The spatial resolution of classical far-field spectroscopy is constrained by the so-called diffraction limit. The workaround of this problem needs a change in the measurement configuration. Near the surfaces we can create electromagnetic fields containing components with much finer spatial information than their propagating counterparts. However, these fields decay quickly as we move away from the surface. With the use of an optical antenna in close proximity to the surface these evanescent fields can be converted to propagating ones and detected with conventional instruments. This is the working principle of the scattering type near-field microscope, a novel optical characterization tool capable of nanometer resolution regardless of the used wavelength.
The instrument in our laboratory is a combination of an atomic force microscope (AFM) and infrared lasers. The laser is focused on the metallic AFM tip and by scanning the tip over the sample we can measure the optical response with nanometer scale resolution. The optical signal and the sample topography are measured simultaneously, thus the correlation of sample features with the optical response is straightforward. Our infrared lasers work in the mid-infrared range where light can interact with molecular vibrations, phonons, free electrons, and other collective excitations like surface plasmon polaritons.
Our group works mainly with low-dimensional materials like hexagonal boron nitride, graphene, carbon nanotubes and boron nitride nanotubes. These materials can be modified with chemical or physical methods. We can fill the inner cavity of the nanotubes with different small molecules or modify the surface of the two-dimensional materials. These modifications can be followed and analyzed with the help of the near-field infrared microscope.
The task of the applicant is to carry out near-field infrared measurements on the aforementioned low-dimensional modified systems, explain their optical response by the use of theoretical models and contribute to the development and modification of the experimental setup.
English language proficiency for reading scientific articles
Interest in experimental work
Optics and solid state physics background