Hydrocarbon Overlayer Research Articles

Iridium thin-film coatings for the BabyIAXO hybrid X-ray optic.

Reflective coatings are an essential feature of X-ray telescopes. Their overall performance relies heavily on substrate compatibility and how well they conform to the optics assembly processes. We use X-ray reflectometry (XRR) to demonstrate the compatibility of shaping flat substrates coated with iridium, and show that specular and nonspecular reflectance before and after shaping is on par with traditional hot-slumped coated substrates. From 1.487 and 8.048keV measurements, we find that the substrates have rms roughness of 0.38nm and magnetron sputtered iridium deposits with rms surface roughness of 0.27-0.35nm. A hydrocarbon overlayer from atmospheric contamination is present with a thickness of 1.4-1.6nm and a density of 1.2-1.6g/cm3. Both the traditional hot slumped and the flat substrates undergoing post-coating shaping have a similar characteristic surface morphology and are equally well-suited for use with X-ray optics. Finally, we demonstrate by simulation the improved effective area achieved by using a low-Z overlayer, and illustrate the performance of a hybrid optic coated with optimized bilayers for a Primakoff axion spectrum emitted by the sun.

Electron spectroscopy and microscopy applied to chemical and structural analysis of hair

The application of surface specific x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) will be shown to be an effective means for the elucidation of hair fiber surface chemistry and structure. Example studies of bleaching and fiber conditioning treatments are discussed. The bleached fiber surface is found to become more hydrophilic due to the loss of the naturally occurring hydrocarbon overlayer and oxidation of surface functional groups as a result of bleaching. Comparison between generic bleaching regimens illustrates the importance of increased pH and the presence of surfactant for effective treatment. Adsorption of conditioning diester quat and dimethicone molecules reintroduces a hydrophobic like surface layer on the hair fiber. Spectroscopic data indicated a segregated adsorption structure of the chemically different conditioning molecules. Electron microscope images of the conditioned hair shows a smooth uniform surface.

Atomic oxygen reactions with semifluorinated and n-alkanethiolate self-assembled monolayers.

The interaction of atomic oxygen (O(3P)) with semifluorinated self-assembled monolayers (CF-SAMs), two different n-alkanethiolate self-assembled monolayers, and a carbonaceous overlayer derived from an x-ray modified n-alkanethiolate SAM have been studied using in situ x-ray photoelectron spectroscopy. For short atomic oxygen exposures, CF-SAMs remain intact, an effect ascribed to the inertness of C-F and C-C bonds toward atomic oxygen and the well-ordered structure of the CF-SAMs. Following this initial induction period, atomic oxygen permeates through the CF3(CF2)7 overlayer and initiates reactions at the film/substrate interface, evidenced by the formation of sulfonate (RSO3) species and Au2O3. These reactions lead to the desorption of intact adsorbate chains, evidenced by the loss of carbon and fluorine from the film while the C(1s) spectral envelope and the C(1s)/F(1s) ratio remain virtually constant. In contrast, the reactivity of atomic oxygen with alkanethiolate SAMs is initiated at the vacuum/film interface, producing oxygen-containing carbon functional groups. Subsequent reactions of these new species with atomic oxygen lead to erosion of the hydrocarbon film. Experiments on the different hydrocarbon-based films reveal that the atomic oxygen-induced kinetics are influenced by the thickness as well as the structural and chemical characteristics of the hydrocarbon overlayer. Results from this investigation are also discussed in the context of material erosion by AO in low Earth orbit.

Hydrogenation of acetylene over low loaded Pd and Pd-Au/SiO 2 catalysts

Acetylene hydrogenation and formation of surface deposits have been investigated on two series of Pd and Pd-Au/SiO 2 catalysts differing in metal particle size ( D=0.47 and 0.08). Gold was deposited via ionization of pre-adsorbed hydrogen over pre-reduced Pd/SiO 2 in order to ensure selective poisoning of the Pd surface. The non-steady-state regime of operation and the accumulation of hydrocarbonaceous overlayer were tested in pulse-flow experiments. Concentration of surface hydrocarbonaceous deposits accumulated during different treatments was also determined by temperature programmed oxidation (TPO). Hydrocarbon overlayer was observed to form immediately and its presence appeared to be a necessary requisite to get steady-state conversion and selectivity data. A large excess of hydrogen suppressed the formation of carbonaceous laydown and increased the over-hydrogenation of acetylene. Presence of Au decreased the carbon coverage and improved the ethene selectivity. Decoration of Pd by Au and the morphology of particles explain the ethene selectivity improvement.

Three-Dimensional Surface Pattern and Chemical Composition of Mucosal Titanium Implant Compartments

Surface topography and chemical composition of mucosal-implant interfaces is thougt to be critical to their clinical success. The aim of our study was to investigate the topography and chemical composition of titanium mucosal-implant interfaces using surface analytical techniques. The mucosal surface compartments of 10 different implant systems were utilized as a test area. The ultramorphological analysis were carried out using Confocal Laser Scanning Microscopy (CLSM), X-ray photoelectron spectroscopy (XPS), Metastable Induced Electron Spectroscopy (MIES), Scanning Electron Microscopy (SEM) and Scanning Force Microscopy (SFM). The surfaces of samples showed different fracturing of metal chips and pitting attack. From the CLSM- and SEM analysis in comparison to the Developed Surface Area (DSA) as ratio of microroughnesses it appears that the diameter of the pits varied in the range of 0,1 to 10 \\micron. MIES showed the presence of Ti, O and C . Several peaks pertaining to titanium and oxygen can be found. The Ti-surface is covered by a 3–5 nm thick TiO2 layer. Only titanium in the oxidic, not in the metallic state is found within the observation depth of 1 nm. We find clear evidence from MIES that saturated hydrocarbon chains form the outermost molecular layer. Virtually no signal from TiO2 is found at the very surface. The results suggest a two-layer structure for the passive film formed on titanium after exposition to the sulcus crevicular fluid. The inner layer has a structure close to TiO2, while the outlayer is dominated by CH2-groups with a few –C=O groups inside the hydrocarbon overlayer. The granular structure observed on mucosal-implant surfaces seems to indicate that the dissolution occurs at localized defects in the passive film influencing the barrier function of implanto-gingival tissues. This was confirmed by the DSA as a hybrid parameter including both spatial and amplitude aspects of the surfaces.

Van der Waals Interaction during Protein Adsorption on a Solid Covered by a Thin Film

We calculate the contribution of van der Waals forces to the energy of protein adsorption on the solid covered by a thin film. Specifically, adsorption is considered to occur on the hydrocarbon layer deposited above the metal. Protein and hydrocarbon layers are separated by an ultrathin water layer. In a particular case when the hydrocarbon overlayer is absent, the van der Waals protein−substrate interaction is found to be appreciable, ≃(0.5−1.5) × 10-20 J/Å2. Covering the metal by hydrocarbon is demonstrated to result in decrease of the van der Waals interaction. Specifically, the interaction drops down to about 10-21 J/Å2 when the hydrocarbon layer becomes thicker than 4 Å.

Surface modification of titanium through amino group implantation

We modified Ti surfaces by implantation of amino (NH2+) groups at 1016 and 1017 cm−2. The implanted surfaces were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning Auger electron spectroscopy (AES), and second ion mass spectroscopy (SIMS). The experimental results showed that the implanted Ti specimens were covered by a dominant hydrocarbon overlayer due to contamination and the surface oxide layer of implanted specimens became thicker. XPS, AES, and SIMS depth profiles showed that implanted elements had a typical ion implantation distribution and that titanium nitride (TiN) was formed. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 55: 442–444, 2001

Surface modification of titanium through amino group implantation.

We modified Ti surfaces by implantation of amino (NH(2+)) groups at 10(16) and 10(17) cm(-2). The implanted surfaces were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning Auger electron spectroscopy (AES), and second ion mass spectroscopy (SIMS). The experimental results showed that the implanted Ti specimens were covered by a dominant hydrocarbon overlayer due to contamination and the surface oxide layer of implanted specimens became thicker. XPS, AES, and SIMS depth profiles showed that implanted elements had a typical ion implantation distribution and that titanium nitride (TiN) was formed.

Substrate sensitivity of dissociative electron attachment to physisorbed aniline

We report dissociative electron attachment (DEA) D − yields, at electron energies, E 0 < 14 eV, from small quantities of aniline- d 7 physisorbed on Pt or on films of O 2 or Kr. Compared to 5.5 monolayers (ML) of pure aniline- d 7, the DEA signal from 0.6 ML of aniline- d 7 on Pt is shifted down in E 0; for 0.6 ML of aniline- d 7 n 5 ML of O 2 the DEA signal is quenched. In the latter case, we observe reactive scattering of O − in the hydrocarbon overlayer. For 0.2 ML of aniline- d 7 on 35 ML of Kr, we observe change and energy transfer from negatively changed excitons, Kr ∗−, to co-absorbed aniline- d 7.

Modification of surface reactivity by adsorbed species on supported palladium and platinum catalysts during the selective hydrogenation of but-1-yne

Studying the butyne hydrogenation on Pd and Pt catalysts by the use of transient methods and in situ IR spectroscopy, it was found that the formation of a surface hydrocarbon overlayer regulates the semi-hydrogenation selectivity. It might be composed of η 2-butyne species. These species are equilibrated with the reactive intermediates which are thought to be vinylic adsorbed species. However, if the reactive intermediates are initially quickly hydrogenated, the coverage of the surface in equilibrium with the gas fugacity is so low that the hydrocarbon overlayer does not form and the catalyst is not selective. We propose a surface picture for butyne hydrogenation in which the reaction takes place on the low coordination sites (top, edge, corner atoms) while the high coordination sites are covered by spectator species ( η 2-butyne ). It is suggested to transpose this picture to an ethylene hydrogenation reaction in which the spectator species might be di-σ-bonded ethene.

Examination of Sputtered Ion Mechanisms Leading to the Formation of C7H7+ during Surface Induced Dissociation (SID) Tandem Mass Spectrometry (MS/MS) of Benzene Molecular Cations

Recent work reported in the literature has shown new evidence of a sputtered ion mechanism for associative ion surface reactions occurring during surface induced dissociation (SID) tandem mass spectrometry (MS/MS). In the context of a sputtered ion mechanism, we have studied selected routes to the formation of C7H7+ during the low-energy collision (ca. 30 eV) of benzene molecular ions with surfaces covered with a hydrocarbon overlayer. A key approach utilized in this work is the use of gas phase ion molecule chemistry to model reactive ion surface collisions. Benzene, 2H6-labeled benzene, and 13C6-labeled benzene have been examined by SID and collision activated dissociation (CAD). The CAD experiments have been used to investigate the fragmentation of hydrocarbon adducts of benzene and labeled benzene formed by methane and isobutane chemical ionization (CI) as models of those ions which may be formed via a sputtered ion mechanism during SID. In addition, the thermodynamics of many of the possible sputtered ion routes to the formation of C7H7+ have been compared using experimental heats of formation as well as total energies and zero-point vibrational energies (ZPVE) obtained by ab initio (MP2 6-31G*//HF 6-31G*) calculations. While there are several seemingly viable sputtered ion routes to the formation of C7H7+ during SID of benzene molecular ions, the combination of thermodynamic considerations and experimental results suggest that a likely sputtered ion route involves the reaction of neutralized benzene ions with C3H5+ ions (sputtered from the hydrocarbon overlayer) followed by the loss of ethene.

Sputtered protons during surface-induced dissociation (SID) tandem mass spectrometry (MS/MS)

A new tandem mass spectrometer has been constructed for the study of ion/surface interactions and the study of surface induced dissociation processes. During the development and initial testing of this new instrument, experiments have been carried out using a stainless steel surface under high vacuum (10 −7-10 −8 Torr) conditions where hydrocarbons (pump oil) would be expected to be adsorbed onto the surface. A surprising result of these experiments has been the observation of sputtered protons. The yield of sputtered protons remains relatively constant with varying incident ion kinetic energy (over the 20–100 eV range) and appears to have little or no dependence on momentum transfer from the incident ions. These findings provide direct evidence (via observation of an excess of the charged intermediate protons) for a charge exchange mechanism for associative ion/surface reactions involving protonation. However, the yield of protonated products (protonated pyridazine ions) due to associative ion/surface reactions is dependent on incident ion kinetic energy. These results suggest that the protonation of pyridazine may depend on interaction times at the surface which, in turn, depend on the depth of penetration of the incident species into the hydrocarbon overlayer. In addition, the observation of sputtered protons as the likely intermediates to associative ion/surface protonation reactions may have implications for the proposed mechanisms of ion/surface reactions where alkylation of incident ions occurs.

A quantitative XPS study of spherically shaped powders coated with an overlayer

Effects of the spherical shape of a small size (< 1 μm) powder and the thickness of a uniform overlayer on the surface elemental compositions measured by X-ray photoelectron spectroscopy (XPS) have been studied. The angular and radial dependence of the path length of photoelectrons generated within the substrate and the overlayer was taken into account in the calculation. The difference in photoelectron inelastic mean free path (IMFP) between the substrate and the overlayer was also considered in calculating the photoelectron intensity. Spherically shaped zinc oxide powder coated with a hydrocarbon overlayer was taken as an example.

Ｐｔ‐Ｉｒ合金キログラム原器表面上のハイドロカーボン層の角度分解Ｘ線光電子分光法による膜厚評価方法

Ｐｔ‐Ｉｒ合金キログラム原器表面上のハイドロカーボン層の角度分解Ｘ線光電子分光法による膜厚評価方法

Description of the influence of elastic scattering of electrons in the specimen and in an adventitious hydrocarbon overlayer on photoelectron signals by effective values of the inelastic mean free path and the asymmetry parameter

AbstractThe influence of elastic scattering of photoelectrons in the substrate and in an adventitious hydrocarbon overlayer on the effective inelastic mean free path and the effective asymmetry parameter has been investigated by Monte Carlo calculation. The results are representative of 27 chemical elements, asymmetry parameters 0.6 ⩽ β ⩽ 2.0, kinetic electron energies 300 ⩽ Ekin ⩽ 1500 eV and overlayer thicknesses 0 ⩽ t ⩽ 26.6 Å. For an application in quantitative surface analysis by XPS we propose the use of the effective inelastic mean free path (0.951 IMFP, tabulated values) and the effective asymmetry parameter βeff. The calculation of βeff is performed by tabulated values of β, inelastic mean free paths and measured reduced thicknesses of the hydrocarbon layer.

Calculation of Carbonaceous Overlayer Thickness in XPS to Yield Substrate Stoichiometries

A method has been developed which calculates the thickness of the hydrocarbon overlayer from x-ray photoemission spectroscopy (XPS) spectra. The method is specific to each sample and utilizes the relative intensity of the C 1 s peak and all other peaks. Attenuations calculated with this overlayer thickness yield more accurate substrate stoichiometries. A rough-sample model is also developed which not only explains previous anomalies in the thickness of hydrocarbon overlayer calculated but is capable of yielding further accuracy in substrate stoichiometries.

Angular-Resolved ESCA Studies of Cadmium Arachidate Monolayers on Si (100): Inelastic Mean-Free Path and Depth Profile Analysis

AbstractAngular-resolved ESCA was used to study single cadmium arachidate monolayers transferred to Si (100) wafers by the Langmuir-Blodgett technique. We find the monolayers to be of high integrity with respect to those defects which enhance the escape probability of substrate photoelectrons through the overlayer. The inelastic mean-free pathlengths of Si (2p) and C (1s) electrons were calculated to be 49±6 Å and 45±6 Å for the kinetic energies of 1388 eV and 1202 eV, respectively. The overall ordering of the hydrocarbon chains is less than for alkane thiols assembled on noble metals. We find that the precision of the Tyler algorithm to deconvolute angular-resolved ESCA data into depth profiles is accurate within 10% for predicting the thickness of the hydrocarbon overlayer but less precise for intermediate layers.

TIME DEPENDENT FORMATION OF SULFIDIC FILMS ON COPPER SUBSTRATES WHEN EXPOSED TO HYDROCARBONS CONTAINING ELEMENTAL SULFUR

ABSTRACT Hydrocarbon fuels containing elemental sulfur can cause copper and copper alloy components of a fuel delivery system to severely corrode. Experiments were undertaken to study the composition, thickness and rate of growth of films formed in sulfur containing fuels. The time dependent growth of these films was studied using Auger electron spectroscopy in combination with standard ion sputtering techniques. Initially, the thickness of the films increased rapidly, but slowed after longer exposures. This behavior was shown to obey the parabolic law that is used to describe oxide film growth in air. The relative amount of sulfur in a layer directly beneath a thin hydrocarbon overlayer was found to increase with exposure of copper to the fuel. For long exposures this layer appeared to be predominantly CuS with Cu2-xS and then Cu2S below it, while the film was composed of predominantly Cu2S after short exposures to the hydrocarbon. X-ray photoelectron spectroscopy supported this conclusion.

The chemisorption of acetylene and ethylene on Rh(111): A low energy electron diffraction (LEED), high resolution electron energy loss (ELS), and thermal desorption mass spectrometry (TDS) study

We report the results of a detailed investigation of the chemisorption and reactivity of acetylene (C2H2) and ethylene (C2H4) on the Rh(111) single crystal surface. Below 270 K ELS measurements indicate that acetylene chemisorbs on Rh(111) with its C–C bond oriented parallel to the surface forming an approximately sp2 hybridized species. LEED investigations show that both C2H2 and C2H4 form metastable (2×2) surface structures on Rh(111) below 270 K. An irreversible order–order transformation occurs between 270 and 300 K to a stable c(4×2) hydrocarbon overlayer. The stable species formed from both molecules are identical. Hydrogen addition to chemisorbed acetylene is necessary to complete this conversion. The geometry of the adsorbed ethylene species does not change during this transformation although the overlayer structure does. This stable hydrocarbon species is identical to the hydrocarbon species formed from the chemisorption of either C2H4 or C2H4 and hydrogen on Pt(111) above 300 K. The addition of H2 to chemisorbed C2D2 or C2D4 results in H–D exchange, but no change in the adsorbate geometry is detected by ELS. Decomposition of these molecules occurs on the Rh(111) surface above ∼420 K.