Axial Modulation of Metal–Insulator Phase Transition of VO2 Nanowires by Graded Doping Engineering for Optically Readable Thermometers

Temperature measurement is critical for many scientific experiments and technological applications. Diverse thermometers have been developed for the thermal sensing at macroscopic length scales. However, in situ and quantitative temperature measurement of nanoscale objects in a convenient approach is still a challenge. Here, we demonstrate a new type of optically readable VO2 nanowire-based thermometer, based on the unique axial gradient phase transition behavior along single-domain VO2 nanowires, which is attributed to the hydrogen doping of single-crystalline VO2 nanowires through hydrothermal fabrication and the hydrogen engineering via a postannealing process. Besides the appropriate microscopic size and user-friendly operation, the as-prepared optically readable VO2 nanowire-based thermometers have ultrahigh relative sensitivity (∼17.4%/K) and temperature resolution (∼0.026 K), enabling the sensitive monitoring of the thermal environment of small spaces or the temperature of even nanoscale structures.