Topic 2: Functionalization of surfaces

Topic supervisors:

Ludovic Thilly (ludovic.thilly@univ-poitiers.fr / +33 5 49 49 68 31 )
Jérémie Drévillon (jeremie.drevillon@univ-poitiers.fr / +33 5 49 45 35 42 )

The functionalization of a surface aims to improve its field of application and / or to add new properties to it, via an “by-design” engineering process. Here, the functionalization techniques are based on the fine structuring of the surface (or “patterning” in the broad sense) and some of them were studied during Labex I. They include the FIB “toolbox” but also other types of surface modification methods, such as physical vapor deposition of thin nanostructured layers and multilayer coatings, wide beam ion spraying of solid surfaces, l implantation of ions, and nano-mechanical engineering (surface reconstruction, tensile and compression loads, etc.). The new functions can be optical, electronic, thermal, tribological, catalytic, etc. and are complementary to the properties studied in the other two themes.

The objectives of this subject are to overcome some of the challenges associated with surface functionalization: 1) the fundamental understanding of the processes behind surface structuring, 2) the impact of specific surface structures on new macroscopic properties not studied in the other subjects, and 3) the stability of surface structures for long-term applications.

These challenges require the use of advanced techniques allowing the characterization of multi-scale surfaces, from the atomic scale (for example, TEM, AFM-STM, EELS, X-ray diffraction and scattering, etc.) to the macroscopic scale. (including in situ and real). real-time diagnostics). Understanding the surface structuring processes and their impact on functional properties requires both experimental and theoretical approaches, while the stability of the structuring can be assessed by specific small-scale metrology techniques.

Again, drawing on the solid expertise developed during Labex I, several examples can be given to illustrate the type of studies that could be developed, based on proposals from the community:

In the field of optical and thermal functionalities, 1D and 2D networks have been studied theoretically and initial experimental applications have shown promise for the design of coherent heat sources and high performance radiative cooling devices. Then, the steps would consist in optimizing the parameters of the networks through a digital / experimental feedback loop, but also by developing new bi-periodic networks and / or by using new bulk materials (VO2, NiTi) as well. than multi-layer coatings.

The fine atomic organization of surfaces finds its extreme cases in the form of 2D materials (graphene, silicene, MoS2, MXene …) presenting the advantage of an ultimate thickness of only a few atomic layers. Understanding how atomic reconstructions or 2D materials modify or even control their functional properties would offer technological breakthroughs in various fields such as nanoelectronics, photovoltaics or catalysis.

Structuring / modeling large areas to reduce friction in industrial applications with a cheaper and faster method is difficult prospecting work. This requires modifying the shape of the surface to obtain improved lubrication behavior similar to that of harder and more resistant materials, such as hydrophilic metals. Another interesting prospect would be to obtain an anisotropic friction behavior via a specific pattern leading to a mixture of hydrophobic / hydrophilic zones on the surface.

Other studies developed within the framework of this theme could relate to the identification of the fundamental mechanisms involved in the structuring / functionalization of the surface itself (ion-matter interaction, mass transport induced by stress or heat, kinetics of growth of nanoparticles and thin layers, etc.). Here, the general objective is to provide new information which would be essential to adapt the morphology and properties of solid surfaces to various targeted applications (for example, transport, environment, energy or medical sector) not included in the other two themes. For example, new strategies could emerge for manufacturing plasma mechanical systems or optoelectronic devices, on rigid or flexible substrates, which could be very promising for applications such as (bio) sensors and high performance detectors.

Finally, the durability of the functionalized surfaces must be evaluated, under representative service conditions, the impact of which can be chemical (sintering, oxidation, etc.) or physical (phase transformation, structuring, formation of stresses and delamination, etc.). .). The identification of the key parameters of aging and damage implies an experimental characterization and an appropriate modeling: this step is of capital importance to optimize the functionalization of the surface, not only according to the function, but also of its durable character. .

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Topic 2: Functionalization of surfaces