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 technique known as XPS (X-Ray Photoelectron Spectroscopy) involves x-ray irradiation of surface samples under high vacuum. Electrons escaping from the samples are sorted and arranged to form a spectrum. A compilation of data for binding energy and kinetic energy of sample electrons from all elements has been collected. Depending on the nature of the chemical bond, the chemical shift can be as much as 10 eV. Over the past 6 years the author has indexed articles related to this subject area. The data bank contains a total of 13,200 records, from a total of 800 papers.The data are organized into 13 fields.1. Atomic numberThis needs no elaboration.2. Elemental symbolThe elements are presented in order of atomic number.3. Spectral lineIncluded are not only photoelectron and Auger lines, but also various useful line energy differences. The following describes the different designations shown: Photoelectron lines -Self-explanatory. In Figure 1 is shown a photoelectron line at 0-1070 binding energy in the reverse direction. Doublet separation in photoelectron lines -This is indicated by Figure 2, simply by a A followed by the line, e.g., A2p, A3p, A3d, A4p, A4d, A4f. Included also is the multiplet splitting of 3s, as in A3s.Auger lines -The common Auger lines shown will be KL23L23('D), L3M45M45('G), M4N45N45, M5N67N67, and sometimes, N6O45O45. This in the case of KL23L23 is exemplified by Figure 1, on the kinetic energy direction. Valence type Auger lines, sometimes designated CVV, with final vacancies in valence levels, will ordinarily not be included; if they are, the notation will have V standing for CHARLES D. WAGNER the final vacancy, as in KW. Other Auger lines will ordinarily be cited only as energy difference values from the above principal lines of each series (see below). Separation from the sharpest Auger line -This category (Fig. 4) will be used for all Auger line energies other than KW or KL23L23('D), LW or L3M45M45('G), M4N45N45, M5N67N67, and N6O45O45. The kinetic energy of the minor line cited will be subtracted from the standard line in its series, and the energy value will have a " + " or " -." Examples of the line designations are:Auger parameter -In the modified form, used here in Figure 1, is the kinetic energy of the sharpest Auger line (one of those above) plus the binding energy of the most intense photoelectron line. a3d5,M4N45N45If the Auger line and the photoelectron line are supplied but not the Auger parameter, the Auger parameter was derived by the reviewer from the data. The connotation (AP derived) is indicated in the column (see Sec. 9 -Method of compensation for steady state charge). With charge references of photoelectron and Auger lines of doubtful value, both are omitted but the Auger parameter is retained.Chemical shift from the elemental form -This is shown in Figure 3 when publications present both peaks in the same spectrum, or when the elemental peak is not in the same spectrum but in the same article. The absolute scale is not necessary because the chemical shifts are based ...

Earlier observations on the magnitudes of chemical shifts of photoelectron and core-type Auger lines, and the concept of the role of polarizability, have been combined to produce a unified concept of the role of polarization in determining line position. With core-type Auger lines, polarization effects are more important in determining chemical shifts than are changes in electron density on the atom in the ground state. A parameter, termed the Auger parameter, is proposed as a specific property of a chemical and physical state. It is accurately determinable to k 0.1 eV, and with most elements to which it is applicable the range among compounds is several eV. Differences in the Auger parameter are attributable solely to changes in the polarizability of the solid compounds.

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...

Silicon–oxygen and aluminum–oxygen compounds exhibit significant XPS Auger and photoelectron chemical shifts that are accurately measurable. Chemical state plots of KLL Auger kinetic energy versus 2p photoelectron energy permit identification of chemical species from the locations of their points on the plots. The KLL Auger electrons of Al and Si were generated by the bremsstrahlung component of the radiation, with conventional instrumentation. The location of points on the plots can be understood on the basis of polarizability of the environment (on the Auger parameter grid of lines, slope +1) and on the basis of the factors contributing to the energy of the final state ion in the Auger transition (a grid of line, slope −1). Tetrahedral aluminum has a significantly smaller Auger parameter than octahedral aluminum, and this difference is repeated, but with reduced magnitude on the similar plots for silicon and oxygen lines for the same compounds. Otherwise, the Auger parameters for this class of compounds are remarkably uniform. The Auger parameter values for oxygen and sodium in these compounds, using the 1s and KLL lines, are relatively small compared to those of other compounds of oxygen and sodium. For compounds of similar Auger parameter, differences in Auger final state ion energy are interpretable on the basis of electron density on aluminum and silicon atoms in the initial state, due to extent of bonding to oxygen, or to amount of negative formal charge on the silicate structure. Inclusion of tetrahedral aluminum enhances the negative charge and decreases the final state ion energy in high alumina zeolites. The difference between the energies of the O1s and Si2p lines in the inorganic silicon compounds is almost invariant, 429.0 to 429.6 eV. The three silicon polymers examined have a significantly larger line difference, 429.8 to 430.1 eV, making possible a differentiation between silicones and silicates. The oxygen KVV lines, with Auger transition final vacancies in valence levels, have shapes characteristic of chemical structure. The uncharged Si–O–Si structure exhibits a well-defined shoulder; in Al–O–Si the shoulder is so close in energy it merely gives rise to asymmetry in the peak; Al–O–Al and charged Si–O–Si give oxygen KVV lines as single sharp peaks.