Abstract
A dual atomic force/near-field scanning optical microscope (AFM/NSOM) with an 800-nm ultrafast laser excitation source was used to investigate apertureless, tip-enhanced second harmonic generation (SHG) of ZnO nanowires. Data from far-field single-particle SHG microscopy images and spectra show little to no contributions from band-gap or other emission. The SHG microscope image and the simultaneous tapping mode AFM and apertureless SHG NSOM images indicate that ZnO nanowires exhibit a strong SHG signal consistent with uniform crystallinity, whereas other ZnO particles found with the wires had a variable, weaker SHG signal. Polarization data established values for Chi(33)/Chi(31) close to previous estimates. Our AFM/SHG NSOM data suggest a particle degradation mechanism under atmospheric conditions starting at the endpoints of the nanowire.