In-situ fabricated gas sensors based on one dimensional core-shell TiO2-Al2O3 nanostructures

A novel in-situ sensor fabrication method consisting of one dimensional (1-D) core-shell TiO 2 -Al 2 O 3 nanostructures is reported. The 1-D nanostructures were synthesized on Ti-6Al-4V (Ti64) particles by a robust, simple, inexpensive and highly scalable route based on thermal oxidation . The in-situ fabricated sensors were tested in various reducing and oxidizing gases including hydrogen (H 2 ), hydrogen sulfide (H 2 S), carbon monoxide (CO), methane (CH 4 ), methanol (CH 3 OH), ethanol (C 2 H 5 OH), ethylene (C 2 H 4 ), nitrogen dioxide (NO 2 ) and oxygen (O 2 ). The selectivity, sensitivity, optimum operating temperature, response time and recovery time of the sensors were examined. Results reveal that the as-grown 1-D nanostructures are 1–5 μm long with diameter of 30–100 nm. The core and shell of the 1-D nanostructures consist of rutile-TiO 2 and corundum-Al 2 O 3 , respectively. The growth direction of TiO 2 and Al 2 O 3 are 〈002〉 and 〈110〉, respectively. The sensors consisting of 1-D core-shell TiO 2 -Al 2 O 3 nanostructures show n -type sensing behavior. Selective sensitivity is seen towards H 2 S, CH 3 OH and C 2 H 5 OH in N 2 background with response values of 38.7, 349.6 and 1108.9, respectively. The response time of the sensors decreases and recovery time increases with increasing the concentration of target gases. An electron tunneling assisted surface depletion model is proposed to explain the sensing mechanism of these sensors.