Using Ag disc array to tune infrared transmittance of ITO-based multilayer films

Abstract

Ag disc array (200 and 300 nm in diameter) was first adopted to realise the high-infrared-transmittance of ITO-based multilayers, whose array was defined by nanoimprint lithography. The electrical and optical properties of the ITO/Ag disc array/ITO samples were compared with ITO-only and ITO/Ag/ITO samples. Unlike the ITO/Ag/ITO sample, the transmittance of Ag disc array multilayer samples exhibited undulation in the visible region and large depression in the infrared spectral region. The 200-nm Ag disc, 300-nm Ag disc, ITO/Ag/ITO, and ITO-only samples had a transmittance of 20.8%, 95.1%, 32.5% and 86.8% at 982 nm, respectively. This implies that the transmittance in the IR region can be tuned by controlling size of the Ag discs. The sheet resistances of the Ag disc array, ITO/Ag/ITO, and ITO-only samples were 75.7–79.7, 4.77 and 147.96 Ω/sq., respectively. The Ag disc array samples showed mobilities of 32.11–33.91 cm2/V, while the ITO/Ag/ITO sample gave 17.45 cm2/V. The 200-nm Ag disc array sample exhibited higher Haacke's figure of merit (FOM) than the ITO/Ag/ITO sample. Finite-difference time-domain (FDTD) simulations were performed to understand the measured transmittance behaviour and the undulating transmittance of the Ag disc array samples was attributed to localised surface plasmon resonance (LSPR) effect.