@article{DietrichGlamschEhlertetal.2016,
  author    = {Dietrich, Paul M. and Glamsch, Stephan and Ehlert, Christopher and Lippitz, Andreas and Kulak, Nora and Unger, Wolfgang E. S.},
  title     = {Synchrotron-radiation XPS analysis of ultra-thin silane films: Specifying the organic silicon},
  series = {Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces},
  volume    = {363},
  journal   = {Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0169-4332},
  doi       = {10.1016/j.apsusc.2015.12.052},
  pages     = {406 -- 411},
  year      = {2016},
  abstract  = {The analysis of chemical and elemental in-depth variations in ultra-thin organic layers with thicknesses below 5 nm is very challenging. Energy- and angle-resolved XPS (ER/AR-XPS) opens up the possibility for non-destructive chemical ultra-shallow depth profiling of the outermost surface layer of ultra-thin organic films due to its exceptional surface sensitivity. For common organic materials a reliable chemical in-depth analysis with a lower limit of the XPS information depth z(95) of about 1 nm can be performed. As a proof-of-principle example with relevance for industrial applications the ER/AR-XPS analysis of different organic monolayers made of amino- or benzamidosilane molecules on silicon oxide surfaces is presented. It is demonstrated how to use the Si 2p core-level region to non-destructively depth-profile the organic (silane monolayer) - inorganic (SiO2/Si) interface and how to quantify Si species, ranging from elemental silicon over native silicon oxide to the silane itself. The main advantage of the applied ER/AR-XPS method is the improved specification of organic from inorganic silicon components in Si 2p core-level spectra with exceptional low uncertainties compared to conventional laboratory XPS. (C) 2015 Elsevier B.V. All rights reserved.},
  language  = {en}
}
@article{EhlertUngerSaalfrank2014,
  author    = {Ehlert, Christopher and Unger, Wolfgang E. S. and Saalfrank, Peter},
  title     = {C K-edge NEXAFS spectra of graphene with physical and chemical defects: a study based on density functional theory},
  series = {Physical chemistry, chemical physics : a journal of European Chemical Societies},
  volume    = {16},
  journal   = {Physical chemistry, chemical physics : a journal of European Chemical Societies},
  number    = {27},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1463-9076},
  doi       = {10.1039/c4cp01106f},
  pages     = {14083 -- 14095},
  year      = {2014},
  abstract  = {Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.},
  language  = {en}
}
@misc{EhlertUngerSaalfrank2014,
  author    = {Ehlert, Christopher and Unger, Wolfgang E. S. and Saalfrank, Peter},
  title     = {C K-edge NEXAFS spectra of graphene with physical and chemical defects},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-74429},
  pages     = {14083 -- 14095},
  year      = {2014},
  abstract  = {Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.},
  language  = {en}
}
@article{EhlertUngerSaalfrank2014,
  author    = {Ehlert, Christopher and Unger, Wolfgang E. S. and Saalfrank, Peter},
  title     = {C K-edge NEXAFS spectra of graphene with physical and chemical defects},
  series = {physical chemistry, chemical physics : PCCP},
  volume    = {2014},
  journal   = {physical chemistry, chemical physics : PCCP},
  number    = {16},
  issn      = {1463-9076},
  doi       = {10.1039/c4cp01106f},
  pages     = {14083 -- 14095},
  year      = {2014},
  abstract  = {Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.},
  language  = {en}
}
@article{EhlertHolzweberLippitzetal.2016,
  author    = {Ehlert, Christopher and Holzweber, Markus and Lippitz, Andreas and Unger, Wolfgang E. S. and Saalfrank, Peter},
  title     = {A detailed assignment of NEXAFS resonances of imidazolium based ionic liquids},
  series = {Physical chemistry, chemical physics : a journal of European Chemical Societies},
  volume    = {18},
  journal   = {Physical chemistry, chemical physics : a journal of European Chemical Societies},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1463-9076},
  doi       = {10.1039/c5cp07434g},
  pages     = {8654 -- 8661},
  year      = {2016},
  abstract  = {In Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy X-Ray photons are used to excite tightly bound core electrons to low-lying unoccupied orbitals of the system. This technique offers insight into the electronic structure of the system as well as useful structural information. In this work, we apply NEXAFS to two kinds of imidazolium based ionic liquids ([C(n)C(1)im](+)[NTf2](-) and [C(4)C(1)im](+)[I](-)). A combination of measurements and quantum chemical calculations of C K and N K NEXAFS resonances is presented. The simulations, based on the transition potential density functional theory method (TP-DFT), reproduce all characteristic features observed by the experiment. Furthermore, a detailed assignment of resonance features to excitation centers (carbon or nitrogen atoms) leads to a consistent interpretation of the spectra.},
  language  = {en}
}
@misc{EhlertHolzweberLippitzetal.2016,
  author    = {Ehlert, Christopher and Holzweber, Markus and Lippitz, Andreas and Unger, Wolfgang E. S. and Saalfrank, Peter},
  title     = {A detailed assignment of NEXAFS resonances of imidazolium based ionic liquids},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394417},
  pages     = {8654 -- 8661},
  year      = {2016},
  abstract  = {In Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy X-Ray photons are used to excite tightly bound core electrons to low-lying unoccupied orbitals of the system. This technique offers insight into the electronic structure of the system as well as useful structural information. In this work, we apply NEXAFS to two kinds of imidazolium based ionic liquids ([CnC1im]+[NTf2]- and [C4C1im]+[I]-). A combination of measurements and quantum chemical calculations of C K and N K NEXAFS resonances is presented. The simulations, based on the transition potential density functional theory method (TP-DFT), reproduce all characteristic features observed by the experiment. Furthermore, a detailed assignment of resonance features to excitation centers (carbon or nitrogen atoms) leads to a consistent interpretation of the spectra.},
  language  = {en}
}