PHOTOACUSTIC CHARACTERIZATION OF RANDOMLY ORIENTED SILVER NANOWIRES FILMS

Metallic nanowires have cross-sectional diameters included between few to hundreds nanometers, while their lengths span from several to some hundreds microns. Metallic nanowires films show peculiar optical properties, such as high optical transmittance in the visible range, connected to the extremely reduced dimension of wires diameter, while still allowing for good electrical conduction, thus being suitable for those applications where transparent electrodes are required. As a consequence, metallic nanowires mesh, both randomly of systematically oriented, can be employed to tune the effective optical constants of the resulting film, and get peculiar spectral absorbance properties. In this work we present the photoacustic characterization in the UV/VIS range of randomly oriented silver nanowires films deposited onto either quartz or polymeric substrate. This study was performed over a set of films differing in both metallic nanowires’ dimensions, as well as metal content. Samples were prepared using suspensions of Ag-nanowires in isopropanol (IPA) (25 mg/ml), purchased from Seashell Technology, differing by both nanowires’ length and diameter. The starting IPA dispersion was added to de-ionized water, and then ultrasonicated for few minutes, filtrated and transferred onto the substrate by drop casting. The obtained films were characterized by scanning electron micrography (SEM images), thus the metal filling factor was retrieved with a matlab software based on visual method [1]. Following the morphological characterization, we employed photoacoustic spectroscopy (PAS) to investigate in details the absorbance spectra of silver nanowires films, in order to evidence their peculiar ab sorbance properties in the UV/VIS range. The us of PAS is particularly useful to investigate film that my display relevant scattering phenomena, as for silver nanowires films. We applied PAS in the UV/VIS range from 250 to 650 nm by using a low modulation frequency from 1Hz to 100Hz. The experimental results show that the choice of metal filling factor may affect the absorbance spectra of the resulting mesh. Acknowledgments This work has been performed in the framework of “FISEDA” program granted by Italian Ministry of Defence.