Palladium crystals of various morphologies for SERS enhancement

Palladium (Pd) nanostructures with urchin-like, hemispherical, flower-like, and plate-like morphologies were controllably deposited on silicon substrates in aqueous hydrogen fluoride (HF) solution at room temperature. The morphology of the Pd nanostructures changed from urchin-like to hemispherical and flowerlike in the presence of polyvinyl pyrrolidone (PVP, MW = 55 000) and cetyltrimethylammonium bromide (CTAB), respectively. The Pd nanostructures were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, field emission scanning electron microscopy, energy-dispersive X-ray, and X-ray diffraction. The size and shape of palladium nanostructures were investigated as a function of metal precursor concentration, reaction time and organic additive concentration. The possible formation mechanisms were discussed. In addition, the morphology-dependent surface-enhanced Raman scattering (SERS) of the as-synthesized Pd nanostructures were investigated. The results showed that urchin-like Pd nanostructures had the highest SERS activity than the other Pd nanostructures for Rhodamine 6G (R6G) probe molecules.