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(Color online) (a) SEM image of a typical inverted rolled-up tube from Si. (b) Cross sectional TEM image (upper part) combined with an oxygen element map (lower part) of a tube wall consisting of (bright area) and (dark area). The blue region in the lower part originates from the area, which contains oxygen. (c) Cross sectional STEM image of a tube wall consisting of (bright area) and (dark area).
(Color online) [(a) and (b)] Cross sectional TEM image of a tube and a tube wall consisting of (bright area) and (dark area) after annealing at for . (c) Fluorescence spectroscopy image at room temperature of Si tubes. The inset is a light microscopy image.
(Color online) (a) PL spectrum at of a single freestanding microtube with diameters of (upper spectrum) and (lower spectrum). (b) Refractive index contrast of the rolled-up tube used for the FDTD simulations. The tube wall consists of Si. (c) Energy position of the modes extracted from the lower spectrum in (a) compared to the mode energies as a function of the azimuthal number () obtained from FDTD simulation. (d) Intensity pattern of the resonant mode at with and from the structure shown in (b).
(Color online) PL measurement at room temperature of a single freestanding microtube for different polarization configurations. (a) PL spectrum polarized parallel (upper spectrum) and perpendicular (lower spectrum) to the tube axis. (b) Average PL peak-to-valley ratio as a function of the polarization angle with respect to the tube axis. Zero degree represents polarization parallel the tube axis.
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