Tunnel field-effect transistors for sensitive terahertz detection.

The rectification of electromagnetic waves to direct currents is a crucial process for energy harvesting, beyond-5G wireless communications, ultra-fast science, and observational astronomy. As the radiation frequency is raised to the sub-terahertz (THz) domain, ac-to-dc conversion by conventional electronics becomes challenging and requires alternative rectification protocols. Here, we address this challenge by tunnel field-effect transistors made of bilayer graphene (BLG). Taking advantage of BLG's electrically tunable band structure, we create a lateral tunnel junction and couple it to an antenna exposed to THz radiation. The incoming radiation is then down-converted by the tunnel junction nonlinearity, resulting in high responsivity (>4 kV/W) and low-noise (0.2 pW/[Formula: see text]) detection. We demonstrate how switching from intraband Ohmic to interband tunneling regime can raise detectors' responsivity by few orders of magnitude, in agreement with the developed theory. Our work demonstrates a potential application of tunnel transistors for THz detection and reveals BLG as a promising platform therefor.

[Pulse oximetry screening for sleep-disordered breathing in stroke]. / Pulsoximetrie als Schlafapnoescreening bei Schlaganfallpatienten.

BACKGROUND: The prevalence of sleep-disordered breathing, particularly obstructive sleep apnea, among stroke patients is high. Routine screening with the current diagnostic gold standard of polysomnography is not feasible. Pulse oximetry could be a simple screening test. METHODS: The signal of pulse oximetry, recorded during full polysomnography in 184 stroke patients during neurological rehabilitation, was analyzed automatically by software for desaturations >/= 4 %. The polysomnographic apnoea-hypopnoea-index (AHI) was used as the diagnostic gold standard and compared with the oxygen desaturation index (ODI). RESULTS: Correlation between AHI of PSG and ODI of oximetry was r = 0.84 (p < 0.001). Dependent on the definition of SDB (AHI 10, 15, 20 or 30/h) and the cut-off-point for the ODI (e. g. 15/h) sensitivity was 32 - 83 % and specificity 99 - 96 %. The diagnostic accuracy as determined by the area under the ROC-curve was 96 %. CONCLUSION: Automated analysis of pulse oximetry gives reasonable results for screening for SDB in stroke patients and could be used in populations with high pre-test probability.