Chung Chin Yu

Enhancements in intensity and stability of surface-enhanced Raman scattering on optimally electrochemically roughened silver substrates

In this work, different conditions for electrochemically roughening silver substrates were investigated to obtain the best surface-enhanced Raman scattering (SERS) performance. Experimental results indicate that Ag electrodes can be cycled in deoxygenated aqueous solutions containing 0.1 N HCl from −0.3 to +0.2 V vs.Ag/AgCl at 25 mV s−1 for five scans to obtain the strongest SERS effects. Using this substrate, the SERS intensity of adsorbed Rhodamine 6G (R6G) can be increased 9-fold, compared with that of R6G adsorbed on an Ag substrate prepared using the general literature methods. Moreover, the SERS enhancement capabilities of the newly developed Ag substrate seriously decays at 200 °C, compared to 125 °C for the generally roughened Ag substrates. The reduction of the SERS intensity upon aging is also lessened for this newly developed substrate. Further investigations revealed that surface morphology and the Cl content on the roughened Ag substrates have significant influence on the corresponding SERS performances.

Temperature effect of electrochemically roughened gold substrates on polymerization electrocatalysis of polypyrrole

In this work, electrochemical methods were used to prepare complexes with Au and Cl species on bulk Au substrates. Then the electrochemically roughened Au substrates were further heat-treated at different temperatures. The effect of temperatures used in heat treatments between 25 and 100 degrees C on electrocatalytical polymerization of polypyrrole (PPy) formed on the prepared gold substrates was first investigated. The result indicates that the optimally electrocatalytical capability of the heat-treated Au substrate for PPy polymerization is at 75 degrees C. Moreover, the autopolymerized PPy on the roughened Au substrate treated at 75 degrees C demonstrates the highest oxidation level and oxidation degree of 0.32 and 0.50, respectively. Primary results indicate that complexes with positively charged Au act as oxidants, and perchlorate and chloride ions act as dopants for the oxidation-polymerization of PPy.

Simple strategy to improve surface-enhanced Raman scattering based on electrochemically prepared roughened silver substrates.

We develop an easy and effective pathway to improve surface-enhanced Raman scattering (SERS) effects of probe molecules of Rhodamine 6G (R6G) adsorbed on electrochemically prepared roughened Ag substrates. In general SERS studies, SERS-active metal substrates are first prepared. Then probe molecules are adsorbed on them to evaluate the relative SERS effects. In this study, we employ electrochemical oxidation-reduction cycle (ORC) treatments in 0.1 M KCl solutions containing probe molecules of 2 x 10(-5) M R6G to prepare R6G-adsorbed SERS-active Ag substrates for one step. Encouragingly, based on this strategy, the SERS intensity of adsorbed R6G can be increased by 1 order of magnitude, as compared with that of R6G adsorbed on a roughened Ag substrate beforehand, which was generally shown in the literature. Moreover, this improved SERS effect based on this strategy is also effective for 2 x 10(-9) M probe molecules, which is at a level of single molecule detection based on Ag colloids. It is also effective for probe molecules of ClO(4)(-) with low Raman cross section and for other electrochemically prepared SERS-active substrates of Au. Further analyses indicate that the increase in SERS activity in this new method is most likely due to the incorporation of more chloride ions into the substrate.

Novel surface-enhanced Raman scattering-active silver substrates containing visible light-responsible Tio2 nanoparticles

We report here the first electrochemically prepared surface-enhanced Raman scattering (SERS)-active silver substrates containing visible light-responsible TiO2 nanoparticles. The SERS-active Ag substrates with TiO2 nanoparticles were prepared by roughening the substrates using electrochemical oxidation–reduction cycles (ORC) in 0.1 M HCl aqueous solutions containing 1 mM visible light-responsible TiO2 nanoparticles. Based on these prepared substrates, the SERS of Rhodamine 6G (R6G) exhibits a higher intensity by one order of magnitude, as compared with that of R6G adsorbed on a roughened Ag substrate without TiO2 nanoparticles. Moreover, the practical limit of detection (LOD) of R6G can be reduced by five orders of magnitude from 2 × 10−10 to 2 × 10−15 M owning to the additional contribution of TiO2 nanoparticles to the whole SERS effects.

Surface-enhanced Raman scattering-active silver nanostructures with two domains.

Generally, a controllable and reproduced surface roughness for surface-enhanced Raman scattering (SERS) studies can be generated through control of the electrochemical oxidation-reduction cycles (ORC) procedure. In this work, we propose a new sonoelectrochemical approach to prepare SERS-active substrates with two domain-Ag nanostructures. The method is based on a strategy of deposition-dissolution cycles (DDCs) by using a cathodic overpotential and an anodic overpotential from open circuit potential (OCP) in turn under sonication. The prepared SERS-active substrate demonstrates large Raman scattering enhancement for adsorbed Rhodamine 6G (R6G) with an enhancement factor of 2.3×10(8) and a limit of detection of 2×10(-13)M. The improved SERS performances can be successfully explained from the viewpoints of electromagnetic (EM) and chemical (CHEM) enhancements.

Electrochemically prepared surface-enhanced Raman scattering-active silver substrates with improved stabilities

In this work, SiO2 nanoparticles-modified surface-enhanced Raman scattering (SERS)-active silver substrates were prepared by electrochemical oxidation-reduction cycles (ORC) methods in 0.1 N HCl aqueous solutions containing 1 mM SiO2 nanoparticles to improve their thermal stabilities and anti-aging abilities in SERS performances. Then these SERS-active substrates were further modified with different contents of SiO2 nanoparticles to improve their corresponding SERS performances. Experimental results indicate that the operation temperature can be significantly raised from 125 to 175°C based on this modified SERS-active Ag substrate. Also, the aging in SERS intensity is also depressed on this modified Ag substrate due to the contribution of SiO2 nanoparticles. Moreover, the SERS enhancement capability on this modified Ag substrate is gradually raised from 25°C to a maximum at 55°C and monotonically decreased from 55 to 60°C. This is a 10°C delay as compared with the similar phenomenon observed on the unmodified Ag substrate.