Thermal sintering of solution-deposited nanoparticle silver ink films characterized by spectroscopic ellipsometry

Low-temperature sintering of metal nanoparticle inks is a promising technique in realizing large area and flexible electronics. It is demonstrated in this letter that spectroscopic ellipsometry in the spectral region of 0.75–3.5 eV can be employed to characterize the sintering process manifested by the evolution of film thickness, effective dielectric function, and percolation transition. A two-oscillator model can be used to model the effective dielectric function. The oscillator energy shifts lower and correlates well with the increase in dc conductance as demonstrated by both in situ and ex situ ellipsometric measurements. A simple model based on two-dimensional $R-L-C$ impedance network was adopted to explain experimental results quantitatively.