C1s X-ray Photoelectron Spectroscopy Research Articles

Interface formation between poly(9,9-dioctylfluorene) and Ca electrode investigated using photoelectron spectroscopy

Ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy (XPS) have been used to study the interface formation between poly(9,9-dioctylfluorene) (PFO) and Ca electrode. As the Ca coverage increases, the vacuum energy level of PFO decreases gradually in order to match the Fermi level ( E F) of Ca. The original highest occupied molecular orbital of PFO moves away from the E F, and vanishes eventually. Bipolaron states with 1.8 eV in peak interval are formed in the former energy gap. The original lowest occupied molecular orbitals of PFO are broadened resulting in a featureless shake-up in the XPS C1s core level.

Carbon nitride thin films deposited by reactive plasma beam sputtering

Carbon nitride thin films have been deposited on silicon substrates by reactive sputtering of a pure graphite target. In this process, argon plasma, generated by a hot cathode discharge, diffuses through a diaphragm into a deposition chamber towards the target which is biased at −300V. The current density on the target is about 30mAcm−2. Nitrogen gas is injected into the deposition chamber during the sputtering. Evolution of the deposition rate is measured versus the partial N2 pressure. The films are characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red spectroscopy (FTIR) and Raman spectroscopy. The atomic ratios of N and C in films are evaluated by XPS. At high N2 partial pressure, the atomic fraction saturates at a value of 38at.%. The curve fitting of the C1s and N1s XPS peak spectra indicates that C and N atoms in films exhibit two different chemical states, representative of different CN chemical bonds. These XPS results, combined with FTIR and Raman analysis, suggest the existence of two amorphous carbon nitride phases in films, one with a stoichiometry similar to C3N4 and the other with an increasing fraction of nitrogen as the total N content in the films increases. These two carbon nitride phases seem to be present as soon as nitrogen is incorporated in films, even at low atomic concentration of nitrogen.

Surface structure of poly(ethylene terephthalate) film grafted with poly(methacrylic acid)

Poly(methacrylic acid) (PMAAc) chains were immobilized onto the surface of poly(ethylene terephthalate) (PET) film by graft polymerization induced by light irradiation. Monomer conversion and density of grafted PMAAc increased almost linearly with irradiation time and monomer concentration. The viscosity-average molecular weight of the tethered chains was roughly estimated as 1–3×10 6 when polymerization was carried out at 2–8 wt% monomer concentrations for 2 h. The structure of the grafted surface was studied using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The AFM image of the grafted surface was observed after staining with a cationic dye to form the ion complex. The grafted polymer chains were found to form a cluster structure. New peaks appeared in the C1s and O1s XPS spectra of the PMAAc grafted surface and were assigned to the carboxylic group of PMAAc. The grafted surface had two peaks in the Cu2p XPS spectrum, when the surface was brought into contact with Cu ions. The chemical composition estimated from the XPS spectra of the grafted film suggested that the carboxylic groups of PMAAc chains were linked to Cu ions through coordinate bonding.

Structure and electrochemical behavior of a flavin sulfide monolayer adsorbed on gold

The electrochemical behavior and structure of monolayers of the synthetic flavin 10-(3′-methylthiopropyl)-isoalloxazinyl-7-carboxylic acid adsorbed on gold is reported. The redox behavior of the compound is quasi-reversible. The surface concentration is estimated to be 1.5×10−10 mol cm−2. An electron transfer rate constant of 340 s−1 is estimated for the cathodic process and a value of 540 s−1 is estimated for the anodic process. The reduction potential of the monolayer is found to shift with pH as expected for a 2e−, 2H+ process. The monolayers have also been characterized by X-ray photoelectron spectroscopy (XPS) and low voltage field emission secondary electron microscopy (LVFESEM). The most likely orientation would have the long axis parallel to the surface with the carboxyl group exposed to the solution. A comparison of the C1s XPS spectra at glancing and normal emission indicates that the carboxyl group is at the film surface. The LVFESEM images indicate that the molecules pack in domains that do not follow the topology of the gold grains. Semi-quantitative examination of the micrographs shows that 10–15% of the gold surface is uncovered. The bare gold substrate catalyzes the oxidation of NADH; the presence of the flavin film reduces the observed catalysis by the gold substrate.

Characterization of silane-modified ZrO2 powder surfaces

Polymerizable organic silane molecules such as 3-(trimethoxysilyl)propylmethacrylate (γ-MPS) have been grafted onto the surface of ZrO2 powders, via hydroxyl groups, to obtain hybrid ‘macromonomers’. A combination of x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and 29Si nuclear magnetic resonance (NMR) spectroscopy have been employed to study the interaction between organic silane molecules and the surface of the ZrO2 powders. The core-level XPS regions, Zr3d, O1s, C1s and Si2p, have been studied to determine the nature of chemical bonding between the organic grafted monomer and inorganic phase and correlated with NMR results. Based upon the results obtained, it is proposed that grafting results in γ-MPS bonded to the ZrO2 powder surface via ZrOSi bonds accompanied by interlinkage of γ-MPS molecules through SiOSi bonding. © 1997 John Wiley & Sons, Ltd.

Formation of Carbon Nitride Films by Nitrogen Ion Bombardment on C60 Films

The synthesis of covalent carbon nitride films becomes an important subject in the materials research field. As a new synthetic method two low-energy (400 and 1000 eV) nitrogen ion beams are used to bombard on C60 thin films individually. The bombarded films are used for Raman and x-ray photoelectron spectroscopy (XPS) measurements. The results of the analyses show that under the bombardment of 400 eV nitrogen ion beam, the film still contains a large amount of undestructed C60 molecules. In the case of 1000 eV bombardment, only a little amount of C60 molecules is kept undestructed. The experimental results also show that the destructed carbon species will combine chemically with nitrogen ions to form stable covalent carbon nitride, confirmed by the Raman peaks of, e.g., 2240 cm-1. The XPS N1s and C1s lines also indicate the formation of covalent carbon nitride in the bombarded films.

XPS measurement of lubricant layer thickness on magnetic recording disks

We have studied the measurement of perfluoropolyether layer thicknesses by X-ray photoelectron spectroscopy (XPS). We used a model with a perfluoropolyether layer on a silicon dioxide substrate for the XPS analysis. By using the XPS O1s signal ratio of perfluoropolyether and silicon dioxide, the perfluoropolyether thickness could be determined from the following equation d( A ̊ ) = 16ln [7.2 I 1 I 2 + 1] where the O1s escape depths of organic substances and silicon dioxide were 16 Å and 20 Å, respectively. I 1 is the O1s signal intensity of perfluoropolyether and I 2 is that of silicon dioxide. A C1s XPS signal cannot be used to measure the thickness because the amount of hydrocarbon contamination varies and the perfluoropolyether has many C1s peaks.

Saturated ethylene coverage on Pt(111): a comparison of nuclear reaction analysis and X-ray photoemission data

Abstract Using the same Pt(111) crystal and identical procedures for preparing the c(4 × 2)-CO and saturated C2H4 (C2D4) layers on Pt(111), new nuclear reaction analysis (NRA) measurements and C1s X-ray photoelectron spectroscopy (XPS) measurements yield consistently a molecular coverage of C2H4 (C2D4) of 0.25 ML (ML = monolayer = 1.5 × 1015 atoms cm−2). The saturated coverage of ethylidyne (C2H3) at 300 K on Pt(111) was determined by XPS to be 0.25 ML.

Defect-induced dissociation of CO on palladium

The adsorption and reaction of carbon monoxide with a polycrystalline Pd foil, containing variable amounts of defect sites, has been studied by means of temperature-programmed desorption and reaction (TPD, TPR), temperature-programmed static secondary ion mass spectrometry (TPSSIMS) and X-ray photoelectron spectroscopy (XPS). On a well-annealed Pd surface a molecular adsorption state is found, with no evidence for dissociation. In contrast, the same but Ar + ion sputtered Pd sample is seen to dissociate part of the adsorbed CO. It is concluded that a high amount of defect sites is responsible for this phenomenon. The intensity ratios, Pd 2 O + Pd 2 + and Pd 2 C + Pd 2 + , measured by TPSSIMS, have been used to monitor the build-up of surface car and oxygen under in situ reaction conditions. The onset temperature for CO ad dissociation is found to be ∼ 410 K at which temperature nearly half of the molecular adsorption state has already undergone thermal desorption. C1s XPS provides corroborating evidence for carbon deposition on the surface. Recombination with oxygen followed by thermal desorption of CO is associated with the occurrence of high temperature desorption features at ∼ 640 and ∼ 725 K in the TPD spectra and with the disappearance of the carbidic and oxidic relative intensities in TPSSIMS. Evidence has been obtained for reversible subsurface diffusion of oxygen and carbon.