Results 1 - 10 of 14654
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[en] Electrostatic modes of atomic force microscopy have shown to be non-destructive and relatively simple methods for imaging conductors embedded in insulating polymers. Here we use electrostatic force microscopy to image the dispersion of carbon nanotubes in a latex-based conductive composite, which brings forth features not observed in previously studied systems employing linear polymer films. A fixed-potential model of the probe-nanotube electrostatics is presented which in principle gives access to the conductive nanoparticle's depth and radius, and the polymer film dielectric constant. Comparing this model to the data results in nanotube depths that appear to be slightly above the film–air interface. Furthermore, this result suggests that water-mediated charge build-up at the film–air interface may be the source of electrostatic phase contrast in ambient conditions.
[en] Individual carbon nanotubes (CNTs) exhibit exceptional mechanical properties. However, difficulties remain in fully realizing these properties in CNT macro-assemblies, because the weak inter-tube forces result in the CNTs sliding past one another. Here in this study, a simple solid-state reaction is presented that enhances the mechanical properties of carbon nanotube fibers (CNTFs) through simultaneous covalent functionalization and crosslinking. This is the first chemical crosslinking proposed without the involvement of a catalyst or byproducts. The specific tensile strength of CNTFs obtained from the treatment employing a benzocyclobutene-based polymer is improved by 40%. Such improvement can be attributed to a reduced number of voids, impregnation of the polymer, and the formation of covalent crosslinks. This methodology is confirmed using both multiwalled nanotube (MWNT) powders and CNTFs. Thermogravimetric analysis, differential scanning calorimetry, x-ray photoelectron spectroscopy, and transmission electron microscopy of the treated MWNT powders confirm the covalent functionalization and formation of inter-tube crosslinks. This simple one-step reaction can be applied to industrial-scale production of high-strength CNTFs.
[en] This study examined the optical properties of an oxidized form of maghemite (γ-Fe2O3) nanoparticles and their protective effects against the photoaging of human skin fibroblasts irradiated with ultraviolet (UV) light. Nanoparticles with diameters ranging from 8.7 to 12 nm were prepared using a chemical co-precipitation method. The nanoparticles were coated with two surfactants to obtain a water-based product. The onset of the absorption of the γ-Fe2O3 nanoparticles in the UV-visible absorption spectra increased with increasing particle size. The γ-Fe2O3 nanoparticles significantly inhibited the production of matrix metalloproteinase-1 in human skin fibroblast HS 68 cells by 60% compared with the UV-irradiated control. These results suggest that γ-Fe2O3 nanoparticles have photoprotective properties, and have potential use as an agent against photoaging
[en] Ba-doped CeO2 nanowires were obtained from CeO2 particles through a facile composite-hydroxide-mediated (CHM) route. The products were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscope (HRTEM). The formation process of the product was discussed. Humidity sensors based on the source material CeO2 particles, Ba-doped CeO2 nanowires grown for 12 and 72 h, were fabricated. The responses to humidity for static and dynamic testing proved that both doping Ba into CeO2 and converting morphology into a nanowire can improve the humidity sensitivity. The resistance changes from 465 to 3.9 MΩ as the relative humidity (RH) increases from 25% to 88%, indicating promising applications of Ba-doped CeO2 nanowires in environmental monitoring
[en] Hard magnetic nanoparticles based on the Sm2Co17 and SmCo5 systems have been successfully produced using a surfactant-assisted ball milling technique. A size-selection process has been developed to obtain nanoparticles of different sizes with narrow size distribution. Significant room-temperature coercivity up to 3.1 kOe has been achieved with the Sm2Co17-based nanoparticles of an average size of 23 nm. It has been found that surfactants play multifold roles in the processing
[en] Menisci form between two solid surfaces with the presence of an ultra-thin liquid film. Meniscus and viscous forces contribute to an adhesive force when two surfaces are separated. The adhesive force can be very large and can result in high friction, stiction and possibly high wear. The situation may become more pronounced when the contacting surfaces are ultra-smooth and the normal load is small, as is common for micro-/nanodevices. In this study, equations for meniscus and viscous forces during separation of two flat surfaces, and a sphere and a flat surface, are developed, and the corresponding adhesive forces contributed by these two types of forces are examined. The geometric meniscus curvatures and break point are theoretically determined, and the role of meniscus and viscous forces is evaluated during separation. The influence of separation distance, liquid thickness, meniscus area, separation time, liquid properties and contact angles are analyzed. Critical meniscus areas at which transition in the dominance of meniscus to viscous forces occurs for different given conditions, i.e. various initial liquid thicknesses, contact angles and designated separation time, are identified. The analysis provides a fundamental understanding of the physics of separation process, and insights into the relationships between meniscus and viscous forces. It is also valuable for the design of the interface for various devices
[en] The phase transformations of Si under nanogrinding have been studied by transmission electron microscopy and Raman spectroscopy. Nanocrystalline high-pressure phases (Si-III/Si-XII) were found in the amorphous layer of the subsurface of heavily ground Si. The sequence of the phase transformation in nanogrinding has been found to be different to that in nanoindentation. The formation mechanism of the nanocrystalline high-pressure phases in nanogrinding is proposed based on experimental results
[en] We present a robust, shadow mask method for fabricating break-junctions (BJs). The method uses electromigration and results in devices comprising 100 μm wide gold wires separated by nanogaps. By functionalizing the BJs with alkanedithiols and using electrostatic trapping, we incorporate single gold nanoparticles (NPs) in the gaps with high yield. The resulting single-NP devices exhibit single-electron charging thresholds that can be probed using both voltage and temperature measurements. Both voltage thresholds and thermal activation energies scale with NP size as expected
[en] Uniform core-shell gold-polyaniline (Au-PANI) nanoparticles were successfully fabricated by in situ polymerization of aniline using poly(N-isopropylacrylamide)-co-poly(acrylic acid) (PNIPAM-co-PAA)/AuNP hybrid microgel particles as a template. TEM images gave direct evidence of the core-shell nanostructure of Au-PANI particles, which were composed of gold nanoparticles as the core and polyaniline as the shell. The shell thickness of as-prepared core-shell Au-PANI nanoparticles can be easily tuned by controlling the reaction time. A possible mechanism for the formation of core-shell Au-PANI nanostructures was proposed. This novel synthetic method may be extended to the synthesis of other core-shell nanostructures with diverse functionality and high colloidal stability
[en] Diamond nanotips were synthesized on diamond/Si substrates by using a microwave plasma-enhanced chemical vapor deposition process. The diamond nanotips are ∼1 μm in height and the diameter at the bottom of a nanotip is ∼200 nm. The as-grown diamond nanotips exhibit excellent field emission characteristics after treating with nitrogen plasma immersion ion implantation (PIII) for 10 min. A low turn-on field of 3 V μm-1 and a high current density of 4 mA cm-2 at 9 V μm-1 are achieved. The morphologies of diamond nanotips are unchanged after the nitrogen PIII treatment. The diamond quality reduces with treatment time. The sp3 bonds in diamond can be broken by the nitrogen ions accelerated by the pulse voltage of -25 kV, which results in G peak broadening in Raman spectra. Several nanoscale amorphous regions are generated in a crystalline diamond nanotip, observed by the high resolution transmission electron microscope. The improvement of field emission properties is correlated to the amorphous regions and possible implantation-induced atomic defects