Nanostructured materials for photonics and spectroscopy

Georgetown University, Washington DC

Investigators

Abstract

Title: Materials with reduced dimensions for light detection. Non-technical: Materials with a layered structure similar to graphite, where the atoms within each layer are strongly bonded, but the layers are weakly coupled and can be easily separated, have become the focus of intense research efforts worldwide. This is because it is now possible to reduce their thickness down to a few or even a single layer to create atomically thin devices or transparent conductors that are suitable for flexible substrates. However, the full potential of their drastic reduction in thickness and their new physical properties has not been realized. This project focuses on the study and applications of novel photodetectors based on graphene, a single layer of graphite, and single-layer MoS2. The PI will further reduce their dimensions by patterning single layers into structures that are just tens of nanometers wide, to create high-performance photodetectors that will work in the visible range, as well as in other regions of the electromagnetic spectrum, including terahertz radiation. Terahertz radiation comprises the electromagnetic spectrum between microwave and infrared radiation, in the frequency range between 100 GHz and 30 THz. Because it can penetrate through most plastics and non-conducting materials without the damaging ionization effects of x-rays, it has promising potential applications for security and medical imaging. Other applications include chemical fingerprinting (to identify chemical compounds), communication, either terrestrial short-range or between satellites, and imaging of blackbody radiation emitted by the landscape, to allow aircraft to land in conditions of poor visibility due to fog or smoke. Notwithstanding the potential for application in many fields, terahertz technology is far from advanced, because powerful sources and sensitive detectors are scarce. This project builds on previous work by the PI demonstrating that nanometer-patterning of graphene yields terahertz detectors with extraordinary performance. Technical: Graphene has material properties that are ideal for bolometric application: small electronic heat capacity and weak electron-phonon coupling, making it easy to create hot electrons with the incident electromagnetic radiation. This project will build on recent work by the PI who demonstrated that graphene quantum dots can yield extremely high-performance THz bolometers. This was done by measuring the current of hot electrons formed in the graphene source and drain electrodes and propagating through the graphene quantum dot. New work will extend the study to gated quantum dot bolometers to better understand the underlying physics of their extraordinary performance. This study will include the frequency and power dependence of their response and the coupling of these bolometers to antennas. In addition to graphene, hybrid structures based on graphene and MoS2 will also be investigated for hot-electron bolometer applications. Finally, this project will investigate detection of visible radiation in nanopatterned MoS2-based photosensors.