Embedded nanostructures Revealed in Three Dimensions

Figure 2 (a) shows a low magnification cross-sectional TEM (X-TEM) bright field (BF) image of as-deposited 2 nm Ag/17 nm GeOx/SiOx/Si(100). This confirms the presence of spherical silver nanoparticles on top of an amorphous GeOx layer. It should be noted that a physical vapor deposition of Ge in high vacuum condition yielded GeOx layer. The as-deposited Ag thin film showed isolated irregular nanostructures. From figure 2 (a), the thicknesses of the GeOx and the native oxide (SiOx) layers were found to be ≈17 nm and ≈2 nm, respectively. Figure 2 (b) depicts a low magnification BF X-TEM micrograph of 2 nm Ag/17 nm GeOx/SiOx/Si (100) at ≈800°C (annealing done in air for 30 minutes). From this micrograph, the thickness of GeOx is found to be ≈75 nm where SiOx is ≈20 nm thick. Following the annealing in air, the GeOx and SiOx layer thicknesses have been increased by a factor of ≈3.4 and ≈9, respectively. The cross-sectional image taken (for 2 nm Ag/17 nm GeOx/SiOx/Si(100) @800°C), shown in figure 2 (b), confirms the intrusion of silver into the silicon substrate. Figure 2 (c) represents a high resolution lattice image of a small area shown in Figure 2 (b). This lattice image confirms the presence of Ag (111) (0.238 ± 0.005 nm) and Si (111) (0.315 ± 0.005 nm) lattice planes as an endotaxial structure. nostructures in silicon. The Moiré fringe spacing can be determined by

where d1, d2 are lattice spacings of the planes which are constituents of Moiré fringes and β is the angle between the planes. The Moiré fringe spacing of 0.96 nm was calculated between Ag(111) and Si(111) planes with β = 0. This matches well with the measured fringe spacing from our measurements (Figure 2 (c)) is 0.95 ± 0.01 nm. Figure 2 (d) is the synchrotron XRD spectrum of the 2 nm Ag/17 nm GeOx/SiOx/Si(100) @800°C in air for 30 minutes, which depicts the single crystalline nature of the silver nanostructures on silicon (100) substrate. In the XRD spectrum, only Ag(002) and Ag(004) peaks were observed along with the Si(004) peak that belongs to the substrate. Due to the larger x-ray beam size (250 μm × 250 μm), the XRD show the macroscopic ordering. Hence, the XRD data confirms the presence of crystalline Ag structures over a larger scale compared to TEM. The inset of figure 2(d) shows the selected area electron diffraction (SAED) pattern taken on a single endotaxial nanostructure, confirming that the silver nanostructures are single crystalline in nature. XRD and SAED confirm the macroscopic and microscopic coherent nature of the Ag nanostructures, respectively.

Figure 2: X-TEM Micrographs of 2 nm Ag/17 nm GeOx/SiOx/Si (100) (a) Low Mag of as-deposited (b) Low Mag of 800 °C annealed in air (c) HR-XTEM depicts endotaxial structures (with Moire fringes) and (d) X-Ray Diffraction Pattern showing the single crystalline nature of the Ag nano structures which also complimented by a Selected Area Electron Diffraction (SAD) pattern taken on a single structure.