ARTICLE TYPE www.rsc.org/xxxxxx | XXXXXXXX

This journal is © The Royal Society of Chemistry [year] Journal Name, [year], [vol], 00–00 | 1

Supplementary material for Shaping Patterned Gold Nanoparticles using PDMS templates

Colm T. Mallon, Robert J. Forster and Tia E. Keyesa

Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X First published on the web Xth XXXXXXXXX 200X 5

DOI: 10.1039/b000000x

Materials and methods

Polystyrene spheres (600 nm) were obtained from Bangs Laboratories Inc. Polydimethylsiloxane (Sylgard 184-Dow Corning) was obtained from Farnell. Sputter coating was 10

performed using a Quorum Technologies (SC7640) sputter coater. SEM images were collected using an Hitachi S-3000N scanning electron microscope. Gold was deposited using a commercially available salt (Techni Gold 25, from Technic Inc) in a conventional three electrode cell using a platinum 15

flag counter electrode and a Ag/AgCl (sat. KCl) reference electrode. A CH Instruments (model 660) was used to hold the potential at -0.95 V to deposit gold. Reflectance spectra were collected using an Analytical Instrument Systems Model DT1000 CE light source and an Ocean Optics Inc S2000 fibre 20

optic detector. All spectra were normalised with reference to the reflection of a silver mirror, which showed complete reflection in the visible region. Atomic force images were obtained using a Nano-scope III (Digital Instruments) and silicon tips (Veeco Probes HMX-10). 25

The polystyrene sphere template was assembled on a cleaned glass slide by placing the slide upright into a 1% sphere solution (w/w) and allowing evaporation in ambient conditions. PDMS is pored onto the array template and is 30

cured at 1000 C for one hour. After curing the PDMS is cut and peeled off the glass slide. Stretching is performed using a vice and the stretched template is glued while held by the vice to a glass slide to maintain the stretched position. Sputtering a 60 nm gold layer on these arrays creates the gold nano-void 35

structure. The nanoparticle arrays are created by electrochemical deposition of gold onto these sputtered samples, which are now conducting. After the electrodeposition step the exposed freshly deposited gold surface is glued to another glass slide. The gold film can be 40

striped from the PDMS array by leveraging the glass slide glued to the PDMS template against the glass slide glued to the gold. This results in the removal of the gold film from the PDMS template and reveals the nanoparticle array. The affintity of the gold for the PDMS mould appears low as the 45

gold film is typically completely removed from the template. Concave arrays of NPs can be fabricated by a similar process. The PDMS template is glued to a convex glass surface and gold coated as described above. Then the exposed gold surface is glued to a concave glass surface. The concave 50

nanoparticle array is revealed by pulling apart the two glass mounts.

Atomic force microscopy of PDMS templates

55

Fig. 1 (A) AFM of a PDMS template created using 600 nm spheres. The image dimensions are 5 x 5 μm. (B) Height profile of the PDMS array.

Figure 1 shows an AFM image and height profile for a PDMS 60

template formed using 600 nm spheres. These templates are created by poring and curing PDMS on top of an array of

Electronic Supplementary Material (ESI) for Chemical CommunicationsThis journal is © The Royal Society of Chemistry 2011

2 | Journal Name, [year], [vol], 00–00 This journal is © The Royal Society of Chemistry [year]

close packed polystyrene spheres on a glass slide. After curing, the PDMS is peeled off the glass slide. Figure 1A shows that the imprint of the spheres is transferred to the PDMS to make a nano-void hexagonal packed array. From this image it is clear that the spheres are not stripped form the 5

glass by the peeling process. Figure 1B indicates that the maximum depth of the cavity is approximately 160 nm, or approximately one quartor of the sphere diameter. The dish-like structure of the cavity is also evident from this height profile. 10

Notes and references a School of Chemical Sciences, Dublin City University, Dublin 9, Ireland. Fax: XX XXXX XXXX; Tel: XX XXXX XXXX; E-mail: tia.keyes@dcu.ie 15

Electronic Supplementary Material (ESI) for Chemical CommunicationsThis journal is © The Royal Society of Chemistry 2011