| 1. |
- Heister, K., et al.
(författare)
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Odd-even efffects at the S-metal interface and in the aromatic matrix in biphenyl-substituted alkanethiol self-assembled monolayers
- 2001
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Ingår i: Journal of Physical Chemistry B 105, 6888 (2001).
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Tidskriftsartikel (refereegranskat)abstract
- Synchrotron-based high-resolution X-ray photoelectron spectroscopy was applied to characterize self-assembled monolayers (SAM) of biphenyl-substituted alkanethiols CH3(C6H4)2(CH2)nSH (BPn, n = 1-4) on Au and Ag substrates. Beyond previously identified odd-even changes in the packing density and the tilt angle of the biphenyl moieties, the high-resolution spectra reveal a number of additional odd-even effects upon variation of the number of methylene groups in the aliphatic part in the BPn molecule. Their occurrence and mutual correlation suggests that a BPn SAM represents a strongly correlated, highly ordered molecular assembly. In particular, periodical changes of a shake up feature in the C 1s region are observed, which are related to the differences in the arrangement of the aromatic matrix. The width and binding energy position of the S 2p signals also exhibit odd-even changes. The width changes are associated with the occupation of either equivalent or nonequivalent adsorption sites on the polycrystalline (111) Au and Ag substrates. The comparison of the width values with those for conventional alkanethiols implies that the substrate bonding of alkanethiols on gold cannot be described by a single adsorption site
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| 2. |
- Meyer, F., et al.
(författare)
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"Building Block Picture" of the Electronic Structure of Aqueous Cysteine Derived from Resonant Inelastic Soft X-ray Scattering
- 2014
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:46, s. 13142-13150
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the amino acid l-cysteine in an aqueous environment was studied using resonant inelastic soft X-ray scattering (RIXS) in a 2D map representation and analyzed in the framework of a building block approach. The element selectivity of RIXS allows a local investigation of the electronic structure of the three functional groups of cysteine, namely, the carboxyl, amino, and thiol groups, by measuring at the O K, N K, and S L-2,L-3 edges, respectively. Variation of the pH value allows an investigation of molecules with protonated and deprotonated functional groups, which can then be compared with simple reference molecules that represent the isolated functional groups. We find that such building blocks can provide an excellent description of X-ray emission spectroscopy (XES) and RIXS spectra, but only if all nearest-neighbor atoms are included. This finding is analogous to the building block principle commonly used in X-ray absorption spectroscopy. The building blocks show a distinct spectral character (fingerprint) and allow a comprehensive interpretation of the cysteine spectra. This simple approach opens the path to investigate the electronic structure of more complex biological molecules in aqueous solutions using XES and RIXS.
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| 3. |
- Shaporenko, A., et al.
(författare)
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Odd-even effects in photoemission from terphenyl-substituted alkanethiolate self-assembled monolayers
- 2005
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Ingår i: Langmuir 21(10), 4370 (2005).
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Tidskriftsartikel (refereegranskat)abstract
- Self-assembled monolayers (SAMs) formed from 4,4'-terphenyl-substituted alkanethiols C6H5(C6H4)2(CH2)nSH (TPn, n = 1-6) on polycrystalline (111) gold and silver substrates have been characterized by synchrotron-based high-resolution X-ray photoelectron spectroscopy. The intensities, binding energy positions, and width of most photoemission lines exhibited pronounced odd-even effects, i.e., systematic and periodic variation, depending on either odd or even number of the methylene units in the aliphatic linker of the TPn molecules. The detailed analysis of these effects provides important information on the bonding and arrangement of the chemisorbed sulfur headgroups in the TPn films and balance of the structural forces in alkanethiolate SAMs
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| 4. |
- Shaporenko, A., et al.
(författare)
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Spectroscopic characterization of 4´-substituted aromatic self-assembled monolayers on GaAs (100) surface
- 2004
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Ingår i: Journal of Physical Chemistry B 108, 17964 (2004).
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy were applied to characterize GaAs(100) surface engineered by self-assembled monolayers (SAMs) of 4'-substituted aromatic molecules: 4'-methyl-4-mercaptobiphenyl (CH3-BPT) and 4'-hydroxy-4-mercaptobiphenyl (OH-BPT). Both of these molecules formed ordered and densely packed SAMs on GaAs, which were able to protect the substrate from degradation under ambient conditions. The molecular attachment in the SAMs is mediated by As-thiolate bond while the intact aromatic backbones have an upright orientation with average tilt angles of 31.0 and 37.2 for CH3-BPT and OH-BPT films, respectively. The difference in the tilt angle is attributed to a higher (by 7-10%) packing density of the former SAM, suggesting that the character of 4'-substitution affects the quality of the resulting SAM on the GaAs substrate
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| 5. |
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| 6. |
- Heister, K., et al.
(författare)
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Adsorption of alkanethiols and biphenylthiols on Au and Ag substrates: A high resolution X-ray photoelectron spectroscopy study
- 2001
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Ingår i: Journal of Physical Chemistry B 105, 4058 (2001).
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Tidskriftsartikel (refereegranskat)abstract
- Synchrotron-based high-resolution X-ray photoelectron spectroscopy was applied to monitor the formation of self-assembled monolayers (SAM) of alkanethiols (AT) and biphenylthiols on Au and Ag substrates. Pronounced chemical shifts in the adsorbate- and substrate-related photoemission lines upon SAM formation were observed. Only one sulfur species could be detected in the S 2p spectra of the investigated SAMs, consistent with a thiolate bond. From the fwhm's of the core level photoemission spectra conclusions on the heterogeneity of the adsorption sites and adsorption geometry can be made. The experimental data imply several (at least two) slightly different adsorption geometries for the AT moieties in AT/Au. Significant final state effects in the C 1s photoemission were found for both the aliphatic and aromatic SAMs
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| 7. |
- Heister, K., et al.
(författare)
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Characterization of X-ray induced damage in alkanethiolate monolayers by high resolution photoelectron spectroscopy
- 2001
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Ingår i: Langmuir 17, 8 (2001).
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Tidskriftsartikel (refereegranskat)abstract
- Synchrotron-based high-resolution X-ray photoelectron spectroscopy was for the first time applied to investigate the damage in self-assembled monolayers (SAMs) of alkanethiols (AT) on Au caused by soft X-rays. The observed changes in AT SAMs and, in particular, the appearance of a new, irradiation-induced sulfur species are identical to those caused by electron bombardment, implying that most of the damage is produced by the photoelectrons and secondary electrons. The irradiation-induced sulfur species is identified as a dialkyl sulfide distributed within the AT film. Only minutes of monochromatized X-ray irradiation at an undulator beamline destroys the AT adlayer completely.
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| 8. |
- Shaporenko, A, et al.
(författare)
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Functionalization of GaAs Surfaces with Aromatic Self-Assembled Monolayers: A Synchrotron-Based Spectroscopic Study
- 2003
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Ingår i: Langmuir 19, 4992 (2003).
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Tidskriftsartikel (refereegranskat)abstract
- Stoichiometric GaAs(100) surfaces were functionalized with monolayers of an aromatic compound, 1,1'-biphenyl-4-thiol (BPT), and the engineered surfaces were studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy. BPT molecules were found to form a well-ordered and densely packed self-assembled monolayer on these substrates. The attachment to the substrate occurs over the thiolate headgroup while the intact biphenyl moieties have an upright orientation with an average tilt angle of 31.5 ± 5. The functionalization of GaAs by BPT was found to prevent an oxidation and contamination of the substrate, keeping the GaAs surface in a pristine state. The surface engineering of GaAs with functionalized aromatic monolayers can provide a crucial link for combining GaAs-based semiconductor nanostructures with bio-organic molecular assemblies
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