We have made additional evaluations of the electron inelastic mean free paths ([MFPs) and of the predictive IMFP formula TPP-2 presented in papers I1 and I11 of this series. Comparisons have been made with other formulae for the IMFPs and electron attenuation lengths (ALs). We find substantial differences between our IMFP results for 27 elements and 15 inorganic compounds and the AL formulae of Seah and Dench; these differences include different dependences on electron energy and on material parameters. We present IMFP calculations for A1,0, and GaAs from TPP-2 in which each parameter of the formula is varied in some physically reasonable range about the true value for each compound; these results show the sensitivity of the computed IMFPs to the choices of parameter values. Finally, we give a summary of sources of uncertainty in the IMFP algorithm, in the experimental optical data from which IMFPs are calculated, and of the TPP-2 formula. We conclude that TPP-2 is robust and useful for predicting IMFPs for electron energies and material parameter values in ranges for which the formula was developed and tested.

Calculations of Electron Inelastic Mean Free Paths (IMFPs) IV. Evaluation of Calculated IMFPs and of the Predictive IMFP Formula TPP-2 for Electron Energies between 50 and 2000 eV

Reactive element-sulfur interaction and oxide scale adherence

A new and a radically different mechanism to account for the beneficial effects that small additions of elements such as yttrium have on the adherence of oxide scales is proposed. It has been long:known and has been reaffirmed here that indigenous impurities such as sulfur, known to be present at tramp levels (<100 ppm) within nickel and nickel-based alloys, can segregate to metal surfaces. However, here it has been disclosed that such sulfur segregation can also markedly affect the adherence of the protective oxide scale. In the absence of elements like yttrium, such segregation effects weaken the bond between the protective scale and the substrate metal. The role of the yttrium is to interact with such indigenous sulfur to form a refractory sulfide. This interaction lessens the amount of sulfur available to segregate to and concentrate at the critical scale-metal interface. Results reported here have focused on sulfur because sulfur has been long known to be a common tramp impurity in nickel and nickel-based alloys. However other elements, e.g., phosphorus, chlorine, etc., could very probably produce similar effects. The results of experiments involving Auger spectroscopy, optical, scanning electron microscopy, scanning electron microprobe, and scanning transmission electron microscopy techniques in conjunction with isothermal and cyclic oxidation testing which have led us to propose this mechanism are presented.

A Relationship between Indigenous Impurity Elements and Protective Oxide Scale Adherence Characteristics

There is a growing concern within the surface science community that the massive increase in the number of XPS articles over the last few decades is accompanied by a decrease in work quality including in many cases meaningless chemical bond assignment. Should this trend continue, it would have disastrous consequences for scientific research. While there are many factors responsible for this situation, the lack of insight of physical principles combined with seeming ease of XPS operation and insufficient training are certainly the major ones. To counter that, we offer a comprehensive tutorial written in the form of a step-by-step guide starting from experimental planning, through sample selection and handling, instrument setup, data acquisition, spectra analysis, and results presentation. Six application examples highlight the broad range of research questions that can be answered by XPS. The topic selection and the discussion level are intended to be accessible for novices yet challenging possible preconceptions of experienced practitioners. The analyses of thin film samples are chosen for model cases as this is from where the bulk of XPS reports presently emanate and also where the author's key expertise lies. At the same time, the majority of discussed topics is applicable to surface science in general and is, thus, of relevance for the analyses of any type of sample and material class. The tutorial contains ca. 160 original spectra and over 290 references for further reading. Particular attention is paid to the correct workflow, development of good research practices, and solid knowledge of factors that impact the quality and reliability of the obtained information. What matters in the end is that the conclusions from the analysis can be trusted. Our aspiration is that after reading this tutorial each practitioner will be able to perform error-free data analysis and draw meaningful insights from the rich well of XPS.

https://aip.scitation.org/doi/pdf/10.1063/5.0086359

A step-by-step guide to perform x-ray photoelectron spectroscopy

Photoelectron peak areas are measured using various background removal methods. Linear, horizontal, Shirley's and Tougaard's backgrounds have been tested on many spectra for different pass energies in the spectrometer. These four values, obtained for each photoelectron line, are compared together and it is shown that the first three methods give proportional results. These values are then compared to theoretical intensitities for five elements (Au, Ag, Cu, Ni, Cr) and one oxide (Al2O3). These theoretical calculations are based on the knowledge of the spectrometer transmission, photoionization cross-sections and inelastic mean free path, the product of which is commonly called the relative sensitivity factor. The best agreement is obtained when Tougaard's background is removed.

Comparison of background removal methods for XPS

The work of VAMAS-SCA project no. 25 is reported. The project was an XPS round robin with thgree different compositions of AuCu alloys (Au 25 at.%,–Cu 75 at.%, Au 50 at.%–Cu 50 at.%, Au 75 at.%–Cu 50 at.%.). These alloys were alson the subject of an earlier AES round robin ( VASMAS-SCA project no. 17). Pure gold and pure copper was used as the standard materials. By using peak areas of the Au 4f doublet and Cu 2p3/2 for the calculation, the effects of measurement conditions and data processing on quantification were examined. The reliability of quantification by three methods, namely the ‘relative sensitivity factors’ method, the ‘pure metals as standard materials’ method and the ‘alloy as standard material’ method, was compared. It is concluded that measurement conditions such as photoelectron emission angle and energy resolution did not affect quantification and that there was no effect of the different background subtraction methods on quantification. With the ‘alloy as standard material’ method, variations of the measured surface concentrations were the smallest, namely ∼2–6%.

Quantitative surface chemical analysis of AuCu alloys with aes

A matrix effect correction is required to improve the accuracy of quantitative AES analysis. The correction includes terms involving the atomic density (n), electron back-scattering factor (R) and electron escape depth (L). Many schemes have been proposed by various people for corrections of the R and L terms. However, up to now, there have been no systematic investigations of the correction accuracy of the proposed schemes. We have evaluated the correction accuracy, based on measured intensity data for AuCu alloys of different compositions. Comparison was made between the observed intensity ratio K (=Iunk/Istd) and the calculated intensity, ratio K′ (= C(nunk/nstd)(Runk/Rstd)(Lunk/Lstd)), where C and I represent the concentration and intensity, respectively. The superscripts ‘unk’ and ‘std’ denote that the parameters are for unknown and standard specimens, here the pure elements. If the correction works well, the error Er (= K′ K)/(K) will become smaller. Evaluations were carried out on three schemes for the R correction and on seven schemes for the L correction using the Au 239 eV, Au 2024 eV and Cu 920 eV transitions. The root mean square (RMS) of the calculated errors showed several per cent for the best case and 20–30% for the worst case. The RMS error varied a few per cent between schemes for the R correction but it varied ∼30% for the L correction.

Evaluation of correction accuracy of several schemes for AES matrix effect corrections

The Segregation Behavior of Sulfur, Oxygen and Phosphorus at the (100) Surface of Iron Single Crystal

The Japanese VAMAS-SCA working group is composed of 19 institutes. Three kind of AuCu alloys (Au 75 at.-%–Cu 25 at.-%, Au 50 at.-%–Cu 50 at.-%, Au 25 at.-%–Cu 75 at.-%) were prepared, and these specimens, pure Au and pure Cu were distributed to the members of the VAMAS-SCA working group. The surface concentrations of these alloys were calculated from the Auger peak amplitudes in two ways. One method used the published relative sensitivity factors, and the other used pure Au and Pure Cu as the standard materials. The mean values of the surface concentrations calculated with the published relative sensitivity factors were almost the same as those calculated with the standard materials. This means that the published relative sensitivity factors are reliable to some extent. The error of the surface concentration calculated with pure Au and pure Cu as the standard materials lay between about 3% and 10%, and that with the relative sensitivity factors lay between about 7% and 20%. The calculated surface concentrations of Au were larger than the bulk concentrations of Au when the matrix effect was neglected.

Masayasu Kurahashi

Papers

Quantitative surface chemical analysis of AuCu alloys with aes

Evaluation of correction accuracy of several schemes for AES matrix effect corrections

The Segregation Behavior of Sulfur, Oxygen and Phosphorus at the (100) Surface of Iron Single Crystal

The reliability of quantitative analysis with AES

The Segregation Behavior of Sulfur, Oxygen and Phosphorus at the (100) Surface of Iron Single Crystal