Growth of spatially ordered Ge nanoclusters in an amorphous matrix on rippled substrates

A rippled substrate highly influences the arrangement of Ge quantum dots in a matrix; it ensures a substantial improvement in the regularity of their ordering and a narrowing of their size-distribution. The grazing incidence small angle x-ray scattering (GISAXS) technique was shown to be amazingly efficient in the determination of the above mentioned structural properties and the characterization of the self-assembly process. Recently we have developed a method for the production of self-assembled Ge QDs in amorphous silica matrix. The method is based on diffusion-induced nucleation combined with the effect of surface morphology. Ge QDs were created by the deposition of (Ge+SiO2)/SiO2 multilayer films on a flat Si(111) substrate at an elevated temperature. The benefits of the method are a simple and efficient production of the material, a relatively narrow size distribution as well as a rather regular arrangement of the dots in the matrix. The main problem with the produced material is that the regular ordering appeared in small domains randomly rotated with respect to the normal to the film surface.
Our latest investigation however solved this problem and resulted in a further improvement of the material properties. Instead of flat substrates, we have now used periodically corrugated-rippled substrates. These substrate surfaces exhibit a very small periodicity (10-20 nm) and they can be easily produced on large surface areas by ion erosion.

Our GISAXS measurements showed that the QDs appear in the valleys between theripples, so they follow the substrate morphology. The regularity of the quantum dots positions is nicely visible in the GISAXS maps of the films. The GISAXS map of the rippled substrate prior to deposition shows only two lateral streaks stemming from the periodicity of the ripples. After the deposition of a 5 bi-layer film a beautiful GISAXS intensity distribution is obtained showing that the arrangement of the formed QDs follows the morphology of the rippled substrate. Increasing the number of deposited layers to ten, the lateral features in the GISAXS images become slightly broader, showing a small increase in the QD position disorder with increasing number of layers.

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Growth of spatially ordered Ge nanoclusters in an amorphous matrix on rippled substrates;
M. Buljan, J. Grenzer, A. Keller, N. Radić, V. Valeš, S. Bernstorff, T. Cornelius, H.T. Metzger, and V. Holý,
Physical Review B, Vol. 82 (12), pp. 125316 (2010)..
doi: 10.1103/PhysRevB.82.125316

Last Updated on Tuesday, 14 May 2019 17:05