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Semiconductor-based freestanding membranes (FSMs) have recently become central to the rapidly expanding frontiers of nanoscience and technology, and a highly promising area of advanced materials research. FSMs offer an extra degree of freedom for implementations that cannot be obtained by conventional methods such as heteroepitaxy, which often involves significant lattice mismatch in crystalline structures. Fabrication of FSMs from various materials allows for layer-by-layer stacking, enabling an easy coupling of the physical properties of dissimilar materials. Additionally, FSM structures offer unprecedented lightweight, and flexibility compared to conventional substrates. This demonstrates their high potential for the fabrication of novel applications, such as stretchable on-skin electronics or vertically stacked devices, flexible optoelectronics, etc., as well as a straightforward path for heterointegration. Furthermore, the use of FSMs provides significant cost savings in device production, especially for materials with orders of magnitude higher prices than that of silicon, as only a fraction of the material is being used when compared to conventional wafers. In this context, group IV materials FSM attract a lot of attention for their applications in high-performance optoelectronics and high-speed telecommunication, as well as for their biocompatibility and nontoxicity compared to III-V counterparts. However, the fabrication of high-quality group IV FSMs is still a challenging task. In this thesis, we demonstrate two promising paths for production of group IV FSMs using substrate engineering and advanced epitaxial growth. The first part of this work focuses on 2D-assisted epitaxy. We introduce the Anchor Point Nucleation approach enabling the growth of high-quality FSMs over a graphene-covered surface. Through plasma treatment defects, such as dangling bonds and nanoholes, are introduced in the graphene layer, acting as preferential nucleation sites., Les membranes autoportantes à base de semi-conducteurs (FSMs) sont récemment devenues cruciales pour l’expansion rapide de la nanoscience et de la technologie, représentant un domaine très prometteur de recherche avancée sur les matériaux. Les FSMs offrent un degré de liberté supplémentaire pour des mises en œuvre impossibles à obtenir par des méthodes conventionnelles telles que l’hétéroépitaxie de matériaux avec un désaccord de mailles cristallines très important. La fabrication de FSMs à partir de divers matériaux permet un empilement couche par couche, facilitant un couplage des propriétés physiques de matériaux différents. De plus, les structures FSMs offrent une légèreté et une flexibilité sans précédent par rapport aux substrats conventionnels. Cela démontre leur fort potentiel pour la fabrication de nouveaux dispositifs, notamment l’électronique sur la peau, les dispositifs empilés verticalement, l’optoélectronique flexible, etc., ainsi qu’une voie direct pour l’hétéro-intégration. De plus, l’utilisation de FSMs permet des économies significatives de coûts dans la production de dispositifs, en particulier pour des matériaux dont les prix sont plusieurs ordres de grandeur supérieurs à ceux du silicium, car seule une fraction du matériau est utilisée par rapport aux substrats conventionnels. Dans ce contexte, les FSMs de matériaux du groupe IV attirent beaucoup d’attention pour leurs applications dans l’optoélectronique haute performance et les dispositifs de télécommunication à haute vitesse tels que les guides d’ondes, les transmissions THz, les photodétecteurs et les lasers, ainsi que pour leur biocompatibilité et leur non-toxicité par rapport aux contreparties en matériaux III-V. Cependant, la fabrication de FSMs de haute qualité à partir des matériaux de groupe IV reste une tâche difficile. Dans cette thèse, nous démontrons deux voies prometteuses pour produire des FSMs du groupe IV en développant les méthodes de l’ingénierie des substrats et de la croiss

Amphiphilic nanoparticles can adsorb at interfaces between immiscible phases and form membranes. The ability to handle nanoparticle monolayers/bilayers as freestanding membranes independently from the interfaces on which they form can be of significant practical interest. Janus nanoparticles (JNPs) could generate membranes that have tunable pore size and are amphiphilic. Here it is shown how freestanding membranes from JNPs can be generated. First, strongly amphiphilic Janus nanoparticles that generate foams in surfactant-free conditions are synthesized. Upon drying the foam lamellae remain as freestanding membranes consisting of perfectly oriented bilayers or monolayers of JNPs, thus providing direct evidence of structural organization of amphiphiles in foam lamellae. The wet foam lamellae can be picked up on grids and upon drying generate freestanding membranes. Sturdy freestanding membranes by transferring monolayers of JNPs from the air–water interfaces onto grids with fine openings are also prepared.

The discovery of 2D conductivity at the LaAlO3/SrTiO3 interface has been linking, for over a decade, two of the major current research fields in materials science: correlated transition-metal-oxide systems and low-dimensional systems. Notably, despite the 2D nature of the interfacial electron gas, the samples are 3D objects with thickness in the mm range. This prevented researchers so far from adopting strategies that are only viable for fully 2D materials, or from effectively exploiting degrees of freedom related to strain, strain gradient and curvature. Here a method based on pure strain engineering for obtaining freestanding LaAlO3/SrTiO3 membranes with micrometer lateral dimensions is demonstrated. Detailed transmission electron microscopy investigations show that the membranes are fully epitaxial and that their curvature results in a huge strain gradient, each layer showing a mixed compressive/tensile strain state. Electronic devices are fabricated by realizing ad hoc circuits for individual micro-membranes transferred on silicon chips. The samples exhibit metallic conductivity and electrostatic field effect like 2D-electron systems in bulk heterostructures. The results open a new path for adding oxide functionalities into semiconductor electronics, potentially allowing for ultra-low voltage gating of a superconducting transistors, micromechanical control of the 2D electron gas mediated by ferroelectricity and flexoelectricity, and on-chip straintronics.