Highly sensitive gas sensor by the LaAlO₃/SrTiO₃heterostructure with Pd nanoparticle surface modulation

LAO/STO 2DEG (two-dimensional electron gas) heterostructure were fabricated with surface being modulated by palladium (Pd) nanoparticles in order to trigger the LAO/STO heterostructure's gas sensing ability. The Pd surface modulation method has been utilized to enhance the gas response of some semiconducting systems such as ZnO nanowires. The LAO/STO heterostructures with LAO thickness of 5, 10, 20 and 40 unit cells (uc) were deposited on TiO2?terminated (001) STO substrate. Pd nanoparticles (Pd NP) with size around 2 nm were deposited by d.c. magnetron sputtering in pure argon ambient to the surface of LAO/STO heterostructure at room temperature. The conducting interface was contacted by ultrasonic bonding with Al wire. Hall measurement and sheet resistance measurements were carried out to illustrate the 2DEG nature of the LAO/STO interface. Water molecules adsorbed on the Pd NPs surface with slower evaporation rate lead to fewer surface adsorption site for chemisorptions of oxygen species, results in a slower recovery rate. With the charge coupling between the gas molecules and Pd NPs as well as the interface through either a direct charge exchange or change of electron affinity.