5 research outputs found

    Infrastructure for Performance Monitoring and Analysis of Systems and Applications

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    The growth of High Performance Computer (HPC) systems increases the complexity with respect to understanding resource utilization, system management, and performance issues. HPC performance monitoring tools need to collect information at both the application and system levels to yield a complete performance picture. Existing approaches limit the abilities of the users to do meaningful analysis on actionable timescale. Efficient infrastructures are required to support largescale systems performance data analysis for both run-time troubleshooting and post-run processing modes. In this dissertation, we present methods to fill these gaps in the infrastructure for HPC performance monitoring and analysis. First, we enhance the architecture of a monitoring system to integrate streaming analysis capabilities at arbitrary locations within its data collection, transport, and aggregation facilities. Next, we present an approach to streaming collection of application performance data. We integrate these methods with a monitoring system used on large-scale computational platforms. Finally, we present a new approach for constructing durable transactional linked data structures that takes advantage of byte-addressable non-volatile memory technologies. Transactional data structures are building blocks of in-memory databases that are used by HPC monitoring systems to store and retrieve data efficiently. We evaluate the presented approaches on a series of case studies. The experiment results demonstrate the impact of our tools, while keeping the overhead in an acceptable margin

    Quantum Chemical Studies on Bonding and Reactivity at Hybrid Organic-Inorganic Interfaces

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    In this cumulative dissertation organic-inorganic hybrid interfaces with relevance for nanoelectronic applications are investigated with theoretical methods. An emphasis is put on the elucidation of interface reaction mechanisms and the employment of bonding analysis to better inform synthetic design choices. Furthermore, electronic structure related properties are calculated in order to explain experimental observations. The dissertation is organized in two parts. In the first part, the covalent attachment of organic layers on the (001) facet of the inorganic semiconductor silicon is studied. The second part is concerned with the creation of interface models for organic semiconductors on Ag(111). In the past it was shown that cyclooctyne is a particularly suitable platform molecule for the purpose of creating a contact layer with Si(001) due to its highly selective adsoption. Building on this prior work, the focus of this dissertation is hence the growth of a second layer on the contact layer. For this purpose, promising reactions schemes with “click”-characteristics (fast, excellent yield, solvent tolerant) are studied. These are the azide-alkyne cycloaddition (AAC), the enolether-tetrazine inverse electron demand Diels-Alder reaction (IEDDA) as well as the nucleophilic substitutions of an acid chloride mediated esterification (ACE) and the sulfonylfluoride exchange (SuFEx). The second main topic of this dissertation is the chemical interplay of the Ag(111) surface with nature inspired organic semiconductors based on pyrrole units. In comparison to silicon, the coinage metal surface has a comparatively low reactivity. This property is crucial for keeping the π-systems of the organic semiconductors intact after interface formation. Still, various bonding patterns can emerge at the interface. Besides van der Waals interactions, an exchange of electron density between the surface and the organic π-system is observed. The strength of this interaction is determined primarily by the frontier orbitals of the molecule. In summary, the collected work of this dissertation shows that quantum chemical methods are a valuable tool for better understanding the chemistry and electronic structure of hybrid interfaces. Insights gained from theory not only explain experimental observations but can also be used to guide synthetic efforts even though, different terminologies and concepts exist for metal and semiconductor surfaces. Furthermore, the studies presented here highlight that various types of interfaces can be described efficiently within an ab inito framework

    Investigations of Metal/Organic Interfaces and Metalation Reactions of Organic Semiconductors

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    Modern electronic devices are increasingly based on organic semiconductors. The performance of such devices crucially depends on the properties of the interface between the organic semiconductors and the metal contacts. Understanding the influence of the topology of the organic semiconductor’s conjugated pi-electron system on the interface interaction could greatly improve the device’s performance. Furthermore, the knowledge about reactions of heteroatomic organic semiconductors with metal atoms during electrode fabrication may lead to enhanced lifetimes of such devices. This cumulative dissertation comprises several publications and a number of so far unpublished results, addressing metal/organic interface interactions and metalation reactions of heteroatomic organic semiconductors. The properties of the interfaces are tailored by investigating the alternant aromatic molecules naphthalene and pyrene as well as the nonalternant aromatic molecules azulene and azupyrene on different metallic singlecrystal surfaces. Investigations by means of temperature-programmed desorption reveal stronger desorption energies for the non-alternant molecules on both Ag(111) and Cu(111). The biggest difference is observed on Cu(111), on which azulene and azupyrene are chemisorbed, whereas naphthalene and pyrene are physisorbed. The enhanced interface interaction of the non-alternant molecules is associated with the formation of surface dipoles that lead to stronger intermolecular repulsion between the adsorbed molecules. These results are supported by additional surface science methods, such as X-ray photoelectron spectroscopy or near-edge X-ray absorption fine structure spectroscopy, as well as density functional theory calculations conducted by group members and external collaboration partners. Detailed quantitative analysis of temperature-programmed desorption data of benzene on Cu(111) and Ag(111) yields experimental desorption energies that can be used as a benchmark for theoretical adsorption energies derived by density functional theory calculations. The interactions of metal/organic interfaces are compared with organic/inorganic interfaces in the case of pentacene and its fluorinated derivative perfluoropentacene on Au(111) as well as on bulk and two-dimensional MoS2 in a collaboration project. Organic semiconductors often interact weakly with inorganic surfaces, e.g., the thermal desorption of the first molecular layer is indistinguishable from multilayer desorption. No monolayer desorption peaks are observed as is mostly the case on metal surfaces. However, monolayer desorption of pentacene and perfluoropentacene on MoS2 occurs at significantly higher temperatures than the multilayer desorption. Detailed analysis reveals that the monolayers of both molecules are entropically stabilized. Codeposition of both molecules results in strong attractive intermolecular interactions on MoS2, while these interactions are weaker on Au(111). Metalation reactions of organic semiconductors with metal atoms, e.g., Co on tetraphenylporphyrin and Ca on alpha-sexithiophene, during interface preparation were investigated by means of hard X-ray photoelectron spectroscopy and temperature-programmed desorption mass spectrometry. The thickness of the reaction zone is changed by variation of experimental properties during interface formation. It is found that only the sample temperature during metal atom deposition and the metal atom flux in the case of Ca have an impact on the reaction depth, which is usually limited to few nanometers. In contrast to Co and Ca, Li atoms readily diffuse into the organic bulk and react with tetraphenylporphyrin over several tens of nanometers, forming dilithium tetraphenylporphyrin or monolithium monohydrogen tetraphenylporphyrin depending on the deposited Li amount. Furthermore, the transmetalation reaction of lead(II) tetraphenylporphyrin with Cu atoms on the Cu(111) surface was proven by temperature-programmed desorption. In addition, the Ullmann coupling reaction of bromo- and iodobenzene on Cu(111) was examined. While bromobenzene molecules desorb intact from the Cu(111) surface, iodobenzene molecules dissociate into iodine atoms and phenyl radicals. The latter form biphenyl that desorbs in three distinct desorption peaks at different temperatures. In a collaborative project, the oxidation state and electronic structure of Pb atoms in the newly synthesized Pb3F8 were studied by hard X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy giving evidence for the presence of Pb(II) and Pb(IV) species. The experimental results are complemented by constructional work to improve the temperatureprogrammed desorption setup. Moreover, two Igor Pro 8 scripts were written to quickly import data from different experimental setups and speed up the data treatment

    Energy analysis of code regions of HPC applications using EnergyAnalyzer tool

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