Analysis Of Auger Electron Spectra Research Articles

Analysis of AES of 2nd Period Element-containing Substances and Valence XPS of the Four Solid Ones by DFT Calculations Using the Model Molecules

Experimental Auger electron spectra (AES) of 2nd period elements and valence X-ray photoelectron spectra (VXPS) of four solid substances [LiF, graphite, GaN, SiO2] are analyzed by density-functional theory (DFT) calculations using the model molecules of the unit cell. For the calculations, we use Gaussian09 program at B3LYP/6-31G (d, p) level to estimate VXPS, core-electron binding energies, and (Li ~ F)-KVV AES of the solid substances. In the AES simulations, we evaluate theoretical kinetic energies of the AES with our modified calculation method. The modified kinetic energies correspond to the final-state holes at the ground state in DFT calculations. Simulated KVV AES of the (Li ~ O) atoms with the maximum kinetic energies of the atoms agree considerably well to the experimental AES results. Calculated VXPS of the four substances are also in good accordance with the experimental ones. The kinetic energy formula of AES at the ground state appears to work better, despite its great simplicity.

Analysis of valence XPS and AES of (PP, P4VP, PVME, PPS, PTFE) polymers by DFT calculations using the model molecules

We simulated valence X-ray photoelectron spectra (VXPS) of five [(CH2CH(CH3))n {poly(propyrene) PP}, ((CH2CH(C5NH4))n {poly(4-vinyl-pyridine) P4VP}, (CH2CHO(CH3))n {poly(vinyl methyl ether) PVME}, (C6H4S)n {poly(phenylene) sulphide PPS}, (CF2CF2)n {poly(tetrafluoroethylene) PTFE}] polymers by density-functional theory (DFT) calculations using the model oligomers. The spectra reflect the differences in the chemical structures between each polymer, since the peak intensities of valence band spectra are seen to be due to photo-ionization cross-section of (C, N, O, S, F) atoms by considering the orbital energies and cross-section values of the polymer models, individually. In the Auger electron spectra (AES) simulations, theoretical kinetic energies of the AES are obtained with our modified calculation method. The modified kinetic energies correspond to two final-state holes at the ground state and at the transition-state in DFT calculations, respectively. Experimental peaks of (C, N, O)- KVV, and S L2,3VV AES for each polymer are discussed in detail by our modified calculation method.

Analysis of valence XPS and AES of C, N, O, and F-containing substances by DFT calculations using the model molecules

Experimental valence X-ray photoelectron spectra (VXPS) and Auger electron spectra (AES) of (Li, C, N, O, F) elements of four solid substances [graphite, GaN, SiO2, LiF] are analyzed by density-functional theory calculations using the model molecules of the unit cell. For the calculations, we use deMon density functional theory (DFT) program to estimate VXPS, core-electron binding energies, and (Li, C, N, O, F)-KVV AES of the solid substances. In the AES simulations, we evaluate theoretical kinetic energies of the AES with our modified calculation method. The modified kinetic energies correspond to two final-state holes at the ground state and at the transition-state in DFT calculations, respectively. Experimental KVV AES of the (Li, C, N, O) atoms in the substances agree considerably well to simulation of AES obtained with the maximum kinetic energies of the atoms, while, the experimental F KVV AES of LiF is almost in accordance with the spectra from the transition-state kinetic energy calculations.

Theoretical X-ray photoelectron and Auger electron spectra of polymers by density functional theory calculations using model dimers

We present theoretical X-ray photoelectron spectra (XPS) and Auger electron spectra (AES) for polymers by density functional theory (DFT) calculations with the Slater's transition-state concept. The simulated XPS and AES of three polymers [poly(ethylene) (PE), poly( cis-butadiene) (PcBD), and poly(styrene) (PS)] by DFT calculations using model molecules are in good accordance with the experimental ones. The combined analysis of AES and XPS enable us to clarify the electronic structure of single and double excitation for polymers from the theoretical viewpoint.

Theoretical auger electron spectra of polymers by density functional theory calculations using model dimers

We propose a new approach for analysis of Auger electron spectra (AES) of polymers by density functional theory (DFT) calculations with the Slater's transition-state concept. Simulated AES and X-ray photoelectron spectra (XPS) of four polymers [(CH2CH2)n (PE), (CH2CH(CH3))n (PP), (CH2CH(OCH3))n (PVME), and (CH2CH(COCH3))n (PVMK)] by DFT calculations using model dimers are in a good accordance with the experimental ones. The experimental AES of the polymers can be classified in each range of 1s–2p2p, 1s–2s2p, and 1s–2s2s transitions for C KVV and O KVV spectra, and in individual contributions of the functional groups from the theoretical analysis. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 394–401, 2002

Theoretical X-ray Photoelectron and Auger Electron Spectra of Polymers by Density Functional Theory Approaches Using Model Molecules

We propose a new approach for analysis of Auger electron spectra (AES) of polymers by density functional theory (DFT) calculations with the Slater’s transition state concept. Simulated AES and X-ray photoelectron spectra (XPS) of three polymers (PE, PcBD, and PS) by our DFT calculations using model dimers are in good accordance with the experimental ones. The combined analysis of AES and XPS can help us to clarify the electronic structure of polymers from the theoretical viewpoint.

Theoretical Auger electron spectra of polymers by density functional theory calculations using model dimers.

We propose a new approach for analysis of Auger electron spectra (AES) of polymers by density functional theory (DFT) calculations with the Slater's transition-state concept. Simulated AES and X-ray photoelectron spectra (XPS) of four polymers [(CH2CH2)n (PE), (CH2CH(CH3))n (PP), (CH2CH(OCH3))n (PVME), and (CH2CH(COCH3))n (PVMK)] by DFT calculations using model dimers are in a good accordance with the experimental ones. The experimental AES of the polymers can be classified in each range of 1s-2p2p, 1s-2s2p, and 1s-2s2s transitions for C KVV and O KVV spectra, and in individual contributions of the functional groups from the theoretical analysis.

Shape Analysis of Auger Electron Spectra Induced by Highly Charged Ion Impact on Carbon

We measured energy distributions of electrons emitted in backward direction from sputter cleaned amorphous carbon foils under swift HCI bombardment. The shape of these spectra was found to depend strongly on the projectile charge qp (qp = 6 ... 39) for fixed velocity vp (vp = 19 atomic units, 9 MeV/u). We observe (for high projectile charge only) a K2VV hyper satellite line at 310 eV due to the double ionization of the K-shell in addition to the well known KVV peak of carbon (at 257 eV). From a careful analysis of the shape of these carbon Auger spectra including background subtraction and deconvolution techniques, we clearly observe a projectile charge dependence of the shape of the primary Auger electron spectrum. This effect is strongly connected to a modification of the electronic structure of the solid target at the moment of the Auger decay. We discuss different possible interpretations of this effect, such as an increase of the mean electronic temperature or a structural modification of the material.

Data Preprocessing in Peak Shape Analysis of Auger Electron Spectra

Factor analysis is an established method of peak shape analysis in Auger electron spectrometry. The influence of different commonly used data preprocessing tools onto the results of factor analysis is demonstrated on AES depth profiles of multilayers and implantation profiles. For the analysis of Auger electron spectra it has been traditional to differentiate spectra by Savitzky and Golay’s method to remove background and to elucidate changes in peak shape. For phosphorus implanted in titanium it is shown that background removal works not ideal so that inelastic losses of the Ti(LMM) Auger peak can affect the result of factor analysis for the P(LVV) peak located at ca. 250 eV lower in kinetic energy. The contribution of such losses to the background can be corrected by shifting the spectra so that the high energy side above the peak equals zero. Numerical differentiation can introduce correlated error into the data set. To diminish edge effects the reduction of filter width at the edges and cutting off the outermost data points is recommended. The precision of spectrum reproduction is considered as a crucial test for the number of principal components. The reliability factor is investigated as a measure for the goodness of spectrum reproduction.

Emission and life characteristics of thin film top-layer scandate cathode and diffusion of Sc 2O 3 and W

We investigated top-layer scandate cathodes, which are the most promising of scandate cathodes. Among the cathodes which we prepared with a layer of various thickness, the best pulse emission of 80 A/cm 2 at 1300 K was recorded with cathodes having a top layer consisting of a Sc 2O 3 layer 2 nm thick on a W layer 8 nm thick. The emission variation of these cathodes was evaluated in life tests. The life characteristics were good in both diode and triode evaluation. We also determined diffusion coefficients of W and Sc 2O 3 with unporous W pellets covered with a Sc 2O 3 and W layer. Variations of surface concentrations of these pellets during life tests were measured using Auger electron spectroscopy. The diffusion coefficients were 6.4×10 −19, 1.0×10 −18, and 1.6×10 −18 cm 2/s at 1220 K, 1300 K, and 1370 K. Chemical states of O, Sc, and W are discussed based on detailed analysis of Auger electron spectra.

Savitzky and Golay differentiation in AES

For the analysis of Auger electron spectra it is popular and very useful to differentiate the acquired direct spectra numerically by Savitzky and Golay's method to provide peaks whose peak-to-peak height may be measured. To compare data recorded at different channel separations, ε (number of eV per channel), it is important to be able to assign an energy equivalent, E D, to the differentiating function which is independent of ε. It is shown that the adoption of 2 mε for the differential width, where 2 m + 1 is the number of points in the Savitzky and Golay function, leads to errors and inconsistencies. It is recommended that (2 m + 1) ε be identified with E D. To obtain E D values intermediate between those possible with Savitzky and Golay's method, a modified function is developed with added ±( m + 1)th terms. The strength of these terms is between 0 and ±(m + 1) N , where N is the normalisation constant, and the exact value is roughly in proportion to the fractional excess of E D in the interval between the values permitted in Savitzky and Golay's original approach. An accurate assessment is made for the value to be used for E D values mid-way between those usually obtained by Savitzky and Golay's method.

Determination of sp 2/sp 3 carbon bonding ratio in a-C:H including irradiation damage by factor analysis of Auger electron spectra

While in most cases the determination of carbon bondings by Auger electron spectroscopy (AES) is carried out only qualitatively, we present a quantitative method to obtain the sp 2/sp 3 ratio in the sample. AES spectra of various a-C:H films produced in a plasma-CVD process were recorded to analyse the chemical bonding of carbon. The carbon KLL Auger peak changes its shape depending on the bonding configuration. The peak shapes of the carbon transitions are evaluated by means of factor analysis. The results were compared with NMR measurements of the same films. For an adequate evaluation, electron and ion beam damage has to be taken into account. For this reason variations of the sp 2 concentration in dependence of the irradiation dose have been investigated. Beam damage was observed in an ion dose range from 2 × 10 15 to 2 × 10 17 cm −2. For electron irradiation doses up to 6 × 10 17 electrons per cm 2, a small damage compared with ion bombardment could be detected.

Neue Methode zur quantitativen Analyse von AES-Spektren

The quantitative analysis of Auger electron spectra may lead to problems using Auger peak-to-peak heights (APPH), especially in connection with chemical peak deformation and peak overlap. To eliminate these problems a method has been developed and was applied to metalnonmetal compounds. An integral spectrum is fitted with reference spectra and correction spectra, background differences are compensated. To deal with chemical effects a digital filter process is used. In order to test this method a copper-palladium alloy series has been measured and evaluated according to this method. The results show that a more accurate quantification could be obtained than by using APPHs and sensitivity factors. As a further advantage, relative sensitivity factors are no longer necessary due to peak/background standardization.

Direct observation of the nucleation and growth modes of Ag/Si(111)

Direct observation in an ultrahigh vacuum scanning electron microscope (SEM) has revealed the growth modes of Ag on Si(111), previously deduced indirectly from analysis of Auger electron spectra, and the form and number of crystallites as a function of deposition time and temperature. At high temperatures, T s > 200°C, the silver grows definitively in a Stranski-Krastanov (layer plus island) growth mode, with a very strong dependence of the island density on the deposition temperature, varying from ≲ l0 6 to ∼ 10 10 cm −2 between T s = 500 and 200°C. The crystals have more or less regular hexagonal forms with (111) and {1 1 1} faces predominating with a height to width ratio which decreases with deposition time in the range 0.1–0.6. At temperatures below 200°C, the island density is too high to be observed directly by SEM, and silver appears to grow in a Frank-van der Merwe (layer by layer) mode. However, this uniform deposit is unstable on heating above 200°C, and annealed deposits recreate rather similar islands. An analysis of published Auger amplitude-time curves is made to estimate the initial island density produced by depositions below T s = 200° C, and it is shown that these densities constitute a very reasonable extrapolation of the higher temperature SEM values. A model of Stranski-Krastanov growth is given in outline and applied to Ag/Si(111). It is argued that the island density is determined largely by island instability at high temperatures, even though condensation is complete. At low temperatures it is argued that Stranski-Krastanov growth becomes essentially equivalent to Frank-van der Merwe growth for high enough island density, for kinetic rather than thermodynamic reasons, without any change in the basic Stranski-Krastanov mechanism.

Some Problems in the Analysis of Auger Electron Spectra

Auger electron spectroscopy has been used in this study to determine common impurities found on the transition metals Sc, Ti, V, Cr, Fe, Co, Ni, Y, Zr, Nb, Mo, Ru, Rh, La, Hf, Ta, W, Re, Ir, Pt, and Au. Single crystal and polycrystal specimens were used, with both specimen types giving similar results. The most prevalent impurity on most of these surfaces is not carbon as had been previously supposed but rather is sulfur. Mild heat treatment causes sulfur to segregate at the surfaces of these materials, while more drastic heating, to 1000 °C or greater, will normally remove all the sulfur. Clean Mo surfaces exhibit a peak in the Auger spectrum at 150 V, the location of the sulfur peak, but arguments are given to suggest that this peak is characteristic of the clean rather than the contaminated surface. Observations of chemical shifts in Auger spectra have been made and are also discussed.