AVS 46th International Symposium
    Nanometer-scale Science and Technology Division Wednesday Sessions
       Session NS-WeP

Paper NS-WeP4
Dual-Wavelength Scanning Near-Field Optical Microscopy

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: P.R. LeBlanc, McGill University, Canada
Authors: P.R. LeBlanc, McGill University, Canada
M. Gu, McGill University, Canada
P. Grutter, McGill University, Canada
D. Gray, PAPRICAN, Canada
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We have developed a dual-wavelength Scanning Near-Field Optical Microscope to investigate biological samples in air. Using a helium-cadmium laser, we couple 442 nm and 325 nm light into a tapered optical fiber. Light transmitted through the sample is detected in a confocal arrangement. A dichroic mirror separates the two optical channels which are then detected by photomultipliers. The fiber tip is shaped, by immersion into a buffered hydrofluoric acid solution, to an aperture of less than 100nm and then coated with aluminum, defining a true sub-wavelength light source. Once coated, the tip is glued onto one of the tines of a quartz tuning fork which is then oscillated either parallel or perpendicular to the sample surface a few nanometers away. We have found that the latter method (gently tapping the surface) yields a resolution of greater than 20 nm topographical and 50 nm optical. An optical and topographical standard was created by lift-off of a 100 nm aluminum film evaporated on a close-packed monolayer of 500 nm diameter polystyrene spheres. Our initial focus for this instrument has been centered on the investigation of the lignin distribution in Black Spruce fibers. Lignin, a cross-linked phenolic polymer, is of paramount importance in the pulp and paper-making processes. It is a primary component of the wood cell wall and absorbs preferentially in the ultraviolet (it is the only component of the cell to do so). The dual-wavelength capability of our instrument permits the discrimination between chemical species density and topographical variations of the sample as well as near-field optical artifacts.