We report the observation of photoconductivity in gold colloidal crystal formed based on a dielectrophoresis (DEP) plus self-assembly technique. By using dielectrophoresis and capillary force, we have successfully confined the gold colloidal crystal formation between two electrodes and characterized the electronic properties of the crystal. We have found that the resistance of these crystals (in the MQ range) has a linear relationship with the intensity of light and hence could serve as optical sensors. We envision that the process developed could be used to potentially fabricate extremely low-cost photo-detector efficiently.
We have studied the magnetic and electrical properties of LaySr1−yTi0.9Fe0.1O3−δ films for compositions where y=0, 0.2, 0.5, and 0.7. All the films exhibited room temperature ferromagnetism with a magnetic moment ranging from 0.7 μB/Fe to 0.2 μB/Fe. The SrTi0.9Fe0.1O3−δ (y=0) sample is an insulator with a small polaron like temperature dependence of resistivity. On the other hand y=0.2 and y=0.5 films exhibited a metallic type of resistivity which can be described by a power law. The largest magnetic moment was observed in the most resistive member (y=0) of the LaySr1−yTi0.9Fe0.1O3−δ family. This is in contrast to the carrier mediated magnetism models. The origin of the magnetism in highly resistive y=0 film could be attributed to the mixed valence state of Fe. On the other hand, La doped sample (y>0) exhibited features of carrier mediated magnetism as well as the mixed valence magnetism. The origin of the observed magnetism in all films has been discussed.
We report that the La(0.35)Sr(0.65)Ti(1-x)Fe(x)O(3) system forms a solid solution within the composition range 0≤x≤0.5 and a room temperature magnetic semiconductor phase exists at x = 0.20. This system shows an anomalous Hall effect and is ferromagnetic with a large moment per Fe ion. The results show that the strong La doping provides sufficient carriers to the system to maintain carrier-mediated ferromagnetism for low Fe doping. Furthermore, the presence of ferromagnetism within this phase space raises the possibility that the conduction, and hence the magnetism, could be electronically controlled.
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