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In this study, we attempt to find the origin of atypical doping concentration dependant electrical properties of group III element (Al, Ga, In) doped ZnO thin films. The carrier density and mobility of these films are measured and compared for a wide range of doping concentrations. It is found that donor density determines the electrical properties of the films for a low level of doping, whereas lattice defects play a dominant role beyond a certain level of doping concentration. We also demonstrate an interrelationship between the electrical properties and the structural/optical properties of the films. We find 2% as optimum doping concentration for Al-, Ga- or In-doped ZnO for obtaining highest conducting layers and Ga emerges as the most effective dopant among all. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen gas sensors based on graphene oxide (GO) nanostructures have been fabricated using ac dielectrophoresis (DEP) process. The GO nanostructures synthesized by an improved Hummer's method were first characterized by atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. GO nanostructures were assembled into gold electrodes using DEP process by varying parameters such as frequency, peak-to-peak voltage (V pp), and processing time (t). The devices were investigated by scanning electron microscopy, current-voltage measurement, and hydrogen sensing experiment at room temperature. It was found that the optimum DEP parameters that manipulates GO nanostructures in precise manner for hydrogen gas sensing were V pp =10V, frequency=500kHz, and t =30s. The optimized device was proved to be an effective and better hydrogen gas sensor over a typical drop-dried device with a good sensing response of 5%, fast response time (<90s), and fast recovery time (<60s) for 100ppm hydrogen gas concentration at room temperature. [Copyright &y& Elsevier]

The room temperature ferromagnetism in doped and co-doped ZnO is reported here. X-ray photoelectron spectroscopy revealed the mixed oxidation states of Cu and Ag in ZnO:Cu and ZnO:Ag films, respectively. However, co-doping of Cu and Ag with Al does not alter their bonding characteristics in ZnO. Al in +3 oxidation state indicates that substitution of Al to Zn site gives an extra electron which increases the conductivity of ZnO:Ag and ZnO:Cu films. Mott variable range hopping dominates the conduction in ZnO:Cu and ZnO:Ag films whereas thermally activated conduction dominates in Al co-doped ZnO:Ag and ZnO:Cu films. We show that Ruderman–Kittel–Kasuya–Yosida mechanism is not responsible for ferromagnetism in Cu and Ag doped ZnO as the increase in carrier concentration due to Al co-doping does not enhance the ferromagnetism. Finally, possible mechanism behind the ferromagnetism is discussed. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) gas sensors functionalized with platinum (Pt) nanoparticles were fabricated. An alternating current dielectrophoresis technique was used for the precise alignment of the Pt-GO nanohybrid between microgap electrodes, proceeded by the mid-temperature thermal annealing. The gas sensing response was determined for the assembled rGO nanostructure-based devices with and without Pt decoration at various ambient temperature and gas concentrations. The tested device exhibited sensitivities of 14% (7%), 8% (5%), and 10% (8%), for 1000 ppm hydrogen, ammonia, and nitric oxide gases, respectively with (without) Pt nanoparticles, at room temperature. The Pt-decorated samples show an improvement of 100%, 60% and 25% to hydrogen, ammonia, and nitric oxide gases, respectively, over without Pt decorated sensors. Besides, improving the sensitivity, the dielectrophoresis assembled rGO-Pt nanohybrid sensors have been demonstrated as a viable material for multiple gas sensors. [ABSTRACT FROM AUTHOR]