< Back to previous page

Project

Optical characterization of 2D metal dichalcogenides

Several innovations have been made to improve to investigate the atomic structure or the mesostructured of the materials i.e., scanning electron microscopy (SEM), atomic force microscopy (AFM), near-field scanning microscopy, X-ray microscopy, fluorescence microscopy. These innovative methods are optimized for a clearly defined target, but these methods are not without drawbacks. Two-dimensional (2D) transition metal dichalcogenides (TMDs) hold great potential for application in different fields, in particular, nanoelectronics and photonics. In nanoelectronics, large energy dissipation due to heating in chips is unsustainable in terms of both costs and performance drop and 2D TMDs hold great potential to alleviate these problems. In photonics, the integration of 2D TMDs is predicted to enhance the energy harvesting. Towards such applications, it is crucial to investigate the electronic/optical/thermal dynamics of this few-atom-thick films, in order to optimize fabrication processes.  To characterize the electronic and thermal degrees of freedom of such films on the time-scale on which they develop, ultrafast time-resolved optical spectroscopy is needed. In such techniques, the reaction is instigated by a femtosecond laser pump. By shifting the time of arrival of a probe pulse relative to the pump pulse, it is possible to monitor the changes in sample properties (e.g., absorption, reflection, fluorescence, etc.) stimulated by the pump, with a time resolution of the order of the duration of the laser pulses. Joining this along with a microscope, we will construct a unique scheme, using ultrafast fiber lasers, to implement the time-resolved experiments with spatial resolution of few hundreds of nanometers, useful to investigate the homogeneity of the films. To enhance the sensitivity of the optical probe to the few-atom-thick films beyond the possibilities of standard microscope objectives, we will also try to use microsphere assisted microscopy, recently discovered and used to develop super-resolution optical microscopes. In our case, the aim of microsphere assisted microscopy is to increase ligth-matter interaction through the so called photonic nanojets, that develop near the shadow side of a transparent glass microsphere with a diameter of 10-100 μm when it is illuminated by a laser beam. The microspheres will collect the light reflected from the sample with a resolution of the order of 100 nanometers, amplifying the response from the few atomic layers constituting the surface termination, where the thin films are adhered. A microsphere scanning technique will be needed to explore a large region of the sample. In conclusion, our primary goals are to develop time-resolved optical microscopy methods to investigate the electronic and thermo-mechanical aspects of 2D TMDs deposited on a bulk substrate. We aim to develop a microsphere-assisted optical microscopy to make fast optical surface mapping in various environments (i.e., air and liquids) to assess the film optical response and its uniformity with a truly non-contact technique.

Date:3 Aug 2021 →  9 Feb 2022
Keywords:2D materials, dichalcogenides, microsphere, ultrafast spectroscopy, time-resolved optical microscopy, optical characterization
Disciplines:Lasers and quantum electronics, Nonlinear optics and spectroscopy, Optical properties of materials
Project type:PhD project