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InGaAs/GaAs rolled-up microtube geometry, crystallographic orientations, and coordinate system. The inset shows the initial dimensions of the unit cell for the simulations. The origin is at the sacrificial layer, the cell “rolls up” during the simulations as shown in the main figure.
(a) Raman spectra of the tube with R = 0.7 μm. The spectra have been collected from the tube (B) and the nearby regions: as grown (C) and the material left over after tube formation (A). (b) Raman shift as a function of tube radius. The dashed lines represent the LO phonon mode of GaAs and InGaAs unstrained bulk materials. (c) Calculated average radial strains in the InGaAs and GaAs layers for tube fixed to substrate (solid lines) and free-standing tubes (dashed lines) as function of GaAs thickness. Symbols are experimental values: dots (this work), squares (x-ray from Ref. 5).
(a) Phonon dispersion curves of folded acoustic modes calculated by the elastic continuum theory for the tube with radius of 0.7 μm. The dashed vertical line corresponds to the phonon wavevector excited in our experimental setup. (b) Micro-Raman spectra of all samples taken when the incident polarization is parallel to (100) direction in He atmosphere. The grey line presents the Raman spectra of the GaAs substrate measured under the same conditions. The intense peak around 40 cm −1 is a plasma line of the excitation laser.
Material parameters used in the valence force field calculations and the deformation potential approximation. The In0.215Ga0.785As parameters are calculated by linear interpolation.
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