Nonlinear Optical Nanoscale Chemical Imaging

Nanoscale chemical imaging is crucial for understanding chemical surface processes on a molecular length scale.

We have created a tool for imaging nanoparticles where the contrast is derived from the sample characteristic that drives the second harmonic generation (SHG) process. Here 800 nm light is converted to 400 nm light.

SHG images are in spatial registration with atomic force microscope (AFM) images that are collected simultaneously and provide topographical information, for example the wire diameter, for reference.

The Applied Spectroscopy journal cover shows AFM, near-field SHG, and far-field SHG images of a 70 by 1500 nm ZnO wire. Sub-diffraction limit imaging is achieved for near-field SHG.

ZnO nanowires show promise as lasers and for electro-optic applications, but their utility is compromised by reaction with ambient CO2 to form surface carbonates.

We are able to monitor that process because the carbonate product is not SHG active due to its symmetry.

Project Results

Experiment for Sum Frequency Generation Imaging