Self-assembly of highly oriented palladium-based nanowires on mica surface

The self-assembly of various nanostructures is recently attracting a great deal of research attention. In this paper, we demonstrate that a palladium chloride aqueous solution, mixed with a proper ammonia solution, can produce Tetra-amminepalladous chloride (Pd(NH₃)₄Cl₂·H₂O) nanowires. These nanowires can spontaneously form the two-dimensional hexagon-oriented Pd(NH₃)₄Cl₂·H₂O arrays on mica surfaces. We can control the length and height of these nanowires by adjusting their deposit time on the mica substrate. This method can be potentially used in making sensors or in making templates to wire and position nanodevices.     

Aqueous synthesis of interconnected ZnO nanowires using spray pyrolysis deposited seed layers

Interconnected ZnO nanowires were grown in a two-stage process, using spray pyrolysis deposited ZnO seed layers as a nucleation platform for subsequent hydrothermal growth. We present a comparison between the effect of these spray pyrolysis deposited seed layers and well-ordered sputter deposited seed layers, along with their respective ZnO nano-morphologies that were obtained via hydrothermal growth. It will be shown that the growth of interconnected ZnO nanowires was influenced by the physical and crystallographic orientations of the underlying seed crystallites. Sputtered seed layers resulted in fairly vertical nanorods which were approximately 80 nm in width, while seed layers deposited by spray pyrolysis resulted in arrays of interconnected ZnO nanowires measuring approximately 15 nm in width.     

Controlled deposition of gold nanowires on semiconducting and nonconducting surfaces

One of the pressing problems in advancing nanoelectronic applications and systems is to develop a simple means of freely connecting at a nanometric level electronic components under ambient conditions without the need for vacuum or electron or ion beam operational steps. Such environments may have detrimental effects on the molecular or biomolecular constituents of molecular electronic circuits. Although there has been defined progress in connecting structures that are of nanometric dimension, new methods in this area of nanotechnology with general applicability add to the arsenal of tools for addressing this standing problem. This paper addresses freely placing under ambient conditions, with fountain pen nanolithography, a 120 nm dimension line of gold nanocolloids deposited with precise registration in a 100 nm gap between two 250 nm wide conducting electrodes patterned by electron beam lithography.     

Pathways for oriented assembly of inorganic crystals at organic surfaces

Oriented inorganic films can be grown under Langmuir monolayers floating on supersaturated aqueous solutions. This process mimics biomineralization, and is potentially an easy method for growing designed inorganic films. Grazing-incidence X-ray diffraction (in situ) and scanning electron microscopy (of films transferred to substrates) reveal that oriented growth occurs via two distinct mechanisms. First, there can be epitaxial growth, with organic and inorganic lattices relaxing to allow an exact match. A variant is the appearance of a reconstructed surface superlattice that mediates between the unstrained organic and bulk inorganic structures. Second, the alignment of crystals already formed can be enhanced via spontaneous self-aggregation into oriented chains.     

Case study: the impact of assembly reorientations on assembly time

Many prior-assembly planners have considered the number of assembly direction reorientations as an assembly sequence evaluation and selection criterion for assembly sequence planning. However, little study has been conducted to evaluate the effectiveness of the selected assembly sequences. This paper studies the impact of assembly direction reorientations on assembly time. Results of the case study show that, for both robot and human operator assembly processes, the number of reorientations in an assembly sequence has a significant impact on assembly time. The results support the study research hypothesis that using an assembly sequence which requires more assembly direction reorientations results in longer assembly time. The study conducted in this paper helps verify and quantify the importance and effectiveness of reducing the number of assembly direction reorientations in assembly sequence planning.     

Influence of the contacting scheme in simulations of radial silicon nanorod solar cells

Silicon nanorod solar cells were simulated using the Silvaco Technical Computer Aided Design (TCAD) software suite. For reasons of speed optimization the simulations were performed in cylinder coordinates taking advantage of the model's symmetry. Symmetric doping was assumed with a dopant density of 10¹⁸ cm⁻³ in the p-type core and in the n-type shell, and the location of the pn-junction was chosen such that the space charge region was located adjacent to the shell surface. Two contact configurations were explored. In configuration A the cathode contact was wrapped around the semiconductor nanorod, while in configuration B the cathode was assumed just on top of the nanorod. In both cases the anode was located at the bottom of the rod. Cell efficiency was optimized with regard to rod radius and rod length. Optimization was performed in a three-step procedure consisting in radius optimization, length optimization and again radius optimization. A maximum in efficiency with respect to rod length L was visible in configuration A, leading to an optimum value of L = 48 μm. This maximum is explained by the combination of an increase of short-circuit current density J_sc and a decrease of open-circuit voltage U_oc with L. In configuration B, J_sc also increases with L, but U_oc stays rather constant and the maximum in efficiency only appears at very large values of L ≈ 12 mm. We restricted the rod length to L ≤ 100 μm for further optimization, in order to stay in an experimentally feasible range. During the optimization of rod radius R in configuration A the open circuit voltage increased continuously, while short circuit current density stayed rather constant. This leads to an increase in efficiency with R, which only stops at very large radii, where R starts to be comparable with L. In configuration B efficiency is almost independent of R, provided that the radius is large enough to comprise a well-formed space charge region, here only a shallow maximum can be estimated. With the demand of rod lengths being smaller than 100 μm, optimum parameters L = 48 μm, R = 32 μm and L = 96 μm, R = 2 μm were extracted for configuration A and B, respectively.     

A comparative study on the NO2 gas sensing properties of ZnO thin films, nanowires and nanorods

ZnO thin films were fabricated using the spin coating method, ZnO nanowires by cathodically induced sol-gel deposition by the means of an anodic aluminum oxide (AAO) template, and ZnO nanorods with the hydrothermal technique. For thin film preparation, a clear, homogeneous and stable ZnO solution was prepared by the sol-gel method using zinc acetate (ZnAc) precursor which was then coated on a glass substrate with a spin coater. Vertically aligned ZnO nanowires which were approximately 65 nm in diameter and 10 μm in length were grown in an AAO template by applying a cathodic voltage in aqueous zinc nitrate solution at room temperature. For fabrication of the ZnO nanorods, the sol-gel ZnO solution was coated on glass substrate by spin coating as a seed layer. Then ZnO nanorods were grown in zinc nitrate and hexamthylenetetramine aqueous solution. The ZnO nanorods are approximately 30 nm in diameter and 500 nm in length. The ZnO thin film, ZnO nanowires and nanorods were characterized by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). The NO₂ gas sensing properties of ZnO thin films, nanowires and nanorods were investigated in a dark chamber at 200 °C in the concentration range of 100 ppb-10 ppm. It was found that the response times of both ZnO thin films and ZnO nanorods were approximately 30 s, and the sensor response was depended on shape and size of ZnO nanostructures and electrode configurations.     

Synthesis of vertical arrays of ultra long ZnO nanowires on noncrystalline substrates

Vertically aligned arrays of ultralong ZnO nanowires were synthesized on SiO₂ substrates with carbothermal vapor phase transport method with Au seeding layer. High density of vertically aligned ZnO nanowires with lengths from a few to ∼300 μm could be grown by controlling growth conditions. Supply of high concentration of Zn vapor and control of the ratio between Zn vapor and oxygen are found to have the most significant effects on the growth of long ZnO nanowires in the vapor-solid growth mechanism. The nanowires are of high crystalline quality as confirmed by various structural, compositional, and luminescent measurements. Luminescent and electrical properties of ZnO nanowires with different growth conditions were also investigated.     

Photoconductive and polarization properties of individual CdTe nanowires

Metal-Cd_0.42Te_0.58-metal nanowires were electrodeposited into the pores of anodized aluminum oxide (AAO) membranes, and the polarization sensitive photoconductance was analyzed for individual nanostructures. Non-linear I-V curves were observed, and the short-circuit current density, open-circuit voltage, and fill factor were determined. These nanowires exhibited a power conversion efficiency of 0.56%, which is higher than some comparable nanomaterials of greater complexity.     

Microwave-assisted preparation of calcium sulfate nanowires

We have successfully developed a new synthetic route for the rapid preparation of calcium sulfate nanowires by thermal transformation of calcium dodecyl sulfate (CDS) in organic solvents of ethylene glycol (EG) and N,N-dimethylformamide (DMF). The products are characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), and determined to be single-phase CaSO₄·0.5H₂O consisting of single-crystalline nanowires with aspect ratio up to about 62. In this method, the different types of organic solvents used have no obvious influences on the morphology, phase, and formation time of the product. The microwave heating can remarkably shorten the reaction time compared with conventional heating methods.     

Thermoelectric properties of p-type PbSe nanowires

The thermoelectric properties of individual solution-phase synthesized p-type PbSe nanowires have been examined. The nanowires showed near degenerately doped charge carrier concentrations. Compared to the bulk, the PbSe nanowires exhibited a similar Seebeck coefficient and a significant reduction in thermal conductivity in the temperature range 20 K to 300 K. Thermal annealing of the PbSe nanowires allowed their thermoelectric properties to be controllably tuned by increasing their carrier concentration or hole mobility. After optimal annealing, single PbSe nanowires exhibited a thermoelectric figure of merit (ZT) of 0.12 at room temperature.      

Large-scale synthesis of defect-free silver nanowires by electrodeless deposition

We report a new method that generates high-density, long aspect ratio and large-area silver nanowire arrays within the pores of anodic aluminum oxide (AAO) membrane by reducing silver nitrate with ethylene glycol. The freestanding and defect-free silver nanowires can be obtained at high yields. In a typical procedure, the as-prepared silver nanowires have a mean diameter of ∼ 53 nm. It is found out that both temperature and reaction time are important factors in determining the morphology and aspect ratios of nanowires. Lower temperature and longer time are favorable to form polycrystalline silver nanowires with high uniformity and aspect ratios.     

A comprehensive survey of augmented reality assembly research

In the past two decades, augmented reality(AR) has received a growing amount of attention by researchers in the manufacturing technology community, because AR can be applied to address a wide range of problems throughout the assembly phase in the lifecycle of a product, e.g., planning, design, ergonomics assessment, operation guidance and training. However, to the best of authors' knowledge, there has not been any comprehensive review of AR-based assembly systems. This paper aims to provide a concise overview of the technical features, characteristics and broad range of applications of ARbased assembly systems published between 1990 and 2015. Among these selected articles, two thirds of them were published between 2005 and 2015, and they are considered as recent pertinent works which will be discussed in detail. In addition, the current limitation factors and future trends in the development will also be discussed.     

Photoresponse of hydrothermally grown lateral ZnO nanowires

In this paper, a simple self-assembled lateral growth of ZnO nanowires (NWs) photodetector has been synthesized by a hydrothermal method at a temperature as low as 85 °C. The ZnO NWs exhibit single-crystalline wurtzite with elongated c-axis and can be selectively lateral self-assembled around the edges of ZnO seeding layer. The current of ZnO NWs is sensitive to the variation of ambient pressures, i.e. 4.47 μA was decreased to 1.48 μA with 5 V-bias as 1.1 × 10^− 6 Torr changed to 760 Torr, accordingly. Moreover, the current-voltage characteristics of ZnO NWs photodetectors can be evidently distinguished by UV illumination (i.e. λ = 325 nm). The photocurrent of ZnO NWs with UV illumination is twice larger than dark current while the voltage biased at 5 V. Consequently, this faster photoresponse convinces that the hydrothermally grown lateral ZnO NWs devices have a fairly good for the fabrication of UV photodetectors.     

Effect of surface morphology of metallic zinc films deposited by ion beam sputter deposition on the formation of ZnO nanowires

Metallic zinc film with various surface roughnesses was deposited on Si (100) substrates by ion beam sputter deposition utilizing beam energies at 8, 12 and 16 keV. The surface roughness of the metallic zinc film increased as ion beam energy increased and was found to act as a crucial factor for the formation of ZnO nanowires by subsequent thermal oxidation. ZnO nanowires with diameters of ∼30 nm and average length of ∼1 μm were obtained from 12 to 16 keV ion beam deposited samples while no ZnO nanowires were found on 8 keV ion beam deposited samples. Photoluminescence study of ZnO nanowires exhibits a strong UV emission at 377.2 nm (3.287 eV) with a full-width at half maximum of 95.0 meV and negligible defect related deep level emission. The ZnO nanowires are grown along the [110] direction and the growth mechanism is likely due to a solid state based-up diffusion process. Field-emission measurement shows a turn-on field of 7.9 MV/m and a field enhancement factor β of 691 is achieved.     

Ultrahigh sensitive and selective triethylamine sensor based on h-BN modified MoO3 nanowires

In this work, a novel structure of 1D MoO₃ nanowires wrapped by 2D hexagonal boron nitride (h-BN) was synthesized via a simple solvothermal method with subsequent annealing process for triethylamine (TEA) detection. The samples were characterized by XPS, SEM, HRTEM and N₂ adsorption-desorption. Gas sensing performance test results illuminate that the typical 2 wt% h-BN/MoO₃ sensor possesses an ultrahigh response (8616) toward 500 ppm TEA. The promoted sensing performance of TEA may be caused by the forming of heterojunction between h-BN and MoO₃, the increased specific surface area of h-BN modification, providing a highly active sites for the adsorption of TEA gas, which greatly enhance the response of the sensor. The adsorption energy of a single oxygen molecule on MoO₃ (0 1 0) surface was calculated by DFT, indicating the most stable site is the terminal oxygen position (Top O-1), with an adsorption energy of ?2.075 eV. This work provides an inspiration to design highly efficient TEA gas sensor on basis of h-BN/MoO₃ nanocomposites.     

Influence of O contamination and Au cluster properties on the structural features of Si nanowires

Silicon nanowires (Si NWs) are the emerging nanostructures for future nanodevices. In this work we have prepared them by electron beam evaporation (EBE) through the vapor-liquid-solid (VLS) mechanism. We discuss the growth of epitaxial NWs by EBE and the possibility to control their orientation and length by changing the experimental conditions. Moreover, the effects of the surface contamination and of the Au cluster preparation on the NWs structural properties and density will be discussed. We demonstrate that any O contamination has to be avoided since just a very thin native SiO₂ layer stops ad-atom diffusion on the surface and inhibits the NWs growth. Au cluster preparation has a determinant role too: by varying the procedure for their formation, it is possible to change NWs density and length. In particular, we observed that by evaporating Au on the heated substrate, the droplets active to promote NW growth are immediately formed and a faster growth process starts. The growth rate is about a factor of 4 times higher than in the sample where the Au is evaporated at room temperature and the cluster formed after a subsequent thermal annealing. On the contrary, the slower process allows the atom arrangement and ordering in an epitaxial manner, and a precise control of NW orientation can be achieved.     

Self-assembly of polyaniline nanowires into polyaniline microspheres

High quality microspheres self-assembled from nanowires of polyaniline (PANI) are prepared by a self-assembly process using ammonium peroxydisulfate as oxidant in aqueous solution. The microspheres of about 2.6 μm average diameter are composed of uniform nanowires with 40-60 nm in diameter. The formation process of PANI microsphere indicates that its evolution of morphologies can be divided into three stages. First, a large quantity of PANI nanowires form, then porous microspheres develop, and finally most of nanowires transform into microspheres. The morphology and uniformity of the PANI microspheres mainly depend on the mole ratio of aniline to ammonium peroxydisulfate. The BET specific surface area and conductivity of the polyaniline porous microsphere at room temperature are 53 m² g^− 1 and 3.3 × 10⁻¹ S cm^− 1, respectively.     

Enhancement of green emission from Sn-doped ZnO nanowires

Oxygen vacancies play a crucial role in the emission characteristics of oxide nanomaterials. In this study, we found that the green emission intensity of ZnO nanowires can be enhanced through a Sn-doping concentration which increases the number of oxygen vacancies. Undoped ZnO nanowires showed blue emission at 380 nm, but as the concentration of Sn was increased, the green emission peak at around 500 nm, which is attributed to oxygen vacancies, showed drastic enhancement. On the basis of XPS compositional analysis, it was confirmed that the green luminescence intensity was closely related to the number of oxygen vacancies in Sn-doped ZnO nanowires. These results pave the way to a greater understanding of tunable light emission from nanowires, which could be a key technology for next-generation display devices, including flexible and transparent displays.     

Surface dislocation nucleation mediated deformation and ultrahigh strength in sub-10-nm gold nanowires

The plastic deformation and the ultrahigh strength of metals at the nanoscale have been predicted to be controlled by surface dislocation nucleation. In situ quantitative tensile tests on individual 〈111〉 single crystalline ultrathin gold nanowires have been performed and significant load drops observed in stress-strain curves suggest the occurrence of such dislocation nucleation. High-resolution transmission electron microscopy (HRTEM) imaging and molecular dynamics simulations demonstrated that plastic deformation was indeed initiated and dominated by surface dislocation nucleation, mediating ultrahigh yield and fracture strength in sub-10-nm gold nanowires.