© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim OP29 wileyonlinelibrary.com www.MaterialsViews.com www.advopticalmat.de COMMUNICATION X. Zheng, Dr. V. Volskiy, Prof. G. A. E. Vandenbosch SAT-TELEMIC, Katholieke Universiteit Leuven B-3001 Leuven, Belgium Dr. C. Reinhardt, Prof. B. N. Chichkov Laser Zentrum Hannover e.V., D-30419 Hanover, Germany Dr. A. I. Kuznetsov Advanced Concepts Group Data Storage Institute 5 Engineering Drive I, 117608, Singapore Dr. G. Tsutsumanova, Prof. S. Russev Department of Solid State Physics Faculty of Physics Sofia University Sofia 1164, Bulgaria E. J. Osley, Dr. P. A. Warburton London Centre for Nanotechnology University College London 17-19 Gordon Street, London, WC1H 0AH, United Kingdom Department of Electronic and Electrical Engineering University College London Torrington Place, London, WC1E 7JE, United Kingdom Dr. V. K. Valev, Prof. T. Verbiest Molecular Electronics and Photonics INPAC, Katholieke Universiteit Leuven, BE-3001, Belgium E-mail: v.k.valev@fys.kuleuven.be D. Denkova, Y. Jeyaram, Prof. V. V. Moshchalkov Superconductivity and Magnetism & Pulsed Fields Group INPAC, Katholieke Universiteit Leuven, BE-3001, Belgium Prof. A. V. Silhanek Département de Physique Université de Liège Bât. B5, Allée du 6 août, 17, Sart Tilman, B-4000, Belgium B. De Clercq, Prof. M. Ameloot University Hasselt and transnational University Limburg BIOMED, Diepenbeek, Belgium Prof. O. A. Aktsipetrov Department of Physics Moscow State University 11992 Moscow, Russia Dr. V. Petkov Dept. Metallurgy and Materials Engineering Katholieke Universiteit Leuven Kasteelpark Arenberg 44, B-3001, Belgium DOI: 10.1002/adma.201103807 When a pebble drops on the surface of water, it is often observed that a water column, or “back-jet”, surges upwards. Counter-intuitive though it might be, a similar phenomenon can occur when light shines on a metal film surface. Indeed, tightly focused femtosecond laser pulses carry sufficient energy to locally melt the surface of gold film and the impact from these laser pulses produces a nanojet, as has been theo- retically described [1,2] and experimentally demonstrated. [3–5] In particular, these studies show that the very fast cooling rate of the nanojet, allows it to “freeze” in shape, as the temperature drops below the melting point. [6] The gold surface can therefore be imprinted with nanostructures, each marking the point of impact of a laser pulse. Moreover, just as is the case with water, nanojet can result in the projection of a small droplet. Recently, this phenomenon led to the development of a nanofabrication technique, whereby gold spheres with very regular dimensions are collected and assembled into nanopatterns. [7–10] Nanopat- terns can also be produced on the gold surface itself with the help of local field enhancements resulting from bringing either a sharp tip [11,12] or spheres close to the surface. [13] But what if the gold surface was nanopatterned to begin with, see Figure 1a? For nanostructures with thickness much smaller than the wavelength of light, because the absorption length of the laser radiation is larger than the thickness of the nanostructure, it was first reported that the temperature stays almost homoge- neous over the whole volume of each nanostructure. [14] Conse- quently, upon illumination and melting of the nanostructures the shape change starts from the sharpest regions, where the forces due to surface tension are high. The reshaping process continues until the nanostructure forms a sphere, minimizing surface tension. At this point the nanostructure constitutes a droplet of melted material and it can be ejected from the sur- face. This physical mechanism was later refined since it was shown that the temperature over the volume of the nanopar- ticles can become inhomogeneous. [15] More specifically, it was reported that near curved surfaces, optical near-fields can locally heat up the material and lower the ablation threshold. The mechanism of the ablation was not demonstrated directly. Ventsislav K. Valev,* Denitza Denkova, Xuezhi Zheng, Arseniy I. Kuznetsov, Carsten Reinhardt, Boris N. Chichkov, Gichka Tsutsumanova, Edward J. Osley, Veselin Petkov, Ben De Clercq, Alejandro V. Silhanek, Yogesh Jeyaram, Vladimir Volskiy, Paul A. Warburton, Guy A. E. Vandenbosch, Stoyan Russev, Oleg A. Aktsipetrov, Marcel Ameloot, Victor V. Moshchalkov, and Thierry Verbiest Plasmon-Enhanced Sub-Wavelength Laser Ablation: Plasmonic Nanojets Adv. Mater. 2012, 24, OP29–OP35