Laboratory of Physics of Interfaces and Thin Films

Long-term storage and cryopreservation of biological tissues is a global challenge in the fields of regenerative medicine, tissue engineering and implants, because of the formation of large ice crystals that may damage cellular membranes and extracellular matrix (ECM) of collagen. In our studies different thawing mechanisms were tested to achieve more uniform warming of 3D in vitro tissue models, prepared from magnetic nanoparticles (NPs)-modified 3D electrospun nanofiber fleeces and fibroblasts. 3D tissue models frozen in liquid nitrogen were defrosted either with water bath or with radio-frequency (RF) inductive heating of the magnetic NPs and their morphology was compared to that of a non-frozen tissue model using a transmission Mueller microscope and thin sections of all three types of tissue models. Our results demonstrate a sensitivity of the polarimetric parameters obtained with the differential decomposition of Mueller matrices to small changes in sample morphology caused by the different thawing methods. A detailed statistical analysis proved the statistical significance of the experimental data from the three groups of all tissue models.

TIPS-PPP, a novel TIPS-PEN derivative, features a vertically extended pentacene core for increased π–π overlap, enabling exploration of structure–morphology–property connections and exhibiting enhanced stability/electronic performance.

The study of the intermolecular interactions of polycyclic aromatic compounds, considered as important pollutants of the Earth's atmosphere since they are emitted by the partial combustion of fuels, is essential to understand the formation and aging of their aerosols. In this study, the hydration of α-naphthaldehyde and β-naphthaldehyde isomers was investigated through a combination of Fourier transform microwave spectroscopy and quantum chemical calculations. Monohydrate structures were observed experimentally for both isomers, with two hydrate structures observed for β-naphthaldehyde and only one for α-naphthaldehyde, consistent with computational predictions. Analysis of the monohydrate structures indicated that the β-isomer exhibits higher hydrophilicity compared to the α-isomer, supported by electronic densities, hydration energies, and structural considerations. Further computational calculations were conducted to explore the planarity of the naphthaldehyde hydrates. Different levels of theory were employed, some of these revealing slight deviations from planarity in the hydrate structures. Low-frequency out-of-plane vibrational modes were examined, and the inertial defect was used to assess the planarity of the hydrates. The results suggested that the hydrates possess a predominantly planar structure, in agreement with the highest level of computational calculations and the absence of c-type transitions in the experimental spectra. Additionally, calculations were extended to dihydrate structures by attaching two water molecules to the naphthaldehyde isomers. The most stable dihydrate structures were predicted to be combinations of the observed monohydrate positions. However, experimental observation of the most stable dihydrate structures was challenging due to their very low vapour pressure, calling for complementary experiments using laser ablation nozzles.

Single-walled carbon nanotubes (SWCNTs) are promising candidates for gas sensing applications, providing an efficient solution to the device miniaturization challenge and allowing low power consumption. SWCNT gas sensors are mainly based on field-effect transistors (SWCNT-FETs) where the modification of the current flowing through the nanotube is used for gas detection. A major limitation of these SWCNT-FETs lies in the difficulty to measure their transfer curves, since the flowing current typically varies between 10−12 and 10−3 A. Thus, voluminous and energy consuming systems are necessary, severely limiting the miniaturization and low energy consumption. Here, we propose an inverter device that combines two SWCNT-FETs which brings a concrete solution to these limitations and simplifies data processing. In this innovative sensing configuration, the gas detection is based on the variation of an electric potential in the volt range instead of a current intensity variation in the microampere range. In this study, the proof of concept is performed using NO2 gas but can be easily extended to a wide range of gases.

The presented work concerns the study of solution sheared organic thin film transistors based on a 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES-ADT) polymer blend.

fingerprints are a commonly exploited type of evidence and can be crucial in a criminal investigation. The process of individualization or exclusion of a donor relies on the comparison of ridge detail characteristics between a fingermark, found at a crime scene, and reference fingerprints, collected under controlled conditions (either or not stored in a database). Although this process has been successfully used for over a century, fingermarks found at a crime scene are of limited value for a criminal trial if the corresponding reference fingerprint is not available, or the found fingermark is of poor quality. Fingerprints consist of donor secretion, mainly eccrine and sebaceous, of which the exact composition is likely influenced by many (both endogenous and exogenous) factors, including donor traits, habits and activities. Analysis of the chemical composition could thus potentially lead to the retrieval of donor information from those fingerprints that yielded no information in the traditional comparison process. The main aim of this dissertation was to determine what donor information can reliably and validly be derived from the chemical analysis of the fingerprint composition, in order to be used in forensic investigations...

Recent advances in structural control during the synthesis of SWCNTs have in common the use of bimetallic nanoparticles as catalysts, despite the fact that their exact role is not fully understood. We therefore analyze the effect of the catalyst's chemical composition on the structure of the resulting SWCNTs by comparing three bimetallic catalysts (FeRu, CoRu and NiRu). A specific synthesis protocol is designed to impede the catalyst nanoparticle coalescence mechanisms and stabilize their diameter distributions throughout the growth. Owing to the ruthenium component which has a limited carbon solubility, tubes grow in tangential mode and their diameter is close to that of their seeding nanoparticles. By using the as-synthesized SWCNTs as a channel material infield effect transistors, we show how the chemical composition of the catalysts and temperature can be used as parameters to tune the diameter distribution and semiconducting-to-metallic ratio of SWCNT samples. Finally, a phenomenological model, based on the dependence of the carbon solubility as a function of catalyst nanoparticle size and nature of the alloying elements, is proposed to interpret the results.

A short lifetime is the main factor hindering the wider implementation of low-cost organic photovoltaics in large-area and outdoor applications. Ingress of oxygen and water vapour through non-ideal encapsulation layers is a known cause of degradation for polymer/fullerene based solar cells. To better understand the origin of this performance degradation, we study the effect of intentional exposure of the photo-active layer to simulated sunlight (AM1.5) in air both on the solar cell performance and on the molecular semiconductor materials. Cathode-free thin films of a blend of the electron donor polymer poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) and the electron acceptor fullerene derivative [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM) were exposed to simulated sunlight in air. Fourier-transform infrared spectra demonstrate the formation of carbonyl photo-oxidation products in the blend films, as well as in the pristine polymer and fullerene films. Solar cells prepared with photo-oxidized active layers show increasingly degraded electrical performance (lower short circuit current, open circuit voltage and fill factor) with increasing exposure time. The increased diode ideality factor indicates that trap-assisted recombination hinders device operation after exposure. The external quantum efficiency decreases drastically with increasing exposure time over the whole photon energy range, while the UV-vis absorption spectra of the blend films only show a mild photo-induced bleaching. This demonstrates that not only the photo-induced degradation of the solar cell performance is not predominantly caused by the loss in light absorption, but charge transport and collection are also hampered. This is explained by the fact that photo-oxidation of PC70BM causes bonds in its conjugated cage to break, as evidenced by the decreased π* intensity in C1s-NEXAFS spectra of PC70BM films. This degradation of unoccupied states of PC70BM will hinder the transport of photo-generated electrons to the electrode. Surface photovoltage spectroscopy gives direct evidence for gap states at the surface of a PC70BM film, formed after 2 hours of exposure and resulting in upward band bending at the PC70BM/air surface. These observations indicate that the photo-oxidation of PC70BM is likely to be the main cause of the performance degradation observed when the photoactive layer of a TQ1:PC70BM solar cell is intentionally exposed to light in air.

Controlled modification of the semiconductor surface work function is of fundamental importance for improvements in the efficiency of (opto-)electronic devices. Binding amino acids to a semiconductor surface through their common carboxylic group offers a versatile tool for modulation of surface properties by the choice of their side chain. This approach is demonstrated here by tailoring the surface work function of indium tin oxide, one of the most abundant transparent electrodes in organic optoelectronic devices. We find that the work function can be systematically tuned by the side chain of the amino acid, resulting in either an increase or a decrease of the work function, over a large range of ∼250 meV. This side chain effect is mostly due to alteration of the dipole component perpendicular to the surface, with a generally smaller contribution for changes in surface band bending. These findings also shed light on electronic interactions at the interface between proteins and semiconductors, which are of importance for future bio-electronic devices.

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