TY  - JOUR
A1  - Ehlert, Christopher
A1  - Holzweber, Markus
A1  - Lippitz, Andreas
A1  - Unger, Wolfgang E. S.
A1  - Saalfrank, Peter
T1  - A detailed assignment of NEXAFS resonances of imidazolium based ionic liquids
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - 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.
Y1  - 2016
U6  - https://doi.org/10.1039/c5cp07434g
SN  - 1463-9076
SN  - 1463-9084
VL  - 18
SP  - 8654
EP  - 8661
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Ehlert, Christopher
A1  - Unger, Wolfgang E. S.
A1  - Saalfrank, Peter
T1  - C K-edge NEXAFS spectra of graphene with physical and chemical defects: a study based on density functional theory
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - 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.
Y1  - 2014
U6  - https://doi.org/10.1039/c4cp01106f
SN  - 1463-9076
SN  - 1463-9084
VL  - 16
IS  - 27
SP  - 14083
EP  - 14095
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - GEN
A1  - Ehlert, Christopher
A1  - Holzweber, Markus
A1  - Lippitz, Andreas
A1  - Unger, Wolfgang E. S.
A1  - Saalfrank, Peter
T1  - A detailed assignment of NEXAFS resonances of imidazolium based ionic liquids
N2  - 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.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 315 
KW  - ray absorption-spectroscopy
KW  - fine-structure
KW  - spectra
KW  - simulations
KW  - molecules
KW  - dynamics
KW  - graphene
KW  - surface
KW  - salts
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-394417
SP  - 8654
EP  - 8661
ER  - 
TY  - GEN
A1  - Ehlert, Christopher
A1  - Unger, Wolfgang E. S.
A1  - Saalfrank, Peter
T1  - C K-edge NEXAFS spectra of graphene with physical and chemical defects
BT  - a study based on density functional theory
N2  - 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.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 173 
KW  - absorbtion fine-structure
KW  - graphite
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-74429
SP  - 14083
EP  - 14095
ER  - 
TY  - JOUR
A1  - Ehlert, Christopher
A1  - Unger, Wolfgang E. S.
A1  - Saalfrank, Peter
T1  - C K-edge NEXAFS spectra of graphene with physical and chemical defects
BT  - a study based on density functional theory
JF  - physical chemistry, chemical physics : PCCP
N2  - 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.
KW  - absorbtion fine-structure
KW  - graphite
Y1  - 2014
U6  - https://doi.org/10.1039/c4cp01106f
SN  - 1463-9076
SN  - 1463-9084
VL  - 2014
IS  - 16
SP  - 14083
EP  - 14095
ER  -