Influence of annealing conditions on the formation of regular lattices of voids and Ge quantum dots in an amorphous alumina matrix

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

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.

Deposition of Thin Alumina Films Containing 3D Ordered Network of Nanopores on Porous Substrates

Self-supporting thin films containing nanopores are very promising materials for use for multiple applications, especially in nanofiltration. Here, we present a method for the production of nanomembranes containing a 3D ordered network of nanopores in an alumina matrix, with a diameter of about 1 nm and a body centered tetragonal structure of the network nodes. The material is produced by the magnetron sputtering deposition of a 3D ordered network of Ge nanowires in an alumina matrix, followed by a specific annealing process resulting in the evaporation of Ge. We demonstrate that the films can be easily grown on commercially available alumina substrates containing larger pores with diameters between 20 and 400 nm. We have determined the minimal film thickness needed to entirely cover the larger pores. We believe that these films have the potential for applications in the fields of filtration, separation and sensing.

Tuning the growth properties of Ge quantum dot lattices in amorphous oxides by matrix type

Self-assembled growth of Ge quantum dot lattices in oxide matrices prepared by the quite simple magnetron sputtering deposition method allows the preparation of a variety of structures tunable by their shape, size and arrangement. The driving mechanism for the self-assembly was attributed to the surface morphology features originating from the quantum dots' growth. Here it is shown specifically that the matrix type is another critical factor that enables the control of the self-assembly process and the tuning of the ordering type and degree of regularity of quantum dot systems. The effectiveness of the matrix factor is demonstrated through the analysis of quantum dot arrangements in amorphous silica, alumina and mullite matrices. Using the same deposition conditions, different ordering types and degrees of disorder were found in the quantum dot systems based on different matrices. The matrix factor is shown to be driven by different matrix tendencies to smooth the surface during the growth of the films. The obtained results are relevant for understanding and tailoring of the self-assembled growth of quantum dot lattices in amorphous systems.