Metastable Induced Electron Spectroscopy Research Articles

Adsorption of silver on cellobiose and cellulose studied with MIES, UPS, XPS and AFM

Metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy as well as atomic force microscopy were employed to study the adsorption of silver on cellulose as well as its precursor cellobiose. The formation of silver nanoparticles encapsulated by the organic film previously found for the monomer glucose is well reproduced for the dimer cellobiose. For the polymer cellulose on the other hand, no nanoparticle formation is found even though the surface is covered with silver atoms. No significant chemical interaction is found in any of these cases.

Adsorption of silver on glucose studied with MIES, UPS, XPS and AFM

The adsorption behavior of silver atoms on a glucose film and their interaction was investigated by metastable induced electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy as well as atomic force microscopy. Glucose is found to form micro droplets on gold substrates with typical diameters/dimensions of about 400nm. The discussion of the valence band structures is carried out in comparison to various model systems. The adsorbed silver atoms on top of the glucose have been found to form silver nanoparticles that get encapsulated by a large film of glucose. Furthermore, the reduction of the glucose in the presence of these silver particles is observed. This effect is discussed with the most probable origin of the reduction being the charging by electron spectroscopy.

Surface Electronic Structure of [XMIm]Cl Probed by Surface‐Sensitive Spectroscopy

We apply electron spectroscopy methods with different surface sensitivities to elucidate the DOS of the surface and the near-surface region of [XMIm]Cl (X=octyl, hexyl, butyl, and ethyl alkyl chain) ionic liquids. Using metastable induced electron spectroscopy (MIES) we are able to detect the density of states in front of the outermost surface, whereas ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) measurements provide lower surface sensitivity. The assignment of certain structures in the valence band spectra to particular atoms/functional groups of the ionic liquid based on DFT calculations and the reconstruction of PES spectra enables us to obtain information on the dominating groups at the surface, or in other words, on the molecular/ionic arrangement and orientation at the surface. From angular resolved XPS it is concluded that the alkyl chains dominate at the outermost surface. In agreement with this a decreasing chlorine signal is observed in the UPS spectra for ionic liquids with increasing alkyl chain length. The analysis of the MIES data shows that in case of [OMIm]Cl--in contrast to UPS and XPS--no Cl-induced features are visible in the MIES spectra at all and that the MIES spectra are dominated by the [OMIm](+) alkyl chain.

Molecular Structure of 3-Aminopropyltriethoxysilane Layers Formed on Silanol-Terminated Silicon Surfaces

The use of the coupling agent, 3-aminopropyltriethoxysilane (APTES), in the silanization reaction with silanol-terminated silicon is an important surface modification reaction. Of particular importance is that the terminal amine functionalities of APTES are sufficiently exposed to the gas or liquid phase for further modifications, such as amide coupling reactions. Here, metastable induced electron spectroscopy (MIES) and UV photoelectron spectroscopy (UPS) were used to study the composition of the outermost layer of a silanol-terminated Si surface after silanization with APTES. High-resolution X-ray photoelectron spectroscopy (XPS) was used to validate the attachment of APTES to the surface. Density of States (DOS) calculations were employed for interpreting the MIE spectra. Findings showed that amine functionalities covered only a small fraction of the APTES-modified Si surface.

The interaction of H2O molecules with iron films studied with MIES, UPS and XPS

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.

Silver nano particle formation on Ar plasma – treated cinnamyl alcohol

Metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy are employed to study the adsorption of silver on cinnamyl alcohol films prepared on Au(111) substrates by thermal evaporation. Additionally, the impact of an Ar atmosphere dielectric barrier discharge plasma applied to the cinnamyl alcohol film preliminary to the Ag adsorption is investigated. In both cases silver nano particles with an average diameter of 9 nm are formed. These particles do not interact chemically with the underlying cinnamyl alcohol film. We do not find any influence of the preliminary Ar plasma-treatment on the adsorption behavior at all.

Silicon dioxide coating of titanium dioxide nano particles from dielectric barrier discharge in a gaseous mixture of silan and nitrogen

Titanium dioxide nanoparticles are used commonly in various applications due to their high catalytic activity. Many of these applications require subsequent treatments after the deposition of the TiO2 particles. Some of these include thermal processing at high temperatures, e.g. roof tiles. For all of these applications, the crystal structures as well as the microscopic properties are essential. Thus, sintering severely affects the catalytic activity in most of the cases. During thermal processing, the nanoparticles transform from the catalytical highly active anatas structure to the substantially less active rutil structure. This structural change has been found to be significantly retarded when coating the TiO2 nanoparticles with a closed film of SiO2. During the thermal treatment, these films break open, revealing the underlying TiO2 [i]. Thus, the film thickness has to be appropriate for the designated treatment subsequent to the nanoparticle deposition. In this study, we present an approach of SiO2 film deposition making use of silane gas. Pure silane gas is highly demanding on safety standards and technical installations, since it acts self-igniting and highly explosive when getting in contact with air or any oxygen containing gas. Thus, diluted process gases are used for most technical implementations, which contain just about 3% silane in 97% helium, neon, argon, hydrogen or nitrogen. While noble gases and hydrogen are used as dilution for a wide range of applications, the process gas consisting of nitrogen and silane is only implemented for silicon nitride deposition. Nevertheless, this gas should be the most suitable for many applications regarding economics and handling. Closed films produced by dielectric barrier discharges in such mixtures of gases consist of mainly non-stoichiometric silicon nitride, while the other diluted process gases produce metallic silicon films. The deposition of silicon dioxide films is rather complicated, since the silane reacts instantaneously with every oxygen-rich gas. Thus, both gases must not get in contact until they have arrived in front the surface that is to be coated. Most of the existing work found in the literature focuses on the implementation of this condition, to merge the silane and the oxygen right at the surface being coated. Taking a quite different approach, we divided the film deposition into two steps: In the first step, a silicon nitride film was deposited from the process gas with the silane diluted in nitrogen employing a dielectric barrier discharge plasma. As a second step, the silicon nitride film has been tried to convert into silicon dioxide by means of a second plasma discharge using either oxygen for a process gas or even environmental air. All studies have been carried out in an ultra high vacuum apparatus, while the plasma treatments have been carried out up to atmospheric pressure. During the investigations we employed Metastable Induced Electron Spectroscopy (MIES), Ultraviolet Photoelectron Spectroscopy (UPS) and X-ray Photoelectron Spectroscopy (XPS), as well as Atomic Force Microscopy (AFM). The microscopic measurements showed the deposited film to enclose the particles in a Frank van der Merwe – type growth mode. Film thicknesses determined by increased particle diameters in AFM were in good accordance to calculated film thicknesses from XPS peak intensity attenuation. Spectroscopic results show a formation of a silicon nitride film with substoichiometric nitrogen content, though free of oxynitrides. Surface impurities and adsorbates from the ex-situ preparation procedure were strongly removed and seemed to notably increase the growth rate. The second step gained a transformation of the film up to 98% silicon dioxide according to XPS. Remaining carbon impurities from the initially uncleaned surface were removed by both of the oxidizing plasmas. The transformation was found to be even more effective for the air plasma treatment than for the oxygen plasma treatment at a comparable oxygen partial pressure.

In situ preparation of calcium carbonate films

The in situ preparation of calcium carbonate films in an ultra high vacuum (UHV) is inhibited by the decomposition of CO 2 molecules at the surface and the absence of CO 2 bulk diffusion. Therefore, it is not possible to prepare such films simply by CO 2 exposure to a calcium layer. We investigated different approaches for the preparation of CaCO 3 films in an UHV. Among these, only the simultaneous evaporation of Ca atoms in a mixed O 2 and CO 2 atmosphere is able to produce well defined stoichiometric calcium carbonate films. Metastable Induced Electron Spectroscopy, Ultraviolet Photoelectron Spectroscopy and X-ray Photoelectron Spectroscopy are employed to verify quality and purity of the films.

Surface modification and chemical surface analysis of biomaterials

The chemical composition of the surface layers of synthetic biomaterials used for human medical devices and in biotechnology plays a key role in determining interfacial interactions between biological media (such as protein solutions, cells, tissue) and the synthetic material. Accordingly, considerable research efforts focus on improving the 'biocompatibility' of biomaterials by applying various surface modification and thin film coating approaches. Here we focus on the patterning of surface chemistries, often designed to exercise spatial control over events such as cell attachment and spreading. Secondly, we review recent developments in chemical characterisation of biomaterials surfaces, which is essential both for verifying the success of intended surface modification strategies and for reliable interpretation of observed biological responses. Biomaterials surface analysis by imaging ToF-SIMS and XPS and compositional depth profiling are discussed, as is the emerging complementary technique of Metastable Induced Electron Spectroscopy.

Plasma-oxidation of Ge(100) surfaces using dielectric barrier discharge investigated by metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy, and x-ray photoelectron spectroscopy

The radical oxidation of Ge(100) applying a dielectric barrier discharge plasma was investigated using metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy, and x-ray photoelectron spectroscopy. The plasma treatments were performed in a pure oxygen atmosphere as well as under environmental conditions at room temperature. In both atmospheres GeO2 layers up to thicknesses of several nm were formed on the Ge(100) surface.

The interaction of CO2 and CO with Fe‐doped SrTiO3(100) surfaces

The interaction of CO2 and CO with 0.013 at.% Fe‐doped SrTiO3(100) was investigated in situ with Metastable Induced Electron Spectroscopy (MIES) and XPS at room temperature. To clear up the influence of surface defects, cleaned and sputtered SrTiO3 surfaces were investigated. Sputtering results in the breaking of TiO bonds in the surface and the formation of oxygen‐related defects as well as reduced titanium on the surface.Cleaned SrTiO3 surfaces do neither interact with CO2 nor with CO. Sputtered surfaces show a CO formation during CO2 exposure and—to a lesser extent—during CO exposure. The CO groups can be detected very well with MIES because of its extreme surface sensitivity. With XPS, the characteristic carbonate peak shift of the C 1s orbitals can be detected. Copyright © 2011 John Wiley & Sons, Ltd.

In situ preparation of Calcium hydroxide films

The in situ preparation of Calcium hydroxide films in an ultra high vacuum (UHV) is constrained by the decomposition of species at the surface and the absence of OH bulk diffusion. Therefore, it is not possible to prepare such films simply by water exposure to a Calcium layer. We present four different approaches for the preparation of Ca(OH) 2 films in an UHV. Two of these methods are found to be ineffective for the preparation, the other two are shown to produce Calcium hydroxide films. Both of the two effective procedures make use of H 2 gas exposure. Metastable Induced Electron Spectroscopy, Ultraviolet Photoelectron Spectroscopy, and X-ray Photoelectron Spectroscopy are employed to verify quality and purity of the films.

Surface termination of BaTiO 3 (001) single crystals: A combined electron spectroscopic and theoretical study

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.

The interaction of H2O with Fe‐doped SrTiO3(100) surfaces

AbstractThe interaction of H2O with 0.013 at.% Fe‐doped SrTiO3(100) was investigated in situ with Metastable Induced Electron Spectroscopy (MIES), Ultraviolet Photoelectron Spectroscopy (UPS) and XPS at room temperature. Low Energy Electron Diffraction (LEED) was applied to gather information about the surface termination. To clear up the influence of surface defects, untreated and weakly sputtered SrTiO3 surfaces were investigated. The sputtering results in the formation of oxygen‐related defects in the top surface layer.The interaction of untreated SrTiO3 surfaces with H2O is only weak. Small amounts of OH groups can be identified only with MIES due to its extreme surface sensitivity. Sputtered surfaces show a larger OH formation. Nondissociative H2O adsorption is not observed. We therefore conclude that the exposure of H2O to SrTiO3(100) results in the dissociation near surface defects only, resulting in the formation of surface hydroxyl groups. Copyright © 2010 John Wiley & Sons, Ltd.

Water as a source for oxygen incorporation into acceptor doped SrTiO 3 single crystals

The possibility of the incorporation of oxygen and deuteron stemming from the dissociation of water into iron doped strontium titanate single crystals with two different iron concentrations (0.13 and 0.013 at.% Fe) has been investigated. Double labeled water ( 2H 2 18O) was used for Isotope Exchange Depth Profiling. It acts as an incorporation source of 18O into Fe-doped SrTiO 3(100) single crystals. Total dissociation of the water takes place in the vicinity of the SrTiO 3 surface and both oxygen and deuteron incorporate into the SrTiO 3. The results of the diffusion profile evaluation confirm that oxygen and deuteron migrate independently in the bulk. Oxygen incorporates into the material at high incorporation rates, practically comparable with the ones resulting from an O 2 atmosphere. The interaction of H 2O with SrTiO 3(100) surfaces was further studied with Metastable Induced Electron Spectroscopy and Ultraviolet Photoelectron Spectroscopy. Neither partial dissociation of water molecules nor any significant formation of surface OD groups was observed.

The interaction of oxygen molecules with iron films studied with MIES, UPS and XPS

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.

Surface Electronic Structure of Imidazolium-Based Ionic Liquids Studied by Electron Spectroscopy

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]

Oxygen incorporation into strontium titanate single crystals from CO2 dissociation

Oxygen incorporation from CO(2) into Fe-doped SrTiO(3)(100) single crystals (0.013 at% Fe, 0.039 at% Fe and 0.13 at% Fe) was investigated. Oxygen incorporation processes using (13)C(18)O(2) as the gas source were studied by isotope exchange depth profiling (IEDP) and subsequent secondary-ion mass spectroscopy (SIMS). The interaction of CO(2) with SrTiO(3) (100) surfaces was further studied with different surface analytical techniques like metastable induced electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). Results indicate that CO(2) interaction with SrTiO(3) (100) surfaces does not change the surface at all. It seems that CO(2) provides a very low sticking probability on the surface as it is not traced by valence band spectroscopy even at room temperature. Nonetheless, (13)C(18)O(2) acts as an incorporation source of (18)O into the Fe-doped SrTiO(3) single crystals. The diffusion coefficient exhibits a peculiar behaviour when Fe concentration increases. No carbon incorporation is observed at all.

Valence band spectroscopy on lignin

Abstract The valence band of lignin and sputtered lignin was studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and metastable induced electron spectroscopy (MIES). The corresponding spectra were compared with those from fingerprint molecules, representing the various chemical groups of lignin. The results of this analysis show that valence band spectroscopy, in particular a combination of XPS, UPS and MIES, allows an identification of hydroxyl, methoxy and phenyl groups at the lignin surface.

Growth of nickel nanoparticles on NiO/Ni(0 0 1): Evidence of adsorbed oxygen on metal particles by metastable induced electron spectroscopy (MIES)

We present results – obtained with X-ray as well as ultraviolet photoelectron spectroscopy (XPS and UPS) and metastable induced electron spectroscopy (MIES) – for the deposition of nickel on a NiO film of about 10 monolayers. It was found that up to a coverage of 0.5 monolayers single atoms or non-metallic clusters with up to 7 nickel atoms are formed. A MIES reference spectrum for this situation has been reconstructed from the experimental spectral series and the surface density of states has been obtained by deconvolution of this spectrum. Above 0.5 monolayer nominal nickel coverage a metallic nickel overlayer is formed as indicated by UPS. However, only MIES with its perfect surface sensitivity provides direct experimental evidence that on top of the metallic nickel a small amount of oxygen is adsorbed which originates from the underlying oxide.