Bei der Produktion von Steckverbinderkontakten für die Elek­tronikindustrie nimmt die Oberflächenvergütung einen entscheidenden Platz ein. Für hohe Anforderungen an die Zuverlässig­keit werden nach wie vor Edelmetalle eingesetzt, die eine sichere Kontaktgabe gewährleisten. Die Entwicklung der Preise und der Verfügbarkeit zwingen jedoch zu weitgehenden Sparmaßnahmen beim Einsatz dieser Materialien bzw. zur völligen Substitution durch Unedelmetalle.

In this paper it is shown that a completely analytical theory based on the extended Hertzian approach together with additional considerations taking into account the geometrical conditions of a curved surface provide an appropriate model for the theoretical “simulation” of a variety of asperity contact problems. This model yields relatively fast and easy to use tools for the analysing of contact problems arising in connection with rough surfaces. In this study the results are shown on the example of a 3µm-DLC-coating on a steel substrate with asperities of about 100µm in diameter and 15µm height. It is found, that – under a general average pressure of 1GPa – the ideal asperity tip contact situation would lead to severe damage due to plastic flow within the steel substrate. On the other hand a rather conforming contact situation appears to be completely non critical.

In dieser Promotionsarbeit wurden das Wachstum und die Oberfläche von Lanthanoidphosphat-Nanopartikeln (LnPO4) untersucht. Mit Hilfe optischer Spektroskopie konnte die Größenentwicklung von NdPO4-Nanopartikeln genauer beobachtet werden: Etwa 3 nm kleine LnPO4-Nanokristalle werden bei Raumtemperatur durch die Zugabe von H3PO4 zu einer Lösung aus LnCl3 x n TBP gebildet. Während der Erhöhung der Temperatur auf 200 °C bilden diese Nanopartikel ein Gel, das sich beim Erhitzen auf höhere Temperaturen zersetzt. Der Zerfall des Gels führt zu LnPO4-Nanokristallen mit einem Durchmesser von etwa 4-5 nm. Bei 200 °C heilen die Defekte der Nanopartikel aus, ein weiteres Partikelwachstum ist bei Standard-Synthese-Verhältnissen nicht zu beobachten. Ändert man die Amin- oder die Phosphonsäurediethylester-Konzentration in der Synthese, so beeinflusst dies die Partikelgröße. Je geringer die Konzentration dieser Komponenten ist, desto größer wird der Durchmesser der Nanokristalle. So ist es durch Variation der Aminmenge möglich, Nanopartikel mit einem Durchmesser von 4-24 nm zu synthetisieren. Bei der Änderung der Phosphonsäurediethylester-Konzentration können Partikeldurchmesser von 4-15 nm erreicht werden. Darüber hinaus ermöglicht die Variation der Alkylkettenlänge dieser Komponenten, die Redispergierbarkeit der Nanokristalle zu kontrollieren. Die Präparation einer LaPO4-Schale um diese Nanokristalle erhöht ihre Lumineszenzquantenausbeute um das 35-fache. Zudem verbessert die Wahl geeigneter Stabilisatoren die Redispergierbarkeit der Kern-Schale-Nanopartikel. Die Synthese einer weiteren dünnen LaPO4-Schale ermöglicht es mit Hilfe von Phosphonsäurediethylestern, die Oberfläche der CePO4:Tb- und CePO4:Tb/LaPO4-Nanopartikel nachträglich zu modifizieren und so deren Redispergierbarkeit zu verändern.

This work aimed to elucidate basic aspects of the influence of chemical structure and surface topography on the surface properties of a polymer material in order to minimize the work of adhesion. End-functionalised aromatic perfluorinated oligo/polyesters have been chosen to clarify effect of chemical structure. Here, the comprehensive investigation of the influence of molecular architecture on processes of fluorine segregation in the topmost surface layer and surface properties of the end-functionalised aromatic perfluorinated linear and branched oligo-and polyesters were performed. It has been shown, that the character of the surface segregation of fluorinated moieties can be influenced by different factors i.e. conditions of preparation of polymer layers (by means of spin-coated and melt films), chemical structure of fluorinated tail and polymer backbone and slightly by molecular weight. Analysis of obtained results allows distinguishing contribution of each factor. Experimentally obtained results showed a good correlation with Scheutjens-Fleer self-consistent mean-field theory extended by Kumar and Koberstein, which corresponds to the surface segregation of various chemical functional moieties located on functional polymers of different architectures. In correlation with a self-consistent field approach, observed results confirmed that polymers with end fluorinated groups are promising for producing of low-energy surfaces.The effect of surface topography has been studied on the example of regular and irregular structured surfaces fabricated from core-shell particles. A simple and effective approach for designing regularly patterned surfaces with specifically designed surface roughness and chemistry using core-shell colloidal particles was demonstrated. The chemistry was varied by covalent grafting of polymer brushes onto silica particles or by chemisorption of fluorosilane. The modified colloidal spheres were organized into closely packed hemispherical hexagonal arrays either by a vertical deposition technique or by sedimentation on slightly inclined coated silicon wafers. In this way, an increase in the vertical roughness was achieved with increasing particle radius, but without changing the Wenzel roughness factor. Controllable variations in the surface chemistry and morphology were used for a systematic study of the wetting phenomenon on regular structured arrays. The regularity and periodicity of particle structures allowed modelling of wetting. The wetting was modelled according to WENZEL, CASSIE-BAXTER, EXTRAND theories as well as minimal and maximal possible contact angles introduced by SHUTTLEWORTH and BAILEY.It has been found that none of these theories completely describe the experimental results for all particle sizes except for the surfaces made from 0.2 Mikrometer large particles. It was revealed that wetting behaviour on fluorosilane modified particles with the diameter of 0.2 Mikrometer is close to the equilibrium contact angle described by WENZEL and CASSIE-BAXTER theories. It has been shown that the deviations contact angle from equilibrium state increase with increasing particle size, decreasing intrinsic contact angle, and increasing solid free energy of the particle ´shell´. This provides the experimental evidence for the theory proposed by JOHNSON and DETTRE. It was revealed that ultrahydrophobic surfaces couldn´t be observed on layers made from regularly packed core-shell particles. Design of fractal irregular surfaces is an appropriate way for preparation of ultrahydrophobic self-cleaning surfaces. It was demonstrated that fluorination is not an obligatory factor for design of water repellent coatings. The obtained results are of essential interest for industrial application.

Motivated by the structure of the normal surface stress of the extended Hertzian approach [1] given due to terms of the form r^2n*(a^2-r^2)^(1/2) (n=0, 2, 4, 6…) it seems attractive to evaluate the complete elastic field also for shear loadings of this form. The reason for this lays in the demand for analytical tools for the description of mixed loading conditions as they appear for example in scratch experiments. [1] N. Schwarzer, "Elastic Surface Deformation due to Indenters with Arbitrary symmetry of revolution", J. Phys. D: Appl. Phys., 37 (2004) 2761-2772

CuI is a p-type transparent conductive semiconductor with unique optoelectronic properties, including wide band gap (3.1 eV), high hole mobility (>40 cm2 V−1 s−1 in bulk), and large room-temperature exciton binding energy (62 meV). The difficulty in epitaxy of CuI is the main obstacle for its application in advanced solid-state electronic devices. Herein, room-temperature heteroepitaxial growth of CuI on various substrates with well-defined in-plane epitaxial relations is realized by reactive sputtering technique. In such heteroepitaxial growth the formation of rotation domains is observed and hereby systematically investigated in accordance with existing theoretical study of domain-epitaxy. The controllable epitaxy of CuI thin films allows for the combination of p-type CuI with suitable n-type semiconductors with the purpose to fabricate epitaxial thin film heterojunctions. Such heterostructures have superior properties to structures without or with weakly ordered in-plane orientation. The obtained epitaxial thin film heterojunction of p-CuI(111)/n-ZnO(00.1) exhibits a high rectification up to 2 × 109 (±2 V), a 100-fold improvement compared to diodes with disordered interfaces. Also a low saturation current density down to 5 × 10−9 Acm−2 is formed. These results prove the great potential of epitaxial CuI as a promising p-type optoelectronic material.

Polyelectrolyte complexation is a rapidly growing field with applications in functional multilayer (PEM) and nanoparticle (PEC) generation, where PEM films are deposited using Layer-by-Layer technique initiated by Decher and PECs are prepared using mixing-centrifugation technique initiated by our group. Its advantages (e.g. easy preparation) result in various applications in aqueous solution, especially in pharmaceutical and biomedical fields. Therefore, the objectives in this study are to explore interesting applications of polyelectrolyte complexation in the field of low molecular chiral compound and high molecular protein binding. Due to the rapidly growing demands for preparing optically pure compounds in the pharmaceutical field, herein, enantiospecific PEM and PEC were prepared using chiral polyelectrolytes (e.g. homo-polypeptide) and their ability of chiral recognition was investigated by ATR-FTIR, UV/Vis etc.. Chiral PEM and PEC showed pronounced enantiospecificity for both small (amino acids, vitamin) and large (protein) chiral compounds. This chiral recognition is performed by a diffusion process of chiral compounds into PEM based on the structures of chiral selector (PEM, PEC) and chiral probes (chiral compounds). However, the influences, e.g. pH value, ionic strength, surface orientation etc., were found to affect significantly the enantiospecificity. Beside planar substrates, porous membranes (e.g. PTFE) were modified using chiral PEM and successfully applied in enantiospecific permeation. Additionally, protein binding properties of PEC particle dispersions or PEC particle films were also studied. Due to the properties of polyelectrolytes used for PEC (e.g. molecular weight, charge density) and proteins (e.g. isoelectric point, size, hydrophobicity), PEC showed different uptake characteristics towards different proteins. Electrostatic and hydrophobic interaction as well as counterion release force were considered as possible driving forces for protein binding.

Bei der Interaktion zwischen Mensch und Maschine werden Informationen vorrangig über die haptischen, optischen und akustischen Kanäle ausgetauscht. In diesem Beitrag steht die bislang kaum untersuchte Forschungsfrage im Fokus, ob und, wenn ja, wie haptische und optische Einschätzungen von Probanden differieren. In dem Beitrag wird eine Laborstudie zur grundlagenorientierten Untersuchung von Oberflächen vorgestellt. Dabei werden Materialien des Interieurs und Exterieurs von Automobilen untersucht. Es zeigt sich, dass in bestimmten Bewertungsdimensionen ein Unterschied zwischen den Modalitäten besteht.

Polyaromatic molecules functionalized with carboxylic groups have served as model systems for the growth of organic semiconducting films on a large variety of substrates. Most non-reactive substrates allow for a growth mode compatible with the bulk phase of the molecular crystal with two molecules in the unit cell, but some more reactive substrates including Ag(111) and Ag(110) can induce substantial changes in the first monolayer (ML). In the specific case of Ag(110), the adsorbate unit cell of both NTCDA and PTCDA resembles a brickwall structure, with a single molecule in the unit cell. From this finding, it can be concluded that the adsorbate-substrate interaction is stronger than typical inter-molecular binding energies in the respective bulk phases. In the present work, the interactions between small Ag(110) clusters and a single NTCDA or PTCDA molecule are investigated with different ab initio techniques. Four major ingredients contribute to the binding between adsorbate and substrate: Directional bonds between Ag atoms in the topmost layer and the oxygen atoms of the molecule, Pauli repulsion between filled orbitals of molecule and substrate, an attractive van-der-Waals interaction, and a negative net charge on the molecule inducing positive image charges in the substrate, resulting therefore in an attractive Coulomb interaction between these opposite charges. As both Hartree-Fock theory and density functional theory with typical gradient-corrected density functional do not contain any long range correlation energy required for dispersion interactions, we compare these approaches with the fastest numerical technique where the leading term of the van-der-Waals interaction is included, i.e. second order Møller-Plesset theory (MP2). Both Hartree-Fock and density functional theories result in bended optimized geometries where the adsorbate is interacting mainly via the oxygen atoms, with the core of the molecule repelled from the substrate. Only at the MP2 level, the inclusion of the major part of the attractive van-der-Waals interaction brings the adsorbate back to an arrangement close to parallel to the substrate, with very small differences in height between the different subunits. With respect to experimental data obtained on Ag(111), the calculated distance between adsorbate and substrate is somewhat smaller, indicating that the open Ag(110) surface interacts more strongly with the organic compounds. This is consistent with the fact that only Ag(110) induces a brickwall unit cell of the adsorbate, a clear sign for a particularly large adsorption energy. The resulting model geometries are analysed in terms of cohesive energy, Mulliken charges, core level shifts, and vibrational properties. / Polyaromatische Moleküle, die mit Carboxylgruppen funktionalisiert wurden, haben als Modellsysteme für das Wachstum von organischen Halbleiterfilmen für eine breite Palette von Substraten gedient. Für die meisten nichtreaktiven Substrate ist ein zum molekularen Kristall kompatibles Wachstum mit zwei Monolagen pro Einheitszelle möglich, jedoch erzeugen reaktivere Substrate wie z.B. Ag(111) oder Ag(110) bereits substanzielle Modifikationen in der ersten Monolage. Im speziellen Fall von Ag(110) bildet die Adsorbateinheitszelle sowohl von NTCDA als auch PTCDA eine sogenannte brickwall structure heraus mit einem einzigen Molekül pro Einheitszelle. Aus dieser Beobachtung kann geschlussfolgert werden, dass die Adsorbat-Substrat-Wechselwirkung stärker ist als die typischen intermolekularen Bindungsenergien in der entsprechenden Bulk-Phase. In der vorliegenden Arbeit werden die Wechselwirkungen zwischen kleinen Ag(110)-Clustern und einem einzelnen NCTDA oder PTCDA-Molekül mit verschiedenen ab initio-Techniken untersucht. Im Wesentlichen tragen vier Hauptbestandteile zur Bindung zwischen Adsorbat und Substrat bei: Gerichtete Bindungen zwischen Ag-Atomen in der obersten Substratschicht und den Sauerstoffatomen des Moleküls, Pauli-Abstoßung zwischen besetzten Orbitalen von Molekül und Substrat, eine anziehende Van-der-Waals-Wechselwirkung sowie einer negativen Ladung des Moleküls und der dazugehörigen positiven Spiegelladung im Substrat, die zu einer anziehenden Coulombwechselwirkung führen. Da weder die Hartree-Fock-Theorie noch die Dichtefunktionaltheorie mit dem typischen gradientenkorrigierten Dichtefunktional die für Dispersionswechselwirkungen benötigte langreichweitige Korrelationsenergie beinhalten, vergleichen wir diese beiden Ansätze mit der schnellsten numerischen Methode, die den dominierenden Term der Van-der-Waals-Wechselwirkung beinhaltet, nämlich der Møller-Plesset-Theorie zweiter Ordnung (MP2). Sowohl die Hartree-Fock-Theorie als auch die Dichtefunktionaltheorie sagen verbogene optimierte Geometrien voraus, die vorwiegend durch die Sauerstoffatome interagieren, wohingegen die zentralen Teile des Moleküls vom Substrat abgestoßen werden. Lediglich die MP2, die den wesentlichen Teil der anziehenden Van-der-Waals-Wechselwirkung beinhaltet, sagt eine beinahe parallele Anordnung des Moleküls an das Substrat voraus, wobei die einzelnen Untereinheiten des Moleküls nur unwesentlich verschiedene Abstände zum Substrat haben. Im Vergleich zu experimentellen Daten für Ag(111) ist die berechnete Distanz zwischen Adsorbat und Substrat etwas kleiner, woraus sich schlussfolgern lässt, dass die offene Ag(110)-Oberfläche stärker mit den organischen Verbindungen interagiert. Das ist im Einklang mit der Tatsache, dass nur Ag(110) die brickwall-Struktur des Adsorbats besitzt, was ein deutliches Zeichen für eine hohe Adsorptionsenergie ist. Die resultierenden Modellgeometrien wurden bezüglich ihrer Kohäsionsenergie, Mullikenladungen, Kernelektronenniveauverschiebungen und vibrationeller Eigenschaften untersucht.

We report on the surface-catalyzed formal [2+2] and [2+2+2] cycloadditions of ortho-activated tetracene species on a Ag(111) substrate under ultrahigh vacuum conditions. Three different products are obtained: tetracene dimers, trimers, and tetramers. The former results from the formation of a four-membered ring while the other two arise from cyclization into six-membered rings. These on-surface reactions have been monitored by scanning tunneling microscopy and rationalized by density functional theory calculations. Our approach, based on the reaction of ortho-dihalo precursor monomers via formal cycloadditions, establishes an additional method for the highly active field of on-surface synthesis and enables the development of novel 1D and 2D covalent carbon nanostructures.