Plasmonic Heating-Assisted Transformation of SiO 2 /Au Core/Shell Nanospheres (Au Nanoshells): Caveats and Opportunities for SERS and Direct Laser Writing Ivano Alessandri & Matteo Ferroni & Laura E. Depero Received: 11 May 2012 / Accepted: 12 August 2012 / Published online: 6 November 2012 # Springer Science+Business Media New York 2012 Abstract The selective modification of silica/gold nano- spheres (gold nanoshells) driven by plasmonic heating is demonstrated. Direct laser writing and reshaping of nano- shell assemblies can be easily controlled and exploited for nanofabrication purposes. The modified nanoshells exhibit improved surface enhanced Raman scattering, allowing to settle most of the issues related to nanoshell stability under working conditions. Keywords Gold nanoshells . Laser writing . Plasmonic heating . SERS Silica/gold core/shell nanospheres, also known as gold nanoshells, are intensively investigated because of their exciting plasmonic properties, which make them suitable candidates for a number of applications in nanotechnology. The Halas’ group and collaborators demonstrated that nano- shells can tune both their surface plasmon resonance posi- tion and scattering-to-absorption contributions by changing the core-to-shell ratio [1]. This tunability makes nanoshells promising substrates for surface enhanced Raman scattering (SERS) [2] and photothermal therapy [3]. Moreover, nano- shell clusters can be conveniently assembled to support tunable electric, magnetic, and Fano-like resonances [4]. Hentschel et al. recently demonstrated the transition from isolated to collective optical modes in plasmonic oligomers fabricated by electron beam lithography, so remarking the crucial role of geometrical design in tailoring the optical properties of these systems [5]. Developing new routes for modifying shape and geometry of nanoshells is a pushing task for nanoplasmonics. Lassiter et al. demonstrated that single Au nanoshells can be controllably transformed into nanoeggs and nanocups by electron beam- induced ablation [6]. In that case, the direct modification of nanoshell morphology caused an impressive change in light scattering, and novel shapes supporting both electric and mag- netic plasmon modes can be easily generated. Now, a new challenging question arises: could silica nanoshells and nano- shell assemblies be modified by exploiting their own optother- mal properties? Addressing this issue is critical not only in view of adding a new powerful tool to the nanofabrication palette but also to assess the thermal stability of nanoshell assemblies to be used as substrates for SERS experiments. In recent years, we have demonstrated that polystyrene core-based nanoshells assembled in form of colloidal crystal can develop strong plasmonic heating effects even upon low power, continuous wave (c.w.) laser irradiation. These effects were successfully exploited to write 2D patterns and introduce line and point defects in colloidal crystals [7]. Further exten- sions of the “plasmonic heating-based” approach allowed the local transformation of amorphous titania into anatase at se- lected sites of colloidal crystals and nanoshells [8–11]. In all of these cases, the exothermic decomposition of either the poly- meric cores or organic capping agents provided an important contribution for local heating generation and pressure buildup. On the contrary, silica cores do not melt below 1,000 °C, so that their high thermal stability could be a major barrier for plasmonic heating-based approaches. Aguirre et al. [12] dem- onstrated that high-power pulsed femtosecond lasers can re- shape and destroy Au nanoshells dispersed in water. However, a reliable experimental route for achieving selective reshaping I. Alessandri (*) : L. E. Depero INSTM and Chemistry for Technologies Laboratory, University of Brescia, via Branze 38, 25123 Brescia, Italy e-mail: ivano.alessandri@ing.unibs.it M. Ferroni CNR-INFM, IDASC, Sensor Laboratory, University of Brescia, via Valotti 9, 25123 Brescia, Italy Plasmonics (2013) 8:129–132 DOI 10.1007/s11468-012-9455-0