ESCA Technique Research Articles

The ESCA molecule—Historical remarks and new results

The C 1s photoelectron spectrum of ethyl trifluoroacetate (CF3COOCH2CH3), also known as the ‘ESCA molecule’, is the most illustrative showcase of chemical shifts in photoelectron spectroscopy. The binding energies of the four carbon atoms of this molecule spread over more than 8eV with energy separations ranging from 1.7 to 3.1eV owing to different chemical environments and hence different charge states of these atoms. The paper discusses history and importance of this spectrum in the field of photoelectron spectroscopy starting from the time of invention of the ESCA technique. The main focus of the paper is a ‘revisit’ of this spectrum using the most modern experimental and computational tools. Large geometrical changes, different for each ionization site, and the presence of two conformers of ethyl trifluoroacetate influence the spectral lineshapes of all four C 1s lines. These effects are carefully modeled by theory and investigated in the experimental spectrum.

Spray-dried microparticles containing polymeric nanocapsules: Formulation aspects, liquid phase interactions and particles characteristics

Up to now, the full potential of polymer-based nanoparticles is not yet exploited because of a lack of stability when conserved in aqueous medium. The present paper reports the water elimination from nanocapsules (NC) dispersions by means of the spray-drying technique with the aim to achieve dried solid forms of interest using colloidal silicon dioxide as drying auxiliary. The influence of formulation parameters on the suspension behaviour and on the powders characteristics was also evaluated. Our findings demonstrated that the mixing protocol, the concentrations of both NC and silica are crucial parameters that affect the feed behaviour and the spray-dried particles characteristics. Interactions occurring in the feed are directed by hydrogen bounds and were more sensitive to the silica concentration than that of NC as evidenced by rheological measurements. The NC are entrapped within solid dried matrixes following their interaction with silica particles in the feed. SEM analyses of the obtained powders showed spherical separated microparticles formed by the association of NC and silica when they are mixed at adequate concentrations in the feed before spray-drying. On the other hand, fused agglomerated particles presenting NC at their surface, characterised by irregular shapes and a strong adhesiveness were prepared when the silica concentration was not sufficient. The surface composition of the spray-dried powders was investigated using the ESCA technique and revealed the NC exclusion from the surface to obtain powders suitable for further handling.

On the Indirect Polyelectrolyte Titration of Cellulosic Fibers. Conditions for Charge Stoichiometry and Comparison with ESCA

The effect of electrolyte (NaHCO3) concentration on the adsorption of poly-DADMAC (poly-diallyldimethylammonium chloride) onto cellulosic fibers with different charge profiles was investigated. Surface carboxymethylated fibers were obtained by grafting carboxymethyl cellulose (CMC) onto the fiber surface and bulk carboxymethylated fibers were obtained by reacting the fibers with monochloroacetic acid. It was shown that nonionic interactions do not exist between cellulose and poly-DADMAC, rather electrostatic interactions govern the adsorption. Charge stoichiometry prevails under electrolyte-free conditions, whereas surface charge overcompensation occurs at higher electrolyte concentrations. It was shown that charge stoichiometry prevails if the thickness of the electric double layer kappa(-1) was larger than the mean distance between the charges on the fiber surface, as predicted by polyelectrolyte adsorption theories, taking lateral correlation effects into account. In a second set of experiments the ESCA technique served to independently calibrate the polyelectrolyte titrations for determining the surface charge of cellulosic fibers. Various molecular masses of poly-DADMAC were adsorbed to carboxymethylated fibers having different charge profiles. The adsorption of low M(w) poly-DADMAC (7.0 x 10(3)), analyzed by polyelectrolyte titration, was about 10 times higher than that of the high M(w) poly-DADMAC (9.2 x 10(5)). Despite the difference in accessibility of these two polyelectrolytes to the fiber cell wall, ESCA surface analysis showed, as expected, only slight differences between the two polyelectrolytes. This gives strong credibility to the idea that surface charge content of cellulosic fibers can be analyzed by means of adsorption of a high-molecular-mass cationic polymer, i.e., by polyelectrolyte titration.

Surface properties of CTMP fibers modified with xylans

This study investigated the effect of modification with xylan on the surface properties of chemithermomechanical pulp (CTMP) from spruce. The surface modifications were carried out by controlled sorption of birch xylan from solution at high temperature and high pH. Several different analysis techniques were used to study the effects on fiber surface composition and morphology. The ESCA technique showed a reduction in the amount of carbons not bound to oxygen in the C(1s) resolved peak after treatment. Variations in surface topography between untreated samples and samples with xylan were studied with SEM and AFM in the tapping mode. Scanning electron micrographs show micrometersized xylan particle structures spread over the fiber surfaces. AFM images reveal differences in the fine structure of fibers. The modified fibers exhibit a nanometersized, bumplike morphology not seen on the untreated fibers. The wetting properties of single fibers were determined with the Wilhelmy plate technique and the water sorption of CTMP paper sheets was studied using a dynamic contactangle tester. The surface modification of CTMP with xylan significantly decreased the advancing contact angle of single fibers and also improved the water sorption of sheets.

Biodegradation of Titanium Implants After Long-Time Insertion Used for the Treatment of Fractured Upper and Lower Jaws Through Osteosynthesis: Element Analysis by Electron Microscopy and EDX or EELS

Twelve patients underwent an osteosynthesis with titanium to treat upper and lower jaw fractures. Six to 12 months later, the miniplates were removed. Tissue samples were analyzed by light and electron microscopy for detection of a metallosis. The analysis showed new bone formation like callus tissue around the miniplates. In some cases small, rounded deposits and accumulation of colloid-like particles located next to bigger titanium artifacts were detected in the cytoplasm of histiocytes and in the matrix of connective tissue. The titanium was identified by elemental analysis using EDX in SEM as well as by EELS and electron diffraction in TEM. Both kinds of particles contain titanium, but they seem to be different in composition and derivation. The bigger particles seem to consist of metallic titanium and sourced by working on the metallic implants during the implantation itself. On the other hand, the colloidal-like, small, rounded particles in tissue macrophages and outside the cells in the matrix of connective tissue are presumably of other origin; for example, they could be derived from biodegradation and chemical conversion of the metallic implants. The titanium miniplates were examined before and after implantation by using ESCA technique and revealed metallic titanium and different compositions with other elements. The amount of titanium load of the tissue was very low in most cases and presumably not of biomedical relevance.

Structure of Molybdenum Supported on α-, γ-, and χ-Aluminas in Relation to Its Epoxidation Activity

The structures of Mo supported on α-, γ-, and χ-aluminas were analyzed by ESCA, XRD, IR, and XAFS techniques, and the relationship between the structure of Mo and its catalytic activity for the epoxidation of allyl alcohol was discussed. The ranges of the Mo-monolayer formation as estimated by the ESCA technique were less than 18, 15, and 1 wt% of Mo-loading for γ-, χ-, and α-aluminas, respectively. However, MoO3was detected by an XRD analysis at 10 wt% of Mo-loading for γ- and χ-aluminas; the ESCA technique overestimated the range of the monolayer. The monolayer on γ- and χ-aluminas as apparently determined by the ESCA analysis consisted of isolated tetrahedral Mo, octahedral polymolybdate, and a small amount of MoO3. The monolayer on α-alumina contained only tetrahedral Mo-species. MoO3was predominantly formed after the completion of the monolayer on all aluminas. The epoxidation activity of Mo was low in the monolayer region; especially, isolated tetrahedral Mo was completely inactive. MoO3was the most active species for the epoxidation, and peroxo-type oxygen bound to Mo was deduced to be the active species.

2-hydroxyethyl methacrylate-terminated polyurethane/polyurethane interpenetrating polymer networks.

The interpenetrating polymer networks (INPs) of polyurethane (PU) and 2-hydroxyethyl methacrylate (MEHA)-terminated polyurethane (HPU) were prepared by solution polymerization. PU prepolymer was synthesized from 4,4-diphenyl methane diisocyanate (MDI) and poly(propylene oxide) glycol (PPG). HPU prepolymer was synthesized from MDI, poly(tetramethylene oxide) glycol and HEMA. Dynamic mechanical analysis showed that the resultant IPN membranes have good compatibility between their constituents. As the HPU content increased, the tensile strength of the IPNs first increased and then decreased. For the highest tensile strength, the optimum HPU content was about 25 wt %. The value of surface tension of IPNs varied from 44.4 to 50.5 dyne/cm, and polarity ranged from 0.59 to 0.91. The relative index of platelet adhesion (RIPA) of the IPN membranes was measured by the dynamic thrombosis test at constant shaking speed and temperature. By the criteria of this test, the IPN membranes with HPU content of about 25 wt% to the minimum platelet adhesion. When measured by the angular dependent ESCA technique on the surface of IPN samples, the variation in the RIPA correlated to the change in the surface soft segment to hard segment ratio. Higher HPU content resulted in more migration of soft segments toward the surface. The platelet adhesion was observed to be minimized when the surface O/N ratio was around 12.

Degradation in CdS-Cu2S photovoltaic cells

The degradation of the photovoltaic properties of CdS-Cu2S solar cells stored in the dark and under illumination has been investigated. Unencapsulated devices maintained in air at room temperature degraded much less rapidly in the dark than those maintained under constant illumination. Examination using the ESCA technique showed that the illuminated devices developed a higher concentration of surface oxygen. The degradation, which is attributed to the formation of surface oxide with consequent loss of copper from the Cu2S layer could be retarded significantly by replacing the ambient air with argon. However, if cells were stored in argon at 50 degrees C instead of 22 degrees C, copper diffused from the Cu2S into the CdS, leading to degradation by this process.

Characterization of low-temperatureplasma treated silk fibroin fabrics by ESCA and the use of the fabrics as an enzyme-immobilization support

Bombyx mori silk fibroin fabrics were treated with low-temperature-plasma using various gases. Alkaline phosphatase was immobilized onto the fabrics using the CNBr method. The enzyme activity was much improved by plasma treatment, especially when both O 2 and CF 4 were used. Using the ESCA technique it was found that the activities of the immobilized enzyme were strongly correlated with the C1s peak intensities of the atomic group -C-O-CF 3. The apparent Michaelis constant for the enzyme decreased with increasing amounts of -C-O-CF 3.

ESCA spectroscopy of poly(methyl methacrylate) grafted onto wood fibers

AbstractThe incompatibility of hydrophilic wood fiber and hydrophobic polymers is the main difficulty with wood thermoplastic polymer composites. To overcome this issue, many researchers suggest grafting polymer onto wood fiber for improving the interfacial adhesion during mixing. A systematic ESCA study of chemi‐thermo‐mechanical pulp (CTMP) grafted fiber has been performed to provide chemical information about surface composition modification. The material analyzed included initial CTMP fiber, the pure polymer i.e., poly(methyl methacrylate) (PMMA) as reference material, and grafted fiber at different polymer loadings. Interest is focused on the carbon and oxygen spectra. Samples at high polymer loading or high grafting level have an O/C, C1, C2, C4, O1, and O2 intensities much similar to those of the PMMA but a little different since some wood fiber sites have still not fixed the polymer. ESCA spectra provide information on about 1–5 nm depth. The ESCA technique allows the monitoring of grafting polymer onto wood fiber as a surface phenomenon.

Phosphorus removal from wastewater by half-burned dolomite

The possibility of phosphorus removal from wastewater by fixation with half-burned dolomite grains was investigated. The results obtained showed the formation of a non-stochiometric calcium phosphate on the surface of the grains, undoubtedly of an amorphous nature as structure identification could not be made when X-ray diffraction techniques were employed. Identification by ESCA technique indicated a structure having a (Ca + Mg)/P ratio of 1.4. Equilibria experiments carried out at 25°C between the solid and a phosphate-containing solution showed that the fixation could be modelled following a Freundlich type isotherm. The fixation capacity of grains with a 0.5 mm mean particule size was 10 mg PO 4-P g −1 solid. The influences of hydraulic conditions and grain specific area on the fixation capacity were investigated. Acid regeneration of the spent material seemed to be of no practical interest. From an engineering point of view, this treatment could serve as a tertiary step after biological treatment of a wastewater. Finely pulverized powder (diameter < 100 μm) should be directly added at the outlet of a poor axial mix aeration basin, in order that the powder incorporates into the biological floc which will enhance separation of the sludge in the sedimentation tank.

Luminescence and ESCA analysis of laser-ablated materials

An investigation on laser-induced luminescence of simple solid oxides, their mixtures and other compounds is reported. Both a pulsed TEA CO 2 and a frequency-doubled Nd:YAG laser have been used. The luminous plume produced under the laser action by these compounds has been analyzed by an optical multichannel analyzer. The emission spectra show the presence of atomic, diatomic and more complex species. The ablated material was deposited on gold and SrTiO 3 substrates and analyzed by the ESCA technique.

On the use of “pseudo-atoms” in cluster calculations for modelling molecular fragments, solids and surfaces

A procedure is developed for performing cluster calculations within the framework of the standard CNDO/2 formalism, in which some atoms of the cluster may be replaced by “pseudo-atoms” possessing only one or two hybrid orbitals directed to selected atoms of the cluster. The method is similar to those of László and Litisnkij and seems promising in calculating chemically important fragments of large (bio)organic systems, as well as in modelling the bulk of the solids and their surfaces. Correlations between the calculated quantities and some experimental results obtained by using the ESCA technique are also discussed.

Nuclear corrosion monitoring—

Nuclear corrosion technique has been developed for the assay of various heavy metals released through corrosion and abrasion into electrolytes from various biomaterials like amalgams, chromium- cobalt and gold alloys, steel, and titanium. Application of the technique in measurement of selective release rates under static or dynamic conditions, i.e., during cyclic loading, is discussed. The elements chromium, cobalt, copper, gold, iron, mercury, molybdenum, silver, titanium, and zinc have been quantitatively assessed. In vivo corrosion measurements are further included. By combining the present nuclear tracer technique with ESCA technique, knowledge about reaction mechanisms occurring at the interface solid/liquid is obtained. Exposure of humans to various heavy metals from biomaterials, e.g., dental materials, can be estimated using the NCM technique. The technique also has a potential for selective release measurements of several nuclides possessing suitable radioanalytical properties from other types of alloys immersed in various liquid environments.

Surface Composition of Stainless Steels during Anodic Dissolution and Passivation Studied by ESCA

A molybdenum containing austenitic steel was exposed in hydrochloric acid at various potentials in the active and passive ranges of the alloys. The surface compositions were analyzed by the ESCA technique. The influence of pretreatment by ion bombardment and mechanical polishing on the passivation behavior was investigated. The passive film formed on the surface consists mainly of a mixed Fe‐Cr‐Mo oxide. The average content of Cr3+ in the oxide is about 70%. The inner layers of the oxide product consist mainly of Cr oxide. The Ni content in the oxide is low. The concentration and the chemical state of Mo is potential dependent. At low potentials in the passive range, the four‐valency state is predominant, while at high potentials Mo exists mainly in its six‐valency state. On the surface of the oxide, a layer of hydroxide is present. Chloride ions are incorporated into the passive film. The thickness of the passive film increases with the potential in the passive range from 10 to 15Å. The composition of the metal phase changes during active dissolution. Thus, the alloying elements are enriched on the surface and thereby control the dissolution rate, control overpotentials, and provoke passivation of the alloy.

Fluoride retention in clean and plaque-covered demineralized enamel in vivo after application of monofluorophosphate.

The retention of fluoride in clean and plaque-covered demineralized enamel in vivo was measured 1 wk after a single application of a MFP solution with low or high content of free fluoride. Demineralization of the enamel was induced in vivo during a 4-wk period prior to application of fluoride by applying orthodontic bands on a pair of premolars scheduled for extraction of orthodontic reasons. The band from one tooth of each pair was then removed and the tooth cleaned (clean enamel lesion). The band on the contralateral tooth (plaque-covered enamel lesion) was left in place. The MFP solutions were applied and the teeth extracted after one more week. The chemical form of fluorine in the lesions was analyzed by conventional acid etching of the enamel combined with KOH dissolution and by a nondestructive surface analysis using ESCA to detect intact monofluorophosphate ions. The ESCA measurements showed that MFP was only present in the clean enamel lesions, indicating complete hydrolysis by dental plaque. Alkali soluble fluoride could be extracted from both plaque-covered and clean enamel lesions. Conflicting results regarding the amount of fluoride uptake in the lesions were obtained with the acid etching and the ESCA technique. It was thus not clearly established whether plaque enhanced fluoride uptake in carious lesions after MFP application.

ESCA studies of carbon fibres: Part III—Surface reactions of carbon fibres with amines

The reactions between amines and Courtaulds AS carbon fibre surfaces have been studied by the ESCA technique. The carbon fibres were oxidized in a mixture of H 2SO 4 and HNO 3, and then refluxed in amines or in solutions of amines. The formation of amine overlayers on the carbon fibres is confirmed. The average amine depths have been calculated from the ESCA data. The fractions of the carbon fibre surfaces covered by amine monolayers are also estimated. The paper gives evidence supporting the idea that the amines are covalently bonded to the fibre surfaces.

ESCA studies of carbon fibres: Part II—Surface reactions of carbon fibres with epoxides

The reactions between epoxides and Courtaulds AS carbon fibre surfaces have been studied by the ESCA technique. The carbon fibres were oxidized in a mixture of H 2SO 4 and HNO 3, and then refluxed in epoxide. The formation of epoxide overlayers on the carbon fibres is confirmed. The average epoxide depths (in Å) have been calculated from the ESCA data. The fractions of the carbon fibre surfaces covered by epoxide monolayers are also estimated. The epoxides are assumed to be covalently bonded to the fibre surfaces by ether and ester links.

Applications of the small spot ESCA system SSX 100 in surface analysis

Evidence is presented that old ESCA limitations and restrictions (e.g. big X-ray beam diameter or small “unrealistic” size of samples) are not valid any longer. The new SSX 100 ESCA spectrometer with its unique combination of ESCA innovations (focusing monochromator, parallel imaging detectors, high throughput electron optics and improved sample handling) makes solving surface problems much easier. Two applications on semiconductors and insulators using the small spot X-ray beam (diameter: 150 μm) demonstrate that small spot ESCA technique now can be applied on problems which could not be solved with conventional ESCA technique hitherto.

ESCA studies of carbon fibres: part I—The chemical composition of a carbon fibre subsurface

Courtaulds AS carbon fibres have been studied by the ESCA technique after oxidation treatments in a mixture of H 2SO 4 and HNO 3 to increase the amount of oxygen containing groups on the fibre surface. The elements C, O, N, S, Cl, Na, Ca and Si were observed within the fibre subsurface, and their mole fractions are given. It was possible to distinguish between the contributions to the ESCA spectra originating from the fibre subsurface and the contributions coming from overlayers formed on these fibres after treatments with epoxides or amines. The analysis of the ESCA spectra taken of the epoxy or the amine treated fibres revealed that there exist oxygen and carbon concentration gradients within the fibre subsurface.