Schematic drawing of the implantation and annealing processes to obtain metal nanoparticles for subsequent growth of semiconductor NWs by the VLS process. Structural appearance (a) after room temperature implantation of Au, (b) after annealing at temperatures , and (c) after annealing at temperatures for about .
Energy-filtered TEM of the as-implanted sample [cf. schematic in Fig. 1(a)]. Top: (left) bright-field TEM image and (right) map of the carbon distribution; bottom: (left) silicon distribution ( edge) and (right) oxygen distribution.
(Color online) STEM dark-field micrograph (upper left) with a line indicating where the EELS data on the right are taken. Series of EEL spectra taken across the layers.
(Color online) Combined STEM/PEELS analysis of the very /native oxide interfacial zone, STEM dark-field image (left corner), and corresponding series of EEL spectra taken along a line across the interface.
(Color online) Topographic atomic force micrograph of Au droplets at a Si(111) substrate after implantation of and annealing for at .
Cross-sectional TEM micrographs of the Au-implanted and annealed silicon wafer that serves as a metal template for subsequent CVD NW growth. (a) High-resolution blow up of sample shown in (b). Micrographs show that the implanted Au agglomerates form nanoparticles or droplets that reach the substrate surface. Due to this fact VLS growth of NWs can occur from these droplets.
Secondary-electron images of Si NWs grown on Au-implanted and annealed Si(111) substrates. (a) It is visible that only in implanted areas NW growth occurs (implantation through a mask, area on the left is unimplanted); [(b) and (c)] blow ups showing straight Si NWs with a gold droplet at their tips. The NW orientations are partly perpendicular, partly oblique to the substrate surface. The NW diameters are determined by the Au droplet size and show a comparably narrow distribution with sizes well below .
Cross-sectional TEM micrograph of a Au-implanted Si(111) wafer. The implantation was carried out at . Due to the elevated temperature, no amorphization of the Si wafer takes place and the implanted Au resides in the form of tiny nanoparticulates distributed within the top of the wafer. In addition, extended lattice defects such as voids, stacking faults, and dislocation loops are visible in this part of the wafer.
Cross-sectional TEM micrograph of a Au-implanted Si wafer. The implantation was carried out at room temperature at a fluence of . The wafer was subsequently annealed at for . The annealing yields agglomeration of the Au as visible in form of darker, partly nanocrystalline, partly amorphous particulates which are distributed all over the top from the wafer surface.
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