Anisotropic optical properties of oriented silver nanorice and nanocarrots in stretched polymer films

Stretching-induced orientation of both silver nanorice and silver nanocarrots dispersed in or deposited on the surface of poly(vinyl alcohol) (PVA) films was investigated using polarized UV-visible-near-infrared (NIR) spectroscopy and atomic force microscopy (AFM). The results show that the film stretching not only aligns the long axis of individual nanorice or nanocarrots preferentially along the stretching direction, but also induces assembly of these nanostructures into oriented arrays of random lengths in the deformation process. Consequently, the longitudinal surface plasmon resonance peaked at 820 nm for nanorice and 1050 nm for nanocarrots before stretching can be replaced by continuous extinction over the entire 800-1800 nm NIR spectral range after stretching. Stretched PVA films containing either silver nanorice or nanocarrots thus display polarization-dependent transmission of NIR light.