Optical response and surface morphology of In/Ag bilayer thin films

In/Ag bilayer thin films were fabricated by maintaining the Ag layer thickness constant at 5 nm while varying the In layer thickness between 3 and 30 nm. It was observed that the grain size in the films increased with increase in thickness. In the case of the single layer In films the grain size increased from 60 to 350 nm as the thickness increased from 3 to 30 nm while the grain size increased from 80 to 280 nm in as the bilayer thickness increased from 8 to 35 nm. There is a red shift in the plasmon resonance from 372 to 522 nm in the case of the pure In layers whereas it was from 492 to 618 nm for the bilayer system. The Ag single layers exhibit a plasmon resonance at 540 nm. On coupling the In and Ag layers in the bilayers, additional resonances appear in the spectrum. The origin of the additional plasmon resonance peaks can be traced to the excitation of localized surface plasmons.