Ultrafast optics of room-temperature ballistic graphene devices

As Moore’s law approaches its physical limit in silicon-based electronics, the research community has been actively searching for other material options as a new toolbox for electronics. The emerging alternative, two-dimensional (2D) materials has grown appreciably since the isolation of monolayer graphene flakes by mechanical exfoliation of bulk graphite in 2004 by Geim and Novoselov. Since then, many other 2D materials have been explored, offering a full spectrum of physical properties, from conducting graphene to semi-conducting transition metal dichalcogenides, such as molybdenum disulfide, to insulating boron nitride. Their proprieties are usually very different from their 3D counterparts, which makes each new material to bring excitement and puzzles. Else, 2D materials offer a unique combination of mechanical properties, with extremely low flexural rigidity while having high in-plane stiffness and strength. These properties could lead to transparent and bendable electronic systems, which motivates for systems solely based in 2D materials. Nevertheless, to realize their potential in practical applications, device design must be rethought to take full advantage of the unique assets and to do that, their full characterization is of utmost importance. This research project was devoted to characterize these 2D materials using near field scanning methods in the THz and mid-IR frequency range. These frequency ranges cover frequencies from 0.1 THz to 10 THz and 10 THz to 100 THz, which corresponds to 3-0.03 mm and 30-3 µm respectively. Measurements in this spectral region provide crucial information of both amplitude and phase of the electric field. The resolution of an optical imaging system is limited due to the physics of diffraction which arises from the wave nature of light and its interaction with the optical systems it passes through. With the emerging need to understand 2D materials on a micro/nanoscale, near-field imaging techniques are employed which allow for comprehensive examination of the underlying mechanisms carried by the near field of such material systems.