The memory effects of ZnO nanoparticles embedded in a polyimide (PI) matrix were investigated. Transmission electron microscopy images and selected area electron diffraction patterns showed that ZnO nanocrystals were created inside the PI layer. Capacitance-voltage (C-V) measurements on Al/PI/nanocrystalline ZnO∕PI∕p-Si structures at 300K showed a metal-insulator-semiconductor behavior with a flatband voltage shift due to the existence of the ZnO nanocrystals, indicative of trapping, storing, and emission in the electrons in the ZnO nanocrystals. Possible electronic structures corresponding to the writing and erasing operations for the Al/PI/nanocrystalline ZnO∕PI∕p-Si device are described on the basis of the C-V results.
20 nm diameter SiO(2) nanopore arrays on gradient-thickness membranes were formed by a focused electron beam with in situ transmission electron microscopy (TEM). Nanopore shrinkage was seen in nanopores on thicker membranes, with the rate of diameter change remaining constant during the shrinkage process. In contrast, pore expansion was observed in thinner membranes, with the expansion rate being constant at the initial stage but with a slight increase at the later stage. The geometry model of shrinkage and expansion of the nanopores in relation to the electron irradiation time was investigated by utilizing the TEM tilting method.
The effects of Mn delta-doping on the magnetic properties of (Ga1−xMnx)N thin films grown on GaN buffer layers by molecular-beam epitaxy were studied. The magnetization curve as a function of the magnetic field as 5K indicated that ferromagnetisms existed in the Mn delta-doped (Ga1−xMnx)N and (Ga1−xMnx)N thin films and that the magnetization in the Mn delta-doped (Ga1−xMnx)N thin film was significantly enhanced. The magnetization curve as a function of the temperature showed that the Curie temperature of the Mn delta-doped (Ga1−xMnx)N thin film was estimated to be above room temperature. The increase of the magnetization in the Mn delta-doped (Ga1−xMnx)N thin film in comparison with that in the (Ga1−xMnx)N thin film was attributed to the enhancement of the carrier-mediated ferromagnetism due to increased hole concentrations. The theoretical results showed that Ga vacancies near the Mn delta-doping layer were likely to cause p-type conductance, indicating that the enhancement of the magnetic properties in (Ga1−xMnx)N thin films originated from Mn delta doping.
The strain effects in and the crystal structures of self-assembled InAs/GaAs quantum dots (QDs) were investigated by using transmission electron microscopy (TEM). The in-plane lattice constant of the InAs QDs was larger than that of the GaAs substrate, and the vertical lattice constant of the InAs QDs was smaller than that of the InAs bulk. The variation of the lattice constant for the InAs QD originated from the strain effect. A schematic diagram of a strained InAs QD based on the TEM results, indicative of the strain distribution around the QD, is presented.
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