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A B S T R A C T S THURSDAY, JULY 1 N A N O S E A 2 0 1 0 2 – Abstract Using low-energy electron microscopy (LEEM) and Grazing Incidence Small Angle X-ray Scattering (GISAXS), we have studied the evolution of the morphology and structure of dewetted thin-films from the nucleation of voids/holes until the growth of isolated Si nanocrystals. Depending on the surface preparation cleanness we find different dewetted morphologies [9]. For cleaned samples (see Fig. 1a) the dewetted areas are square-shaped holes with -oriented sides. Inside the holes, fingers form aligned in well-defined crystallographic directions , and . The fingers then break into Si aggregates. As shown by GISAXS (see Fig. 1b) and surface X-ray diffraction the Si nanocrystals keep the initial crystallographic orientation of the film. It is noteworthy that the dewetting of the layer occurs on an amorphous material (SiO2) showing that the crystallographic orientation of the top Si layer is a key parameter. We have quantitatively characterized the shape evolution, size, and ordering of the Si nanocrystals at different stages of the dewetting process, and as function of film thickness and temperature. We find that the activation barrier of the dewetting is dependent on the thickness of the SOI. We measure the dewetting kinetics using LEEM darkfield imaging. This technique reveals contrast between adjacent terraces by selecting a (2×1) reconstruction diffraction spot (Fig.2). We have measured during dewetting the mass transfer at the atomic level measuring the atomic step motion close to the edge of the hole, as well as the nucleation of new layers at the top of the (001) facet of the rim. These results are compared with theoretical models proposed in the literature [4,10,11]. Fig. 1 : (a) LEEM image of a dewetted SOI(001) thin film (20 nm) annealed at 850°C (10 min). Field of view 25 μm. (b) GISAXS image with a X-ray beam aligned along direction. Extended {113} and {111} facets are measured on the Si nanocrystals. 3 – Conclusion Fig. 2 LEED/LEEM of dewetting of 22 nm-thick SOI films prepared by (T = 910 °C, FOV 25 µm, E = 7.8 eV ). Solid state dewetting of silicon-on-insulator templates have been studied in real time and in situ. The combination of real space imaging by LEEM and reciprocal space characterization by GISAXS has provided a detailed description of the process and a unique way to extract the key mechanisms involved in solid 97
A B S T R A C T S THURSDAY, JULY 1 N A N O S E A 2 0 1 0 dewetting. We will show that a more complete theory is needed to understand all the aspects of the dewetting of Si on SiO2. Support by ANR PNANO (ANR 08-Nano-036) is gratefully acknowledged [1] P. Zhang et al., Nature 439 (9) 703 (2006). [2] Lundstrom, W. Schoenfeld, H. Lee, and P. M. Petroff, Science 286, 2312 (1999). [3] M. Leong, B. Doris, J. Kedzierski, K. Rim, M. Yang, Science 306, 2057 (2004) [4] D. T. Danielson et al. J. Appl. Phys. 100, 83507 (2006). [5] R. Nuryadi, et al., J. Vac. Sci. Technol. B, 20(1), 167 (2002). [6] B. Yang et al., Phys. Rev. B 72, 135413 (2005). [7] E. Dornel et al. , Phys. Rev. B 73, 115427 (2006). [8] Z.A. Burhanudin et al. Appl. Phys. Lett. 87, 121905 (2005) [9] E. Bussmann, F. Cheynis, F. Leroy, P. Müller, submitted [10] E. Jiran and C. V. Thompson Thin Solid Films, 208 23-28 ( 1992). [11] D.J. Srolovitz, S.A. Safran, J. Appl. Phys, 60, 255 (1986). 12H10-12H30 Dewetting of Solid films. O. Pierre-Louis(1), A. Chame(2), Y. Saito(3), M. Dufay(1) (1- la Doua, Bâtiment Léon Brillouin, 43 Boulevard du 11 Novembre 1918, F 69622 Villeurbanne, France ; 2- Universidade Federal Fluminense,Avenida Litoranea s/n, 24210-340 Niteroi RJ, Brazil ; 3- Keio University, 3-14-1, Hiyoshi, Kohoku-ku, Yokohama, Kanagawa, 223-8522 Japan). 1 – Introduction Solid films with sub-micron thicknesses may break-up into islands to lower their energy. Such a "dewetting" process was observed in many experimental systems . Up to now, the theoretical analysis of solid-film dewetting has been based on the Mullins continuum model for surface diffusion. This approach predicts the formation of a smooth dewetting rim at the edge of the film, with scaling laws for the increase of the radius of a hole $\sim t^{1/4}$[Srolovitz et al 1986], and for the position of straight fronts $\sim t^{2/5}$[Wong et al 2000]. However, the presence of facets, the evolution of which is controlled by 2D nucleation, leads to novel phenomena which cannot be accounted for within the frame of the Mullins model. Examples include the relaxation of nano-crystals[Combe et al 2000, Mullins et al 2000], the drift of islands on vicinal substrates[Ling et al 2004], layer-by-layer dewetting of ice islands[Thurmer et al 2008], or the formation of labyrinthine patterns of bilayer islands during the dewetting of a monolayer[1]. 2 – Abstract We use the Solid on Solid KMC model of Ref.[1]. On a square lattice with lattice unit $a$ and periodic boundary conditions, the local height is $z\geq 0$. The substrate surface, at $z=0$, is flat and frozen. Epilayer atoms hop to nearest neighbor sites with rates $\nu_0\,{\rm e}^{-E/T}$, where $\nu_0$ is an attempt frequency, and $T$ is the temperature (in units with $k_B=1$). The hopping barrier is $E=nJ- \delta_{z,1}E_S$, where $n$ is the number of in-plane nearest neighbors, $J$ is the bond energy, $\delta$ is the Kronecker symbol, and $E_S$ is the adsorbate-substrate excess energy. Our energy unit is $J$, so that $J=1$. When $E_S\gg1$, the energy is minimized by creating high islands\cite{PierreLouis2007}. When $E_S\rightarrow 0$ the epilayer spreads on the substrate. We choose $0.3
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