Henrik Bødker Lassen (Technical University of Denmark)
THz nanoscopy: Characterizing materials at the nanoscale
Scattering-type scanning near-field optical microscopy (s-SNOM) is a technique which allows for the study of materials with a spatial resolution only limited by the apex radius of the atomic force microscopy (AFM) tip. Combining this technique with terahertz time-domain spectroscopy (THz-TDS) allows us to characterize material properties such as the dielectric function, refractive index, and conductivity with a spatial resolution below 50 nm. Using this technique, coined THz nanoscopy, we have investigated molybdenum-disulfide (MoS2) nanorods, grown by pulsed laser deposition (PLD), and using state-of-the-art theory pertaining s-SNOM, we have extracted the complex permittivity of these nanorods. State-of-the-art theory, however, does not currently explain the situation when a highly conductive surface is present, which we show by examining platinum (Pt) thin films. The thin films have been characterized by micro-four-point probe (M4PP), from which the conductance has been determined for thicknesses ranging from 3 nm to 15 nm. M4PP, however, suffers from being an invasive technique, and thus the non-invasive THz nanoscopy technique is a promising method to characterize thin films. Full wave 2D finite-element-method (FEM) simulations of the metal thin film configuration has been performed and show agreement with the experimental results, further suggesting that the state-of-the-art theory needs refinement.
Joo-Hiuk Son (University of Seoul)
Toward Cancer Treatment Using Terahertz Radiation
Carcinogenesis involves DNA methylation which is a primary alteration in DNA in the development of cancer before genetic mutation. Because the abnormal DNA methylation is found in most cancer cells, the assessment of DNA methylation using terahertz radiation can be a novel optical method to detect and control cancer. The methylation has been directly observed by terahertz time-domain spectroscopy and this epigenetic chemical change could be manipulated to the state of demethylation using resonant terahertz radiation. Demethylation of cancer cells is a key issue in epigenetic cancer therapy and our results may lead to the treatment of cancer using electromagnetic waves.