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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 [EMIm]Tf2N and [OMIm]Tf2N 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 [XMIm]Tf2N 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.

We investigated the effect of ion-beam irradiation of the 3C-SiC(111) surface on the growth of graphene by the SiC surface-decomposition method. When a 3C-SiC(111) surface was irradiated by 1 keV Ar+ions at a dose of 4.5 × 1015cm2in an ultra-high-vacuum chamber and then annealed at 1200 °C for 1 min, the formation of graphene layers was promoted in comparison with that in the absence of ion-beam irradiation. X-ray photoelectron spectroscopy studies showed that Ar ion bombardment of the 3C-SiC(111) caused breakage of surface bonds and helped Si atoms to desorb from the surface.

Radiation induced degradation effects are studied for a model ionic liquid (IL)--[EMIm]Tf(2)N--in order to distinguish in which way the results of X-ray based material analysis methods can be falsified by the radiation supplied by typical X-ray sources itself. Photoelectron spectroscopy is commonly used for determining the electronic structure of ionic liquids. Degradation effects, which often occur e.g. in organic materials during X-ray or electron irradiation, are potentially critical for the interpretation of data obtained from ionic liquids. The changes of the chemical composition as well as the radiation-induced desorption of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm]Tf(2)N) fragments are analysed by X-ray photoelectron spectroscopy (XPS) as well as quadrupole mass spectroscopy (QMS) upon exposure to monochromated or non-monochromated AlKα X-rays from typical laboratory sources. During the irradiation of [EMIm]Tf(2)N, an increasing carbon concentration is observed in both cases and especially the [Tf(2)N](-) ion is strongly altered. This observation is supported by the results from the QMS analysis which revealed a variety of different IL fragments that are desorbed during X-ray irradiation. It is shown that the decomposition rate is directly linked to the photon flux on the sample and hence has to be considered when planning an XPS experiment. However, for typical experiments on this particular IL the measurements suggest that the changes are on a larger time scale as typically required for spectra acquisition, in particular if monochromated X-ray sources are used.

We have measured the bulk and surface electronic structure of several ionic liquids of alkyl-imidazolium cations with different alkyl chains (EMIm, BMIm, HMIm, OMIm) and bis(trifluoromethylsulfonyl)imide anions (Tf2N) by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS He I and He II) as well as metastable induced electron spectroscopy (MIES). The results are compared with the densities of states (DOS) calculated by density functional theory (DFT). By XPS we found the stoichiometry of the respective ILs reproduced, and different carbon atom positions reflected by the splitting of the C(1s) - from the trifluor-methyl groups (CF3) of the anion with highest binding energy to the alkyl chains of the cation with the lowest one. Furthermore with increasing alkyl chain length the peak related to the alkyl group appears at slightly lower binding energy. The more bulk-sensitive XPS spectra reveal only minor differences in the valence band structure for the studied ionic liquids, whereas the more surface-sensitive methods UPS and especially MIES display distinct changes in the peak-intensities for varying the alkyl chain length. This is a strong indication for either a non-stoichiometric composition of the upmost molecular layer of the IL-surface and/or a reorientation of the cations, probably turning the alkyl chains to the surface. [DOI: 10.1380/ejssnt.2010.241]

We report the effect of a Cr layer on the glass substrate during the growth of carbon nanotubes (CNTs) by chemical vapor deposition. When Fe was used as a catalyst in the CNT growth, longer CNTs were obtained by increasing the thickness of the Cr layer. However, CNTs were not grown on the surface with a thick Cr film and Co or Ni catalyst. These results arise from a difference in the mechanism of CNT formation when using different catalyst metals.

Reaction between deposited Ca layers and the Si(111) substrate has been studied by metastable-induced electron spectroscopy (MIES) and low-energy electron diffraction (LEED). When a Ca-deposited (about 1ML) Si(111) surface was annealed at temperatures in the range 470-570 K, the MIES spectrum showed a peak, named Ps, at a binding energy of about 7 eV which is assigned to be an isolated Si3s state. By referring electronic structure calculations for the bulk Ca-silicides, we confirmed that a solid-phase reaction at the Ca/Si interface to induce Ca2Si-like phases takes place at rather low annealing temperatures around 570 K. When Ca-covered (about 0.6 ML) Si(111) surfaces were annealed at temperatures in the range 770-870 K, the LEED showed 2× 1, 5× 1 and quasi-3× 2 reconstructions, depending on the temperature. We obtained MIES spectra from these surfaces involving spectral features which reflect local atomic structures of those Ca+Si surface phases. Correlations between the local atomic structure and the electronic structure probed by the MIES are discussed. [DOI: 10.1380/ejssnt.2007.89]

We used scanning tunneling microscopy, low-energy electron diffraction, and Raman spectroscopy to investigate the growth of graphene on 3C-SiC(111)/SiO2/Si(111) surfaces with ion-beam irradiation via the SiC surface decomposition method. We were unable to obtain graphene after annealing the 3C-SiC(111) surface at 1100 °C for 3 min without Ar+ ion-beam irradiation. When a 3C-SiC(111) surface was irradiated with an Ar+ ion beam at an acceleration voltage of 1 keV and an incident angle of 80° and subsequently annealed at 1100 °C for 3 min, graphene formed on the SiC surface. However, when an Ar+ ion beam was used at an incident angle of 70 or 60°, graphene layers were not formed. These results indicate that the breakage of bonds in the surface region of the SiC(111) substrate by ion-beam irradiation promotes the formation of graphene.

We have investigated influence of thickness of the Cr buffer layer on the glass substrate in the growth process of carbon nanotubes (CNTs) by chemical vapor deposition method. The Cr film of 3, 35 or 100 nm as a buffer layer was formed on a glass substrate by RF-sputtering method. A catalyst such as Fe, Co, or Ni in the CNT growth was also deposited on the buffer layers. The Cr buffer layer with a catalyst and the CNTs grown on the surfaces were observed by scanning electron microscopy. The lengths and the densities of the CNTs grown on the surfaces decreased with the increase in thickness of the Cr buffer layers.

We have recently measured core level and valence band XPS, UPS, and MIES spectra of two room temperature ionic liquids composed of bis(trifluoromethylsulfonyl)imide anions ([Tf(2)N](-)) and either 1-ethyl-3-methyl-imidazolium ([EMIm](+)) or 1-octyl-3-methyl-imidazolium cations ([OMIm](+)). [T. Ikari, A. Keppler, M. Reinmöller, W. J. D. Beenken, S. Krischok, M. Marschewski, W. Maus-Friedrichs, O. Höfft and F. Endres, e-J. Surf. Sci. Nanotechnol., 2010, 8, 241.] In the present work we analyze these spectra by means of partial density of states (pDOS) as calculated from a single ion pair of the respective ionic liquid using density functional theory (DFT). Subsequently we reconstruct the XPS and UPS spectra by considering photoemission cross sections and analyze the MIES spectra by pDOS, which provides us decisive hints to the ionic liquid surface structure.

We have investigated the formation of graphene on the SiO2/Si (111) surfaces using scanning tunneling microscopy. When the SiC (111) film [1500 nm] formed on the SiO2 surfaces was annealed at 980oC, graphene layer was obtained on the SiC surface. When the thickness of the SiC film was 5 nm, the graphene was not observed. However, graphene layer was obtained on the SiO2 surfaces after annealing the C-covered SiC (111) [5 nm] film on the SiO2/Si (111) surfaces at 980oC.

We investigated the influence of ion-beam irradiation of the SiC(0001̄) surface on the growth of carbon nanotubes (CNTs) by the SiC surface decomposition method. After an SiC(0001̄) surface was irradiated by Ar+ ions at 1 keV with a dose of 4.5×1015 cm-2 in an ultrahigh vacuum chamber, and then annealed at 1700 °C for 2 h at a pressure of 2×10-2 Pa, CNTs formed on the surface that were longer than CNTs grown without ion-beam irradiation. When 5 keV Ar+ ions were used, no CNTs formed, but instead an amorphous carbon layer formed on the surface.