1s Signal Research Articles

Electrochemical nitriding of Sn in LiCl–KCl–Li 3N systems

Electrochemical nitriding of a liquid phase tin metal has experimentally been confirmed by using the oxidation of nitride ions in molten LiCl–KCl–Li 3N melts according to the following reactions: N 3 − = N ads + 3 e − N ads + Sn = SnN x From the XPS analysis, N 1s signal and Sn 3d signals are observed, which corresponds to the formation of SnN x , after conducting argon ion sputtering for 1000 s. This showed that a thick and stable nitride film was formed by electrochemical nitriding.

Looking 100 Å deep into spatially inhomogeneous dilute systems with hard x-ray photoemission

We present hard x-ray photoemission measurements from GaAs samples with a 10-Å-thick layer of AlAs buried at different depths. The intensity trend versus kinetic energy of the Al 1s signal allows extraction of the x-ray attenuation length, which we find to reach ∼100Å at a kinetic energy of 6 keV. On one sample exposed to air for several days we obtain qualitative information on the oxidation at different depth scales by exploiting the energy dependence of the attenuation length. This suggests the strong potential of hard x-ray photoemission in the nondestructive characterization of diluted materials on a depth scale interesting to modern nanotechnologies.

XPS and FT‐IR spectroscopy study of albumin adsorption on the surface of a π‐conjugated polymer film

AbstractThe interaction between thin films of polyphenylacetylene (PPA) and bovine serum albumin (BSA) dissolved in phosphate buffer solution (PBS) was studied by x‐ray photoelectron spectroscopy (XPS) and Fourier‐transform infrared spectroscopy (FT‐IR) performed in reflectance mode. PPA is a semiconducting π‐conjugated polymer consisting of a polyene backbone with phenyl pending groups, that has been used in the preparation of humidity sensors; therefore, we have tried to pre‐test PPA films for possible applications as biosensors.Thin films of PPA were incubated in buffered albumin solution (BSA/PBS) for increasing exposure times (24–96 hours). BSA adsorption on the PPA film surface takes place as demonstrated by the appearance of the N 1s signal and by the modifications in the C 1s core‐level signal in the XPS spectra of the samples treated with albumin solution; time‐dependent adsorption is also observed. Phosphate salts are co‐adsorbed on the PPA surface upon treatment with BSA/PBS solution. Albumin adsorption on the PPA surface was confirmed by FT‐IR measurements. Copyright © 2004 John Wiley & Sons, Ltd.

On surface distributions in natural cellulosic fibres

AbstractIn x‐ray photoelectron spectroscopy (XPS), knowledge of elemental depth distributions within the first 10 nm is often essential. However, none of the conventional XPS methods can reliably discern, for example, a thin overlayer from clusters on rough surfaces. Therefore, reliable experimental data on the actual distributions of lignin and extractives on the fibre surfaces is needed, although there are numerous XPS studies on cellulosic fibres and paper.We have studied surface distributions of organic compounds on natural cellulosic fibre materials (cotton, flax and softwood pulps) with XPS, using a novel approach introduced by Tougaard. We were able to model the surface composition of rough fibre surfaces via simple spectral analysis of the O 1s signal. The simple spectral background analyses used show that in the case of cotton and flax, the non‐cellulosic compounds cover the cellulosic fibre surface much more effectively than in softwood pulps, in spite of the smaller amount of non‐cellulosic material present. Copyright © 2004 John Wiley & Sons, Ltd.

High resolution X-ray photoelectron spectroscopy of 3-mercaptopropionic acid self-assembled films

Self-assembled layers of 3-mercaptopropionic acid deposited on Au(1 1 1) from solution have been investigated with synchrotron based, high resolution X-ray photoemission spectroscopy. Results obtained from pristine, X-ray irradiated and heated samples are reported. Pristine samples are characterized by an intense, dominant S 2p state at a binding energy of 162 eV (2p 3/2 level) assigned to thiolates. A less intense doublet around 163.3 eV is tentatively attributed to physisorbed molecules forming a partially occupied upper layer. Irradiation and heating cause the development of a third S 2p doublet around 161 eV which, by comparison with the literature, is assigned to atomic sulfur generated by S–C bond scission. The decrease of the C 1s and O 1s signals with annealing and irradiation, together with the increase of the S 2p state assigned to atomic sulfur, confirms the breaking of the C–S bond.

The early oxynitridation stages of hydrogen-terminated (100) silicon after exposure to N2:N2O. II. Silicon and oxygen bonding states

The early oxidation stages of hydrogen-terminated single-crystalline (100) silicon have been studied by X-ray photoemission spectroscopy, following the evolution of the Si 2p and O 1s signals after exposure to N2:N2O ambient at 850 °C for different durations. Evidence is given that the usual analysis of the film in terms of the Si 2p peak leads to inconsistencies, related to the presence in the film of non-siloxanic bridges, as oxygen-rich defects (like hydroxyl terminations or peroxo bridges) or oxygen-deficient defects (like amino bridges). Information on the film structure is obtained by combining the analysis of the Si 2p peak with that of the O 1s peak.

Studies of Electrochemically Transformed Ferritin Adsorbed at Tin-Doped Indium Oxide Electrodes Using X-ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy (XPS) was used to (1) confirm the presence of ferritin on tin-doped indium oxide (ITO) as suggested by voltammetry, (2) determine whether ferritin desorbs upon reduction, (3) verify whether iron is released when ferritin is reduced in the presence of an iron-chelating agent, and (4) ascertain whether the protein-iron complex could be electrochemically reconstituted. The N 1s signal increases dramatically after the ITO electrode is exposed to ferritin. Substantial decreases in the Fe/N peak ratio support the hypothesis that iron release can be electrochemically induced by reducing ferritin in the presence of an iron-chelating agent. These data reveal that ferritin adsorbs onto ITO from solution at controlled electrode potential and that ferritin can be electrochemically induced to release iron without the need for homogeneous reducing agents. However, following the exposure of an ITO/ferritin (emptied) to ferrous ion at positive electrode potential, the XPS spectrum reveals a substantial increase in the iron signal and a decrease in substrate signals. These results indicate that iron deposits directly onto the ITO substrate, casting doubt on the previous conclusion that adsorbed ferritin can be electrochemically reconstituted.

Phase segregation in pulsed laser deposited carbon nitride thin films

Carbon nitride thin films have been deposited at room temperature by plasma assisted pulsed laser deposition and the effect of varying the KrF excimer laser intensity was studied by examination of the bonding and hardness of the films. X-ray photoelectron spectroscopy shows that the nitrogen content in the films decreases from 24 to 16 at.% when laser intensity is increased from 2.5×10 7 to 9.4×10 8 W/cm 2 and that the nitrogen atoms are incorporated in the films under two different bonding configurations, as deduced by two distinct contributions to the N 1s signal at 398.4±0.2 and 400.1±0.2 eV. However, it was found that the stoichiometry of the CN bonded structures is independent of laser intensity as it remains constant at 33±3 at.% of N. This suggests that the microstructure of the films consists of a nearly stoichiometric C 2N phase mixed with amorphous carbon regions. Such a picture is further supported by the observation that the binding energy of the two components of the N 1s XPS signal is not affected by laser intensity. By using continuous stiffness measurement nanoindentation, a hardness value of 24 GPa, was determined for the film synthesized at the highest laser intensity used in this work but it was found to deteriorate with increasing nitrogen content. These effects could be explained in terms of an intermixing between the C 2N phase and pure carbon domains rather than a modification of nitrogen bonding configuration in the films.

NH 3 probing of the surface acidity of passive films on chromium

The acid–base properties of passive films formed on chromium have been investigated with a probe molecule. The adsorption of NH 3, a Lewis base, has been studied by X-ray photoelectron spectroscopy (XPS) on passive films formed on Cr(1 1 0) in 0.5 M H 2SO 4. A single N 1s signal resulted from the exposure of the passive film to gaseous ammonia (25°C, pNH 3=20 mbar ). The comparison with NH 3 probing of dry oxide films reveals that the oxide surface reactivity is markedly reduced by the layer of OH. The Lewis acid sites of the oxide surface are not directly available on the passive film. The data indicate that NH 3 reacts with Brönsted acid sites consisting of hydrogen termination of the hydroxyl or hydroxide groups on the passive film surface. The implications of these findings for the interactions of chloride ions with passive films (passivity breakdown and initiation of pitting) are discussed.

Spectroscopic Studies of the Modification of Crystalline Si(111) Surfaces with Covalently-Attached Alkyl Chains Using a Chlorination/Alkylation Method

A two-step procedure, involving radical-initiated chlorination of the Si surface with PCl5 followed by reaction of the chlorinated surface with alkyl-Grignard or alkyl-lithium reagents, has been developed to functionalize crystalline (111)-oriented H-terminated Si surfaces. The surface chemistry that accompanies these reaction steps has been investigated using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), temperature programmed desorption spectroscopy (TPDS), high-resolution electron energy loss spectroscopy (HREELS), infrared (IR) spectroscopy in both glancing transmission (TIR) and attenuated total multiple internal reflection (ATR) modes, ellipsometry, and contact angle goniometry. The XPS data show the appearance of the Cl signal after exposure to PCl5 and show its removal, and concomitant appearance of a C 1s signal, after the alkylation step. Auger electron spectra, in combination with TPD spectroscopy, demonstrate the presence of Cl after the chlorination process and it...

Triarylamine on Nanocrystalline TiO2 Studied in Its Reduced and Oxidized State by Photoelectron Spectroscopy

The electronic and molecular structures of an electrochemically reduced and oxidized triarylamine layer (((3-ethyl(p-N,N-dimethylamino)phenyl)amino)propyl-1-phosphonic acid) adsorbed on a nanocrystalline TiO2 film have been investigated. Photoelectron spectroscopy (PES) measurements on electrochemically prepared surfaces and density functional theory (DFT) calculations for the free triarylamine molecule were performed. The major electronic difference between the reduced and oxidized state of the triarylamine molecules appears on the nitrogen atom. In the PES measurement a shift of the N 1s signal of 1.5 eV toward higher binding energies was measured between triarylamine in its reduced and oxidized states. The molecular structure of the surface layer was found to depend on the electrolyte used in the electrochemical preparation. The oxidized triarylamine molecule is positively charged and must therefore be accompanied by a negative counterion. The identity of the counterion was found to influence electron transfer between adjacent molecules, as explained by geometrical differences of the surface layer. During the measurements the PES N 1s signal was affected by the continuous X-ray illumination. Interestingly, a reversible photoreduction of the oxidized triarylamine was observed. The effect is accounted for by X-ray induced electron hole-pair generation in the TiO2 and subsequent electron transfer from the TiO2 conduction band to the singly occupied molecular orbital of the adsorbed molecule.

Chemical Vapor Deposited Fe2O3 Thin Films Analyzed by XPS

In the present study, x-ray photoelectron spectroscopy (XPS) was employed to investigate the principal core levels of a Fe2O3 thin film. The sample was deposited on glass in a N2+O2 atmosphere by chemical vapor deposition (CVD), using Fe(acac)3 (Hacac = 2,4-pentanedione) as the source compound. XPS surface data for the Fe 2p3/2, O 1s, and C 1s photoelectrons, obtained by an Al Kα monochromatized excitation source, are reported. Deconvolution of the O 1s signal revealed the presence of –OH groups along with the major component ascribed to lattice oxygen. The relatively high carbon content in the film indicated an incomplete decomposition of the used precursor.

Segregation effects and chemical properties of nickel monolayers on Cu(1 1 1)

Temperature-dependent structural changes of Ni monolayers on Cu(1 1 1) and the adsorption of benzene on these layers were investigated using photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). Ni films evaporated at 120 K show a sharp (1×1) LEED pattern after annealing to 300 K. Further annealing to 600 K leads to the segregation of Cu atoms on top of the Ni film. This is seen from the appearance of a surface core level shift in the Cu 2p 3/2 XPS signal. The Ni 2p 3/2 signal does not show any shifts in this temperature range; only annealing to 800 K leads to a change in the Ni 2p 3/2 peak energy which indicates the formation of a Cu–Ni bulk alloy. Adsorption of benzene on the Ni-adlayer (annealed to 300 K) causes a small peak shift in the Ni 2p 3/2 signal. The C 1s signal indicates molecularly chemisorbed benzene up to 300 K. Further annealing to 500 K leads to the decomposition of benzene into hydrogen and carbon which remains on the surface and forms a stable bond with the Ni-adlayer, preventing Cu segregation up to 500 K.

CO adsorption on Pd clusters deposited on pyrolytically prepared SnO 2 studied by XPS

The sensitivity and selectivity of SnO 2-based gas sensors could be improved by doping of small amount of noble metals. In this work, we used X-ray photoelectron spectroscopy to investigate Pd particles evaporated on the SnO 2 thin layers, prepared by spray pyrolysis. We compared the binding energy and initial state variations as a function of Pd coverage. CO–Pd interaction was investigated using the C 1s photoelectron spectra that exhibited two CO-related components. The dissociation activity was monitored as a rise of C 1s signal at 285 eV while the molecularly adsorbed CO exhibited the peak intensity at 287 eV.

XPS and TPD study of CO interaction with Pd–Al and Pd–Al2O3 systems

The metal–substrate and metal–metal interactions represent important effects determining the properties of supported catalysts. We investigate the CO adsorption mechanism on Pd particles supported on Al2O3 and Al by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). CO–metal interaction is investigated by TP desorption of CO and by XPS of C 1s intensities that exhibit three CO-related components. The dissociation activity is monitored as a rise of C 1s signal at 285 eV while the molecularly adsorbed CO exhibits the intensity at 287 eV. Pd–substrate interaction is determined from the Pd core- and valence-level binding energy variations. The influence of the Pd–Al alloying process on the Pd MNN Auger transition is shown. The studies show that the metal–substrate and metal–metal interactions play an important role in CO–Pd adsorption process.

Molecular Packing of Semifluorinated Alkanethiol Self-Assembled Monolayers on Gold: Influence of Alkyl Spacer Length

The structures of semifluorinated alkanethiol self-assembled monolayers (SAMs) generated by the adsorption of CF3(CF2)9(CH2)nSH (F10HnSH, n = 2, 6, 11, 17, 33) onto gold were investigated with atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and surface plasmon resonance spectroscopy. Images obtained by AFM of the F10H2SH SAM showed a remarkably ordered 2D hexagonal lattice with a lattice constant, a = 5.9 ± 0.1 A, on Au(111)/mica. As the total number of carbon atoms in the alkyl spacer groups (n) was increased, the fluorocarbon adlayer structure appeared more disordered in the AFM images; however, the thicknesses of the fluorocarbon layers estimated from the C 1s (CF3), C 1s (CF2), and F 1s XPS signal intensities were indistinguishable in all of the SAMs. In contrast, the C 1s (CH2) signals revealed that the tilt angles of the alkyl spacer groups depended strongly on n. We utilized a contrast variation SPR technique with various contacting media for an independent determination of t...

Photoelectron spectroscopy on silver electrodes on yttria stabilized zirconia under applied potential

Silver electrode layers of different porosity on yttrium stabilized zirconia (YSZ) were investigated by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS resp.). By applying different potentials in a three electrode arrangement oxygen could be transported from a gaseous reservoir to the working electrode. The change in the work function of the working electrode as a function of applied potentials was monitored by UPS. It showed significant different behavior for dense and porous silver electrodes. On a dense silver electrode a change in work function of up to 0.6 eV was observed at potentials at which a considerable current passed through the electrolyte. In the UP spectra of the valence band an additional structure appeared at a binding energy of 3.3 eV. These changes were also reflected in the appearance of oxygen O 1s signals in the XP spectra at 529 eV assigned to subsurface oxygen. On a porous silver electrode the work function at equilibrium (open circuit) was higher than that of metallic silver and increased linearly with increasing potential, although yet no current through the electrolyte could be observed. With the onset of considerable currents at larger anodic potentials the work function increase became stronger. As reason for the linear increase of the measured work function contributions of the solid electrolyte YSZ are considered.

Study of Cerium Dioxide Thin Films by X-ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy measurements of cerium dioxide thin films have been performed. The samples were prepared by chemical vapor deposition (CVD) using Ce(dpm)4 (Hdpm = 2,2,6,6-tetramethyl-3,5-heptanedione) as precursor on alumina and glass substrates. In this work, the spectra of the principal core levels for a CeO2 film on glass are presented. The Ce 3d photopeak has the typical structure of Ce(IV) compounds. By deconvolution of the O 1s signal, the presence of –OH groups and adsorbed water are evidenced. Sputtering treatments confirm that carbon contamination is limited to the outermost layers, while resulting hydrated species are bonded tenaciously to the oxide network.

Zirconium Dioxide Thin Films Characterized by XPS

In this work we use x-ray photoelectron spectroscopy (XPS) to analyze the principal core levels of a ZrO2 thin film deposited on glass using Zr(OPri)3(dpm) (OPri=isopropoxy; hdpm=2,2,6,6-tetramethyl-3,5-heptanedione) as precursor. Besides the general survey, charge corrected binding energies for the Zr 3d5/2, Zr 3d3/2, O 1s, and C 1s photoelectrons are reported. Deconvolution of the O 1s signal reveals the presence of –OH groups and adsorbed water, whose presence can be related to the air exposure of the film between its preparation and XPS analysis.

CO adsorption on Al 2O 3-supported Pd clusters: XPS study

The adsorption of carbon monoxide on small alumina-supported Pd particles have been studied by X-ray photoelectron spectroscopy (XPS). The results showed clearly different surface properties of bulk metal and supported clusters. The effect of partial CO dissociation was observed on Pd deposited on γ-alumina and on clean aluminium, but not on small Pd particles prepared on thin amorphous oxide film on Al substrate. CO–Pd interaction was determined from C 1s photoelectron spectra that exhibited two CO-related components. The dissociation activity was monitored as a rise of C 1s signal at 285 eV, while the molecularly adsorbed CO exhibited the intensity at 287 eV. The study showed that beside the particle size, the metal–substrate interaction (MSI) plays an important role in CO–Pd adsorption process.