Surface bonding of a functionalized aromatic molecule : Adsorption configurations of PTCDA on coinage metal surfaces

The present work aims at establishing a comprehensive model for the bonding mechanism for the adsorption of the organic prototype molecule 3,4,9,10-perylenetetracarboxylic 3,4:9,10-dianhydride (PTCDA) on coinage metal surfaces. Due to its chemical constitution, the PTCDA molecule allowed studying the effects of both the ϖ-conjugated system and the presence of functional groups, including heteroatoms, on the interfacial bonding. As a basic principle, the surface bonding mechanism of large ϖ-conjugated molecules is of immense interest for understanding the structural and electronic properties of organic thin films. Insight into relevant interaction channels and their relative contribution to the bonding can be obtained from a detailed determination of the bonding configuration of the same molecule on different crystal faces of chemically related substrates (or one substrate), including the positions of all relevant atoms. Within the context of the present work, we have investigated the geometric adsorption configurations of PTCDA on the Cu3Au(111), the Ag(100), the Ag(110), and the K:Ag(110) surface [i.e., a potassium-modified, reconstructed Ag(110) surface] with the x-ray standing waves (XSW) technique under normal incidence. Thereby, we have amended the series of earlier XSW results on the adsorption configurations of PTCDA on coinage metal (111) surfaces, namely, on Au(111), Ag(111), and Cu(111). In addition, we have employed low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) in combination with x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) as well as theoretical calculations [at density functional theory (DFT) level] for clarifying both the lateral geometric structures and the electronic properties at the metal/organic interfaces, complementing earlier results. The adsorption height of the PTCDA molecules decreases in the series Au(111), Cu3Au(111) (in the initial, more Au-analogous and the final, more Cu-analogous adsorption state), Cu(111), Ag(111), Ag(100), and Ag(110), as was revealed by XSW. In addition, the intrinsically planar PTCDA molecules exhibit distortions in the adsorbed state which alter from one surface to the next. On the Au(111) surface, PTCDA is concluded to be essentially undistorted while on Cu3Au(111) and Cu(111) [4] PTCDA exhibits a boat-like distortion with the perylene core of the molecule being closer to the surface than the atoms within the functional groups. On the canonical Ag surfaces, however, the situation is reversed. The distortion of the PTCDA molecule is saddle-like on Ag(111) and arch-like on Ag(100) and Ag(110), respectively, with the carbon and the oxygen atoms within the functional groups being closer to the surface than the perylene core now. The distortion of the molecular C backbone increases with decreasing surface atom coordination number for PTCDA/Ag(hkl). On K:Ag(110), PTCDA adsorbs in a saddle-like configuration, too. On the basis of our structural and spectroscopic results, we propose a universal bonding mechanism for the adsorption of PTCDA on coinage metal surfaces. This bonding mechanism is composed of several constituents (bonding channels). Besides the inevitable van der Waals (vdW) interactions, the main bonding channels are (a) a metal-to-molecule charge transfer and (b) local O-M bonds (M = Ag, K) on the anhydride groups; (c) in some cases - especially in the case of strong surface bonding -, local C-M bonds (M = Ag, Cu) may evolve, too. Note that these bonding channels (a)-(c) are of chemical nature, that is, actual chemical bonds are formed between the surface (atoms) and the adsorbate molecules.Ziel der vorliegenden Arbeit ist die Entwicklung eines schlüssigen Modells für den Bindungsmechanismus der Adsorption des prototypischen organischen Moleküls 3,4,9,10-Perylentetracarbonsäure-3,4:9,10-dianhydrid (PTCDA) auf Münzmetalloberflächen. Aufgrund seines chemischen Aufbaus ermöglicht es das PTCDA-Molekül, die Auswirkungen sowohl des ausgedehnten ϖ-Systems als auch der Gegenwart funktioneller Gruppen mitsamt deren Heteroatomen auf die Grenzflächenbindung zu untersuchen. Grundsätzlich ist der Oberflächenbindungsmechanismus für große ϖ-konjugierte Moleküls von immensem Interesse für das Verständnis sowohl struktureller als auch elektronischer Eigenschaften von dünnen organischen Filmen. Einblicke in die relevanten Wechselwirkungskanäle und deren relativen Beitrag zur Gesamtbindung können gewonnen werden durch die Bestimmung der Bindungskonfiguration, inklusive der Positionen aller relevanten Atome, ein und desselben Moleküls auf verschiedenen Flächen chemisch verwandter (oder identischer) Substrate. Im Rahmen der vorliegenden Arbeit wurden die geometrischen Adsorptionskonfigurationen von PTCDA auf der Cu3Au(111)-, der Ag(100)-, der Ag(110)- sowie der K:Ag(110)-Oberfläche [d.h. einer Kalium-modifizierten, rekonstruierten Ag(110)-Oberfläche] mit Hilfe der Absorption im stehenden Röntgenwellenfeld (x-ray standing waves, XSW) unter senkrechtem Einfall untersucht. Im Zuge dessen wurde die Serie früherer XSW-Ergebnisse über die Adsorptionskonfigurationen von PTCDA auf Münzmetall-(111)-Oberflächen, nämlich auf Au(111), Ag(111) und Cu(111), ergänzt. Zusätzlich wurden die Beugung niederenergetischer Elektronen (LEED) und Rastertunnelmikroskopie (STM) in Verbindung mit Röntgenphotoelektronenspektroskopie (XPS) und Ultraviolettphotoelektronenspektroskopie (UPS) sowie theoretischen Rechnungen [auf Dichtefunktionaltheorie-Niveau (density functional theory, DFT)] zur Aufklärung der lateralen geometrischen Strukturen sowie der elektronischen Eigenschaften an den Metall-/Organik-Grenzflächen eingesetzt, um frühere Ergebnisse zu ergänzen. Die Adsorptionshöhe des PTCDA-Moleküls verringert sich in der Serie Au(111), Cu3Au(111) (im initialen, eher Au-analogen und im finalen, eher Cu-analogen Adsorptionszustand), Cu(111), Ag(111), Ag(100) und Ag(110). Zusätzlich weisen die intrinsisch planaren PTCDA-Moleküle im adsorbierten Zustand Verzerrungen auf, die sich je nach Oberfläche unterscheiden. Auf der Au(111)-Oberfläche wird PTCDA als im Wesentlichen planar angenommen, während auf Cu3Au(111) und Cu(111) PTCDA eine bootartige Verzerrung aufweist. Dabei ist der Perylenrumpf des Moleküls näher an der Oberfläche als die Atome innerhalb der funktionellen Gruppen. Auf Ag(111) ist die Verzerrung sattelartig bzw. auf Ag(100) sowie Ag(110) gewölbeartig, wobei hier die Kohlenstoff- und Sauerstoff-Atome in den funktionellen Gruppen näher an der Oberfläche sind als der Perylenrumpf. Die Verzerrung des Perylenrückgrates nimmt für PTCDA/Ag(hkl) mit abnehmender Koordinationszahl der Oberflächenatome zu. Auf K:Ag(110) adsorbiert PTCDA ebenfalls in einer sattelartigen Konfiguration. Ausgehend von unseren strukturellen und spektroskopischen Ergebnissen wird ein allgemeingültiger Bindungsmechanismus für die Adsorption von PTCDA auf Münzmetalloberflächen vorgeschlagen. Dieser Bindungsmechanismus besteht aus mehreren Komponenten (Bindungskanälen). Abgesehen von van der Waals-Wechselwirkungen (vdW), die immer vorliegen, sind die Hauptbindungskanäle (a) ein Metall-zu-Molekül Ladungstransfer sowie (b) lokale O-M Bindungen (M = Ag, K) an den Anhydridgruppen; (c) in einigen Fällen - insbesondere im Falle starker chemischer Bindung - können auch lokale C-M Bindungen (M = Ag, Cu) ausgebildet werden

Work-life imbalance and mental health among male and female employees in Switzerland

Objectives: To investigate the prevalence and mental health effects of an unequal work-life balance (WLB) including potential gender differences. Methods: A cross-sectional study based on a representative sample of the Swiss employed population aged 20 to 64 (women: n = 1661; men: n = 1591). Results: Based on a single-item measure, more than every seventh employee in Switzerland indicated major difficulties combining work and private life. In certain socio-demographic categories, up to 30% showed such work-life conflict (WLC). For both genders, work-life imbalance turned out to be a risk factor affecting mental health. Employees with self-reported WLC presented a significantly higher relative risk for poor self-rated health (women: aOR = 2.6/men: aOR = 2.0), negative emotions and depression (aOR = 3.0/3.1), low energy and optimism (aOR = 2.1/1.6), fatigue (aOR = 2.4/2.6), and sleep disorders (aOR = 1.8/1.5) compared to employees with no WLC. Conclusions: Internationally, few data on the prevalence of WLC exist. In Switzerland, work-life imbalance is not a marginal phenomenon among the workforce and needs to be addressed as a notable public and mental health issu

Restriction of task processing time affects cortical activity during processing of a cognitive task: an event-related slow cortical potential study

As is known from psychometrics, restriction of task processing time by the instruction to respond as quickly and accurately as possible leads to task-unspecific cognitive processing. Since this task processing mode is used in most functional neuroimaging studies of human cognition, this may evoke cortical activity that is functionally not essential for the particular task under investigation. Using topographic recordings of event-related slow cortical potentials, two experiments have been performed to investigate whether cortical activity during processing of a visuo-spatial imagery task is substantially influenced by the time provided to process the task. Furthermore, it was investigated whether this effect is additionally modulated by a subject’s task-specific ability. The instruction to respond as quickly and accurately as possible led to increased negative slow cortical potential amplitudes over parietal and frontal regions and significantly interacted with task-specific ability. While cortical activity recorded over parietal and frontal regions was different between subjects with low and high spatial ability when processing time was unrestricted, no such differences were found between ability groups when subjects were instructed to answer both quickly and accurately. These results suggest that restricting processing time has considerable effects on the amount and the pattern of brain activity during cognitive processing and should be taken into account more explicitly in the experimental design and interpretation of neuroimaging studies of cognition

Catastrophe Bonds: An Interview with Oliver Ressler

An Interview with Brandon Bauer and Oliver Ressler on the occasion of his exhibition at St. Norbert College and the University of Wisconsin - Green Bay: Catastrophe Bonds , the first survey of Oliver Ressler‘s work in the United States. The exhibition focuses on forms of grassroots democracy as well as economic and political alternatives to the existing state of global affairs. This interview was published in the book that accompanied the exhibition.https://digitalcommons.snc.edu/faculty_staff_works/1010/thumbnail.jp

Familien von Jacobivarietäten über Origamikurven

Origamikurven sind algebraische Kurven im Modulraum der Riemannschen Flächen von vorgegebenem Geschlecht. In dieser Arbeit werden Origamikurven als Familien Riemannscher Flächen über einer eindimensionalen Basis aufgefasst und der Zusammenhangs zwischen der Monodromieaktion der Fundamentalgruppe der Basis und Fixanteilen in der zugehörigen Familie von Jacobivarietäten untersucht. Es wird ein Algorithmus zur Bestimmung einer oberen Schranke für die Dimension solcher Fixanteile angegeben

Familien von Jacobivarietäten über Origamikurven

Origamikurven sind algebraische Kurven im Modulraum der Riemannschen Flächen von vorgegebenem Geschlecht. In dieser Arbeit werden Origamikurven als Familien Riemannscher Flächen über einer eindimensionalen Basis aufgefasst und der Zusammenhangs zwischen der Monodromieaktion der Fundamentalgruppe der Basis und Fixanteilen in der zugehörigen Familie von Jacobivarietäten untersucht. Es wird ein Algorithmus zur Bestimmung einer oberen Schranke für die Dimension solcher Fixanteile angegeben

A neuronal relay mediates a nutrient responsive gut/fat body axis regulating energy homeostasis in adult Drosophila

The control of systemic metabolic homeostasis involves complex inter-tissue programs that coordinate energy production, storage, and consumption, to maintain organismal fitness upon environmental challenges. The mechanisms driving such programs are largely unknown. Here, we show that enteroendocrine cells in the adult Drosophila intestine respond to nutrients by secreting the hormone Bursicon α, which signals via its neuronal receptor DLgr2. Bursicon α/DLgr2 regulate energy metabolism through a neuronal relay leading to the restriction of glucagon-like, adipokinetic hormone (AKH) production by the corpora cardiaca and subsequent modulation of AKH receptor signaling within the adipose tissue. Impaired Bursicon α/DLgr2 signaling leads to exacerbated glucose oxidation and depletion of energy stores with consequent reduced organismal resistance to nutrient restrictive conditions. Altogether, our work reveals an intestinal/neuronal/adipose tissue inter-organ communication network that is essential to restrict the use of energy and that may provide insights into the physiopathology of endocrine-regulated metabolic homeostasis