Electrochemical applications of a Au nanoparticle array fabricated using highly ordered dimpled Ta templates

Nonlithographic Formation of Ta2O5 Nanodimple Arrays Using Electrochemical Anodization and Their Use in Plasmonic Photocatalysis for Enhancement of Local Field and Catalytic Activity

We demonstrate the formation of Ta₂O₅ nanodimple arrays on technologically relevant non-native substrates through a simple anodization and annealing process. The anodizing voltage determines the pore diameter (25-60 nm), pore depth (2-9 nm), and rate of anodization (1-2 nm/s of Ta consumed). The formation of Ta dimples after delamination of Ta₂O₅ nanotubes occurs within a range of voltages from 7 to 40 V. The conversion of dimples from Ta into Ta₂O₅ changes the morphology of the nanodimples but does not impact dimple ordering. Electron energy loss spectroscopy indicated an electronic band gap of 4.5 eV and a bulk plasmon band with a maximum of 21.5 eV. Gold nanoparticles (Au NPs) were coated on Ta₂O₅ nanodimple arrays by annealing sputtered Au thin films on Ta nanodimple arrays to simultaneously form Au NPs and convert Ta to Ta₂O₅. Au NPs produced this way showed a localized surface plasmon resonance maximum at 2.08 eV, red-shifted by ∼0.3 eV from the value in air or on SiO₂ substrates. Lumerical simulations suggest a partial embedding of the Au NPs to explain this magnitude of the red shift. The resulting plasmonic heterojunctions exhibited a significantly higher ensemble-averaged local field enhancement than Au NPs on quartz substrates and demonstrated much higher catalytic activity for the plasmon-driven photo-oxidation of p-aminothiophenol to p,p'-dimercaptoazobenzene.

A gold coated polystyrene ring microarray formed by two-step patterning: construction of an advanced microelectrode for voltammetric sensing

A two-step patterning process was developed based on nanosphere lithography and plasma etching to fabricate an array of electrodes with two different gold ring structures: the arrays of Au micro-ring electrode (Au-MRE) and Au covered with polystyrene micro-ring electrode (Au-PS-MRE). The Au-MRE structure was fabricated by etching a monolayer of polystyrene (PS) spheres on indium tin oxide (ITO) surface to generate PS rings on ITO glass. PS rings served as a mask in secondary etching for blocking an interaction of oxygen plasma and ITO surface to create a ring-patterned ITO surface. Then, the PS residue was removed and gold was deposited. The site-selective electrodeposition of gold was carried out and an array of a gold ring structure was formed on the ITO glass. The Au-PS-MRE structure was fabricated by keeping the PS residue from second etching before deposition of gold. The Au-PS-MRE microelectrode was studied by using hexacyanoferrate as an electrochemical probe where it displayed steady state current in cyclic voltammetry. The respective calibration plots were acquired at a working potential of 0.31 V and 0.12 V (vs. Ag/AgCl) for oxidation and reduction reaction, respectively. The sensitivity is as high as 163.4-220.7 μA·mM^-1·mm^-2 which is larger by a factor of 95-132 compared to a conventional gold film macroelectrode. The detection limit (at a signal-to-noise ratio of 3) is 2.2 μM. This approach thus yields relatively effective and low-cost fabrication without resorting to high resolution instruments. Conceivably, the technique may be used to produce microelectrode arrays on a large scale. Graphical abstract Schematic presentation of a novel fabrication process of micro-ring electrode arrays. Two-step patterning based on nanosphere lithography leads to electrodes with great electrochemical performance. Direct deposition metal in the presence of polystyrene (PS) mask induces the formation of a new structure with arrays of gold covered with PS microring on the indium tin oxide (ITO) coated glass. The microelectrode-like behavior has been achieved using this fabrication process.

Carbon nanotube diameter control via catalytic Co nanoparticles electrodeposited in porous alumina membranes

Co nanoparticles electrodeposited into porous alumina membranes catalyse growth of CNTs with diameters smaller than the membrane pores.