Th. Gross

VAMAS TWA2 Project A2 : evaluation of static charge stabilization and determination methods in XPS on non-conducting samples. Report on an inter-laboratory comparison

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 3p 3/2 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 (s r ), between standard deviations (s b ), reproducibility standard deviations (s R ) 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.

Some remarks on fitting standard- and high resolution C 1s and O 1s x-ray photoelectron spectra of PMMA

Abstract Thin PMMA films were investigated by high- and standard-resolution XPS and variable-angle NEXAFS. The results of fitting of the respective C 1s and O 1s XP spectra are compared with the latest literature data. It is found that using a non-constrained “1:1:1:2” fitting strategy good agreement between standard-resolution C 1s spectra and high-resolution spectra can be achieved with regard to BE shifts and trends in intensity and FWHM of the spectral C 1s components. A non-constrained fit of standard-resolution O 1s spectra reveals the same characteristic BE differences as well as non-stoichiometric relative component intensities and FWHM as observed in high-resolution XPS experiments. Comparison of the XPS results obtained with low-energy (380 eV) photons with those obtained with MgKα X-ray photons supported by inspection of the C K-edge NEXAFS spectrum reveals that there should be an outermost PMMA film layer dominated by methyl groups. O 1s NEXAFS spectra also suggest a non-isotropic orientation of the molecules in the surface region.

Uncertainty in measurement of overlayer thickness of thermally oxidized silicon using x-ray photoelectron spectroscopy

Overlayers of SiO 2 (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.

Reference materials for composition-depth profiles of TiN, Ti(C,N) and (Ti,Al)N with different chemical composition

Abstract Titanium nitride TiN x , titanium carbonitride Ti[C x ,N y ] and titanium aluminium nitride [Ti x ,Al y ]N coatings—each with four different chemical compositions—were deposited by d.c. magnetron sputtering on a low carbon steel. In a first step the coatings of one part of the layers were analysed with a wet chemical method. The other samples were studied by Auger electron spectroscopy, energy-dispersive X-ray analysis, glow discharge optical spectroscopy, secondary ion mass spectrometry, secondary neutral mass spectrometry and X-ray photoelectron spectroscopy in a round robin experiment. The results of the spectroscopic analyses showed significant deviations as compared with the wet chemical analyses, especially for substoichiometric composition. Possible reasons for this behaviour are discussed. It can be concluded that the now well-examined samples can be used as reference materials for all spectroscopic methods.

Static charge correction in XPS on Cu-Zn-Al oxide catalyst precursors with the help of deposited Pd particles as a reference material

Abstract To obtain binding energy (BE) data from a photoelectron spectroscopy experiment (XPS) with poorly conductive samples, one needs a reliable inner BE reference. The problem of an inner static charge reference for Cu-Zn-Al oxide catalysts is studied on different samples including ZnO, defined hydroxycarbonates, precipitated precursors and calcined catalysts. With the help of an external reference material, i.e. deposited 20 ± 10 nm Pd particles, the suitability of the C 1s, Zn 2p 3/2 and Al 2s spectra to provide an inner static charge reference is tested. The Zn 2+ 2p 3/2 BE may serve as a reference when thoroughly calcined samples are exclusively investigated. Provided the Cu/Al surface concentration ratio is not to high, the Al 2s BE can be used in case of many calcined and precipitated samples when some care is taken. Considering C 1s BE related charge correction high systematic errors may occur due to the complexity of the C 1s spectra together with the known C 1s BE variation based on extra-atomic relaxation between the substrate and the contaminant hydrocarbon adsorbate.

Standard operating procedure (SOP) for the quantitative determination of organic silicon compounds at the surface of elastomeric sealants

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.