Effect of Heating and H gas Exposure on MgZnO Nanoparticle Conductivity.

Changes in the conductivity of Mg$_{x}$Zn$_{1-x}$O (x = 0.15) nanoparticles as a function gas exposure and temperature are reported. The nanoparticles were prepared using wet chemical techniques on insulating thermally grown SiO$_{x}$ Si substrates. Contact to the nanoparticle film was by gold wires laid across about 2 mm apart. The experiments were performed in a custom-built environmental chamber with the ability to evacuate or introduce various gases. For these experiments, the temperature was varied over a range of about 300 K to 420 K. Our measurements showed history-dependant behavior in changes of the conductance of the nanoparticle film. When the device was heated to $\sim $120 K in vacuum or in an Ar the current increased by the same amount. When repeated with H$_{2}$, the current increase was less. Initially, the effect was quite pronounced with a relative change by a factor of 20. With repetitions of the experiments, the same effect was observed but to a lesser degree suggesting a saturation phenomena. When the experiment was modified so that the H$_{2}$ gas was introduced at a high temperature to an evacuated chamber the current dropped but not by the same degree as before. A similar response to exposure to H$_{2}$ was found for exposure to O$_{2}$. Possible explanations for the observations will be presented.