Lateral diffusion of three different dye molecules (terrylene and two perylene diimides) in 4 to 225 nm thin films of 8CB liquid crystals in the smectic-A phase has been investigated on a single molecule level. The influence of film thickness on tracer diffusion can be qualitatively modeled by a hydrodynamic approach. Molecular tracking experiments as well as fluorescence correlation (FCS) studies reveal the presence of diffusion dynamics which span a range of at least more than one order of magnitude in time, which is much larger than the reported anisotropic self-diffusion observed for 8CB bulk samples. We tentatively assign the heterogeneity to the formation of diffusion limiting domains on a micrometer scale within the 8CB films or at the interfaces.

Thin films (1−200 nm) of the title compounds were prepared by vapor deposition on glass at a controlled temperature. Film growth was studied in situ by optical absorption spectroscopy and measurement of the electrical conductivity. Independent of substrate temperature, a layered growth was found for ultrathin films of F16PcZn. During further deposition, this was followed by island formation (Stranski−Krastanov). Island growth from the beginning of deposition (Volmer−Weber) was found for MePTCDI. Both growth modes were confirmed by atomic force microscopy (AFM). Substrate temperature had a clear influence on the crystal structure of F16PcZn. A structure consisting of parallel stacks of molecules is formed first under all conditions. At lower temperature, this growth continues including, however, an increasing portion of amorphous material, whereas a square lattice of molecules is formed at higher temperature. This was found to be the stable modification of F16PcZn since films deposited at lower temperature could be irreversibly transformed into this structure by annealing of the films. A reversible dependence of optical absorption spectra on temperature was found for the stable modification of both materials in the range from 78 to 450 K. Bands were found to narrow considerably at lower temperature, and shifts were observed that were characteristic for stronger intermolecular interaction which was very well- defined at lower temperature. A considerable mobility of molecules on the lattice site as well as between sites is indicated by the results of this study. The optical data are discussed in terms of an established model of transition dipole coupling.

Alkyl monolayers covalently bound to silicon were prepared through the reaction between 1-alkene molecules and hydrogen-terminated Si. The surfaces were anodized in nanometer scale with a contact-mode atomic force microscope (AFM) by applying positive bias voltage to the surface with respect to a conducting cantilever under ambient conditions. Following the anodization, patterned areas were selectively modified by chemical etching and coating with different molecules. The alkyl monolayers showed high resistance against chemical etching and protected Si surfaces from oxidation. AFM lithography of monolayers on Si was found to be useful for nanofabrication of organic/inorganic interfaces based on the Si–C covalent bond.

We present a case study about inkjet printing as a tool for molecular patterning of silicon oxide surfaces with hydrophobic functionality, mediated by n-octadecyltrichlorosilane (OTS) molecules. In contrast to state-of-the-art techniques such as micro contact printing or chemical immersion with subsequent lithography processes, piezo drop-on-demand inkjet printing does not depend on physical masters, which allows an effective direct-write patterning of rigid or flexible substrates and enables short run-lengths of the individual pattern. In this paper, we used mesithylene-based OTS inks, jetted them in droplets of 10 pL on a silicon oxide surface, evaluated the water contact angle of the patterned areas and fitted the results with Cassie's law. For inks of 2.0 mM OTS concentration, we found that effective area coverages of 38% can be obtained. Our results hence show that contact times of the order of hundred milliseconds are sufficient to form a pattern of regions with OTS molecules adsorbed to the surface, representing at least a fragmented, inhomogeneous self-assembled OTS monolayer (OTS-SAM).

Thin films (100–150 nm) of 1,6,7,10-tetra-chloro-N, N′-dimethyl-perylene-tetracarboxylic- bisimide (Cl4MePTCDI) were grown by physical vapour deposition on glass and characterized as being widely amorphous with a rather small degree of intermolecular electronic coupling. A slow reorganization process was detected upon conditioning the films in air by optical microscopy. Polarized microscopy and scanning force microscopy revealed the formation of crystalline domains. Locally resolved absorption and photoluminescence measurements were used to analyse changes in intermolecular coupling. Individual domains were studied by micro-photoluminescence and temperature-dependent photoluminescence was used to characterize the degree of intermolecular coupling in the crystalline domains. The results are discussed in view of recently proposed applications of such perylene imides with a twisted aromatic core in organic inverters and organic photovoltaic cells.

Nanoporous zinc oxide films can be prepared by electrochemical codeposition with the dye eosin Y (EY) as a template and its subsequent desorption with aqueous KOH. In this contribution, the partial dissolving and reorganization of the zinc oxide film during the desorption step was studied in detail using X-ray diffraction, Kelvin probe force microscopy, and atomic force microscopy. It was found that the reorganization leads to an enhancement of crystal orientation and a reduction of the oxygen defect concentration at the surface of the zinc oxide, which is supposed to be a reason for suppressed recombination of electrons in these films.Aside from TiO 2 , ZnO is one of the most promising materials for porous electron transport layers in dye-sensitized solar cells (DSSCs). Both materials exhibit very similar band gaps (ZnO, 3.2 eV; TiO 2 , 3.0 eV) and conduction band edge positions (ZnO, -4.3 eV; TiO 2 , -4.5 eV). 1 An advantage of ZnO is the direct electrodeposition of fully crystalline and highly porous ZnO films from aqueous solution without the need of high temperature treatment. 2,3 The pores are introduced by codeposition of structure-directing additives and their subsequent removal.The ZnO films showing the highest porosity to date were prepared by codeposition with water-soluble dye molecules. Especially ZnO/eosin Y films electrodeposited from O 2 -saturated ZnCl 2 aqueous solution with concentrations of the disodium salt of eosin Y in the order of some tens of µM have been investigated in detail in recent years. 4,5 An especially high dye content could be achieved at deposition potentials of < -0.9 V vs SCE, leading to highly porous ZnO films after removal of the dye by extraction with aqueous KOH. 6 In this potential region, the eosin Y dianion EY 2-is reduced to EY 4-, which forms a strong complex with Zn 2+ , 7 meaning that it can also strongly interact with Zn-terminated surfaces of the growing ZnO films. In addition, EY 4-and Zn 2+ can form a polymeric structure, which acts as a template for the pores. 8 After desorption of the eosin Y agglomerates and the formation of a porous ZnO film, eosin Y or another dye can be readsorbed, typically from 0.5 mM ethanolic dye solution, in order to form a dye monolayer suitable for DSSCs on the ZnO surface. 6 Efficiencies of up to 5.6% have been achieved with such cells using the indoline dye D149 as a sensitizer, which is the highest efficiency achieved with ZnO-based DSSCs so far. 9 However, many details of the ZnO/eosin Y hybrid film electrodeposition and the influence of the further preparation steps on the film properties, e.g., crystallographic orientation and surface topography, are still unknown. In this contribution, we present recent results on changes within the ZnO matrix occurring especially during desorption of the dye. In order to understand the underlying processes, we investigated ZnO/eosin Y samples directly after their electrodeposition ("as deposited") and after extraction of the dye ("desorbed") by means of X-ray diffraction (XRD) and atomic f...

SummaryThis study investigates the controlled chemical functionalization of silicon oxide nanostructures prepared by AFM-anodization lithography of alkyl-terminated silicon. Different conditions for the growth of covalently bound mono-, multi- or submonolayers of distinctively functional silane molecules on nanostructures have been identified by AFM-height investigations. Routes for the preparation of methyl- or amino-terminated structures or silicon surfaces are presented and discussed. The formation of silane monolayers on nanoscopic silicon oxide nanostructures was found to be much more sensitive towards ambient humidity than, e.g., the silanization of larger OH-terminated silica surfaces. Amino-functionalized nanostructures have been successfully modified by the covalent binding of functional fluorescein dye molecules. Upon excitation, the dye-functionalized structures show only weak fluorescence, which may be an indication of a relatively low surface coverage of the dye molecules on length scale that is not accessible by standard AFM measurements.

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