•Adsorption Study of 4-alkoxybenzoic acids and terephthalic acid (TPA) on HOPG with MIES.•Flat adsorption of the molecules in the monolayer range.•For 4-decoxy benzoic acid, a reorientation of the ...long alkyl chains in transition to the multilayer.
The adsorption behavior of thin films of 4-alkoxybenzoic acids (with either hydroxy-, methoxy-, propoxy-, pentoxy- and decoxy-chains) and terephthalic acid, evaporated on a Highly Oriented Pyrolytic Graphite (HOPG) surface was studied. The orientation of the molecules was characterized by Metastable Induced Electron Spectroscopy (MIES) and Ultraviolet Photoelectron Spectroscopy (UPS(HeI)). On HOPG the 4-alkoxybenzoic acids and the terephthalic acid show a layer like growth at the beginning. Since the MIE spectra for the molecules on HOPG show all molecular orbitals, especially the π orbitals of the phenyl ring, a flat laying orientation on the graphite surface is assumed. The only exception is observed for 4-decoxy-benzoic acid. After a coverage of approximately 1 monolayer (ML) the spectrum is dominated by the spectral features of the alkyl structures.
X-Ray Photoelectron Spectroscopy (XPS), Metastable Induced Electron Spectroscopy (MIES) and Ultraviolet Photoelectron Spectroscopy (UPS) were applied to study the interaction of H2O molecules with ...iron films.
During the interaction with H2O molecules under ultrahigh vacuum conditions, an oxide film is formed on the iron surface. UPS and XPS still show metallic contributions, even for a surface which is exposed to about 103L. The oxide film thickness amounts to about 1.8nm. No hydroxide formation is observed at all, neither in UPS nor in MIES. Further impinging H2O molecules do not interact with the surface, because the oxide film inhibits the dissociation of impinging molecules.
H2O exposure beyond 109L does not lead to a significant increase of the oxide layer, which saturates at a thickness of 1.8nm. In particular, no surface hydroxide is observed at this exposure. Neither XPS UPS nor MIES reveal any indication for this.
► MIES is used to investigate the adsorption of H2O molecules on iron films. ► Formation of a stable iron oxide layer is observed. ► The oxide layer growth saturates at 1.8nm thickness. ► Beyond 109L H2O, no contribution by adsorbed hydroxide is observed in MIES.
•Valence electron spectroscopy was performed on an insulating polymer using different charge compensation methods.•MWCNT were embedded in PDMS and found to be the most effective method for reducing ...the charging of the insulating polymer.•The valence band spectrum of PDMS was obtained via MIES and UPS.•Ion scattering spectroscopy was used to determine the concentration depth profile of the PDMS in the sample.
The use of polydimethylsiloxane (PDMS) is increasing with new technologies working toward compact, flexible and transparent devices for use in medical and microfluidic systems. Electronic characterization of PDMS and other insulating materials is difficult due to charging, yet necessary for many applications where the interfacial structure is vital to device function or further modification. The outermost layer in particular is of importance as this is the area where chemical reactions such as surface functionalization will occur. Here, we investigate the valence band structure of the outermost layer and near surface area of PDMS through the use of metastable induced photoelectron spectroscopy (MIES) paired with ultraviolet photoelectron spectroscopy (UPS). The chemical composition of the samples under investigation were measured via X-ray photoelectron spectroscopy (XPS), and the vertical distribution of the polymer was shown with neutral impact collision ion scattering spectroscopy (NICISS). Three separate methods for charge compensation are used for the samples, and their effectiveness is compared.
Metastable Induced Electron Spectroscopy (MIES), Ultraviolet Photoelectron Spectroscopy (UPS), and X-ray Photoelectron Spectroscopy (XPS) are employed to study the adsorption of CO2 and CO on Ca and ...CaO films. Ca films are prepared by evaporation of Ca onto clean Si(100) substrates. CaO films are produced by Ca evaporation in an oxygen atmosphere at a substrate temperature of 670K. CO2 interaction with the Ca films is initiated by dissociation of the impinging molecules leading to the formation of Ca–O bonds. These Ca–O bonds are subsequently consumed in the formation of a closed CaCO3 layer on top of the surface. CO interaction with the Ca surfaces also leads to the dissociation of the molecule and the formation of Ca–O bonds. We find evidence for the subsequent formation of CO32- complexes on top of the surface. On CaO surfaces, both CO2 and CO lead to the formation of a closed CaCO3 top layer, though displaying very different reaction rates.
•Adsorption study of terephthalic acid (TPA) with MIES.•Flat adsorption of the molecules on gold.•Upright adsorption of the TPA molecules on oxidized aluminum.
The adsorption behavior of thin films ...of terephthalic acid (TPA) evaporated on a gold surface as well as on an aluminum foil was studied. The orientation of the molecules was characterized by metastable induced electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS). To make sure that the evaporation of TPA is nondestructive, additional X-ray photoelectron spectroscopy (XPS) was performed. These measurements also exclude any radiation damage.
TPA on the gold surface shows a well-ordered layer growth up to 7.5nm. Since the MIES spectra show both the acid structure and the phenyl group, a flat-laying orientation is assumed. In contrast, the phenylic carbon structure could not be observed while evaporating TPA on the oxidized aluminum foil. The MIES/UPS spectra only show the COOH group. To exclude a random arrangement of the molecules we also performed low temperature measurements. It can be concluded from these measurements, in addition to the fact that the work function increases during the evaporation, that TPA has a perpendicular arrangement on the aluminum foil.
The metastable induced electron spectroscopy (MIES), in combination with photoelectron spectroscopies, is a powerful tool to analyze the molecular arrangement at surfaces due to its high surface ...sensitivity. In this contribution MIES is applied to analyze structural changes at the surface of EMImTf2N and OMImTf2N films on two different substrates, Highly Ordered Pyrolytic Graphite (HOPG) and Au(111), as a function of the film thickness, starting from submonolayer coverage up to multilayers. The discussion is based on previous MIES studies of the vacuum–liquid interface of ionic liquids with imidazolium cations and on available DFT calculations. The presented data indicate that – in contrast to multilayers where the surface is dominated by the alkyl chains of the imidazolium cations – the structure of the first adlayer of XMImTf2N molecules on solid surfaces depends on the strength of their interaction with the surface resulting in alkyl chains aligned parallel or oblique to the substrate surface.
X-ray Photoelectron Spectroscopy (XPS), Metastable Induced Electron Spectroscopy (MIES) and Ultraviolet Photoelectron Spectroscopy (UPS) were applied to study the interaction of oxygen molecules with ...iron films. Supplementarily, iron oxide was investigated for comparison.
With XPS from the Fe 2p
3/2 range contributions of metallic Fe as well as Fe
2+ and Fe
3+ can be distinguished. During the interaction with oxygen an oxide film is formed on the iron surface. Nevertheless, XPS still shows metallic contributions even for a surface which is saturated with more than 10
4
L. The oxide film hinders the dissociation of further impinging oxygen molecules.
The interaction of He* atoms with iron oxide surfaces during MIES is dominated by Auger Neutralization. This surprising result follows from the high work function and the fact that intrinsic defects result in a Fermi level pinning to the conduction band.
The surface termination of oxide surfaces is of crucial importance for the growth of a second material like metals or other oxides. In this study we have investigated the surface of a BaTiO
3 (001) ...single crystal during sample preparation by various electron spectroscopic methods. It is shown by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and metastable induced electron spectroscopy (MIES) that during sputtering a Ba rich overlayer is formed, in which the Ba
2+ ions are under coordinated. Below this layer, an oxygen deficient BaTiO
3 layer is found. During annealing, we observe the reformation of the crystalline structure. UP and MIE spectra provide clear evidence of a BaO terminated surface. X-ray photoelectron diffraction studies support this result, comparing recorded polar angle scans with calculated intensity modulations using multiple scattering cluster models.
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![Surface structure of [XMIm]...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0168-583X/small "Surface structure of [XMIm]Tf2N ultrathin ionic liquid films probed by metastable He atoms and photoelectron spectroscopies (UPS and XPS)")