Surface Structure

The formation of highly ordered surface structures is fundamental for various applications. Due to their rapidity of implementation and their cost, the templateless processes are extremely interesting alternatives to the use of templates or lithographic processes. In the aim to prepare porous structures such as nanotubes, the templateless electropolymerization was find to be a unique process. Based on previous works, we have synthesized 3,4-naphthalenedioxythiophene (NaPhDOT) monomers substituted with alkyl chains (n = 2 to 10), phenyl and naphthalene substituents. In particular, NaphDOT substituted with naphthalene (NaphDOT-Na) leads for the first time to relatively densely packed nanorings while their internal diameter is controllable with the number of deposition scans. Compared to previous works, which lead to nanotubes from non-substituted NaphDOT and 3,4-phenylenedioxythiophene substituted with naphthalene (PheDOT-Na), with NaphDOT-Na we observed a very important decrease in the polymer growth. As a consequence, only the initial peripherical nucleation around the gas bubbles is possible leading to nanorings while their growth in nanotubes is impeded by their low conductivity.

Here, a bioinspired strategy is used to prepare well-ordered nanotubular structures, as observed in animals and plants such as gecko toepads or corals. The nanotubes are obtained by templateless electropolymerization of thieno[3,4-b]thiophene-based monomers with various aromatic groups in organic solvent (dichloromethane). The most interesting and robust structures were obtained with carbazole and pyrene substituents to the base monomer structure, since these groups participate significantly in the polymerization and also have strong -stacking interactions. The addition of water to electropolymerization solvent significantly impacted the formation of nanotubes, as it caused release of a significant amount of H2 and O2 bubbles, depending on the electropolymerization method. Identifying templateless approaches to vary nanotubular structures is very interesting, as these materials are sought-after for applications in water harvesting systems.

Here, we control the shape of the resulting porous structures by templateless electropolymerization, by adjusting the alkyl spacer between thieno[3,4-b]thiophene and pyrene used as the monomer and the substituent, respectively. A huge change is observed from nanotubular structures (1D growth) without alkyl chain to huge hollow spheres (3D growth) for longer alkyl chains (≥ C4H8) passing through ribbon-like structures (2D) for short C2H4 spacer. The presence of a significant amount of water is necessary for the formation of these porous structures because it allows releasing a high amount of gas bubbles. Moreover, this change in surface structures is also observed by varying H2O content. Here, the higher hydrophobic properties with extremely high water adhesion are obtained with the presence of ribbon-like structures. This work is extremely important to investigate the effect of surface structures on surface properties for various potential applications.

... studies [14 and 17] have shown that water dissociatively adsorbed on TiO 2 (100) 1×1 surfaces at 300 K. Based on their results, for the defect-free surface, the O 1s peak broadening after water exposure is assumed to be solely due to the hydroxyl species (OH) adsorbed on the ...

In this paper we show the latest achievements of HgCdTe-based infrared bispectral focal plane arrays (FPAs) at LETI infrared laboratory. We present and compare the two different pixel architectures that are studied now in our laboratory, named ''NPN'' and ''pseudo-planar''. With these two technologies, a wide range of system applications in dual-band detection can be covered. Advantages of both architectures will be pointed out. We also review performances obtained with these different architectures. The first one has been studied for several years in our laboratory, and we review results obtained on FPAs of size 256 · 256 pixels on a 25 lm pitch, in the MWIR/MWIR (3 lm/5 lm) range. Very high noise equivalent temperature difference (NETD) operability is obtained, at 99.8% for the k c = 3 lm band and 98.7% for the k c = 5 lm band. The second one has been developed more recently, to address other applications that need temporal coherence as well as spatial coherence. We show detailed performances measured on pseudo-planar type FPAs of size 256 · 256 pixels on a 30 lm pitch, in the MWIR/LWIR (5 lm/9 lm) range. The results are also very promising for these prototypes, with NETD as low as 15 mK for an integration time as short as 1 ms, and good operability. The main manufacturing issues are also presented and discussed for both pixel architectures. Challenging process steps are, firstly, molecular beam epitaxy (MBE) HgCdTe heterostructure growth, on large substrates (cadmium zinc telluride) and heterosubstrates (germanium), and, secondly, detector array fabrication on a nonplanar surface. In particular, trenches or hole etching steps, photolithography and hybridization are crucial to improve uniformity, number of defects and performances. Some results of surface, structural and electrical characterizations are shown to illustrate these issues. On the basis of these results, the short-term and longterm objectives and trends for our research and development are presented, in terms of pixel pitch reduction, wavelengths, and dual-band FPA size.

Vegetal and animal reigns offer many examples of surfaces with surprising and interesting wetting properties. As example, springtails present superoleophobic properties allowing to live in soil and Lotus leaves show self-cleaning ability even under rainfalls. Indeed, it is known that self-cleaning properties can help to remove dust and particles during rainfalls and as a consequence to clean the surface. The bioinspiration of these surface properties is of a real interest for industrial applications in the nanotechnology field such as photovoltaic systems or anti corrosive material. Here, we use a strategy based on electropolymerization to obtain these properties. The Staudinger-Vilarrasa reaction is used to prepare innovative 3,4-ethylenedioxypyrrole (EDOP) monomers with fluorinated chains. Using C6F13 or C8F17 chains, the polymer surfaces formed after electrodeposition show superhydrophobic and superoleophobic features. Here we study the surface wettability depending on the surface energy (based on the perfluorinated chain length), the surface roughness and morphology.

In the aim to tune the surface nanostructures and the resulting surface hydrophobicity and water adhesion, we report the preparation of surfaces by electropolymerization of 3,4ethylenedioxypyrrole (EDOP) and 3,4-propylenedioxypyrrole (ProDOP) with both a short fluorocarbon chain (C4F9) and an alkyl chain of various length (C2H5 to C12H25). The surface properties are very different following the choice of the polymerizable core (EDOP or ProDOP) and the alkyl chain length. The PEDOP polymers are here easier to electrodeposit while the ProDOP could be electrodeposited only with long alkyl chains (≥ C8H17). Their electrodeposition leads to the formation of both nanoparticles and wrinkles. The highest properties with apparent contact angle (w) ≈ 141° and extremely strong water adhesion (parahydrophobic properties) are obtained with EDOP monomers and using intermediate alkyl chains (C6H13 and C8H17). Such properties could be exploited in the future in applications where the control of the interaction forces with the media is required such as in oil/water separation membranes or in water harvesting systems.