Silicon carbonitride nanolayers — Synthesis and chemical characterization

SiC_xN_y thin films were produced by plasma-enhanced chemical vapor deposition and characterized by ellipsometry, Fourier transform infrared and Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, as well as, by near-edge X-ray absorption fine structure measurements in total-reflection X-ray fluorescence geometry. The temperature of synthesis was varied between 100 °C and 800 °C, the precursors hexamethyldisilazane or hexamethylcyclotrisilazane were used with an addition of N₂, He, and NH₃, respectively. The composition of the products was determined to be constant in Si with about 20 at.%, whereas the sum of C and N results in 80 at.% (each varying between 20 and 60 at.%). Consequently, it can be stated, that in the produced silicon carbonitride a network of Si is built with SiCSi, SiCCSi, and SiNSi bridges. The comparison of the chemical composition and of the physical properties shows for the samples produced with He or N₂, respectively (without NH₃) that the refractive index and the absorption coefficient are increasing with an increasing content of carbon in the final formula SiC_4 − nN_n (with n = 1, 2, or 3).     

A vapor phase deposition of self-assembled monolayers: Vinyl-terminated films of volatile silanes on silicon oxide substrates

Vinyl-terminated self-assembled monolayers (SAMs) offer significant flexibility for further chemical modification and can serve as a versatile starting point for a tailoring of surface properties. A vapor phase deposition of such films would offer advantages in cases where the preparation from solution is not an option or not desired, for example in connection with silicon microstructures such as micro-electromechanical systems. We show that SAMs of 9-decenyltrichlorosilane (CH₂CH(CH₂)₈SiCl₃), 10-undecenyltrichlorosilane (CH₂CH(CH₂)₉SiCl₃), 14-pentadecenyltrichlorosilane (CH₂CH(CH₂)₁₃SiCl₃), decyltrichlorosilane (CH₃(CH₂)₉SiCl₃), and octadecanetrichlorosilane (CH₃(CH₂)₁₇SiCl₃) can be prepared both from solution and from the vapor phase. The resulting layers were compared by static contact angle measurements, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy to determine their surface wettability, the film thickness, the smoothness and homogeneity of the respective films, and their chemical composition and each method gave films of comparable quality. Deposition of functionalized SAMs from the vapor phase is rare. Here we report the parameters for the preparation of well-ordered vinyl-terminated SAMs from the vapor phase.     

Multiferroic properties of Co and Nd co-substituted Bi5Ti3FeO15 thin films

Co and Nd co-substituted Bi₅Ti₃FeO₁₅ thin films were prepared on Pt/Ti/SiO₂/Si substrates via metal organic decomposition method. The structural and multiferroic properties of the films were investigated. It was found that Co ions enter into the lattice and occupy the Fe site. The Bi_4.15Nd_0.85Ti₃Fe_0.5Co_0.5O₁₅ films simultaneously exhibit ferroelectric and ferromagnetic properties at room temperature, and its 2P_r and 2M_r are 38 μC/cm² and 3 kA/m, respectively. Moreover, substitutions create local ferromagnetic order and antiferromagnetic order depending on whether the local bonding is FeOCo or FeOFe/CoOCo, respectively. The competing interaction of the ferromagnetic and antiferromagnetic phases results in an interesting magnetic behavior of the films.     

Ultraviolet irradiation effect on the properties of leakage current and dielectric breakdown of low-dielectric-constant SiOC(H) films using comb capacitor structure

Low-dielectric constant SiOC(H) films were deposited on p-type Si(100) substrates by plasma-enhanced chemical-vapor deposition (PECVD) using dimethyldimethoxy silane (DMDMS, C₄H₁₂O₂Si) and oxygen gas as precursors. To improve the physicochemical properties of the SiOC(H) films, the deposited SiOC(H) films were exposed to ultraviolet (UV) irradiation in a vacuum. The bonding structure of the SiOC(H) films was investigated by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrical characterization of SiOC(H) films were carried out through I-V measurements using the comb-like patterns of the TiN/Al/Ti/SiOC(H)/TiN/Al/Ti metal-insulator-metal (MIM) structure. Excessive UV treatment adversely affected the SiOC(H) film, which resulted in an increased dielectric constant. Our results provide insight into the UV irradiation of low-k SiOC(H) films.     

A new phase diagram for the CaOAl2O3SiO2H2O hydroceramic system at 200 °C

A new phase diagram is reported for the CaOAl₂O₃SiO₂H₂O (CASH) system at 200 °C. This system is rare in nature but has applications in cementing geothermal and deep oil wells. The phase diagram was constructed by synthesising a range of hydroceramics with CASH assemblages from oilwell cement, silica flour (quartz) and alumina (corundum). A hydroceramic is defined as any ceramic material incorporating water as H₂O or OH. At 200 °C, gyrolite, hillebrandite, jaffeite, portlandite, quartz, 11 Å tobermorite, xonotlite, hibschite and katoite were observed as product phases. The mineral assemblages produced the following three-phase triangles in the CaOAl₂O₃SiO₂ diagram: Gyr + Qtz + Xon; Crn + Tob + Xon; Crn + Hib + Xon; Crn + Hib + Jaf; Crn + Jaf + Kat; Hib + Jaf + Por; Hib + Jaf + Xon; and two reactions are found to be in progress at 200 °C. When alumina is present in the reaction mixture, the thermal stability of tobermorite is extended to higher temperature, and the crystallinity of tobermorite and xonotlite enhanced.     

Synthesis and structural refinement of polycrystalline ceramic powder Pr0.1Ca0.9TiO3

Perovskite structure-based ceramic precursors have a characteristic property of substitution in the ‘A’ site of the ABO₃ structure. This makes them a potential material for nuclear waste management in synthetic rock (Synroc) technology. In order to simulate the mechanism of rare earth fixation in perovskite, Pr_xCa_1−xTiO₃ (where x = 0.1) has been synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and Pr as starting materials. The ceramic phase has been characterized by its powder diffraction pattern. The Rietveld analysis of the X-ray diffraction data has been carried out using GSAS software to achieve the convergence which gives the R_p = 5.74% and R_wp = 8.17%. The (h, k, l) values for different lattice planes have been calculated. The praseodymium substituted perovskite crystallizes in orthorhombic symmetry with space group: Pbnm, Z = 4. The unit cell parameters at room temperature are a = 5.39609(31) Å, b = 5.44869(30) Å and c = 7.6565(5) Å. The calculated and observed values of the corresponding intensities, 2θ and density of the polycrystalline powder show good agreement. GSAS-based calculation for bond distances TiO, CaO and bond angles OTiO, OCaO has been reported.     

Raman spectroscopic study of structure of WO3La2O3B2O3 glasses with no color and crystallization of LaBWO6

Glasses with the nominal compositions of xWO₃25La₂O₃(75 − x)B₂O₃ (mol%) with x = 15, 25, and 50 were prepared using a conventional melt quenching method, and their structure and crystallization behavior were examined from Raman scattering spectra and X-ray diffraction analyses. The glasses are colorless in the visible light region and give the optical band gap energy of 3.49-3.61 eV. The glass transition and crystallization temperatures and the thermal stability against crystallization decrease with increasing WO₃ content. The strong Raman bands at 840 and 940-960 cm⁻¹ suggest that the main coordination state of W⁶⁺ ions in the glasses is isolated (WO₄)²⁻ tetrahedral units. The formation of WO₆ octahedral units is also suggested in the glasses with high WO₃ contents. The main crystallization mechanism in the glasses is the surface crystallization, and the glass of 50WO₃25La₂O₃25B₂O₃ shows the crystallization of LaBWO₆ single phase. The present study proposes that WO₃La₂O₃B₂O₃ glasses and crystallized glasses are very interesting as optical functional materials.     

Optical properties and scanning probe microscopy study of some AgAsSSe amorphous films

Doping of AsSSe amorphous films by silver photo-dissolution leads to a decrease of the optical gap and to an increase of the refractive index in forming AgAsSSe films. The difference of the optical gap and refractive index between undoped and doped films has been found in case of Ag₁₅As₂₆S₂₉Se₃₀ film up to 0.37 eV and 0.26, respectively. Transreflectance in far infrared spectral region indicates formation of AgAsS₂ and AgAsSe₂ entities in Ag₁₅As₂₆S₂₉Se₃₀ film. Scanning probe microscopy, namely atomic force microscopy, atomic force acoustic microscopy (AFAM) and Kelvin probe force microscopy (KPFM) was used for studying AgAsSSe films. It was found that silver growth is rather three dimensional and it is reminiscent of the Stranski-Krastanov growth mode. Observed silver protuberances represent silver reservoirs responsible for a local increase of silver content. Hence, the silver growth mode enhances formation of nano/meso inhomogeneities of the surface and near surface density/stiffness, seen in AFAM, and in the surface electric potential, seen in KPFM.     

Preparation and characterization of NaSm9(SiO4)6O2 powders with infrared absorptive properties

NaSm₉(SiO₄)₆O₂ powders were synthesized by mild hydrothermal method at 180 °C for 24 h. The infrared optical properties and structure of the obtained powders were characterized. There existed two narrow and sharp absorptive bands near 943 cm^− 1 (10.6 μm). The band at 938 cm^− 1 was assigned to the stretching vibrations of SiOSm groups connecting to Q¹ species and the band at 989 cm^− 1 was attributed to the stretching vibrations of SiOSm groups linking with Q⁰ species. The reflectivity was lower than 1% from 900 to 1200 nm and reached the minimum of 0.46% at 1073 nm. The prepared powders exhibit potential to act as a new kind of absorptive material for the infrared light of 10.6 μm and 1.06 μm.     

Determination of silicon nitride film chemical composition to study hydrogen desorption mechanisms

To go further in the comprehension of hydrogen desorption mechanisms from PECVD (Plasma Enhanced Chemical Vapour Deposited) silicon nitride, a method to determine the chemical composition of amorphous silicon nitride films using fast and non destructive characterization techniques has been developed. In particular, SiH, NH, SiSi and SiN bond concentrations are calculated from Fourier transform infra red spectroscopy, ellipsometry and mass measurement. Next, different PECVD silicon nitride films were annealed at 600 °C during 2 min. Results show that hydrogen desorption from PECVD silicon nitride depends on film mass density and main chemical reactions leading to hydrogen desorption are identified thanks to the determination of SiSi and SiN bond concentrations.     

Effects of photoirradiation in UV and VUV regions during plasma exposure to polymers

Interactions between photons irradiated from Ar-O₂ mixture plasmas and polymer surfaces were investigated on the basis of depth analyses of chemical bonding states in the nano-surface layer of polyethylene terephthalate (PET) films via hard X-ray photoelectron spectroscopy (HXPES) and conventional X-ray photoelectron spectroscopy (XPS). The PET films were exposed to photons from the Ar-O₂ mixture plasmas by covering the PET samples with MgF₂ and quartz windows as optical filters for evaluation of photoirradiation effects in ultraviolet (UV) and vacuum ultraviolet (VUV) regions. The HXPES results indicated that the degradation of the chemical bonding states due to photoirradiation in regions was insignificant in deeper regions up to about 50 nm from the surface. Whereas, conventional XPS analysis showed that CO bond, OCO bond and CO bond increased after photoirradiation in UV and VUV regions. These results suggest that the increase in oxygen functionalities (CO bond, OCO bond and CO bond) may be attributed to chemical reactions and/or terminations of scissed bonds via photodecompositions of the polymer with oxygen and/or OH species (oxygen molecules and radicals during plasma exposure and/or oxygen molecules and moisture after taking the PET samples out of the plasma reactor to the ambient air) in the vicinity of the sample surface.