Ordered nanocells – a new phase of carbon – NANOCELLS

Different growth experiments as well as the characterization will be carried out from the atomic to the microscopic scale by transmission electron microscopy in Strasbourg. The microscopic scale will be explored by using substrates of centimeter dimensions, due to the access of the Institut Néel to a low-energy electron microscope. Growth experiments at the macroscopic scale and characterizstion by in-situ diffraction at the synchrotron will be carried out in Grenoble. The different experiments of growth that are realized on the microscopic as well as on the macroscopic scale will be coupled to chemical and structural characterization by electron energy-loss spectroscopy in Châtillon. The structures will be modeled in Grenoble by ab initio calculations that will allow to determine the most stable structures, the properties of defects, and the electronic structure.

The work within the frame of the project is in progress and has already shown interesting results. A first publication has recently been submitted to ACS Nano (F. Ben Romdhane et al., In-situ growth of cellular two-dimensional silicon oxide on metal substrates). The first studies concentrate on the growth of new cellular structures of carbon and silica. While the cellular carbon phase is still difficult to synthesize, a cellular phase of silica was observed that resembles the cellular carbon phase and merits a detailed study. The nanocells of crystalline silica are of much interest for the realization of novel insulating layers with a well-defined thickness that might be technically superior to amorphous silicon layers.
The understanding of epitaxial growth is indispensable for the synthesis of cellular structures. In-situ electron microscopy experiments have shown that it is possible to synthesize layers of silica on different metallic substrates.
Further work is devoted to the realization of carbon cells. The synthesis and characterization of carbon layers is in progress.

The synthesis of the two phases (silica and carbon) with similar structure and under similar conditions promises a large variety of studies on different scales in the near future. In view of the in-situ synthesis in the electron microscope, ongoing experiments on larger scales will be the principal aim of the project. If successful, the cellular carbon and silica structures will be most interesting materials for different applications in nanoelectronics. For example, silica layers have a well-defined thickness and could serve as insulating layers in gates of transistors.

A publication about the cellular silica phase has been submitted to ACS Nano.

The proposal suggests a collaboration between the Institut de Physique et Chimie des Matériaux in Strasbourg (F. Banhart, coordinator), the Institut Néel in Grenoble (J. Coraux), and the Laboratoire d’Etude des Microstructures (LEM) CNRS-ONERA in Paris-Châtillon (A. Loiseau). The project is devoted to the investigation of a new structure of carbon that has recently been discovered by one of the applicants. The formation of an ordered cellular phase of carbon on metallic substrates has been observed in an in-situ electron microscopy study at the IPCMS in Strasbourg. The elementary unit of the structure is based on a carbon nanotube, but with mixed sp2/sp3 bonding. The structure grows in competition with graphene on catalytically active metal surfaces and shows many common features with graphene, e.g., the same hexagonal ordering on suitable metal substrates and the same type of structural defects.
The aim of the project is to take advantage of the advance that the applicants have at present relative to other groups that did not start research on this subject yet. The knowledge about this new carbon phase is still in its beginnings and therefore very limited. Now, detailed growth and characterization studies are necessary to find the conditions for the growth of this phase, in particular on a macroscopic scale, and to study its properties by different techniques of characterization. The nucleation, growth, and structure of the phase will be studied on different scales. Experiments and characterization will be carried out on a microscopic scale down to the atomic resolution in a transmission electron microscope in Strasbourg and up to a mesoscopic scale on centimeter-size substrates through the privileged access of the Institut Néel to a low-energy electron microscope. Macroscopic growth experiments and a characterization of the phase by in-situ diffraction with synchrotron light will be conducted in Grenoble. All these different experiments from microscopic to macroscopic scale growth will be coupled with chemical and structural characterization by electron energy-loss spectroscopy, which will be conducted in Châtillon. Theoretical studies will be carried out in parallel to experiments on systems as close as possible to the ones studied experimentally (more than 1000 atoms can be addressed).