X-ray Photoelectron Spectra Measurements Research Articles

Capacity fading mechanism in lithium sulfur cells using poly(ethylene glycol)-borate ester as plasticizer for polymer electrolytes

Plasticizers of poly(ethylene glycol)-borate (PEG-B) esters are added into lithium-conducting gel polymer electrolyte (GPE) in Li–S cells in order to inhibit the unrestrained migration of polysulfide anions. An improvement of the electrochemical properties of the Li–S cell using GPE is observed upon addition of the plasticizers at room temperature. However, a slow decrease of discharge capacities follows after stable cycles. To understand the origin of the capacity fading, electrochemical impedance spectroscopies (EIS), scanning electron microscopy (SEM), X-ray Diffraction (XRD) and X-ray photoelectron spectra (XPS) are adopted. EIS measurements indicate that the decrease of capacity in the Li–S cell using GPE is related to the increase of interfacial resistance between GPE and anode. SEM studies combined with XRD and XPS measurements reveal the increase of interfacial resistance between GPE and anode is results from Li2S corrosion products. Accordingly, the polysulfide anions precipitate on the anode surface, which leads to a reduction of the cycle life of the Li–S cell using GPE. Li-ion transference number measurement shows an increase of transference number before 20th cycles, and then decreased, which suggests that the GPE using PEG-B esters as plasticizers could inhibit the unrestrained migration of polysulfide anions at some time but not permanently.

Paramagnetic One-Dimensional Chains Comprised of Trinuclear Pt–Cu–Pt and Paddlewheel Dirhodium Complexes with Metal–Metal Bonds

One-dimensional (1-D) chain complexes constructed by metal-metal bonds containing three types of metal species-platinum, rhodium, and copper-have been rationally synthesized and characterized by single-crystal X-ray analyses and physical measurements. The paddlewheel or lantern type complex, [Rh2(O2CCH3)4] (i.e., [Rh2]), has a vacant σ* orbital which accepts the electrons from the filled dz(2) orbital of cis-[Pt(piam)2(NH3)2]·2H2O (1, i.e. [Pt], where piam = pivalamidate) to afford a tetranuclear complex, [{Rh2(O2CCH3)4}{Pt(piam)2(NH3)2}2]·2H2O (2). Compound 2 forms a linear alignment as [Pt]-[Rh2]-[Pt] with unbridged Rh-Pt bonds, where the oxygen atoms of the piam ligands in the [Pt] are noncoordinated, showing the capability of binding another metal ion. Simply mixing [Rh2] and the heterometallic trinuclear complex [Pt2Cu(piam)4(NH3)4](PF6)2 (3, i.e. [Pt-Cu-Pt]) in a ratio of 1:1 in MeOH, EtOH, or Me2CO affords [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n (4), [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n (5), or [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n·6nMe2CO (6), respectively. Compounds 4-6 form infinite chains with the repetition of -{[Rh2]-[Pt-Cu-Pt]}n-, which to our knowledge, are the first examples of heterometallic 1-D chains comprised of three types of metal species with direct metal-metal bonds. The CF3CO2(-), ClO4(-), and water molecules influence the crystal packing to form an octanuclear complex of [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}2](CF3CO2)2(ClO4)2·2H2O (7) with [Pt-Cu-Pt]-[Rh2]-[Pt-Cu-Pt] alignment. Considering the crystal structures and X-ray photoelectron spectra (XPS) measurements in 4-7, the oxidation states of the metal atoms are -{[Rh2(II,II)]-[Pt(II)-Cu(II)-Pt(II)]}n- or [Pt(II)-Cu(II)-Pt(II)]-[Rh2(II,II)]-[Pt(II)-Cu(II)-Pt(II)], which are unchanged from those in the starting compounds. Electron paramagnetic resonance spectra of 4-7 show axially symmetric spectra with g∥ > g⊥, indicating that the HOMO (SOMO) is a Cu d(x(2)-y(2)) orbital. In 7, the hyperfine coupling in the spectrum indicates that the unpaired spin on Cu is perturbed by the Pt atoms.

Preparation of acid–base bifunctional core–shell structured Fe3O4@SiO2 nanoparticles and their cooperative catalytic activity

An acid–base bifunctionalized magnetic nanoparticles catalyst Fe3O4@SiO2-A/B was successfully synthesized by immobilization of both organic base and acid groups together over silica-coated magnetite nanoparticles. The catalyst has been characterized by transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS) measurements. The bifunctionalized magnetic nanoparticles act as an easily recovered, highly efficient catalyst for the Henry reaction of 4-nitrobenzaldehyde with nitromethane at mild reaction conditions, even exceeding any monofunctionalized catalyst or physical mixture of two monofunctionalized nanoparticles in the catalytic behavior. In addition, a probable mechanism has been proposed to explain the cooperative interactions from the presence of the immobilized base and acid groups in close proximity. Importantly, the catalyst can be simply recoverable from the reaction mixture by magnetic decantation and recycled without significant degradation in reactivity.

Electronic Structure and Auger-Free Luminescence in Cs2ZnCl4Crystals

On the basis of the electronic structure determined from measurements of reflection and X-ray photoelectron spectra, Auger-free luminescence (AFL) of Cs 2 ZnCl 4 has been studied under the outermost-core band excitation in a temperature range of 10–300 K. A band is found at 4.8 eV, in addition to the 3.3 and 4.2 eV bands observed previously. The present study clarifies that the 4.8 eV band, as well as the 3.3 and 4.2 eV bands, originates from the Auger-free transition between the Cs 5 p outermost-core band and the Cl 3 p valence band. When the sample temperature is increased, spectral widths of the 3.3 and 4.8 eV bands become broadened, while that of the 4.2 eV band is almost kept unchanged. This suggests that the core hole created on a Cs + ion interacts with the surrounding lattice vibration. The decay profiles are found to be essentially the same for all the AFL bands. Three-peaked structure of AFL is discussed in comparison with experimental and theoretical results in CsCl.

Resonant photoemission at the L3 absorption edge of Mn and Ti and the electronic structure of 1T-Mn0.2TiSe2

Resonant valence band x-ray photoelectron spectra (ResPES) excited near the 2p3/2 core level energies, 2p x-ray photoelectron spectra (XPS) and L3,2 x-ray absorption spectra (XAS) of Ti and Mn in single crystals of 1T-Mn0.2TiSe2 were studied for the first time. The ionic–covalent character of the bonds formed by the Mn atoms with the neighboring Se atoms in the octahedral coordination is established. From the XPS and XAS measurements compared with the results of atomic multiplet calculations of Ti and Mn L3,2 XAS, it is found that the Ti atoms are in the ionic state of 4 + and the Mn atoms are in the state of 2 + . In ResPES of Mn0.2TiSe2 excited near the Ti 2p3/2 and Mn 2p3/2 absorption edges the Ti 3d and Mn 3d bands at binding energies just below the Fermi level are observed. According to theoretical calculations of E(k) the Ti 3d states are localized in the vicinity of the Γ point and the Mn 3d states are localized along the direction K–Γ–M in the Brillouin zone of the crystal.

Non-magnetic impurity induced magnetism in rutile TiO2:K compounds

Recent ab initio studies have theoretically predicted room temperature ferromagnetism in several oxide materials of the type AO2 in which the cation A4+ is substituted by a non-magnetic element of the 1 A column. Our purpose is to address experimentally the possibility of magnetism in Ti1−xKxO2 compounds. The samples have been synthesized via the solid state route method at equilibrium. Our study has shown that Ti1−xKxO2 is thermodynamically unstable and leads to a phase separation, in contradiction with the hypothesis of ab initio calculations. In particular, the crystalline TiO2 grains appear to be surrounded by K-based phase. The oxidization state of the Ti ion is found to be in Ti4+ as confirmed from the x-ray photoelectron spectra measurement. Nevertheless, K:TiO2 compounds exhibit weak paramagnetism with the highest magnetic moment of ∼0.5 μB K−1 but no long-range ferromagnetic order. The observed moment in these compounds remains much smaller than the predicted moment of 3 μB by ab initio calculation. The apparent contradictions between our experiments and first-principles studies are discussed.

Fabrication of fluorine-terminated diamond-like carbon thin film using a hyperthermal atomic fluorine beam

Surface modification of diamond-like carbon (DLC) film was performed using a hyperthermal atomic fluorine beam on the purpose of production of hydrophobic surface by maintaining the high hardness of DLC film. By the irradiation of atomic fluorine beam of a 1.0 × 10 20 atoms/cm 2, the contact angle of a water drop against the DLC surface increased from 73° to 111°. The formation of CF 3, CF 2 and CF bonding on the modified DLC surface was confirmed from the measurements of X-ray photoelectron spectra and near-edge X-ray absorption fine structure spectra. Irradiation of hyperthermal atomic fluorine beam was concluded to produce insulator fluorine-terminated DLC film, which has high F content on the surface, by the taking of the use of neutral atomic beam as a fluorine source.

The photoluminescence and magnetism of nitrogen-implanted ZnO

Single crystal ZnO was implanted using nitrogen ions with an energy of 60 keV. The microstructure, photoluminescence (PL) and magnetism were studied in detail. Except for nitrogen, no other impurity can be detected by x-ray photoelectron spectra measurements. The room temperature PL of pure ZnO consists of a weak ultraviolet (UV) emission band and a strong green emission band. The PL and electrical conductivity can be suppressed by nitrogen implantation or by annealing in air. However, the two emission bands of pure ZnO can be enhanced intensively by Ar+ etching. The PL is related to the structure defects. Moreover, the intensity of UV luminescence is likely correlated to the electrical conductivity. Ferromagnetism cannot be obtained in the nitrogen-implanted sample from 77 to 300 K. The absence of ferromagnetism in nitrogen-implanted ZnO may be because there is no strong interaction between N 2p and O 2p electrons as nitrogen is a deep acceptor in ZnO.

Study on synthesis and optical properties of Al-doped ZnO hierarchical nanostructures

Highly densified Al-doped ZnO (denoted as Al-ZnO) hierarchical nanostructures were synthesized on transparent quartz substrate by chemical vapor deposition. It is found that the heating temperature plays a key role on controlling the morphologies of the Al-ZnO hierarchical nanostructures through a temperature dependent migration of Al atoms. Such uneven distribution of Al element in the hierarchical nanostructures is clearly evidenced by the x-ray photoelectron spectrum (XPS) measurements. The obtained Al-ZnO hierarchical nanostructures have transmittance of above 60% in the visible region. The photoluminescence (PL) spectra at low-temperature (20 K) were also measured.

MnO x/Ce 0.5+ xZr 0.4− xLa 0.1O 1.95-Al 2O 3 catalysts used for benzene catalytic combustion

Complete oxidation of benzene over supported manganese oxides catalysts was studied. Composite supports Ce 0.5+ x Zr 0.4− x La 0.1O 1.95-Al 2O 3 ( x=0, 0.1, 0.2, 0.3, 0.4), and CeO 2-Al 2O 3 were prepared by co-precipitation method, and manganese oxides (MnO x ) catalysts were prepared by incipient wetness method. Catalytic activity was performed in a conventional fixed bed flow reactor. Among these catalysts, MnO x supported on Ce 0.8Zr 0.1La 0.1O 1.95-Al 2O 3 was found to have the highest catalytic activity for benzene oxidation. The complete conversion temperature of benzene on MnO x /Ce 0.8Zr 0.1La 0.1O 1.95-Al 2O 3 was 328 °C. The catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) specific surface area, X-ray photoelectron spectra (XPS) and H 2-temperature programmed reduction (H 2-TPR). The results of BET and XRD measurements indicated that the addition of ZrO 2 improved the textural properties. XPS measurements showed that MnO x was composed of MnO 2 and Mn 2O 3. The catalysts reported in this work have significant potential in industrial application for their high performance and low cost.

Surface‐initiated nitroxide‐mediated radical polymerization of 4‐vinylpyridine on magnetite nanoparticles

AbstractPoly (4‐vinylpyridine) (P4VP) brushes had been prepared by the surface‐initiated nitroxide‐mediated radical polymerization of 4‐VP on the surface of 3‐methacryloxyproyltrimethoxysilane (3‐MPS)‐modified magnetite nanoparticles with an average diameter of 30 nm. The grafting polymerization was accomplished by nitroxide‐mediated polymerization of 4‐VP, using 4‐hydroxyl‐2,2,6,6‐tetramethyl‐1‐piperidinyl‐oxy (HTEMPO·) free radical as capping agent and benzoyl peroxide (BPO) as initiator. X‐ray photoelectron spectra (XPS) measurement demonstrated that the alkoxysilane initiator layer had formed on the magnetite surface. Gel permeation chromatograph analysis and XPS measurement suggested that the amount of grafted P4VP increases with increasing grafting time. The amount of P4VP grafted on the surface could be determined to be 0.09 chains/nm2 by thermogravimetric analysis. The P4VP‐grafted magnetite particles exhibited the characteristics of multidomain system, distinct from the single domain attributes of the pure magnetite particles. Atomic force‐microscopy analysis revealed the diameter of the grafted P4VP magnetic latex particles is in the range of 120 nm to 150 nm. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Synthesis of Cu-doped WO3 materials with photonic structures for high performance sensors

Cu-doped photonic crystal (PC) WO3 replicas from Morpho butterfly wings have been prepared by using a combined sol–gel templating and calcination method. The exact replications in the Cu-doped PC WO3 replicas at the micro- and nanoscales were confirmed by scanning electronic microscopy (SEM) and transmission electron microscopy (TEM). A combination of X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Raman and X-ray photoelectron spectra (XPS) measurements revealed that copper does not form clusters, but is randomly distributed inside the WO3 matrix lattice. The optical properties of the Cu-doped PC WO3 replica as well as the Morpho butterfly wing template were investigated by using reflectance spectroscopy, and it was found that the reflected light chromaticity of the Cu-doped PC WO3 replica was inherited from the PC Morpho butterfly wings. Cu-doped WO3 replicas without photonic crystal structures (Cu-W replica) were also fabricated in the same way as the Cu-doped PC WO3 replica but using Euploea mulciber butterfly wings as the template. Chemical sensors fabricated from the Cu-doped PC WO3 as well as the non-PC Cu-doped WO3 replicas were tested for a range of gases: (CH3)3N (TMA), NH3, C2H5OH, HCHO, CH3OH, acetone, H2, CO and NO2 and they showed a high selectivity for TMA. The sensitivity of the Cu-doped PC WO3 replica sensors can reach up to 2.0 for a trimethylamine concentration as low as 0.5 ppm at 290 °C. The high sensitivity of the Cu-doped WO3 replica sensors to TMA is attributed to the catalytic effect of Cu on the reaction between the testing gas and the oxide surface. Furthermore, the Cu-doped PC WO3 replica sensor is twice as sensitive as the Cu-doped non-PC WO3 replica to trimethylamine. This may be explained by the photonic crystal structure of the Cu-doped PC WO3.

Contribution ofFe 3dstates to the Fermi level ofCaFe2As2

We present density functional theory (DFT) calculations and soft x-ray spectra (soft x-ray spectroscopy and x-ray photoelectron spectra) measurements of single-crystal ${\text{CaFe}}_{2}{\text{As}}_{2}$. The experimental valence-band spectra are consistent with our DFT calculations. Both theory and experiment show that the $\text{Fe}\text{ }3d$ states dominate the Fermi level and hybridize with $\text{Ca}\text{ }3d$ states. The simple shape of x-ray photoelectron $\text{Fe}\text{ }2p$ core level spectrum (without any satellite structure typical for correlated systems) suggests that the $\text{Fe}\text{ }3d$ electrons are weakly or at most moderately correlated.

Block Copolymer of Polyphosphoester and Poly(l-Lactic Acid) Modified Surface for Enhancing Osteoblast Adhesion, Proliferation, and Function

Surface modification is often needed in tissue engineering to enhance the interaction between cells and synthetic materials and improve the cytocompatibility and cellular functions. In this study, block copolymers of poly(L-lactic acid) and poly(ethyl ethylene phosphate) (PLLA-b-PEEP) were synthesized and used to modify the PLLA surface via a spin-coating process, to understand whether surface modification with polyphosphoester-based polymer will be osteoinductive for potential bone tissue engineering applications. X-ray photoelectron spectra measurements revealed that phosphorus atomic compositions after surface modification increased from 2.09% to 4.39% with increasing PEEP length of PLLA-b-PEEP from 58 to 224 units, which also led to a more hydrophilic surface property compared with unmodified PLLA. The initial osteoblast attachment and proliferation on the modified surfaces were significantly enhanced. Moreover, cellular alkaline phosphatase activity and mineral calcium depositions were also promoted by PEEP modification. The gene expression determined by reverse transcription polymerase chain reaction further revealed that type I collagen and osteocalcin expression were upregulated in osteoblasts cultured on the modified surfaces, indicating that PEEP modification might be potentially osteoinductive and favorable for further application in bone tissue engineering.

Oxygen Plasma Treated Aluminum as a Gate Dielectric for AlGaN/GaN High Electron Mobility Transistors

AlGaN/GaN high electron mobility transistors (HEMTs) grown on 4 in. silicon substrates were demonstrated using different treatments at the Schottky gate terminal, namely (i) a regular Schottky contact made of Pd/Ti/Au (HEMT), (ii) an Al-based metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using 3 nm Al/Pd/Ti/Au, and (iii) a plasma oxidized 3 nm Al/Pd/Ti/Au (plasma treated MOS-HEMT). A high drain current density of 1086 mA/mm and a transconductance of 209 mS/mm were obtained for Al-based MOS-HEMTs. In the process of plasma oxidized Al, the aluminum-based oxide formed was identified as by X-ray photoelectron spectrum measurements. For HEMTs with regular Schottky contact, a gate bias beyond leads to excess gate leakage limiting the gate bias application. However, for the MOS-HEMTs, a gate bias as high as could be applied without any gate leakage. Further, a low two-terminal gate leakage was observed for our MOS-HEMTs. A two-dimensional electron gas channel at an increased depth was observed for the MOS-HEMTs because of an insulating oxide layer at the Schottky contact. The out-diffusion of oxide states at the AlGaN barrier layer into thin Al facilitates the formation of as a gate dielectric for AlGaN/GaN HEMTs.

Is Auger-free luminescence present in CeF 3?

It is well known that Auger-free luminescence (AFL) is observable when the condition E g> E VC is satisfied, where E g is the band-gap energy between the lowest unoccupied band and the highest occupied band and E VC the energy difference between the top of the highest occupied band and the top of the next lower occupied band. From measurements of reflection and X-ray photoelectron spectra, CeF 3 is demonstrated to really satisfy this condition. No evidence for AFL is found, nevertheless. The absence of AFL in CeF 3 is related to a characteristic nature of its highest and next lower occupied bands, which are quite different from those of previously studied AFL-materials.

Reversible Insertion Properties of Zinc Ion into Manganese Dioxide and Its Application for Energy Storage

The reversible intercalation of Zn 2+ ions into manganese dioxide was first reported in an aqueous system and a large capacity (210 mAh g -1 ) was measured. A cycle life test was performed at 1 A g -1 , and after 50 cycles, no capacity fading was found, which indicates the good cycling properties of manganese dioxide toward the insertion of zinc ions. X-ray photoelectron spectrum measurements indicated that Zn 2+ ions in the electrolyte are involved in the charge storage process of manganese dioxide. X-ray diffraction results exhibited the kinetic stability of the host structure in allowing high-capacity, single-phase, and reversible zinc-ion intercalation.

Synthesis of MnV2O6 nanoflakes via simple hydrothermal process

A single phase of monoclinic MnV2O6 nanoflakes was prepared by a hydrothermal process at 180°C for 18 h, using Mn (CH3COO)2·4H2O and NH4VO3 as starting materials and using acetic acid to adjust the pH value of the reaction solution. The as-prepared samples were characterized by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). X-ray photoelectron spectrum (XPS) measurements further confirm the component of MnV2O6. Results indicated that the products consisted of a large quantity of compact accumulated nanoflakes, with average width of 0.85 μm, thickness of 100 nm and lengths up to 1.7 μm.

X-ray photoelectron spectra and the electronic band structure for non-centrosymmetric Bi 2ZnB 2O 7 nonlinear single crystal

We have synthesized and characterized the bismuth borate Bi 2ZnB 2O 7 single crystals. The results of the experimental measurements of the X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) along with an ab initio theoretical study of the electronic band structure, and density of states, are reported. The theoretical calculations are based on crystal structure built from our experimentally determined atomic parameters. The theoretical calculations have been done by using the full potential linearized augmented plane wave (FP-LAPW) method. We applied the Perdew–Burke–Ernzerhof generalized gradient approximation (GGA) and the Engel–Vosko GGA formalism. The observed XPS pattern is in good agreement with the theoretical one, confirming the pure phase of Bi 2ZnB 2O 7. The purity and composition of the as-prepared sample are studied by XPS analysis. XPS measurements show that the bismuth possesses +3 valence state, and Zn and B species exist only in the traditional valence states of Zn 2+ and B 3+. The O 1s spectra are broad and asymmetric and can be deconvoluted into two peaks. The lower and higher binding energy peaks (around 530.1 and 531.5 eV) are assigned to originate from O 1s(1) and O 1s(2) terms, respectively, which are attributed to non-bridging oxygen (B–O − bonds) and bridging oxygen (B–O–B bonds), respectively. Our calculations show that Bi 2ZnB 2O 7 has an indirect energy gap and that Bi–O bonds are of strong covalent character.

Combining oxygen plasma treatment with anchorage of cationized gelatin for enhancing cell affinity of poly(lactide- co-glycolide)

Surface characteristics greatly influence attachment and growth of cells on biomaterials. Although polylactone-type biodegradable polymers have been widely used as scaffold materials for tissue engineering, lack of cell recognition sites, poor hydrophilicity and low surface energy lead to a bad cell affinity of the polymers, which limit the usage of polymers as scaffolds in tissue engineering. In the present study, surface of poly ( l-lactide- co-glycolide) (PLGA) was modified by a method of combining oxygen plasma treatment with anchorage of cationized gelatin. Modification effect of the method was compared with other methods of oxygen plasma treatment, cationized gelatin or gelatin coating and combining oxygen plasma treatment with anchorage of gelatin. The change of surface property was compared by contact angles, surface energy, X-ray photoelectron spectra (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM) measurement. The optimum oxygen pretreatment time determined by surface energy was 10 min when the power was 50 W and the oxygen pressure was 20 Pa. Analysis of the stability of gelatin and cationized gelatin anchored on PLGA by XPS, ATR-FTIR, contact angles and surface energy measurement indicated the cationized gelatin was more stable than gelatin. The result using mouse NIH 3T3 fibroblasts as model cells to evaluate cell affinity in vitro showed the cationized gelatin-anchored PLGA (OCG-PLGA) was more favorable for cell attachment and growth than oxygen plasma treated PLGA (O-PLGA) and gelatin-anchored PLGA (OG-PLGA). Moreover cell affinity of OCG-PLGA could match that of collagen-anchored PLGA (AC-PLGA). So the surface modification method combining oxygen plasma treatment with anchorage of cationized gelatin provides a universally effective way to enhance cell affinity of polylactone-type biodegradable polymers.