Identification of dispersion-dependent hexagonal cavity modes of an individual ZnO nanonail
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(a) A low-magnification plane view FESEM image of an array of ZnO nanonails. (b) A cross-sectional image of isolated individual ZnO nanonails. (c) Light paths corresponding to WGM (path 1), quasi-WGM (path 2), and FP-type (path 3) resonator modes, respectively, in ZnO-nanonail’s hexagonal head.
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(a) A CL spectrum (solid line) from an individual ZnO nanonail shows a series of peaks corresponding to dielectric-cavity resonance modes convoluted with a broad oxygen-vacancy band while a large-area CL spectrum (dash-dot) shows only a broad band. The integers are the mode numbers for respective resonant mode peaks. The inset is a top-view SEM image of a ZnO nanonail with a side length of , and the position bombarded with electron beam is marked with a cross. (b) The series of scanted solid and dash lines are, respectively, the inverse functions of TM-WGM [Eq. (1)] and TE-WGM [Eq. (2)] mode equations with the corresponding mode numbers in (a). The intersection points determine the birefringent refractive indices at peak wavelengths: solid circles for TM modes and solid triangles for TE modes. (c) The dispersion curves for and were deduced by fitting the peak-position refractive indices (solid circles and sold triangles) to Sellmeier’s equations. The dispersions of refractive indices of epitaxially grown films and bulk crystals are shown for comparison. The inset show the inversion point of bulk crystals.
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