Typologie d'événements : Conférences

Two-dimensional nanostructures: Synthesis and optoelectronic transport

In my talk I will briefly review the fields of my research and then, I will show that two-dimensional colloidal nanosheets represent very attractive optoelectronic materials. They combine good lateral conductivity with solution-processability and geometry-tunable electronic properties. The formation of ordered and densely packed surface layers of amphiphilic ligand molecules on certain crystal facets can drive the normally isotropic into a two-dimensional crystal growth, resulting in semiconducting nanosheets. The electronic confinement in height allows tuning the effective bandgap of the materials.
I will present the syntheses of the materials and the analyses of the electrical transport through these materials in field-effect transistors, solar cells, and spintronic devices. It turns out that the electronic confinement allows for an optimization of their performances.

Pr. Christian KLINKE
Institute of Physical Chemistry, University of Hamburg, Germany
& Chemistry Department, Swansea University, United Kingdom

Vendredi 22 Juin 2018 à 15h45 – 16h45

Séminaire présenté par Pr. Maurice BROGLY
LPIM, Université de Haute Alsace, Mulhouse
Adsorption, structuration and crystallisation of adhesion promoters and polymer thin films on metal substrates: analysis by PM-IRRAS and AFM

This presentation will give an overview of the laboratory LPIM’s research activities related to thin polymer films at interfaces. The presented works will focus on the understanding on how polymers (either homopolymers or copolymers) organize in thin films and how this organization can be directed adhesion promoters used to control the surface chemistry of the metal substrate. Various polymers and copolymers were adsorbed by spin-coating on metal substrates. The surface chemistry of the substrates was controlled by chemical grafting of adhesion promoters (coupling agents). The influence of the hydrophilic or hydrophobic nature of the substrate on the organization and structuration of polymers and copolymers of different compositions was then studied.
Characterization of thin films of copolymers requires the use of specific characterization techniques. Polarization-Modulation Infrared Reflection Absorption Spectroscopy (PM- IRRAS) spectroscopy is and innovative and original vibrational spectroscopy that was used for « in situ » reflectivity experiments to characterize thin films of polymers and copolymers deposited on reflective substrates. Due to the polarization modulation of the incident IR wave, its reflection at the interface according to surface selection rules increases the sensitivity of the spectral response, allowing determination of molecular orientation and structuring effects. Atomic Force Microscopy (AFM) analyses were also performed on the same thin films, in order to access the surface morphology and to distinguish the amorphous and crystalline phases.
Chains orientations and conformations as well as surface morphologies were thus characterized in order to understand the competition between polymer/polymer and polymer/substrate interactions, which will have a direct effect on the crystallization. This was explained by changes in the balance of polymer/polymer vs polymer/substrate interactions. Substrate surface chemistry alters the balance between these interactions significantly. As an example, in the case of amphiphilic block copolymers, an hydrophilic substrate favors the crystallization of the polar block whereas an hydrophobic substrate will favor the non-polar block crystallization. The modification of the crystalline phase content, morphology and molecular orientation of the crystalline structures of the adsorbed films reflects the strong competition between interfacial forces and intra and intermolecular forces.