Structural and optical properties of the SiCN thin films prepared by reactive magnetron sputtering

Silicon carbonitride (SiCN) thin films were deposited on n-type Si (1 0 0) and glass substrates by reactive magnetron sputtering of a polycrystalline silicon target in a mixture of argon (Ar), nitrogen (N₂) and acetylene (C₂H₂). The properties of the films were characterized by scanning electron microscope with an energy dispersive spectrometer, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry and ultraviolet-visible spectrophotometer. The results show that the C₂H₂ flow rate plays an important role in the composition, structural and optical properties of the films. The films have an even surface and an amorphous structure. With the increase of C₂H₂ flow rate, the C content gradually increases while Si and N contents have a tendency to decrease in the SiCN films, and the optical band gap of the films monotonically decreases. The main bonds are Si-O, N-H_n, C-C, C-N, Si-N, Si-C and Si-H in the SiCN films while the chemical bonding network of Si-O, C-C, C-O, C-N, N-Si and CN is formed in the surface of the SiCN films.     

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.     

Vibration-rotation Fourier transform infrared spectrum of the C-D and CC stretching fundamental, ν1 and ν2, band systems of deuterated monobromoacetylene

A high resolution vibration-rotation spectrum of deuterated monobromoacetylene (DCCBr) has been recorded with a Bruker IFS 120 Fourier Spectrometer in the wavenumber region 1700-2800 cm⁻¹, which covers the C-D and CC stretching fundamental (ν₁ and ν₂, respectively) and the CC and C-Br stretching vibrational combination (ν₂ + ν₃) band systems. The analysis of the spectrum provides accurate vibrational term values and rotational constant for 20 vibration-rotation bands for both isotopic species, DCC⁷⁹Br and DCC⁸¹Br.     

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.     

Binuclear transition metal complexes on gold: Molecular orientation by angular dependent NEXAFS spectroscopy

The influence of the transition metals on the molecular orientation and molecule-substrate interaction has been investigated by angular dependent NEXAFS spectroscopy for the recently synthesised dialkynyl bridged complexes M₂-DEBP (Cl(PBu₃)₂M-CC-C₆H₄-C₆H₄-CCM(PBu₃)₂Cl, M = Pt, Pd; DEBP = diethynyl-biphenyl, i.e. CC-C₆H₄-C₆H₄-CC-). Thin films of both samples have been deposited on Au/Si(1 1 1), and the angular dependent analysis of the main π^∗ feature deriving by the superimposition of the resonances due to benzene and acetylene carbon orbitals showed a polarisation effect for Pd₂-DEBP only. A tendency to a preferential molecular orientation at nearly 50° to the surface was calculated. Furthermore, for Pd₂-DEBP, the two π^∗ resonances already assigned to benzene and acetylene carbon atoms showed different angular effects; a likely explanation for this behaviour bear in mind the interaction between sp and sp² carbons of the organic DEBP moieties with Pd centres of neighbouring macromolecules, giving rise to interchain interactions then leading to an enhancement of the already assessed self-assembling properties.     

Magnesia formed on calcination of Mg(OH)2 prepared from natural bischofite

Calcination of magnesium hydroxide, which was prepared from natural bischofite MgCl₂·6H₂O, leading to dehydration 2(MgOH) → MgOMg + H₂O, is accompanied by transition of phase not only to MgO but also to MgO_x at x < 1 (assigned to Mg₄O₃) at moderate temperatures. At higher temperatures, MgO_x is completely transformed into MgO. Magnesium hydroxide and oxide heated at different temperatures were studied using the TEM, XRD, IR, PCS, TG-DTA, nitrogen and argon adsorption methods. The electronic structure of MgO and Mg₄O₃ was studied using the ab initio quantum chemical method with periodic conditions. According to TEM images, the morphology of particles changing from Mg(OH)₂ laminae to aggregates of interpenetrated MgO cubelets and foils depend strongly on the calcination temperature. Significant changes in surface area are observed mainly at 325-470 °C on desorption of a major portion of eliminated water corresponding to 28.4 wt.% at its total amount of 30.9 wt.%. Pore size distribution (PSD) is sensitive to treatment conditions and the main PSD peaks shift towards larger pore size with elevating temperature. The characteristics of the surface hydroxyls as well as of the bulk MgO bonds depend on heating conditions, as noticeable changes are observed in the XRD patterns and the IR spectra of the samples undergoing the mentioned transformation of phase Mg(OH)₂ → MgO_x → MgO.     

Resonant Auger spectroscopy study of charge transfer phenomena in N 1s core-excited acetonitrile adsorbates on Si(0 0 1)-2 × 1

Acetonitrile (CH₃CN) adsorbs on Si(0 0 1)-2 × 1 at room temperature under two forms, a cycloaddition-like adduct (Si-CN-Si) and a pendent cyano (Si-CH₂-CN) resulting from the decomposition of the molecule. Resonant Auger spectroscopy has been used to study the excited-state-dependent electron transfer from the N 1s core-excited molecular adsorbate to the silicon substrate, using the core-hole lifetime (∼6 fs) as an internal clock. It is shown that the π_CN^∗ NEXAFS state lies within the silicon bandgap because of a core-excitonic effect. Therefore no charge transfer of the excited electron to the substrate is observed. On the other hand the π_CN^∗ NEXAFS state is placed within the silicon conduction band. Excitation to this orbital leads to valence/Auger spectra in which both resonant and normal Auger contributions are observed. Therefore there is evidence for a charge transfer from the pendent CN to the silicon surface, on a timescale estimated to tens of femtoseconds.     

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.     

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 ν7, ν8, and ν11 bands of propynal, C2HCHO, in the 650 cm region

The infrared spectrum of propynal, C₂HCHO, is studied at high resolution (0.003 cm⁻¹) in the range 570-640 cm⁻¹. The relatively intense ν₁₁ (CC-H out-of-plane bend, 693 cm⁻¹) and ν₇ (CC-H in-plane bend, 651 cm⁻¹) fundamental bands are linked by a strong a-type Coriolis interaction. The somewhat weaker ν₈ (CCO in-plane bend, 614 cm⁻¹) fundamental has a significant Fermi-type interaction with the “dark” background state 3ν₉ (∼618 cm⁻¹). About 1400 lines are assigned and analyzed in terms of a four-state fit in order to obtain accurate band origins, rotational and centrifugal distortion parameters, and Fermi and Coriolis interaction parameters. This represents the first systematic high-resolution infrared study of propynal.     

S180 cell growth on low ion energy plasma treated TiO2 thin films

X-ray photoelectron spectroscopy (XPS) was used to characterise the effects of low energy (<2 eV) argon ion plasma surface modification of TiO₂ thin films deposited by radio frequency (RF) magnetron sputter system. The low energy argon ion plasma surface modification of TiO₂ in a two-stage hybrid system had increased the proportion of surface states of TiO₂ as Ti³⁺. The proportion of carbon atoms as alcohol/ether (COX) was decreased with increase the RF power and carbon atoms as carbonyl (CO) functionality had increased for low RF power treatment. The proportion of C(O)OX functionality at the surface was decreased at low power and further increase in power has showed an increase in its relive proportion at the surface. The growth of S180 cells was observed and it seems that cells are uniformly spreads on tissue culture polystyrene surface and untreated TiO₂ surfaces whereas small-localised cell free area can be seen on plasma treated TiO₂ surfaces which may be due to decrease in C(O)OX, increase in CO and active sites at the surface. A relatively large variation in the surface functionalities with no change in the surface roughness was achieved by different RF plasma treatments of TiO₂ surface whereas no significant change in S180 cell growth with different plasma treatments. This may be because cell growth on TiO₂ was mainly influenced by nano-surface characteristics of oxide films rather than surface chemistry.     

The chemistry of C2 perfluoroalkyl iodide on the Cu(1 1 1) single crystal surface

The thermal chemistry of perfluoroethyl iodide (C₂F₅I) adsorbed on Cu(1 1 1) has been investigated by temperature-programmed reaction/desorption (TPR/D), reflection-absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). I 4d and F 1s XPS spectra show that dissociative adsorption of C₂F₅I to form the surface-bound perfluroethyl (Cu-C₂F₅) moieties occurs at very low temperature (T < 90 K), while the C-F bond cleavage in adsorbed perfluroethyl (Cu-C₂F₅) begins at ca. 300 K. XPS and TPR/D studies further reveal that the reactions of ^βCF₃^αCF_2(ad) on Cu(1 1 1) are strongly dependent on the surface coverage. At high coverages (?0.16 L exposure), the adsorbed perfluroethyl (Cu-C₂F₅) evolves, via α-F elimination, into the surface-bound tetrafluoroethylidene moieties (CuCF-CF₃) followed by a dimerization step to form octafluoro-2-butene (CF₃CFCFCF₃) at 315 K as gas product. The surface-bound (Cu-C₂F₅) decomposes preferentially, at low coverages (?0.04 L), via consecutive α-F abstraction to afford intermediate, trifluoroethylidyne (CuCCF₃), resulting in the final coupling reaction to yield hexafluoro-2-butyne (CF₃CCCF₃) at 425 K. However, at middle coverages (ca. 0.08-0.16 L exposure), the adsorbed perfluroethyl (Cu-C₂F₅) first experiences an α-F elimination and then prefers to loss the second F from β position to yield the intermediate of Cu-CF₂-CFCu (μ-η,η-perfluorovinyl), which may further evolve into hexafluorocyclobutene (CF₂CFCFCF₂) at 350 K through cyclodimerization reaction. Our results have also shown that the surface reactions to yield the products, CF₃CFCFCF₃ and CF₃CCCF₃, obey first-order kinetics, whereas the formation of CF₂CFCFCF₂ follows second-order kinetics.     

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.     

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.     

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.     

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.     

CF4 radio frequency plasma surface modification of silicone rubber for use as outdoor insulations

For further prolonging the serve life of silicone rubber (SIR) for outdoor insulation and increasing its resistance of pollution flashover, surface modifications of SIR were carried out via CF₄ capacitively coupled plasma at radio frequency (RF) power of 60, 100 and 200 W for a treatment time up to 20 min under CF₄ flow rate of 20 sccm. Static contact angle measurement was employed to estimate the change of hydrophobicity of the modified SIR. The variation of the surface functional groups of the modified SIR was observed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrum and X-ray photoelectron spectroscopy (XPS). The surface topography was observed by atom force microscopy (AFM). The results indicate that the static contact angle of SIR surface is improved from 100.7° to 150.2° via the CF₄ plasma modification, and the super-hydrophobic surface of modified SIR, which corresponds to a static contact angle of 150.2°, appears at RF power of 200 W for a 5-min treatment time. According to the results, it is suggested that the formation of super-hydrophobic surface is ascribed to the co-action of the increase of roughness created by the ablation reaction of CF₄ plasma and the formation of [SiF_x(CH₃)_2−xO]_n (x = 1, 2) structure produced by the direct attachment of F atoms to Si.     

Ultrasound promoted the synthesis of N-propargylic β-enaminones

The synthesis of 14 novel N-propargylic β-enaminones from the reaction of β-alkoxy vinyltrihalomethyl[carboxyethyl] ketones [R³C(O)CHC(R¹)OMe, where R³ = CF₃, CCl₃, CO₂Et and R¹ = Me, Et, Pr, Bu, i-Pent, CH₂CH₂CO₂Me] with propargyl amines [R²NHCH₂CCH, where R² = Pr, PhCH₂] is reported. Yields, solvents and reaction times needed for reaction completion, by microwave irradiation (MW), conventional thermal heating (TH) and under ultrasound irradiation (US) are compared. The best results were obtained under US irradiation in good to excellent yields (70-93%).     

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.     

Interaction of amines with native aluminium oxide layers in non-aqueous environment: Application to the understanding of the formation of epoxy-amine/metal interphases

Interaction of propylamine (PA), 1,2-diaminoethane (DAE) or 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophorone diamine, IPDA) with native aluminium oxide layers in non-aqueous environment has been studied using time-resolved inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The formation of several surface complexes has been evidenced. Monodentate and bidentate metal-bond surface complexes (MBSC) result from interactions between the amine terminations of the molecule and aluminium cations by donation of the N lone electron pair to the metal ion (Lewis-like mechanism leading to OAl?N bonds). Monodentate and bidentate hydrogen-bond surface complexes (HBSC) are due to interaction of the amino group with surface hydroxyl groups by protonation of the amine termination (Brønsted-like mechanism leading to the formation of AlOH?N bonds) or interaction with carbonaceous contamination (C_xO_yH_z?N bonds). Diamines can also form mixed complexes with one amino group forming an O-Al?N bond and the other group forming an AlOH…N or C_xO_yH_z?N bond. AlOH?N and C_xO_yH_z…N bonds are less stable under vacuum than OAl?N bonds, leading to partial desorption of the DAE molecules in vacuum and modification of the interaction modes. Only DAE and IPDA can lead to partial dissolution of the aluminium native (hydr)oxide films. A detailed mechanism of dissolution has been proposed based on the formation of mononuclear bidentate (chelate) MBSC by ligand exchange between the terminal η¹-OH and bridged μ₂-OH surface sites and the amino terminations of the molecule. The detachment of this complex from the surface is likely to be the precursor step to the formation of the interphase in epoxy-amine/metal systems.