Plasmonic Properties Of Anchored Nanoparticles Fabricated By Reactive Ion Etching And Nanosphere Lithography

Aqueous environments pose unique challenges to the use of nanoparticle platforms for development of robust in vitro and in vivo sensors. A method is developed to anchor nanoparticles into a glass substrate by combining nanosphere lithography (NSL) and reactive ion etching (RIE) to create a mechanically durable sensing platform. The increased mechanical performance is attributed to the higher adhesion strength of NSL nanoparticles anchored in shallow nanowells formed by RIE. Using atomic force microscopy (AFM), anchored and conventional NSL nanoparticle arrays were subjected to increasing normal forces. The anchored nanoparticles were able to withstand normal forces 3 times greater (35.1 nN) compared to the conventional NSL nanoparticles (12.4 nN) prior to separation from the glass substrate. Superior adhesion in a constant flow aqueous environment is demonstrated by extinction measurements. After 1 h of 1.5 mL/min flow, extinction intensity decreased by 53% for bare and 13% for functionalized nanoparticles that were not anchored while extinction intensity decreased by only 15% for bare and less than 1% for functionalized nanoparticles that were anchored. A systematic shift to longer wavelengths is observed in the localized surface plasmon resonance (LSPR) spectra of the nanoparticle arrays as the embedded depth increases. This systematic shifting behavior of the LSPR wavelength maximum, λmax, in the range from 678 to 982 nm, can be used to tune the plasmon position. LSPR shifting is used to demonstrate the detection of Alzheimer\u27s precursor ligands as a potential biosensing application of the anchored nanoparticle arrays. Furthermore, we estimate the enhancement factors for SERS of the anchored nanoparticles are on the same order of magnitude (108) as the nanoparticles on flat substrates. Theoretical modeling is conducted to understand the shifting behavior of the anchored nanoparticle arrays. © 2007 American Chemical Society

Preferred Orientation in Sputtered TiO₂ Thin Films and Its Effect on the Photo-Oxidation of Acetaldehyde

Crystal orientation is not typically considered when investigating the reactivity of thin films. We propose that accounting for the preferred crystallographic orientation may serve as an indirect measure of the active sites along the solid–solid interface that are difficult to measure with direct techniques. The goal of this work is to identify the preferred orientation, examine its evolution as a function of synthesis parameters, and determine its effect on photoreactivity. We examine the effect of substrate radio frequency (RF) bias and reactive gas partial pressure on the structure and photoreactivity of TiO₂ films synthesized by reactive direct current (DC) magnetron sputtering. We characterize these films using ellipsometry, scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD), and pole figure scans, and test their photoreactivity with the degradation of acetaldehyde under 365 nm UV light. We find that, in the parameter space investigated, changes in RF bias strongly influence both film texture and reactivity, and that the orientation of the crystallites is the best predictor of photoreactivity. Under the synthesis conditions tested, we observe an optimum RF bias of −50 V at which the films exhibit biaxial texture with the <i>c</i>-axis parallel to the surface with maximum crystallinity and degree of orientation, corresponding to a maximum in the reactivity as well. Beyond this point a change in the preferred orientation is observed, and the films transition to a fiber texture with the <i>c</i>-axis normal to the film surface and the appearance of small amounts of rutile. The effect of texture on reactivity is discussed

Effect of Dimensionality on the Photocatalytic Behavior of Carbon–Titania Nanosheet Composites: Charge Transfer at Nanomaterial Interfaces

Due to their unique optoelectronic structure and large specific surface area, carbon nanomaterials have been integrated with titania to enhance photocatalysis. In particular, recent work has shown that nanocomposite photocatalytic performance can be improved by minimizing the covalent defect density of the carbon component. Herein, carbon nanotube–titania nanosheet and graphene–titania nanosheet composites with low carbon defect densities are compared to investigate the role of carbon nanomaterial dimensionality on photocatalytic response. The resulting 2D–2D graphene–titania nanosheet composites yield superior electronic coupling compared to 1D–2D carbon nanotube–titania nanosheet composites, leading to greater enhancement factors for CO₂ photoreduction under ultraviolet irradiation. On the other hand, 1D carbon nanotubes are shown to be more effective titania photosensitizers, leading to greater photoactivity enhancement factors under visible illumination. Overall, this work suggests that carbon nanomaterial dimensionality is a key factor in determining the spectral response and reaction specificity of carbon–titania nanosheet composite photocatalysts