Imaging XPS Research Articles

Spatial resolution in X-ray photoelectron spectroscopy

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Drummond I. W. 1996Spatial resolution in X-ray photoelectron spectroscopyPhil. Trans. R. Soc. A.3542667–2682http://doi.org/10.1098/rsta.1996.0122SectionRestricted accessArticleSpatial resolution in X-ray photoelectron spectroscopy I. W. Drummond Google Scholar Find this author on PubMed Search for more papers by this author I. W. Drummond Google Scholar Find this author on PubMed Search for more papers by this author Published:15 November 1996https://doi.org/10.1098/rsta.1996.0122AbstractX-ray photoelectron spectroscopy (XPS) is a well established surface analytical technique capable of giving elemental and chemical state information for nearly all elements. Recent improvements in the sensitivity of the method have made spatially resolved XPS a viable technique with, at present, a resolution of 5-30 μm in commercial instrumentation. The different methods are described and their application to semiconductor devices and materials is outlined with reference to spatial resolution and information in depth. Future prospects for imaging XPS are briefly discussed.FootnotesThis text was harvested from a scanned image of the original document using optical character recognition (OCR) software. As such, it may contain errors. Please contact the Royal Society if you find an error you would like to see corrected. Mathematical notations produced through Infty OCR. Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Kersell H, Falling L, Shavorskiy A and Nemšák S (2021) Some Future Perspectives in Ambient Pressure X-ray Spectroscopies: Atmospheric Pressure, Spatially Resolved and Multi-modal Experiments Ambient Pressure Spectroscopy in Complex Chemical Environments, 10.1021/bk-2021-1396.ch014, (333-358) Nguyen L, Tao P, Liu H, Al-Hada M, Amati M, Sezen H, Tang Y, Gregoratti L and Tao F (2018) Studies of surface of metal nanoparticles in a flowing liquid with XPS, Chemical Communications, 10.1039/C8CC03497D, 54:71, (9981-9984) Scheithauer U, Kolb M, Kip G, Naburgh E and Snijders J (2016) Round robin: Quantitative lateral resolution of PHI XPS microprobes Quantum 2000/Quantera SXM, Journal of Electron Spectroscopy and Related Phenomena, 10.1016/j.elspec.2016.04.007, 210, (13-15), Online publication date: 1-Jul-2016. Béchu S, Richard-Plouet M, Fernandez V, Walton J and Fairley N (2016) Developments in numerical treatments for large data sets of XPS images, Surface and Interface Analysis, 10.1002/sia.5970, 48:5, (301-309), Online publication date: 1-May-2016. Scheithauer U (2014) Characterization of the primary X-ray source of an XPS microprobe Quantum 2000, Journal of Electron Spectroscopy and Related Phenomena, 10.1016/j.elspec.2014.03.009, 193, (58-62), Online publication date: 1-Mar-2014. Wolstenholme J (2008) Summary of ISO/TC 201 Standard: XXX. ISO 18516: 2006-Surface chemical analysis-Auger electron spectroscopy and X-ray photoelectron spectroscopy-Determination of lateral resolution, Surface and Interface Analysis, 10.1002/sia.2771, 40:5, (966-968), Online publication date: 1-May-2008. Blomfield C (2005) Spatially resolved X-ray photoelectron spectroscopy, Journal of Electron Spectroscopy and Related Phenomena, 10.1016/j.elspec.2004.09.026, 143:2-3, (241-249), Online publication date: 1-May-2005. Vancso G, Hillborg H and Schönherr H (2005) Chemical Composition of Polymer Surfaces Imaged by Atomic Force Microscopyand Complementary Approaches Polymer Analysis Polymer Theory, 10.1007/b135560, (55-129), . Kibel M (2003) X-Ray Photoelectron Spectroscopy Surface Analysis Methods in Materials Science, 10.1007/978-3-662-05227-3_7, (175-201), . This Issue15 November 1996Volume 354Issue 1719 Article InformationDOI:https://doi.org/10.1098/rsta.1996.0122Published by:Royal SocietyPrint ISSN:1364-503XOnline ISSN:1471-2962History: Published online01/01/1997Published in print15/11/1996 License:Scanned images copyright © 2017, Royal Society Citations and impact

Differential Charging in XPS. Part II: Sample Mounting and X-ray Flux Effects on Heterogeneous Samples

Factors which affect photoelectron peak positions on heterogeneous samples are evaluated using patterned indium tin oxide (ITO) on glass. Local sample environment, sample mounting and spatial variation in x-ray flux are all shown to contribute to differential charging effects if no charge neutralization is used. X-ray photoelectron spectroscopy data acquisition using both Mg Kα and monochromatic Al Kα x-ray sources shows that confusing and potentially misleading results can be obtained if samples are mounted such that only part of the surface is grounded to the spectrometer. In this case, multiple photoelectron peaks were observed for each photoelectron line of each element in the sample. However, more significant differential charging artifacts were observed from the insulating glass than from the ITO. The proximal causes of the photoelectron peak shifts were evaluated using imaging XPS in conjunction with small-area spectroscopy.

Differential Charging in XPS. Part I: Demonstration of Lateral Charging in a Bulk Insulator Using Imaging XPS

Differential Charging in XPS. Part I: Demonstration of Lateral Charging in a Bulk Insulator Using Imaging XPS

Characterization of PTFE on Silicon Wafer Tribological Transfer Films by XPS, Imaging XPS and AFM

Atomic force microscopy (AFM) shows that PTFE-on-silicon wafer tribological transfer films consist of narrow ribbons of PTFE, <1 μm wide and <10 nm high, aligned with the film draw direction. Within the ribbons the PTFE molecular chains are also aligned with the draw direction. Such materials are of interest as substrates for the epitaxial crystallization of polymers and small molecules. X-ray photoelectron spectroscopy demonstrates that the amount of PTFE put down increases with deposition temperature and pressure. The XPS azimuthal angle dependence at low electron take-off angle is consistent with the aligned ribbon morphology. Azimuthal and polar angle dependence and charging studies show that hydrocarbon contamination observed in the XPS spectrum is located on top of the silicon wafer substrate, in the channels between the PTFE ribbons. Imaging XPS confirms the pressure dependence of PTFE coverage, and at low deposition pressure reveals tracks of PTFE ∼100 μm wide, aligned with the film draw direction. Together with the AFM data this leads to a description of PTFE transfer films as fractal materials.

XPS Imaging of Patterned Self-assembled Monolayers Containing Perfluorinated Alkyl Chains

X-ray photoelectron spectroscopy (E-X) imaging has been applied to the study of perfluorinated self-assembled monolayers (SAM) adsorbed on gold surfaces. Patterned monolayers were formed using a 'stamping' procedure which enabled the formation of 'two-component' monolayers. The E-X images yield spatial information, with a 30 μm resolution, on the quality and chemical composition of the resulting monolayer structures.

Interfacial chemistry of adhesive joint failure: an investigation by small area XPS, imaging XPS and TOF-SIMS

The strength and mode of failure of adhesively bonded iron substrates has been investigated. Joints were assembled from polished iron and from iron substrates that had been pretreated in a novel manner by the cathodic deposition of yttrium. Joints were exposed to an aqueous environment and a reduction in joint strength with increasing exposure time was noted. Failure surfaces of joints exposed to water for 1200 and 7500 h were examined by small-area XPS, imaging XPS and TOF-SIMS. An interfacial failure was observed, and although all surfaces were rich in nitrogenous species from the curing agent, no evidence of epoxy residues on the interfacial metal failure surfaces was recorded by TOF-SIMS. The metal failure surface at extended exposure times shows that there are two delamination fronts advancing from the exposed edge of the adhesive joint: one is associated with bond cleavage and gives rise to a ‘zero-volume debond’ and proceeds faster than the other, which is associated with gross separation of the adhesive and substrate, oxide growth on the exposed metal adherend and mass transport within the disbondment crevice.

Differential Charging in XPS. Part I: Demonstration of Lateral Charging in a Bulk Insulator Using Imaging XPS

Differential Charging in XPS. Part I: Demonstration of Lateral Charging in a Bulk Insulator Using Imaging XPS

Differential Charging in XPS. Part I: Demonstration of Lateral Charging in a Bulk Insulator Using Imaging XPS

Recent literature has drawn a distinction between charging across the surface (lateral differential charging) and charging with depth (vertical differential charging) for insulating samples. In this study, differential charging in a bulk insulator was investigated using imaging and small-area spectra acquired with a monochromatic x-ray source. With no charge neutralization, reproducible photoelectron images and spectra could be acquired from a glass sample after ∼90 min of x-ray exposure. The charge shifts and photoelectron peak shapes vary as a function of x-ray flux on the sample, indicating that lateral charging is the dominant mechanism on a bulk insulator. Uniform binding energies, photoelectron peak shapes and images are acquired with the charge neutralizer on.

Photoelectron and NEXAFS microscopy of radiation induced changes in cadmium arachidate films

The radiation induced changes caused by both low energy Ar + ion bombardment and high energy H + ion bombardment on Langmuir-Blodgett (LB) films of cadmium arachidate were investigated using a commercial photoelectron microscope installed at the German synchrotron facility BESSY. For the low energy situation, XPS imaging was performed using damage induced differential charging as the contrast mechanism. The high energy H + bombardment produced less damage and no resolvable charging shift, so this contrast mechanism cannot be used for imaging. However, chemical shifts in the C NEXAFS (near edge X-ray absorption fine structure), caused by the H + bombardment, are sufficiently large to use as a contrast mechanism. NEXAFS, of course, requires tunable radiation and hence spectromicroscopy in conjunction with synchrotron radiation offers the possibility for imaging chemical changes in organic films which are not observable using fixed energy laboratory sources. In principle, molecular orientation changes are also imageable, as the relative intensities of different features in a NEXAFS spectrum often vary with orientation.

XPS analysis of metal grain boundary surfaces

AbstractX‐ray photoelectron spectroscopy (XPS) can provide a quantitative analysis of the surface and determine the chemical state of elements present. However, until recently the spatial resolution has not been adequate to analyse small particles. As a result, Auger electron spectroscopy has been used to obtain elemental information where good spatial resolution is required. Analysis of grain boundary surfaces has therefore been restricted to this technique, with the result that no chemical‐state information has been obtained relating to the elements present on the grain boundary. This paper describes results in which grain boundary surfaces exposed in an imaging XPS instrument have been analysed using XPS. In particular, tin and phosphorus are shown to segregate to the grain boundary surface in the elemental state.

Interphase Formation and the Characterisation of Polymer/Ceramic Adhesion

Abstract The adhesion of photocured resins to ceramic substrates has been investigated using a variety of surface analytical techniques. Work has been aimed at establishing the physical and chemical interactions between resin and substrate in the interphase region and the effect of environmental exposure on these Analysis was aided by use of specially-designed, in-situ fracture facilities attached by an X-ray photoelectron spectrometer. Specific attention was focused on identification of localised regions of varying chemical composition in adhesive and adherend by imaging spectroscopies (imaging XPS and ToF SIMS imaging) and the study of the significance of such heterogeneities on adhesion and subsequent failure mechanisms.

Use of parallel imaging XPS to perform rapid analysis of polymer surfaces with spatial resolution &gt;5 μm

AbstractX‐ray photoelectron spectroscopy (XPS or ESCA) is one of the most common surface analytical techniques available. It has proved over many years to be invaluable in the analysis of elemental and chemical species on surfaces. The recent developments of this technique towards spatially resolved XPS information has made it possible to use XPS for analysis of very small features on insulating materials such as polymer surfaces, on which other high spatial resolution techniques such as Auger electron spectroscopy (AES) suffer difficulties generated by, for example severe sample charging effects.The new VG ESCALAB 220iXL from VG Scientific (Fisons Instruments) uses parallel imaging together with a magnetic objective lens to provide chemical images of better than 5 μm spatial resolution in just a few minutes. Subsequent point analysis using selected small‐area XPS can be performed on any feature in the images down to 7 μm resolution. In combination with this unique parallel imaging facility, a new high‐intensity x‐ray monochromator source makes fast chemical state imaging at high spatial resolution relatively routine. Several examples of the analysis of polymer surfaces wil be shown, including chemical state imaging of the C 1s, CC, and CO bonding states from 15 μm features.

Deposition of cationic yttrium on heterogeneous surfaces

AbstractThe cathodic deposition of yttrium on iron and steel surfaces is known to improve the bond strength of joints treated in such a manner. This work explores the effect of large and small heterogeneities on the spatial distribution of the deposited species. Two systems are investigated: 98% iron with micrometre‐scale inclusions, and a micro‐hardness indentation on gold‐coated iron. In the former case yttrium is identified (by XPS and SAM) to have been deposited in two concentration regimes: close to the inclusion (the cathodic area) the concentration is higher than elsewhere, and also contains iron produced by back‐deposition. At the identation the iron substrate is exposed at the corners to provide the prerequisite anodic site, cathodic deposition of yttrium is then observed both within the identation and on the undamaged gold surface at a lower concentration. The provision of spatially resolved analytical information by SAM, time‐of‐flight SIMS and imaging XPS enables the interrelationship of microstructural features and extent of cathodic deposition to be readily appreciated.

Scanning XPS; low kinetic energy source scanning: some design considerations

The logistics of electron-beam scanning in two special applications in surface-analysis are discussed, particularly with a view to multitechnique surface-analysis. For electron-beam charge-neutralisation it is necessary first to produce an x,y-positionable beam at low (a few eV) kinetic energies, with a significant space-charge, and submillimetre focus. These performance requirements seem at first sight to be at odds with the requirement for multitechnique surface-analysis, namely that the solid-angle subtended by each technique be kept to a minimum. Here both the high space-charge, and the small, positionable focus requirements indicate a larger solid-angle is required. Similarly, in scanning small-area (imaging) XPS, a requirement arises for keeping the solid-angle to a modest value, whilst not compromising the ‘large-collection-angle’ electron-spectroscopy techniques, on a ‘component’ hemispherical-sector electron energy analyser. Tested solutions for either case, satisfying all criteria, are presented.

Computer-aided resolution enhancement for XPS imaging of an uncharged single chemical species

Imaging XPS can be performed by an application of the double focusing properties of the hemispherical electron energy analyser. The x-ray photoelectron spectra originating from an area of the specimen are depicted on a multichannel plate electron detector. An increasing size of this specimen area helps to reduce the total time for the generation of an XPS image. But, together with a reduction of the time of measurement, a loss of lateral resolution has to be expected. The present paper deals with the concept of computer-aided compensation for the loss of resolution due to an increase of the observed specimen area. The principle of this concept is based on a deconvolution of the measured x-ray photoelectron spectra.

Improved images with the scanning photoelectron microscope at the national synchrotron light source

AbstractWe present recent developments with the scanning photoelectron microscope at beam line X1A (X1‐SPEM) at the National Synchrotron Light Source. It was the first to demonstrate elemental and chemical imaging with primary photoelectrons and achieve submicron resolution [Appl. Phys. Lett. 56, 1841–1843 (1990)]. Subsequent improvements allow us now to acquire XPS images with lateral resolution approaching 0.1 μm. We have utilized the instrument to examine artificial structures such as microelectronic devices and describe here our preliminary work in the study of photon‐beam‐mediated chemistry on aluminum surfaces.

Surface modifications introduced to a polytetrafluorethylene‐filled polycarbonate compound by dry sliding against steel as revealed by imaging XPS

AbstractImaging XPS has been used to study surface modifications in a polytetrafluoroethylene (PTFE)‐filled polycarbonate compound as a result of dry sliding wear testing. The novel observation of the formation of a PTFE film over the polymer compound surface (in addition to a transfer film on the steel counterface) will be of significance to the understanding of friction and wear mechanisms and to the performance of polymer systems in tribological applications.

XPS study of a SiC film produced on Si(100) by reaction with a C 2H 2 beam

A Si(100) surface reacted with a well-collimated C 2H 2 beam was studied by XPS after storing it in air for about one year. The SiC film formation was confirmed by the characteristic XPS peaks of Si2p (101.3 eV) and Cls (283.3 eV) for SiC. The chemical maps on the surface were obtained by imaging XPS. The ≈ 1 mm diameter SiC region was clearly identified on the Si substrate by the method. In the SiC and the non-reacted Si regions the Si2p XPS peak for SiO 2 (103.6 eV) and the O 1s peak were also observed. The intensities of the O 1s and Si 2p (SiO 2) peaks in the SiC region were smaller by a factor of 0.75 than in the surrounding Si region. This indicates that the carbide (SiC) film was less reactive to O 2 than the Si surface. There was very little evidence of any SiO x ( x < 2) products which may be transients in the formation of SiO 2 or complexes like CSiO.

A comparison of two XPS methods for quantification of concentration profiles

Binary AlLi alloys are known for well pronounced segregation at ambient temperatures. Literature provides a good knowledge of segregation behaviour of these alloys. An exponential concentration profile with depth can be assumed. We compare the concentration profiles obtained from SIMS measurements with results from XPS. SIMS measurements [M. Vonbank and P. Varga, Vak.-Tech., 37 (1988) 220.] performed on a specimen with 9.1 at.% Li after storage at room temperature for more than 48 h gave a surface composition of 50 at.% Li and a gradient of −20 at.% Li nm −1. We investigated the same specimen after heat treatment for 2 h 20 min at 150°C. For comparison, XPS with variable take-off angle gives 75 at.% Li and −17.8 at.% Li nm −1 assuming an exponential depth profile, 70 at.% Li and −9.9 at.% Li nm −1 with a linear response and our new imaging XPS method with a linear response gives 92 at.% Li and −15.4 at.% Li nm −1. The standard deviations of surface concentration and gradient are approximately 9 at.% Li and 8 at.% Li nm −1. The differences are due to: the statistical significance of measured data (8% relative error in case of variable take-off angle experiments and 25% for imaging experiments) especially due to weak Li1s signals; the necessity of a specimen transfer in ambient atmosphere; and uncertainties in sputter depths of about 10%. In principle the imaging method is similar to methods in which the surface is etched with a constant flux Ar ion beam and changes in the composition of the surface with time are monitored using XPS.

Application of surface analysis techniques to the study of paint/metal interfaces related to adhesion and corrosion performance

AbstractInterfaces between galvanized steel and automotive cathodic electrocoat paint systems were characterized by imaging XPS and static SIMS, using time‐of‐fight SIMS and quadrupole SIMS with an SF6 primary source. Variables were the pretreatment of the metal (phosphate coating) and the cure state of the pain system. Analyses were carried out prior to and following exposure in an accelerated cyclic corrosion test. In systems without phosphate pretreatments, severe delamination was observed in non‐corroded areas. In such areas, zinc hydroxycarbonate was found at the interface. In corroded areas, adhesion was retained, probably as a result of an interaction between cathodically generated O− ions and the paint. In phosphated systems, an undercure of the paint led to an increase of the underfilm corrosin. Static SIMS analysis of the paint/metal interface demonstrated that the state of cure of cathodic electrocoat systems can be detected by this technique and, furthermore, that certain paint constituents are preferentially adsorbed on the metal surface. The degree of cure of the paint was shown to change in going from the air/paint surface to the buld and on to the paint/metal interface. The adhesion behaviour of epoxy electrocoat systems to metallic substrates can be described in terms of acid–base interactions.