Spectroscopic ellipsometry and polarimetry for materials and systems analysis at the nanometer scale: state-of-the-art, potential, and perspectives

This paper discusses the fundamentals, applications, potential, limitations, and future perspectives of polarized light reflection techniques for the characterization of materials and related systems and devices at the nanoscale. These techniques include spectroscopic ellipsometry, polarimetry, and reflectance anisotropy. We give an overview of the various ellipsometry strategies for the measurement and analysis of nanometric films, metal nanoparticles and nanowires, semiconductor nanocrystals, and submicron periodic structures. We show that ellipsometry is capable of more than the determination of thickness and optical properties, and it can be exploited to gain information about process control, geometry factors, anisotropy, defects, and quantum confinement effects of nanostructures

Towards the optimization of materials and processes for flexible organic electronics devices

It is well known that the implementation of flexible organic electronic devices (FEDs) in our everyday life improve and revolutionize several aspects of our behavior. Although there has been considerable progress in the area of flexible inorganic devices (based on Si), there are numerous advances in the organic (semiconducting, conducting and insulating), inorganic and hybrid (organic-inorganic) materials that exhibit customized properties and stability, and in the synthesis and preparation methods, which are characterized by a significant amount of multidisciplinary efforts. The understanding of the organic material properties can lead to the fast progress of the functionality and performance of flexible organic electronic devices. An crucial ingredient for this is the strong interdisciplinary nature of the area of organic electronics, which brings together experts in chemistry, physics, and engineering, removing the traditional boundaries between the individual disciplines. Therefore, the understanding of the properties of organic insulators, semiconductors, and conductors as well as the effect of their synthesis process, microstructure and morphology is the goal of the current research efforts. In this work, we summarize on the latest advances in the fields of organic (semi-) conducting materials and hybrid barrier layers to be used as active layers and for the encapsulation of the materials components for the production of FEDs (such as flexible organic light-emitting diodes, and organic solar cells)

Fine tuning of PEDOT electronic properties using solvents

Non-destructive method of spectroscopic ellipsometry (SE) from IR to FUV was applied to study PEDOT/PSS thin films deposited by spin coating from aqueous dispersions of the material with different N,N-Dimethylformamide (DMF) volume percent. In our work we used the Tauc-Lorentz model to describe the dielectric function of PEDOT/PSS:DMF films in the Vis-FUV energy region. First, the spectrum analysis showed that the thickness and the fundamental band gap Eg of the film is being decreased with the increase of DMF content in the dispersion. Taking into account that the heating temperature is below the boiling point of DMF we assume that DMF molecules are incorporated in the film volume and act as dopants. Further more, this means that carrier concentration is being increased and thus we have higher electrical conductivity. The existence of DMF molecules in the film proved from FTIR SE, which can probe the bonding structure of the materials. The results showed lowering of peak intensity assigned to PEDOT/PSS and appearing of peaks assigned to DMF in the imaginary part of spectrum. In conclusion, SE is a potential tool for the evaluation of electronic properties for conductive polymers

Surface modification of poly(ethylene terephthalate) polymeric films for flexible electronics applications

The production of Flexible Electronic Devices (FEDs) by roll-to-roll large-scale manufacturing processes is a rapidly growing sector and the development of functional (inorganic and/or organic) thin layers onto flexible polymeric substrates represents one of the key issues for the low cost production of FEDs. However, the flexible substrates should meet advanced demands, as high optical transparency, high barrier properties and increased adhesion of the subsequent functional layers, which will have a major affect on their performance, efficiency and lifetime. Plasma treatment can be successfully employed for the improvement of the bonding structure and surface properties of flexible polymeric substrates. In this work, we report on the effect of Pulsed DC N+ ion bombardment using different ion energies, on the bonding structure, electronic and optical properties and surface nanotopography of Poly(Ethylene Terephthalate) (PET) substrates. For the investigation of the optical properties, we have used in-situ and real-time Spectroscopic Ellipsometry from the IR to Vis-farUV spectral region, in combination to advanced modeling procedures, whereas Atomic Force Microscopy has been employed for surface nanotopography investigation. As it has been found, the N+ bombardment leads to the appearance of new chemical bonds (C-N or C-O bonds in Φ-NH2, Φ-NHR, C({double bond, long}O)-NHR, Φ-OH, or (C{double bond, long}O)-OH), as well as partial disappearing of the C-O bond of ester group, on a surface layer of PET

Evolution of vertical phase separation in P3HT:PCBM thin films induced by thermal annealing

The achievement of the desirable morphology at the nanometer scale of bulk heterojunctions consisting of a conjugated polymer with fullerene derivatives is a prerequisite in order to optimize the power conversion efficiency of organic solar cells. The various experimental conditions such as the choice of solvent, drying rates and annealing have been found to significantly affect the blend morphology and the final performance of the photovoltaic device. In this work, we focus on the effects of post deposition thermal annealing at 140 °C on the blend morphology, the optical and structural properties of bulk heterojunctions that consist of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM). The post thermal annealing modifies the distribution of the P3HT and the PCBM inside the blend films, as it has been found by Spectroscopic Ellipsometry studies in the visible to far-ultraviolet spectral range. Phase separation was identified by AFM and GIXRD as a result of a slow drying process which took place after the spin coating process. The increase of the annealing time resulted to a significant increase of the P3HT crystallinity at the top regions of the blend films. © 2011 Elsevier B.V. All rights reserved