Tunable broadband, wide angle and lithography-free absorber in the near-infrared using an ultrathin VO 2 film

Here we demonstrate a tunable broadband near-infrared absorber composed of VOalt;subagt;2alt;/subagt; /Alalt;subagt;2alt;/subagt;Oalt;subagt;3alt;/subagt;/ITO layers with a facile lithography-free method. Simulated and experimental spectra show absorption bands with above 90% absorptance can be tuned from 1.62 ~2.42 μm to 1.2~1.5 μm by thermally induced VOalt;subagt;2alt;/subagt; phase transition. Furthermore, the absorber with VOalt;subagt;2alt;/subagt; in the intermediate state can yield a broadband perfect absorption over the wavelength range of 1.2~2.5 μm. Besides high absorption performance can still be remained at the incident up to 70° for both polarizations due to the presence of ultrathin layer of VOalt;subagt;2alt;/subagt; (λ/52) in the absorber.