Set-up of a scanning near field infrared microscope (SNIM)

We have realized a scanning near-field infrared microscope in the 3-4 µm wavelength range. As a light source, a tunable high power continuous wave infrared optical parametric oscillator with an output power of up to 2.9 W in the 3-4 µm range has been set-up. Using scanning near field infrared microscopy (SNIM) imaging we have been able to obtain a lateral resolution of ≤30 nm at a wavelength of 3.2 µm, which is far below the far-field resolution limit of λ/2. Using this ``chemical nanoscope'' we could image a sub-surface structure of implanted gallium ions in a topographically flat silicon wafer giving evidence for a near-field contrast. We could further demonstrate that a monolayer iis able to yield reasonable contrast. We have perforemed a lateral measurement on a structured self assembled monolayer. The distinct 2-dim images could be attributed to the specific spectroscopic absorption spectra of the functional groups in the infrared region. The future use of the setup for nm imaging in the chemically important OH, N-H and C-H stretching vibration and its further applications is discussed.