Authors: X. Vidal, W.J. Kim, A. Baev, H. S. Jee, V. Tokar, M.T. Swihart, and P.N. Prasad.
Affilation: The Institute for Lasers, Photonics and Biophotonics, Spain
Pages: 234 - 237
Keywords: chirality, two-photon, nano-particles, plasmon
We present an approach to produce micropatterns of metallic nanoparticles (NPs) that preserve key optical properties of the individual NPs. The technique uses a photothermal reaction induced by two-photon direct laser writing. The studied NP property is plasmon chirality, which was obtained via chemical conjugation of Ag NPs with chiral ligands. This was achieved using a facile surface treatment of silver NPs functionalized with thermally cleavable chiral ligands: N-(tertbutoxycarbonyl)-L-cysteine methyl ester. The ligand cleavage initiated by a femtosecond pulsed laser induced thermal reaction results in a significant change in dispersiblility of the nanocrystals, thereby enabling a solvent selective development process after photo-patterning. We analyzed the optical chirality of the Ag NP films before and after micropatterning by two-photon lithography. We show that this patterning technique allows the patterned film to maintain this predefined optical property. In contrast, we show the disadvantage of the common use of a photo-acid generator for the cleavage of solubilizing groups via protonation. In this case, the ligand protonation results in the loss of the chiral behavior. In conclusion, we show both bottom-up and top-down techniques working simultaneously to obtain patterned structure with submicron resolution and optical properties conferred by the nanoparticle constituents. The two-photon absorption process occurs at the localized surface plasmon resonance of Ag NPs. It is the strong two-photon absorption of the Ag NPs that allows this highly localized photochemistry to be initiated in subwavelength domains without addition of any photosensitizer.