Size-dependent correlations between strain and phonon frequency in individual ZnO nanowires

The effect of uniaxial tensile strain on individual ZnO nanowires with diameters ranging from 500 nm to 2.7 μm and the effect of pure bending strain on ZnO microwires are systematically investigated by Raman spectroscopy. It is found for the first time that the tensile and compressive strains result in a linear downshift and upshift of the phonon frequencies of the E2L, E2H, E1TO, and second-order modes compared with the strain-free state, respectively, while the A1TO mode is not influenced by the strain. Furthermore, the strain modulation on phonons depends strongly on the nanowire diameter. The E2H phonon deformation potential is ~3 cm(-1)/% for the 500 nm nanowire, while 1% tensile strain results only in ~1 cm(-1) downward frequency shift for the 2.7 μm ZnO wire. The results provide a versatile "local-self-calibration" and nondestructive method to measure and monitor the local strains in ZnO micro/nanostructures.