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(a) and (b) SEM images of two sets of ZnO microwires with (a) blunt and (b) sharp corners. The length of the white bar represents m. (c) EBSD micrograph recorded on a ZnO microwire facet. The main crystallographic index family is indicated by a vertical black line. (d) and (e) AFM images of ZnO microwires with (d) blunt and (e) sharp corners. The white squares show magnified sections of the microwire top facets. The white lines highlight line scans along the microwire corners as shown above.
Angular-resolved PL spectra along angle (along wire cross section, perpendicular to the wire axis) with characteristic WGMs in a microwire with blunt corners (a) and FPMs in a microwire with sharp corners (b).
FDTD simulations of WGMs (N = 54) in hexagonal resonators with (a) diminished and (b) perfectly shaped corners. The corners were shortened by 0.025 d in (a). The color scale is logarithmic and spans over the same intensity range in (a) and (b).
(a) Excitation-dependent PL spectra of a ZnO microwire with sharp corners and m recorded at T = 10 K. Inset at lower left corner: SEM image of the investigated microwire. Length of the scale bar represents m. Inset at upper right corner: Integrated PL intensity vs. excitation density. The vertical dotted line marks the lasing threshold . The color of the dots corresponds to the color of the spectra. (b) PL spectra of a ZnO microwire with m below (red line) and above (black line) lasing threshold. The spectral positions of FPMs at low excitations are highlighted by vertical dashed lines.
Integrated PL intensity in dependence of excitation density at T = 10 K ((a) and (b)) and room temperature (c) for WGMs in ZnO microwires with blunt corners (a) and sharp corners ((b) and (c)). The corresponding wire cross sections are schematically drawn in each plot. The vertical dotted lines indicate the onset of stimulated emission and mark the lasing threshold .
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