Nanoparticle Film Thickness Research Articles

Uniformly spaced nanoscale cracks in nanoparticle films deposited by convective assembly

Rapid convective deposition is used to assemble nanoparticle coatings from suspension, with controllable thickness. Varying film thickness generates stress-induced linear cracks with highly monodisperse spacing. Film thickness is controlled through mechanical means, suspension volume fraction, and the use of applied thermal gradients. These cracks extend in the deposition direction, and a uniform crack spacing from 2 to 160μm is observed. The nanoparticle film thickness is the relevant length scale for hydrodynamic flow, and films will crack with this spacing, in a characteristic manner to minimize the system energy and capillary stresses. As expected from this energy minimization problem and relevant theory, the correlation between coating thickness and crack spacing is highly linear. Because this process is continuous, continuous cracks have potential as a high-throughput method of fabricating nanoscale channels for microfluidics and MEMS.

Theoretical investigation of absorption and sensitivity of nano-plasmonic tapered fiber optic sensors

In this paper, a theoretical investigation for the performance a tapered fiber optic sensor based on surface plasmon resonance (SPR) is proposed. The tapered fiber optic sensor is considered for three different taper profiles, namely, linear, parabolic, and exponential-linear. The tapered fiber optic sensor is coated with thin nanoparticle metallic films. The nanoparticle metallic film consists of spherical metallic nanoparticles embedded in a host material. The performance has been analyzed in terms of sensitivity and absorption of the sensor. It is shown that sensitivity and absorption of sensors depends on parameters such as taper ratio, taper profile, nanoparticle film thickness, nanoparticle radius, sensing region length, fiber core diameter, and concentration of sensing layer.

Effects of magnetic nanoparticle films on the electrical characteristics of dc superconducting quantum interference devices

We evaluated the effects of Fe3O4 magnetic nanoparticle (NP) films on the electrical characteristics of superconducting quantum interference devices (SQUIDs) at 4.2 K to enhance the performance of superconducting circuits. The NP films were formed directly on the SQUIDs. For SQUIDs with 5-nm-NP films, the SQUID inductance increased almost linearly with the NP film thickness, reaching 19.7% at an NP film thickness of 990 nm. An increase in NP size from 5 to 20 nm reduced that in the SQUID inductance. On the other hand, no clear effects on the current–voltage characteristics of SQUIDs were observed for 5- and 10-nm-NP films, while the critical currents of some SQUIDs with 20-nm-NP films were reduced.

Immobilization of Magnetic Nanoparticles onto Conductive Surfaces Modified by Diazonium Chemistry

Core-shell γ-Fe(2)O(3)@SiO(2) nanoparticles (NPs) substituted by PEG and NH(2) groups may be immobilized on metal surfaces (glassy carbon or gold) substituted by 4-carboxyphenyl groups through electrostatic interactions. Such immobilization is evidenced by (i) IRRAS owing to the Si-O band, (ii) SEM images, which show that the surface coverage by the NPs is nearly 100%, and (iii) the NPs film thickness measured by ellipsometry or AFM, which corresponds to about one NPs monolayer. Such NPs film is permeable to redox probes, which allows us to propose electrochemical methods based on direct or local measurements as a way to inspect the NPs assembly steps through their ability to alter mass and charge transfer. This process also applies to patterned polystyrene surfaces, and selective immobilization of NPs substituted by amino groups was carried out onto submillimeter patterns obtained by local oxidation. Biological applications are then expected for hyperthermia activation of the NPs to trigger cellular death. Finally, some tests were performed to further derivatize the immobilized NPs onto surfaces through either a covalent bond or electrostatic interactions. Future work will be dedicated to the recovery of such Janus NPs from the substrate surface.

Dye-sensitized solar cells based on a double layered TiO2 photoanode consisting of hierarchical nanowire arrays and nanoparticles with greatly improved photovoltaic performance

A novel double layered photoanode consisting of oriented hierarchical anatase TiO2 nanowire arrays (HNW) and nanoparticles (NP) has been successfully fabricated on a Ti-foil substrate via a two-step hydrothermal and screen-printing process, respectively. Compared to a NP based cell, the photovoltaic performance of the TiO2 HNW cell highlights several outstanding properties, including superior light scattering, rapid electron transport and lower electron recombination rate. Furthermore, the effect of the TiO2 NP film thickness (top layer) on the power conversion of the DSSCs has been investigated in detail. The DSSC based on a Ti/TiO2 HNW + NP photoelectrode with a total thickness of 31 μm (HNW: 13 μm; NP: 18 μm) shows the highest power conversion efficiency of 7.92%, which is remarkably higher than those of 13 μm HNW (4.52%), 18 μm NP (6.50%) and 31 μm NP (5.99%) photoelectrodes. The enhancement of the efficiency for the double layered photoanode based cell compared to the single NP is mainly attributed to better light scattering capability, faster electron transport and lower electron recombination for the former.

Characterization of the Sensor Response of Gold Nanoparticle Chemiresistors

The response time of chemiresistors consisting of gold nanoparticles coated with self-assembled monolayers (SAM) of 1-hexanethiol, exposed to different hydrocarbons dissolved in water, is investigated with respect to the analyte SAM/water partition coefficient, the analyte−water flow velocity, and the nanoparticle film thickness. We show experimentally that the response time is proportional to the analyte SAM/water partition coefficient and that for sufficiently large velocities the response time becomes flow velocity independent. The dependence of the response time on film thickness is found to be different in the two different flow velocity regimes examined. We outline in detail a theoretical model that explains our experimental data.

Parts per Billion-Level H2S Detection at Room Temperature Based on Self-Assembled In2O3 Nanoparticles

Homogenous In2O3 nanoparticles (NPs) with diameters in the range of 6−10 nm were synthesized via a chemical solution method, and nanoparticles were assembled on Si substrate for H2S detection. The sensor demonstrates ultrahigh sensitivity to H2S to part per billion (ppb) levels at room temperature. Different sensor parameters were then investigated in terms of electrode gap, In2O3 NP film thickness, and surface modification by noble metals. It was found that sensitivity was slightly improved by reducing the electrode gap or increasing NP film thickness. However, sensitivity was dramatically enhanced (from 20 ppm to 20 ppb) after surface modification with 0.3 nm Au deposition. In addition, the sensor also shows a certain selective detection to H2S in comparison with other gases such as CO and NO2.

Linker-Molecule-Free Gold Nanorod Layer-by-Layer Films for Surface-Enhanced Raman Scattering

This paper reports a methodology for synthesizing and ordering gold nanorods into two-dimensional arrays at a water/hexane interface. This preparation method allows the systematic control of the nanoparticle film thickness. An investigation into the thickness-dependent surface-enhanced Raman scattering (SERS) of the adsorbed molecules revealed the nanorod (NR) films to have 1 order of magnitude stronger SERS enhancement than the nanosphere (NS) under similar experimental conditions. The exposed surface areas of the prepared NR and NS films were analyzed using electrochemical methods, and it was found that they had comparable exposed surface areas. Therefore, the order of magnitude difference in the enhancement factor was not due to the differences in surface area but to their intrinsic difference in the optical coupling of each film. The difference was attributed to the high density of junction points with the NR films in comparison with the corresponding NS films. Scanning emission microscopy showed that the NR films have line contacts with each other but the NS films have point contacts, which can explain the difference in SERS intensity between the NR and NS films.

Top-Down Approaches to the Formation of Silica Nanoparticle Patterns

This article reports a simple, versatile approach to the fabrication of lithographically defined mesoscopic colloidal silica nanoparticle patterns over large areas using spin-coating, interferometric lithography, and reactive-ion etching. One-dimensional nanoparticle films (bands) and 2D discs, diamonds, and holes with sub-micrometer periodicity, high quality, and excellent uniformity were successfully fabricated over large areas. The well-defined shape and period of the patterned nanoparticle film were controlled in the interferometric lithography step, while the thickness of nanoparticle film was easily tuned in the spin-coating step. This approach can extend to other deposition methods such as convective self-assembly, electrostatic self-assembly, and other materials such as metallic and ferromagnetic nanoparticles. We have also been able to generate sparse, random, isolated particle patterns, using a combination of interferometric lithography and layer-by-layer deposition as an extension of this approach to another deposition method, and to generate disc nanoparticle patterns using colloidal lithography as an extension of this approach to another lithography technique. These patterned films will find important applications in the fields of material growth, biosensors, and catalysis, as well as serving as building blocks for further fabrication.

Electrochemical properties of ferrocenylalkane dithiol-gold nanoparticle films prepared by layer-by-layer self-assembly

Abstract To explore charge transfer between nanostructured assemblies and an electrode surface, we have performed cyclic voltammetry (CV) of films self-assembled layer-by-layer using gold nanoparticles (NPs) and l-(hexanethiol)-1′-(ethanethiol) ferrocene (FDT). Reflection–Absorption Fourier Transform Infrared Spectroscopy (RAIRS) and Ultraviolet–visible Spectroscopy (UV–vis) of films on aminosilane-functionalised glass slides were used to confirm self-assembly. CV of films on gold electrodes was used to monitor redox peaks of the films following self-assembly of each FDT and NP layer. Addition of a NP layer consistently resulted in a significant decrease in redox peak height, while addition of a subsequent FDT layer resulted in a net overall increase. Occasionally, redox activity dropped substantially but recovered with increasing number of NP–FDT layers. All samples exhibited an increase in redox peak width and a slight increase in peak separation with increasing FDT-linked NP film thickness for the first 4–5 layers. No systematic trend was observed from sample to sample for subsequent layers. These results are consistent with a disordered, porous film structure. Importantly, because of increasing surface area and nanoparticle hopping sites, charge transfer between outer layers and underlying electrodes in such devices is not significantly hampered by increasing number of deposited NP/FDT layers, despite addition of intervening insulating material.