TERATOMO - Near-field Spectroscopic Nanotomography at Infrared and Terahertz Frequencies

The TERATOMO project is focused on the fundamental understanding and engineering of composite materials, biological structures, and building blocks for electrical and optical devices of nanoscale dimensions necessitate the availability of advanced microscopy tools for mapping their local chemical, structural, and free-carrier properties. But while optical spectroscopy, particularly in the infrared (IR) and terahertz (THz) frequency range, has tremendous merit in measuring such properties optically, the diffraction-limited spatial resolution has been preventing IR and THz microscopy applications for the longest time to be used in nanoscale materials and device analysis, bioimaging, industrial failure analysis, and quality control.

During the last few years, we pioneered the field of IR and THz near-field microscopy, which allows two-dimensional (2D) spectroscopic IR and THz imaging of a sample surface with nanoscale spatial resolution, independent of the wavelength. Key achievements of our work are the nanoscale resolved near-field mapping of chemical compositions of polymer blends, mechanical strain fields in ceramics, and free-carrier concentrations in doped semiconductor transistors.

The core objective of this proposal is to develop a three-dimensional (3D) spectroscopic imaging method in a wide spectral range between infrared (IR) and terahertz (THz) frequencies with nanoscale spatial resolution. Our approach will be based on scattering-type scanning near-field optical microscopy (s-SNOM), even though s-SNOM is generally considered to be a surface mapping technique. Instead of scanning the surface, it is here proposed to scan a volume above the sample surface. By using appropriate reconstruction methods, the three-dimensional structure of the sample volume below the sample surface could be obtained in principle. We recently conducted a theoretical study, which confirmed the fundamental feasibility of this novel approach that shall be experimentally realized within this proposal.

The proposed method of IR and THz nanotomography could become a new paradigm in nanoscale optical imaging. Near-field nanotomography will have the potential to open new and even unexpected avenues for optical characterization throughout all nanosciences, such as non-invasive, chemical identification of single (biological) nanoparticles in complex 3D nanostructures or the measurement of the local free-carrier concentration and mobility in semiconductor nanowires or devices with 3D architecture.