Reduced Graphene Oxide−Carbon Nanotube Composite Fibers for Stable, High-Sensitivity Cryogenic Temperature Sensing

Resistive cryogenic temperature sensors based on metal-free carbon architectures are highly desirable for non-invasive thermal monitoring in quantum and aerospace systems, where minimal self-heating and rapid response are critical. Herein, we report reduced graphene oxide−multiwalled carbon nanotube composite fibers (rGOCFs) as an intrinsically self-sensing platform, wherein the mass ratio of graphene oxide (GO) to multiwalled carbon nanotube (MWCNT) is systematically engineered to tune low-temperature performance. Among the five compositions studied, a GO/MWCNT ratio of 16:6 gives the highest temperature coefficient of resistance (TCR), 0.15 K−1 (equivalent to 15% K−1) at 20 K, (over 75 times higher than that of platinum). It also features an ultrafast thermal response time of 0.23 s (sample 1; 0.44 s for sample 2) and minimal self-heating (ΔT < 1 K) in the 20−40 K range. Current-induced annealing preserves the R−T characteristics while healing structural defects and improving graphitic order, as indicated by XPS and thermal reffusivity analysis. This work demonstrates that compositional control in carbon-based composite fibers enables the concurrent improvement of sensitivity, response speed, and thermal stability, offering a promising route toward high-performance cryogenic temperature sensors.