Sunwoo Jung

Platinum-functionalized black phosphorus hydrogen sensors

Black phosphorus (BP), especially in its two-dimensional (2D) form, is an intriguing material because it exhibits higher chemical sensing ability as compared to other thin-film and 2D materials. However, its implementation into hydrogen sensors has been limited due to its insensitivity toward hydrogen. We functionalized exfoliated BP flakes with Pt nanoparticles to improve their hydrogen sensing efficiency. Pt-functionalized BP sensors with back-gated field-effect transistor configuration exhibited a fast response/decay, excellent reproducibility, and high sensitivities (over 50%) at room temperature. Langmuir isotherm model was employed to analyze the Pt-catalyzed BP sensors. Furthermore, the activation energy of hydrogen adsorption on Pt-decorated BP was evaluated, which is equal to the change in work function resulting from hydrogen adsorption on the Pt(111) surface. These results demonstrate that Pt-catalyzed BP exhibits a great potential for next-generation hydrogen sensors.

Detection of ammonia at low concentrations (0.1–2 ppm) with ZnO nanorod-functionalized AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors with ZnO nanorod functionalized gates were used for detecting NH3 in the concentration range of 0.1–2 ppm balanced with air at ambient temperatures from 25 to 300 °C. A decrease in the high electron mobility transistor drain current was observed for exposure to the NH3-containing ambients, indicating an increase in negative charge at the heterointerface. The detection sensitivity increased monotonically with ammonia concentration at all temperatures, from 0.28% (25 °C) and 3.17% (300 °C) for 0.1 ppm to 1.32% (25 °C) and 13.73% (300 °C) for 2 ppm for a drain–source voltage of 1 V. The latter condition is attractive for low power consumption. The sensitivity was also a function of applied voltage and was generally higher in the linear region of the current–voltage characteristic of the transistor. The activation energy of the sensitivity was 0.09 eV, and the sensors showed no response to O2 (100%), CO2 (10%), CO (0.1%), CH4 (4%), and NO2 (0.05%) under the same detection conditions as used for the NH3. The response was less than 1 s, and recovery times were of order ∼53 s at 25 °C.AlGaN/GaN high electron mobility transistors with ZnO nanorod functionalized gates were used for detecting NH3 in the concentration range of 0.1–2 ppm balanced with air at ambient temperatures from 25 to 300 °C. A decrease in the high electron mobility transistor drain current was observed for exposure to the NH3-containing ambients, indicating an increase in negative charge at the heterointerface. The detection sensitivity increased monotonically with ammonia concentration at all temperatures, from 0.28% (25 °C) and 3.17% (300 °C) for 0.1 ppm to 1.32% (25 °C) and 13.73% (300 °C) for 2 ppm for a drain–source voltage of 1 V. The latter condition is attractive for low power consumption. The sensitivity was also a function of applied voltage and was generally higher in the linear region of the current–voltage characteristic of the transistor. The activation energy of the sensitivity was 0.09 eV, and the sensors showed no response to O2 (100%), CO2 (10%), CO (0.1%), CH4 (4%), and NO2 (0.05%) under the same de...