Sébastien Nénon

Origin of the Surface-Induced First Hyperpolarizability in the C60/SiO2 System: SCC-DFTB Insight.

Using the self-consistent charge density functional tight binding (SCC-DFTB) method, C60 molecules physisorbed on an α-quartz slab are shown to display a first hyperpolarizability, whereas, owing to their symmetry, both the α-quartz slab and C60 molecule have no first hyperpolarizabilities. A larger first hyperpolarizability is achieved when the lowest-lying (five- or six-membered) ring is situated in between two hydroxyl rows, rather than on top, because this situation favors orbital overlaps and charge transfer. Further analysis has demonstrated that (i) the first hyperpolarizability originates from the MO overlap and field-induced charge transfers from the neighboring substrate/adsorbate moieties but not to geometric relaxation of the C60 molecules at the interface and that (ii) larger first hyperpolarizabilities are associated with low surface coverage and with small distances between C60 and the surface. This contribution is a clear illustration of the emergence of second-order nonlinear optical responses (first hyperpolarizability) as a result of breaking the centrosymmetry.

Comparative time resolved shadowgraphic imaging studies of nanosecond and picosecond laser transfer of organic materials

A comparative study of the ejection dynamic of organic materials by Laser-Induced Forward Transfer technique has been performed using nanosecond and picosecond pulses for applications in plastic micro-electronics. The ejection of organic materials has been carried out with various thicknesses and with and without a sacrificial metallic release layer inserted between the substrate and the organic donor film. The advantage of this technique is to preserve organic layers from being damaged by thermal and photochemical effects during the interaction. The dynamic of the process has been investigated by shadowgraphic imaging during 1.5 μs after the laser irradiation, under atmospheric conditions. We have determined the velocity of the transferred material and studied the influence of the metallic layer during the ejection using a wide range of fluencies. The high directivity of the ejected material offers the possibilities of high spatial resolution for the manufacture of micro-structures in non contact LIFT technique. The study of the influence of the distance between the donor and acceptor substrates on the deposit functionality is discussed.

Pulsed-Laser Printing Process for Organic Thin Film Transistors Fabrication

This paper presents a Pulsed‐Laser Printing process applied to metals, liquid, polymers and oligomers with the goal to fabricate Organic Thin‐Film Transistors. The Laser‐Induced Forward Transfer (LIFT) technique has been used as a spatially‐resolved laser deposition method. All materials have been transferred from a donor substrate onto a receiver substrate upon laser pulses in the picosecond regime. The broad nature of transferred patterns and the efficiency of the LIFT confirm the important potential of a laser printing technique in the development of the plastic microelectronics.