XPS study of carboxylic acid layers on oxidized metals with reference to particulate materials

Low‐molecular‐weight organic additives such as stearic acid are commonly used as surface additives in powder injection moulding (PIM). It is therefore important to know how the additives interact with the surface of the powder used. In this study, such interactions are studied by means of controlled adsorption of carboxylic acids on the oxides of interest. The oxides are prepared by oxidation of flat samples of Fe, Cr, Mn and Si. Surface chemical characterization is done by means of XPS, the main approach on flat samples being a comparison of angle‐resolved analysis and the use of the Tougaard nanostructure analysis technique. Taking advantage of this comparison, the Tougaard method is then applied in the evaluation of XPS analyses of stainless‐steel powder with adsorbed stearic acid. In addition, time‐of‐flight SIMS analysis is used to verify the adsorption of stearic acid on the powder surface. It is shown that Tougaard nanostructure analysis can be used for determining the thickness of an organic layer on particulate material. The layer thickness of adsorbed stearic acid was estimated to be ～20 Å, corresponding to monolayer adsorption. Time‐of‐flight SIMS analysis verified the adsorption of stearic acid on the powder surface. From the XPS analysis of flat samples it was determined that the use of the metal/oxide universal cross‐section in Tougaard nanostructure analysis best described the increased background due to adsorption of carboxylic acids, and that information about molecular orientation could be gained. Copyright © 2003 John Wiley & Sons, Ltd.     

XPSSurfA: An open collaborative XPS data repository using the CMSShub platform

X‐ray photoelectron spectroscopy (XPS) is a widely used surface analysis technique employed in fundamental research, applied research, service laboratories, and industry. Good‐quality analytical outcomes depend critically on spectral references. Many examples of XPS reference databases exist, including print editions, sets of spectral peak positions drawn from the literature, and digital archives and libraries. We report the development of a new digital XPS database comprising survey spectra and region spectra for a range of materials types, collected under a common set of analytical conditions. Each material is described using spectra collected at multiple pass energies with all photoelectron and X‐ray induced Auger transitions represented. Detailed metadata are provided for each material and each spectrum, presented using a schema that incorporates the ISO 16243 and 14976 standards and extensions developed in this work. Spectra are shared under a Creative Commons International (4.0) attribution, non‐commercial licence (CC BY‐NC) in Kratos (.dset), VAMAS (.vms), and XML (.xml) formats. It is intended that reference spectra be imported directly into XPS data analysis software packages for reference and comparison purposes, matching either the peak or transition of interest and the instrument pass energy. The database is flexible and scalable in structure and has the potential to become a core XPS reference resource.     

Mathematical topographical correction of XPS images using multivariate statistical methods

For rough heterogeneous samples, the contrast observed in XPS images may result from both changes in elemental or chemical composition and sample topography. Background image acquisition and subtraction are frequently utilized to minimize topographical effects so that images represent concentration variations in the sample. This procedure may significantly increase the data acquisition time. Multivariate statistical methods can assist in resolving topographical and chemical information from multispectral XPS images. Principal component analysis (PCA) is one method for identification of the highest correlation/variation between the images. Topography, which is common to all of the images, will be resolved in the first most significant component. The score of this component contains spatial information about the topography of the surface, whereas the loading is a quantitative representation of the topography contribution to each elemental/chemical image. The simple‐to‐use self‐modelling mixture analysis (Simplisma) method is a pure variable method that searches for the source of most differences in the data and therefore has the potential to distinguish between chemical and topographical phases in images. The mathematical background correction scheme is developed and validated by comparing results to the experimental background correction for samples with differing degrees of topography. Copyright © 2004 John Wiley & Sons, Ltd.     

Summary of ISO/TC 201 Standard: ISO 18115‐1:2013 – Surface chemical analysis – Vocabulary – General terms and terms used in spectroscopy

Amendments have been made to International Standards Organization (ISO) 18115‐1:2010 extending the number of terms and, in a few cases where usage has changed, incorporating revisions. Part 1 covers 600 terms used in Auger electron spectroscopy, elastic peak electron spectroscopy, reflected electron energy loss spectroscopy, SIMS, UPS, XPS, etc. as well as 75 acronyms. The terms cover words or phrases used in describing the samples, instruments and theoretical concepts involved in surface chemical analysis. © 2014 Crown copyright. Surface and Interface Analysis © 2014 John Wiley & Sons, Ltd.     

XPS and XAES analysis of copper,arsenic and sulfur chemical state in enargites

Enargite, a copper arsenic sulfide with the formula Cu₃AsS₄ is of environmental concern due to its potential to release toxic arsenic species. The oxidation and dissolution of enargite are governed by the composition and chemical state of the outermost surface layer. Qualitative and quantitative analysis of the enargite surface can be initially obtained on the basis of X‐ray photoelectron spectroscopy (XPS) binding energy and intensity data. However, a more precise determination of the chemical state of the principal elements of enargite (copper, arsenic and sulfur) in the altered surface layer and in the bulk of the mineral requires a combined analysis based on XPS photoelectron lines and the corresponding X‐ray excited Auger lines. On the basis of results obtained on natural and synthetic enargite samples and on standards of sulfides and oxides, the Auger parameter α′ of different compounds was calculated and the Wagner chemical state plots were drawn for arsenic, copper and sulfur. Arsenic in enargite is found to be in a chemical environment similar to that of arsenides or elemental arsenic, whereas copper in enargite is in a chemical state that corresponds to copper sulfide, Cu₂S, for all samples irrespective of surface treatment (natural or freshly cleaved). Only sulfur changed from a chemical state similar to that of copper or iron sulfide in freshly cleaved samples to another state in natural enargite in the as‐received state. Thus, it is the sulfur atom at the surface of enargite that is most susceptible to changes in the enargite surface state and composition. A more detailed interpretation of this behavior, based on differences in the initial and final state effects, is proposed here. The concept of Auger parameter and chemical state plot, used here for the first time for investigating enargite, has proved to be a method to unambiguously assign the chemical state of the principal elements copper, arsenic and sulfur in these minerals. Copyright © 2006 John Wiley & Sons, Ltd.     

Gas chromatography vacuum ultraviolet spectroscopy: A review

Accelerated technological progress and increased complexity of interrogated matrices imposes a demand for fast, powerful, and resolutive analysis techniques. Gas chromatography has been for a long time a ‘go‐to’ technique for the analysis of mixtures of volatile and semi‐volatile compounds. Coupling of the several dimensions of gas chromatography separation has allowed to access a realm of improved separations in the terms of increased separation power and detection sensitivity. Especially comprehensive separations offer an insight into detailed sample composition for complex samples. Combining these advanced separation techniques with an informative detection system such as vacuum ultraviolet spectroscopy is therefore of great interest. Almost all molecules absorb the vacuum ultraviolet radiation and have distinct spectral features with compound classes exhibiting spectral signature similarities. Spectral information can be ‘filtered’ to extract the response in the most informative spectral ranges. Developed algorithms allow spectral mixture estimation of coeluting species. Vacuum ultraviolet detector follows Beer–Lambert law, with the possibility of calibrationless quantitation. The purpose of this article is to provide an overview of the features and specificities of gas chromatography–vacuum ultraviolet spectroscopy coupling which has gained interest since the recent introduction of a commercial vacuum ultraviolet detector. Potentials and limitations, relevant theoretical considerations, recent advances and applications are explored.     

X-ray photoelectron spectroscopy characterization of Cu compounds for the development of organic protection treatments dedicated to heritage Cu objects preservation

The preservation of bronze and copper heritage objects is challenging. Exposure to water or pollution in outdoor conditions leads to corrosion phenomena, which can highly degrade the objects or structures. We aim to develop an alternative nontoxic corrosion inhibiting treatment, based on the use of a carboxylate (HC₁₀) treatment. Electron spectroscopies (X-ray photoelectron spectroscopy and scanning Auger microscopy) are used to determine, from micrometric to nanometric scale, the composition and chemical environments (oxidation degrees) of the copper compounds commonly found in the corrosion product layer. In the present study, we focus on the evaluation of X-ray beam irradiation damage when performing surface analysis on cuprite, brochantite, and Cu decanoate reference samples. The reduction phenomenon has already been reported, especially for Cu(II) compounds, but not clearly explained. Different behavior has been observed depending on the X-ray source used, and the nature and hydration level of the compounds. The photoreduction issue is critical, as it guarantees the reliability of the chemical information obtained and sheds light on the best analysis pathway to adopt when multitechnique analyses are implemented. An analytical procedure is employed to track the reduction of Cu(II) reference samples during XPS analysis evidencing practically instantaneous modifications of the spectra and thus, the instability of these phases except for the dehydrated cuprite sample.     

Melanin Biopolymers: Tailoring Chemical Complexity for Materials Design

Melanins, a group of dark insoluble pigments found widespread in nature, have become the focus of growing interest in materials science for various biomedical and technological applications, including opto‐bioelectronics, nanomedicine and mussel‐inspired surface coating. Recent progress in the understanding of melanin optical, paramagnetic redox, and conductivity properties, including photoconductivity, would point to a revision of the traditional concept of structural disorder in terms of more sophisticated and interrelated levels of chemical complexity which however have never been defined and codified. Herein, we bring to focus the various levels of structural disorder that emerged from spectral and chemical signatures over the past decade. A revised approach to structure–property relationships in terms of intermolecular interactions is also provided that may pave the way towards the rational design of next‐generation melanin‐based functional materials.     

Quantification of enantiomers by mass spectrometry based on chemical derivatization and spectral shape deformation quantitative theory

A facile mass spectrometric kinetic method for quantitative analysis of chiral compounds was developed by integrating mass spectrometry based on chemical derivatization and the spectral shape deformation quantitative theory. Chemical derivatization was employed to introduce diastereomeric environments to the chiral compounds of interest, resulting in different abundance distribution patterns of fragment ions of the derivatization products of enantiomers in mass spectrometry. The quantitative information of the chiral compounds of interest was extracted from complex mass spectral data by an advanced calibration model derived based on the spectral shape deformation quantitative theory. The performance of the proposed method was tested on the quantitative analysis of R‐propranolol in propranolol tablets. Experimental results demonstrated that it could achieve accurate and precise concentration ratio predictions for R‐propranolol with an average relative predictive error (ARPE) of about 4%, considerably better than the corresponding results of the mass spectrometric method based on chemical derivatization and the univariate ratiometric model (ARPE: about 12%). The limit of detection (LOD) and limit of quantification (LOQ) of the proposed method for the concentration ratio of R‐propranolol were estimated to be 1.5% and 6.0%, respectively. The proposed method is complementary to the existing methods designed for the quantification of enantiomers such as the Cooks kinetic method.     

Differentiating calcium carbonate polymorphs by surface analysis techniques—an XPS and TOF‐SIMS study

Calcium carbonate has evoked interest owing to its use as a biomaterial, and for its potential in biomineralization. Three polymorphs of calcium carbonate, i.e. calcite, aragonite, and vaterite were synthesized. Three conventional bulk analysis techniques, Fourier transform infrared (FTIR), X‐ray diffraction (XRD), and SEM, were used to confirm the crystal phase of each polymorphic calcium carbonate. Two surface analysis techniques, X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectroscopy (TOF‐SIMS), were used to differentiate the surfaces of these three polymorphs of calcium carbonate. XPS results clearly demonstrate that the surfaces of these three polymorphs are different as seen in the Ca(2p) and O(1s) core‐level spectra. The different atomic arrangement in the crystal lattice, which provides for a different chemical environment, can explain this surface difference. Principal component analysis (PCA) was used to analyze the TOF‐SIMS data. Three polymorphs of calcium carbonate cluster into three different groups by PCA scores. This suggests that surface analysis techniques are as powerful as conventional bulk analysis to discriminate calcium carbonate polymorphs. Copyright © 2008 John Wiley & Sons, Ltd.     

Photoelectron spectroscopy on organic surfaces: X‐ray degradation of oxygen‐plasma‐treated and chemically reduced poly(propylene) surfaces in comparison to conventional polymers

The X‐ray‐induced sample damage during mono XPS analysis of an oxygen‐plasma‐oxidized and subsequently wet‐chemically reduced poly(propylene) film was investigated as a showcase for plasma‐modified or plasma‐deposited samples. By doing this, the degradation index approach as introduced by Beamson and Briggs in the Scienta ESCA300 high‐resolution XPS database of organic polymers has been adopted. As to be expected, the sample degrades by loosing oxygen as revealed by observation of decreasing O/C and C OR/C_sum ratios. However, the X‐ray degradation indices are definitely higher than those of conventional reference polymers. Moreover, the C OR/C_sum degradation index is significantly higher in comparison with one obtained for the O/C ratio. In that context, there is no difference between the plasma sample and a conventional poly(vinyl alcohol) polymer. It is concluded that for reliable quantitative surface chemical analysis, the quality of spectra in terms of acquisition times must be optimized aimed to a minimization of X‐ray degradation. Finally, it is proposed to describe the photon flux of an X‐ray gun in an XPS experiment, which defines the degradation rate at the end, by using the sample current simply measured with a carefully grounded sputter‐cleaned reference silver sample. Copyright © 2009 John Wiley & Sons, Ltd.     

Radiation‐induced migration of additives in PVC‐based biomedical disposable devices Part 2. Surface analysis by XPS

Extruded parts of non‐sterilized and β‐irradiated (25 and 50 kGy) plasticized poly(vinyl chloride) (PVC) used for disposable medical devices have been studied to investigate the effect of sterilization on surface chemical composition. The polymer surfaces were analysed using angle‐resolved x‐ray photoelectron spectroscopy. The inner surface of the blood tubing lines showed a fairly smooth surface both before and after sterilization, so a laterally homogeneous surface can be assumed for XPS analysis. The XPS survey spectra exhibited no signals besides carbon, chlorine, oxygen and calcium. Detailed analysis of the regions showed the C 1s, Cl 2p and O 1s signals to be multi‐component, presenting signals of the PVC, the plasticizer and the other additives. Binding energies remained constant irrespective of β‐radiation dosage, but the amount of chlorine component at 198.4 ± 0.1 eV (associated with modified PVC) decreased with sterilization dosage. Angle‐resolved XPS revealed that this component is located at the outermost surface of the polymer. It can be hypothesized that the production processes themselves (extrusion and/or injection molded) already induce modifications of the polymer surface and also lead to surface segregation of the plasticizer. During the subsequent thermal sterilization of the polymer dehydrochlorination continues but, because of the very short time required by the β‐irradiation technology to sterilize devices, the atmospheric oxygen is unable to diffuse into the irradiated material, thus inhibiting further side‐degradation of the materials, such as thermo‐oxidative degradation. Copyright © 2003 John Wiley & Sons, Ltd.     

XPS characterization of wood chemical composition after heat‐treatment

XPS was used to characterize the chemical changes occurring after drying or applying a heat‐treatment to beech wood samples. Our results indicate that the surface of this air‐exposed material could be strongly affected either by the ambient atmosphere during storage or by the complex atmosphere in the oven during drying or heat‐treatment. However, the O/C ratio measured after removal of a thin slice of a few millimetres of an untreated sample is in reasonable agreement with that calculated from the well‐established chemical composition of beech. Through this methodology (equivalent to scraping for hard materials) it is expected to get a realistic characterization of the wood. The reliability and repeatability of the XPS measurements have been checked and the method applied to the study of the chemical changes of the beech samples subjected to heat‐treatment. Heating at 240 °C induces a significant decrease of the O/C ratio from 0.55 before to 0.44 after the treatment. Heat‐treatment induces also a decrease of the C₂ carbon contribution (carbon atom bound to a single non‐carbonyl oxygen) associated with an increase of the C₁ carbon contribution (carbon atoms bound only to carbon or hydrogen atoms), in agreement with chemical modifications reported previously in the literature. Thanks to the small analysed area of the equipment used in this study, different spots were analysed to demonstrate the presence or absence of a gradient of chemical composition due to thermal degradation or migration of extractives from within the wood structure to its surface. At the scale of our observations, the different wood samples investigated (dried or heat treated) appear to be homogeneous. Copyright © 2006 John Wiley & Sons, Ltd.     

A study of surface modification and anchoring techniques used in the preparation of monolithic microcolumns in fused silica capillaries

Based on a survey of the literature on pretreatment of fused silica capillaries, 3 etching procedures and 11 silanization protocols based on the vinylic silane 3-((trimethoxysilyl)propyl) methacrylate (gamma-MAPS) were found to be most representative as a means of ensuring attachment of in situ prepared vinylic polymers. These techniques were applied to fused silica capillaries and the success in establishing the intended surface modification was assessed. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical state of the surface, providing information regarding presence of the reagent bound to the capillary. Wetting angles were measured and correlated with the XPS results. An adherence test was done by photopolymerization of a 2 mm long plug of 1,6-butanediol dimethacrylate in the prepared capillaries and evaluation of its ability to withstand applied hydraulic pressure. SEM was also performed in cases where the plug was released or other irregularities were observed. Finally, the roughness of the etched surface, considered to be of importance, was assessed by atomic force microscopy. Alkaline etching at elevated temperature provided a surface roughness promoting adhesion. The commonly used silanization protocols involving water in the silanization or washing steps gave inadequate surface treatment. The best silanization procedure was based on toluene as a solvent.     

Chitosan‐capped sulfur microparticles grafted on UV‐treated PET surface

Antimicrobial materials with immobilized particles are of considerable interest. Sulfur, as one of the abundant elements on earth, is cheap and environmentally friendly; therefore, sulfur particles (SPs) can be used as an effective, nontoxic and low‐cost alternative to metal particles. SPs were prepared by precipitation method using sodium thiosulfate and hydrochloric acid in the presence of chitosan as a stabilizer. Further, SPs were grafted on polyethylene terephthalate (PET) foil activated by ultraviolet radiation. The changes in surface properties of modified foils were characterized by contact angle measurement, electrokinetic analysis and X‐ray photoelectron spectroscopy (XPS). The contact angle decreased on the UV‐treated sample, owing to the formation of oxidized groups. The presence of nitrogen and sulfur on the polymer surface, revealed by XPS, showed that chitosan‐capped SPs were bound to this surface. The surface morphology of samples and particle sizes were examined by scanning electron microscopy. The size of SPs increased after grafting on surface to a few micrometres. The antibacterial activity of the PET samples was tested against Staphylococcus epidermidis and Escherichia coli bacteria strains. UV‐treated samples grafted with one of the tested chitosan‐capped SPs demonstrated antibacterial effect against both of the bacteria strains. This new nanocomposite has potential to be used in medical applications as an antibacterial agent or in food processing as an antimicrobial food packaging material. Food spoilage caused by microorganisms such as E. coli during distribution and storage has a major impact on food quality and shelf life.     

Comparison of the chemical profiles of fresh‐raw and dry‐processed Juglans mandshurica

The processing of Juglans mandshurica Maxim. is important to reduce its toxicity and enhance its efficacy. Simple, efficient, and sensitive ultra‐high performance liquid chromatography coupled with a time‐of‐flight mass spectrometry based chemical profiling approach was proposed to rapidly evaluate the chemical difference between fresh and dry samples. Under the optimized ultra‐high performance liquid chromatography and quadrupole time‐of‐flight tandem mass spectrometry conditions, 81 significantly different compounds were rapidly discovered using principal component analysis, and then tentatively identified by comparison with reference substances or inferred through mass spectral fragment ion analysis and literature data. These compounds included 35 naphthoquinones, 11 diarylheptanoids, nine flavonoids, eight triterpenes, 12 phenolic acids, and six aliphatics. The results demonstrated that chemical reactions occurring during processing could be used to elucidate the processing mechanism of Juglans mandshurica Maxim. This study provides a novel approach to identifying complicated components of various complex mixtures in fresh‐raw and dry‐processed traditional Chinese medicines, which could be used as a valid analytical method to further understand the processing mechanisms of these medicines, as well as providing intrinsic quality control of the medicines and their processed products.     

白烟灰的物相分析及酸浸脱砷工艺

白烟灰因其含有砷等有毒化合物,其安全堆存是冶金企业面临的难题。 对白烟灰进行物相分析是处理该烟灰,使其达到环保要求堆存的重要依据。 采用X射线光电子能谱(XPS)和X射线粉末衍射(XRD)研究了河南某企业白烟灰的物相组成及化学结合状态,确定其所含化学成分及元素含量。 结果表明,样品中元素As相对含量高达20.99%,其中11%以游离态As₂O₃形式存在,其余以PbAs₂O₆形式存在。 样品中还含有少量的Cu、Pb、Zn等金属及其氧化物。 根据被测样品物相组成,提出了一种氧化酸浸脱砷的方法,并确定了最佳脱砷工艺,在最佳工艺条件下,砷的浸出率高达97.1%,高于文献报道的砷的浸出率。     

Quantitative analysis of saccharides by X‐ray photoelectron spectroscopy

A series of saccharides, including several monohydrates and one amorphous phase, has been investigated by XPS, providing the first database of survey and high‐resolution spectra for this class of compounds. Known stoichiometries and XPS‐determined elemental compositions agree well. XPS has sufficient precision for distinguishing the stoichiometries of mono‐, di‐, and polysaccharides. The C 1s chemical shifts of the acetal and alcohol groups are similar for all samples, albeit with slight binding energy increases in the series from mono‐ to di‐ and polysaccharides. Increasing X‐ray exposure causes a radiation‐induced increase of the aliphatic hydrocarbon emission at 285 eV, concomitant with the appearance of a high binding energy C 1s emission peak at 289.1 eV and a decrease in the O 1s/C 1s emission intensity ratio. Formation of aliphatic hydrocarbon groups is proposed to arise from dehydroxylation, while the increase in the 289.1 eV peak can be attributed to double dehydroxylation at the C₁ position or partial oxidation of an alcohol or acetal group. The rate of radiation damage correlates with previously reported rates of thermally induced caramelization. Copyright © 2009 John Wiley & Sons, Ltd.     

Use of local rank‐based spatial information for resolution of spectroscopic images

Spectroscopic images are singular chemical measurements that enclose chemical and spatial information about samples. Resolution of spectroscopic images is focused on the recovery of the pure spectra and distribution maps of the image constituents from the sole raw spectroscopic measurement. In image resolution, constraints are generally limited to non‐negativity and the spatial information is generally not used. Local rank analysis methods have been adapted to describe the local spatial complexity of an image, providing specific pixel information. This local rank information combined with reference spectral information allows the identification of absent compounds in pixels with low compound overlap. The introduction of this information in the resolution process under the form of constraints helps to increase the performance of the resolution method and to decrease the ambiguity linked to the final solutions. Copyright © 2008 John Wiley & Sons, Ltd.