Quantitative information from electron spectroscopy for chemical analysis requires the use of suitable atomic sensitivity factors. An empirical set has been developed, based upon data from 135 compounds of 62 elements. Data upon which the factors are based are intensity ratios of spectral lines with F l s as a primary standard, value unity, and K2p3/2 as a secondary standard. The data were obtained on two instruments, the Physical Electronics 550 and the Varian IEE-15, two instruments that use electron retardation for scanning, with constant pass energy. The agreement in data from the two instruments on the same compounds is good. How closely the data can apply to instruments with input lens systems is not known. Calculated cross-section data plotted against binding energy on a log-log plot provide curves composed of simple linear segments for the strong lines: Is, 2~,~, 3d5/2 and 4f712. Similarly, the plots for the secondary lines, 2s, 313312, 4dSl2 and 5dSl2, are shown to be composed of linear segments. Theoretical sensitivity factors relative to F l s should fall on similar curves, with minor correction for the combined energy dependence of instrumental transmission and mean free path. Experimental intensity ratios relative to F l s were plotted similarly, and best fit curves were calculated using the shapes of the theoretical curves as a guide. The intercepts of these best fit curves with appropriate binding energies provide sensitivity factors for the strong lines and the secondary lines for all of the elements except the rare earths and the first series of transition metals. For these elements the sensitivity factors are lower than expected, and variable, because of multi-electron processes that vary with chemical state. From the data it can be shown that many of the commonly-accepted calculated cross-section data must be significantly in error-as much as 40% in some cases for the strong lines, and far more than that for some of the secondary lines. I N T R O D U C T I O NOf the techniques useful for analyzing the first few atomic layers of surfaces, ESCA (electron spectroscopy for chemical analysis), known also as XPS (X-ray photoelectron spectroscopy) is the most useful for quantitative analysis. If we assume a solid that is homogeneous to a depth of 10-20 nm (several electron mean free paths), the number of photoelectrons detected per second from an orbital of constituent atoms is given by(1) where n is the number of atoms per cm3 of the element of interest, f is the flux of X-ray photons impinging on the sample, in photons cmp2 spl, (T is the photoelectric cross-section for the particular transition in cm2 per atom, 4 is the angular efficiency factor for the instrumental arrangement (angle between photon path and emitted photoelectron that is detected), y is the efficiency of production in the photoelectric process to give photoelectrons of normal energy (with final ionic state the ground state), A is the area of the sample from t Author to whom correspondence should be addressed. which photoelectrons c...

The comblned use of both photoelectron and X-ray excited Auger llnes increases the utility of ESCA for identifying chemical states. A useful format for displaying reference data is the two-dimenslonal plot where the kinetic energy of the sharpest Auger llne is plotted vs. the binding energy of the most Intense photoelectron line. A compilation of data for 24 elements is presented, including critically evaluated data from the literature which have been referenced to a uniform calibration line. The format of the plots is applicable to data obtained with Ionizing photons of any energy. The data included for silicon, bromine, and tungsten were obtained with higher energy X-rays from a Au X-ray source.The ESCA (Electron Spectroscopy for Chemical Analysis) or XPS (X-Ray Photoelectron Spectroscopy) technique has a special value among methods for analysis of surfaces because it furnishes information on the nature of chemical states. This is possible because the X-radiation used ordinarily does not produce chemical changes in the surface layers.In the original concept (I), chemical shifts in photoelectron energies were stressed as the means by which chemical states can be identified. This feature is limited, however, since ranges in chemical shifts for some elements are small, and because there are difficulties in defining accurately the spectral line energies from insulating samples due to static charging.There are other spectral features that can be useful in identifying chemical states. I t has been found that chemical shifts in X-ray excited Auger lines are usually larger and very different from those in photoelectron lines ( 2 ) . Those Auger lines that originate from Auger transitions resulting in vacancies in core levels have at least one sharp, intense component (3). Chemical shifts in this component can be measured as accurately as those in photoelectron lines, and this extra information is of significant value.Since the chemical shifts of photoelectrons and Auger electrons are different, the differences between their kinetic energies constitute a special spectral property. This difference has been called the Auger parameter ( 4 ) and its numerical value is unique to each chemical state. It is more accurately determinable than either the photoelectron or Auger electron energy alone, because the static charge corrections in these lines then cancel. The chemical shift in the Auger parameter between two chemical states is related to the difference in extra-atomic relaxation energy between the two chemical states ( 5 ) .The Auger parameter is still a one-dimensional quantity, like the photoelectron energy or the Auger electron energy alone. A concept that makes independent use of the energies of the photoelectrons and the Auger electrons, as well as the Auger parameter, is the two-dimensional chemical state plot (6). In this, for each element, the kinetic energies of phoPresent address: 29 Starview Drive, Oakland, California 94618. 0003-2700/79/0351-0466$0 1 .OO/Otoelectrons for various chemical states are plotted...

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Asphaltenes, the key intermediates in the liquefaction of bituminous coals, consist of hydrogen bonded complexes which can be separated into their acidic and basic components. The acidic components contain all, while the basic components contain none, of the exchangeable protons present. The significance of these findings with respect to coal structure and coal solubilization is discussed.

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