Stoichiometric and non-stoichiometric films in the Si–O–N system: mechanical,electrical, and dielectric properties

A novel low-temperature (600–850 °C), chemical vapor deposition method, involving a simple reaction between disiloxane (H₃Si–O–SiH₃) and ammonia (NH₃), is described to deposit stoichiometric, Si₂N₂O, and non-stoichiometric, SiO_xN_y, silicon oxynitride films (5–500 nm) on Si substrates. Note, the gaseous reactants are free from carbon and other undesirable contaminants. The deposition of Si₂N₂O on Si (with (1 0 0) orientation and a native oxide layer of 1 nm) was conducted at a pressure of 2 Torr and at extremely high rates of 20–30 nm min⁻¹ with complete hydrogen elimination. The deposition rate of SiO_xN_y on highly-doped Si (with (1 1 1) orientation but without native oxide) at 10⁻⁶ Torr was ∼1.5 nm min⁻¹, and achieved via the reaction of disiloxane with N atoms, generated by an RF source in an MBE chamber. The phase, composition and structure of the oxynitride films were characterized by a variety of analytical techniques. The hardness of Si₂N₂O, and the capacitance–voltage (C–V) as a function of frequency and leakage current density–voltage (J_L–V) characteristics were determined on MOS (Al/Si₂N₂O/SiO/p-Si) structures. The hardness, frequency-dispersionless dielectric permittivity (K), and J_L at 6 V for a 20 nm Si₂N₂O film were determined to be 18 GPa, 6 and 0.05–0.1 nA cm⁻², respectively.     

Potentiometric urea biosensor based on multi-walled carbon nanotubes (MWCNTs)/silica composite material

A novel potentiometric urea biosensor has been fabricated with urease (Urs) immobilized multi-walled carbon nanotubes (MWCNTs) embedded in silica matrix deposited on the surface of indium tin oxide (ITO) coated glass plate. The enzyme Urs was covalently linked with the exposed free –COOH groups of functionalized MWCNTs (F-MWCNTs), which are subsequently incorporated within the silica matrix by sol–gel method. The Urs/MWCNTs/SiO₂/ITO composite modified electrode was characterized by Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA) and UV–visible spectroscopy. The morphologies and electrochemical performance of the modified Urs/MWCNTs/SiO₂/ITO electrode have been investigated by scanning electron microscopy (SEM) and potentiometric method, respectively. The synergistic effect of silica matrix, F-MWCNTs and biocompatibility of Urs/MWCNTs/SiO₂ made the biosensor to have the excellent electro catalytic activity and high stability. The resulting biosensor exhibits a good response performance to urea detection with a wide linear range from 2.18 × 10^? 5 to 1.07 × 10^? 3 M urea. The biosensor shows a short response time of 10–25 s and a high sensitivity of 23 mV/decade/cm².     

Enhancement of photoluminescence properties of CaAl2Si2O8:Eu2+ by SiO2 addition

SiO₂ added phosphors, CaAl₂Si₂O₈:Eu²⁺ + xSiO₂ (x = 0, 1, 2, 3, 4, 5, 6 and 13 mol) were synthesized by a novel liquid phase precursor (LPP) method. The photoluminescence properties of phosphor added by 5 mol of SiO₂ showed 110% enhancement in the emission intensity compared to the CaAl₂Si₂O₈:Eu²⁺ phosphor. A broad emission and excitation wavelength was observed approximately from 400 nm to 600 nm centered at 430 nm and from 280 nm to 400 nm centered at 365 nm, respectively. Photoluminescence intensity of the phosphors increased continuously by SiO₂ addition up to x = 5 mol and then it decreased with further addition of SiO₂. The observed photoluminescence properties of the phosphors were discussed related to their crystalline structure and morphology.     

Interfacial SiC formation in polysiloxane-derived Si–O–C ceramics

Poly(methylsilsesquioxane) (CH₃SiO_1.5)_n (PMS) loaded with 40 vol.% Si-filler powder was pyrolyzed in inert atmosphere up to 1400 °C to fabricate Si–O–C composite ceramics. The evolution of the interface microstructure between the filler and the matrix was studied by high resolution electron microscopy (HREM), energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy. While below pyrolysis temperatures of 1000 °C no filler reaction was observed (inert filler regime), a porous interface layer of nanosized ß-SiC was formed at reaction temperatures above 1200 °C. Due to a high fraction of open porosity of 13% (1000 °C) to 19% (1400 °C) in the polymer-derived Si–O–C matrix, gas-phase transport and reaction processes involving CO and SiO as the dominant species are likely to occur at the interface boundary layer.     

Amorphous InGaZnO thin film transistors with SiO2/HfO2 double-layer gate dielectric fabricated at low temperature

Amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) with double-layer gate dielectric were fabricated at low temperature and characterized. A stacked 150 nm-thick SiO₂/50 nm-thick HfO₂ dielectric layer was employed to improve the capacitance and leakage characteristics of the gate oxide. The SiO₂/HfO₂ showed a higher capacitance of 35 nF/cm² and a lower leakage current density of 4.6 nA/cm² than 200 nm-thick SiO₂. The obtained saturation mobility (μ_sat), threshold voltage (V_th), and subthreshold swing (S) of the fabricated TFTs were 18.8 cm² V^?1 s^?1, 0.88 V, and 0.48 V/decade, respectively. Furthermore, it was found that oxygen pressure during the IGZO channel layer deposition had a great influence on the performance of the TFTs.     

High-speed deposition of dense,dendritic and porous SiO2 films by Nd: YAG laser chemical vapor deposition

Dense, dendritic and porous SiO₂ films were prepared by laser chemical vapor deposition (LCVD) using a high-power continuous-wave mode Nd: YAG laser (206 W) and a TEOS (tetraethyl orthosilicate) precursor. The effects of laser power (P_L) and total chamber pressure (P_tot) on the microstructure and deposition rate (R_dep) were investigated. Amorphous SiO₂ films were obtained independent of P_L and P_tot. Flame formation was observed between the nozzle and the substrate at P_L > 160 W and P_tot > 15 kPa. At P_L = 206 W, dense, dendritic and porous SiO₂ films were obtained at P_tot < 20 kPa, P_tot = 23 kPa and P_tot > 25 kPa, respectively. The R_dep increased thousands of times under flame formation conditions, the highest R_dep being reached at 1200 μm h^?1, 22,000 μm h^?1 and 28,000 μm h^?1 for the dense, dendritic and porous SiO₂ films, respectively.     

Fatigue and retention properties of Bi3.25La0.75Ti3O12 films using LaNiO3 bottom electrodes

Fatigue-free Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were grown on LaNiO₃ bottom electrodes grown in a microwave furnace at 700 °C for 10 min from the polymeric precursor method. It was found that LaNiO₃ (LNO) bottom electrode with pseudocubic structure strongly promote the formation of (00l) texture of BLT films. The remanent polarization (P_r) and the drive voltage (V_c) were 11 μC/cm² and 1.3 V respectively, and are better than the values found in the literature. The polarization of the Au/BLT/LNO/SiO₂/Si (100) capacitors with a thickness of 280 nm exhibited no degradation after 1 × 10¹⁰ switching cycles at an applied voltage of 5 V with a frequency of 1 MHz. After several tests the capacitors retain 77% of its polarization upon a retention time of 10⁴ s.     

Influence of nanocrystalline structure of surface on boron gettering from silicon

The boron gettering from nanocrystallites of porous silicon with rate significantly greater in comparison with planar structure has been for the first time observed. As a probe of gettering process, the EPR signal intensity of P_b center was used. It was established that strain effect during the surface oxidation stimulates strongly the boron gettering process from nanocrystallites bulk to SiO₂/Si interface of porous layer.Phenomenon of strong absorption of microwave radiation by porous layer after the sample was annealed in air at 400–500 °C was also detected at 37 GHz. This absorption is equivalent to high conductivity of layer (ρ = 10^− 2–10^− 3 Ω cm) and it is much higher (at least in 10⁴ times) than of c-Si substrate. Removal of porous layer (thickness of ∼ 20 μm) from 400-μm substrate leads to where Q-factor of cavity is restored completely. The high conductivity of the porous layer comes mainly from conduction along the nanocrystalline grains, while SiO₂ layer essentially insulates their interface. One possible effect explanation is that high concentration of positive charge states formed in SiO₂ layer can lead to the creation of high density of free electrons in the SiO₂/Si interface with formation of conductive channels along each nanocrystallite. On the other hand, appreciable microwave absorption is not detected on 9.4 GHz (X-band); therefore, we cannot exclude the existence of quasi-resonant microwave absorption that is related with nanocrystallites sizes, i.e. quantum confinement and electrons tunneling between grains.     

Eggshell- and fur-like microstructures of yttrium silicate film prepared by laser chemical vapor deposition

Yttrium silicate (Y–Si–O) films with eggshell- and fur-like microstructures were prepared by laser chemical vapor deposition using a Nd:YAG laser, and tetraethyl orthosilicate (TEOS) and yttrium dipivaloylmethane (Y(dpm)₃) precursors. Amorphous Y–Si–O films were prepared at deposition temperature below 1200 K. The crystalline Y–Si–O films with mixtures of Y_4.67(SiO₄)₃O and α-Y₂Si₂O₇ phases were obtained at deposition temperature above 1200 K. y-Y₂Si₂O₇ and X1-Y₂SiO₅ minor phases were also formed at a higher deposition temperature. At deposition temperature ranging between 1285 and 1355 K, a dome-like structure covered with fine fur-like projections was formed under a total pressure of 3.5 kPa, whereas an eggshell-like structure 200–300 μm in diameter and 10–20 μm in shell thickness was formed at 7.5 kPa. The deposition rate for the Y–Si–O films with fur- and eggshell-like microstructures reached 300 and 1000 μm h^?1, respectively.     

The role of operations after the deposition on the performance of SiOx films in optoelectronics devices

In this study, we have investigated phase separation, silicon Nano crystal (Si-NC) formation and optoelectronics properties of Si oxide (SiO_x, 0.7 < x < 1.3) films in high-vacuum annealing and ion bombardment conditions. The SiO_x films were deposited by physical vapor deposition (PVD). The internal structure properties of these films were the main factor in applications of optoelectronic. Possible changes in the structure, composition and electro physical properties were investigated by FTIR and TEM spectroscopy. The measurements show that SiO_x film is the dominant phase in the ultra-thin layer. Also, high-temperature annealing ion bombardment results in further increase of the phase separation of the whole layer.     

Quaternary thiospinel CuCrTiS4 as an electroactive material for copper(II)-sensitive and selective electrode

CuCrTiS₄ was obtained by solid-state synthesis methods. The crystal structure of the quaternary phase was investigated by X-ray powder method and is described in the thiospinel structure (space group Fd¯3m) with the lattice parameter а = 0,99388(1) nm. Atomic parameters were refined in the isotropic approximation (R_I = 0.0465, R_P = 0.1060). The possibility of the use of this compound as an electroactive substance in graphite-paste electrodes for the measurement of Сu²⁺ ions was investigated. The electrodes exhibit a Nernstian response towards copper (II) ions with a cationic slope. The optimal electrode composition, detection limit (6 · 10^− 7 M), selectivity coefficient for major interfering elements, рН range and practical applicability of such electrodes were established.     

Studies on the electrochemical preparation of MgCeCo alloy thin films on Cu substrates in urea–DMSO system

Cyclic voltammetry was used to investigate the electrochemical behaviors of Mg(II), Ce(III) and Co(II) in 3.00 mol L^− 1 urea–DMSO (dimethylsulfoxide). The electrode processes of Mg(II), Ce(III) and Co(II) reducing on Pt electrodes were irreversible steps. The transfer coefficient of Mg(II), Ce(III) and Co(II) in 3.00 mol L^− 1 urea–DMSO system was calculated as 0.07, 0.05 and 0.05 at 298.15 K, respectively. The diffusion coefficient of Mg(II), Ce(III) and Co(II) in 3.00 mol L^− 1 urea–DMSO system was calculated as 2.27 × 10^− 10, 1.77 × 10^− 10 and 3.16 × 10^− 10 m² s^− 1 at 298.15 K, respectively. The MgCeCo alloy thin films with smooth, uniform and metallic luster were obtained on Cu substrates by cyclic electrodeposition in 0.01 mol L^− 1 Mg(ClO₄)₂–0.01 mol·L^− 1 Ce(CH₃SO₃)₃₋0.01 mol L^− 1 CoCl₂–3.00 mol L^− 1 urea–DMSO system. The potential sweep rate was found to be important with respect to the adhesion of the thin films.     

A comparative study on fabrication of Mn2 + selective polymeric membrane electrode and coated graphite electrode

Poly(vinyl chloride)-based membranes of two ligands 2,4-bis(2-acetoxybenzylamino)-6-phenyl-1,3,5-triazine (L₁) and N2,N4-di(cyanoethyl)-2,4-bis(2-acetoxybenzylamino)-6-phenyl-1,3,5-triazine (L₂) were fabricated and explored as Mn^2 + ion selective electrodes. The performance of the polymeric membranes electrodes of ionophores with different plasticizers (dibutylphthalate, benzoic acid, o-nitrophenyloctyl ether, 1-chloronapthalene and tri-n-butylphosphate) and anion excluders (sodium tetraphenylborate and potassium tetrakis p-(chloro phenyl)borate) was looked in to and the better results were obtained with the membrane having composition L₂: NaTPB: DBP: PVC as 6: 3: 56: 35 (w/w; mg). The coated graphite electrode (CGE) with same composition was also fabricated and investigated as Mn^2 + selective electrode. It was found that CGE showed better response characteristics than PME. The potentiometric response of CGE was independent of pH in the range 3.0–9.0 exhibiting the Nernstian slope 29.5 ± 0.3 mV decade^? 1 of activity and working concentration range 4.1 × 10^? 7–1.0 × 10^? 1 mol L^? 1 with a limit of detection 6.7 × 10^? 8 mol L^? 1. The electrode showed a fast response time of 12 s with a shelf life of 105 days. The proposed CGE could be successfully used for the determination of Mn^2 + ions in different water, soil, vegetables and medicinal plants also used as an indicator electrode in potentiometric titration with EDTA.     

Structural and pyroelectric properties of sol–gel derived multiferroic BFO thin films

Multiferroic BFO/PZT multilayer films were fabricated by spin-coating method on the (1 1 1)Pt/Ti/SiO₂/Si substrate alternately using PZT(30/70), PZT(70/30) and BFO alkoxide solutions. The structural and ferroelectric properties were investigated for uncooled infrared detector applications. The coating and heating procedure was repeated six times to form BFO/PZT multilayer films. All films showed the typical XRD patterns of the perovskite polycrystalline structure without presence of the second phase such as Bi₂Fe₄O₃. The thickness of BFO/PZT multilayer film was about 200–220 nm. The ferroelectric properties such as dielectric constant, remnant polarization and pyroelectric coefficient were superior to those of single composition BFO film, and those values for BFO/PZT(70/30) multilayer film were 288, 15.7 μC/cm² and 9.1 × 10^?9 C/cm² K at room temperature, respectively. Leakage current density of the BFO/PZT(30/70) multilayer film was 3.3 × 10^?9 A/cm² at 150 kV/cm. The figures of merit, F_V for the voltage responsivity and F_D for the specific detectivity, of the BFO/PZT(70/30) multilayer film were 6.17 × 10^?11 Ccm/J and 6.45 × 10^?9 Ccm/J, respectively.     

Immobilization of Acidithiobacillus ferrooxidans on sulfonated microporous poly(styrene–divinylbenzene) copolymer with granulated activated carbon and its use in bio-oxidation of ferrous iron

The immobilization efficiencies of Acidithiobacillus ferrooxidans cells on different immobilization matrices were investigated for biooxidation of ferrous iron (Fe^2 +) to ferric iron (Fe^3 +). Six different matrices were used such as the polyurethane foam (PUF), granular activated carbon (GAC), raw poly(styrene–divinylbenzene) copolymer (rawSDVB), raw poly(styrene–divinylbenzene) copolymer with granular activated carbon (rawSDVB-GAC), sulfonated poly(styrene–divinylbenzene) copolymer (sulfSDVB) and sulfonated poly(styrene–divinylbenzene) copolymer with granular activated carbon (sulfSDVB-GAC). The sulfSDVB-GAC polymer showed the best performance for Fe^2 + biooxidation. It was used at packed-bed bioreactor and the kinetic parameters were obtained. The highest Fe^2 + biooxidation rate (R) was found to be 4.02 g/L h at the true dilution rate (D_t) of 2.47 1/h and hydraulic retention time (τ) of 0.4 h. The sulfSDVB-GAC polymer was used for the first time as immobilization material for A. ferrooxidans for Fe^2 + biooxidation.     

Growth and characterization of (Pb,La)TiO3 films with and without a special buffer layer prepared by RF magnetron sputtering

The (Pb, La)TiO₃ (PLT) ferroelectric thin films with and without a special buffer layer of PbO_x have been deposited on Pt/Ti/SiO₂/Si(100) substrates by RF magnetron sputtering technique at room temperature. The microstructure and the surface morphology of the films annealed at 600 °C for 1 h have been investigated by X-ray diffraction (XRD) and atomic force microscope (AFM). The surface roughness of the PLT thin film with a special buffer layer was 4.45 nm (5 μm × 5 μm) in comparison to that of 31.6 nm (5 μm × 5 μm) of the PLT thin film without a special buffer layer. Ferroelectric properties such as polarization hysteresis loop (P–V loop) and capacitance–voltage curve (C–V curve) of the films were investigated. The remanent polarization (P_r) and the coercive field (E_c) are 21 μC/cm² and 130 kV/cm respectively, and the pyroelectric coefficient is 2.75 × 10^− 8 C/cm² K for the PLT film with a special buffer layer. The results indicate that the (Pb, La)TiO₃ ferroelectric thin films with excellent ferroelectric properties can be deposited by RF magnetron sputtering with a special buffer layer.     

Compressive strength and microstructural characteristics of class C fly ash geopolymer

Geopolymers prepared from a class C fly ash (CFA) and a mixed alkali activator of sodium hydroxide and sodium silicate solution were investigated. A high compressive strength was obtained when the modulus of the activator viz., molar ratio of SiO₂/Na₂O was 1.5, and the proper content of this activator as evaluated by the mass proportion of Na₂O to CFA was 10%. The compressive strength of these samples was 63.4 MPa when they were cured at 75 °C for 8 h followed by curing at 23 °C for 28 d. In FTIR spectroscopy, the main peaks at 1036 and 1400 cm^?1 have been attributed to asymmetric stretching of Al–O/Si–O bonds, while those at 747 cm^?1 are due to the Si–O–Si/Si–O–Al bending band. The main geopolymeric gel and calcium silicate hydrate (C–S–H) gel co-exist and bond some remaining unreacted CFA spheres as observed in XRD and SEM–EXDA. The presence of gismondine (zeolite) was also observed in the XRD pattern.     

Phase separation and crystallization in LiNbO3/SiO2 glasses

Various samples with the compositions (100 ? x)LiNbO₃·xSiO₂ (with x = 10, 20, 25, 30, 35, 40, 50 and 60) were prepared by conventional melting technique. Samples with 20 ≤ x ≤ 35 were transparent, while products with x = 10 or x ≥40 were at least partly opaque under the conditions supplied. TEM-micrographs of replicas gave evidence on phase separation in these glasses. At SiO₂-concentrations >30 mol%, the formed structures consist of SiO₂-rich droplets in a LiNbO₃-rich matrix phase. The size of the structures increases with increasing SiO₂-concentration. At an SiO₂-concentration of 50 mol%, the droplets are as large as 450 nm. During thermal treatment, the LiNbO₃-rich matrix phase crystallizes and forms lithium niobate.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Microstructure and photoluminescent properties of Sr2SiO4:Eu3+ phosphors with various NH4Cl flux concentrations

In this paper, effect of NH₄Cl flux concentrations (0, 1, 2, 3 and 4 wt%) on the crystal structure, morphology and photoluminescent properties of Sr₂SiO₄:Eu³⁺ phosphors synthesized by a microwave sintering at 1200 °C for 1 h was investigated and discussed. X-ray powder diffraction analysis showed the crystal structure was not affected and the pure Sr₂SiO₄ phase was formed without second phase or phases of starting materials when adding with the NH₄Cl flux. The SEM images indicated that increase of the NH₄Cl flux enlarged the particle size of the phosphor particles. The photo-luminescence results showed the addition of 1 wt% NH₄Cl flux much improved the emission intensity at λ_em of 617 nm as the excitation spectrum at λ_ex of 395 nm. The decay times of Sr₂SiO₄:Eu³⁺ phosphors with different NH₄Cl flux concentrations were obtained around 2.47–2.52 ms.