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Controlled Growth and Positioning of Functional Materials By Unconventional Nanoscale Patterning.

Cojocaru, Christian Victor (2007). Controlled Growth and Positioning of Functional Materials By Unconventional Nanoscale Patterning. Thèse. Québec, Université du Québec, Institut national de la recherche scientifique, Doctorat en sciences de l'énergie et des matériaux, 213 p.

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The growth of functional nanostructures with controlled size and shape, precisely registered on a substrate of choice, using a minimal number of processing steps, represents a widely discussed, critical issue in Nanotechnology. Furthermore, the fabrication and patterning of novel complex materials with integrated functionality represents an interesting challenge for the development and the application of smart materials. Probing new routes to prepare these materials and understanding the relationship between their fabrication process, their size/structure and their properties is therefore essential. In this context, a variety of conceptually simple forms of lithographysuch as molding, stamping, imprinting - are now being revisited for their potential as alternative nanofabrication and patterning techniques. However, there is a common drawback associated with almost all alternatives to traditional lithographic approaches: they still require some type of resist (polymer) processing and consequently numerous chemical, thermal and etch associated steps. The approach that we have adopted and further built on in this work is nanostenciling, i.e. the controlled growth of nanostructures by direct deposition through miniature shadow-masks. The use of a nanostencil or tiny mask with nano-apertures opened in ultrathin solid-state membranes, allows for a direct, selective and clean deposition of various materials on almost any type of surface. Nanostenciling is a "resistfree", parallel fabrication process, very much compatible with high and ultra high vacuum technology and thus a valuable approach to pursue fundamental research in a university environment. Through the combination of pulsed laser deposition (PLD) with nanostencilirig, we have focused on patterning of two representative material-systems: (i) semiconductor germanium-silicon heterostructures and (ii) functional perovskite-type ferroelectric and multiferroic oxides. The work undertaken on patterning of Ge/Si heterostructures was two-fold. Firstly, using deposition through nanostencils mechanically attached to the substrate, we demonstrate a resist-free and site-selective growth approach of arrays of Ge nanocrystalline structures, with possible applications in optoelectronics. Secondly, using nanostencils as fabrication and patterning tools, we provide new insights into kinetic phenomena that lead to the growth of crystalline Ge dots during the PLD process. We further demonstrated the method's high flexibility and its suitability for virtually any deposited material on any substrate, by fabricating ferroelectric oxides (e.g. BaTi0₃) nanostructures. Their local ferroelectric properties were investigated using piezoresponse force microscopy, a unique method which enables studies of polar properties at the nanoscale and permits to investigate size effects (i.e. suppression of ferroelectricity below a critical size at room temperature) in patterned ferroelectric nanostructures. In the case of multiferroic complex oxides (e.g. BiFe0₃ and BbFeCr0₆), stenciling proved to be a valuable tool for enabling investigations into the multifunctionality of individual nanostructures. In the particular case of the newly predicted quaternary Bi₂FeCr0₆ multiferroic, we obtained for the first time, epitaxial structures which we proved to be both ferroelectric and magnetic at room temperature. This work demonstrates the generality of nanostenciling and · its suitability as an excellent alternative approach to nanofabrication and patterning, since different material systems, ranging from metals to semiconductors to complex oxides, can be treated with the same ease.

Type de document: Thèse Thèse
Directeur de mémoire/thèse: Rosei, Federico
Co-directeurs de mémoire/thèse: Pignolet, Alain
Mots-clés libres: nanotechnology; nanostencil; Semiconductor Ge/Si Heterostructures; Pulsed Laser Deposition
Centre: Centre Énergie Matériaux Télécommunications
Date de dépôt: 28 févr. 2018 16:39
Dernière modification: 28 févr. 2018 16:39
URI: http://espace.inrs.ca/id/eprint/6833

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