RESUMEN
For two-dimensional electron gas device applications, it is important to understand how electrical-transport properties are controlled by gate voltage. Here, we report gate voltage-controllable hysteresis in the resistance-temperature characteristics of two-dimensional electron gas at LaAlO3/SrTiO3 heterointerface. Electron channels made of the LaAlO3/SrTiO3 heterointerface showed hysteretic resistance-temperature behavior: the measured resistance was significantly higher during upward temperature sweeps in thermal cycling tests. Such hysteretic behavior was observed only after application of positive back-gate voltages below 50 K in the thermal cycle, and the magnitude of hysteresis increased with the applied back-gate voltage. To explain this gate-controlled resistance hysteresis, we propose a mechanism based on electron trapping at impurity sites, in conjunction with the strong temperature-dependent dielectric constant of the SrTiO3 substrate. Our model explains well the observed gate-controlled hysteresis of the resistance-temperature characteristics, and the mechanism should be also applicable to other SrTiO3-based oxide systems, paving the way to applications of oxide heterostructures to electronic devices.
RESUMEN
We control the hydrophobicity of submicrometer silica spheres by modifying their surface with -CH3, -CH=CH2, -(CH2)(2)CH3, -CH2(CH2)(4)CH2-, -C(6)H(5), -(CH2)(7)CH3, and -(CH2)(11)CH3 groups through a modified one-step process. The scanning electron microscopy (SEM), quasi-elastic light scattering (QELS), UV-visible spectra, nitrogen sorption, and water vapor adsorption methods are used to characterize the particles. The SEM micrographs of the particles demonstrate that the modified particles are uniformly spherical, monodisperse, and well-shaped with the particle size ranging from 130 to 149 nm depending on the modified organic groups. In aqueous solution, the particles modified with phenyl groups have an obvious UV absorption peak at around 210 nm, whereas the other modified particles and unmodified particles do not have any UV-visible absorption peaks. There exist obvious differences in the amount of water vapor adsorbed depending on the type of surface functional groups of the modified particles. Compared with the unmodified particles, the modified particles have a lower water vapor adsorption because of the improved hydrophobicity of the particle surface. As a potential application, we prepared polystyrene/SiO2 nanocomposites by blending polystyrene with the synthesized particles. Water contact angle measurements show that the surface of the composite prepared with the modified particles are more hydrophobic. Confocal microscopy demonstrates that the particles are less agglomerated in the nanocomposite as the particles become more hydrophobic. These comprehensive experimental results demonstrate that the hydrophobicity of the particles can be easily controlled by surface modification with different organosilanes through a modified one-step process.