Low temperature catalytic performance of nanosized TiNiO for oxidative dehydrogenation of propane to propene

Nanosized TiNiO catalysts prepared by a modified sol-gel method have been investigated in the oxidative dehydrogenation of propane (ODP) to propene. At 300 °C the yield to propene of 12.1% was obtained on 9.1 wt.% TiNiO catalyst with the selectivity of 43%. The continued variety of lattice parameter and variation of chemical value of nickel and titanium ion on the surface indicates that there are strong interactions of TiO₂ and NiO. The decreased low temperature oxygen desorption and the weaker reducibility seems to be responsible for the decreased activity and enhanced selectivity of propane oxidative dehydrogenation over TiNiO catalysts.     

Enhancement of Ti-containing hydrogenated carbon (TiC:H) films by high-power plasma-sputtering

Ti-containing amorphous hydrogenated carbon (TiC:H) thin films were deposited on stainless steel SS304 substrates by high-power pulsed magnetron sputtering (HPPMS) in an atmosphere of mixed Ar and C₂H₂ gases using titanium metal as the cathodic material. The multilayer structure of the deposited film had a TiTiCDLC gradient to improve adhesion and reduce residual stress. This study investigates the effects of substrate bias and target-to-substrate distance on the mechanical properties of TiC:H films. Film properties, including composition, morphology, microstructure, mechanical, and tribology, were examined by glow discharge spectroscopy (GDS), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and a nanoindenter and a pin-on-disk tribometer. Experiments revealed impressive results.     

Influence of thermal treatment of low dielectric constant SiOC(H) films using MTES/O2 deposited by PECVD

Low dielectric constant SiOC(H) films are deposited on p-type Si(100) substrates by plasma enhanced chemical vapor deposition (PECVD) using methyltriethoxysilane (MTES, C₇H₁₈O₃Si) and oxygen gas as precursors. The SiOC(H) films are deposited at room temperature, 100, 200, 300 and 400 °C and then annealed at 100, 200, 300 and 400 °C temperatures for 30 min in vacuum. The influence of deposition temperature and annealing on SiOC(H) films are investigated. Film thickness and refractive index are measured by field emission scanning electron microscopy and ellipsometry, respectively. Chemical bonding characteristics of as-deposited and annealed films are investigated by Fourier transform infrared (FTIR) spectroscopy in the absorbance mode. As more carbon atoms are incorporated into the SiOC(H) films, both film density and refractive index are decreased due to nano pore structure of the film. In the SiOC(H) film, CH₃ group as an end group is introduced into OSiO network, thereby reducing the density to decrease the dielectric constant thereof. The dielectric constant of SiOC(H) film is evaluated by C-V measurements using metal-insulator-semiconductor (MIS), Al/SiOC(H)/p-Si structure and it is found to be as low as 2.2 for annealed samples deposited at 400 °C.     

The microwave spectrum of methyl chlorodifluoroacetate: Methyl internal rotation and chlorine nuclear electric quadrupole coupling

A chirped pulse microwave spectrometer has been used to record microwave spectra of the ³⁵Cl and ³⁷Cl isotopologues of methyl chlorodifluoroacetate, CClF₂C(O)OCH₃, between 8 GHz and 16 GHz. The target compound was spectroscopically examined as it participated in a supersonic expansion of argon. Only one conformer was observed. The rotational spectra were recorded with sufficient resolution to observe (i) splittings due to the internal rotation of the methyl group, and (ii) splittings from the coupling of the chlorine quadrupolar nucleus. A total of 785 transitions have had quantum numbers assigned. Analysis of the spectra observed has produced an experimental barrier to the methyl group internal rotation, V₃, of 370(2) cm⁻¹. It is noted that this barrier is a little lower than that determined for methyl acetate [V₃ = 425 cm⁻¹, J. Sheridan, W. Bossert and A. Bauder, J. Mol. Spectrosc., 80 (1980) 1-11], and this is rationalized through a comparison of molecular structures. Lastly, all components of both the ³⁵Cl and ³⁷Cl chlorine nuclear electric quadrupolar coupling tensor have been determined.     

Structural study of thin films prepared from tungstate glass matrix by Raman and X-ray absorption spectroscopy

Thin films were prepared using glass precursors obtained in the ternary system NaPO₃BaF₂WO₃ and the binary system NaPO₃WO₃ with high concentrations of WO₃ (above 40% molar). Vitreous samples have been used as a target to prepare thin films. Such films were deposited using the electron beam evaporation method onto soda-lime glass substrates. Several structural characterizations were performed by Raman spectroscopy and X-ray Absorption Near Edge Spectroscopy (XANES) at the tungsten L_I and L_III absorption edges. XANES investigations showed that tungsten atoms are only sixfold coordinated (octahedral WO₆) and that these films are free of tungstate tetrahedral units (WO₄). In addition, Raman spectroscopy allowed identifying a break in the linear phosphate chains as the amount of WO₃ increases and the formation of POW bonds in the films network indicating the intermediary behavior of WO₆ octahedra in the film network. Based on XANES data, we suggested a new attribution of several Raman absorption bands which allowed identifying the presence of WO⁻ and WO terminal bonds and a progressive apparition of WOW bridging bonds for the most WO₃ concentrated samples (above 40% molar) attributed to the formation of WO₆ clusters.     

Pre-treatments applied to oxidized aluminum surfaces to modify the interfacial bonding with bis-1,2-(triethoxysilyl)ethane (BTSE): Part I. High-purity Al with native oxide

A remote microwave-generated H₂ plasma and heating to 250 °C were separately used to modify high-purity oxidized aluminum surfaces and to assess whether these treatments can help enhance adhesion with bis-1,2-(triethoxysilyl)ethane (BTSE) coatings. Different initial oxide surfaces were considered, corresponding to the native oxide and to surfaces formed by the Forest Products Laboratory (FPL) treatment applied for either 15 or 60 min. BTSE is applied from solution at pH 4, and competing processes of etching, protonation (to form OH groups) and coupling (to form AlOSi interfacial bonds) occur at the solid-liquid interface. Scanning electron microscopy (SEM) was used to determine how the topographies of the modified Al surfaces changed with the different pre-treatments and with exposure to a buffer solution of pH 4. Secondary-ion mass spectrometry (SIMS) was used to determine the direct amount of AlOSi interfacial bonds by measuring the ratio of peak intensities 71-70 amu, while X-ray photoelectron spectroscopy (XPS) was used to determine the overall strength of the silane coating adhesion by measuring the Si 2p signals before and after application of an ultrasonic rinse to the coated sample. Measured Al 2p and O 1s spectra helped assess how the different pre-treatments modified the various Al oxidized surfaces prior to BTSE coating. Pre-treated samples that showed increased AlOSi bonding after BTSE coating corresponded to surfaces, which did not show evidence of significant etching after exposure to a pH 4 environment. This suggests that such surfaces are more receptive to the coupling reaction during exposure to the BTSE coating solution. These surfaces include all H₂ plasma-treated samples, the heated native oxide and the sample that only received the 15 min FPL treatment. In contrast, other surfaces that show evidence of etching in pH 4 environments are samples that received lower amounts of AlOSi interfacial bonding. Overall, heating improved the BTSE adhesive bonding for the native Al oxide, while H₂ plasma treatment improved the BTSE bonding for surfaces that had initially been FPL-treated for 15 and 60 min.     

Preparation of visible-light responsive PF-codoped TiO2 nanotubes

Fabrication of PF-codoped TiO₂ nanotubes was carried out using a one-step electrochemical anodization process by tailoring the composition of the electrolyte with the aim of PF-codoping to extend the optical absorption of TiO₂ to the visible-light region. The as-prepared PF-codoped TiO₂ nanotubes were characterized by SEM, XPS, and UV-vis diffuse reflectance absorption spectra (DRS). The results showed that the tube diameter of the nanotubes was approximately 100 nm and the tube length was approximately 510 nm. The phosphorus and fluorine were successfully doped into TiO₂ nanotubes, as evidenced by XPS. Moreover, the PF-codoped samples displayed remarkably strong visible-light response.     

Asymmetric surface modification of poly(ethylene terephthalate) film by CF4 plasma immersion

Poly(ethylene terephthalate) (PET) films were treated with CF₄ plasma immersion. The samples were processed at different RF powers and treatment time. The surface modification of PET films was evaluated by water contact angle (CA), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). Decrease in contact angle of both sides of PET films was observed under mild treatment conditions. However, as raising treatment power and/or time, the change in contact angle between the two sides of PET films was different. The relatively hydrophobic and hydrophilic surfaces were being in situ formed on the two sides of PET films, respectively. And the extreme values of water contact angle reached 108.63 and 7.56°, respectively. XPS analyses revealed that there was a substantial incorporation of fluorine and/or oxygen atoms in both side surfaces. The relative chemical composition of the C (ls) spectra's showed the incorporation of non-polar fluorine-based functionalities (i.e. CFCF_n, CF₂ or CF₃ groups) and polar oxygen-based functionalities (i.e. COOH or OH groups) in the surfaces. Correlation between the plasma parameters and the surface modification of PET films is also discussed.     

Ammonia adsorption and decomposition on silica supported Rh nanoparticles observed by in situ attenuated total reflection infrared spectroscopy

Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) is applied to study NH₃, adsorbed from the gas phase, and its decomposition products, i.e. NH_x species, on Rh nanoparticles, produced by spincoating from a RhCl₃ solution in water followed by reduction. A silicon ATR crystal with a hydroxilated SiO₂ layer acts as the support for the nanoparticles. Upon exposure to NH₃ in the vacuum chamber, NH₃ adsorbed to both silica and Rh is detected (sensitivity ∼5 × 10⁻⁵ absorbance units). Interaction of the NH₃ with the silica OH groups is observed around ∼2840 cm⁻¹ in combination with peaks showing the disappearance of unperturbed OH vibrations between 3500 and 3700 cm⁻¹. In addition, NH bend vibrations at 1634 cm⁻¹ and NH stretch vibrations at 3065 and 3197 cm⁻¹ are observed for substrate temperatures between 20 and 100 °C. The latter two correspond to NH on Rh, as verified with a sample without Rh, and probably correspond to undecomposed NH₃. Moreover, they remain after evacuation, suggesting strongly bound species. For a substrate temperature of 75 and 100 °C, additional NH stretch peaks at 3354 and 3283 cm⁻¹ are observed, possibly due to NH₂ intermediates, indicating NH₃ decomposition. It is shown that ATR-FTIR can contribute to the sensitive detection of adsorption and decomposition of gaseous species on realistic planar model catalysts.     

Effects of NH3, O2, and N2 co-implantation on Cu out-diffusion and antimicrobial properties of copper plasma-implanted polyethylene

Metal antibacterial reagents are effective in the enhancement of the antimicrobial properties of medical polymers. However, incorporation of metal antibacterial reagents into polymers using conventional methods usually results in unstable antimicrobial effects. Our previous research demonstrates that plasma immersion ion implantation (PIII) can be used to effectively incorporate metal antibacterial reagents such as Cu into polyethylene (PE) in the near surface region up to several hundred nanometers without causing noticeable damage to the polymer matrix. In this work, various gases including NH₃, O₂, and N₂ were plasma-implanted in concert with Cu plasma immersion ion implantation to study the effects of these gas species on the release rate of Cu from the substrate. Our experimental results reveal that the copper depth profiles are not affected significantly by NH₃, O₂, or N₂ co-implantation and these gas elements have similar depth profiles as Cu. Chemical analyses demonstrate that polar functional CO, CO, CN, CN, and CN bonds formed in the substrate play an important role in regulating Cu out-diffusion. Among the three gas species, N₂ shows the best effects in regulating Cu out-diffusion and produces the best long term antibacterial properties. The Cu retention and out-diffusion mechanism in the ion-implanted polyethylene is described.     

Near infrared spectroscopy of organic acids: comparing OH and CH oscillator frequencies and intensities

This work investigates the vibrational spectroscopy of a series of organic acids, CH₃(CH₂)_nCOOH (n = 1-5), previously unobserved in the IR and near-IR (2000-15 000 cm⁻¹). The work obtains frequencies and relative intensities for all OH and CH stretching transitions. Comparison of the frequencies and intensities of CH and OH stretching transitions reveal interesting trends in acid chain length that are discussed. Literature values for acetic acid (CH₃COOH) and formic acid (HCOOH) are used to gain a broader understanding for the spectroscopy of the organic acids CH₃(CH₂)_nCOOH. The observation of several combination bands involving the CH and OH stretching vibrations and possible rotational isomer and hot band transitions are reported.     

Improvement of photoluminescence properties of porous silicon by silica passivation

Porous silicon (PS) was passivated by silica film using a sol-gel method; the photoluminescence (PL) properties were significantly improved; namely, PL intensity and stability increased and PL peak shifted to shorter wavelength. Scanning electron microscope (SEM) and Fourier transformed infrared spectroscope (FTIR) results indicated that silica passivation produced a compact film on the PS surface and modified the surface state of PS. The number of stable surface bonds (HSiO₃, HSiSiO₂ and H₂SiO₂) increased due to the oxidation of SiH back-bonds during the gelation process, and thus the PL intensity and stability were improved. Moreover, the blue-shift of PL peak was determined due to the increase in the ratio of SiO/SiH.     

Effect of oxidation on the optical and surface properties of AlGaN

The chemical properties of Al_xGa_1−xN surfaces exposed to air for different time periods are investigated by atomic force microscopy (AFM), photoluminescence (PL) measurement and X-ray photoelectron spectroscopy (XPS). PL and AFM results show that Al_xGa_1−xN samples exhibit different surface characteristics for different air-exposure times and Al contents. The XPS spectra of the Al 2p and Ga 2p core levels indicate that the peaks shifted slightly, from an AlN to an AlO bond and from a GaN to a GaO bond. All of these results show that the epilayer surface contains a large amount of Ga and Al oxides.     

The active role played by nonmagnetic Sr in magnetostructural coupling in SrTcO3 from first principles

The total energies and structural parameters of SrTcO₃ are calculated by means of the generalized gradient approximation (GGA) plus on-site Coulomb interaction corrections (GGA+U) method. G-type antiferromagnetic (G-AFM) is found to be ground state, in consistence with the previous experimental result. The distortions around Sr and Tc upon magnetic transition are compared and the change of distortion for SrO bond upon magnetic transition is found to be 25.83 times of the change for TcO bond. Our results point to an active role played by Sr in magnetostructural coupling in SrTcO₃.     

Ab initio studies of electronic spectra of the linear aluminum-bearing carbon chains AlC2nH (n = 1-5)

Geometries and stabilities of the linear aluminum-bearing carbon chains AlC_2nH (n = 1-5) in their ground states have been explored by the DFT-B3LYP and RCCSD(T) methods. Structures of the X¹Σ⁺ and 1¹Π electronic states have also been optimized by the CASSCF approach. The studies indicate that these species have single-triple bond alternate pattern, AlCCCC?CCH, and the electronic excitation from X¹Σ⁺ to 1¹Π leads to the shortening of the AlC bonds. The vertical excitation energies of the 1¹Π ← X¹Σ⁺ and 2¹Π ← X¹Σ⁺ transitions for AlC_2nH (n = 1-5) have been investigated by the CASPT2, EOM-CCSD, and TD-B3LYP levels of theory with the cc-pVTZ basis set, respectively. CASPT2-predicted 1¹Π ← X¹Σ⁺ transition energies are 3.57, 3.44, 3.33, 3.26, and 3.21 eV, respectively. For AlC₂H, our estimate agrees very well with the experimental value of 3.57 eV. In addition, the AlC bond dissociation energies and the exponential-decay curves for these vertical excitation energies are also discussed.     

Modification of H-terminated Ge surface in hydrochloric acid

Various amounts of H-termination on a Ge surface were prepared by dipping a Ge wafer in differentially diluted hydrofluoric acid solutions for different periods of time. Formation of GeH_x in hydrofluoric acid and its disappearance in hydrochloric acid (HCl) were directly measured by using multiple internal reflection Fourier transform infrared spectroscopy (MIR FT-IR). Peak intensity of GeH_x vibration mode was increased with diluted hydrofluoric acid (DHF) treatment time and the concentration of HF solution. Therefore, it is suggested that microroughness of a Ge surface changes depending on the concentration of HF. Peak intensity of GeH_x vibration mode was reduced when the GeH_x surface was treated in HCl solution. With an increase in HCl treatment time, peak intensity of GeH_x vibration mode was reduced. Ge surfaces treated in a more diluted HF solution were barely modified, because it was thought to have fewer kink sites, dihydrides and trihydrides.     

Chemistry of l-proline on Pd(1 1 1): Temperature-programmed desorption and X-ray photoelectron spectroscopic study

The surface chemistry of proline is explored on Pd(1 1 1) using a combination of temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy. Proline adsorbs on Pd(1 1 1) at temperatures of 250 K and below into second and subsequent layers prior to the saturation of the first layer, where approximately 70% of the adsorbed proline is present in its zwitterionic form. Molecular proline desorbs between ∼315 K and ∼333 K depending on coverage. When adsorbed at ∼300 K, only the first monolayer is formed, and the proline is present as zwitterions, oriented such that all of the carbons are detected equally by XPS. Proline decomposes by scission of the C-COO bond, where the carboxylate moiety desorbs as carbon monoxide and carbon dioxide, while the nitrogen-containing moiety desorbs as to HCN, and evolves pyrrole at ∼390 K, pyrrolidine at ∼410 K, and final species that desorbs at ∼450 K that cannot be unequivocally assigned but may be 2-butenenitrile (CH₃-CHCH-CN), 3-butenenitrile (CH₂CH-CH₂-CN), 2-methyl-2-propenenitrile (CH₂C(CH₃)-CN) or cyclopropanecarbonitrile.     

Chemisorption of 1,1-dichloroethene on the Si(1 1 1)-7 × 7 surface

Chemisorption of 1,1-dichloroethene (Cl₂CCH₂) to a Si(1 1 1)-7 × 7 surface was studied by means of X-ray photoelectron spectroscopy using synchrotron radiation, recording chlorine 2p and carbon 1s spectra. For carbon 1s, spectral assignment of the chemisorbed species is based on quantum chemical calculations of chemical shifts in model compounds.The results confirm the identity of covalently bonded 1-chlorovinyl (-CClCH₂) and vinylidene (CCH₂) adspecies. Upon chemisorption at room temperature it was found that about one-third of the molecules break one C-Cl bond while about two-thirds of the adsorbates break two C-Cl bonds. We do not, however, find evidence for isomerization of CCH₂ to di-bonded vinylene (-CHCH-).     

Effect of CCC bond bending vibration on the photodissociation of cyclobutane

The effect of CCC bond bending on the photodissociation of cyclobutane to form two ethylene molecules was investigated by performing semiclassical electron-radiation-ion dynamics simulations and also by examining the potential energy surfaces of the electronic ground state and lowest excited states. These potential energy surfaces, calculated at the CASSCF/MRPT2 level with 6-31G* basis sets along a reaction path determined by the semiclassical dynamics simulations, show well-defined energy minima and maxima in the intermediate state region. It is found that in addition to rotation of the molecule around the central CC bond, CCC bond bending plays an important role in determining the features of the potential energy surfaces for the intermediate species.     

Pulsed laser ablation of borax target in vacuum and hydrogen DC glow discharges

The aim of our experiment was to produce a material with BH bonds for applications in hydrogen storage and generation. By using KrF excimer laser (λ = 248 nm) ablation of borax (Na₂B₄O₇) target, thin films were deposited on KBr and silicon substrates. Ablation was performed both in vacuum and in hydrogen atmosphere. DC glow discharge technique was utilized to enhance hydrogen gas ionization. Experiments were performed using laser fluence from 5 to 20 J/cm². Films were deposited under gas pressure of 1 × 10⁻⁵ to 5 × 10⁻² mbar and substrate temperatures of 130-450 °C. Scanning electron microscopy analysis of films showed presence of circular particulates. Film thickness, roughness and particulates number increased with increase in laser fluence. Energy dispersive X-ray spectroscopy analysis shows that sodium content in the particulates is higher than in the target. This effect is discussed in terms of atomic arrangements (both at surface and bulk) in systems where ionic and covalent bonds are present and by looking at the increased surface/bulk ratio of the particulates with respect to the deposited films. The Fourier transform infrared spectroscopy measurements showed presence of BO stretching and BOB bending bonds. Possible reasons for absence of BH bonds are attributed to binding enthalpy of the competing molecules.