon exciting laser and 1 kW/cm2 for argon exciting laser. The variation of thresholds is suggested to be due to the different light penetration depths at these wavelengths in Ge. The crystalline volume fraction was determined and reached maximum value of 6–7%, the divergence of which can be explained by the difference in the distribution of Ge nanowire diameters.

Room temperature detection of NO2 gas under UV irradiation based on Au nanoparticle-decorated porous ZnO nanowires

ZnO nanowires were prepared by oxidized ZnS nanowires. The sensing performance of these ZnO nanowires for NO2 gas was enhanced by decorating Au nanoparticles on their surface. The scanning electron microscopy results revealed that diameter and length of the ZnO nanowires showed 150–200 nm and up to a few hundreds of μm, respectively. The diameters of Au nanoparticles which were decorated on the ZnO nanowires were 5–20 nm and they were distributed evenly on the surface of the nanowires. The transmission electron microscopy results revealed that the ZnO nanowires obtained after 2 h of the oxidation treatment process were composed of lots of nanograins with a diameter of 50–100 nm, which rendered the surface of the nanowires rough and full of void spaces. The hierarchical structure of the nanowires increased their surface-to-volume ratio and contributed to the adsorption of gas on their surface, improving their sensing performance. In this study, the NO2 gas sensing mechanism of the Au nanoparticle-decorated ZnO nanowires sensors were investigated under UV illumination at room temperature.

Large-Scale Synthesis of Highly Uniform Silicon Nanowire Arrays Using Metal-Assisted Chemical Etching.

The combination of metal-assisted chemical etching (MACE) with colloidal lithography has emerged as a simple and cost-effective approach to nanostructure silicon. It is especially efficient at synthesizing Si micro- and nanowire arrays using a catalytic metal mesh, which sinks into the silicon substrate during the etching process. The approach provides a precise control over the array geometry, without requiring expensive nanopatterning techniques. Although MACE is a high-throughput solution-based approach, achieving large-scale homogeneity can be challenging because of the instability of the metal catalyst when the experimental parameters are not set appropriately. Such instabilities can lead to metal film fracture, significantly damaging the substrate and thus compromising the nanowire array quality. Here, we report on the critical parameters that influence the stability of the metal catalyst layer for achieving large-scale homogeneous MACE: etchant composition, metal film thickness, adhesion layer thickness, nanowire diameter and pitch, metal film coverage, Si/Au/etchant interface length, and crystalline quality of the colloidal template (grain size and defects). Our results investigate the origin of the catalyst film fracture and reveal that MACE experiments should be optimized for each Si wire array geometry by keeping the etch rate below a certain threshold. We show that the Si/Au/etchant interface length also affects the etch rate and should thus be considered when optimizing the MACE experimental parameters. Finally, our results demonstrate that colloidal templates with small grain sizes (i.e., <100 μm2) can yield significant problems during the pattern transfer because of a high density of defects at the grain boundaries that negatively affects the metal film stability. As such, this work provides guidelines for the large-scale synthesis of Si micro- and nanowire arrays via MACE, relevant for both new and experienced researchers working with MACE.

GaN Nanowire Array for Charge Transfer in Hybrid GaN/P3HT:PC71BM Photovoltaic Heterostructure Fabricated on Silicon.

We demonstrate that a GaN nanowire array can be used for efficient charge transfer between the organic photovoltaic layer and silicon in a Si/GaN/P3HT:PC71BM inverted hybrid heterostructure. The band alignment of such a material combination is favorable to facilitate exciton dissociation, carrier separation and electron transport into Si. The ordered nature of the GaN array helps to mitigate the intrinsic performance limitations of the organic active layer. The dependence of photovoltaic performance enhancement on the morphology of the nanostructure with nanowire diameters 30, 50, 60, 100 and 150 nm was studied in detail. The short circuit current was enhanced by a factor of 4.25, while an open circuit voltage increase by 0.32 volts was achieved compared to similar planar layers.

Multi-scale analysis of aligned ZnO nanowires reinforced hybrid composites under three-point bending

ABSTRACT This paper presents novel multi-scale modeling and failure analysis of hybrid carbon fiber reinforced polymer (CFRP) composites enhanced by zinc oxide (ZnO) nanowires. Vertically aligned ZnO nanowires on CFRP plies create enhancement layers, leading to the increased interfacial properties in composites. A multi-scale model bridging from micro-scale to macro-scale investigates the enhanced interlaminar shear properties in the hybrid composite. At the micro-scale, the effective material properties of the enhancement layer are extracted by the homogenization of an appropriate representative volume element. At the mesoscale, the cohesive zone model is employed to investigate the adhesion bonding and the delamination between the plies. At the macro-scale, the progressive intralaminar failure analysis is developed to explore damage initiation and evolution in fiber and matrix utilizing the user subroutine to define material behavior (VUMAT). Finite element analysis of a three-dimensional hybrid composite short beam under three-point bending (3PB) load is performed to extract the damage behavior. Numerical results demonstrate that interlaminar shear strength of the hybrid CFRP composites is improved by 43% under 3PB load. The effect of diameter and length of ZnO nanowires on the shear strength of the hybrid laminated structure is discussed.

Directed Self-Assembly of Block Copolymers for the Fabrication of Functional Devices.

Directed self-assembly of block copolymers is a bottom-up approach to nanofabrication that has attracted high interest in recent years due to its inherent simplicity, high throughput, low cost and potential for sub-10 nm resolution. In this paper, we review the main principles of directed self-assembly of block copolymers and give a brief overview of some of the most extended applications. We present a novel fabrication route based on the introduction of directed self-assembly of block copolymers as a patterning option for the fabrication of nanoelectromechanical systems. As a proof of concept, we demonstrate the fabrication of suspended silicon membranes clamped by dense arrays of single-crystal silicon nanowires of sub-10 nm diameter. Resulting devices can be further developed for building up high-sensitive mass sensors based on nanomechanical resonators.

Direct Three-Dimensional Imaging of an X-ray Nanofocus Using a Single 60 nm Diameter Nanowire Device

Nanoscale X-ray detectors could allow higher resolution in imaging and diffraction experiments than established systems but are difficult to design due to the long absorption length of X-rays. Here, we demonstrate X-ray detection in a single nanowire in which the nanowire axis is parallel to the optical axis. In this geometry, X-ray absorption can occur along the nanowire length, while the spatial resolution is limited by the diameter. We use the device to make a high-resolution 3D image of the 88 nm diameter X-ray nanofocus at the Nanomax beamline, MAX IV synchrotron, by scanning the single pixel device in different planes along the optical axis. The images reveal fine details of the beam that are unattainable with established detectors and show good agreement with ptychography.

Effect of Interactions and Non-uniform Magnetic States on the Magnetization Reversal of Iron Nanowire Arrays

Ordered ferromagnetic nanowire arrays are widely studied due to the diversity of possible applications. However, there is still no complete understanding of the relation between the array’s parameters and its magnetic behavior. The effect of vortex states on the magnetization reversal of large-diameter nanowires is of particular interest. Here, we compare analytical and micromagnetic models with experimental results for three arrays of iron nanowires with diameters of 33, 52 and 70 nm in order to find the balance between the number of approximations and resources used for the calculations. The influence of the vortex states and the effect of interwire interactions on the remagnetization curves are discussed. It has been found that 7 nanowires treated by a mean field model are able to reproduce well the reversal behavior of the whole array in the case of large diameter nanowires. Vortex states tend to decrease the influence of the structural inhomogeneities on reversal process and thus lead to the increased predictability of the system.

Adsorption effect of NO2 on ZnO (100 nm) nanowires, leading towards reduced reverse leakage current and voltage enhancement

Here, we report the adsorption effect of NO2 on ZnO (100 nm) nanowires. We have studied the effect of adsorbed NO2 molecules on ZnO nanowire-based energy harvester for an exposure time of 1, 2, 3, 4, 5 and 6 h in a sealed chamber at 50 ppm which yielded piezoelectric voltage of 543.6 mV, 834.6 mV, 1.071 V, 1.78 V, 1.969 V and 2.835 V, respectively. We have thoroughly investigated the behaviour of ZnO nanowires in the presence of NO2 and observed a maximum output piezoelectric voltage of 2.835 V with a power density 158.2 mW cm−2. This is the first time that ZnO-based piezoelectric energy harvester is being used for the voltage enhancement in the presence of NO2. We have used vertically integrated nanowire generator (VING) structure. X-ray diffraction pattern revealed the growth orientation of ZnO nanowires were along the c-axis from the substrate. ZnO nanowires were grown on indium tin oxide-coated polyethylene terephthalate substrates via a hydrothermal route. Surface morphology has been examined by scanning electron microscopy images and diameter of ZnO nanowires was found to be around 100 nm. Piezoelectric voltage has been generated by the VING by applying minute external force of ~50 nN. Periodic output voltage peaks were being measured by picoscope 5204.

Regulation of substrate surface topography on differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) have been extensively used in the field of tissue engineering and regenerative medicine. The effect of surface properties on the differentiation of MSCs is a very important issue for the design and fabrication of scaffolds or biomaterials. This review is mainly focused on the morphological or topographic characteristics of cell adhesion substrate, i.e. cell area and shape for individual cell, cell density and cell–cell contact for multiple cells, substrate roughness, ridge width, micropillar height, nanoparticle diameter and aspect ratio of nanowire. The results from different studies were quantitatively analyzed using comparable or unified parameters and definitions under the specific experimental conditions such as cell source, culture time, induction medium, matrix material and differentiation marker. Some interesting phenomena and properties were discovered by this integrated and systematic analysis, which might give insights into the regulatory mechanism of surface morphology or topography on MSCs differentiation.