Binding Energy Region Research Articles

X-Ray Photoelectron Spectroscopy of Compounds Simultaneously Containing Zinc and Iron: Alert on Fe 2p Region

Many interesting materials in a broad range of applications have in their composition the coexistence of zinc and iron. Their characterization by XPS should identify and quantify both elements. The most intense regions for these elements Zn 2p and Fe 2p are, therefore, used to accomplish that purpose. By using sphalerite as an example of a material where Zn and Fe may coexist and using XPS with two different X radiation sources to study them, it is demonstrated that the Fe 2p region, when the iron is the minor component, may be seriously affected by the Auger Zn L3M1M23 structure. The sphalerite (Zn1−xFexS) here studied has x ≈ 0 and is a good example to show how an XPS spectrum obtained with the X-ray Al Kα, the most used radiation in monochromatic equipment, leads to a wrong assignment of the structures existing in the binding energy region of Fe 2p. The simultaneous use of Mg Kα radiation showed that the Fe 2p is below the XPS detection in this specific sample of sphalerite. Its attested absence reveals that the structure detected, when using Al Kα in the “Fe 2p” region, is assigned to a zinc Auger multiple peak and not to the expected 2p photoelectron doublet peak of iron.

Roles of hygrothermal aging temperature and time in degradation of the fracture toughness of highly cross‐linked epoxy

AbstractThe evolution of plane‐strain fracture toughness in highly cross‐linked epoxies was assessed for different hygrothermal aging temperatures (25, 50, and 75°C) and durations (0–75 days). The absorption of water increased with hygrothermal aging, but at a diminishing rate and without saturating. A fraction of the absorbed water persisted despite prolonged drying. Thermogravimetric analysis revealed that the epoxy‐decomposition temperature decreased with hygrothermal aging. 13C solid‐state nuclear magnetic resonance spectroscopy indicated an increase in the de‐shielding of carbon atoms in the vicinity of electronegative elements like oxygen with hygrothermal aging severity, indicating the development of intermolecular hydrogen bonding. X‐ray photoelectron spectroscopy tracked the chemical bonding state of carbon by using a narrow scan on the C1s binding energy region. Upon hygrothermal aging, there was a decrease in CC/CC groups, indicating main chain scission through hydrolysis. A simultaneous increase in the CO species indicates the formation of alcohols as hydrolysis reaction products. In this manner, retained water was involved in hydrogen bonding and chemical reactions with the epoxy. With increasing severity of hygrothermal aging, the fracture toughness decreased. This was consistent with fracture surface micrographs that showed a greater distance amongst crack stretch marks in specimens with less toughness.

MCDAD investigation to characterize the magnetic behavior of thin Pd films on Co(0001)

The magnetic characteristics of Pd thin films on Co(0001) were investigated by means of Magnetic Circular Dichroism in the Angular Distribution of photoelectrons (MCDAD). For uncovered Co it was found that significant photoelectron intensity differences occur for electrons emitted from the 3d band near the Fermi level in the situation of a fixed helicity of the incoming circularly polarized radiation and opposite magnetization of the magnetic layer.After deposition of Pd in the submonolayer regime up to a thickness of a few layers, the new features which are present in the photoemission spectra exhibit asymmetries, too. A strong hybridization takes place at the interface which is due to the intermixing of Pd 4d and Co 3d states. This interface state shows no dispersion and nearly no change of the asymmetry value for different photon energies. Additionally, the sign of the asymmetry is opposite to that of the ferromagnetic substrate. The reason is the strong hybridization which results not in a rigid band shift as found for less-interacting adsorbates but in new states being different in the majority and minority spin band. As a consequence, the interface layer exhibits an induced magnetic polarization. The structure near the Fermi energy exhibit the same sign of the asymmetry but with lower values. For a thickness of more than 2 monolayers the spectrum is comparable to bulk measurements and shows no MCDAD asymmetries in the entire binding energy region.

Density of gap states in CH3NH3PbI3 single crystals probed with ultrahigh-sensitivity ultraviolet photoelectron spectroscopy

The advantages of methylammonium triiodideplumbate (CH3NH3PbI3)-based organic–inorganic hybrid halide perovskite have led to devices with power conversion efficiencies of >20%. The CH3NH3PbI3 structure is prone to be more sensitive towards external effects due to its higher flexibility than inorganic counterparts. Nevertheless, a direct photoemission spectroscopy study is still lacking on the density of gap states (DOGS) influenced by air exposure and synchrotron light-induced degradation. In this paper, we investigate the evolution of electronic structure in CH3NH3PbI3 single crystals after air exposure and intense synchrotron light irradiation to reveal the effects on its density of states distribution below and above the valence band maximum (VBM) by using ultrahigh-sensitivity photoelectron spectroscopy. We find that the PbI2 compounds, decomposed from CH3NH3PbI3 after air exposure, could not affect the DOGS distribution but only give the VBM shift in the high binding energy region, which is dramatically different from the impacts of an impurity found for other organic or inorganic counterparts. A further study using intense synchrotron irradiation confirms the decomposed processes for CH3NH3PbI3: (i) the initial degradation would induce the formation of PbI2, which gives a negligible impact on the DOGS above the VBM; (ii) the continuous intense light irradiation could further degrade PbI2 to metallic Pb, in which DOGS appears in the energy bandgap.

An event excess observed in the deeply bound region of the 12C (K−, p) missing-mass spectrum

Abstract We have measured, for the first time, the inclusive missing-mass spectrum of the $^{12}$C$(K^-, p)$ reaction at an incident kaon momentum of 1.8 GeV/$c$ at the J-PARC K1.8 beamline. We observed a prominent quasi-elastic peak ($K^-p \rightarrow K^-p$) in this spectrum. In the quasi-elastic peak region, the effect of secondary interaction is apparently observed as a peak shift, and the peak exhibits a tail in the bound region. We compared the spectrum with a theoretical calculation based on the Green’s function method by assuming different values of the parameters for the $\bar{K}$–nucleus optical potential. We found that the spectrum shape in the binding-energy region $-300 \, \text{MeV} < B_{K} < 40$ MeV is best reproduced with the potential depths $V_0 = -80$ MeV (real part) and $W_0 = -40$ MeV (imaginary part). On the other hand, we observed a significant event excess in the deeply bound region around $B_{K} \sim 100$ MeV, where the major decay channel of $K^- NN \to \pi\Sigma N$ is energetically closed, and the non-mesonic decay modes ($K^- NN \to \Lambda N$ and $\Sigma N$) should mainly contribute. The enhancement is fitted well by a Breit–Wigner function with a kaon-binding energy of 90 MeV and width 100 MeV. A possible interpretation is a deeply bound state of a $Y^{*}$-nucleus system.

Mechanism of Ag sulfurization resistance improvement by alloying solutes in Ag-based alloy films

The Ag sulfurization resistance of the pure Ag film and four Ag-based alloy films was evaluated by the reflectance decay after the Ag sulfurization test. Among all Ag-based alloy films, the In alloying solute in the Ag-In alloy film shows the best resistance to the Ag sulfurization. Using x-ray photoelectron spectroscopy analysis, the chemical state of the alloying solutes in the Ag-based alloy films was examined. It is found that, with being alloyed in the Ag matrix phase, the 3d5/2 core-level peak positions of the alloying solutes (In, Sn, and Pd) shift toward the lower binding energy region, which is defined as a negative chemical shift. The chemical shifts of In, Sn, and Pd alloying solutes are –0.31 eV, –0.23 eV, and –0.2 eV, respectively. The absolute value of the negative chemical shift represents the tendency of Ag atoms losing valence electrons to the alloying solutes. As the Ag atoms lose valence electrons to the alloying solutes, the Ag atoms have a less tendency to provide the valence electrons to form covalent bonding with S atoms, which suppresses the Ag sulfurization reaction (2Ag + S → Ag2S). Therefore, the larger the absolute value of the negative chemical shift, the higher is the reflectance decay (lesser Ag sulfurization resistance).

Exceptional properties of the magnetic interface state of Pd on Fe(1 1 0)

The magnetic characteristics of Pd thin films on Fe(110) were investigated by means of Magnetic Circular Dichroism in the Angular Distribution of photoelectrons (MCDAD). For uncovered Fe it was found that significant photoelectron intensity differences occur for electrons emitted from the 3d band near the Fermi level in the situation of a fixed helicity of the incoming circularly polarized radiation and opposite magnetization of the magnetic layer. The corresponding MCDAD asymmetry shows a strong dependence on the excitation energy in the VUV range and exhibits values up to about 10%.After deposition of Pd in the submonolayer regime up to a thickness of a few layers, the new features which are present in the photoemission spectra exhibit asymmetries, too. A strong hybridization takes place at the interface which is due to the intermixing of Pd 4d and Fe 3d states. This interface state shows no dispersion and no change of the asymmetry value for different photon energies. Additionally, the sign of the asymmetry is opposite to that of the Fe substrate. The reason is the strong hybridization which results not in a rigid band shift as found for less-interacting adsorbates but in new states being different in the majority and minority spin band. As a consequence, the interface layer exhibits an induced magnetic polarization. The structure near the Fermi energy exhibit the same sign of the asymmetry but with lower values. For a thickness of 3 monolayers the spectrum is comparable to bulk measurements and shows no MCDAD asymmetries in the entire binding energy region.

Dissociation kinetics of excited ions: PEPICO measurements of Os3(CO)12 - The 7-35 eV single ionization binding energy region.

In this article, we study the photoinduced dissociation pathways of a metallocarbonyl, Os3(CO)12, in particular the consecutive loss of CO groups. To do so, we performed photoelectron-photoion coincidence (PEPICO) measurements in the single ionization binding energy region from 7 to 35 eV using 45-eV photons. Zero-energy ion appearance energies for the dissociation steps were extracted by modeling the PEPICO data using the statistical adiabatic channel model. Upon ionization to the excited ionic states above 13 eV binding energy, non-statistical behavior was observed and assigned to prompt CO loss. Double ionization was found to be dominated by the knockout process with an onset of 20.9 ± 0.4 eV. The oscillator strength is significantly larger for energies above 26.6 ± 0.4 eV, corresponding to one electron being ejected from the Os3 center and one from the CO ligands. The cross section for double ionization was found to increase linearly up to 35 eV ionization energy, at which 40% of the generated ions are doubly charged.

Effect of substrate temperature and post annealing temperature on ZnO:Zn PLD thin film properties

The pulsed laser deposition (PLD) substrate temperature and post-annealing temperature are effective methods to control the film optical and structural properties. The structure, morphology and optical properties of the deposited and post-annealed PLD ZnO:Zn films were studied. The films were deposited at different substrate temperatures of 50 °C, 200 °C and 400 °C. The films deposited at the substrate temperature of 50 °C and 200 °C were post-annealed in air at 400 °C and 600 °C for two hours. The films all had a highly preferential orientation with the hexagonal c-axis perpendicular to the substrate surface. The stress was found to be compressive stress with values −3.289 GPa, −4.864 GPa and −4.425 GPa for the film deposited at 50 °C, 200 °C and 400 °C, respectively. After post-annealing treatments, the stress of the films was almost completely released and stress-free films were obtained. The crystallite sizes were 19 nm, 25 nm and 39 nm, while the average particles sizes were 95 nm, 85 nm and 129 nm for the film deposited at 50 °C, 200 °C and 400 °C respectively. The crystallite sizes and particles sizes seemed to increase with the increase in the substrate temperature. Contrary to this, the change in crystallite sizes were inversely proportional to the particles size when increasing the post-annealing temperatures. Deconvoluted X-ray photoelectron spectroscopy peaks of the O1s binding energy region revealed that the films deposited at different substrate temperatures contained oxygen-related defects. Photoluminescence studies revealed that the films all emitted ultra-violet emission around 379 nm. The film deposited at 50 °C emitted a broad green emission centered at ∼524 nm. By increasing the substrate temperature up to 200 °C and 400 °C a new orange emission around 621 nm and 634 nm as well as a weak emission around 416 nm and 500 nm were observed, respectively. After post-annealing treatments, new bands over the visible region (blue, green and orange-red) were observed, the orange-red emissions at ∼ 626 nm to 681 nm being dominant for the annealed samples. The defects-related visible emission was discussed in detail and it was in good agreement with previous studies.

UPS and DFT investigation of the electronic structure of gas-phase trimesic acid

Benzene-1,3,5-tricarboxylic acid (trimesic acid, TMA) molecules in gas-phase have been investigated by using valence band photoemission. The photoelectron spectrum in the binding energy region from 9 to 22eV is interpreted by using density functional theory calculations. The electronic structure of TMA is compared with benzene and benzoic acid in order to demonstrate changes in molecular orbital energies induced by addition of carboxyl groups to benzene ring.

Theoretical Studies on the Effect of Fapy-G on Base Pair Hydrogen Bond Complexes†

One of the primary oxidative DNA damage is 2,6-diamino-4-hydroxy-5-formamido pyrimidine,named Fapy-guanine( Fapy-G),which is the product of guanine oxidized at C8. The properties of 20 oxidative base pairs which contains Fapy-G were investigated via quantum chemistry methods. All model molecular structures were optimized with B3 LYP /6-31 + G*method and the frequency calculations were carried out to confirm that all the structures obtains were geometrically stable. The energies were determined at the MP2 /aug-cc-p VDZ level with BSSE corrections. The calculation results show that N7,N9 became hydrogen bond donor from accepter. Natural atomic charge of N7,N9 and O6 get more negative. The ability of O6 as H-bond donor enhanced. The bond lengths of C5—N7 and N7—C8 were increased by 0. 0045 and 0. 0063 nm,C4—N9 was decreased by 0. 0015 nm. Compared with bases monomers,natural atomic charge of proton acceptors in hydrogen bond complexes increased by 0. 05 e averagely,which is 8% of the original charge;natural atomic charges for proton donors have a decrease of 0. 02 e,which is 4% of the original charge. Compared with Fapy-G,when the N atom in Fapy-G six-membered ring was formed H-bond,the ring breathing and N-para-C vibrational frequencies were blue shifts. The vibrational frequencies were related to H-bond red shifts in all the base pairs. NH…N is stronger than NH…O in all the base pairs and in NH…N the hydrogen bond energy of donor N atom in six-membered ring are bigger than donor N atom in NH2 or open-ring. When Fapy-G pairs with base A,the binding energy region order is 1 2 4 3. When Fapy-G pairs with base T( R),the binding energy region order is 3 = 4 1 2. In water solvent,the binding energies of Fapy-G pairs with base C reduced to 41. 84—58. 58 k J / mol,and the order of the binding energy was changed.

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.

Alloying and oxidation of in situ produced core-shell Al@Yb nanoalloy particles--an "on-the-fly" study.

Core-shell-structured nanoalloy particles with an Al-dominated interior covered by few Yb monolayers have been fabricated using a vapor-aggregation method involving magnetron sputtering. The radially segregated structure of the Yb-Al nanoparticles has been disclosed by "on-the-fly" photoelectron spectroscopy monitoring of the nanoparticle beam in Yb 4f and Al 2p electron binding energy regions. Both, the binding energy values and the electron microscopy images taken on the deposited nanoparticles, allow estimating their dimensions to be in the 5-10 nm range. The photoelectron spectroscopy results suggest that in these nanoparticles no trivalent Yb--the typical case for the macroscopic Yb-Al alloy--is present. The oxidation of preformed Yb-Al nanoparticles was successfully attempted, leading to the appearance of divalent Yb surface oxide--in contrast to the bulk macroscopic Yb which is trivalent in the oxide. Our results suggest that at intermediate oxygen exposures "sandwich-like" nanoparticles of YbO/Yb/Al were synthesized. At higher O2 exposures, the oxygen seems to penetrate all the way to the Yb-Al interface. The results of the present study have to be considered when photonic applications of Yb-doped garnet nanoparticles are planned.

Anomalous temperature dependence in valence band spectra: A resonant photoemission study of layered perovskite Sr2CoO4

Valence band spectra (VBS) and its modification across Curie temperature (TC) of Sr2CoO4 thin film are studied using resonant photoemission spectroscopy. It is found that VBS mainly consists of hybridized states of Co-3d t2geg and O-2p; however, Co-3d eg states show its prominence only in the ferromagnetic temperature regime. Below TC, spectral weight transfer takes place anomalously from high binding energy (B.E.) region to low B.E. region, signifying the enhanced intermediate or low spin state Co4+ ions. It is suggested that spin-lattice coupling and many-body effects in Sr2CoO4 derived from the strong electron correlations lead to such temperature dependence of VBS.

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.

Revealing the Adsorption Mechanisms of Nitroxides on Ultrapure, Metallicity-Sorted Carbon Nanotubes

Carbon nanotubes are a natural choice as gas sensor components given their high surface to volume ratio, electronic properties, and capability to mediate chemical reactions. However, a realistic assessment of the interaction of the tube wall and the adsorption processes during gas phase reactions has always been elusive. Making use of ultraclean single-walled carbon nanotubes, we have followed the adsorption kinetics of NO2 and found a physisorption mechanism. Additionally, the adsorption reaction directly depends on the metallic character of the samples. Franck–Condon satellites, hitherto undetected in nanotube–NOx systems, were resolved in the N 1s X-ray absorption signal, revealing a weak chemisorption, which is intrinsically related to NO dimer molecules. This has allowed us to identify that an additional signal observed in the higher binding energy region of the core level C 1s photoemission signal is due to the C=O species of ketene groups formed as reaction byproducts . This has been supported by density functional theory calculations. These results pave the way toward the optimization of nanotube-based sensors with tailored sensitivity and selectivity to different species at room temperature.

Photoemission study of amorphous and crystalline GeTe and (Ge,Mn)Te semiconductors

Resonant photoemission spectroscopy was applied to compare the valence band structure of Ge0.9Mn0.1Te and GeTe semiconductor layers deposited on BaF2 substrate in monocrystalline and amorphous forms. In (Ge,Mn)Te the contribution of Mn 3d5 electronic orbitals to density of states was found in three binding energy regions: below the top of the valence band (Eb<4.2eV), at the binding energy range 4.2–4.4eV, and in many-body satellite at 9–13eV. The comparative analysis of the photoemission spectra based on configuration interaction model showed that p–d hybridization effects, important for magnetic and optical properties of (Ge,Mn)Te, are stronger in monocrystalline than in amorphous (Ge,Mn)Te layers.

Temperature dependence study of Pd–Cu supported bimetallic films by photoelectron spectroscopy and cyclic voltammetry

Vapor deposition method is used to prepare layered Pd–Cu bimetallic films, with different thickness of Pd over a Cu film supported on glassy carbon. X-ray photoelectron spectroscopy (XPS) measurements of core level binding energy (BE) and valence band region are used to investigate the contribution of charge transfer resulting from the bonding of these two dissimilar metals in a layered structure. As this layered bimetallic film is annealed at increasing temperature from 298 to 650K, atomic inter-diffusion occurs to form an alloy. We differentiate this interfacial charge transfer effect between these two dissimilar metals from that of surface alloying resulting from the annealing effect. Cyclic voltammetry (CV) tests combined with XPS confirm that (1) the surface is free of Cu atoms for Pd films with thicknesses between 2.0 and 7.0±0.3nm at room temperature and (2) Pd–Cu inter-diffusion propagates to the surface and the formation of surface alloys take place at temperature greater than 350K. For these Pd thicknesses, the difference in BE shifts of Cu 2p and Pd 3d peaks between layered and alloyed structures are +0.16eV and −0.17eV, respectively. This difference in BE shifts allows for a clear distinction between these two bimetallic structures and the tailoring of the optimum configuration that enhances catalytic activity toward formic acid. Additionally, angle resolved XPS data as a function of temperature and XPS depth profiling at room temperature provide insight about the inter-diffusion length. Furthermore, CV measurements in H2SO4 and formic acid confirm that for a Pd–Cu bimetallic surface with a 3.8±0.3nm Pd film over Cu shows significantly improved activity toward formic acid oxidation compared to bulk Pd at 298K and after being annealed at temperature of 350K.

Threshold photoelectron spectroscopy of acetaldehyde and acrolein

High-resolution (6meV and 12meV) threshold photoelectron (TPE) spectra of acetaldehyde and acrolein (2-propenal) have been recorded over the valence binding energy region 10–20eV, employing synchrotron radiation and a penetrating-field electron spectrometer. These TPE spectra are presented here for the first time. All of the band structures observed in the TPE spectra replicate those found in their conventional HeI photoelectron (PE) spectra. However, the relative band intensities are found to be dramatically different in the two types of spectra that are attributed to the different dominant operative formation mechanisms. In addition, some band shapes and their vertical ionization potentials are found to differ in the two types of spectra that are associated with the autoionization of Rydberg states in the two molecules.