Fifty years of dramatic advances in microelectronics have reshaped the way we communicate and work, but progress on silicon-based technologies could well be reaching their limits. This calls for fresh research on new materials for the electronic industry. In this context, fabrication of high quality oxide heterostructures (HS) lies at the heart of the emerging field of oxide electronics. Indeed, Ohtomo and Hwang (2004) have shown that a two dimensional electron gas (2DEG) can be formed in HS based on the wide-gap band insulator SrTiO3 (STO). This is appealing, as STO is a member of the transition metal oxides (TMOs). These materials present unique properties, such as high temperature superconductivity in cuprates, colossal magnetoresistance in manganites, multiferroic behaviour in bismuth ferrites. Owing to their similar perovskite structure, one can combine them into a large variety of HS, hoping for novel emerging properties at their interfaces. A recent breakthrough due to the Coordinator and several members on this project may open a new way to create and study 2DEGs in TMOs: we found that a 2DEG can be obtained at the bare surface of insulating STO by simply fracturing a crystalline sample in vacuum. An exciting perspective, which is at the core of the present proposal, is that the underpinning mechanism of such a 2DEG may be generic to other perovskites, and that the ensuing 2DEGs might inherit some of the properties of their host compounds, which are often correlated electron systems. Thus, we will aim at the creation and engineering of novel 2D electronic states at the surface of TMOs endowed with technologically promising functionalities. Materials to be investigated include the ferroelectric BaTiO3 (BTO), as well as manganites and multiferroics, which could present strongly spin-polarized 2DEGs allowing the creation of electrically controllable spintronic devices. Furthermore, very recent results from our consortium suggest original routes to craft non-trivial topological states in oxide surfaces. In this project, we will explore the realization of new topological 2DEGs at the surface of TMOs. Moreover, in order to search for optimal or new functionalities, we will tailor in-situ their microscopic properties, like carrier density, spin-orbit or spin-spin interactions, and directly follow the evolution of their electronic structure. At the core of our strategy, we will use a combination of state-of-the-art in-situ preparation and characterization techniques and photoemission spectroscopy. Understanding such surface metallic states requires detailed studies of the role of oxygen vacancies created during the fracturing process. Key issues to be addressed include identifying the mechanisms that can form, stabilize and allow an engineering of the oxygen vacancies at the surface of TMOs. Furthermore, we will find ways to protect the surface 2DEGs to render them usable for transport measurements and for applications. This project is a re-submission of our project “LACUNES”. We have taken into account the remarks made by the Evaluation Committee, and made sure to allay their concerns. Outcomes of this project can open new avenues for the development of electronics based on TMOs. The consortium combines the necessary skills to meet the challenges of the present proposal, as our recent experimental/theoretical collaboration shows. Our discovery and recent preliminary results, described below, demonstrate the feasibility and potential of our approach to create novel 2DEGs in several TMOs.