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.     

UV assisted oxidation and nitridation of hafnia based thin films for alternate gate dielectric applications

The synergistic effects of NH₃ ambient and ultraviolet illumination on the dielectric properties of hafnia based gate dielectrics are reported in this paper. The films were processed at relatively low temperatures (∼400 °C) by pulsed laser ablation and UV oxidation technique. UV illumination and the NH₃ ambient created a thin and a denser interfacial layer (at the film-Si interface) comprised of HfSiON bonding. As a result of the interfacial layer modification, a leakage current density lower than 10⁻⁴ A/cm² and a dielectric constant of ∼21.7 were extracted from the best samples processed in NH₃ and under UV illumination. The nitrogen doped HfO₂ also exhibited a thinner interfacial layer (∼12 Å) in comparison to the films processed without NH₃ ambient.     

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.     

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.     

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.     

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.     

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.     

The surface modification of nanoporous SiOx thin films with a monofunctional organosilane

The surfaces of nanostructured, porous SiO_x/Si (air-oxidized Si) and SiO_x thin films, deposited by excimer laser ablation in He and He + O₂ gas ambients, respectively, have been modified by the deposition of a monofunctional organosilane. They were characterized using photoacoustic Fourier-transform infrared (FTIR) X-ray photoelectron (XPS) spectroscopies, and field-emission scanning electron microscopy (FESEM). Photoacoustic FTIR analysis indicates that the organosilane has hydrolyzed to form a silanol, which has chemically reacted with SiO_x through its surface silanol (SiOH) group, to form siloxane (SiOSi) structures. An enhanced IR spectral signal is found, due to the expansion and contraction of both the pores of the solid and the gas within them.     

The cleavage of the methane CH bond over PdO/H-BEA: A density functional theory study

Cluster models were used to represent the β-type cationic sites of the protonated beta zeolite (H-BEA) and the loading of PdO on these sites. The properties of these clusters and the cleavage of methane CH bond over these clusters were studied using density functional theory (DFT) method. The stability of H-BEA was enhanced due to the formation of hydrogen bonds. After PdO loading, the Pd atom bonds to four oxygen atoms among which three H-BEA framework oxygen atoms are included to form an approximate planar structure with Pd in the centre. This structure is very similar to that of bulk PdO. The acidic proton of H-BEA and the oxygen atom of PdO participate in the cleavage of methane CH bond, indicating that PdO is the active species for the activation of methane. Over the clusters constructed in the present work, the calculated energy barriers for the cleavage of methane CH bond are in the region between 17.54 and 21.02 kcal mol⁻¹.     

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.     

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.     

Surface modification of poly(propylene carbonate) by oxygen ion implantation

Poly(propylene carbonate) (PPC) was implanted by oxygen ion with energy of 40 keV. The influence of experimental parameters was investigated by varying ion fluence from 1 × 10¹² to 1 × 10¹⁵ ions/cm². XPS, SEM, surface roughness, wettability, hardness, and modulus were employed to investigate structure and properties of the as-implanted PPC samples. Eight chemical groups, i.e., carbon, CH, COC, CO, OCO, CO, , and groups were observed on surfaces of the as-implanted samples. The species and relative intensities of the chemical groups changed with increasing ion fluence. SEM images displayed that irradiation damage was related strongly with ion fluence. Both surface-recovering and shrunken behavior were observed on surface of the PPC sample implanted with fluence of 1 × 10¹⁵ ions/cm². As increasing ion fluence, the surface roughness of the as-implanted PPC samples increased firstly, reached the maximum value of 159 nm, and finally decreased down the minimum value. The water droplet contact angle of the as-implanted PPC samples changed gradually with fluence, and reached the minimum value of 70° with fluence of 1 × 10¹⁵ ions/cm². The hardness and modulus of the as-implanted PPC samples increased with increasing ion fluence, and reached their corresponding maximum values with fluence of 1 × 10¹⁵ ions/cm². The experimental results revealed that oxygen ion fluence closely affected surface chemical group, morphology, surface roughness, wettability, and mechanical properties of the as-implanted PPC samples.     

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.     

Carbon monoxide adsorption on Pd-deposited Cu(1 1 0) surface: Infrared reflection absorption and temperature programmed desorption studies

We investigated carbon monoxide (CO) adsorption and desorption behaviors on 0.1-nm-, 0.15-nm-, and 0.3-nm-thick-Pd-deposited Cu(1 1 0) surfaces using infrared reflection absorption (IRRAS) and temperature-programmed desorption (TPD) spectroscopic methods. CO was exposed to the 0.1-nm-thick-Pd/Cu(1 1 0) surface at the substrate temperature of 90 K. The IR band attributable to CO bonded to Cu atoms emerged at 2092 cm⁻¹: the band was located at 2100 cm⁻¹ at saturation coverage, with a shoulder at 2110 cm⁻¹. In addition to these bands, weak absorptions attributable to the PdCO bonds appeared at 2050 and 1960 cm⁻¹. With increasing Pd thickness, the Pd related-bands became increasingly prominent. Particularly at the early stage of exposure, the band at 2115 cm⁻¹ became visible. The band at 2117 cm⁻¹ dominated the spectra all through the exposures for the 0.3-nm-thick-Pd surface. The TPD spectra of the surfaces showed two remarkable features at around 220-250 and 320-390 K, ascribable ,respectively, to CuCO and PdCO. The desorption peaks shifted to higher temperatures with increasing Pd thickness. Based on the TPD and IRRAS results, we discuss the adsorption-desorption behaviors of CO on the Pd/Cu(1 1 0) surfaces.     

An XPS study of pulsed plasma polymerised allyl alcohol film growth on polyurethane

The growth of highly functionalised poly allyl alcohol films by pulsed plasma polymerisation of CH₂CHCH₂OH on biomedical grade polyurethane has been followed by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Film thickness is observed to increase approximately linearly with plasma modification time, suggesting a layer-by-layer growth mode of poly allyl alcohol. Water contact angle measurements reveal the change in the surface free energy of wetting decreases linearly with plasma modification up to the monolayer point after which a constant limiting value of −24 mJ m⁻² was attained. Films prepared at 20 W plasma power with a duty cycle of 10 μs:500 μs exhibit a high degree of hydroxyl (OH) retention with minimal fragmentation of the monomer observed. Increasing the plasma power up to 125 W is found to improve OH retention at the expense of ether formation generating films close to the monomer stoichiometry. Duty cycle plays an important role in controlling both film composition and thickness, with longer off times increasing OH retention, while longer on times enhance allyl alcohol film growth.     

Effect of defects on the reflectivity of Cr/C multilayer soft X-ray mirror at 4.48 nm

Cr/C is a promising material combination for multilayer mirror in the “near water window region” (4.4-6.7 nm). In the present paper, the effect of defects on the reflectivity of Cr/C soft X-ray multilayer mirror deposited by magnetron sputtering was studied. Formation of thin interlayer due to the interdiffusion, rough interface due to the non-sharp layer and contamination of O happened during the deposition process were found by a method combined by XPS, soft X-ray reflectivity at 4.48 nm and grazing incidence hard X-ray reflectivity at 0.154 nm. The XPS results show that both interlayers (Cr-on-C and C-on-Cr) are mixture composed of C sp2, C sp3, CO, CO, CrCr and CrO bondings. No chromium carbide was found at the interlayer probably due to the blocking of oxides’ formation. Through the analysis of X-ray reflectivity, we obtained the multilayer structure parameters (thickness and roughness) and optical constants of each layer at 4.48 nm. Based on those results, a further calculation was carried out. The result shows that the formation of the thin interlayer contributes little to the decrease of the reflectivity, the rough interface decreases the reflectivity most and the contaminant (O) not only decreases the reflectivity but also shifts the position of the peak.     

Hydrogen related point defects in silicon based layers: Si(·)H and SiOOH

Layers prepared by pulsed TEA CO₂ pulsed laser ablation (PLA) of SiO and SiO₂ targets in helium were exposed to hydrogen and deuterium atmosphere up to several kPa. The deposited layers were investigated by FTIR, EPR and XP spectroscopy. Among various Si species silyl radical Si(·)H (Si(·)D) at 2166 (1568) cm⁻¹—H(I) center—and silyl hydroperoxide SiOOH (SiOOD) at 3587 (2648) cm⁻¹ were identified in FTIR spectra. Chemical pathways for production of these species are discussed. Experimental results are supported by quantum chemical calculations.     

Reaction of acetonitrile with the silicon(0 0 1) surface: A combined XPS and FTIR study

The adsorption of acetonitrile on the Si(0 0 1) surface has been investigated using X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). XPS and FTIR spectra indicate that adsorbed acetonitrile forms two correlated binding configurations, a CN species with a strong FTIR absorption at 1540 cm⁻¹ and a CCN (ketenimine) species that has a very strong FTIR absorption at 1952 cm⁻¹. The CCN FTIR peak at 1952 cm⁻¹ shows a striking polarization dependence, with the infrared transition dipole almost entirely in the plane of the sample and parallel to the SiSi dimer axis. Our data suggests that the primary CCN structure results from cleavage of two C-H bonds, forming a structure in which the N and terminal C atom are both linked to the surface. Temperature-dependent experiments help to elucidate the complicated reaction mechanism for acetonitrile adsorbing onto the Si(0 0 1) surface. Dosing at higher temperature increases the amount of CCN relative to CN species while heating leads to direct transformation of the CN to the CCN species. Our results indicate that previous studies, which considered only products formed by cleavage of a single C-H bond, have misidentified the primary ketenimine product. A reinterpretation of the earlier results, combined with data presented here, sheds new light onto the products and mechanism of interaction of acetonitrile with Si(0 0 1).