Nanoparticles of Au, Pd, and Pt form spontaneously as thin, morphologically complex metallic films upon various semiconducting or metal substrates such as Ge(100), Cu, Zn, and Sn, via galvanic displacement from aqueous metal salt solutions. Patterning of these high surface area metal films into ordered structures utilizing photolithography, microcontact printing (µ-CP), and dip-pen nanolithography (DPN) is demonstrated on flat Ge(100), and (for µ-CP) on rough Zn foil.There is presently enormous interest in patterning surfaces with micro-and nanometer resolution for both fundamental investigations and technological applications.1 Recent developments, such as dip-pen nanolithography (DPN) 2 and microcontact printing (µ-CP), 1 employ a liquid-phase "ink" to pattern a solid "paper" substrate. Established inks for DPN and µ-CP include thiols, 2 DNA, 3 polymers, 4 proteins, 5,6 hexamethyldisilazane, 7 alkylsiloxanes, 8 palladium colloids, 9 sols (Al, Si, Sn oxides), 10 metal complexes, 11 and gold. 12 In this paper, we demonstrate that Au, Pd, and Pt nanoparticle films, produced through a spontaneous electroless deposition reaction, are amenable to patterning via photolithography, µ-CP, and DPN. Because many properties of the Au, Pd, and Pt nanoparticle films, including film thickness, particle size, and roughness, can be controlled, 13 Figure 1. Deposition proceeds via galvanic displacement 20 in the absence of fluoride, pH buffers, complexing agents, or external reducing agents, in contrast to earlier work. 21-30 Patterning of these particle film assemblies is essential for their subsequent incorporation into higher order architectures and devices. 31,32 The first patterning motif tested, photolithography, was carried out as outlined in Figure 2a. Approximately 0.1 mL of neat dodecene was applied to a 1 cm 2 hydride-terminated Ge(100) surface, which was subequently exposed to 254 nm UV light (9 mW cm -2 intensity) through a metal grid contact mask under an inert atmosphere. 33 The illuminated regions undergo hydrogermylation at room temperature within thirty minutes. A related functionalization approach has been shown on silicon.34 This leads to spatially defined 5-25 µm-sized domains of dodecyl and hydride. Immersion of the hydride/alkyl surface into aqueous noble metal salt solutions results in preferential deposition in the hydride areas since the alkyl monolayer functions as an effective dielectric barrier (Figure 3). The hydride surface oxidizes in-situ and subsequently dissolves in the aqueous medium. Metal salt reduction and deposition can then occur, leading to metallization between the alkylated domains. In this case, the germanium oxide dissolves in water, 35 leading to intimate electrical contact between the semiconductor bulk and the metal salts and affording a faster rate of deposition. In the case of silicon, however, this approach is not feasible because the native oxide has been shown to effectively prevent metal deposition due to its insolubility in water. 20 Attempts to use spatially define...
Carbon nanotubes (CNTs) have numerous exciting potential applications and some that have reached commercialization. As such, quantitative measurements of CNTs in key environmental matrices (water, soil, sediment, and biological tissues) are needed to address concerns about their potential environmental and human health risks and to inform application development. However, standard methods for CNT quantification are not yet available. We systematically and critically review each component of the current methods for CNT quantification including CNT extraction approaches, potential biases, limits of detection, and potential for standardization. This review reveals that many of the techniques with the lowest detection limits require uncommon equipment or expertise, and thus, they are not frequently accessible. Additionally, changes to the CNTs (e.g., agglomeration) after environmental release and matrix effects can cause biases for many of the techniques, and biasing factors vary amongst the techniques. Five case studies are provided to illustrate how to use this information to inform responses to real-world scenarios such as monitoring potential CNT discharge into a river or ecotoxicity testing by a testing laboratory. Overall, substantial progress has been made in improving CNT quantification during the past ten years, but additional work is needed for standardization, development of extraction techniques from complex matrices, and multi-method comparisons of standard samples to reveal the comparability of techniques.
Four techniques for analyzing single molecule tracking data--confinement level analysis, time series analysis and statistical analysis of lateral diffusion, multistate kinetics, and a newly developed method, radius of gyration evolution analysis--are compared using a set of sample fluorophore trajectories obtained from the lipophilic carbocyanine dye 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine, DiIC(18), partitioned into surface tethered poly(n-isopropylacrylamide). The purpose here is two-fold: first to test that these techniques can be applied to single molecules trajectories, which typically contain a smaller total number of frames than those obtained from other particles, e.g. quantum dots or gold nanoparticles; and second to critically compare the information obtained from each method against the others. A set of five SMT trajectories, ranging in length from 41 to 273 steps with a 30 ms frame transfer exposure, were all successfully analyzed by all four techniques, provided two important criteria were met: enough steps to define the motion were acquired in the trajectory, generally on the order of 50 steps, and the fast and slow diffusion coefficients differ by at least a factor of 5. Beyond that the four trajectory analysis methods studied provide partially confirmatory and partially complementary information. SMT data resulting from more complex physical behavior may well benefit from using these techniques in succession to identify and sort populations.
We describe the fabrication and performance of a passive, microfluidics-based H2-O2 microfluidic fuel cell using thin film Pt electrodes embedded in a poly(dimethylsiloxane) (PDMS) device. The electrode array is fully immersed in a liquid electrolyte confined inside the microchannel network, which serves also as a thin gas-permeable membrane through which the reactants are fed to the electrodes. The cell operates at room temperature with a maximum power density of around 700 microW/cm(2), while its performance, as recorded by monitoring the corresponding polarization curves and the power density plots, is affected by the pH of the electrolyte, its concentration, the surface area of the Pt electrodes, and the thickness of the PDMS membrane. The best results were obtained in basic solutions using electrochemically roughened Pt electrodes, the roughness factor, R(f), of which was around 90 relative to a smooth Pt film. In addition, the operating lifetime of the fuel cell was found to be longer for the one using higher surface area electrodes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.