Self-assembled monolayers (SAMs) formed from thiophenol, 1,1′-biphenyl-4-thiol, 1,1′;4′,1′′-terphenyl-4-thiol, and anthracene-2-thiol on polycrystalline Au and Ag were characterized by X-ray photoelectron spectroscopy and angle-resolved near-edge X-ray absorption fine structure spectroscopy. With the exception of the poorly defined thiophenol film on Au, all thioaromatic molecules were found to form highly oriented and densely packed SAMs on both substrates. The molecular orientation and orientational order of the adsorbed thioaromatic molecules depends on the number of aromatic rings, the substrate, and the rigidity of the aromatic system. The molecules, which on average are slightly inclined with respect to the surface normal, show a less tilted orientation with increasing length of the aromatic chain, and as observed for aliphatic SAMs, they exhibit smaller tilt angles on Ag than on Au. However, the difference in the tilt angles for aromatic SAMs on Au and Ag is smaller than that observed in the aliphatic films. A comparison of the monolayers formed from p-terphenylthiol and anthracenethiol films suggests that a higher molecular rigidity has only a slight effect on the final molecular orientation within the respective SAMs.

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.

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.

The low energy electron induced damage in self-assembled monolayers of dodecanethiolate, octadecanethiolate, and perdeuterated eicosanethiolate on gold and octadecanethiolate on silver has been investigated in situ by X-ray photoelectron spectroscopy and angle resolved near edge X-ray absorption fine structure spectroscopy. All investigated systems exhibit qualitatively similar behavior with respect to low energy electron irradiation. The most noticeable processes are the loss of orientational and conformational order, partial dehydrogenation with CC double bond formation, desorption of the layer fragments, reduction of the thiolate species, and the appearance of new sulfur species. The cross sections for the rates of the individual irradiation-induced processes have been determined. For the films on gold all these processes are found to evolve with similar rates, except for the formation of CC double bonds and desorption of sulfur-containing fragments. The extent of the latter process is noticeably smaller in the longer-chain films as compared to their shorter-chain counterparts. The response of the alkyl matrix and the S−Au interface to electron irradiation are not directly correlated. Whereas the irradiation-induced processes in the alkyl matrix are found to be essentially independent of the alkyl chain length and the substrate material, the extent and rate of the thiolate species reduction and new sulfur species formation are mainly determined by the strength and character of the thiolate−substrate bond. No large isotopic effect in the irradiation-induced dehydrogenation process was observed. Deuterated films are found to be only slightly less sensitive to electron irradiation as compared to their hydrogen-containing counterparts.

Synchrotron-based high-resolution X-ray photoelectron spectroscopy was applied to characterize self-assembled monolayers (SAM) of biphenyl-substituted alkanethiols CH 3 (C 6 H 4 ) 2 (CH 2 ) n SH (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.

Self‐assembled monolayers (SAMs) formed from semifluorinated alkanethiols (SFATs) CF3(CF2)9(CH2)nSH (F10HnSH: n = 2, 11, and 17) on poly‐crystalline Au and Ag were characterized by X‐ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and near edge X‐ray absorption fine structure spectroscopy. SFATs were found to form highly ordered and densely packed SAMs on both substrates. The molecules are strongly bonded to the substrates via their sulfur head groups, in the same manner as conventional alkanethiol (AT) SAMs. The hydrocarbon (except for n = 2) and fluorocarbon parts of the adsorbed SFATs retain the expected planar zigzag and helical conformations of the respective bulk materials. The orientation of the fluorocarbon chains does not depend on the substrate. These entities are almost perpendicular to the substrate in F10H2S/Au and F10H2S/Ag and become slightly more tilted in SFAT SAMs with longer hydrocarbon moieties. However, the alkyl parts of the SFAT films exhibit tilt and twist angles that are similar to those of normal alkanethiol films on Ag and Au substrates despite the reduced packing density in the SFAT films as compared to normal AT SAMs. We suggest that the substrate‐related differences in tilt and twist angles for both systems are associated with the different character of the head‐group‐substrate bonding on Au and Ag.

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The low-energy electron-induced damage in self-assembled monolayers (SAMs) formed from ω-(4‘-methylbiphenyl-4-yl)alkanethiols CH3(C6H4)2(CH2) n SH (BPn, n = 0, 1, 4, 5, and 12) on gold substrates was studied. The pristine and heavily (8000 μC/cm2) irradiated films were characterized in detail by X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, infrared reflection absorption spectroscopy, and advancing contact angle measurements. In contrast to SAMs of conventional alkanethiols but similar to pure aromatic thiol-derived systems, only minor damage is observed for the aliphatic−aromatic BPn films. In particular, the orientational order and anchoring to the substrate are retained upon the irradiation. At the same time, C−H bond scissions in the aromatic part occur, leading to a cross-linking between the neighboring biphenyl moieties. Whereas the general behavior of the BPn SAMs with respect to electron irradiation is qualitatively similar, the extent of the irradiation-induced changes depends on the packing of these systems. The densely packed BP1 and BP5 SAMs are much more stable with respect to electron bombardment than the less densely packed BP4 films. The relation between the packing density and the extent of the irradiation-induced changes seems to be a general phenomenon in monomolecular films, which provides a tool to tailor the reaction of these systems toward ionizing radiation for lithographic applications.