KLL Auger Peak Research Articles

Quantification of aluminium and silicon‐containing materials using Ag Lα X‐rays

In recent years, instrument manufacturers have been providing laboratory‐based HAXPES (hard X‐ray photoelectron spectroscopy) instruments that have monochromated silver Lα, chromium Kα and gallium Kα X‐ray sources. To be more than a qualitative tool, two things are required: calibration of the signal intensity as a function of kinetic energy (spectrometer response function) and relative sensitivity factors. This is now possible because of routines being available to generate the spectrometer response functions for dual Al Kα/Ag Lα X‐ray sources and the availability of Cant average matrix relative sensitivity factors (AMRSFs). However, to improve accuracy when using the Cant AMRSF care needs to be taken in the definition of the peak areas being used. This is because they need to include the total intrinsic signal that often extends beyond the main peak. This is a particular challenge when quantifying using the Al 1s peak generated with Ag Lα X‐rays as some of the intrinsic signal overlaps with the Al KLL Auger peak. When materials include both aluminium and silicon atoms, the Si 2s and 2p peaks sit upon extended signals coming from the Al 2s and 2s peaks, respectively. Thus, quantification should be limited to using the main peak area, which necessitates different relative sensitivity factors (RSFs). Using polydimethylsiloxane (PDMS) and sapphire (Al2O3) as model systems, experimental RSFs have been determined for use with the main peaks for O 1s, Al 1s, Al2s Al 2p, Si 1s, Si 2s and Si 2p subshells normalized to the RSF of the carbon 1s main peak.

Exfoliation methods for compositional and electronic characterization of interfacial Mo(Sex,Sy) in Cu(In,Ga)(Se,S)2 solar cells by X‐ray and UV photoelectron spectroscopy

Mo(SexSy) is a transition metal dichalcogenide typically applied as a back contact interlayer in Cu(In,Ga)(Se,S)2 (CIGSSe) solar cells. Band alignment at the buried Mo/CIGSSe junction mediated by Mo(SexSy) is important for current transport and enables quasi‐ohmic behavior between the CIGSSe absorber and the Mo back electrode. Furthermore, the S/(Se + S) ratio is a crucial parameter that determines the height of the valence band offset at the CIGSSe/Mo(SexSy) interface. Because the interlayer is formed during rapid thermal processing, an MoSe2 or MoS2 thin film grown on free substrate surfaces will not be representative for a realistic solar cell device. Thus, for fundamental thin‐film material analysis, as well as functional characterization and modeling, appropriate preparation and analytical techniques are required in order to prevent artifacts. In principal, the weak van der Waals forces between two‐dimensional stacked Mo(SexSy) sheets allow the implementation of exfoliation procedures to generate free Mo(SexSy) surfaces out of CIGSSe solar cell layer stacks. In this article, two different exfoliation‐based Mo(Sex,Sy) preparation methods are investigated and evaluated with respect to subsequent surface analytical characterization by X‐ray and ultraviolet photoelectron spectroscopy. A special focus is laid on an artifact‐free characterization of chemical and electronical properties of the exposed layers for a number of samples. In a first instance, the compositional Se/S and (Se + S)/Mo ratios at the surface are quantitatively analyzed on the basis of dedicated peak‐fitting routines. Artifacts from carbonaceous contamination due to different exfoliation glues can be prevented through a detailed comparative analysis of carbon 1s and KLL Auger peaks. Furthermore, a significant surface band bending is observed that can be reduced by low‐energy Ar ion in situ sputtering. A simple model for the sputter removal of a charged surface layer is presented, which allows to approximately calculate the absolute valence band maximum (VBM) positions required for band alignment and numerical device simulations. The presented exfoliation surface analysis methodology is important for the whole CIGS(Se) solar cell community and may be of general interest for emerging applications of further 2D transition metal dichalcogenides as well.

Raman spectroscopy and X-ray photo-spectroscopy analysis of graphite media irradiated at low doses

We explore the utility of controlled low-doses (0.2–100 Gy) of photon irradiation as initiators of structural alteration in carbon-rich materials. To-date our work on carbon has focused on β-, x- and γ-irradiations and the monitoring of radiotherapeutic doses (from a few Gy up to some tens of Gy) on the basis of the thermoluminescence (TL) signal, also via Raman and X-ray photo-spectroscopy (XPS), providing analysis of the dose dependence of single-walled carbon nanotubes (SWCNT). The work has been extended herein to investigate possibilities for analysis of structural alterations in graphite-rich mixtures, use being made of two grades of graphite-rich pencil lead, 8H and 2B, both being in the form produced for mechanical pencils (propelling or clutch pencils). 2B has the greater graphite content (approaching 98 wt %), 8H being a mixture of C, O, Al and Si (with respective weight percentages 39.2, 38.2, 9.8 and 12.8). Working on media pre-annealed at 400 °C, both have subsequently been irradiated to penetrating photon-mediated doses. Raman spectroscopy analysis has been carried out using a 532 nm laser Raman spectrometer, while for samples irradiated to doses from 1 to 40 Gy, XPS spectra were acquired using Al Kα sources (hv ∼1400 eV); carbon KLL Auger peaks were acquired using 50 eV Pass Energy. At these relatively low doses, alterations in order-disorder are clearly observed, defect generation and internal annealing competing as dominating effects across the dose range.

X-ray absorption spectroscopy to determine originating depth of electrons that form an inelastic background of Auger electron spectrum

In Auger electron spectroscopy (AES), the spectral background is mainly due to inelastic scattering of Auger electrons that lose their kinetic energy in a sample bulk. To investigate the spectral components within this background for SiO2(19.3 nm)/Si(100) with known layer thickness, X-ray absorption spectroscopy (XAS) was used in the partial-electron-yield (PEY) mode at several electron kinetic energies to probe the background of the Si KLL Auger peak. The Si K-edge PEY-XAS spectra constituted of both Si and SiO2 components at each kinetic energy, and their component fractions were approximately the same as those derived from the simulated AES background for the same sample structure. The contributions of Auger electrons originating from layers at different depths to the inelastic background could thus be identified experimentally.

Time of flight spectra of electrons emitted from graphite after positron annihilation

Low energy (~2 eV) positrons were deposited onto the surface of highly oriented pyrolytic graphite (HOPG) using a positron beam equipped with a time of flight (TOF) spectrometer. The energy of the electrons emitted as a result of various secondary processes due to positron annihilation was measured using the University of Texas at Arlington’s (UTA) TOF spectrometer. The positron annihilation-induced electron spectra show the presence of a carbon KLL Auger peak at ~263 eV. The use of a very low energy beam allowed us to observe a new feature not previously seen: a broad peak which reached to a maximum intensity at ~4 eV and extended up to a maximum energy of ~15 eV. The low energy nature of the peak was confirmed by the finding that the peak was eliminated when a tube in front of the sample was biased at -15 V. The determination that the electrons in the peak are leaving the surface with energies up to 7 times the incoming positron energy indicates that the electrons under the broad peak were emitted as a result of a positron annihilation related process.

Oxidation and thermal reduction of the Cu(1 0 0) surface as studied using positron annihilation induced Auger electron spectroscopy (PAES)

Changes in the surface of an oxidized Cu(1 0 0) single crystal resulting from vacuum annealing have been investigated using positron annihilation induced Auger electron spectroscopy (PAES). PAES measurements show a large increase in the intensity of the annihilation induced Cu M 2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 °C. The intensity then decreases monotonically as the annealing temperature is increased to ∼600 °C. Experimental probabilities of annihilation of surface-trapped positrons with Cu 3p and O 1s core-level electrons are estimated from the measured intensities of the positron annihilation induced Cu M 2,3VV and O KLL Auger transitions. Experimental PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface, surface reconstructions, and electron–positron correlations effects. The effects of oxygen adsorption on localization of positron surface state wave function and annihilation characteristics are also analyzed. Possible explanation is proposed for the observed behavior of the intensity of positron annihilation induced Cu M 2,3VV and O KLL Auger peaks and probabilities of annihilation of surface-trapped positrons with Cu 3p and O 1s core-level electrons with changes of the annealing temperature.

VALENCE ELECTRONIC STRUCTURE OF OXYGEN-MODIFIED α-Mo2C(0001) SURFACE: ANGLE-RESOLVED PHOTOEMISSION STUDY

Adsorption of oxygen on α- Mo 2 C (0001) is investigated with Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES) utilizing synchrotron radiation. It is found that C KLL Auger peak intensity does not change during O 2 exposure, indicating that the depletion of C atoms does not proceed. It is deduced from ARPES and LEED results that adsorbed oxygen atoms from a well-ordered (1 × 1) lattice on the α- Mo 2 C (0001) surface. The ARPES study shows that oxygen adsorption induces a peculiar state around Fermi level (E F ). Off-normal-emission measurements prove that the state is a half-filled metallic state.

Quantitative Auger electron spectroscopy of SiC

The article is devoted to quantitative Auger electron spectroscopy (AES) of silicon carbide (SiC). It compares the results obtained by various procedures applied to LVV and KLL Auger peaks of silicon (Si) for determining the Auger current. We have found that reliable results for the content of Si in SiC can be achieved by the method in which the Auger current is determined as the area below the Auger peak in the direct N( E) spectrum after subtracting the background of inelastically scattered Auger electrons of the given peak and of the so-called true secondary electrons. The achieved results have also shown that bombardment of SiC by Ar + ions with energy 1 keV at an angle of 68° with respect to the surface normal while the sample rotates at 6 rpm leads to Si depletion of SiC in comparison with its stoichiometric composition.

Surface study and thickness control of thin Al2O3 film on Cu–9%Al(111) single crystal

We were successful in growing a uniform flat Al2O3 film on the Cu–9%Al(111) surface using the improved cleaning process, low ion energy and short time sputtering. The growth of ultra-thin film of Al2O3 on Cu–9%Al was investigated using Auger electron spectroscopy (AES) and a scanning electron microscope (SEM). The Al2O3 film whose maximum thickness was about 4.0nm grew uniformly on the Cu–9%Al surface. The Al and O KLL Auger peaks of Al2O3 film shifted toward low kinetic energy, and the shifts were related to Schottky barrier formation and band bending at the Al2O3/Cu–9%Al interface. The thickness of Al2O3 film on the Cu–9%Al surface was controlled by the oxygen exposure.

On the determination of carbon sp 2/sp 3 ratios in polystyrene–polyethylene copolymers by photoelectron spectroscopy

A series of monodisperse polystyrene/polyethylene tapered block copolymers, with known carbon sp 2/sp 3 ratios, was evaluated by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The principal component of the C1s peak exhibited no useful variation in shape as the sp 2 concentration was varied. The valence band spectra, however, were found to vary in a systematic manner with the sp 2 concentration. This variation was reflected in the X-ray excited C KLL Auger peak, the structure of the Auger peak providing a ready characterization of the carbon sp 2 concentration. The problem of determining the sp 2/sp 3 ratio in hydrogenated amorphous carbon is discussed.

The chemical state vector: a new concept for the characterization of oxide interfaces

AbstractFor certain metal oxides deposited as a thin film on the surface of another oxide, changes may occur in the binding energy (BE) of the photoelectron peaks as well as in the kinetic energy (KE) of the Auger peaks of the deposited cation and consequently in its Auger parameter. These changes are illustrated here for the systems formed by SiO2 deposited onto TiO2 and Al2O3. Shifts by −1.3 and −1.0 eV in the Si 2p BE and by 2.3 and 0.7 eV in the KE of the Si KLL Auger peak are found for these two systems when comparing the values obtained for small amounts of SiO2 directly interacting with the support with those of a thick film of this material.The different values of these electronic parameters obtained for increasing amounts of SiO2 can be represented in a Wagner plot. The tendency and magnitude of the changes are similar to those found for Si in phyllosilicate or zeolite compounds with different Si/Al ratios.To systematize these changes in the electronic parameters of the deposited phase the new concept of ‘chemical state vector’ is proposed. It is defined as the vector that connects the two extreme points of a Wagner plot dot graph where the BE of photoelectron peaks is represented versus the KE of the Auger peaks for a cation M of a given MO/M′O interface. The possibilities and limitations of this concept are discussed with regard to the SiO2/TiO2 and SiO2/Al2O3 interface systems reported in this paper and the data for other MO/M′O systems taken from previous works. Copyright © 2001 John Wiley & Sons, Ltd.

Structure, microstructure and electronic characterisation of the Al 2O 3/SiO 2 interface by electron spectroscopies

Al 2O 3 has been deposited by evaporation and post-oxidation of Al on a flat SiO 2 substrate. The obtained films have been analysed by X-ray photoemission spectroscopy (XPS) and reflection electron energy loss spectroscopy (REELS). It has been found that the modified Auger parameter of Al varies by ∼2.2 eV between a low coverage situation (below an equivalent monolayer) and the bulk material. This change has been attributed to variations in the coordination state of the aluminium atoms. Some minor contributions due to bonding and polarisation effects are also detected. Valence band photoemission and REELS have shown that the band gap energy of the deposited Al 2O 3 increases as the coverage decreases. These effects are discussed in terms of the bonding interactions between the SiO 2 and Al 2O 3 at the interface between the two oxides. Sandwich structures formed by approximately one equivalent monolayer of Al 2O 3 intercalated between SiO 2 present Auger parameter and band gap energy values which are larger than those of a monolayer-like Al 2O 3 thin film supported on SiO 2. Also, it has been shown that the energy of the plasmon losses behind the Al KLL Auger peak can be used as a fingerprint to discriminate between supported Al 2O 3 thin films or layers of this material embedded within a sandwich structure of two SiO 2 layers.

Anomalous behaviour in resonant Auger emission of SiO x thin films

Silicon oxide (SiO x , x≈1.3) films ∼100 Å thick were prepared by evaporation from a silicon monoxide source. The stoichiometry and chemical state of the samples were characterised by X-ray photoemission spectroscopy showing that they can be described as a mixture of Si + and Si 3+ species. Further characterisation was done by X-ray absorption spectroscopy at the Si K edge. Resonant Auger effects were studied by tuning the photon energy across the Si K edge and measuring the corresponding excited Auger spectra. A strong and ‘anomalous’ dispersion is found for the resonant Si KLL Auger peak, probably associated to Si + species: in this case, the energy of the Si KLL signal decreases when the photon energy is increased across the Si K edge. This behaviour is the opposite of that observed for Si 4+ species in SiO 2 and for similar Auger resonant phenomena studied for many materials. It is also in apparent contradiction with the prediction of the available theories of resonant Auger emission. Resonant Auger spectroscopy appears to be an adequate technique to distinguish between different electronic environments in SiO x interfaces or compounds. Moreover, for the range of compositions studied here, it is proposed as a mean to establish whether the different Si n+ species are distributed through a common SiO network or are segregated into separated phases.

Mobile UHV set-up for the investigation of electron spectra at large accelerators: First results on high charge effects

We measured energy spectra of electrons from sputter cleaned amorphous carbon targets induced by swift ions of constant velocity (Ep/Mp=9 MeV/u) with a new mobile ultra high vacuum set-up designed for large scale accelerators. We varied the projectile charge qp from 6 to 27. The shape of the spectra was found to depend strongly on qp: a qp2 scaling law at large electron energies and a strong saturation with increasing qp for low energy electrons (below the 1 s ionization threshold) are observed. We also observed an additional feature on the high energy side of the KLL Auger peak, for large projectile charges only. This additional peak may be interpreted as a hypersatellite line due to the double ionization of the K shell.

High-resolution AlKα and high-photon energy CrKβ-excited X-ray photoelectron spectroscopy of titanium nitride

Abstract Samples of titanium nitride were magnetron sputter deposited and transferred in situ to be studied by X-ray photoelectron spectroscopy using high-energy Cr K β radiation and high-resolution Al K α radiation. The determination of the Auger parameter of titanium in titanium nitride using the Ti KLL Auger peak has been carried out at a series of compositions using the Cr K β radiation. The Auger parameter changes by a relatively small amount with composition showing that the extra-atomic relaxation in TiN x is similar to that of the metal, and suggests that charge transfer is largely responsible for the titanium core level peak shifts. The spectral structure of the N1s photoemission peak at high-energy resolution revealed the development of multiple nitrogen environments at high nitrogen concentration, suggesting vacancies on the titanium sublattice or a highly defective structure. The various titanium photoelectron and Auger peaks reveal satellites which can be explained either by two or more local environments for the titanium atoms in fcc titanium nitride, or by a screening mechanism giving two different peaks for equivalent titanium environments.

K Auger electron emission from hollow Ne atoms in solids

We studied the K Auger emission of hollow Ne atoms in an Al solid using the recently developed multiple cascade model that describes the filling of inner shells of highly charged ions in solids. In particular we have taken into account the KLC Auger transition that occurs early in the filling sequence of the hollow atom. In the KLC Auger process the emitted electrons originate from the induced screening cloud (C) that surrounds the highly charged ion in the solid. The KLC Auger electrons appear in the measured electron spectra well separated at the high energy side of the KLL Auger peak. From the comparison of the experiment and the model we obtain a fair estimate of the KLC Auger rate.

CEMS and AES Investigations on Iron Silicides

Thin layers of iron silicides produced by ion implantation were investigated by 57 Fe conversion electron Miissbauer spectroscopy and Auger electron spectroscopy. The Mossbauer hyperfine parameters were calculated and compared with results obtained at crystalline layers to determine the phases formed. It was found that, depending on the implantation conditions, the phases α- and β-FeSi 2 , e-FeSi or mixtures of them are formed. Auger electron spectroscopy was used to analyse the depth distribution of the elements in the layer. The iron concentrations necessary, according to the equilibrium phase diagram, to form the compounds mentioned above were not reached as a result of the implantation. Therefore, the formation of precipitates is concluded. Furthermore, it was found that the Si KLL Auger peak is very sensitive to silicide bonding. Its energy shift can be used as an indicator for silicide formation.

Multistep cascade model for the deexcitation of highly charged ions impinging on a solid surface.

We introduce a multistep cascade model for the deexcitation of highly charged ions in the presence of a solid. We apply this model to analyze the yield of the KLL-Auger peak as measured in angular resolved electron energy spectra. The calculation makes use of three probability densities, one for the time distribution of the Auger decay, one for the transport of the ions through the first atomic layers of the target, and the last one for the transport of the electrons from the source to the detector. Each of these probabilities is discussed and modeled. The calculations are compared to measurements of KLL-Auger electrons from low-energy ${\mathrm{Ne}}^{9+}$ ions impinging on solid Al. The results support previous estimations that the L-shell sidefeeding of the projectile depends on the incident velocity. For ion energies greater than 1000 eV, the mean path length needed to capture an electron is found to be approximately equal to the next-neighbor distance in the Al lattice. We estimate the yield of KLL electrons emitted from Ne ions with 2,3,...,8 electrons in the L shell. The mean depth of emission of the KLL electron is determined.

KLL and LMM Auger peak intensity ratio dependence on bond ionicity

A study of the influence of element bond ionicity on ratios shows that a decrease of the ratios of the KL 23 L 23 to KL 1 L 23, L 23 M 23 M 23 to L 23 M 1 M 23, and L 23 M 23 M 23 to L 3 M 23 M 45 peak intensities occurs with an increase in the effective negative charge of the atom. These dependences are explained by decreasing spatial separation of the 2s and 2p, 3s and 3p, and 3p and 3d electrons. The decreasing spatial separation of the 2s and 2p and the 3p and 3d electrons with increase of the atom effective negative charge becomes less abrupt with increasing element atomic number.

Titanium Carbide by AES

The Auger electron spectra for titanium carbide are presented. The first derivative Auger electron spectrum for the C KLL line is characteristic of a carbide. The differentiated C KLL peak contains three components present at the approximate kinetic energies of 250, 260, and 270 eV, with the peak at 270 eV having a greater intensity in the positive direction than adventitious hydrocarbon. The unique shape of the differentiated C KLL Auger peak can be used to identify this carbide compound.