Graphene-based nanomechanical detectors of terahertz radiation

• Applicant: Professor Dr. Kirill Bolotin
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449506295

Graphene is a unique material for the detection of radiation in the terahertz (THz) range. First, graphene features a plasmon mode in the THz range. The absorption maximum of that mode can be controlled via electrostatic gating. Because of that, graphene-based detectors can resolve the spectral content of the THz radiation. Second, the thermal mass of graphene is very small. This means that even a tiny amount of absorbed light significantly changes the temperature and consequently electronic and mechanical properties of graphene. As a result, graphene THz detectors reach high sensitivity, potentially down to the single-photon range. However, the understanding of detection mechanisms is incomplete as several critical parameters including scattering frequency, radiation frequency, and electron-phonon scattering rates have the same order of magnitude. Additional complications arise due to the interaction of graphene with the substrate. It results in additional heat sinking, doping of the channel, and screening of electron-electron interactions. In this project, we for the first time use suspended graphene as a platform for terahertz radiation detection. The advantages of suspended graphene include low carrier scattering, the lack of uncontrolled screening, and the ability to implement new all-mechanical detection mechanisms. In the first part of the project, we explore a more conventional approach to the THz detection, where the absorbed radiation is detected by measuring photovoltage/photocurrent. We will explore the effect of reduced dielectric screening on suspended graphene devices and use it to improve the detection sensitivity and the quality factor of the plasmon resonance. Next, we will study controllably crumpled suspended devices. The crumpling-dependent THz absorption peak is expected to allow for extending the detection range and achieving wavelength-specific detection. In the second part of the project, we explore a novel approach to THz bolometry where a temperature change caused by THz absorption is detected by measuring the effect it has on the mechanical resonance frequency of suspended graphene nanoelectromechanical (NEMS) device. The advantages of these devices include high sensitivity and easy multiplexing of detector signals allowing for designing detector matrices.The project is based on the synergy between the experts in graphene THz photodetection (the Moscow-based Fedorov group) and the experts in graphene nanomechanics and electrical transport (the Berlin-based Bolotin group). Recent results of both groups established the cornerstones of the project - tunable and sensitive detection of THz radiation by high-mobility graphene, ultrahigh mobility in suspended graphene, and bolometry using graphene NEMS. The project will be initially driven by the PhD student who fabricated supported graphene-based THz detectors in the Fedorov group and is now working on suspended devices in the Bolotin group.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Foundation for Basic Research, until 3/2022
• Cooperation Partner: Professor Georgy Fedorov, Ph.D., until 3/2022