Mesoporous silica films as hard templates for electrodeposition of nanostructured gold

Abstract

Metallic nanostructures have widespread applications in fields including materials science, electronics and catalysis. Mesoporous silica films synthesised by evaporation induced self-assembly and electrochemically assisted self-assembly with pores below 10 nm were used as hard templates for the electrodeposition of Au nanostructures. Electrodeposition conditions were optimised based on pore orientation and size. The growth of nanostructures was initiated at the electrode surface as confirmed by microscopy. The hard templates and Au electrodeposits were characterised electrochemically as well as with X-ray diffraction, small angle scattering and transmission electron microscopy. Finally, mesoporous silica hard templates were removed by hydrofluoric acid etching and stable Au nanoparticles on different electrode surfaces were achieved.

Fig. 1. The GISAXS patterns of (a) the mesoporous silica film template 1 synthesised by evaporation-induced self-assembly, (b) template 2 synthesised by electrochemically assisted self-assembly, and (c) and (d) the vertical and horizonal integration of (a) and (b) respectively. The incident angle was 0.3° and scan time set for 20 min. The peak information was calculated using GIXSGUI.

Fig. 2. (a) Top-view FE-SEM images of template 1; (b) a cross section FE-SEM image of template 1; (c) the size distribution histogram of the pores in (a); and (d) TEM of template 2. Software “Image J” was used to analyse the pore size distribution and “Origin” was used to draw the histogram. A Gaussian distribution in “Origin” was conducted to fit the histogram and calculate pore size.

Fig. 3. (a) Cyclic voltammograms obtained from an electrolyte of 0.5 mmol dm⁻³ K[AuCl₄] and 0.1 mol dm⁻³ KCl aqueous solution on a bare TiN substrate (black) and on a mesoporous silica film dip-coated on a TiN substrate (blue). (b) Cyclic voltammograms obtained from an electrolyte containing 1 mmol dm⁻³ K[AuCl₄] and 0.1 mol dm⁻³ KCl aqueous solution on a bare ITO (black) and on a mesoporous silica film coated on an ITO working electrode (blue). Scan rate 50 mV s⁻¹.

Fig. 4. Current transients during pulsed potential deposition (a) in 0.5 mmol dm⁻³ K[AuCl₄]: nucleation at −1.5 V for 1 s, followed by growth at −0.1 V for 1 s for 100 cycles (template 1), first 20 cycles are shown. (b) In 1.0 mmol dm⁻³ K[AuCl₄]: nucleation at −1.0 V for 5 s, followed by growth at 0 V for 25 cycles (template 2).

Fig. 5. In-plane GISAXS patterns of template 1 (a) and template 2 (b), mesoporous silica film template 1 and 2 (black), template 1 and 2 with surfactant F127 and C₂₀TAB (red) and gold-electrodeposited template 1 and 2 (blue). The incident angles for templates 1 and 2 were 0.25° and 0.30°, respectively.

Fig. 6. The grazing incidence XRD patterns of gold electrodeposited into templates 1 (TiN substrate) and 2 (ITO substrate), with substrate patterns and the standard intensities for gold shown for comparison. The incident angle was 1°.

Fig. 7. Top-view (a) and cross-view (b) FE-SEM images of gold electrodeposited in template 1; (c) A cross-view FE-SEM image of gold electrodeposited in template 2; (d) the size distribution histogram of the particles in (c). These images were obtained by Zeiss Gemini FE-gun SEM. HF vapour etching of MSFs to reveal Au electrodeposits.

Fig. 8. Top-view FE-SEM images of gold nanoparticles arrangements at the surface after etching template 1 (a) and template 2 (c). (b) and (d) are the size distribution histograms of the particles in (a) and (c) respectively.