Mid-IR imaging of doped silicon gratings at a decananometer scale

However, in a recent paper we have calculated that the phonon confinement occurring in decananometric scale objects such as near-field probes can lead to a drastic modification of the probe´s permittivity. This effect can be very useful as for a range of probe permittivity, much stronger contrast can be expected. To experimentally demonstrate these theoretical expectations, we have built a mid-lR near field microscope and imaged doped Si gratings with a period of 2 μm (fabricated in CEA-LETI) with carefully prepared tungsten tip stuck on a tuning fork. The detection has been done using tips with different radius (30 nm to 100 nm) and a very strong contrast between P doped and P⁺ doped can be observed for a variety of small-radius probes. An example of highly contrasted profile obtained on the doped silicon grating is shown in the paper.