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Eingeladener Vortrag
- nein (9)
Carbohydrate films on gold based on dimannoside thiols (DMT) were prepared, and a complementary surface chemical analysis was performed in detail by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), near-edge X-ray absorption fine structure (NEXAFS), FT-IR, and contact angle measurements in order to verify formation of ω-carbohydrate-functionalized alkylthiol films. XPS (C 1s, O 1s, and S 2p) reveals information on carbohydrate specific alkoxy (C–O) and acetal moieties (O–C–O) as well as thiolate species attached to gold. Angle-resolved synchrotron XPS was used for chemical speciation at ultimate surface sensitivity. Angle-resolved XPS analysis suggests the presence of an excess top layer composed of unbound sulfur components combined with alkyl moieties. Further support for DMT attachment on Au is given by ToF-SIMS and FT-IR analysis. Carbon and oxygen K-edge NEXAFS spectra were interpreted by applying the building block model supported by comparison to data of 1-undecanethiol, poly(vinyl alcohol), and polyoxymethylene. No linear dichroism effect was observed in the angle-resolved C K-edge NEXAFS.
We investigated the ageing of amine-terminated
self-assembled monolayers (amine-SAMs) on different silica
substrates due to exposure to different ambient gases,
pressures, and/or temperatures using time-of-flight secondary
ion mass spectrometry (ToF-SIMS) with principal component
analysis and complementary methods of surface
analysis as X-ray photoelectron spectroscopy (XPS) and
near edge X-ray absorption fine structure (NEXAFS). The
goal of this study is to examine the durability of primary
amine groups of amine-SAMs stored in a user laboratory
prior to being used as supports for biomolecule immobilization
and other applications. We prepared amine-SAMs on
the native oxides of silicon wafers and glass slides using 3-
aminopropyl triethoxysilane, by using optimized conditions
such as anhydrous organic solvent and reaction time scale of
hours to avoid multilayer growth. Selected commercial
amine-SAM slides have been investigated, too. When the
amine-SAMs are exposed to air, oxygen incorporation
occurs, followed by formation of amide groups. The formation
of oxygen species due to ageing was proved by ToFSIMS,
XPS, and NEXAFS findings such as CNO- secondary
ion emission at m/z 42, observation of the N 1s HNC=O
component peak at 400.2400.3 eV in XPS, and, last but not
least, by formation of a π*(HNC=O) resonance at 401 eV in
the N K-edge X-ray absorption spectrum. It is concluded
that the used multi-method approach comprising complementary
ToF-SIMS, XPS, and NEXAFS analyses is well
suited for a thorough study of chemical aspects of ageing
phenomena of amine-SAM surfaces.
Functionalised surfaces are of interest in many fields, e.g. in biomedicine, materials science and molecular electronics. In this study a series of self-assembled aliphatic and aromatic monolayers on gold substrates with terminal amino groups was investigated. Four different thiol molecules were used: aliphatic 11-aminoundecane-1-thiol (AUDT), aromatic 4-aminobenzenethiol (ABT) and aromatic ω-amino thiols with an alkyl spacer as 4-aminophenylbutane-1-thiol (APBT) and 3-(4''-amino-1,1':4',1''-terphenyl-4-yl)propane-1-thiol (ATPT). Evaluation of N 1s XPS data revealed that on the aromatic self-assembled monolayers (SAMs) amino groups exist preferentially as primary amines, whereas on the aliphatic SAM protonated and/or hydrogen-bonded amines are the major species. This result is crosschecked by N K edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy and can be rationalised by the different basicity of aliphatic and aromatic amines.
The chemical composition of the functional surfaces of substrates used for microarrays is one of the important parameters that determine the quality of a microarray experiment. In addition to the commonly used contact angle measurements to determine the wettability of functionalized supports, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) are more specific methods to elucidate details about the chemical surface constitution. XPS yields information about the atomic composition of the surface, whereas from ToF-SIMS, information on the molecular species on the surface can be concluded. Applied on printed DNA microarrays, both techniques provide impressive chemical images down to the micrometer scale and can be utilized for label-free spot detection and characterization. Detailed information about the chemical constitution of single spots of microarrays can be obtained by high-resolution XPS imaging.
Catalyst characterization
(1998)
Catalyst characterization
(2009)
Cr2O3, CrCl3, α-CrF3, CrF3·3H20 and Cr(OH)3 were investigated by x-ray photoelectron (XPS) and x-ray excited Auger electron spectroscopy (XAES) using a latest generation XPS spectrometer. Non-conductive powders are analyzed with ultimate energy resolution. Multiplet splitting features and/or satellite emission were observed in the Cr 2p and Cr 3s spectra. Cr(III) compounds are of interest in many applications as for example in corrosion and catalysis. Chromia and chromium-III-fluoride activated by reaction with fluoroalkanes are very promising industrial catalysts. It is the aim of this selection of spectral reference data to enable deeper insight in the formation of catalytically active fluorinated chromia phases by using XPS analysis.
We present a new synchrotron X-ray photoelectron spectroscopy strategy for surface chemical analysis of materials. Our approach is based on the acquisition of photoelectron spectra at constant kinetic energies with the help of a tunable synchrotron X-radiation source. This ensures both constant and tunable information depth for all elements in a very thin organic layer. Many of the problems known to XPS depth profiling using laboratory equipment are thereby avoided. Using our methodology, the 95% information depth, z95%, can be tuned down to about 0.7 nm in organic materials. The upper limit in our study at the HE-SGM monochromator dipole magnet beamline at the synchrotron radiation source BESSY II is about 4.3 nm. Elemental quantification is achieved through relative sensitivity factors (RSF) specific to the measurement conditions, determined either with the help of calculated photoionization cross sections and inelastic mean free paths or experimentally. The potential of the technique is demonstrated for the in-depth analysis of plasma deposited nitrogen-rich organic thin films used in biomedical applications.
The chemical and microstructural changes occurring during braking simulation tests at the surface of a conventional brake pad material were investigated mainly by scanning and transmission electron microscopy and surface analytical techniques. It can be shown that patches of a third body material develop, comprising a compositional mix of all constituents of the pad and iron oxides from the disk. Milled debris particles still have the crystal structure of barite, the major phase of the pad material, but the grain size is reduced drastically to the nanometer scale. The major wear mechanism is delamination of filler particles from the organic binder, supported by local degradation of the phenolic resin during asperity heating. Quartz crystals are preserved thereby adopting the function of primary contact areas.
Nitrogen rich plasma polymer films (L-PPE:N) were prepared by low-pressure RF plasma using a 1:1 mixture of ethylene and ammonia and aged for 345 d in four different ambient conditions: (i) at room temperature (RT) in air; (ii) at RT in nitrogen; (iii) at -20?°C in air and; (iv) at –20 °C in nitrogen. The films were analyzed by X-ray photoelectron spectroscopy (XPS) and by time-of-flight secondary ion mass spectrometry (ToF-SIMS) at various intervals over the duration of the experiment. The ageing of primary amines, NH2, was followed by chemical derivatization with 4-trifluoromethyl benzaldehyde. Storage at –20 °C, mostly independently of ambient atmosphere, slowed down ageing to almost undetectable levels as evaluated by the analytical methods used for this study.
Results are reported from a pilot study under the Consultative Committee for Amount of Substance (CCQM) to compare measurements of and resolve any relevant measurement issues in, the amount of thermal SiO2 oxide on (100) and (111) orientation Si wafer substrates in the thickness range 1.5 - 8 nm. As a result of the invitation to participate in this activity, 45 sets of measurements have been made in different laboratories using 10 analytical methods: medium-energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), RBS, elastic backscattering spectrometry (EBS), XPS, SIMS, ellipsometry, grazing-incidence x-ray reflectrometry (GIXRR), neutron reflectometry and transmission electron microscopy (TEM). The measurements are made on separate sets of 10 carefully prepared samples, all of which have been characterised by a combination of ellipsometry and XPS using carefully established reference conditions and reference parameters.
The results have been assessed against the National Physical Laboratory (NPL) data and all show excellent linearity. The remaining data sets correlate with the NPL data with average root-mean-square scatters of 0.15 nm, half being better than 0.1 nm and a few at or better than 0.05 nm. Each set of data allows a relative scaling constant and a zero thickness offset to be determined. Each method has an inherent zero thickness offset between 0 nm and 1 nm and it is these offsets, measured here for the first time, that have caused many problems in the past. There are three basic classes of offset: water and carbonadeous contamination equivalent to ~1 nm as seen by ellipsometry; adsorbed oxygen mainly from water at an equivalent thickness of 0.5 nm as seen by MEIS, NRA, RBS and possibly GIXRR; and no offset as seen by XPS using the Si 2p peaks. Each technique has a different uncertainty for the scaling constant and consistent results have been achieved. X-Ray photoelectron spectroscopy has large uncertainties for the scaling constant but a high precision and, critically, if used correctly, has zero offset. Thus, a combination of XPS and the other methods allows the XPS scaling constant to be determined with low uncertainty, traceable via the other methods. XPS laboratories returning results early were invited to test a new reference procedure. All showed very significant improvements. The reference attenuation lengths thus need scaling by 0.986 ± 0.009 (at an expansion factor of 2) deduced from the data for the other methods. Several other methods have small offsets and, to the extent that these can be shown to be constant or measurable, then these methods will also show low uncertainty. Recommendations are provided for parameters for XPS, MEIS, RBS and NRA to improve their accuracy.
The determination of amino groups on surfaces capable of binding biomolecules is important for the understanding and optimization of technologically relevant coupling processes. In this study, three different types of amino-functionalized model surfaces, amino thiolate on Au, amino siloxane on Si, and polyethylene (PE) foils and films reacted with 1,2-diaminoethane (DAE) were derivatized with 3,5-bis(trifluoromethyl)phenyl isothiocyanate. Subsequently, these samples were analyzed by chemical derivatization X-ray photoelectron spectroscopy (CD-XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The determination of amino groups by this analytical approach allows gaining insight into the availability of groups on surfaces that can actually serve as attachment sites for biomolecules in technical applications. In the case of the amino thiolate on Au, almost 90% of the expected amino groups were detected by CD-XPS. Investigation of the amino siloxane films revealed lower yields for the derivatization reaction in the order of 30%. The lowered reaction yields are thought to be due to interactions between the amino siloxane`s amino and silanol groups or the underlying substrate, making them inaccessible to the derivatization agent. The aminated PE samples are characterized by a complex surface chemistry and structure, and reaction yields of the derivatization reaction cannot be unequivocally derived. However, 1-3% of the total carbon atoms in the surface layer were found to be bound to amino groups accessible to the derivatization agent. It can be concluded that, depending on the detailed character of the investigated amino-terminated surface, the amount of amino groups accessible to CD-XPS can be substantially lower than the total amount of amino groups present at the surface.
A first inter-laboratory comparison was conducted to demonstrate and document the capability of interested laboratories to measure the fraction of C—OH species on a plasma oxidised poly(propylene) sample by using a chemical derivatisation XPS approach. This report presents the results from that inter-laboratory comparison and includes the data received for the measured values and their associated standard deviations of laboratory means, at a 95% confidence level. The measurements were guided by a protocol developed within the group before and summarised shortly in the paper. Standard deviations that may characterise the state-of-the-art for the nominally simple and rather often practised case of TFAA chemical derivatisation XPS of C—OH species on a plasma oxidised polyolefin surface are calculated following ISO 5725-2:1994. The main conclusion is that the associated degree of equivalence reached by the participating laboratories in this comparison is still low. Further research to improve chemical derivatisation XPS protocols is mandatory.
The wettability of the surfaces inside the microchannels of a microfluidic device is an important property considering a liquid flows through them. Contact angle measurements usually applied to test the wettability of surfaces cannot be used for an analysis of microchannel walls within microfluidic devices. A workaround is the use of surface analytical methods, which are able to reach points of interest in microchannels and may provide information on the surface chemistry established there. In calibrating these methods by using flat polymer wafers, where the contact angle can be measured as usual, data measured in real microchannels can be evaluated in terms of wetting properties. Reference wafers of bisphenol-A polycarbonate, a polymeric material that is often used in fluidic microdevice fabrication, were treated under different oxygen plasma conditions. The modified surfaces were characterized by using XPS, time of flight (ToF)-SIMS and atomic force microscope (AFM). Surface chemistry and surface topography have been correlated with contact angle measurements. In addition, effects of ageing or rinsing after plasma treatment have also been investigated.
Methods for characterization of epoxy-functionalized substrates used for microarray applications, prepared by silanization with 3-glycidoxypropyltrimethoxysilane, have been developed. Contact angle measurements, X-ray photoelectron spectroscopy, time of flight secondary ion mass spectrometry and fluorescence based methods have been applied to investigate these epoxy-functionalized microarray substrates. The surface density of epoxy-functionalized glass slides was investigated by fluorescence labeling of surface species utilizing Rhodamine 110 as fluorescence probe.
An electron effective attenuation length (EAL) of 1.68nm for Al Kα excited Pd 3d 5/2 photoelectrons with a kinetic energy of 1.152 keV has been determined experimentally using a sputtered Pd film deposited on an ultra flat fused quartz substrate. The film thickness was reduced by Ar ion sputtering several times in order to obtain different Pd film thicknesses which are used to determine experimental EAL values. These results are compared to data generated by using a Simulation of Electron Spectra for Surface Analysis (SESSA) simulation using an inelastic mean free path (IMFP) calculated with the Tanuma–Powell–Penn (TPP)-2M formula and with ‘elastic scattering on and off’. Contributions to the uncertainty budget related to the experimental approach are discussed in detail. Proposals on how to further improve the approach are suggested.
The Key Comparison K67 and the parallel Pilot Study P108 on quantitative analysis of thin alloy films have been completed in the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The aim of these inter-laboratory comparisons is to determine the degree of equivalence in the measurement capability of national metrology institutes (NMIs) and designated institutes (DIs) for the determination of the composition of thin alloy films. The measurand is expressed in atomic percent. A Fe-Ni alloy film with a certified composition was available for the participants of the inter-laboratory comparison. It has been used as a reference specimen to determine the relative sensitivity factors (RSF) of Fe and Ni for the different analytical methods used by the participants to determine the composition of the test sample. As was shown in the preceding Pilot Study P98, the degrees of equivalence in the measurement capabilities of the participants can be improved in that way. The composition of the reference specimen was certified by inductively coupled plasma mass spectrometry (ICP-MS) using the isotope dilution method. The in-depth and lateral homogeneity, determined in terms of elemental composition, of the certified reference sample and the unknown test sample were confirmed by secondary ion mass spectrometry (SIMS) using C60 primary ions by the leading laboratory. Five laboratories participated in the key comparison. Four of them used x-ray photoelectron spectroscopy (XPS) and one Auger electron spectroscopy (AES). One laboratory participated in the parallel P108 pilot study using electron probe micro analysis with an energy-dispersive spectrometer (ED EPMA) and XPS.
In this study, epoxy-terminated silicon oxide surfaces were chemically derivatized with trifluoroacetic anhydride (TFAA) and 4-(trifluoromethyl)-benzylamine (TFMBA) and analyzed by X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and water contact angle measurements. TFAA was used for quantitative derivatization to determine the amount of reactive epoxy groups on these surfaces. Furthermore, epoxy-terminated surfaces were derivatized with TFMBA (a model compound for biomolecules with an amino linker) yielding secondary amines because of formation of covalent C–N bonds between TFMBA and the epoxy films. Fluorine being part of TFAA and TFMBA composition was used to follow the progress of the chemical derivatization reaction. Both derivatization agents – TFAA and TFMBA – gave comparable reaction yields of ~60% on epoxy silicon surfaces, whereas on epoxy glass slides, the derivatization yields were considerably lower (30–40%).The protocol for attachment of TFMBA (model compound) on epoxy-modified surfaces was adapted to (bio)molecules with an amino linker, e.g. carbohydrates to prepare carbohydrate-functionalized biointerfaces.
The combination of complementary characterization techniques such as SEM (Scanning Electron Microscopy), T-SEM (Scanning Electron Microscopy in Transmission Mode), EDX (Energy Dispersive X-ray Spectroscopy) and SAM (Scanning Auger Microscopy) has been proven to be a powerful and relatively quick characterization strategy for comprehensive morphological and chemical characterization of individual silica and titania nanoparticles. The selected real life test materials, silica and titania, are listed in the OECD guidance manual as representative examples because they are often used as commercial nanomaterials. Imaging by high resolution SEM and in the transmission mode by T-SEM allows almost simultaneous surface and in-depth inspection of the same particle using the same instrument. EDX and SAM enable the chemical characterization of bulk and surface of individual nanoparticles. The core–shell properties of silica based materials are addressed as well. Titania nominally coated by silane purchased from an industrial source has been found to be inhomogeneous in terms of chemical composition.
Different, partly complementary and partly redundant characterization methods were applied to study the transition of magnetite, graphite and MoS2 powders to mechanically alloyed nanostructures. The applied methods were: Transmission electron microscopy (TEM), Mössbauer spectroscopy (MS), Raman spectroscopy (RS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The main objective was to prepare a model material providing the essential features of a typical tribofilm forming during automotive braking, and to assess the impact of different constituents on sliding behaviour and friction level. Irrespective of the initial grain size, the raw materials were transferred to a nanocrystalline structure and mixed on a nanoscopic scale during high energy ball milling. Whereas magnetite remained almost unchanged, graphite and molybdenum disulphide were transformed to a nanocrystalline and highly disordered structure. The observed increase of the coefficient of friction was attributed to a loss of lubricity of the latter ingredient due to this transformation and subsequent oxidation.
An international interlaboratory comparison of the measurement capabilities of four National Metrology Institutes (NMIs) and one Designated Institute (DI) in the determination of the chemical composition of thin Fe-Ni alloy films was conducted via a key comparison (K-67) of the Surface Analysis Working Group of the Consultative Committee for Amount of Substance. This comparison was made using XPS (four laboratories) and AES (one laboratory) measurements. The uncertainty budget of the measured chemical composition of a thin alloy film was dominated by the uncertainty of the certified composition of a reference specimen which had been determined by inductively coupled plasma mass spectrometry using the isotope dilution method. Pilot study P-98 showed that the quantification using relative sensitivity factors (RSFs) of Fe and Ni derived from an alloy reference sample results in much more accurate result in comparison to an approach using RSFs derived from pure Fe and Ni films. The individual expanded uncertainties of the participants in the K-67 comparison were found to be between 2.88 and 3.40 atomic %. The uncertainty of the key comparison reference value (KCRV) calculated from individual standard deviations and a coverage factor (k) of 2 was 1.23 atomic %.
Functionalized organic layers prepared by plasma processes have complex surface chemistries. The problem of elucidating such chemistries is an extensively studied subject. One of the preponderant methods used to acquire information on specific functional groups is chemical derivatization XPS. In this communication, we focus on rather popular chemical derivatization XPS approaches, for instance, the quantification of amines with 4-trifluoromethyl benzaldehyde and of hydroxyl groups with trifluoroacetic anhydride. Although these procedures have been used for a long period by various laboratories, the use of varying protocols is obvious. Comparison of results is therefore difficult. We discuss steps toward a valid experimental procedure, in particular, the calculation of concentrations, the preparation of test samples, the pitfalls, and the shortcomings.
A novel coordination oligo/polymer is synthesized by metal-directed self-assembly from equimolar amounts of the (dppp)M(OTf)2 precursor complexes (dppp = bis-(diphenylphosphino)-propane, OTf = triflate; M = PdII or M = PtII) and banana-shaped bidentate dipyridyl ligands. The assemblies were characterized by ESI mass spectrometry and NMR spectroscopy. The analysis of the cloudy suspension prepared by dissolving the coordination polymer in aqueous methanol solutions indicates nanosized spherical objects to form. Evidence for vesicle formation from these metallo-supramolecular oligomers comes from (cryogenic) transmission electron microscopy (TEM, cryo-TEM). Atomic force microscopy revealed stable nanospheres on hydrophilic mica and monolayer formation on hydrophobic highly oriented pyrolitic graphite (HOPG) substrates. On mica, also torus-shaped object were observed, which are rationalized by vesicles that opened during the drying procedure and released the internal solvent. Elemental analysis of the nanoassemblies by X-ray photoelectron spectroscopy (XPS) indicates uncoordinated and coordinated pyridines in the coordination polymers that form the nanospheres. Various control experiments using different metal centers and modified ligands support the conclusions.
A combined XPS, NEXAFS, and ToF-SIMS chemical surface characterization of carbohydrate-functionalized gold and glass surfaces is presented. Spot shape and chemical composition across a spot surface are provided by surface-sensitive methods as ToF-SIMS and XPS, used in their imaging modes. Moreover, the feasibility of this multimethod approach to control relevant production steps of a carbohydrate microarray prototype is demonstrated.
Neues vom Urkilogramm
(1999)
Reference materials without variations in topography are essential for the characterization of imaging XPS (X-ray Photoelectron Spectroscopy) Instruments. Therefore a new fabrication process for this kind of zero-topography reference material was developed at PTB and resulted in first prototypes. The fabrication process and first measurement results will be presented in this paper.
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 COR/Csum ratios. However, the X-ray degradation indices are definitely higher than those of conventional reference polymers. Moreover, the COR/Csum 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.
Plasma-Polymerized C60 Films
(2001)
We studied the polymerization of C60 under different Ar plasma conditions. Films were either deposited in the pressure range between 1.3 and 40 Pa applying input power of 50 W or evaporated C60 films were exposed to Ar plasma of 30 and 50 W. The films were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and carbon K near-edge X-ray-absorption fine structure spectroscopy (NEXAFS). The films were non-uniform and consisted of unpolymerized C60, dimers, linear chains and polymeric planes. In comparison with evaporated C60 the XPS C 1s peak is broader and asymmetric for the C60 polymer and its shake-up satellites diminished. Furthermore, the features of the valence band as well as the features of the p * antibonding orbitals of the C60 polymer are broader and reduced in intensity.
Die Akkreditierung für Prüfverfahren in der Oberflächenanalytik wird gemeinhin als sehr schwierig angesehen. Durch das unlängst eingeführte flexible Konzept der Akkreditierung, auch Prüfartenakkreditierung genannt, eröffnen sich nunmehr neue Möglichkeiten. Aus dem Bereich des Normenwesens in der Oberflächenanalytik erhalten die Prüflaboratorien zusätzliche Unterstützung. Die Validierung von ESCA-Prüfverfahren und ein wohldokumentiertes Prüfmittelmanagement sind weitere Bausteine auf dem Weg zur erfolgreichen Akkreditierung. Oberflächenanalyseverfahren sind akkreditierfähig.
Results of an interlaboratory comparison of XPS data obtained with stainless steel are presented. Only one photoelectron spectrometer model was used. The stainless-steel sample surfaces were analysed in different states by XPS: as received, after sputtering to I(C 1s)/I(Fe 2p3/2) 0.025 and after removing a chromium-enriched oxide layer following a certain protocol. The Fe, Cr and Ni elemental concentrations were evaluated from the respective XPS data submitted by the participants of the interlaboratory test experiment. Total means, repeat standard deviations (sr) and reproducibility standard deviations (sR) are presented. The best reproducibility standard deviations were obtained for the XPS analysis after removal of a chromium-enriched oxide layer and quantification of the XPS intensities without taking the contamination elements of carbon and oxygen into account. The absolute reproducibility standard deviation of the elemental concentrations in that case is as small as 1.1-1.5 at.%. This gives 2%, 6% and 16% for the relative reproducibility standard deviation of the concentrations of iron, chromium and nickel, respectively. The total means of the iron, chromium and nickel concentrations finally obtained agree within 2sR with bulk values determined by wavelength-dispersive x-ray fluorescence spectroscopy. Comparison to an earlier interlaboratory test experiment shows that using only one model of photoelectron spectrometer reduces the reproducibility standard deviations efficiently. Copyright © 2002 John Wiley & Sons, Ltd.
Self-assembled monolayers of aromatic omega-aminothiols on gold: surface chemistry and reactivity
(2010)
Amino-terminated self-assembled monolayers on gold substrates were studied by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) measurements, and atomic force microscopy (AFM). Two different ω-amino-4,4'-terphenyl substituted alkanethiols of the general structure H2N-(C6H4)3-(CH2)n-SH (ATPn) were used: 2-(4''-amino-1,1':4',1''-terphenyl-4-yl)ethane-1-thiol (n = 2, ATP2) and 3-(4''-amino-1,1':4',1''-terphenyl-4-yl)propane-1-thiol (n = 3, ATP3). Moreover, the addressability of amino groups within the films was investigated by chemical derivatization of ATPn SAMs with 3,5-bis(trifluoromethyl)phenyl isothiocyanate (ITC) forming fluorinated thiourea ATPn-F films. Evaluation of high-resolution C 1s and N 1s XPS data revealed successful derivatization of at least 50% of surface amino species. Furthermore, it could be demonstrated by angle-resolved NEXAFS spectroscopy that chemical derivatization with ITC has no noticeable influence on the preferential upright orientation of the molecules in the SAMs.
Elastomeric sealants may contain organic silicon compounds. The use of these sealants for housings for electronic components is harmful for the reliability of electric contacts inside. In order to prevent electronic components from malfunction, quality control of elastomeric sealants is required. An analytical procedure developed to fulfil this requirement was developed. It is based on electron spectroscopy for chemical analysis (ESCA). Information on the silicon compounds existing at the surface of elastomeric sealants is provided by this method. Silicon in organic and inorganic compounds can be differentiated with the help of Si 2p photoelectron spectra. Quantitative results can be obtained too. The uncertainty budget of the quantitative procedure is estimated.
AZ31 Mg alloy sheet was welded using a gas-tungsten arc (GTA) process over inserts containing 2.3-9.3 wt.% Al. The welded specimens were susceptible to SCC in distilled water, with susceptibility increasing with decreasing weld metal Al (or β particle) concentration. Primary stress corrosion cracks initiated at the weld metal-HAZ interface by stress-assisted localised dissolution and propagated through the weld and base metals by transgranular and intergranular H-assisted fracture (TG-HAF and IG-HAF) respectively. The IG fracture mode may be intrinsic to the texture imparted upon the base metal by rolling. The increase in SCC susceptibility with decreasing weld metal Al concentration is contrary to the purported roles of β particles in promoting localised corrosion and as crack nucleation sites, but corresponds with increases in weld - base metal galvanic current density and weld metal localised corrosion susceptibility.
Microarrays are a versatile platform for diagnostics and high-throughput analysis. Carbohydrate microarrays are valuable tools to investigate interactions with other molecules since many glycans are involved in fundamental biological processes. A combined X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) surface analysis was used to investigate the basic steps in the production of carbohydrate microarrays. The preparation included coupling of a thiol-terminated mannoside to maleimide-functionalized glass surfaces derived from γ-aminopropyl silane (GAPS) slides. XPS results clearly demonstrate successful chemical modification in each fabrication step, and ToF-SIMS imaging revealed immobilized carbohydrates in the spotted regions of the final microarray.
Recently, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) instrumentation has been used to address areas of interest within micro-fluidic devices providing full access to the surface chemistry established at the bottom of micro-channels therein. After careful calibration, information on surface chemistry as obtained by ToF-SIMS or XPS can be interpreted in terms of wettability expressed as contact angles which are then characteristic for the inner walls of micro-channels. Standard contact angle measurement is not applicable in micro-channels. The approach has been demonstrated to be successful with two different micro-fluidic devices hot embossed into high-end quality poly(methyl methacrylate) (PMMA) or Polycarbonate wafers. A pre-selected surface chemistry at micro-channel walls can be established by plasma technologies but ageing and rinsing effects have to be under control. A combination of ToF-SIMS, XPS and contact angle measurement techniques has been demonstrated to provide the required information. Finally, it is shown by ToF-SIMS and XPS analysis that in the production of micro-fluidic parts during practical processing using hot embossing technologies, material originating from cover foils will reside on the polymer wafer's surface. Moreover, residues of releasing agents as silicone oil used during processing can be detected by ToF-SIMS. Both cover foil residues and silicones are issues of trouble shooting in micro-fluidics because they will change contact angles efficiently.
Self-assembled octadecyltrichlorosilane (CH3(CH2)17SiCl3, OTS) films were deposited on an oxidized silicon wafer. They were carefully exposed to a low-pressure oxygen direct current (dc) plasma and/or Cr vapor. Subsequently, they were characterized by X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and atomic force microscopy. Detailed information on the oxygen functionalization and the molecular conformation of the OTS films was obtained. The main result was that functionalization conditions can be found where the order of the film remains almost unaffected. Similarly, Cr evaporation of pure OTS films revealed only slight effects on the order in the film. Cr evaporation of an ordered but functionalized OTS film immediately changes its state toward a fully isotropic one. In the course of interaction, oxygen sites at the surface of the functionalized OTS film are reduced whereas Cr becomes oxidized. A redox reaction scheme is proposed for this interfacial reaction. Finally, it is concluded that the given study should be of importance for advanced plasma processing of polyolefins.
Organic thin films with defined chemical structures and physical properties are required for various applications. Plasma polymerization is of technological interest, since the deposition of plasma polymers is possible on any material of any shape in the desired thickness. We report on the TOF-SIMS (TOF: time-of-flight) and XPS investigations of pulse plasma poly(acetylene) and alkali metal doped pulse plasma poly(acetylene) films. The combination of TOF-SIMS and XPS supplies detailed information on the surface chemistry of these films. Application of both methods provides the possibility for cross-checking certain results. Moreover the different sensitivities of the methods can be utilized. According to the TOF-SIMS and XPS data it can be concluded that the interaction of alkali metals with plasma poly(acetylene) results in electrovalent bonds of the type Me?+C?- between carbon and metal. Furthermore carbonoxygenmetal interactions were observed. These interactions are of the type C=O?-cdots, three dots, centeredMe?+ and/or CO?-Me?+.
Nitrogen (N)-rich organic thin films were deposited using both low-pressure plasma- and vacuum-ultraviolet-based techniques, from mixtures of ammonia (NH3) and ethylene (C2H4). These films were investigated using angle-resolved and excitation energy resolved X-ray photoelectron spectroscopy (ARXPS and ERXPS, respectively) in order to determine their sub-surface chemical profiles. These two techniques enable one to tune the “XPS 95%” information depth, z 95%, by varying either the angle or the excitation energy. Using a combination of both techniques, z 95% can be varied continuously from 0.7 to 11 nm. The surface-near chemistry is investigated using both high-resolution C 1s spectra and elemental concentrations derived from elemental peak intensities. Results show that while laboratory XPS, and even ARXPS, suggest homogenous surface chemistries, the novel combination of ARXPS and ERXPS points to the existence of a compositional profile in the extreme outer surface layer. Our conclusions are supported by simulations using SESSA software.
Results from a study conducted between National Metrology Institutes (NMIs) for the measurements of the absolute thicknesses of ultra-thin layers of SiO2 on Si are reported. These results are from a key comparison and associated pilot study under the auspices of the Consultative Committee for Amount of Substance. ´Amount of substance´ may be expressed in many ways, and here the measurand is the thickness of the silicon oxide layers with nominal thicknesses in the range 1.5-8 nm on Si substrates, expressed as the thickness of SiO2. Separate samples were provided to each institute in containers that limited the carbonaceous contamination to approximately < 0.3 nm. The SiO2 samples were of ultra-thin on (100) and (111) orientated wafers of Si. The measurements from the laboratories which participated in the study were conducted using ellipsometry, neutron reflectivity, X-ray photoelectron spectroscopy or X-ray reflectivity, guided by the protocol developed in an earlier pilot study. A very minor correction was made in the different samples that each laboratory received. Where appropriate, method offset values attributed to the effects of contaminations, from the earlier pilot study, were subtracted. Values for the key comparison reference values (agreed best values from a Consultative Committee study) and their associated uncertainties for these samples are then made from the weighted means and the expanded weighted standard deviations of the means of these data. These results show a dramatic improvement on previous comparisons, leading to 95% uncertainties in the range 0.09-0.27 nm, equivalent to 0.4-1.0 monolayers over the 1.5-8.0 nm nominal thickness range studied. If the sample-to-sample uncertainty is reduced from its maximum estimate to the most likely value, these uncertainties reduce to 0.05-0.25 nm or ~1.4% relative standard uncertainties. The best results achieve ~1% relative standard uncertainty. It is concluded that XPS has now been made fully traceable to the SI, for ultra-thin thermal SiO2 on Si layers, by calibration using wavelength methods in an approach that may be extended to other material systems.
Overlayers of SiO2 (nominally 4, 6 and 8 nm thick) on silicon, prepared by thermal oxidation, were investigated using x-ray photoelectron spectroscopy (XPS). The thickness of these overlayers was obtained from a measurement of the photoelectron intensities originating from the substrate and the oxide overlayer by applying an appropriate quantitative model. The uncertainty budget of that thickness measurement method is given. The relative combined standard uncertainty of the method was found to be 15%. The effective attenuation lengths or the corresponding electron inelastic mean free paths are of considerable importance for both the estimated values of overlayer thickness and combined standard uncertainties. The XPS results were compared with ellipsometry data.
First results of an inter-laboratory comparison (27 participants in Europe, Japan and USA) of XPS data obtained with non-conducting samples are presented. Binding energies of Al 2s for alumina, N 1s and imide C 1s for Kapton and Sr 3p3/2 for a strontium titanate film on glass were obtained after static charge referencing with the help of 15 nm gold particles deposited at the surface of the test samples. For the alumina sample C 1s static charge referenced data are also presented. Repeat standard deviations (sr), between standard deviations (sb), reproducibility standard deviations (sR) and total means are evaluated from the experimental data. It can be stated that although the repeat standard deviation is as small as 0.05 eV in the best case, the standard deviation characterizing the reproducibility of the method is obviously not better than 0.15 eV in the best case at the present time. The knowledge of these standard deviations is important for metrology, validations of analytical procedures relying on qualitative photoelectron spectroscopy and XPS databanking.
The chemical constitution of functionalized supports is an important parameter that determines their performance in a broad range of applications, e.g. for immobilization of biomolecules. Supports with amino functionalized surfaces are also often used for DNA microarray experiments. However, spectral data which have been reported for surfaces with amino functionalities suffer from some inconsistencies. In this article a detailed XPS (X-ray photoelectron spectroscopy) and NEXAFS (Near edge X-ray absorption fine structure) database for amino functionalized surfaces is presented. Amino-terminated surfaces prepared from aliphatic and aromatic aminosilanes or aminothiols and a field sample are considered. Effects of aging in air and damage by radiation are addressed as well.