Annemarie Pucci

The strong midinfrared polaronic signal in p‐doped polymers such as P3HT is analyzed in terms of a plasmonic absorption cross section. Quantitative conclusion on the hole mobility along chains of coherently connected thiophene units is derived in that way. This intrachain mobility is more than two orders of magnitude higher than average mobilities of doped polymers which is limited by the much less efficient interchain transport processes.

Currently used elaborate technologies for the detection of bacteria can be improved in regard to their time consumption, labor intensity, accuracy and reproducibility. Well-known electrical measurement methods might connect highly sensitive sensing systems with biological requirements. The development of modified sensor surfaces with self-assembled monolayers (SAMs) from functionalized porphyrin for bacteria trapping can lead to a highly sensitive sensor for bacteria detection. Different A₂BC-type porphyrin structures were synthesized and examined regarding their optical behavior. We achieved the synthesis of a porphyrin for SAM formation on a gold surface as electrode material. Two possible bio linkers were attached on the opposite meso-position of the porphyrin, which allows the porphyrin to react as a linker on the surface for bacteria trapping. Different porphyrin structures were attached to a gold surface, the SAM formation and the respective coverage was investigated.

In situ infrared spectroscopy under ultra-high vacuum conditions reveals the behaviour of an example of a molecular compound, the n-conducting organic semiconductor (2,9-bis-(heptafluoropropyl)-4,7,11,14-tetrabromo-1,3,8,10-tetraazaperopyrene, TAPP-Br), upon condensation on various surfaces and as a mixture with typical dopants. The bending of molecules on Au(111) as previously established by inelastic electron scattering is seen also in infrared spectra of molecules on gold films, but clearly depends on temperature. It is indicated by modified infrared signals from C₃F₇ sidechain vibrations. If deposited onto MoO₃, commonly used as p-dopant and interlayer material in organic electronics, infrared vibrational spectra are similarly modified while MoO₃ deposition onto a preformed condensed layer did not produce any molecular change. Calcium, often used as an n-dopant, leads to further changes of the TAPP-Br vibrations in co-evaporated layers, specifically the modified C–C vibrations on the aromatic rings indicating charge transfer. Upon deposition of TAPP-Br on Ca films, a strong decrease of the metallic absorption of the Ca layer has been observed, which is typical for a chemical interface interaction. In contrast, for Ca deposition onto an already condensed TAPP-Br layer, a pronounced Ca island growth and thus enhanced diffusion and no significant vibrational changes are observed. Thus, chemical doping should be done before the molecules crystallize. Physisorption as well as chemisorption at interfaces strongly depend on the deposition sequence, which should be considered also for other organic semiconductors.

Solution‐processed tin oxide (SnO_x) electron transport layers demonstrate excellent performance in various optoelectronic devices and offer the ease of facile and low cost deposition by various printing techniques. The most common precursor solution for the preparation of SnO_x thin films is SnCl₂ dissolved in ethanol. In order to elucidate the mechanism of the precursor conversion at different annealing temperatures and the optoelectronic performance of the SnO_x electron transport layer, phonon and vibrational infrared and photoelectron spectroscopies as well as atomic force microscopy are used to probe the chemical, physical, and morphological properties of the SnO_x thin films. The influence of two different solvents on the layer morphology of SnO_x thin films is investigated. In both cases, an increasing annealing temperature not only improves the structural and chemical properties of solution‐processed SnO_x, but also reduces the concentration of tin hydroxide species in the bulk and on the surface of these thin films. As a prototypical example for the high potential of printed SnO_x layers for solar cells, high performance perovskite solar cells with a stabilized power conversion efficiency of over 15% are presented.

Capabilities of highly sensitive surface-enhanced infrared absorption (SEIRA) spectroscopy are demonstrated by exploiting large-area templates ($cm^2$) based on self-organized (SO) nanorod antennas. We engineered highly dense arrays of gold nanorod antennas featuring polarization-sensitive localized plasmon resonances, tunable over a broadband near- and mid-infrared (IR) spectrum, in overlap with the so-called 'functional group' window. We demonstrate polarization-sensitive SEIRA activity, homogeneous over macroscopic areas and stable in time, by exploiting prototype self-assembled monolayers of IR-active octadecanthiol (ODT) molecules. The strong coupling between the plasmonic excitation and molecular stretching modes gives rise to characteristic Fano resonances in SEIRA. The SO engineering of the active hotspots in the arrays allows us to achieve signal amplitude improved up to 5.7%. This figure is competitive to the response of lithographic nanoantennas and is stable when the optical excitation spot varies from the micro- to macroscale, thus enabling highly sensitive SEIRA spectroscopy with cost-effective nanosensor devices.

Highly sensitive Surface Enhanced Infrared Absorption (SEIRA) spectroscopy capabilities are demonstrated by exploiting large-area templates (cm2) based on self-organized (SO) nanorod antennas. We engineered highly dense arrays of gold nanorod antennas featuring polarization-sensitive localized plasmon resonances, tunable over a broadband near- and mid-infrared (IR) spectrum, in overlap with the so called ‘functional group’ window. We demonstrate polarization-sensitive SEIRA activity, homogenous over macroscopic areas and stable in time, by exploiting prototype self-assembled monolayers of IR-active octadecanthiol (ODT) molecules. The strong coupling between the plasmonic excitation and the molecular stretching modes give rise to characteristic Fano resonances in SEIRA. The SO engineering of the active hot-spots in the arrays allows to achieve signal amplitude improved up to the 5.7 %. This figure is competitive to the response of lithographic nanoantennas and is stable when the optical excitation spot varies from the micro- to the macroscale, thus enabling highly sensitive SEIRA spectroscopy on cost-effective nanosensor devices.

Conformationally rigid multipodal molecules should control the orientation and packing density of functional head groups upon self-assembly on solid supports. Common tripods frequently fail in this regard, because of inhomogeneous bonding configuration and stochastic orientation. These issues are circumvented by a suitable tetrapodal diazatriptycene moiety, bearing four thiol-anchoring groups, as demonstrated in the present study. Such molecules form well defined self-assembled monolayers (SAMs) on Au(111) substrates, whereby the tetrapodal scaffold enforces a nearly upright orientation of the terminal head group with respect to the substrate, with at least three or the four anchoring groups providing thiolate-like, covalent attachment to the surface. Functionalization by condensation chemistry allows a large variety of functional head groups to be introduced to the tetrapod, paving the path towards advanced surface engineering and sensor fabrication.