Appavoo - Detecting nanoscale size dependence in VO2 phase transition using a split-ring resonator metamaterial
Verification of phase-changing material vanadium dioxide in the gaps of split-ring metamaterial resonators
A series of characterization (high resolution scanning electron microscopy (SEM) and atomic force microscopy (AFM)) before and after deposition of the vanadium dioxide have been carried out to show clear experimental evidence of the presence of phase-changing material VO2 between the arms of the split-ring resonators. In contrast to the 50 nm VO2 film that has been deposited for the purpose of the experiment, we deposit here only ~ 25 nm of VO2 at the same 1.5 nm/s rate as before. The details of the fabrication protocols of the VO2/Au SRRs system have already been provided in the paper.
We first perform SEM on the already fabricated Au SRRs on ITO covered glass only. For simplification purposes, we compare only the SRRs having gap sizes of 80 nm (maximum) and 30 nm (minimum).
Fig. 1 shows scanning electron micrographs of the (a) 80 and (b) 30 nm gap Au SRRs arrays before deposition and annealing of the VO2. The white specks on the substrate (darker grey) are characteristic
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Appavoo - Detecting nanoscale size dependence in VO2 phase transition using a split-ring resonator metamaterial
of the indium tin oxide deposition necessary to render the film conductive. The arrays have dimensions 100 x 100 um and the grating constant for each array is 450 nm.
Fig. 2 shows atomic force micrographs of the (a) 80 and (b) 30 nm gap SRRs arrays before deposition. The insets show the height profiles for the base (line # 1) and for the arms (line #2 and #3). The average step height is about 18 nm. The height profile graphs along with the 3D rendering depict the volume which will be interrogated after the deposition of VO2.
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Appavoo - Detecting nanoscale size dependence in VO2 phase transition using a split-ring resonator metamaterial
Fig. 3 shows scanning electron micrographs of the (a) 80 and (b) 30 nm SRRs arrays after deposition and annealing. The insets show single SRRs that have been magnified to show the presence of VO2 between the gap of the SRRs. We note in (a) the presence of several grains for the 80 nm gap while (b) shows the existence of a single nanocrystal of VO2 between the 30 nm gap.
Fig. 4 shows atomic force micrographs of the (a) 80 and (b) 30 nm SRRs arrays after deposition and annealing. The height profiles from both (a) and (b) show clearly the filling of the gaps with the phasechange material.
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