Highly oriented NiSi2@Si thin-nanocomposite produced by solid state diffusion: Morphological and crystallographic characterization

Abstract

This article describes a morphological and crystallographic multi-technique characterization of a 2D-nanocomposite consisting of highly oriented NiSi2 nanoplates endotaxially grown inside a single-crystalline Si(001) wafer close to its external surface. This nanostructured material is prepared using a novel procedure which promotes the diffusion of Ni atoms from a deposited Ni-dopped-SiO2 thin film into the volume of a Si(001) flat wafer under controlled thermodynamic conditions. High Resolution Scanning Transmission Electron Microscopy images reveal the formations of well oriented thin hexagonal nanoplates totally buried inside a Si(001) wafer and randomly oriented nearly spherical Ni nanocrystals located inside the Ni-doped SiO2 thin film and also inside a thin layer close to external surface of the Si(001) wafer. The NiSi2 nanoplates formed by endotaxial growth have their large hexagonal flat surfaces parallel to one of the four Si{111} crystallographic planes and exhibit coherent 7A-type interfaces with the host Si matrix. Additional analyses of Grazing-Incidence Small-Angle X-ray Scattering patterns - which probe a high number of nanoparticles - indicated that the average thickness and maximum diameter of NiSi2 nanoplates are 12 nm and 118 nm, respectively, and the average radius of Ni nanocrystals is 1.7 nm. The described process for obtaining 2D-NiSi2@Si nanocomposites opens new possibilities for exploiting the structural features of these materials for use in devices requiring anisotropic electrical transport properties.