Narrow Results

Experimental formation of LPO (liquid phase oxidation)-grown InGaP native oxide near room temperature (~60°C) is demonstrated. A high oxidation rate is obtained and checked by SEM and AES. The native oxide is determined to be composed of InPO₄ and Ga₂O₃, analyzed by the results of XPS measurement. Due to the presence of the excellent quality of InGaP native oxide, high hydrogen (H₂) sensitivity in output current of a Pd/oxide/InGaP MOS Schottky diode is observed. Under the applied voltage of -1 V and 50 ppm H₂/air, a high sensitivity of 1090 is obtained. An obvious variation of output current and a short response time due to the exposure to different H₂ concentration are also achieved. For example, the adsorption (τ_a) and desorption (τ_b) time constants under 50 ppm H₂/air are 2.3 s and 2.7 s, respectively.

This paper presents the formation of graphene and its application to hydrogen sensors. In this work, the graphene was synthesized by annealing process of 3C-SiC thin films with Ni transition layer. The Ni film was coated on a 3C-SiC layer grown thermal oxided Si substrates and used extracts of the substrate's carbon atoms under rapid thermal annealing (RTA). Various parameters such as ramping speed, annealing time and cooling rate were evaluated for the optimized combination allowed for the reproducible synthesis of graphene using 3C-SiC thin films. Transfer process performed by Ni layer etching in HF solution and transferred graphene onto SiO₂ shows the I_G/I_D ratio of 2.73. Resistivity hydrogen sensors were fabricated and evaluated with Pd and Pt nanoparticles in the room temperature with hydrogen range of 10–50 ppm. The response factor of devices with the Pd catalyst was 1.3 when exposed to 50 ppm hydrogen and it is able to detect as low as 10 ppm hydrogen at room temperature.

Highly ordered TiO₂ nanotube arrays were fabricated by anodization in an ethylene glycol solution containing NH₄F. A pair of platinum electrodes was deposited on the surface of the nanotube layer to fabricate a Pt/TiO₂ nanotube arrays hydrogen sensor. The subject sensors exhibited a seven order of magnitude change in resistance with a response time of 13 s at room temperature upon exposure to 2000 ppm (parts per million) hydrogen. We investigated the hydrogen response of the Pt/TiO₂ sensors as a function of the length of the nanotubes and compared their activity with that of a reference film.

In this research, palladium silver alloy was chosen as the hydrogen sensitive material. By using RF sputtering, Ta₂O₅ transition layer was coated on the ceramic substrate, and then palladium silver alloy film was prepared by using the DC magnetron sputtering. The performance of palladium silver alloy membranes was characterized by experiment. The results show that hydrogen sensor has good response time and repeat response characteristics in 5% hydrogen concentration at room temperature.