The electron spectra of 27 elemental solids and the 12 compounds measured with the specially designed type CMA were analyzed to interpret the energy distribution of secondary electrons which are emitted through a cascade process due to the excitation of primary electrons. As a result, we found that there are three components in the secondary electron spectra under several tens of eV. The first component is the individual excitation by the primary electron, the second component is the excitation by the Auger electron at several 10 eV, and the third component is the other fine structures caused by the decay of plasmons and other excitations. Assuming all structures depend on the exponential power (E^-γ), the intensities of these components of the N(E) spectrum are calculated. For the elemental solids and the compounds, the intensity of the individual excitation by the primary electrons is positively correlated with the number of the outermost shell electrons in the case of the acceleration voltage between 200 and 5000 V. The intensity of secondary electrons excited by the Auger electrons is positively correlated with the number of the valence electrons in the valence band. On the other hand, the intensity of the other fine structure has no clear relationship with the number of the valence electrons. Furthermore, the dependence for the intensities of the individual excitation on the atomic number is almost the same for the elemental solids and their compounds. The relationship between the intensity of the fine structure with the atomic number is not the same for elemental solids and their compounds.

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In order to verify the practicality of ISO 14701, the thickness of the silicon oxide film was measured using X-ray photoelectron spectroscopy (XPS) with the standard. The resulting thicknesses were in good agreement with the oxide thickness measured by Transmission Electron Microscope with a relative difference of 1.3 %. The position of the SiO₂ peak in the Si 2p spectrum may change due to charging during the XPS measurement, and it may deviate from the specified range in ISO 14701. In this case, it is necessary to focus on minimizing the fitting error according to the amount of charging, rather than the energy range. The procedures described for XPS measurement, peak fitting and the calculation of the oxide thicknesses are easy to understand, and we concluded that ISO 14701 is a practically useful standard.

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The mesh replica method is a means of measuring the ion sputtering rate in Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy, and recommendations for its implementation are set forth in ISO/TR 22335. Despite the usefulness of this method, there are few reports on its implementation. In this paper, the results of tracing experiments using the mesh replica method are presented and their implications are considered. In the tracing experiments, Ar⁺ ion sputtering of the silicon substrate was performed using the mesh replica method by AES. The sputtering depth was measured by stylus profiler. The measured sputtering depth was about the same as that by the Ar⁺ ion sputtering depth profile analysis using silicon thermal oxide film. The mesh replica method was then performed using a single-hole grid. The shapes of the obtained sputtering craters did not require consideration of the ion irradiation orientation or the scanning orientation of the stylus profiler.

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Dr. Martin P. Seah, Emeritus Fellow of National Physical Laboratory, who passed away in June 2021, has made remarkable achievements in the fields of surface chemical analysis for more than 50 years. His top 100 publications are picked up using the number of citations as an index, which is classified by academic fields. Most are related to surface electron spectroscopy, accounting for nearly 60%. Next are related to SIMS or interface segregation. Areas related to SPM also account for 4%. In the 1970s, research on grain boundary segregation was his mainstream. From the 1980s, research on the quantification of surface electron spectroscopy became dominant. Since the 1990s, the weight of the quantification related to SIMS has increased. Furthermore, since the 2000s, research on SPM has increased as a nanoanalysis method. Both for VAMAS-SCA, which was established in the 1980s, and ISO / TC 201, which was created in the 1990s, Dr. Seah made an extraordinary contribution to the international standardization of surface chemical analysis. His great achievements and contributions are overviewed with a focus on the events related to the author.

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One of Seah's important achievements is the establishment of calibration binding energies for X-ray photoelectron spectrometers. The energy calibration method for commercial XPS instruments is described in the ISO standard (ISO 15472), which uses the calibration energy values compiled by Seah in a paper [1] in 1998．In this commentary, I will introduce how the energy standard was established by Seah, mainly referencing the paper [1].

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“Universal Equation for Argon Gas Cluster Sputtering Yield” reported by Martin P. Seah in 2013 is introduced in this article. The sputtering yield of gas cluster ion beams (GCIBs), mainly applied to organic material analysis by X-ray photoelectron spectroscopy and secondary ion mass spectrometry, was simply expressed in Seah’s universal equation. The universal equation provides sputtering yields of various samples including metals and organic materials and useful information on sputtering processes. The background of the development of this equation was also explained and then future applications were discussed.

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[in Japanese]

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[in Japanese]

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The development and analysis of data bases of traceable AES and XPS reference spectra are described. The spectra have all instrumental terms calibrated and removed except the X-ray photon flux density. Auger electron intensities, in terms of the electrons emitted per steradian per incident electron for ionisation of a given shell, correlate with theory with a mean error of a factor of 1.04 with no independent fitting parameters. Correlations for 3 ≤ Z ≤ 83 show that, for AES, Casnati et al´s cross section for ionisation is significantly better than Gryzinski´s. For inelastic mean free paths the equation TPP-2M, of Tanuma et al, is used with a cut-off for the valence electrons at 14 eV binding energy and with all 4f electrons excluded for the lanthanide metals. Correlations of experiment and theory for the data sets are now excellent. For AES a new method of using broadened differential spectra shows accuracies approaching full peak area analysis. This method has promise as a simple method for analytical use.

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For quantitative analysis by AES and XPS, it is important to test the theory and to use the correct sensitivity factors. We develop our previous analyses of peak area intensities for elemental spectra in digital Auger and X-ray photoelectron databases measured using a fully calibrated spectrometer. The intensities, instead of being analysed after removal of a Tougaard background are now analysed after removal of the extrinsic characteristic loss background by deconvolving the elemental angle-averaged reflected electron energy loss spectrum (REELS). The photoelectron spectra now show clear intrinsic shake-up intensities, reduced to around 30% of the total peak intensities. A comparison of theory and experiment within a new matrix-less quantification formulation, using average matrix sensitivity factors, leads to correlations with rms scatters of 8% and 11% for AES and XPS, respectively, for a very wide range of transitions. This gives formulae and values of sensitivity factors, appropriate for use with spectrometers calibrated to give true spectra.

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The physical bases of most of the concepts for the quantitative analysis of solid surfaces by Auger and X-ray photoelectron spectroscopes was clearly established in the late 1960s and the 1970s. For Auger electron spectroscopy (AES) the basic theory involving the ionisation cross sections, backscattering etc was clearly established by Bishop and Rivier in 1969 and the effects of attenuation of the electrons by matter by Palmberg and Rhodin in 1968. The use of the differential method and for studying adsorbed sub-monolayer quantities was already established by Harris in his founding publication in 1968. With X-ray photoelectron spectroscopy (XPS) the cross sections and anisotropy were established by 1976 and, for both techniques, data banks involving intensities for quantification were available by a similar date. Over the next 20 years the theory developed, improving our understanding of many of the parameters, and calculations provided the essential parameters for quantification. The calculations became steadily more sophisticated and developed sub-fields with their own momentum. Underlying all this development has been a general weakness of good supporting experimental data since, as has been the case since surface analysis started, it is still very easy to observe what has happened but it is still very difficult to devise fully controlled experiments. This review will show how far progress has been achieved in these respects. In particular, in an analysis of a new digital Auger database we show how basic terms may be evaluated with full traceability to the SI system.

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A brief review is given of the project to measure the thickness of SiO₂ on Si in the range 1.5 nm to 8 nm by XPS. An outline is provided for the rationale of the work and the way that progress was organised to achieve accuracy better than 1%. Key elements of the uncertainty that needed addressing were the establishment of a reference geometry to avoid forward focusing from the single crystal silicon substrate, adequate signal strength to reduce the signal uncertainty, sufficient angular acceptance in the analyser to average the remaining forward focusing structure but not so large as to cause a bias, and accurate setting of the angle of emission for the reference geometry. With these parameters controlled, XPS becomes a linear and repeatable method for determining the thickness of SiO₂ on Si. By measuring the difference in thicknesses of a series of films against one or more other methods such as ellipsometry, X-ray reflectance, neutron reflectance, etc, the relevant attenuation lengths may be determined, thus converting XPS from a precise method into an accurate and traceable method. This general procedure can be used for any material layer. Details are given that led to a final result with a standard uncertainty better than 1%.

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Quantification in surface analysis using Auger electron spectroscopy and X-ray photoelectron spectroscopy has been the topic of significant work at NPL. A new approach to the quantification of materials that are homogeneous over the analysis volume has been developed using new average matrix relative sensitivity factors. These show agreement between theory and experiment at ∼10% for all peaks and elements analysed. For samples that are not homogeneous, layer thicknesses are often required. For ultra-thin gate oxides, the International Technology Roadmap for Semiconductors requires 1.3% accuracy. For this purpose, angle-resolved XPS is a good candidate. In a wide study under the auspices of the Consultative Committee for Amount of Substance (CCQM), the accuracy of measurements of the thicknesses of SiO₂ layers <8 nm thick on Si have been assessed. This study involved 45 sets of measurements in laboratories using MEIS, NRA, RBS, EBS, XPS, SIMS, ellipsometry, GIXRR, NR and TEM. The relative strengths and weaknesses become clear. These show that if XPS is used under reference conditions it can be reliable and fast with an accuracy, based on a calibration from the study, ∼1%. Inter-method correlations as good as 0.05 nm are achieved over the 8 nm range. Furthermore, certain methods, thought to be accurate, suffer from incompleteness of the measurement method. For thicker layers, sputtering is generally used. Here a new method has been tested to generate a sputter yield database, for argon ions, of 26 critical elements. This database has been used to help evaluate a new semi-empirical theory of sputtering yields that includes terms missing from the current semi-empirical theories and removes errors that are up to, and may exceed, a factor of 5. The new theory agrees with published data at ∼10% and shows why certain elements have anomalously high yields.

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[in Japanese]

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Sputtering using cluster primary ion beams is very important for the future development of static SIMS and the SIMS depth profiling of organic layers. However, different results from different laboratories may be confusing. Analytical models have an important function for enabling the prediction of behaviour for practical analysis. Sigmund's model for sputtering, often used in surface analysis, is helpful and accurate in the linear cascade regime. However, for cluster sputtering this is no longer the case and spike effects need evaluation. Evidence will be presented of the spike model validity for clusters of up to more than 10 atoms over 3 orders of magnitude in sputtering yield. Using data from one primary ion, extremely good descriptions of measurements reported with other primary ions can then be achieved. This theory is then used to evaluate the molecular ion yield behaviour of interest in the static SIMS of organics. This leads to universal dependencies for the de-protonated molecular ion yields, relating all primary ions, both single atom and cluster, which are illustrated by experimental data over 5 decades of emission intensity. This formulation permits the prediction of the (M-H)- secondary ion yield for different, or new, primary ion sources. It is shown how further gains are predicted. For analysing materials, raising the molecular secondary ion yield is extremely helpful but it is the ratio of this yield to the disappearance cross-section (the efficiency) that is critical. The relation of the damage and disappearance cross sections is formulated. Data are evaluated and a description is given to show how these cross sections are related and to provide a further universal relation for the efficiency/yield dependence of all cluster ions.

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In a recent article [1] Sekine presents some interesting aspects of the problems of work functions in electron spectroscopy, and, in particular, for XPS. In his "Summary of the Issue" he defines work function and since that definition is essentially the same as my understanding of the term I, have attempted some discussion of his two question points below. Furthermore, I have added a third point which seems to me to be related. Some interesting comments have already been supplied by Ichimura [2]. For the benefit of English readers the question points are shown in bold below.

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