X-ray Photoemission Spectroscopy Analysis Research Articles

Lattice and Valence Electronic Structures of Crystalline Octahedral Molybdenum Halide Clusters-Based Compounds, Cs2[Mo6X14] (X = Cl, Br, I), Studied by Density Functional Theory Calculations.

The electronic and crystal structures of Cs2[Mo6X14] (X = Cl, Br, I) cluster-based compounds were investigated by density functional theory (DFT) simulations and experimental methods such as powder X-ray diffraction, ultraviolet-visible spectroscopy, and X-ray photoemission spectroscopy (XPS). The experimentally determined lattice parameters were in good agreement with theoretically optimized ones, indicating the usefulness of DFT calculations for the structural investigation of these clusters. The calculated band gaps of these compounds reproduced those experimentally determined by UV-vis reflectance within an error of a few tenths of an eV. Core-level XPS and effective charge analyses indicated bonding states of the halogens changed according to their sites. The XPS valence spectra were fairly well reproduced by simulations based on the projected electron density of states weighted with cross sections of Al Kα, suggesting that DFT calculations can predict the electronic properties of metal-cluster-based crystals with good accuracy.

Enhancement of the crystallinity of barium titanate by using a uniform barium-carbonate surface coating

In this work, we modified the surfaces of BaTiO3 particles by using barium acetate and ammonium bicarbonate, and we studied the characteristics and sintering behaviors of the coated BaTiO3 particles. Transmission electron microscopy showed that the resultant coating layer was smooth and uniform without agglomerates. X-ray photoemission spectroscopy analysis also revealed that the surface coating layer was composed of BaCO3. After calcination at 950 °C for 5 hours, the c/a ratio of the coated particles was found to have increased without size growth while the uncoated particles showed size growth. We finally found that the BaCO3 layer acted as a barrier to inhibit particle growth during calcination.

(Invited) Structural Evolution of Hafnium Methacrylate Nanoclusters Following Electron-Beam Irradiation from in Situ ir Spectroscopy

High absorption metal and main group oxide nanoclusters have recently become the subject of intense investigation due to their potential as alternatives to conventional organic chemically amplified photoresists for negative tone patterning in the extreme ultraviolet (EUV) range. It is believed that the low energy secondary electrons generated from photoionization of the nanoclusters are responsible for the chemistry that occurs following irradiation. Despite their potential, little is known about many aspects of their function as resist materials; in particular, the role of high absorption elements in the absorption/photoionization process, the role of electrons of different energies, the formation of radicals and chemically reactive species and the overall structural changes that occur at each stage of processing. Thus, the precise atomic mechanism underlying solubility switching upon irradiation remains unknown. We have investigated one such class of materials: nanoclusters based on a hafnium oxide core decorated with methacrylic acid ligands (HfMAA) , using a combination of in situ infrared (IR) spectroscopy and x-ray photoemission spectroscopy (XPS). Thin films (10-30 nm) of the HfMAA nanoclusters deposited onto SiO2 from solution are characterized by XPS and IR spectroscopy in conjunction with density functional calculations. The mechanisms of solubility switching following EUV exposure are investigated using irradiation with low energy electrons to emulate the photoexcited carriers generated in the EUV absorption process. Using in situ IR spectroscopy, we are able to monitor the structural evolution of the nanoclusters at each stage of processing, beginning from the initial deposition to post application bake (PAB), electron irradiation, post exposure bake (PEB) and development. Monochromatic electron beams with energies ranging from 5 eV up to the typical EUV wavelength of 92 eV enable a correlation between the role of secondary electron energy with chemistry and functional character. In conjunction with XPS analysis, these measurements detail the structural evolution of the films under typical processing conditions, providing insight into the solubility switching mechanism of this emerging class of inorganic photoresists.

Influence of oxygen-plasma treatment on AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors with HfO2 by atomic layer deposition: leakage current and density of states reduction

The electrical properties of AlGaN/GaN MOSHFETs with HfO2 prepared by atomic layer deposition with and w/o oxygen-plasma treatment (further referred to as PHf-MOS and Hf-MOS) were investigated. The sub-threshold slope of the MOSHFETs (350 and 150 mV dec−1 for Hf-MOS and PHf-MOS, respectively) were lower than that for HFET (450 mV dec−1), which also correspond with lower leakage current of the MOSHFETs (∼10−8 A mm−1 at −9 V for PHf-MOS). In addition, the density of the interface states at the oxide/GaN-cap layer near the conduction band edge and mid-gap (∼5 × 1012 and 2 × 1011 cm−2 eV−1, respectively) after PHf-MOS was lower than that for Hf-MOS (∼3 × 1013 and 2 × 1012 cm−2 eV−1, respectively). From the x-ray photoemission spectroscopy analysis we observed a shift in the Auger Ga LMM peaks (0.6 eV) and an increase of the intensity area of the Ga–O bond in the Ga2p3 spectrum after the oxygen-plasma treatment, mainly because the GaN-cap layer was oxidized and Ga2O3 was formed.

Synthesis and characterization of Cu2FeSnS4 thin films prepared by electrochemical deposition

Quaternary compound Cu2FeSnS4 (CFTS) thin films, a potential absorber layer candidate in thin film solar cells, were successfully synthesized for the first time by electrochemical deposition method with a post-sulfurization treatment at 500°C and 550°C. The samples were analyzed by X-ray diffraction (XRD), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible-near-infrared spectrophotometer (UV–vis-NIR spectrophotometer). XRD data and Raman spectra revealed that the CFTS thin films possess a stannite structure and the crystallinity of the samples was improved with the increasing sulfurization temperature. X-ray photoemission spectroscopy analysis of the four constituent elements indicated Cu(I), Fe(II), Sn(IV) and sulfide ions. The direct band gap values of samples with post-sulfurization treatment at 500°C and 550°C were evaluated to be 1.35eV and 1.40eV by UV–vis-NIR absorption spectra respectively, which show that CFTS is promising for photovoltaic applications.

Mechanism and Thermochemistry of Coal Char Oxidation and Desorption of Surface Oxides

The present study investigates the coal char combustion by a combination of thermochemical and X-ray photoemission spectroscopy (XPS) analyses. Thermoanalytical methods (differential thermogravimetry, differential scanning calorimetry, and temperature-programmed desorption) are used to identify the key reactive steps that occur upon oxidation and heating of coal char (chemisorption, structural rearrangement and switchover of surface oxides, and desorption) and their energetics. XPS is used to reveal the chemical nature of the surface oxides that populate the char surface and to monitor their evolution throughout thermochemical processing. XPS spectra show the presence on the carbon surface of three main components. It is shown that the most abundant oxygen functionality in the raw char is epoxy. It decreases with preoxidation at 300 °C and even more at 500 °C, where carboxyl and ether oxygen functionalities prevail. The rearrangement of epoxy during preoxidation goes together with activation of the more s...

Multiple Roles of Hydrogen Treatments in Amorphous In–Ga–Zn–O Films

The roles of hydrogen introduced by post-deposition hydrogen treatments were investigated for amorphous In–Ga–Zn–O (a-IGZO) films using room-temperature hydrogen plasma (H-plasma) and high-temperature H2 annealing. It was found that these treatments cause different effects as confirmed by hard X-ray photoemission spectroscopy and difference spectrum analyses. The H-plasma treatment increased both the near-valence band maximum (near-VBM) states (observed just above VBM) and the –OH bonds (confirmed by O 1s core spectrum) if a-IGZO films were deposited under an optimum condition, leading to the conclusion that the room-temperature H treatment incorporates H to a-IGZO films as –OH bonds, and the increase in the relatively shallow near-VBM states (peaked at ∼1.0 eV, extended to ∼2.4 eV from VBM) is ascribed to the generated –OH bonds. On the other hand, high-temperature H2 annealing did not increase the O 1s –OH signal, and its difference spectrum showed a different peak centered at ∼0.7 eV. This difference spectrum is similar to that of H-less a-IGZO films deposited without O2 supply by ultra-high vacuum sputtering and assigned to oxygen deficiency. These results will contribute to control the operation characteristics and the instability issues of a-IGZO TFTs. Further, the deconvoluted difference spectra will be the standard fingerprints of these defects in a-IGZO.

Elucidating the Surface Reactions of an Amorphous Si Thin Film as a Model Electrode for Li-Ion Batteries.

We investigated during the first lithiation/delithiation process the electrochemical reaction mechanisms at the surface of 30 nm n-doped amorphous silicon (a-Si) thin film used as a negative model electrode for Li-ion batteries. Usage of thin film allowed us to accurately discern the different reaction mechanisms occurring at the surface by avoiding interference from carbon and binder components. The potential dependency of the evolution of the solid electrolyte interphase (SEI) and the reactions on the a-Si and on the copper current collector were elucidated by coupling galvanostatic cycling with postmortem X-ray photoemission spectroscopy and scanning electron microscopy analyses. Our approach revealed the clear reversibility of lithiation/delithiation in the a-Si and native SiO2 layers; such a reaction for SiO2 has not been previously detected and was considered to be an irreversible process. Quantitative and qualitative analyses of the potential-dependent surface evolution revealed the decomposition products of both the salt (LiPF6) and solvent (dimethyl carbonate/ethylene carbonate), giving insight into the complex SEI formation mechanism on the a-Si film but also underlining the strong influence of "inert" materials such as the role of the current collector in the irreversible charge loss. A model mechanism describing the evolutionary complexity of the a-Si surface during the first galvanostatic cycle is proposed and discussed.

A study on the synthesis and magnetic properties of the cerium ferrite ceramic

This work is a short report on the synthesis of CeFeO3 ceramic nanopowder from a mixture of CeO2 and Fe2O3 powders via a high energy ball milling process and subsequent heat treatment. Investigation of the magnetic, photocatalytic and absorption properties of CeFeO3 and its potential for colossal dielectric constant (CDC) are the main objectives of the present study. The characterization tools were X-ray diffraction (XRD), transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM), thermogravimetry (TG), differential thermal analysis (DTA), X-ray photoemission spectroscopy (XPS), ultraviolet–visible spectroscopy (UV–vis) and Image-J software. According to the obtained results, CeFeO3 nanopowder can be raised as a visible light-driven photocatalyst, a semiconductor material with a narrow bandgap and a weak ferromagnetic material. For the first time the CDC behavior of this ceramic was also assessed by XPS analysis which was indicative of a good colossal dielectric constant. The results were also confirmed by the measured dielectric properties.

In-vacuum thermolysis of ethane 1,2-diamineborane for the synthesis of ternary borocarbonitrides

High-temperature (1000 °C) thermolytic decomposition of ethane 1,2-diamineborane (BH3NH2CH2CH2NH2BH3) deposited onto a Cu foil has been performed in an ultra-high-vacuum environment. A combined thermolytic, structural (x-ray diffraction), microscopic (scanning electron microscopy) and spectroscopic (Raman, x-ray photoemission spectroscopy) analysis, has identified a ternary borocarbonitride (BCN) compound as a result of the process. The obtained BCN compound is nanocrystalline, surrounded by crystallites of ammonium hydroxide borate hydrate. The ternary compound presents a 0.2:0.6:0.2 B:C:N composition in the bulk and 0.11:0.76:0.13 stoichiometry at the very surface, richer in C–C networks with respect to the bulk. Furthermore, the resulting BCN compound does not show oxidation at the surface due to the in-vacuum thermolysis of the single precursor.

Structure of Pr Oxide Films on Si Deposited by Reactive Sputtering

Down scaling of metal-oxide-semiconductor (MOS) devices has led to the drastic increase in leakage current through the gate oxides. This problem has forced us to replace the SiO2 gate dielectric by that with higher dielectric constant (high-k) 1,2). In the device application, the interface with Si plays a key role and in most cases is the dominant factor in determining the overall electrical properties1). For most actively investigated high-k materials typified by Hf oxide, however, the SiO2interfacial layer can be unavoidably formed due to the interface reaction, leading to the increase of the EOT. Praseodymium oxide forms an interfacial silicate layer which has a higher dielectric constant than that of SiO2 3,4). In this work, we will report the structure of Pr oxide films deposited by the sputtering method as well as their chemical states of the elements composing the film based on the analyses by cross-sectional transmission electron microscope (XTEM), X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS). After organic removal cleaning, p-type Si (100) substrates were dipped in the diluted HF solution (4 %) for 2 min to remove the native oxide and leave the Si surface hydrogen-terminated. Praseodymium oxide thin films were deposited by reactive RF magnetron sputtering at room temperature in an ambient of Ar and O2 with the O2 flow rate fraction of 10 % at 1.5 Pa with the RF-power of 50 W using the 2” Pr metal target. The Si substrate was set at the off-centered position with respect to the sputtering cathode to avoid re-sputtering by the O- ions from the target surface5). Deposited film thickness evaluated by XTEM was typically 35 nm. Deposited films were post-annealed in an ambient of nitrogen (N2) for 30 minutes at temperatures of 300, 500 and 800 °C. In the XRD patterns obtained with the fixed grazing incident angle of 2 °, the dominant diffraction line of cubic PrO2 was observed in the course of the annealing up to 500 °C. After annealing at 800 °C, rearrangement of the crystalline structure occurred; the new diffraction line corresponding to hexagonal Pr2O3appeared. In fact, the phase transition was observed from cubic to hexagonal structure. In the XPS spectra observed at the interface between Pr oxides and Si substrates, the peak position of Pr3d5/2 consistently shifted to lower binding energies from 934.4 to 933 eV with increasing annealing temperature up to 800 °C. The Si2p spectrum was observed at lower binding energies than 103.9 eV corresponding to the SiO2. The O1s spectrum was found to be composed by two components at 530.3 eV of Pr2O3 and 531.7 eV of the Pr silicate6). The Pr silicate spectrum faintly observed in the as-deposited film became dominant with increasing annealing temperature. The XPS results revealed that the formation of the Pr silicate progressed as increasing annealing temperature. The XTEM image of deposited films revealed that the SiO2 layer was formed at the interface between the as-deposited film and the Si substrate, although the interfacial SiO2 layer was not detected in the in-depth profile by XPS analysis. The reason for this is probably the surface roughing during in-depth profiling by Ar sputter etching. After annealing at 800 °C, the film structure was completely changed from those after lower temperature annealing; the interfacial SiO2 layer was lost, and the Pr oxide film had three-layered structure composed by the amorphous silicate layer, the Pr2O3layer having poly-crystal islands located with equal spacing and the continuous columnar crystalline layer from the interface to the surface. References 1) G. D. Wilk, R. M. Wallace, J. M. Anthony, J. Appl. Phys. 89 5243 (2001). 2) A. I. Kingon, J. P. Maria, S. K. Streiffer, Nature (Lond.) 406 1032 (2000). 3) H. J. Osten, J. P. Liu, P. Gaworzewski, E. Bugiel, P. Zaumseil, Tech. Dig. Int. Electron Devices Meet. IEEE, Piscataway, NJ, 2000, p. 653. 4) A. Sakai, S. Sakashita, M. Sakashita, Y. Yasuda, S. Zaima, S. Miyazaki, Appl. Phys. Lett. 85 5322 (2004). 5) D. J. Kester, R. Messier, J. Vac. Sci. Technol. A 4, 496 (1986) 6) A. Fissel, J. Dabrowski, H. J. Osten, J. Appl. Phys. 91 8986 (2002).

Magnesium Insertion into the Chevrel Phase Mo6S8: XPS Analysis

Since the earlier works in 2000 by Aurbach et al 1, magnesium-ion batteries emerged as an alternative to lithium-ion batteries thanks to many advantages: magnesium is the 5th most abundant metal in the earth crust, its divalent character and its ionic radius similar to lithium ionic radius gives it a volumetric capacity higher than lithium (3833 Ah/L and 2046 Ah/L respectively). Eventually the absence of dendritic growth on metallic magnesium is a plus in term of security. Several cathode materials were proposed for Mg-ions battery, nevertheless the reference positive electrode material in Mg-Ion technology remained the Chevrel Phase with the formula Mo6S8. The Chevrel phase, synthesized by R. Chevrel et al 2 in 1974, was described as an octahedral cluster of molybdenum located in a cube of sulfur that forms a Mo6S8 pattern. Structural analysis3 (X-Ray Diffraction) showed the existence of 12 insertions sites localized inside a cube of sulfur surrounded by Mo6S8clusters as illustrated in Fig. 1. The electrochemistry highlighted 2 types of insertion sites able to host Mg2+at different potentials. Being considered as the reference cathode material for Mg-ion systems, it has been extensively studied, especially on the structural and electrochemical point of view. However, the precise red-ox processes taking place during Mg insertion-deinsertion remain unclear. In this study X-ray Photoemission Spectroscopy (XPS) has been used to get a direct observation of the redox mecanism during charge/discharge of the material. We performed ex-situ XPS core peak analyses on Mo6S8electrodes at different states of charge to probe the molybdenum and sulfur oxydation state and the environment (polarized or metallic) of inserted magnesium ions. These results were discussed based on a step-by-step XRD and XPS study before and after cycling, and correlated with the electrochemical performance of Chevrel phase. Fig 2 illustrates Mo 3d and Mg 2p orbitals in Mg1.72Mo6S8. In one side we can see the evolution of molybdenum oxidation states during discharge and on the other side the two environments of inserted magnesium is underlined. References : (1) D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich & E. Levi, Nature vol 407 (2000) 724 (2) R. Chevrel et al, Mat. Res. BuLl. Vol. 9, pp. 1487-1498, 1974M. D. Levi, E. Lancry, H. Gizbar, Z. Lu, E. (3) R. Chevrel, M. Sergent Superconductivity in Ternary Compounds I Volume 32 of the series Topics in Current Physics pp 25-86 Figure 1

Modulation of interfacial and electrical properties of ALD-derived HfAlO/Al2O3/Si gate stack by annealing temperature

In current work, effects of rapid thermal annealing on the interface chemical bonding states, band alignment, and electrical properties of atomic-layer-deposition-derived HfAlO/Al2O3 gate stack on Si substrates have been studied by X-ray photoemission spectroscopy (XPS), UV–Vis transmission spectroscopy, and electrical measurements. XPS analyses have shown that HfAlO alloy and mixed silicate (Hf-Al-O-Si) increase after post-deposition annealing process. By means of UV–Vis transmission spectroscopy measurements, reduction in band gap for 400oC-annealed sample has been observed. Accordingly, reduction in the valence band offset and increase in the conduction band offset have been detected for HfAlO/Al2O3/Si gate stack annealed at 400 °C. Various current conduction mechanisms, such as Poole-Frenkel emission, Fowler-Nordheim (FN) tunneling, and space-charge-limited (SCL) conduction, have been analyzed. Detailed electrical measurements reveal that current conduct mechanisms is SCL conduction at lower field region and FN tunneling and SCL conduction are dominant conduction mechanism at higher field region.

Structural and electronic properties of thermally evaporated V2O5 epitaxial thin films

This study investigated the physicochemical properties of a V2O5 thin film deposited on c-plane sapphire through thermal evaporation at a relatively high pressure. Using atomic force microscopy (AFM), X-ray diffraction (XRD) and a suite of X-ray spectroscopic techniques, it was shown that a high quality epitaxial V2O5 thin film was achieved. AFM step height analysis demonstrated that the film thickness was ~50nm with a surface roughness of 1.5Å, as determined by root mean square roughness measurements. XRD analysis verified that the film was highly crystalline with a (0001) orientation on the substrate. Vanadium was predominantly in the 5+ oxidation state, with contributions from V4+ states at the surface, shown by X-ray photoemission spectroscopy analysis X-ray absorption spectroscopy further confirmed the predominant presence of V5+ in an octahedral crystal field. The existence with bulk V4+ states was shown through V L-edge X-ray emission spectroscopy which demonstrated the presence of d-d crystal field transitions in an otherwise d0 transition metal oxide. The data suggests that by increasing the partial pressure of oxygen in the vacuum chamber during growth, thermal evaporation can be used as a cheap and efficient way of growing stoichiometric V2O5 thin films.

Synthesis of MnS microfibers for high performance flexible supercapacitors

Cubic MnS thin films are prepared at 358K bath temperature using chemical bath deposition (CBD) method. MnS phase of manganese sulfide is identified with X-ray diffraction (XRD) and X-ray photoemission spectroscopy analyses. Interconnected porous microfibers like surface texture of MnS thin film is evaluated through field-emission scanning electron microscopy (FE-SEM). Specific surface area of 120.42m2g−1 is measured with Brunauer-Emmett-Teller (BET) technique. The highest specific capacitance (Cs) of 747Fg−1 is obtained using galvanostatic charge discharge (GCD) technique at 1mAcm−2 current rate. Excellent 85% capacity retention is obtained after 2 000CV cycling at 100mVs−1 scan rate. All solid state flexible (ASSF) symmetric supercapacitor devices based on microfiber-MnS thin films are prepared using cost effective stainless steel substrate and PVA-KOH gel electrolyte and practical application is demonstrated by illumination of red LED.

Carbon dioxide capture using a superhydrophobic ceramic hollow fibre membrane for gas-liquid contacting process

This work initiates the development of clean technology in carbon dioxide (CO2) capture using ceramic membrane inspired by gas–liquid contacting system. A low cost, high performance superhydrophobic kaolin-alumina hollow fibre membrane was prepared via phase inversion-based extrusion and sintering techniques, followed by a grafting with fluoroalkylsilane (FAS). The membrane was characterized by scanning electron microscopy (SEM), gas permeation test, contact angle, wetting resistance, X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). The fabricated membrane was highly porous, thus increasing the gas permeation rate. By surface modification, the membrane contact angle was increased from 0° to 142°. In fact, wettability resistance of the membrane was also improved. The membrane was subsequently applied in membrane contactor for carbon dioxide (CO2) absorption. The CO2 absorption flux as high as 0.18 mol m−2 s−1 was achieved at the liquid flow rate of 100 mL min−1 which was far above the fluxes of some commercial and in-house made polymeric and ceramic membranes. In conclusion, the modified kaolin-alumina hollow fibre membrane with the superhydrophobic surface, high permeance, and absorption flux is suitable for CO2 post-combustion capture, due to its outstanding chemical and thermal stabilities.

Utilizing intermixing of conjugated polymer and fullerene from sequential solution processing for efficient polymer solar cells

Efficient polymer solar cells based on poly[2, 6-(4, 4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-fluorobenzothiadiazole)] (PCPDTFBT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are successfully fabricated by a sequential processing (SqP). With appropriate orthogonal solvent and thermal treatment, the SqP film can form an inter-diffused layer, and the SqP devices show efficient photovoltaic performance in both conventional and inverted layouts. The SqP inverted device was firstly demonstrated and the highest power conversion efficiency (PCE) of 5.84% with the enhanced Jsc of 16.4 mA cm−2 was able to be achieved with the high internal quantum efficiency (IQE). Photoluminescence quenching shows the SqP films can provide efficient exciton quenching. X-ray photoemission spectroscopy (XPS) and ellipsometry analysis shows a polymer-rich surface in SqP films after thermal annealing. The charge mobilities in the SqP films were significantly enhanced as measured by space-charge-limited-current (SCLC) method. All these contribute to the improved photovoltaic performance in the inverted SqP device. We believe that these results inspire a new way of forming the active layer with controllable morphology, efficient charge separation and collection in polymer solar cells.

Nonlinear thickness and oxidation-dependent transparency and conductance of sputtered titanium suboxide nanofilms

Optically transparent and electrically conductive semiconducting titanium suboxide nanometer thick films, which are technologically important in a wide variety of applications, show a nonlinear dependency of optical and electrical properties on film thickness and oxidation time. The optical, electrical, chemical, and structural properties of the sputter-deposited titanium suboxide nanofilms on fused quartz glass at room temperature are investigated by varying the film thickness, and the additional oxidation is controlled by the duration of air exposure. The optical properties of the nanofilms are simulated by considering them as both a homogeneous film as well as an inhomogeneous film with the combination of the Lorentz Drude model and the Maxwell Garnett effective medium theory (MG-EMT). Their electrical properties are simulated with the MG-EMT. The optical transmittance, electrical conductivity, secondary ion mass spectroscopy, x-ray photoemission spectroscopy analysis, and simulation of titanium suboxide nanofilms indicate that inhomogeneous film growth and oxidation are responsible for the nonlinear dependency. The oxygen atomic ratios to titanium for the as-deposited films depend on the deposition time and vary in 1.60–1.73, while those exposed to air for seven days increase to 1.79–1.99.

A Simple Method for the Fabrication of Metallic Copper Nanospheres-Decorated Cellulose Nanofiber Composite

Herein, we report a new and simple method for the preparation of metallic copper nanospheres-decorated cellulose nanofiber composite (CuNSs/CNFs). Initially, the cellulose acetate nanofibers (CANFs) were electrospun followed by deacetylation and anionization to produce functional anionic cellulose nanofibers (f-CNFs). The CuCl2 precursor was deposited on the f-CNFs (CuCl2/CNFs) by a simple dipping method. Then the CuCl2/CNFs were reduced under vacuum by using aluminum foil to produce the CuNSs/CNFs. The resultant CuNSs/CNFs composite was characterized by various microscopic and spectroscopic methods. Fourier transform infrared spectroscopy (FT-IR) confirmed the successful functionalization of anionic groups with the CNFs. The field emission scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM) results confirmed the formation of CuNSs on the surface of CNFs. From the scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analysis, the weight percentage of Cu was found to be 23.5 wt%. The successful reduction of CuO to metallic Cu was confirmed by X-ray photoemission spectroscopy (XPS) and X-ray diffraction (XRD) analyses. Mechanism has been proposed for the formation of metallic Cu sphere on CNFs.

Synthesis and Electrochemical Performance of Nano-sized Li4Ti5O12 Coated with Boron-Doped Carbon

A facile method was developed to synthesize B-doped carbon coated nano-sized Li4Ti5O12 by using glucose and boric acid mixture as the precursor of coating layer, and the effect of B-dopant amounts on electrochemical performance was investigated in detail. It is demonstrated that B-dopant can efficiently improve the electronic conductivity of carbon-coating layer. According to X-ray photoemission spectroscopy analysis and electrochemical investigation, it is also found that, BC3 dopant species are important for improving electronic conductivity and electrochemical performance, whereas the B-O dopant species, which increases with the enhancement of B-dopant amount, might hamper the charge transfer on Li+-insertion process. Therefore, the carbon coated nano-sized Li4Ti5O12 with a moderate B-dopant amount exhibits much higher electrochemical performance. For example, with a low carbon content of ∼3wt. %, the optimized B-doped carbon coated Li4Ti5O12 can deliver a capacity of around 90mAhg−1 at a high rate of 20C, which is much higher than that of carbon-coated Li4Ti5O12. The achieved result indicates that approach of B-doped carbon coating is an effective method for improving the performance of Li4Ti5O12.