Real-time tracking of the self-assembled growth of a 3D Ge quantum dot lattice in an alumina matrix

Abstract

A laboratory in situ grazing-incidence small-angle X-ray scattering (GISAXS) tracking of the self-assembled growth of a regular 3D Ge quantum dot (QD) structure in an amorphous Al2O3 matrix during the ion beam sputter deposition of a periodic Ge/Al2O3 multilayer on silicon is reported. A 573 K substrate temperature proved to be necessary to achieve the self-assembly effect. Relying on a fast repeated acquisition of GISAXS patterns, the temporal evolution of the growing 3D Ge QD structure was analyzed bilayer by bilayer to determine its type, lateral and vertical correlation lengths, and inter-QD distance. The QD structure was found to have body-centered tetragonal lattice type with ABA stacking, with the lattice parameters refined by fitting the final GISAXS pattern relying on a paracrystal model. A single set of paracrystal parameters enables one to simulate the temporal evolution of the in situ GISAXS patterns throughout the deposition process, suggesting that the Ge QD self-assembly is driven from the very beginning solely by the growing surface morphology. Ex situ GISAXS and X-ray reflectivity measurements along with a cross-section high-resolution transmission electron microscopy analysis complete the study.

Investigation of physical properties of Si crystallites in W/Si multilayers

“…Perhaps there is a situation in which some of the particles are correlated with roughness and with particles in different layers and give rise to the observed 'ridges', and the other part of the particles have a lateral correlation, but their cross-layer correlation is small, which leads to the appearance of the 'wings'. Shaji et al (2020) found that such correlations between particles/quantum dots can extend up to five bilayers and the first deposited bilayer actually determines the ordering of inclusions in subsequent layers. Fig.…”

“…It is also possible that the observed effects may depend on the specific growth conditions, especially since the authors noted a change in the parameters of these inhomogeneities when ion polishing of the layers had been performed (Nikolaev et al, 2019;Medvedev et al, 2019). Similarly, the formation and growth of quantum dots in Ge/Al 2 O 3 strongly depends on temperature (Shaji et al, 2020). It is necessary to elucidate the physical properties of these inhomogeneities and the correlation with the density of silicon.…”

GisaxStudio—An Open Platform for Analysis and Simulation of GISAXS from 3D Nanoparticle Lattices

“…The software includes theoretical models published in [20][21][22], which take into account the NP ordering properties along each of the basis vectors of the 3D NP lattice. The models and the software are already successfully applied in the GISAXS analysis of many systems, including 3D NP lattices [5,[7][8][9]11,13,20,21,[32][33][34][35][36] and NPs formed within ion tracks [22,[37][38][39], where fitting of the full 2D measured map was performed. We show how the platform is constructed, reveal its main features, and demonstrate its performance.…”

Spatial correlation of embedded nanowires probed by X-ray off-Bragg scattering of the host matrix

“…Grazing-incidence SAXS (GISAXS) is a versatile tool for nano-objects on a surface (Renaud et al, 2009). While GISAXS has also been used to study the correlation of buried objects (Shaji et al, 2020), the signal of the latter is generally very weak relative to the strong scattering from the surface and embedding layer. Therefore, its analysis is complex (Lazzari, 2002) and almost impossible when, for example, the objects and the layer have similar mass densities or when the layer of interest is capped by other layers and structures.…”