Formation of CoSi2 nanohexagons buried in single crystalline Si substrates. Effects of orientation of the Si host.

KELLERMANN, G.; MONTORO, L.; DOS SANTOS CLARO, P.C.; GIOVANETTI, L. J.; ZHANG, L.; REQUEJO, F.G.; RAMÍREZ. A. J.; CRAIEVICH, A.F.

Florianapolis

Congreso; XI Encontro Anual da Sociedade Brasileira de Pesquisa em Materiais (SBPMat); 2012

Sociedade Brasileira de Pesquisa em Materiais (SBPMat)

During the last decades an increasing demand for the development of new methods of preparation of nano-composite materials suited for technological applications has been observed [1]. The interest on these nanomaterials is related to the fact that many of their properties can be varied in a continuous way by changing the size, shape and/or spatial ordering of their basic units. We have recently described a simple method for obtaining buried arrays of CoSi2 plates coherently embedded in a Si host lattice [2]. It was established that thermally activated diffusion of Co atoms embedded in a SiO2 thin film - deposited on the (001) flat surface of a Si wafer - promotes the formation of CoSi2 hexagonal nanoplates inside the Si single crystalline substrate. In order to obtain additional information about the process of thermally activated diffusion of Co atoms into Si single crystals, we have studied three Si wafers with different crystallographic orientations of their external surfaces, namely Si(001), Si(011) and Si(111), subjected to the same deposition procedure and to an equivalent thermal treatment. After deposition of Co containing SiO2 thin films, the three samples were submitted to 1 hour of isothermal treatment at 750C and then characterized by transmission electron microscopy (TEM) and grazing-incidence small-angle X-ray scattering (GISAXS). TEM images evidenced the presence of thin CoSi2 nanoplates buried in Si(001), Si(011) and Si(111) substrates. In all cases the platelets exhibit a hexagonal lateral shape, one of their sides being in contact with the SiO2/Si interface. TEM images also demonstrated that the lattices of the CoSi2 platelets are coherently related to the crystallographic lattices of the host Si single crystal. In addition and regardless the Si crystallographic orientation, we could verify that the hexagonal platelet faces are parallel to crystallographic planes belonging to the Si{111} plane family. Our analysis of GISAXS results indicates that the relevant sizes (lateral side and thickness) of the CoSi2 nanohexagons are functions of the crystallographic orientation of the Si substrate. Particularly, the lateral size of nanohexagons buried in Si(111) wafers is remarkably (~50%) larger than the size of those developed inside Si(001) and Si(011) substrates. Moreover the thicknesses of the platelets vary from 2.8 nm for Si(001) up to 5.7 nm for Si(111). Our TEM and GISAXS analyses also detected the additional presence of spherical metallic Co nanoparticles that remain embedded in the deposited SiO2 thin film, their average radius ranging from 0.6 nm for Si(011) up to 1.5 nm for Si(001). This work was supported by LNLS, LME-LNNano, CNPq and FAPESP, Brazil; ANPCYT and CONICET, Argentina; and CIAM (CONICET/CNPq/NSF) collaborative project. [1] R.C. Chau et al, Nature Mater. Vol. 6 (2007) 810. [2] G. Kellermann et al, Appl. Phys. Lett. Vol.100 (2012) 063116.