Temperature tunable vanadium oxide based nanophotonic structures

In this work, the phase change behavior of vanadium dioxide (VO2) thin films grown by RF magnetron sputtering and post annealing process, has been studied by its optical and electrical parameters. The structures of thin films are investigated by x-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscope (SEM). IR reflectivity measurements are done by using FTIR method. The phase change behavior of VO2 is investigated not only in two extreme regimes: hot (metallic) and cold (insulating) states but also in the transition temperatures, where VO2 acts like an inherent metamaterial with mixed metallic insulating character. In this range, the portions of metallic and insulating inclusions are tuned by temperature, and therefore a gradual change of optical parameters can be achieved. A universal hybrid modeling approach introduced to model VO2 in the intermediate region is used. The measured reflectivity data is analyzed and matched through the transfer matrix method (TMM) simulations where an effective medium theory (EMT) is employed. Based on the findings of this approach, not only the relative portions of inclusions are tailored but also their grain shapes are significantly altered in the transition range. In addition, the hysteretic behaviors on electrical, optical, and structural parameters of the VO2 film along the heating and cooling cycles are demonstrated by the experiments and scrutinized by the simulations. Finally; lithography-free and nano-patterned devices are designed and fabricated, using such techniques; chemical (CVD) and physical vapor deposition (PVD), inductively coupled plasma reactive ion etching (ICP-RIE) and electron beam lithography (EBL) which show tunable reflectance operating at infrared wavelengths.