Higher Binding Energy Region Research Articles

Characteristics and mechanisms of aerosol deposition-based barium titanate by sulfur hexafluoride inductively coupled plasma etching

Aerosol deposition (AD)-derived barium titanate (BTO) micropatterns are etched in SF6/O2/Ar plasmas using inductively coupled plasma (ICP) etching technology. The reaction mechanisms of the proposed sulfur hexafluoride on BTO thin films are verified through X-ray photoelectron spectroscopy (XPS) and static time-of-flight secondary ion mass spectrometry (ToF-SIMS) results. The exact peak positions and chemical shifts of Ba 3d, Ti 2p, O 1s, and F 1s are deduced by fitted XPS narrow-scan spectra on both the as-deposited and etched BTO surfaces. Compared to the as-deposited BTOs, the etched Ba 3d5/2, Ba 3d3/2, Ti 2p3/2, Ti 2p1/2, and O 1s peaks shift towards higher binding energy regions by amounts of 0.55, 0.45, 0.4, 0.35, and 0.76eV, respectively. ToF-SIMS analysis is used to obtain elemental and molecular data for quantitatively studying the interaction between reactive gases and BTO. The combined use of these two techniques is to systematically investigate and analyze the sulfur hexafluoride-based BTO etching mechanisms.

Effect of sulfur hexafluoride gas and post-annealing treatment for inductively coupled plasma etched barium titanate thin films.

Aerosol deposition- (AD) derived barium titanate (BTO) micropatterns are etched via SF6/O2/Ar plasmas using inductively coupled plasma (ICP) etching technology. The reaction mechanisms of the sulfur hexafluoride on BTO thin films and the effects of annealing treatment are verified through X-ray photoelectron spectroscopy (XPS) analysis, which confirms the accumulation of reaction products on the etched surface due to the low volatility of the reaction products, such as Ba and Ti fluorides, and these residues could be completely removed by the post-annealing treatment. The exact peak positions and chemicals shifts of Ba 3d, Ti 2p, O 1 s, and F 1 s are deduced by fitting the XPS narrow-scan spectra on as-deposited, etched, and post-annealed BTO surfaces. Compared to the as-deposited BTOs, the etched Ba 3d 5/2 , Ba 3d 3/2 , Ti 2p 3/2 , Ti 2p 1/2 , and O 1 s peaks shift towards higher binding energy regions by amounts of 0.55, 0.45, 0.4, 0.35, and 0.85 eV, respectively. A comparison of the as-deposited film with the post-annealed film after etching revealed that there are no significant differences in the fitted XPS narrow-scan spectra except for the slight chemical shift in the O 1 s peak due to the oxygen vacancy compensation in O2-excessive atmosphere. It is inferred that the electrical properties of the etched BTO film can be restored by post-annealing treatment after the etching process. Moreover, the relative permittivity and loss tangent of the post-annealed BTO thin films are remarkably improved by 232% and 2,695%, respectively.

Photoelectron spectra of thulium atoms encapsulated C82 fullerene, Tm2@C82 (III) and Tm2C2@C82 (III)

Ultraviolet photoelectron spectra (UPS) and X-ray photoelectron spectra (XPS) of two thulium atoms and thulium-carbide cluster entrapped fullerenes, Tm2@C82 (III) and Tm2C2@C82 (III), were measured using synchrotron radiation and MgKα X-ray light sources. The UPS spectral onset energy of these endohedral fullerenes is around 0.9eV, which is smaller than that of 1.2eV of empty C82. The UPS of Tm2@C82 (III) and Tm2C2@C82 (III) resemble each other. Further, the UPS of Tm2@C82 (III), Y2@C82-C3v and Er2@C82-C3v are almost identical and as well as are Tm2C2@C82 (III), Y2C2@C82-C3v and Er2C2@C82-C3v. The XPS Tm4d5/2 peaks of Tm2@C82 and Tm2C2@C82 appear at higher binding energy region than that of Tm@C82, which suggests the oxidation states of Tm atoms in Tm2@C82 (III) and Tm2C2@C82 are higher than that in Tm@C82.

Microstructure, electrical and magnetic properties of Ce-doped BiFeO3 thin films

Bi 1 − x Ce x FeO 3 (x=0, 0.05, 0.1, 0.15, and 0.20) (BCFO) thin films were deposited on Pt/TiN/Si3N4/Si and fluorine-doped SnO2 glass substrates by sol-gel technique, respectively. The effect of Ce doping on the microstructure, electrical and magnetic properties of BCFO films was studied. Compared to counterparts of BiFeO3 (BFO) film, the fitted Bi 4f7/2, Bi 4f5/2, Fe 2p3/2, Fe 2p1/2, and O 1s peaks for Bi0.8Ce0.2FeO3 film shift toward higher binding energy regions by amounts of 0.33, 0.29, 0.43, 0.58, and 0.49 eV, respectively. Raman redshifts of 2–4 cm−1 and shorter phonon lifetimes for the Bi0.8Ce0.2FeO3 film might be related to anharmonic interactions among Bi–O, Ce–O, (Bi, Ce)–O, and Fe–O bonds in the distorted oxygen octahedron. Compared to the pure counterparts, the dielectric and ferroelectric properties of the Bi0.8Ce0.2FeO3 film are improved due to the decreased oxygen vacancies by the stabilized oxygen octahedron. Current density values for the BFO and Bi0.8Ce0.2FeO3 film capacitors are 9.89×10−4 and 5.86×10−5 A/cm2 at 10 V, respectively. The current density–applied voltage characteristics indicate that the main conduction mechanism for the BCFO capacitors is the interface-controlled Schottky emission. Both the in-plane and out-of-plane magnetization–magnetic field hysteresis loops reveal that the saturation magnetization values of the BCFO films increase with increasing the Ce concentration. The enhanced magnetic properties for the BCFO films might be attributed to the presence of Fe2+ caused by oxygen vacancies, the suppressed spiral spin structure, and/or the increased canting angle induced by Ce doping.

Surface chemical bonding states and ferroelectricity of Ce-doped BiFeO3 thin films prepared by sol–gel process

Bi1−x Ce x FeO3 (x = 0, 0.05, 0.1, 0.15 and 0.20) (BCFO) thin films were deposited on Pt/TiN/Si3N4/Si substrates by sol–gel technique. Crystal structures, surface chemical compositions and bonding states of BCFO films were investigated by X-ray diffraction and X-ray photoelectron spectroscopy (XPS), respectively. Compared to BiFeO3 (BFO) counterparts, the fitted XPS narrow-scan spectra of Bi 4f7/2, Bi 4f5/2, Fe 2p3/2, Fe 2p1/2 and O 1s peaks for Bi0.8Ce0.2FeO3 film shift towards higher binding energy regions by amounts of 0.33, 0.29, 0.43, 0.58 and 0.49 eV, respectively. Dielectric constants and loss tangents of the BCFO (x = 0, 0.1 and 0.2) film capacitors are 159, 131, 116, 0.048, 0.041 and 0.035 at 1 MHz, respectively. Bi0.8Ce0.2FeO3 film has a higher remnant polarization (P r = 2.04 μC/cm2) than that of the BFO (P r = 1.08 μC/cm2) at 388 kV/cm. Leakage current density of the Bi0.8Ce0.2FeO3 capacitor is 1.47 × 10−4 A/cm2 at 388 kV/cm, which is about two orders of magnitude lower than that of the BFO counterpart. Furthermore, Ce cations are feasibly substituted for Bi3+ in the Bi0.8Ce0.2FeO3 matrix, possibly resulting in the enhanced ferroelectric properties for the decreased grain sizes and the reduced oxygen vacancies.

X-ray photoemission spectroscopy and Fourier transform infrared studies of electrochemical doping of copper phthalocyanine molecule in conducting polymer

A conducting polymer polythiophene (PT) film incorporated with copper phthalocyanine (CuPc), which was a highly functional molecule, was synthesized and characterized by Fourier transform infrared (FTIR) spectroscopy and x-ray photoemission spectroscopy (XPS). Electrochemical and casting processes were developed as a doping method of CuPc molecules in a PT film. In the XPS measurements of the CuPc doped PT, CuPc-origin peaks on the higher energy side appeared in the C 1s spectrum. The C 1s spectral profiles between electrochemically doped and cast samples were different in the higher binding energy region. S 2p and N 1s core-level spectra of CuPc doped compounds also showed the difference of the spectral profile between electrochemically doped and cast samples, which suggested the dopant-polymer interaction. A split of Cu 2p spectra indicates the charge transfer between CuPc and the polymer chains. In the FTIR measurements, characteristic vibrational modes to CuPc, in-plane, out-of-plane, and ring stretching modes were observed. A central metal-origin peak was also observed. New peaks at 1545 and 1680cm−1 suggest the polymer-PcCu linkage.

Etching characteristics and plasma-induced damage of Ba 0.65Sr 0.35TiO 3 thin films etched in CF 4/Ar/O 2 plasma

Sol–gel-derived Ba 0.65Sr 0.35TiO 3 (BST) thin films were etched in CF 4/Ar/O 2 plasma using magnetically enhanced reactive ion etching technology. The maximum etch rate of BST film is 8.47 nm/min when CF 4/Ar/O 2 gas mixing ratio is equal to 9/36/5. X-ray photoelectron spectroscopy analysis indicates the accumulation of fluorine-containing by-products on the etched surface due to their poor volatility, resulting in (Ba,Sr)-rich and (Ti,O)-deficient etched surface. Compared to the unetched counterparts, the etched Ba 3d 5/2, Ba 3d 3/2, Sr 3d 5/2, Sr 3d 3/2, Ti 2p 3/2, Ti 2p 1/2 and O 1s photoelectron peaks shift towards higher binding energy regions by amounts of 1.31, 1.30, 0.60, 0.79, 0.09, 0.46 and 0.50 eV, respectively. X-ray diffraction (XRD) analysis reveals that intensities of the etched BST (1 0 0), (1 1 0), (2 0 0) and (2 1 1) peaks are lowered and broadened. Raman spectra confirm that the Raman peaks of the etched film shift towards lower wave number regions with the values of 7, 6, 4 and 4 cm −1, and the corresponding phonon lifetimes are longer than those of the unetched film because of the plasma-induced damage. When the etched films are postannealed at 650 °C for 20 min under an O 2 ambience, the chemical shifts of Ba 3d, Sr 3d, Ti 2p and O 1s peaks, the variations for atomic concentrations of Ba, Sr, Ti and O, and the Raman redshifts are reduced, while the corresponding XRD peak intensities increase. It is conceivable that the plasma-induced damage of the etched film could be partially recovered during the postannealing process.

Effect of oxygen gas and annealing treatment for magnetically enhanced reactive ion etched (Ba0.65,Sr0.35)TiO3 thin films

Sol-gel-derived (Ba0.65,Sr0.35)TiO3 (BST) thin films were etched in CF4∕Ar and CF4∕Ar∕O2 plasmas using magnetically enhanced reactive ion etching technology. Experimental results show that adding appropriate O2 to CF4∕Ar can better the etching effects of BST films for the increase of etching rate and decrease of etched residues. The maximum etching rate is 8.47nm∕min when CF4∕Ar∕O2 gas-mixing ratio is equal to 9∕36∕5. X-ray photoelectron spectroscopy (XPS) data confirm accumulation of reaction products on the etched surface due to low volatility of reaction products such as Ba and Sr fluorides, and these residues could be removed by annealing treatment. The exact peak positions and chemical shifts of the interested elements were deduced by fitting XPS narrow-scan spectra with symmetrical Gaussian-Lorentzian product function for Ba 3d, Sr 3d, and O 1s peaks, meanwhile asymmetrical Gaussian-Lorentzian sum function was used to fit Ti 2p doublet to adjust the multiple splitting and/or shake-up process of transition-metal Ti cations. Compared to the unetched counterparts, the etched Ba 3d5∕2, Ba 3d3∕2, Sr 3d5∕2, Sr 3d3∕2, Ti 2p3∕2, Ti 2p1∕2, and O 1s peaks shift towards higher binding energy regions by amounts of 1.31, 1.30, 0.60, 0.79, 0.09, 0.46, and 0.50eV, respectively. While the etched Ti 2p3∕2 and Ti 2p1∕2 peaks have small chemical shifts for two reasons. One is that Ti fluoride (TiFz) is mostly removed from the etched surface because of its higher volatility in the process of thermal desorption. The other is that there is a shift compensation between TiFz and the etched BST matrix in which Ti4+ cations are partially reduced to form Tix+ (0<x<4) cations in the presence of adequate oxygen vacancies. The simulated formula of each BST surface is obtained to be (Ba0.65,Sr0.35)Ti0.97O2.86, (Ba0.70,Sr0.30)Ti0.24O1.39, and (Ba0.68,Sr0.32)Ti0.95O2.74, and then the average valence of Ti cations is estimated to be +3.84, +3.25, and +3.66 with respect to the electroneutrality principle, respectively. It is inferred that electrical properties of the etched BST film may be partially recovered by postannealed after etched.

Study of the oxidation for Si nanostructures using synchrotron radiation photoemission spectroscopy

We report the oxidation characteristics for Si nanostructures. Synchrotron radiation Si 1s X-ray photoemission spectroscopy (XPS) is used to explain the oxidation process and the modification of the electronic structures of Si. Si films of different thicknesses were grown on a graphite surface. Before oxidation, several photoemission components are observed in thin Si films, such as 2 or 4 Å films. The components observed at the higher binding energy regions are identified as Si nanostructures. After oxidation, photoemission results show that the oxidation process is thickness dependent. Quantitatively, in 2 and 4 Å films, the photoemission signals from oxide phase are 18 and 30%, respectively of total intensity. The present result suggests that the higher binding energy components, i.e., Si nanostructures play some significant role during the oxidation, where the reactivity of nanostructures towards oxygen is relatively low or negligible, and nanostructures impose some restrictions on the oxidation of the film.

Comparative Study on the Electronic Structure of Arc-Discharge and Catalytic Carbon Nanotubes

Electronic structure of multiwall carbon nanotubes has been studied by X-ray emission and photoelectron spectroscopy. The measurements were performed for two samples synthesized by different methods such as arc-discharge graphite evaporation and catalytic decomposition of hydrocarbons on supported catalysts. X-ray spectra of the former sample were shown to be similar to those of the highly oriented pyrolytic graphite, while the C Kα spectrum of catalytic nanotubes exhibited an enhanced density of π occupied states and the C 1s line of sample expanded toward both lower and higher binding energy regions. The models incorporating pentagon−heptagon pair and sp3-hybridized atoms have been calculated by AM1 quantum-chemical method to reveal the influence of defects on the electronic structure of carbon nanotube. Carbon Kα and 1s lines were found to be practically unaffected by inserting pentagon and heptagon into the hexagonal network on diametrically opposite sides of tube. However, the changes observed in the...

XPS and UPS studies on electronic structure of Li 2O

The adsorption behavior of H 2O on Li 2O was studied by X-ray photo electron spectroscopy (XPS) and ultraviolet photo electron spectroscopy (UPS). XPS and UPS spectra of Li 2O single crystals which were exposed to different pressure of H 2O vapor were observed. In O(1s) region, two peaks were observed and they were assigned to O(1s) in precipitated LiOH on the surface and O(1s) in Li 2O. After H 2O exposure, a peak broadening and an appearance of a new peak were observed at the higher binding energy region than O(1s) in Li 2O. They were attributed to surface −OH and H 2O molecule adsorbed on the surface. The adsorption behavior of H 2O was discussed from the observation of electronic structure in Li 2O surface.

Composition dependent electronic structure effects in Nd1−x Sr x TiO3

The development of the electronic structure in Nd1−x Sr x TiO3 as a function of x was investigated using resonant photoelectron spectroscopy. Attention is focussed indication of changes in the Ti 3d-O2p hybridization and on electron-electron correlation effects evident in the Ti 3d intensity within ∼ 3 eV of the Fermi level (E F). The energetic position of the Ti 3d intensity signals the importance of electron correlation effects. The total intensity in this region is found to correlate linearly with composition and changes in the spectral structure are discussed in terms of the one-electron spectral function. For x < 0.25 (insulating or semiconducting compositions), only incoherent intensity associated with the lower Hubbard band is present. Additional intensity, attributed to a coherent quasiparticle contribution, appears at the composition of the metal-insulator transition, x < 0.25. Ti 3d intensity also occurs in the higher binding energy region of the predominantly O 2p band due to Ti 3d O-2p hybridization. Composition-dependent changes in this region are analyzed to determine changes in the Ti 3d-O2p hybridization with composition and structure.

Core level photoelectron spectroscopy on the lanthanide-induced hydrolysis of DNA

The electronic structures of the complexes of diphenyl phosphate (DPP), a model compound of DNA, with lanthanide ions have been investigated to shed light on the mechanism of the cerium (IV)-induced nonenzymatic hydrolysis of DNA. Binding energies of the P 2p core level of DPP were 134.2 eV for the complexes with La(III), Eu(III), and Lu(III), and was 134.4 eV for the Ce(IV) complex, when the metal/DPP molar ratio was 1:1. When the molar ratio was increased, only Ce(IV), the most active metal ion for DNA hydrolysis, showed a chemical shift of ∼0.5 eV toward the higher binding energy region. The chemical shift of ∼0.5 eV toward the higher binding energy region. The chemical shift was due to the systematic increase in the intensity of the higher binding energy component. The observed change in the electronic structure of the DPP-Ce(IV) complex may be related to the superb ability of Ce(IV) for the hydrolysis of DNA.

X-Ray photoelectron spectra of some bioinorganic complexes of the rare earths with N-acetylalanine

X-Ray photoelectron spectra of some bioinorganic complexes of La, Ce, Pr, Nd, Sm and Eu with N-acetylalanine have been measured and the 3d52 and 3d32 main peaks and their satellites have also been assigned. The spin—orbit splitting between the 3d52 and 3d32 core-level of the rare earth ion in these complexes becomes slightly larger than that of the free rare earth atom due to the effect of the crystal field. The satellite for the 3d main peaks of La in the solid state complex are in higher binding energy region and may be attributable to the L → 4ƒ charge-transfer shake-up process. The satellites for the 3d main peaks of Ce, Pr, Nd, Sm and Eu are in the lower binding energy region and may be attributable to the 4ƒ→L charge-transfer shake-down process.

Photoemission Study of the Electronic Structure of the Ferromagnetic Cr1-δTe System

The electronic structure of Cr1-δTe (δ=0.05, 0.25, 0.375) has been studied by photoemission spectroscopy. Structures near the Fermi level are qualitatively explained by the density of states (DOS) given by band-structure calculations, but significant discrepancies exist in the higher binding energy region. Configuration-interaction cluster-model calculations have been performed and the overall experimental features have been explained, indicating significant electron correlation effects in these compounds.