Influence of solution parameters for the fast growth of ZnO nanostructures by laser-induced chemical liquid deposition

ZnO nanorods, nanoneedles, nanoparticles and nanoballs were synthesized on fused quartz substrates upon irradiation of a droplet of methanolic zinc acetate dihydrate solution by an infrared continuous wave CO₂ laser for a few seconds. The addition of monoethanolamine and water to the solution improved the alignment of the nanorods and had a significant effect on the volume and morphology of the deposits. An increase of the zinc acetate concentration was found to lead to an increase of the thickness and area covered by the initial ZnO seed layer on which the nanostructures grew. By investigating the crystal structure of the deposits using x-ray and electron diffraction, we were able to show that the nanorods grow along the c axis with a high crystalline quality. Raman and photoluminescence spectroscopy confirmed the high-quality of the grown ZnO nanostructures. As a matter of fact, their photoluminescence spectra are dominated by an intense UV emission around 390 nm

Pulsed-laser-ablation based nanodecoration of multi-wall-carbon nanotubes by Co–Ni nanoparticles for dye-sensitized solar cell counter electrode applications

Abstract We report here on the use of pulsed KrF-laser deposition technique (PLD) for the decoration of Multi-wall carbon nanotubes (MWCNTs) by Co–Ni nanoparticles (NPs) to form highly efficient counter electrodes (CEs) for use in Dye-sensitized solar cells (DSSC). By varying the number of laser ablation pulses (N LP = 500–60,000) of the KrF laser, we were able to control the average size of the Co–Ni NPs and the surface coverage of the MWCNTs by the nanoparticles. The PLD-based decoration of MWCNTs by Co–Ni NPs is shown to form novel counter electrodes, which significantly enhance the power conversion efficiency (PCE) of the DSSCs. Indeed, the DSSCs based on the PLD-decorated Co–Ni counter electrodes (obtained at the optimal N LP = 40,000) are shown to exhibit a PCE value as high as 6.68%, with high short circuit current (J sc = 14.68 mA/cm2) and open circuit voltage (V oc = 0.63 V). This represents a PCE improvement of ~190% in comparison to the DSSCs with pristine MWCNTs (PCE = 2.3%) and ~7.4% PCE increase than that of the conventional DSSC made with a sputtered Platinum-based counter electrode. By systematically investigating the local nanostructure of the Co–Ni decorated CEs, we found that the Co–Ni NPs layer exhibits a porous cauliflower-like morphology, of which surface roughness (RMS) is N LP dependent. Interestingly, both PCE and roughness of the Co–Ni NPs layer are found to exhibit the same N LP dependence, with a maximum located around the optimal N LP value of 40,000. This enabled us to establish, for the first time, a linear correlation between the achieved PCE of DSSCs and the local roughness of their CEs decorated by Co–Ni NPs. Such a correlation highlights the importance of maximizing the surface area of the Co–Ni coated MWCNTs on the CEs to enhance the PCE of the DSSCs. Finally, Ultra-violet Photoelectron Spectroscopy (UPS) measurements revealed a significant decrease in the local work function (Φ) of Co–Ni NPs decorated MWCNTs based CEs (at N LP = 40,000, Φ = 3.9 eV) with respect to that of either pristine MWCNTs (Φ = 4.8 eV) or sputtered-Pt (Φ = 4.3 eV) counter-electrodes. This Φ lowering of the Co–Ni/MWCNTs based CEs is an additional advantage to enhance the catalytic reaction of the redox couple of the electrolyte solution, and improve thereby the PCE of the DSSCs

Preparation and mechanical characterization of laser ablated single-walled carbon-nanotubes/polyurethane nanocomposite microbeams

We report on the preparation of nanocomposites consisting of laser synthesized single-walled carbon nanotubes (C-SWNTs) reinforcing a polyurethane. Prior to their incorporation into the polymer matrix, the C-SWNTs were purified, and characterized by means of various techniques. The purification in nitric acid added carboxylic groups to the C-SWNTs. A procedure to properly disperse the nanomaterials in the polymer was developed involving high shear mixing using a three-roll mill and a non-covalent functionalization of the nanotubes by zinc protoporphyrin IX molecule. The incorporation of the C-SWNTs into the resin led to an increase of the viscosity and the apparition of a slight shear-thinning behavior. A further increase of the shear-thinning behavior using fumed silica particles enabled the direct-write fabrication of microbeams. Mechanical characterization revealed significant increase in both strength (by ∼64%) and modulus (by more than 15 times). These mechanical enhancements are believed to be a consequence of the successful covalent and the non-covalent functionalizations of the nanotubes

Electrical transport properties of single wall carbon nanotube/polyurethane composite based field effect transistors fabricated by UV-assisted direct-writing technology

We report on the fabrication and transport properties of single-walled carbon nanotube (SWCNT)/polyurethane (PU) nanocomposite microfiber-based field effect transistors (FETs). UV-assisted direct-writing technology was used, and microfibers consisting of cylindrical micro-rods, having different diameters and various SWCNT loads, were fabricated directly onto SiO₂/Si substrates in a FET scheme. The room temperature dc electrical conductivities of these microfibers were shown to increase with respect to the SWCNT concentrations in the nanocomposite, and were about ten orders of magnitude higher than that of the pure polyurethane, when the SWCNT load ranged from 0.1 to 2.5 wt% only. Our results show that for SWCNT loads ≤ 1.5 wt%, all the microfibers behave as a FET with p-type transport. The resulting FET exhibited excellent performance, with an I on/I off ratio of 105 and a maximum on-state current (I on) exceeding 70 µA. Correlations between the FET performance, SWCNTs concentration, and the microfiber diameters are also discussed

Three-dimensional micro structured nanocomposite beams by microfluidic infiltration

Three-dimensional (3D) micro structured beams reinforced with a single-walled carbon nanotube (C-SWNT)/polymer nanocomposite were fabricated using an approach based on the infiltration of 3D microfluidic networks. The 3D microfluidic network was first fabricated by the direct-write assembly method, which consists of the robotized deposition of fugitive ink filaments on an epoxy substrate, forming thereby a 3D micro structured scaffold. After encapsulating the 3D micro-scaffold structure with an epoxy resin, the fugitive ink was liquefied and removed, resulting in a 3D network of interconnected microchannels. This microfluidic network was then infiltrated by a polymer loaded with C-SWNTs and subsequently cured. Prior to their incorporation in the polymer matrix, the UV-laser synthesized C-SWNTs were purified, functionalized and dispersed into the matrix using a three-roll mixing mill. The final samples consist of rectangular beams having a complex 3D skeleton structure of C-SWNT/polymer nanocomposite fibers, adapted to offer better performance under flexural solicitation. Dynamic mechanical analysis in flexion showed an increase of 12.5% in the storage modulus compared to the resin infiltrated beams. The nanocomposite infiltration of microfluidic networks demonstrated here opens new prospects for the achievement of 3D reinforced micro structures

Micro-infiltration of three-dimensional porous networks with carbon nanotube-based nanocomposite for material design

Epoxy composite beams reinforced with a complex three-dimensional (3D) skeleton structure of nanocomposite microfibers were fabricated via micro-infiltration of 3D porous microfluidic networks with carbon nanotube nanocomposites. The effectiveness of this manufacturing approach to design composites microstructures was systematically studied by using different epoxy resins. The temperature-dependent mechanical properties of these multifunctional beams showed different features which cannot be obtained for those of their individual components bulks. The microfibers 3D pattern was adapted to offer better performance under flexural solicitation by the positioning most of the reinforcing microfibers at higher stress regions. This led to an increase of 49% in flexural modulus of a reinforced-epoxy beam in comparison to that of the epoxy bulk. The flexibility of this method enables the utilization of different thermosetting materials and nanofillers in order to design multifunctional composites for a wide variety of applications such as structural composites and components for micro electromechanical systems

Manufacturing composite beams reinforced with three-dimensionally patterned-oriented carbon nanotubes through microfluidic infiltration

Functionalized single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposite suspensions were prepared and injected into three-dimensional (3D) interconnected microfluidic networks in order to fabricate composite beams reinforced with patterned-oriented nanotubes. The microfluidic networks were fabricated by the robotized direct deposition of fugitive ink filaments in a layer-by-layer sequence onto substrates, followed by their epoxy encapsulation and the ink removal. Then, the nanocomposite suspensions prepared by ultrasonication and three-roll mill mixing methods were injected into the empty networks under two different controlled and constant pressures in order to subject the suspensions to different shear conditions in the microchannels. Morphological studies revealed that the SWCNTs were preferentially aligned in the microchannels along the flow direction at the higher injection pressure. The improvement of Young’s modulus of the manufactured 3D-reinforced rectangular beams prepared at the high injection pressure was almost doubled when compared to that of beams prepared at the low injection pressure. Finally, the stiffness of the 3D-reinforced beams was compared with the theoretically predicted values obtained from a micromechanical model. The analytical predictions give a close estimation of the stiffness at different micro-injection conditions. Based on the experimental and theoretical results, the present manufacturing technique enables the spatial orientation of nanotube in the final product by taking advantage of shear flow combined with dimensional constraining inside the microfluidic channels

Reinforcing epoxy nanocomposites with functionalized carbon nanotubes via biotin–streptavidin interactions

We report on the preparation of nanocomposites consisting of biofunctionalized single-walled carbon nanotubes (BF-SWCNTs) reinforcing an ultraviolet curable epoxy polymer by means of biotin–streptavidin interactions. The as-produced laser ablation SWCNTs are biofunctionalized via acid oxidization based purification process and non-covalent functionalization using surfactant, followed by grafting the resulting nanotubes with biomolecules. The biotin-grafted nanotubes are capable of interacting with epoxy groups in presence of streptavidin molecules by which chemical bridges between BF-SWCNTs and epoxy matrix are formed. The biomolecules grafted to the nanotubes surface not only facilitate the load transfer, but also improve the nanotube dispersion into the epoxy matrix, as observed by optical imaging and scanning electron microscopy. Mechanical characterization on the nanocomposite microfibers demonstrates considerable enhancement in both strength (by 76%) and modulus (by 93%) with the addition of only 1 wt.% of BF-SWCNTs. The electrical measurements reveal a clear change in electrical conductivity of nanocomposite microfibers reinforced with 1 wt.% of BF-SWCNTs in comparison to the microfibers containing solely purified carbon nanotubes. These multifunctional nanocomposite materials could be used to fabricate macro and microstructures for a wide variety of applications such as high strength polymer nanocomposite and potential easily-manipulated biosensors

Direct-write fabrication of freestanding nanocomposite strain sensors

This paper deals with the design and microfabrication of two three-dimensional (3D) freestanding patterned strain sensors made of single-walled carbon nanotubes (SWCNTs) nanocomposites with the ultraviolet-assisted direct-write (UV-DW) technique. The first sensor consisted of three nanocomposite microfibers suspended between two rectangular epoxy pads. The flexibility of the UV-DW technique enables manufacturing the sensor and its housing in one monolithic structure. The second sensor was composed of a nanocomposite network consisting of four parallel microsprings, which demonstrates the high capability of the technique when compared to the conventional photolithographic technologies. The performances of the sensors were assessed under tension and compression, respectively. The sensors sensitivities were evaluated by correlating their measured resistivities to the applied displacements/strains. Electrical conductivity measurements revealed that the manufactured sensors are highly sensitive to small mechanical disturbances, especially for lower nanotube loadings when compared to traditional metallic or nanocomposite films. The present manufacturing method offers a new perspective for manufacturing highly sensitive 3D freestanding microstructured sensors