The signal created by the probe is completely different from that of a conventional nearfield scanning optical microscope (NSOM). The plasmonic probe actively generates a signal, like a sensor, while a conventional NSOM probe passively transmits light or receives scattered light from samples. In the study, the plasmonic probe signal was theoretically analyzed for variations in the refractive index and absorption of samples.

Detecting buried objects

The plasmonic nanoscope can detect buried objects that do not fluoresce or have strong background absorption. To detect heterogeneous nanostructures, the scientists imaged rectangular groove arrays on a SiO2 substrate, which are typical patterns of dynamic random access memory (DRAM) circuits. To evaluate the resolution of the plasmonic nanoscope, the team imaged groove arrays ranging from 23 nm ~ 300 nm wide. By comparing the contrast of measured and calculated images of the groove array, the resolution was estimated to be less than 20 nm. Also, the group theoretically confirmed that the plasmonic nanoscope can detect an object underneath a metal film in the range of the penetration depth of the metal film.

The next step is to extend the application of the plasmonic nanoscope by using the tool to detect voids or defects in high-density DRAM circuits.

More information can be found in the journal Nanotechnology.