Effect of TaNx on electrical and optical properties of annealed TaNx/Ag/TaNx films

As‐deposited Ag(10 nm)/glass films exhibited agglomerated nanocrystals with seemingly thick boundaries. Introduction of a TaN_x layer below the Ag films resulted in dense and smooth structures, with a resistance at least three times lower than that of Ag/glass. For TaN_x(10 nm)/Ag(10 nm)/TaN_x(10 nm)/glass multilayer films, Auger electron spectroscopy results indicate that TaN_x acts as an effective barrier restraining the diffusion of Ag. After annealing (up to 573 K), no outward diffusion of Ag through either TaN_x layer was seen. However, partial oxidation of the outermost TaN_x layer to form Ta₂O₅ was observed. The films showed promising optical properties with 73% transmittance in the visible region and ~15% average transmittance in the near‐infrared region. The optical data obtained here was in good agreement with simulated predictions. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of substrate temperature and N2/Ar flow ratio on the stoichiometry,structure and hardness of TaNx coatings deposited by DC reactive sputtering

The effect of substrate temperature and N2/Ar flow ratio on the stoichiometry, structure and hardness of TaN_x coatings prepared on (111) Si substrates by DC reactive sputtering was investigated. For the structural, chemical and morphological analysis, X‐ray diffraction (XRD), Auger electron scanning and atomic force microscopy were respectively used. Hardness values of thin films were determined using the work of indentation model from nanoindentation measurements. TaN stoichiometric coatings were obtained for samples deposited at room temperature. The stoichiometric TaN phase was not obtained by increasing the temperature up to 773 K, even when increasing the N₂/Ar flow ratio. Even when a saturation in nitrogen content was achieved, nitrogen vacancies are still present in those samples. For coatings prepared at 773 K and low N₂/Ar flow ratio, a phase mixture between TaN_x and cubic α‐Ta was observed, while a cubic structure δ‐TaN was formed by increasing the N₂/Ar flow ratio. A maximum in hardness and (38 GPa) was obtained for the sample deposited at 773 K and a N₂/Ar flow ratio of 0.2, which presented a δ‐TaN cubic crystalline structure and a roughness value of 1.6 nm. Copyright © 2015 John Wiley & Sons, Ltd.     

Oxidation of Reduced Ceria by Incorporation of Hydrogen

The interaction of hydrogen with reduced ceria (CeO_2?x) powders and CeO_2?x(111) thin films was studied using several characterization techniques including TEM, XRD, LEED, XPS, RPES, EELS, ESR, and TDS. The results clearly indicate that both in reduced ceria powders as well as in reduced single crystal ceria films hydrogen may form hydroxyls at the surface and hydride species below the surface. The formation of hydrides is clearly linked to the presence of oxygen vacancies and is accompanied by the transfer of an electron from a Ce³⁺ species to hydrogen, which results in the formation of Ce⁴⁺, and thus in oxidation of ceria.     

XANES and XPS characterization of hard amorphous CSixNy thin films grown by RF nitrogen plasma assisted pulsed laser deposition

Amorphous carbon silicon nitride thin films were grown on (100) oriented silicon substrates by pulsed laser deposition (PLD) assisted by an RF nitrogen plasma source. Up to about 30 at. % nitrogen and up to 20 at. % silicon were found in the hard amorphous thin films by XPS in dependence on the composition of the mixed graphite / Si₃N₄ PLD target. The universal nanohardness was measured to be at maximum load force of 0.1 mN up to 23 GPa for thin CSi_xN_y films with reference value of 14 GPa for single crystalline silicon. X-ray photoelectron spectroscopy (XPS) of CSi_xN_y film surfaces showed a clear correlation of binding energy and intensity of fitted features of N 1s, C 1s, and Si 2p peaks to the composition of the graphite / Si₃N₄ target and to nitrogen flow through the plasma source, indicating soft changes of binding structure of the thin films due to variation of PLD parameters. Auger electron spectroscopy (AES) of Si KL₂₃L₂₃;¹D Auger transition gave a detailed view of bonding structure of Si in the CSi_xN_y films. The intensity of π* and σ* resonances at the carbon K-edge X-ray absorption near-edge structure (XANES) of the CSi_xN_y films measured at BESSY I corresponded to the nanohardness of the CSi_xN_y films, thus giving insight into chemical binding structure of superhard amorphous materials.     

XPS calibration study of thin‐film nickel silicides

This paper presents a systematic X‐ray photoelectron spectroscopy (XPS)study of the Ni silicides Ni₃Si, Ni₃₁Si₁₂, Ni₂Si, NiSi and NiSi₂ produced by annealing of sputtered thin films. The in situ XPS study focuses on both the core level peaks and Auger peaks. The peak positions, shapes, satellites as well as Auger parameters are compared for different silicides. The factors that influence the Ni core level peak shifts are discussed. The Ni 2p_3/2 peak shape and satellites are correlated with the valence band structure. The effect of argon ion etching on surface composition and chemical states is also investigated. Copyright © 2009 John Wiley & Sons, Ltd.     

Ultrahigh‐Content Nitrogen‐doped Carbon Encapsulating Cobalt NPs as Catalyst for Oxidative Esterification of Furfural

It is an attractive and challenging topic to endow non‐noble metal catalysts with high efficiency via a nitrogen‐doping approach. In this study, a nitrogen‐doped carbon catalyst with high nitrogen content encapsulating cobalt NPs (CoO_x@N‐C(g)) was synthesized, and characterized in detail by XRD, HRTEM, N₂‐physisorption, ICP, CO₂‐TPD, and XPS techniques. g‐C₃N₄ nanosheets act as nitrogen source and self‐sacrificing templates, giving rise to an ultrahigh nitrogen content of 14.0 %, much higher than those using bulk g‐C₃N₄ (4.4 %) via the same synthesis procedures. As a result, CoO_x@N‐C(g) exhibited the highest performance in the oxidative esterification of biomass‐derived platform furfural to methylfuroate under base‐free conditions, achieving 95.0 % conversion and 97.1 % selectivity toward methylfuroate under 0.5 MPa O₂ at 100 °C for 6 h, far exceeding those of other cobalt‐based catalysts. The high efficiency of CoO_x@N‐C(g) was closely related to its high ratio of pyridinic nitrogen species that may act as Lewis basic sites as well as its capacity for the activation of dioxygen to superoxide radical O₂^.?.     

Deposition of polysiloxane‐like nanofilms onto an aluminium alloy by plasma polymerized hexamethyldisiloxane: characterization by XPS and contact angle measurements

In this work, aluminium (Alclad 2024‐T3) substrates were cleaned by an r.f. (13.56 MHz) plasma, using argon (Ar), oxygen (O₂) and a mixture of O₂/Ar (50:50) gases. The effectiveness of plasma cleaning was checked in situ using X‐ray photoelectron spectroscopy (XPS) and ex situ using water contact angle measurements. XPS O/Al surface atomic ratios are in excellent agreement with those of the crystalline boehmite and the pseudoboehmite. Oxygen O 1s peak‐fitting was used to quantify the proportion of hydroxyl ions and the functional composition on the aluminium surface: the surface cleaned with O₂ plasma contains 50% of aluminium hydroxides, the ones cleaned with Ar plasma and with Ar/O₂ plasma contain, respectively, 25 and 37% hydroxyl ions. The binding energy separation between Al 2p and O 1s is characteristic of AlO(OH). Thin SiO_x films were subsequently deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen. In the absence of oxygen, a hydrophobic (Θ≥ 100° ) film characteristic of polydimethylsiloxane (PDMS) is formed: polysiloxane‐like thinner films (SiO_x) are obtained with the introduction of oxygen. XPS and contact angle measurements confirmed both the composition and the structure of these films. More importantly, contact angle measurements using different liquids and interpreted with the van Oss‐Good‐Chaudhury theory allowed determination of the surface free energy of the deposited films: the calculated values of surface tension of the film formed from HMDSO/O₂: (50/50) are in excellent agreement with those of reference silica‐based materials such as a silicon wafer and cleaned glass. Copyright © 2007 John Wiley & Sons, Ltd.     

XPS Analysis of Lead Zirconate Titanate Thin Films Prepared Via a Sol-Gel Process

The crystalline phase and composition of sol-gel-derived lead zirconate titanate (PbZr _x Ti_{1 – x} O₃, PZT) thin films were determined by an X-ray photoelectron spectroscopic (XPS) data processing technique. As a result, it was proved that existence of the surface layer with several tens nm in thickness, of which the crystalline phase and composition were different from those of the inside of the thin films, was found. The newly developed XPS analytical technique is much applicable for the characterization of PZT thin film surface.     

Electrochemistry of Nitrogen‐Doped Carbon Nanotubes (CNx) with Different Nitrogen Content and Its Application in Simultaneous Determination of Dihydroxybenzene Isomers

The bamboo‐shaped nitrogen‐doped carbon nanotubes (CN_x) with different nitrogen content were synthesized using Fe‐containing SBA‐15 molecular sieve as catalyst with thermal decomposition. The CN_x nanotubes prepared were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (XRD) and Raman spectroscopy. The results suggest that there are a larger amount of defective sites on CN_x nanotubes surfaces due to the nitrogen doping and CN_x nanotube with higher nitrogen content possesses lower graphitic ordering in the framework. Furthermore the effects of nitrogen content on the electrochemistry of CN_x modified electrodes were investigated by cyclic voltammetry (CV). CN_x modified electrodes exhibit better electrocatalytic activities to the oxidation of hydroquinone. Moreover CN_x with lower nitrogen content is in favor of the electron transfer between dihydroxybenzene and electrode surface, while CN_x with higher nitrogen content possesses high surface adsorptive ability. CN_x modified electrodes can be applied to determine dihydroxybenzene isomers directly and simultaneously by linear sweep voltammetry technique without previous separation.     

Photocatalytic Activity and Characterization of the Sol-Gel Derived Pb-Doped TiO2 Thin Films

Photocatalytically active Pb-doped TiO₂ thin films were prepared on a soda-lime glass substrate by sol-gel dip-coating technique using TiO₂ sols containing lead(II) nitrate. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-VIS spectroscopy and X-ray diffraction (XRD). A shift of the UV-VIS absorption towards longer wavelengths was observed, which indicated a decrease in the band-gap of TiO₂ upon Pb doping. XRD results showed both pure and Pb-doped TiO₂ thin films were polycrystalline, anatase type, and oriented predominantly to the (101) plane. A slight shift in the d-spacing for the Pb-doped film indicated the incorporation of Pb into the TiO₂ lattice to form Pb _x Ti_1–x O₂ solid solution. AFM results showed Pb-doped TiO₂ thin films were composed of larger TiO₂ particles and had rougher surface, compared with un-doped TiO₂ thin films. XPS results showed that except for the enrichment of Pb near the surface, Pb exists in the forms of Pb _x Ti_1–x O₂ and PbO. Dimethyl-2,2-dichlorovinyl phosphate (DDVP) was efficiently degraded in the presence of the Pb-doped TiO₂ thin films by exposing the insecticide solution to sunlight. The mechanism of photocatalytic activity enhancement of the Pb-doped TiO₂ thin films was discussed.     

Non‐hydrogenated amorphous germanium carbide with adjustable microstructure and properties: a potential anti‐reflection and protective coating for infrared windows

Amorphous non‐hydrogenated germanium carbide (a‐Ge_1?xC_x) films have been deposited using magnetron co‐sputtering technique by varying the sputtering power of germanium target (P_Ge). The effects of P_Ge on composition and structure of the a‐Ge_1?xC_x films have been analyzed. The FTIR spectrum shows that the C–Ge bonds were formed in the a‐Ge_1?xC_x films according to the absorption peak at ~610 cm^?1. The Raman results indicate that the amorphous films also contain both Ge and C clusters. The XPS results reveal that the carbon concentration decreased as P_Ge increased from 40 to 160 W. The fraction of sp³ C–C bonds remains almost constant when increasing P_Ge from 40 to 160 W. The sp² C–C content of a‐Ge_1?xC_x film decreases gradually to 35.9% with P_Ge up to 160 W. Nevertheless, sp³ C–Ge sites rose with increasing P_Ge. Furthermore, the hardness and the refractive index gradually increased with increasing P_Ge. The excellent optical transmission of annealed a‐Ge_1–xC_x double‐layer coating at 400 °C suggests that a‐Ge_1?xC_x films can be used as an effective anti‐reflection coating for the ZnS IR window in the wavelength region of 8–12 µm, and can endure higher temperature than hydrogenated amorphous germanium carbide do. Copyright © 2012 John Wiley & Sons, Ltd.     

Repair of defects created by Ar+ sputtering on graphite surface by annealing as confirmed using ToF‐SIMS and XPS

Defects were created on the surface of highly oriented pyrolytic graphite (HOPG) by sputtering with an Ar⁺ ion beam, then characterized using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) at 500°C. In the XPS C1s spectrum of the sputtered HOPG, a sp³ carbon peak appeared at 285.3 eV, representing surface defects. In addition, 2 sets of peaks, the C_x⁻ and C_xH⁻ ion series (where x = 1, 2, 3...), were identified in the ToF‐SIMS negative ion spectrum. In the positive ion spectrum, a series of C_xH₂^+• ions indicating defects was observed. Annealing of the sputtered samples under Ar was conducted at different temperatures. The XPS and ToF‐SIMS spectra of the sputtered HOPG after 800°C annealing were observed to be similar to the spectra of the fresh HOPG. The sp³ carbon peak had disappeared from the C1s spectrum, and the normalized intensities of the C_xH⁻ and C_xH₂^+• ions had decreased. These results indicate that defects created by sputtering on the surface of HOPG can be repaired by high‐temperature annealing.     

Photocatalytic Nanocomposite Films Fabricated by Layer‐by‐Layer Self‐assembly of TiO2 Nanoparticles and Lignosulfonates

Photocatalytic multilayer nanocomposite films composed of anatase TiO₂ nanoparticles and lignosulfonates (LS) were fabricated on quartz slides by the layer‐by‐layer (LBL) self‐assembly technique. X‐ray photoelectron spectroscopy (XPS), UV‐vis spectroscopy and atomic force microscopy (AFM) were used to characterize the TiO₂/LS multilayer nanocomposite films. Moreover, the photocatalytic properties (decomposition of methyl orange and bacteria) of multilayer nanocomposite films were investigated. XPS results indicated that the intensities of titanium and sulfur peaks increased with the LBL deposition process. A linear increase in absorbance at 280 nm was found by UV‐Vis spectroscopy, suggesting that stepwise multilayer growth occurs on the substrate and this deposition process is highly reproducible. AFM images showed that quartz slide was completely covered by TiO₂ nanoparticles when a 10‐bilayer multilayer film was formed. The decomposition efficiency of methyl orange by TiO₂/LS multilayer films under the same UV irradiation time increased linearly with the number of TiO₂ layers, and the results of decomposition of bacteria under UV irradiation showed that TiO₂/LS multilayer nanocomposite films exhibited excellent decomposition activity of bacteria (Escherichia coil).     

Atomic Layer Deposition of Iron Sulfide and Its Application as a Catalyst in the Hydrogenation of Azobenzenes

The atomic layer deposition (ALD) of iron sulfide (FeS_x ) is reported for the first time. The deposition process employs bis(N ,N′ ‐di‐tert‐butylacetamidinato)iron(II) and H₂S as the reactants and produces fairly pure, smooth, and well‐crystallized FeS_x thin films following an ideal self‐limiting ALD growth behavior. The FeS_x films can be uniformly and conformally deposited into deep narrow trenches with aspect ratios as high as 10:1, which highlights the broad applicability of this ALD process for engineering the surface of complex 3D nanostructures in general. Highly uniform nanoscale FeS_x coatings on porous γ‐Al₂O₃ powder were also prepared. This compound shows excellent catalytic activity and selectivity in the hydrogenation of azo compounds under mild reaction conditions, demonstrating the promise of ALD FeS_x as a catalyst for organic reactions.     

Characterization and Activity of Cu‐MnOx/γ‐Al2O3 Catalyst for Hydrogenation of Carbon Dioxide

The effect of manganese on the dispersion, reduction behavior and active states of surface of supported copper oxide catalysts have been investigated by XRD, temperature‐programmed reduction and XPS. The activity of methanol synthesis from CO₂/H₂ was also investigated. The catalytic activity over CuO‐MnO_x/γ‐Al₂O₃ catalyst for CO₂ hydrogenation is higher than that of CuO/γ‐Al₂O₃. The adding of manganese is beneficial in enhancing the dispersion of the supported copper oxide and make the TPR peak of the CuO‐MnK_x/γ‐Al₂O₃ catalyst different from the individual supported copper and manganese oxide catalysts, which indicates that there exists strong interaction between the copper and manganese oxide. For the CuO/γ‐Al₂O₃ catalyst there are two reducible copper oxide species; α and β peaks are attributed to the reduction of highly dispersed copper oxide species and bulk CuO species, respectively. For the CuO‐MnO_x/γ‐Al₂O₃ catalyst, four reduction peaks are observed, α peak is attributed to the dispersed copper oxide species; β peak is ascribed to the bulk CuO; γ peak is attributed to the reduction of high dispersed CuO interacting with manganese; δ peak may be the reduction of the manganese oxide interacting with copper oxide. XPS results show that Cu⁺ mostly existed on the working surface of the Cu‐Mn/γ‐Al₂O₃ catalysts. The activity was promoted by Cu with positive charge which was formed by means of long path exchange function between Cu? O? Mn. These results indicate that there is synergistic interaction between the copper and manganese oxide, which is responsible for the high activity of CO₂ hydrogenation.     

Sol‐Gel Synthesis and Photocatalytic Study of Visible Light Active N‐Doped KSbWO6

KSbWO₆ was prepared by sol‐gel method. N‐doped KSbWO₆ (KSbWO_6–xN_x) was obtained by heating KSbWO₆ and urea at 400 °C. Both the compounds are characterized by powder X‐ray diffraction (XRD), TEM, SEM‐EDS, X‐ray photo electronic spectroscopy (XPS), and UV/Vis diffuse reflectance spectroscopy (UV‐DRS). A shift in the peak positions of powder XRD and XPS spectra was observed. The band gap energy (E_g) of KSbWO₆ and N‐doped KSbWO₆ was obtained from their diffused reflectance spectra.E_g was reduced from 3.17 eV to 2.56 eV upon nitrogen doping in KSbWO₆. The reduction of the E_g is attributed to the lifting of valence band of N‐doped KSbWO₆, due to the mixing of O 2p states with N 2p states. The photocatalytic activity of both the samples was studied by degradation of methylene blue (MB). The nitrogen doped KSbWO₆ shows higher photocatalytic activity compared to that of KSbWO₆.     

Deposition of copper‐doped iron sulfide (CuxFe1−xS) thin films using aerosol‐assisted chemical vapor deposition technique

Copper‐doped iron sulfide (Cu_xFe_1?xS, x = 0.010–0.180) thin films were deposited using a single‐source precursor, Cu(LH)₂Cl₂ (LH = monoacetylferrocene thiosemicarbazone), by aerosol‐assisted chemical vapor deposition technique. The Cu‐doped FeS thin films were deposited at different substrate temperatures, i.e. 250, 300, 350, 400 and 450 °C. The deposited thin films were characterized by X‐ray diffraction (XRD) patterns, Raman spectra, scanning electron microscopy, energy dispersive X‐ray analysis (EDX) and atomic force microscopy. XRD studies of Cu‐doped FeS thin films at all the temperatures revealed formation of single‐phase FeS structure. With increasing substrate temperature from 250 to 450 °C, there was change in morphology from wafer‐like to cylindrical plate‐like. EDX analysis showed that the doping percentage of copper increased as the substrate temperature increased from 250 to 450 °C. Raman data supports the doping of copper in FeS films. Copyright © 2010 John Wiley & Sons, Ltd.     

Bioactivity and mechanical properties of nickel‐incorporated hydrogenated carbon nanocomposite thin films

In this paper, the influence of nickel incorporation on the mechanical properties and the in vitro bioactivity of hydrogenated carbon thin films were investigated in detail. Amorphous hydrogenated carbon (a‐C:H) and nickel‐incorporated hydrogenated carbon (Ni/a‐C:H) thin films were deposited onto the Si substrates by using reactive biased target ion beam deposition technique. The films' chemical composition, surface roughness, microstructure and mechanical properties were investigated by using XPS, AFM, TEM, nanoindentation and nanoscratch test, respectively. XPS results have shown that the film surface is mainly composed of nickel, nickel oxide and nickel hydroxide, whereas at the core is nickel carbide (Ni₃C) only. The presence of Ni₃C has increased the sp² carbon content and as a result, the mechanical hardness of the film was decreased. However, Ni/a‐C:H films shows very low friction coefficient with higher scratch‐resistance behavior than that of pure a‐C:H film. In addition, in vitro bioactivity study has confirmed that it is possible to grow dense bone‐like apatite layer on Ni/a‐C:H films. Thus, the results have indicated the suitability of the films for bone‐related implant coating applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Investigation of block depth distribution in PS‐b‐PMMA block copolymer using ultra‐low‐energy cesium sputtering in ToF‐SIMS

Directed self‐assembly of block copolymers (BCPs) is a promising candidate for next generation nanolithography. In order to validate a given pattern, the lateral and in‐depth distributions of the blocks should be well characterized; for the latter, time‐of‐flight (ToF) SIMS is a particularly well‐adapted technique. Here, we use an ION‐TOF ToF‐SIMS V in negative mode to provide qualitative information on the in‐depth organization of polystyrene‐b‐polymethylmethacrylate (PS‐b‐PMMA) BCP thin films. Using low‐energy Cs⁺ sputtering and Bi₃⁺ as the analysis ions, PS and PMMA homopolymer films are first analyzed in order to identify the characteristic secondary ions for each block. PS‐b‐PMMA BCPs are then characterized showing that self‐assembled nanodomains are clearly observed after annealing. We also demonstrate that the ToF‐SIMS technique is able to distinguish between the different morphologies of BCP investigated in this work (lamellae, spheres or cylinders). ToF‐SIMS characterization on BCP is in good agreement with XPS analysis performed on the same samples. Copyright © 2013 John Wiley & Sons, Ltd.     

An EELS and EXELFS study of amorphous hydrogenated silicon carbide

A series of thin films of amorphous hydrogenated silicon carbide (a-SiCH) produced by RF plasma decomposition of propane and silane has been studied by electron energy-loss spectroscopy (EELS) and extended energy-loss fine structure (EXELFS) studies. The composition of the films has been determined by EELS and the nearest neighbour spacings have been determined by EXELFS. These results, along with the energy of the plasmon loss peaks, have been compared with the deposition conditions for each film. The results show that for a large gas ratio (C₃H₈/(C₃H₈+SiH₄)) the films have a high proportion of carbon and are similar to a-CH in structure, whereas those films prepared with Y = 0.4 or 0.5 have nearest neighbour spacings consistent with those for tetrahedrally bonded carbon. The films prepared with lowest Y have nearest neighbour spacings similar to those for amorphous silicon carbide. The results for a-SiCH have been compared with the results of EELS and EXELFS of CVD diamond films, amorphous carbon and amorphous silicon.