We report bilayer-graphene field effect transistors operating as THz broadband photodetectors based on plasma-waves excitation. By employing wide-gate geometries or buried gate configurations, we achieve a responsivity~1.2V/W (1.3 mA/W) and a noise equivalent power~2×10 -9 W/√Hz in the 0.29-0.38THz range, in photovoltage and photocurrent mode. The potential of this technology for scalability to higher frequencies and the development of flexible devices makes our approach competitive for a future generation of THz detection systems.Generation and detection of radiation across the far infrared or Terahertz (THz) region of the electromagnetic spectrum is promising for a large variety of strategic applications, 1 ranging from biomedical diagnostics 2 to process and quality control, 3 homeland security 1 and environmental monitoring. 4 Due to its non-ionizing nature, 1 THz radiation can penetrate many commonly used dielectrics, 1 otherwise opaque for visible and mid-infrared light, allowing detection of specific spectroscopic features 5 with a sub-millimeter diffractionlimited resolution. µV/W and operating in photovoltage mode at much higher frequencies (2.5 THz).Here we report THz detectors operating at RT in either photovoltage or photocurrent mode with a significant enhancement of sensitivity and lowered NEPs compared to the state of the art. This is achieved by using either large (1 µm) gate lengths, or buried gate geometries on a bilayer graphene (BLG) FET. We use BLG instead of single layer graphene (SLG) since the modulation of carrier density was proved to be more effective in the former case, 19 allowing a higher responsivity at THz frequencies.The devices are prepared as follows. Flakes are mechanically exfoliated from graphite 24 on an intrinsic Si substrate covered with 300nm SiO 2 . BLGs are selected and identified by a combination of optical microscopy 25 and Raman spectroscopy. 26,27 These are then used to fabricate two sets of FETs (samples A, B). In A, source (S) and drain (D) contacts are patterned by electron beam lithography (EBL) and metal evaporation (5nm Cr /80 nm Au). The S contact is connected to one lobe of a 50° bow-tie antenna, and D to a 3 metal pad. After placement of 35nm HfO 2 by atomic layer deposition (ALD), the other lobe of the antenna is fabricated, and constitutes the FET gate (g). The channel length is L SD = 2.5 m, while the gate length w G =1 m (Fig. 1a). In B, one lobe of a log-periodic circular-toothed antenna is fabricated by EBL and metal evaporation to act as buried gate. After deposition of 35 nm HfO 2 by ALD, S and D electrodes are fabricated.Similar to sample A, S is the second lobe of the antenna, while the drain is a metal line connecting to a bonding pad. The channel length is 2.5 m, its width 7.5 m, while w G = 0.3m (Fig. 1b). A BLG flake is then placed onto the pre-fabricated electrodes by wet transfer. 28 Fig. 2 compares the Raman spectra of the flake prior and after placement onto the electrodes. The "2D" peak shows the characteristic multi-band s...

Nanomechanical resonators are used with great success to couple mechanical motion to other degrees of freedom, such as photons, spins, and electrons [1,2]. Mechanical vibrations can be efficiently cooled and amplified using photons, but not with other degrees of freedom. Here, we demonstrate a simple yet powerful method for cooling, amplification, and self-oscillation using electrons. This is achieved by applying a constant (DC) current of electrons through a suspended nanotube in a dilution fridge.We demonstrate cooling down to 4.6 ± 2.0 quanta of vibrations. We also observe selfoscillation, which can lead to prominent instabilities in the electron transport through the nanotube. We attribute the origin of the observed cooling and self-oscillation to an electrothermal effect. This work shows that electrons may become a useful resource for quantum manipulation of mechanical resonators. * These authors contributed equally to this work. 1 arXiv:1903.04892v1 [cond-mat.mes-hall]

Mechanical resonators based on a single carbon nanotube are exceptional sensors of mass and force. The force sensitivity in these ultralight resonators is often limited by the noise in the detection of the vibrations. Here, we report on an ultrasensitive scheme based on a RLC resonator and a low-temperature amplifier to detect nanotube vibrations. We also show a new fabrication process of electromechanical nanotube resonators to reduce the separation between the suspended nanotube and the gate electrode down to ∼150 nm. These advances in detection and fabrication allow us to reach displacement sensitivity. Thermal vibrations cooled cryogenically at 300 mK are detected with a signal-to-noise ratio as high as 17 dB. We demonstrate force sensitivity, which is the best force sensitivity achieved thus far with a mechanical resonator. Our work is an important step toward imaging individual nuclear spins and studying the coupling between mechanical vibrations and electrons in different quantum electron transport regimes.

We report on room temperature detection of terahertz radiation by means of antenna-coupled field effect transistors (FETs) fabricated using epitaxial graphene grown on silicon carbide. The achieved photoresponsivity (similar to 0.25 V/W) and noise equivalent power (similar to 80 nW/root Hz) result from the combined effect of two independent detection mechanisms: over-damped plasma wave rectification and thermoelectric effects, the latter ascribed to the presence of carrier density junctions along the FET channel. The calculated plasmonic and thermoelectric response reproduces qualitatively well the measured photovoltages; the experimentally observed sign-switch demonstrates the stronger contribution of plasmonic detection compared to the thermoelectric one. These results unveil the potential of plasmonic detectors exploiting epitaxial graphene on silicon carbide for fast large area imaging of macroscopic samples