1s X-ray Photoelectron Spectroscopy Peak Research Articles

Photoluminescence and cathodoluminescence of spin coated ZnO films with different concentration of Eu3+ ions

ZnO thin films doped with Eu3+ up to 4 mol% were successfully prepared using a sol-gel spin coating technique. The structure, morphology, chemical analysis and luminescence of the films were studied. X-ray photoelectron spectroscopy (XPS) analysis for the Eu 3d core shells confirmed the presence of divalent (Eu2+) and trivalent (Eu3+) states. Time of flight secondary ion mass spectroscopy showed that the Eu3+ions were homogeneously distributed throughout the thin film with Eu2+ mainly only in the surface region of the thin films. The films exhibited ZnO exciton emission around 376 nm, broad defect related emission and the Eu3+ characteristic emission simultaneously when excited at 325 nm. For the excitation at 464 nm, the doped samples exhibited only the characteristic emissions of Eu3+ which were attributed to the 5D0-7FJ (J = 0, 1, 2, 3, 4) transitions, respectively. The film with a 3 mol% of Eu3+ has emitted the highest photo/cathodoluminescence (PL/CL) emission. Therefore, it was subjected to electron beam irradiation in vacuum for about 22 h to establish the effect of the electron beam on the film's surface state, chemical and luminescence stability. Minor surface modification during electron beam irradiation was observed. The O 1s XPS peak revealed the creation of new defects associated with oxygen deficiencies due to the irradiation. Surface modification and creation of defects were identified as the major mechanisms for the initial decrease in the CL intensity. This film was very stable during prolonged electron beam irradiation.

Enhancing oxygen vacancy photocatalytic efficiency of bismuth tungstate using In-doped W site

Pure and In-doped orthorhombic Bi<sub>2</sub>WO<sub>6</sub> are synthesized by sol-gel method through using raw materials Bi(NO<sub>3</sub>)<sub>3</sub>·5H<sub>2</sub>O, In(NO<sub>3</sub>)<sub>3</sub>·6H<sub>2</sub>O, (NH<sub>4</sub>)<sub>2</sub>WO<sub>4</sub> and surfactants citric acid, polyethylene glycol. All samples are in pure phase without impurity phase as indicated by X-ray diffraction characterization. The In-doped sample degradation efficiency for rhodamine B is higher than that for pure phase with the optimal content 7% mole ratio. Because indium impurity adhering to Bi<sub>2</sub>WO<sub>6</sub> nucleus surface may affect the crystallization range, the sample morphology gradually becomes fluffy and regular, which is reveled through scanning electron microscopy analysis. This morphology change plays an important role in electron-hole transport process as well as contact area of carrier and organic molecule. Using X-ray photoelectron spectroscopy (XPS) characterization and Gaussian fitting, it is found that the O 1s XPS peak of pure and In-doped sample each contain three peak sites. The low energy peak around 530 eV originates from W—O and Bi—O bond. The high peak is ascribed to lattice oxygen defect and its intensity is enhanced gradually with the increase of In content. Thus the increase of oxygen vacancies is the main reason for this photocatalytic performance improvement. Comparing with the impurity-free sample, the visible absorption of In-doped Bi<sub>2</sub>WO<sub>6</sub> is enhanced and the corresponding band gap slightly decreases, which is indicated by diffraction reflection spectroscopy measurement. The reduction of forbidden band width further enhances the photocatalytic performance. After configuration relaxation and self-consistence calculation, the formation energy obtained from a single oxygen vacancy model is less than those from the Bi1<sub>In</sub> + V<sub>O</sub> and the Bi2<sub>In</sub> + V<sub>O</sub> co-doping models, and greater than the W<sub>In</sub> + V<sub>O</sub> formation energy. This result indicates that indium replacing W site can promote the generating of oxygen vacancies. The calculation of the 18%-hybridization function electronic structure shows that the Bi<sub>2</sub>WO<sub>6</sub> has indirect band gap semi-conduction with energy gap 2.76 eV, which is consistent with the experimental value 2.79 eV. A series of new local states appears in the band gap and near conduction band bottom based on the oxygen vacancy model. These local states promote light absorption and enhance photocatalytic performance. In conclusion, the enhanced photocatalytic performance of Bi<sub>2</sub>WO<sub>6</sub> is attributed to the indium entering into the tungsten site rather than the bismuth site as indicated by the experimental and theoretical result.

SiO2 nanospheres modified by Ag nanoparticles: Surface charging and CO oxidation activity

SiO2 spheres were modified with Ag nanoparticles (NPs) via a silver-mirror reaction and then examined by scanning electron microscopy (SEM), UV–vis absorption, X-ray diffraction (XRD), Raman, FT-IR, depth-profiling X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction experiments. Ag 3d, Si 2p, and O 1s XPS peaks were found at much higher binding energies (BEs) due to localized surface charging in the Ag/SiO2 sphere. The charging effect was significantly diminished after thermal annealing due to the formation of good interfacial contact. CO oxidation reactions were demonstrated using temperature programmed mass spectrometry. Kinetic parameters were obtained from the CO conversion (%) profiles and the Arrhenius plots versus reaction temperatures. In the first CO oxidation test run, no significant difference was observed in response to differences in Ag particle size and thermal pretreatment in air. However, in the second run the sample pretreated at 450°C in air was completely deactivated. In the second test run, the oxidation activities were all degraded due to aggregation of Ag NPs. Better oxidation performance was observed for SiO2 modified with smaller Ag NPs.

Phase composition and tribomechanical properties of Ti–B–C nanocomposite coatings prepared by magnetron sputtering

Protective nanocomposite coatings based on hard ceramic phases (TiC, TiB2) combined with amorphous carbon (a-C) are of interest because of their adequate balance between mechanical and tribological performances. In this work, Ti–B–C nanocomposite coatings were prepared by co-sputtering of graphite and TiB2 targets. Varying the discharge power ratio applied to the graphite and TiB2 targets from 0 to 2, the a-C content in the coatings could be tuned from 0 to 60%, as observed by means of Raman and x-ray photoelectron spectroscopy (XPS). The microstructural characterization demonstrated a progressive decrease in crystallinity from an initial nanocrystalline (nc) TiB2-like structure to a distorted TiBxCy ternary compound with increasing C concentration. X-ray absorption near-edge structure measurements on the B K-edge helped to determine a hexagonal arrangement around the B atoms in the ternary TiBxCy phase. A fitting analysis of the C 1s XPS peak allowed us to evaluate the relative amount of a-C and TiBxCy components. A drastic change in hardness (from 52 to 13 GPa) and friction coefficient values (from 0.8 to 0.2) is noticed when moving from nc-TiB2 to TiBC/a-C nanocomposites. The fraction of a-C necessary to decrease the friction below 0.2 was found to be 45%. Raman observation of the wear tracks determined the presence of disordered sp2-bonded carbon phase associated with the diminution of the friction level.

Salt or Co-Crystal? Determination of Protonation State by X-Ray Photoelectron Spectroscopy (XPS)

Combined (15)N ssNMR and X-ray photoelectron spectroscopy (XPS) investigations for theophylline, a theophylline co-crystal, and a theophyllinium salt demonstrate that XPS allows direct observation of the degree of proton transfer, and thus identification of whether a salt or a co-crystal has been formed. The presence of a strongly binding-energy-shifted N 1s XPS peak with protonation indicates a salt (C==NH(+)), while this peak is unmistakably absent in the co-crystal. XPS should be considered as an alternative and complementary technique to single crystal X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy (ssNMR).

Interaction of water molecules with bare and deuterated polycrystalline diamond surface studied by high resolution electron energy loss and X-ray photoelectron spectroscopies

In this work we study the interaction of water molecules with deuterated and bare polycrystalline diamond surfaces upon exposure to water vapor by X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HR-EELS). To distinguish the molecular origin of hydrogen bonds (i.e. C–H, O–H, C–O–H, etc.) formed on the diamond surface upon interaction with the water molecules, deuterated and hydrogenated gases were used in our experiments. Diamond films were deposited from a deuterated gas mixture to induce C(di)-D surface terminations. Water adsorption on bare diamond surface gives rise to the appearance of well defined and pronounced C–H and C–OH vibrational HR-EELS peaks and an intense O (1s) XPS peak. These chemically adsorbed water fragments survive 300 °C anneal temperature under ultra-high vacuum conditions. Annealing at 600 °C of the water exposed bare diamond surface results in disappearance of the C–OH vibrational modes alongside with a pronounced reduction of the C–H vibrational modes, whilst only upon annealing to ~ 800 °C the O (1s) XPS peak decreased substantially in intensity. We associate these effects with dissociative adsorption of the water molecules on the bare diamond surfaces. Water exposure onto a deuterated surface, on the other hand, does not result in the appearance of the C–OH vibrational peaks but only to an increase of the C–H vibrational HR-EELS mode along side with the appearance of a weaker XPS O (1) peak, as compared to the same experiment, performed on the bare surface. 300 °C anneal significantly diminishes surface oxygen concentration, as monitored by XPS. We associate these results with H 2O decomposition reactions and also with molecular adsorption on deuterated diamond surfaces. Annealing of the water exposed deuterated diamond surface, results in a pronounced decrease and disappearance of the O (1s) XPS peak at a temperature of ~ 800 °C.

Chemical, Electronic, and Electrical Properties of Alkylated Ge(111) Surfaces

The use of Ge in semiconductor electronics has been constrained by the lack of a simple method of passivating the crystal surface. Toward that end, we have explored the utility of chemically bonded hydrocarbon monolayers. Alkylated Ge(111) surfaces have been prepared by addition of 1-alkenes to the H-terminated Ge(111) surface as well as by a two-step halogenation/alkylation procedure. The chemical compositions of the resulting methyl-, ethyl-, and decyl-terminated surfaces have been evaluated using X-ray photoelectron spectroscopy (XPS). Thermal addition of 1-decene produced hydrophobic surfaces with 0.3 ± 0.1 monolayer of Ge oxide detected by XPS, whereas no oxide was observed on the methyl-, ethyl-, or decyl-terminated surfaces that were prepared using the two-step halogenation/alkylation method. Methyl-terminated Ge(111) surfaces prepared by the two-step method displayed a well-resolved C 1s XPS peak at a binding energy of 284 eV, consistent with carbon bonded to a less electronegative element such as Ge. The electronic properties of all of the alkylated surfaces were characterized by measurements of the surface recombination velocity as a function of an externally applied gate voltage. Treatment of HF-etched Ge(111) surfaces with Br2 vapor, followed by reaction with alkylmagnesium or alkyllithium reagents, yielded air-stable surfaces that had surface recombination velocities of 100 cm s−1 or less under flat-band conditions. The field-dependent surface recombination velocity experiments indicated that, in contact with air, methyl-terminated n-type Ge(111) samples had a negative surface potential approaching 300 mV, in contrast to the oxidized Ge(111) surface, which exhibited a strongly positive surface potential under the same conditions. Mercury contacts to n-type methyl-, ethyl-, or decyl-terminated Ge(111) substrates that were alkylated using the two-step method formed rectifying junctions with barrier heights of 0.6 ± 0.1 eV, whereas no measurable rectification was observed for Hg contacts to p-type Ge(111) substrates that were alkylated by the two-step method, to n-type Ge(111) substrates that were alkylated through addition of 1-decene, or to oxidized n-type Ge(111) samples.

Influence of carbon chemical bonding on the tribological behavior of sputtered nanocomposite TiBC/a-C coatings

The tribological performance of nanocomposite coatings containing Ti–B–C phases and amorphous carbon (a-C) are studied. The coatings are deposited by a sputtering process from a sintered TiB 2:TiC target and graphite, using pulsed direct current and radio frequency sources. By varying the sputtering power ratio, the amorphous carbon content of the coatings can be tuned, as observed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The crystalline component consists of very disordered crystals with a mixture of TiB 2/TiC or TiB xC y phases. A slight increase in crystalline order is detected with the incorporation of carbon in the coatings that is attributed to the formation of a ternary TiB xC y phase. An estimation of the carbon present in the form of carbide (TiB xC y or TiC) and amorphous (a-C) is performed using fitting analysis of the C 1s XPS peak. The film hardness (22 to 31 GPa) correlates with the fraction of the TiB xC y phase that exists in the coatings. The tribological properties were measured by a pin-on-disk tribometer in ambient conditions, using 6 mm tungsten carbide balls at 1 N. The friction coefficients and the wear rates show similar behavior, exhibiting an optimum when the fraction of C atoms in the amorphous phase is near 50%. This composition enables significant improvement of the friction coefficients and wear rates ( μ ∼ 0.1; k < 1 × 10 − 6 mm 3/Nm), while maintaining a good value of hardness (24.6 GPa). Establishing the correlation between the lubricant properties and the fraction of a-C is very useful for purposes of tailoring the protective character of these nanocomposite coatings to engineering applications.

Modification of wetting properties of CR39 by plasma source ion implantation

Plasma source ion implantation (PSII), a hybrid implantation technique between ion beams and immersion plasmas has been used to modify CR39 surfaces for improved wettability providing both advancing ( θ a ) and receding ( θ r ) contact angles below 5 ° . The modifications brought to the polymer surface structure have been characterized by X-ray photoelectron spectroscopy (XPS) and its combination with chemical derivatization (CD-XPS). Oxygen desorption has been observed in spite of the very hydrophilic surfaces. C 1s XPS peak has been displaced toward greater energies, while the opposite has been found for O 1s, both involving new components and strong modifications after ion implantation treatment. Strong evidences about the formation of new chemical functions, like OOH, COOH and C C, have been found and have provided an explanation for the increased wettability.

Oxygen-dependent phosphorus networking in ZnO thin films grown by low temperature rf sputtering

Radio frequency (rf) sputtered films of 10at.% P2O5-doped zinc oxide (ZnO) were deposited at temperatures (Td) below the sublimation point of P2O5 (Td&amp;lt;350°C) and at a range of oxygen pressures p(O2). Ultraviolet-visible optical transmission measurements, x-ray photoelectron spectroscopy (XPS), and x-ray diffraction were used to examine the effects of p(O2) during deposition on the band gap and on the bonding behavior of phosphorus. At both deposition temperatures studied (room temperature with unintentional heating and 125°C), an increase in phosphorus concentration with increasing p(O2) was observed. However, the dependence of the band gap behavior on p(O2) was observed to be dramatically different for the two deposition temperatures: room-temperature-deposited films show a redshift while films deposited at 125°C show a blueshift. Analysis of the oxygen 1s XPS peak shows a progressive formation of nonbridging (Zn–O–P) bond networks for room temperature films, whereas films grown at 125°C show increased (P–O–P) bond networks with increasing p(O2). This indicates that a small degree of thermal activation considerably modifies the bonding behavior of phosphorus in ZnO. Implications of these results for the use of phosphorus as a p-type dopant for ZnO are discussed.

Investigation of monolayer dispersion of benzoic acid supported on the surface of H-titanate nanotubes

Benzoic acid (BA) can disperse spontaneously onto the surface of H-titanate nanotubes (HTNTs) in a sub-monolayer state by heating mechanical mixtures method. The structure of BA–HTNTs system has been characterized by X-ray diffraction (XRD), thermogravimetric (TG), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) in detail. The results show that the H-bond association structure among BA molecules collapses and the carboxyl groups react with the surface hydroxyl group of HTNTs to form a salt-like structure on the surface after dispersion. The monolayer dispersion capacity determined by XRD is ca. 0.305 g BA g −1 HTNTs, which is lower than the utmost monolayer dispersion capacity 0.550 g BA g −1 HTNTs calculated according to a model that the benzene ring in BA molecules is perpendicular to the surface of HTNTs. At the same time, the dispersion capacity is also measurement by the fit of C 1s XPS peak at various BA loadings at first time.

Characterization and protonation behavior of bipyridine thiol self-assembled monolayer on Au(1 1 1) studied using X-ray photoelectron spectroscopy and scanning tunneling microscopy

The adsorption process, molecular arrangement and protonation behavior of self-assembled monolayers (SAMs) of bipyridine thiol on Au(1 1 1) were investigated using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), with a view towards constructing a molecular ion sensor. When the bipyridine SAMs were immersed in a strong CF 3SO 3H solution for protonation of the bipyridine group, additional N(1s) XPS peaks were generated at higher binding peak positions where the origin of the peak was considered to be the N–H species. We further investigated the relationship between the immersion time for the SAMs and the probability of protonation. We observed a decrease in the probability of protonation with a longer immersion time for the SAMs. We consider that both the bipyridine molecular arrangements and the molecular density on the Au surface are crucial for controlling the probability of protonation based on the STM and XPS data.

Size-Induced Changes in Optical and X-ray Photoelectron Spectra of GaN Nanoparticles Deposited at Lower Substrate Temperature

This study reports the synthesis of GaN nanoparticles having hexagonal structure by a simple technique of activated reactive evaporation with substrates kept at comparatively lower temperatures than usually reported. By varying the substrate temperature from 30 degrees C to 350 degrees C, it is possible to vary nanoparticle sizes from 5-30 nm. X-ray diffraction and X-ray photoelectron spectroscopy analysis confirm the formation of GaN on quartz and silicon substrates at room temperature. The observed size dependent shift in energy position, large increase in full width at half maximum value of Ga 3d and N 1s X-ray photoelectron spectroscopy peaks and blue shift in the optical absorption edge are related to nanoparticle character.

Ni/NiO(0 0 1) interface studied by X-ray photoelectron spectroscopy and molecular dynamics simulations

X-ray photoelectron spectroscopy (XPS) results referring to the interface formed upon vapor deposition of Ni atoms on NiO(0 0 1) indicate, that upon annealing the deposited Ni is oxidized forming a NiO overlayer. The oxidation process is activated and becomes very fast above 900 K, resulting in a surface that exhibits identical photoelectron spectrum with the clean substrate. In addition, it was found that during the oxidation process two extra components in the O 1s XPS peak spectra appear, with binding energies above and below the main lattice oxygen peak, manifesting the existence of oxygen atoms carrying charges that deviate from their formal ionic value. Moreover, by molecular dynamics simulations it was found that upon deposition of Ni ions, neighboring O surface atoms become adatoms and combine with the Ni ions forming a series of Ni x O y oxides, most of which eventually coalesce into small NiO islands. Consequently, the lower binding energy component of the O 1s XPS peak may be attributed to intermediate oxides with x> y, while the higher binding energy component to intermediate oxides with x< y.

XPS and XRR studies on microstructures and interfaces of DLC films deposited by FCVA method

Diamond-like carbon (DLC) films have been deposited at room temperature using a filtered cathodic vacuum arc technique. The influence of the negative bias voltage applied to the substrate from 0 to −250 V on the sp 3 hybridized carbon fraction is studied by Raman spectroscopy, which is also compared with the result obtained from X-ray photoelectron spectroscopy (XPS) for C 1s core peak. Based on the depth profiles for C 1s, Si 2p, and O 1s XPS peaks, the DLC film is modeled as a structure having three different layers, such as surface, bulk, and interface. In addition, the X-ray reflectivity is proposed as a method for estimating the density, surface roughness, and thickness of the layers constituting the DLC film. The estimated thickness of DLC film shows good agreement with the result obtained from the transmission electron microscope measurement.

Growth and interfacial studies of conjugated oligomer films on Si and SiO2 substrates

The growth of [2,5-bis(4-styryl)styryl] 1,4-dioctyloxybenzene, (Ooct-OPV5) oligomer films on Si (100)-(2×1) and Si (111)-(7×7) reconstructed surfaces as well as on a SiO2 film over a Si (100) wafer was studied by x-ray photoelectron spectroscopy (XPS). Ooct-OPV5 resembles poly (p-phenylenevinylene) (PPV), a polymer that is widely used in organic light emitting diodes. High purity oligomer films of up to 18 nm thickness were prepared on the clean substrates by stepwise evaporation in ultrahigh vacuum conditions and a layerwise growth of films was observed on all substrates. The electronic structure of the oligomer interface with n-doped Si (111) was investigated by combined x ray and ultraviolet photoelectron spectroscopies (XPS) and (UPS). The C 1s XPS peak of the bulk oligomer consisted of three components, all associated with oligomer functional groups at binding energies 285.05, 285.75, and 287.15 eV, respectively. During growth, both C 1s and O 1s peaks in the film exhibited an upward BE shift of 0.45±0.05 eV, from which the total band bending at the interface was evaluated. The depletion region in the organic film during the interface was found to be ∼90 Å thick. The UP spectra of the oligomeric film exhibited characteristic peaks that resemble those of PPV, and the oligomer work function was found to be 4.00±0.05 eV. The interface between the two materials in contact proved to be nonreactive and no detectable electric dipole was observed.

Electrical, magnetic, and structural properties of chemically and electrochemically synthesized polypyrroles

We report the results of temperature-dependent dc conductivity ( σ dc( T)), EPR (electron paramagnetic resonance) magnetic susceptibility, and XPS (X-ray photoelectron spectroscopy) experiments for chemically and electrochemically synthesized polypyrrole (PPy) samples. For chemically synthesized dodecylbenzenesulfonic acid (DBSA) or naphthalenesulfonic acid (NSA) doped PPy samples (PPy-DBSA or PPy-NSA, respectively) soluble in m-cresol solvent, dc conductivity and its temperature dependence show the strong localization behavior, while those of electrochemically synthesized PPy doped with hexafluorophosphate (PPy-PF 6) are in the critical regime. Pauli susceptibility ( χ p) and the density of states are obtained from the temperature dependence of EPR magnetic susceptibility. The density of states of chemically synthesized PPy is one-third of that of electrochemically synthesized PPy. From the analysis of the area ratio of carbon 1s XPS peak, the disorder effect due to interchain links or side chains of PPy-DBSA ( m-cresol) samples is ∼22%, while that of PPy-PF 6 samples is ∼33%. This result indicates that the percent of interchain links or side chains of chemically synthesized PPy-DBSA ( m-cresol) samples is reduced by ∼10% compared to that of electrochemically synthesized PPy-PF 6 samples. We analyze that the side chains or interchain links of chemically synthesized PPy samples are relatively reduced due to the synthesis method using large size dopants, and subsequently the interchain interaction weakens. The results of EPR experiments of PPy-DBSA ( m-cresol) samples with different doping levels are discussed.

Initial stages of Al(111) oxidation with oxygen–temperature dependence of the integral reactive sticking coefficient

The initial stages of Al(111) oxidation by oxygen were investigated using X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS). The integral reactive sticking coefficient (S) was evaluated by measuring the O(1s) XPS peak area for exposures below 50L. Experiments were carried out at surface temperatures from 95 to 773K. The dissociative adsorption of O2 is proposed to occur by means of a molecular precursor mechanism leading to the non-monotonic behavior of S with changing surface temperature. The kinetics of O2 adsorption are governed by the strong temperature dependent balance of chemisorbed and oxidic species on the surface. Oxidic phase formation then influences the adsorption kinetics, by lowering the adsorption barrier from the precursor state (since stronger OAl bonds are formed by oxide formation compared to chemisorption) and transforming the activated O2 adsorption process into a non-activated one. A rapid onset of the oxidic phase formation was found in the temperature range 473–573K at these low exposures.

Initial stages of Al(111) oxidation by oxygen: Temperature and surface morphology effects

The initial stages of Al(111) oxidation by oxygen were investigated by using x-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy. It was found that surfaces exhibiting no impurities from the Auger electron spectroscopy and low-energy electron diffraction data may show different characteristic adsorption parameters (sticking coefficient, adsorbate vibrational modes, etc.). These parameters change rather dramatically with extended time of Ar+ bombardment followed by annealing prior to O2 adsorption. It was shown that extensive sputtering, followed by 700 K annealing, was necessary to prepare a surface with reproducible behavior. The integral reactive sticking coefficient, S(T), for the carefully prepared surface was evaluated by measuring the O(1s) XPS peak area for O2 exposures below 50 L. At surface temperatures from 95 to 773 K nonmonotonic behavior of S(T) was observed. A molecular precursor state preceding dissociative adsorption is proposed. It was found that the balance between oxidic and chemisorbed oxygen is strongly temperature dependent and influences the oxygen sticking coefficient on Al(111). A step-like formation of the oxidic phase in the temperature range 473–573 K was found to influence the adsorption kinetics. Oxidation causes the transformation of the O2 adsorption process from an activated into a nonactivated one.

Surface analysis of CVD carbon using NEXAFS, XPS and TEM

Chemical and morphological characterization of carbon thin films produced by chemical vapor deposition (CVD) of hydrocarbon gases onto a hard carbon substrate has been performed using various surface analytical techniques. Semiquantitative analyses of the surface concentration of C C double bonds have been conducted using near edge X-ray absorption fine structure (NEXAFS) at the C K edge and core level X-ray photoelectron spectroscopy (XPS). NEXAFS spectra of CVD carbon films are similar to those of well-ordered graphite. Rather surprisingly, however, it has been revealed that the CVD carbon films contain less C C double bonds than that of the hard carbon. Intensities of π-π * shake-up satellite of the C 1s XPS peak have been measured, and the results were consistent with those of NEXAFS. Smaller concentrations of C C double bonds can be attributed to the incomplete dehydrogenation due to the relatively low temperature of the CVD treatment. High resolution transmission electron microscope (TEM) images of CVD carbon showed preferential orientation of graphite-like plane units in the direction parallel to the surface, suggesting the formation of large molecules in gas phase reaction prior to deposition.