The use of polarization-dependent SERS from scratched gold films to selectively eliminate solution-phase interference

Abstract Polarization-dependent surface-enhanced Raman scattering (SERS) was studied for oxazine 720 molecules adsorbed on a scratched gold surface placed in situ and under electrochemical control. A quantitative method for evaluating the observed polarization dependence will be introduced. This method takes into account the polarization artifacts caused by optical elements in the light microscope used for Raman microscopy. Intensity of the SERS obtained from oxazine 720 adsorbed on scratches in gold showed a polarization dependence after correction was made for these artifacts. In contrast, intensity of the ordinary Raman signal obtained from perchlorate ions in the solution above a scratched gold surface was found to be polarization-independent. Therefore, polarization effects can be used to selectively remove solution-phase interference signals from the SERS spectrum of an adsorbed analyte. These polarization effects were found to be independent of the applied potential, meaning the methodology is applicable to electrochemical SERS studies

Cu nanoparticles enable plasmonic-improved silicon photovoltaic devices

This work examines the effect of copper nanoparticles (Cu NPs) on the photocurrent efficiency of silicon photovoltaic (Si PV) devices. An optimized synthesis of stable Cu NPs is reported together with a procedure for their immobilization on the Si PV surface. A comprehensive analysis of the photocurrent and power dependence of the Cu NPs surface coverage and size is presented. A decrease in photoconversion was observed for wavelengths shorter than similar to 500 nm, due to the Cu interband absorption. In the low surface coverage limit, where the level of aggregation was found to be low, the surface plasmon resonance absorption dominates leading to a modest effect on the photocurrent response. As the number of aggregates increased with the surface coverage, the photocurrent efficiency also increased, and a maximum enhancement power conversion of 16% was found for a 54 +/- 6 NPs per mu m(2) PV cell. This enhancement was attributed to SPR light scattering and trapping into the Si PV device. Higher surface coverage yielded numerous aggregates which acted as a bulk coating and caused a decrease in both photocurrent and power measurements.Department of Foreign Affairs and International Trade Canada (DFAIT) through the Emerging Leaders in the Americas (ELAP) programDepartment of Foreign Affairs and International Trade Canada (DFAIT) through the Emerging Leaders in the Americas (ELAP) programCIAMFAPESP programCIAM-FAPESP programCNPqCNPqNSERCNSERCUniversity of VictoriaUniversity of Victori

Surface-Enhanced Resonance Raman Scattering (SERRS) Using Au Nanohole Arrays on Optical Fiber Tips

Abstract Circular and bow tie-shaped Au nanoholes arrays were fabricated on gold films deposited on the tips of singlemode optical fibers. The nanostructures were milled using focused ion beam with a high quality control of their shapes and sizes. The optical fiber devices were used for surfaceenhanced resonance Raman scattering (SERRS) measurements in both back-and forward-scattering geometries, yielding promising performance in both detection arrangements. The effect of the hole shape on the SERRS performance was explored with the bow tie nanostructures presenting a better SERRS performance than the circular holes arrays. The results present here are another step towards the development of optical fiber tips modified with plasmonic nanostructures for SERRS applications

Peering into the formation of template-free hierarchical flowerlike nanostructures of SrTiO3

The development of efficient advanced functional materials is highly dependent on properties such as morphology, crystallinity, and surface functionality. In this work, hierarchical flowerlike nanostructures of SrTiO3 have been synthesized by a simple template-free solvothermal method involving poly(vinylpyrrolidone) (PVP). Molecular dynamics simulations supported by structural characterization have shown that PVP preferentially adsorbs on {110} facets, thereby promoting the {100} facet growth. This interaction results in the formation of hierarchical flowerlike nanostructures with assembled nanosheets. The petal morphology is strongly dependent on the presence of PVP, and the piling up of nanosheets, leading to nanocubes, is observed when PVP is removed at high temperatures. This work contributes to a better understanding of how to control the morphological properties of SrTiO3, which is fundamental to the synthesis of perovskite-type materials with tailored properties

Selective suppression of {112} anatase facets by fluorination for enhanced TiO2 particle size and phase stability at elevated temperatures

Generally, anatase is the most desirable TiO2 polymorphic phase for photovoltaic and photocatalytic applications due to its higher photoconductivity and lower recombination rates compared to the rutile phase. However, in applications where temperatures above 500 °C are required, growing pure anatase phase nanoparticles is still a challenge, as above this temperature TiO2 crystallite sizes are larger than 35 nm which thermodynamically favors the growth of rutile crystallites. In this work, we show strong evidence, for the first time, that achieving a specific fraction (50%) of the {112} facets on the TiO2 surface is the key limiting step for anatase-to-rutile phase transition, rather than the crystallite size. By using a fluorinated ionic liquid (IL) we have obtained pure anatase phase crystallites at temperatures up to 800 °C, even after the crystallites have grown beyond their thermodynamic size limit of ca. 35 nm. While fluorination by the IL did not affect {001} growth, it stabilized the pure anatase TiO2 by suppressing the formation of {112} facets on anatase particles. By suppressing the {112} facets, using specific concentrations of fluorinated ionic liquid in the TiO2 synthesis, we controlled the anatase-to-rutile phase transition over a wide range of temperatures. This information shall help synthetic researchers to determine the appropriate material conditions for specific applications

Present and Future of Surface-Enhanced Raman Scattering.

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article

Recessed Gold Nanoring–Ring Microarray Electrodes

A 6 × 6 recessed Au nanoring–ring electrodes microarray was fabricated over a glass substrate using focused ion beam milling. The electrochemical responses of this device to a reversible redox pair were examined. In redox-cycling mode, the lower ring acts as a generator and the upper ring as a collector. High collection efficiencies (close to 100%) and amplification factors (∼3.5) were achieved with this configuration. The redox-cycling behavior of this device was modeled using COMSOL Multiphysics. The effects of scaling the geometric parameters of the electrodes (ring height and radius), potential sweep rates, and inter-electrode gap distance were evaluated through simulations. The computational models showed that the attainable limiting current depends strongly on the ring radius, while it is almost independent of the ring height variations (for a particular inter-electrode gap). The effects of the scan rate and inter-electrode gap distance on the electrochemical characteristics of the device are also discussed. This study provides insights on the influence of the geometry on the performance of these arrays, which should guide the development of future applications

Comparing the Electrochemical Response of Nanostructured Electrode Arrays

The electrochemical responses from periodic 6 × 6 arrays of recessed gold nanorings were compared to the 6 × 6 recessed gold nanodiscs arrays. The nanostructured arrays were fabricated by focused ion beam milling and their electrochemical response from a reversible redox pair was obtained. Three-dimensional cyclic voltammetry simulations using COMSOL were performed on 6 × 6 periodic arrays of both recessed nanodiscs and nanorings to elucidate the differences in mass transport between these geometries. Specific mass transport properties near the electroactive surface of the electrodes were elucidated by analyzing the calculated concentration profiles of the redox species. Relative contributions from radial diffusion regimes inside the nanoholes play an important role on the electrochemical response of the recessed nanorings. Arrays of nanodiscs are common in different types of applications, particularly in biosensors. The results presented here suggest that the performance and sensitivity of electrochemical nanosensors can be simply improved by implementing electrodes with a geometry which offer greater current density while keeping the overall footprint of the sensor element constant

Comparing the Electrochemical Response of Nanostructured Electrode Arrays

The electrochemical responses from periodic 6 × 6 arrays of recessed gold nanorings were compared to the 6 × 6 recessed gold nanodiscs arrays. The nanostructured arrays were fabricated by focused ion beam milling and their electrochemical response from a reversible redox pair was obtained. Three-dimensional cyclic voltammetry simulations using COMSOL were performed on 6 × 6 periodic arrays of both recessed nanodiscs and nanorings to elucidate the differences in mass transport between these geometries. Specific mass transport properties near the electroactive surface of the electrodes were elucidated by analyzing the calculated concentration profiles of the redox species. Relative contributions from radial diffusion regimes inside the nanoholes play an important role on the electrochemical response of the recessed nanorings. Arrays of nanodiscs are common in different types of applications, particularly in biosensors. The results presented here suggest that the performance and sensitivity of electrochemical nanosensors can be simply improved by implementing electrodes with a geometry which offer greater current density while keeping the overall footprint of the sensor element constant