Lattice-mismatch is an important factor for the heteroepitaxial growth of core-shell nanostructures. A large lattice-mismatch usually leads to a non-coherent interface or a polycrystalline shell layer. In this study, a conformal Ag layer is coated on Cu nanowires with dense nanoscale twin boundaries through a galvanic replacement reaction. Despite a large lattice mismatch between Ag and Cu (∼12.6%), the Ag shell replicates the twinning structure in Cu nanowires and grows epitaxially on the nanotwinned Cu nanowire. A twin-mediated growth mechanism is proposed to explain the epitaxy of high lattice-mismatch bimetallic systems in which the misfit dislocations are accommodated by coherent twin boundaries.

Diluted magnetic semiconductors (DMSs) based on III-V semiconductors, fabricated by incorporating a proper concentration of magnetic ions, have attracted considerable attentions in recent years because of the possibility involving charge and spin degrees of freedom in a single substance. It is expected to provide new functionality for microelectronic devices by exploiting the spin of charge carriers in the ferromagnetic semiconductors [1]. Also, it is desirable to exhibit robust ferromagnetism with Curie temperature Tc above room temperature without second magnetic phase or clusters [1]. However, to understand the correlation of magnetic properties and microstructure in DMSs with spatial resolution of near or even better than nanometer scale is required. The high spatial resolution available on a transmission electron microscopy (TEM) combined with the benefits of electron energy loss spectroscopy (EELS) allows detailed analysis in terms of microstructure and the white-line intensities of the transition metal at the onsets of the L 2 and L 3 absorption edges on the scale of nanometer. In our experiment, GaN-based DMSs with several annealing conditions are investigated by using high resolution TEM coupling with nano-beam energy dispersive x-ray spectroscopy (EDX) and EELS.In this study, for avoiding the formation of second phase (as shown in Fig. 1), we report on the use of a thin protecting layer during implantation with Ni at a dose of 5 × 10 16 cm -2 and the study of corresponding magnetic and structural properties after subsequent annealing. After etching off the protecting layer, subsequent annealing up to 800 o C under flowing N 2 resulted in a p-type GaN with apparent ferromagnetic behavior up to ∼ 320 K. In addition, the ferromagnetic behavior became more manifest with increasing annealing temperature that increases hole concentration. Neither presence of any other second phases nor clusters in the Ni-implanted region was identifiable, at least to the 0.2 nm point-to-point resolution of high resolution transmission electron microscopy. Although implantation damages are still abundant, there are no obvious extra spots contributed from secondary phases, and only the streaking diffraction spots from the GaN hexagonal crystal structure is observed. The streaking diffraction spots are resultant from lattice defects caused by the damages of ion implantation, including dislocation loops or stacking faults, as shown in Fig. 2. Since the 3-d shell is the outermost shell and known to be responsible for the magnetic properties for the 3-d transition metal group ions [2], this work will study the behavior of 3d state electrons in Ni-doped DMSs. Figure 2 shows the electron energy loss spectrum from several nanowires. The characteristic nickel L 2 and L 3 absorption edge can be seen. Further calculations on the ratio of the integrated intensity counts, done on the L 3 and L 2 absorption edge of nickel, correspond to valence state of +2. In analogy with Wahl et al.'s report for Fe implanted GaN [3], we expect that some ...