Highly ordered noble metal nanoparticle (NP) arrays are produced using a glancing angle deposition on stepped substrates. The versatility of the technique is demonstrated by depositing different metals, resulting in shifts of the resonance positions. The behaviour of the NP arrays grown is predicted by a dipolar model, and it is measured using reflectance anisotropy spectroscopy (RAS). Fine tuning of the resonances can be finally realised by selecting the deposition parameters. The combined application of both RAS and deposition at glancing angles provides a unique tool to grow NP arrays with the tunable plasmonic resonances in the entire visible range. 3,4 For these spectroscopic techniques, the resonant energy of the structures needs to match the energy of the exciting laser.5 If the interparticle separation is smaller than the average NP diameter, 6 the electric field in the interstitial space is enhanced at resonance by orders of magnitude.
7The required NP arrangements can be readily obtained using lithographic techniques, 1 but these are unsuitable for the production of large scale active areas. Typical colloidal processes could be a solution, 8 but ordered deposition onto a substrate is required. The resulting optical spectra depend also on the parameters governing the coupling between NPs and on the morphology of the resulting structures. These growth methods are material specific and thus require unique preparation recipes, depending on the material utilised. Glancing angle deposition of adatoms can provide a possible solution (see Fig. 1).9-14 A collimated adatom flux is directed towards the steps, which act as preferential growth sites. Adatoms then diffuse along the steps and coalesce, forming NP arrays. This self-assembled technique is simple, easily scalable, and mainly dependent on geometrical considerations. It is then conceptually independent of the deposition material. This letter demonstrates that NP arrays of different materials can be produced using this deposition method. The resulting resonances can be tuned over the whole visible range once the material choice is combined with different deposition parameters. At the same time, reflectance anisotropy spectroscopy (RAS) can be used to monitor, in situ, the evolution of resonance profiles during the growth. Structures with a particular resonance energy suitable for enhancements spectroscopy can then be obtained following this route.Advantages in a material independent production method of NP arrays can be readily demonstrated by simulations. The anisotropic optical response can be reproduced by modelling each identical NP as a supported ellipsoid placed on a rectangular lattice. Once the dimensions involved are much smaller than the wavelength of light, the NP layer can be approximated as a continuous layer having an effective anisotropic in-plane dielectric function,where i ¼ (x,y), e s , and e m are the dielectric functions of the surrounding medium and of the metal, respectively. The standard shape depolarization factorthus taking into ac...