Tougaard Method Research Articles

Reference survey spectra of elemental solid measured with Cr Kα photons as a tool for Quases analysis (3): Transition metals period 6 elements (Hf, Ta, W, Re, Ir, Pt, Au)

Several pure bulk materials were analyzed using laboratory-based hard x-ray photoelectron spectroscopy. The spectra are surveys measured using monochromatic Cr Kα radiation at 5414.8 eV after removal of surface contamination or oxidation. These aim to be references for inelastic background analysis using the Tougaard method.

Reference survey spectra of elemental solid measured with Cr Kα photons as a tool for Quases analysis (1): Transition metals period 4 elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn)

Several pure bulk materials were analyzed using laboratory-based hard x-ray photoelectron spectroscopy. The spectra are surveys measured using monochromatic Cr Kα radiation at 5414.8 eV after removal of surface contamination or oxidation. These aim to be references for inelastic background analysis using the Tougaard method.

Reference survey spectra of elemental solid measured with Cr Kα photons as a tool for Quases analysis (2): Transition metals period 5 elements (Y, Zr, Nb, Mo, Ru, Rh, Pd, and Ag)

Several pure bulk materials were analyzed using laboratory-based hard x-ray photoelectron spectroscopy. The spectra are surveys measured using monochromatic Cr Kα radiation at 5414.8 eV after removal of surface contamination or oxidation. These aim to be references for inelastic background analysis using the Tougaard method.

Reference survey spectra of elemental solid measured with Cr Kα photons as a tool for Quases analysis (4): Group III and IV elements (B, Al, In, C, Si, Ge, Sn, Pb)

Several pure bulk materials were analyzed using laboratory-based hard x-ray photoelectron spectroscopy. The spectra are surveys measured using monochromatic Cr Kα radiation at 5414.8 eV after removal of surface contamination or oxidation. These aim to be references for inelastic background analysis using the Tougaard method.

Reference survey spectra of elemental solid measured with Cr Kα photons as a tool for Quases analysis (5): Various elements (Mg, Sb, Bi, Se, Gd, Dy, Yb)

Several pure bulk materials were analyzed using laboratory-based hard x-ray photoelectron spectroscopy. The spectra are surveys measured using monochromatic Cr Kα radiation at 5414.8 eV after removal of surface contamination or oxidation. These aim to be references for inelastic background analysis using the Tougaard method.

Toward Understanding the Reactivity of Garnet-Type Solid Electrolytes with H2O/CO2 in a Glovebox Using X-ray Photoelectron Spectroscopy and Electrochemical Methods.

Chemical stability of garnet-type lithium ion conductors is one of the critical issues in their application in all-solid-state batteries. Here, we conducted quantitative analysis of impurity layers on the garnet-type solid electrolytes, Li6.5La3-xAExZr1.5-xTa0.5+xO12 (x = 0 and 0.1; AE = Ca, Sr, and Ba), by means of X-ray photoelectron spectroscopy (XPS) and electrochemical methods. Two complimentary XPS techniques were employed: (i) background analyses by Tougaard's method and (ii) relative intensity analyses of La 3d/La 4d spectra to determine the surface chemical composition. XPS revealed that even after cleaning by annealing and polishing, the surface is covered by LiOH- and Li2CO3-based compounds with a thickness of 4-6 nm within 30 min as a result of the reaction with traces of H2O (<0.5 ppm) and CO2 (<5 ppm) in an Ar-filled glovebox. The sensitivity to H2O and CO2 depends on the basicity of dopants. Ba-doped solid electrolytes exhibited the thickest impurity layers compared to Sr- and Ca-doped compounds. A surface cleaning process, consisting of annealing and polishing, effectively reduces the charge-transfer resistance to 10-15 Ω cm2 because of negligible impurity layers. Highest short-circuit tolerance is obtained for a 700 °C annealed specimen (critical current density: 0.5 mA cm-2), which is possibly due to the strengthened grain boundaries by Li2CO3 among grains around its melting point.

Surface Analysis of 4-Methyl-2-Phenyl-Imidazole on the Cu Surface

Corrosion problems represent a large portion of the total costs in diverse industrial fields for companies every year worldwide. Moreover, appropriate corrosion control can help avoid many potential disasters that can cause serious issues including loss of life, negative social impacts, and water resource and environmental pollution. It is almost impossible to prevent corrosion, however it is possible to control it. Commonly, organic compounds are used as corrosion inhibitors. The studied compound herein, MePhI, is presented for the first time to protect any metallic material against corrosion. This compound effectively protects copper from corrosion in a highly corrosive chloride solution even after 0.5 year of immersion. To study this system X-ray photoelectron spectroscopy was employed. Using the Tougaard method a surface layer thickness of the MePhI was determined to be 0.3-0.5 nm by analyzing the background of the XPS survey spectrum. Moreover, orientation and the manner of bonding of MePhI on the Cu surface is explained especially by examining the XPS-excited Auger Cu L3M4,5M4,5 spectra, which is a “fingerprint” of a Cu(I)-MePhI connection. Angle-resolved XPS measurements suggest that both the C and N atoms of the MePhI molecule are involved in the inhibitor surface bonding. Finally, it is also suggested that MePhI molecules are lying flat on the surface.

Inelastic background analysis of HAXPES spectra: towards enhanced bulk sensitivity in photoemission

We report on quantitative inelastic background analysis in hard X‐ray photoelectron spectroscopy at high excitation energy (12–18 keV) using the Tougaard method implemented with careful optimisation of the inelastic scattering cross section. Such a method enables the determination of the in‐depth elemental distribution over depths up to70 nm. We studied three parameters and investigate their influence on the results: the depth of the layer increases the uncertainty, the thickness and composition of the layer has an influence on statistics, and the excitation energy that must be chosen as a trade‐off between high probing depth and low photoionization cross section. We show how this promising method can be used to follow diffusion of a 1‐ML La layer after annealing a technologically relevant sample. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Cr/Fe Ratio by Xps Spectra of Magnetoelectropolished Aisi 316L SS Using Linear, Shirley and Tougaard Methods of Background Subtraction

In the paper, the analyses of Fe2p3/2 and chromium Cr2p3/2 XPS spectra with fitting by symmetrical and asymmetrical line shapes as well as using Linear, Shirley and Tougaard Method of Background Subtraction are presented. The calculations are performed on AISI 316L SS biomaterial after magnetoelectropolishing MEP operation. It was found, the chromium-to-iron ratio after magnetoelectropolishing MEP for other analyses could be in the range from 2.2 to 6.2 depending on the line shapes as well as type of backgrounds used to XPS spectra fitting. The most important for comparison the surface layers concerning the Cr/Fe ratio is to use the same line shape and backgrounds for all analyses.

Nitrogen plasma functionalization of low density polyethylene

Low density polyethylene (LDPE) films have been treated with different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface and analyzing the changes experienced in their surface tension. Effects of a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure are compared with those obtained by using an atom source supplied with N2 and mixtures Ar+NH3 as plasma gas. X-ray photoelectron spectroscopy (XPS) analysis has provided information about the chemical surface changes whereas the surface topography of the treated samples has been examined by atomic force microscopy (AFM). Non-destructive depth profiles of oxygen and carbon have been obtained for the treated and one month aged samples by means of the non-destructive Tougaard's method of XPS background analysis. Generally, an oxygen enrichment of the deeper region of treated LDPE surfaces has been observed. Chemical derivatization of the treated samples has shown that a DBD plasma with a mixture of Ar+NH3 was the most efficient treatment for nitrogen and amine group functionalization. It is argued that the high concentration of NH* species in this plasma is the most important factor in enhancing the nitrogen functionalization of this polymer. It has been also found that the observed increase in hydrophilicity and surface tension cannot be attributed to the anchored nitrogen functional groups formed on plasma treated LDPE. Differences in the plasma activation behaviour of LDPE and that of other polymers subjected to similar treatments are stressed.

Study of the morphology of NiO nanostructures grown on highly ordered pyrolytic graphite, by the Tougaard method and atomic force microscopy: a comparative study

AbstractWe studied the morphology of the deposits of NiO grown on highly ordered pyrolytic graphite (HOPG), by means of inelastic peak shape analysis and atomic force microscopy. The results obtained by both techniques show an excellent agreement. The results indicate that NiO grows on HOPG by following the Stransky–Krastanov type of growth. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Surface Analysis of 1-Hydroxybenzotriazole and Benzotriazole Adsorbed on Cu by X-Ray Photoelectron Spectroscopy

The surface chemistry of two corrosion inhibitors, 1-hydroxybenzotriazole (BTAOH) and benzotriazole (BTAH), adsorbed on copper from 3% NaCl aqueous solution, was investigated by X-ray photoelectron spectroscopy (XPS). Surface and subsurface chemical structure, composition, and layer thickness were obtained from angle-resolved XPS measurements, from detailed analysis of the background in the XPS spectra by the Tougaard method, and from XPS depth profiling performed by Ar-ion sputtering. The main concern was the shape of the X-ray induced Auger Cu spectrum that offers the possibility to investigate the Cu(I) environment. The Auger Cu spectrum obtained after treatment in the BTAH-containing solution was decomposed into three components originating from the Cu(I)BTA complex layer, the underlayer, and the Cu substrate. This procedure indicates the formation of the Cu(I)BTA surface complex on the underlayer after BTAH treatment. The BTAH molecules [either in the Cu(I)BTA complex or uncomplexed] are directed toward the Cu surface through their triazole N atoms. In contrast to the BTAH treatment, the Cu-BTAOH layer formed on the Cu surface after treatment in the BTAOH solution is less ordered and is much thinner than the Cu-BTAH structure.

Non-destructive depth compositional profiles by XPS peak-shape analysis

The measured peak shape and intensity of the photoemitted signal in X-ray photoelectron spectroscopy (XPS) experiments (elastic and inelastic parts included) are strongly correlated, through electron-transport theory, with the depth distribution of photoelectron emitters within the analyzed surface. This is the basis of so-called XPS peak-shape analysis (also known as the Tougaard method) for non-destructive determination of compositional in-depth (up to 6-8 nm) profiles. This review describes the theoretical basis and reliability of this procedure for quantifying amounts and distributions of material within a surface. The possibilities of this kind of analysis are illustrated with several case examples related to the study of the initial steps of thin-film growth and the modifications induced in polymer surfaces after plasma treatments.

Characterization of gold nanoclusters deposited on HOPG by atmospheric plasma treatment

AbstractThe interest of gold nanoparticles in the field of nanocatalysis and nanosensors is growing. For example, carbon nanotubes covered with gold nanoclusters could present interesting properties in catalysis or/and in devices based on catalytic reaction such as chemical gas sensor. Unfortunately, the characterization of nanoparticles deposited onto a substrate is generally not a trivial exercise. Indeed, in many cases, the amount and size of material deposited is in the range of the sensitivity limits and the spatial resolutions of the techniques used. In that respect, our system, i.e. gold deposited onto a carbon support, is a favourable case, due to the high difference between the atomic numbers of gold and carbon.In this work, gold nanoparticles were deposited onto a HOPG (Highly Oriented Pyrolitic Graphite) substrate using an atmospheric plasma. In this preliminary study, HOPG sample has been used as a model surface that could present the same chemical properties as multiwall carbon nanotubes (MWCNTs).The surface composition was analysed using X‐ray photoelectron spectroscopy (XPS). Narrow region electron spectra were used to extract the chemical‐state information from the C 1s, O 1s and Au 4f peaks. The Au 4f spectral line shape was also analysed using the QUASES–Tougaard software package in order to obtain the in‐depth concentration profile of the resulting nanomaterial. This result evidences a good agreement between experiment and modelling. Indeed, field emission scanning electron microscope (FE‐SEM) and atomic force microscopy (AFM) images highlight a homogeneous distribution of 10 nm‐size gold clusters with a surface coverage of 12% on the HOPG surface, both in agreement with the results obtained with the Tougaard and coworkers method. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Nucleation of ZnTe on the As-Terminated Si(112) Surface

We employ a suite of surface analysis techniques that probe the outermost ZnTe/As-Si(112) surface to generate an understanding of the initial stages of the heteroepitaxial HgCdTe/CdTe/ZnTe/As-Si(112) layer formation. Ion scattering spectroscopy (ISS), reflection-high energy electron diffraction (RHEED), along with nondestructive depth profiles by angle-resolved x-ray photoelectron spectroscopy (XPS) are successfully applied to clarify and support the nucleation stages of ZnTe formation on the As-terminated Si(112) substrate. Data indicate a slow growth of the first ZnTe layer. In addition, no evidence of thick ZnTe island formation exists. The current ZnTe formation process generates full coverage on the Si(112) surface after six to nine MBE cycles. In order to fully understand the details of the ZnTe nucleation process on the Si(112) substrate, we present an inelastic background analysis with the Tougaard method to study surface morphology.

Quantification and IMFP determination of multilayer Langmuir–Blodgett films by AFM and XPS measurements

AbstractXPS spectra of cadmium arachidate Langmuir–Blodgett (LB) multilayer films have been investigated by quantitative peak shape and intensity analysis (the Tougaard method). The structure and film thickness of cadmium arachidate multilayer (1–21 layers) LB films on silicon wafers were observed by atomic force microscopy (AFM). The monolayer and bilayer thickness of cadmium arachidate LB film was determined to be 2.3 and 5.5 nm from AFM images of partially scratched multilayer LB films. The angle‐resolved XPS (ARXPS) spectra of these LB films with well‐defined thickness were analyzed by the Tougaard method. The inelastic mean free paths (IMFPs) in the LB film were determined to be 35.5 Å at 1382 eV and 29.1 Å at 1078 eV from analysis of ARXPS spectra taken at several emission angles (10°, 32° and 45° from the surface normal). These values are in good agreement with the reported values of bulk organic materials. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Surface segregation of photoresist copolymers containing polyhedral oligomeric silsesquioxanes studied by x-ray photoelectron spectroscopy

Copolymers containing polyhedral oligomeric silsesquioxane (POSS) pendant groups and various acrylate type monomers are studied by x-ray photoelectron spectroscopy. These copolymers have potential application as bilayer resist material for next generation lithography. Two methods are used in order to characterize resist surfaces, angular resolved XPS and inelastic background signal quantification (Tougaard method). The existence of a surface layer rich in POSS is proven. About 1.5nm thick, this layer stands above a material with uniform POSS concentration. Evaluation of POSS concentration depth profiles shows that surface segregation depends on the polymer comonomers and on the silicon content.

XPS study of carboxylic acid layers on oxidized metals with reference to particulate materials

AbstractLow‐molecular‐weight organic additives such as stearic acid are commonly used as surface additives in powder injection moulding (PIM). It is therefore important to know how the additives interact with the surface of the powder used. In this study, such interactions are studied by means of controlled adsorption of carboxylic acids on the oxides of interest. The oxides are prepared by oxidation of flat samples of Fe, Cr, Mn and Si. Surface chemical characterization is done by means of XPS, the main approach on flat samples being a comparison of angle‐resolved analysis and the use of the Tougaard nanostructure analysis technique. Taking advantage of this comparison, the Tougaard method is then applied in the evaluation of XPS analyses of stainless‐steel powder with adsorbed stearic acid. In addition, time‐of‐flight SIMS analysis is used to verify the adsorption of stearic acid on the powder surface.It is shown that Tougaard nanostructure analysis can be used for determining the thickness of an organic layer on particulate material. The layer thickness of adsorbed stearic acid was estimated to be ∼20 Å, corresponding to monolayer adsorption. Time‐of‐flight SIMS analysis verified the adsorption of stearic acid on the powder surface. From the XPS analysis of flat samples it was determined that the use of the metal/oxide universal cross‐section in Tougaard nanostructure analysis best described the increased background due to adsorption of carboxylic acids, and that information about molecular orientation could be gained. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Experimental estimation of surface excitation parameter for surface analysis

AbstractThe surface excitation produced by impinging or escaping electrons is a competitive process to elastic backscattering. It affects the intensity of Auger and XPS peaks and is characterized by the surface excitation parameter Pse. This appears in the surface loss peak I(Epls), and possibly a surface plasmon. In our work Pse is defined as the ratio of the probability to create a surface plasmon/elastic scattering and is deduced from the integrated surface loss peak and elastic peak, respectively. Our procedure is based on reflection electron energy loss spectroscopy and elastic peak electron spectroscopy spectra and Kλi spectra (K is the inelastic scattering cross‐section and λi is the inelastic mean free path), determined using Tougaard's method. The normalized Kλi curves are fitted to the spectrum at E = 5 keV (primary energy) and EL = Epl1 (volume plasmon), approximated with the Lorentzian type three‐parameter formula of Tougaard. For E&gt;Epl1, the normalized curves are overlapping and Pse is deduced from the integrated difference spectra fitted with the Tougaard cross‐sections. The procedure was applied on materials exhibiting surface and volume plasmons: III–V semiconductors (GaAs, InSb) and In and Sb metals. The REELS experiments were carried out with an ESA 31 HSA spectrometer covering the E = 0.2–5 keV energy range. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Comparison of the Tougaard, ARXPS, RBS and ellipsometry methods to determine the thickness of thin SiO2 layers

AbstractThe Tougaard and angle‐resolved x‐ray photoelectron spectroscopy (ARXPS) methods were compared with ellipsometry and Rutherford backscattering (RBS) for their ability to determine the amount of SiO2 on an Si substrate. The Tougaard and ARXPS methods give generally consistent results (root‐mean‐square deviation ∼12%), whereas the deviation between the other techniques is significantly larger (∼30–40%). The Tougaard method gives consistent results for all angles of emission θ ≤ 60°. It is found also that the amount of SiO2 determined by the two methods depends approximately linearly on the inelastic mean free path. The ARXPS method also depends on the accuracy with which one can separate the peak area of the bulk and the oxide part of the peaks. The correction for elastic scattering in the ARXPS method gives a reduction of only 5–7% in the determined amount of SiO2. Copyright © 2002 John Wiley &amp; Sons, Ltd.