Crystallographic Characterization of II–VI Semiconducting Nanostructures via Optical Second Harmonic Generation

We demonstrate the utility of optical second harmonic generation (SHG) polarimetry to perform structural characterization of noncentrosymmetric, single-crystalline II–VI semiconducting nanowires, nanobelts, and nanoflakes. By analyzing anisotropic SHG polarimetric patterns, we distinguish between wurtzite and zincblende II–VI semiconducting crystal structures and determine their growth orientation. The crystallography of these nanostructures was then confirmed via transmission electron microscopy measurements performed on the same system. In addition, we show that some intrinsic material properties such as nonlinear coefficients and geometry-dependent optical in-coupling coefficients can also be determined from the SHG experiments in WZ nanobelts. The ability to perform SHG-based structural characterization and crystallographic study of II–VI semiconducting single-crystalline nanomaterials will be useful to correlate structure–property relationships of nanodevices on which transmission electron microscopy measurements cannot be typically performed

Nanotwin Detection and Domain Polarity Determination via Optical Second Harmonic Generation Polarimetry

We demonstrate that optical second harmonic generation (SHG) can be utilized to determine the exact nature of nanotwins in noncentrosymmetric crystals, which is challenging to resolve via conventional transmission electron or scanned probe microscopies. Using single-crystalline nanotwinned CdTe nanobelts and nanowires as a model system, we show that SHG polarimetry can distinguish between upright (Cd–Te bonds) and inverted (Cd–Cd or Te–Te bonds) twin boundaries in the system. Inverted twin boundaries are generally not reported in nanowires due to the lack of techniques and complexity associated with the study of the nature of such defects. Precise characterization of the nature of defects in nanocrystals is required for deeper understanding of their growth and physical properties to enable their application in future devices