Bringing Optics into the Nanoscale - a Double-Scanner AFM Brings Advanced Optical Experiments Within Reach

^{KEYWORDS: Atomic Force Microscopy; AFM; NanoWizard; SNOM; sSNOM; FRET; TIRF; Raman; Single-Molecule Fluorescence; Confocal Optical Microscopy; Tip-Assisted Optics; TAO module; Correlative Microscopy; Metal Colloids; Proteins; Quantum Dots}

Optical microscopy is limited to the lateral resolution of 200-200 nm laterally. To overcome this limit, a technique called scanning near-field optical microscopy (SNOM) can be used. When a small object is used to scatter the light in the near-field, it is known as apertureless or scattering SNOM. An atomic force microscopy (AFM) tip can be used as the scattering object in this technique. As the tip is scanned over the surface, it images the topography using the standard AFM modes, and can simultaneously generate high-resolution optical contrast.

The combination of AFM with two separate scanners controlled by the same software interface facilitates the positioning of the AFM tip or samples features within the optical focus, allowing a wide range of combined AFM and optical experiments. The focus location through scanning is an easy and robust method of finding the precise tip position, and the linearized piezos used throughout provide the stability so that the tip can stay within focus for extended experiments. The tip only needs to be placed manually near the optical focus within the 100 x 100-micron scan range of either the tip or sample. The two applications described here are only small examples of the range of experiments that will benefit from this combined scanner.

Readers can expect to learn about:

• How the TAO module together with Bruker's NanoWizard AFM enables scattering SNOM experiments;
• Application examples showcasing the perfect combination of AFM with advanced optical techniques such as FRET, confocal optical microscopy and TERS; and
• The outstanding capabilities of the combined TAO module and NanoWizard AFM system for protein structure investigations, chemical identification, and nanomanipulation.