Thermodynamic analysis of the high-temperature stability of silicon nitride and silicon carbide

A thermodynamic analysis of the stability of Si₃N₄ and SiC is presented which can be employed to assess their suitability for use at high temperatures in various environments. Specifically, the decomposition and the volatilization of Si₃N₄ and SiC, and of SiO₂, which is the major constituent in the oxide scales formed on their surfaces in oxidizing atmospheres, are discussed in terms of ambient environment and temperature. The calculated values of the lowest oxygen partial pressure up to which a protective SiO₂ layer should be maintained on the surface of Si₃N₄ and SiC are also presented.     

Mass production of very thin single-crystal silicon nitride nanobelts

We report the large-scale synthesis of very thin single-crystalline Si₃N₄ nanobelts with high yield via catalyst-assisted pyrolysis of polymeric precursors. The obtained nanobelts, which show a perfect crystal structure and smooth surface, are up to several millimeters in length with typical width and thickness of ∼800 nm and tens of nanometers, respectively. It is believed that the nanobelts were grown via a vapor-solid process, in which Al catalyst played a key role. This result provides a possibility for mass producing high quality, very thin Si₃N₄ nanobelts.     

Fabrication and characterization of TiO2 photocatalytic thin film prepared from peroxo titanic acid sol

A novel sol–gel technique using the PTA (peroxo titanic acid) sol as precursor for the fabrication of TiO₂ photocatalytic thin film is introduced in this paper. The peroxo titanic acid sol was synthesized from titanyl sulfate (TiOSO₄), ammonia and peroxide solution (H₂O₂). The transparent and porous TiO₂ thin film was prepared via a sol–gel technique using PTA sol and polyethylene glycol (PEG) as precursor and template, respectively. The TiO₂ thin film samples were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectrophotometry (UV–vis), X-ray photoelectron spectrum (XPS) and thermogravimetry and differential thermal analysis (TG-DTA) technique. The PTA sol displayed amorphous TiO₂ below 100 °C. The anatase phase formed at 200 °C to 700 °C. The crystallinity of anatase phase was improved with increasing temperature. The anatase crystals on the surface of TiO₂ film were strip-like, the size being about 100 nm in length and 40 nm in diameter. Addition of PEG to the PTA sol developed porous structures in the film and changed the size and shape of the particles. The surface of the film contained Ti, O and C elements and Na element that diffused into the film from the glass substrate. The photocatalytic performance of TiO₂ film was tested for the degradation of 10 mg/L methyl orange. The degradation of methyl orange solution reached 98.9% after irradiated for 180 min under UV light. The porous TiO₂ thin film exhibited high photocatalytic activity towards degrading methyl orange.     

Fabrication of new polypyrrole/silicon nitride hybrid materials for potential applications in electrochemical sensors: Synthesis and characterization

In this research, an efficient fabrication process of conducting polypyrrole (PPy)/silicon nitride (Si₃N₄) hybrid materials were developed in order to be employed as transducers in electrochemical sensors used in various environmental and biomedical applications. The fabrication process was assisted by oxidative polymerization of pyrrole (Py) monomer on the surface of Si/SiO₂/Si₃N₄ substrate in presence of FeCl₃ as oxidant. To improve the adhesion of PPy layer to Si₃N₄ surface, a pyrrole-silane (SPy) was chemically bonded through silanization process onto the Si₃N₄ surface before deposition of PPy layer. After Py polymerization, Si/SiO₂/Si₃N₄-(SPy-PPy) substrate was formed. The influence of SPy concentration and temperature of silanization process on chemical composition and surface morphology of the prepared Si/SiO₂/Si₃N₄-(SPy-PPy) substrates was studied by FTIR and SEM. In addition, the electrical properties of the prepared substrates were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that the best silanization reaction conditions to get Si/SiO₂/Si₃N₄-(SPy-PPy) substrate with high PPy adhesion and good electrical conductivity were obtained by using SPy at low concentration (4.3 mM) at 90°C. These promising findings open the way for fabrication of new hybrid materials which can be used as transducers in miniaturized sensing devices for various environmental and biomedical applications.     

Amorphous carbon nitride a-CNx microelectrode: Fabrication and characterization

Fabrication and characterization of amorphous carbon nitride a-CN_x microelectrodes are reported. These electrodes were prepared by DC-sputtering of a thin carbon layer on sharpened glass tip. The kinetic parameters (k⁰ and α) and the diffusion coefficient of the ferri-ferrocyanide redox probe were determined by steady-state voltammetry (CV) and by electrochemical impedance spectroscopy (EIS), and were used for characterizing both the electrochemical sensitivity of microelectrodes and their dimensions. The cathodic activation procedure of the electrode resulted in an increase of the electron rate constant. This procedure provides a new way for the fabrication of carbon microelectrodes for local electrochemical measurements.     

Growth of silicon thin film by LPE on porous silicon bilayers

The fabrication of solar cells based on the transfer of a thin silicon film on a foreign substrate is an attractive way to realise cheap and efficient photovoltaic devices. The aim of this work is to realise a thin mono-crystalline silicon film on a double porous silicon layer in order to detach and transfer it on mullite. The first step is the fabrication of a double porous silicon layer by electrochemical anodisation using two different current densities. The low current leads to a low porosity layer and during annealing, the recrystallisation of this layer allows epitaxial growth. The second current leads to a high porosity which permits the transfer on to a low cost substrate. Liquid Phase Epitaxy (LPE) performed with indium (or In+Ga) in the temperature range of 950–1050°C leads to almost homogeneous layers. Growth rate is about 0.35 μm min⁻¹. Crystallinity of the grown epilayer is similar on porous silicon and on single crystal silicon. In this paper, we focus on the realisation of porous silicon sacrificial layer and subsequent LPE growth. This revised version was published online in July 2006 with corrections to the Cover Date.     

Formation and characterization of DNA microarrays at silicon nitride substrates

A versatile method for direct, covalent attachment of DNA microarrays at silicon nitride layers, previously deposited by chemical vapor deposition at silicon wafer substrates, is reported. Each microarray fabrication process step, from silicon nitride substrate deposition, surface cleaning, amino-silanation, and attachment of a homobifunctional cross-linking molecule to covalent immobilization of probe oligonucleotides, is defined, characterized, and optimized to yield consistent probe microarray quality, homogeneity, and probe-target hybridization performance. The developed microarray fabrication methodology provides excellent (high signal-to-background ratio) and reproducible responsivity to target oligonucleotide hybridization with a rugged chemical stability that permits exposure of arrays to stringent pre- and posthybridization wash conditions through many sustained cycles of reuse. Overall, the achieved performance features compare very favorably with those of more mature glass based microarrays. It is proposed that this DNA microarray fabrication strategy has the potential to provide a viable route toward the successful realization of future integrated DNA biochips.     

Magnetron sputtering deposition of silicon nitride on polyimide separator for high-temperature lithium-ion batteries

To date,lithium-ion batteries are becoming increasingly significant in the application of portable devices and electrical vehicles,and revolutionary progress in theoretical research and industrial application has been achieved.However,the commercial polyolefin separators with unsatisfying electrolytes affinity and poor thermal stability have extremely restricted the further application of lithium-ion batteries,especially in the high-temperature fields.In this work,magnetron sputtering deposition technique is employed to modify the commercial polyimide separator by coating silicon nitride on both sides.Magnetron sputtering deposition modified polyimide(MSD-PI)composite separator shows high thermal stability and ionic conductivity.More importantly,compared with the cells using Celgard separator,the cells with MSD-PI separator exhibit superior electrochemical performance,especially long-term cycle performance under high temperature environment,owing to the high thermal conductivity of surface Si3 N4 particles.Hence,lithium-ion batteries with MSD-PI separator are capable of improving thermal safety and capacity retention,which demonstrates that magnetron sputtering deposition technique could be regarded as a promising strategy to develop advanced organic/inorganic composite separators for high-temperature lithium-ion batteries.     

CdS thin film: Synthesis and characterization

CdS thin films have been deposited by dip technique using succinic acid as a complexing agent. The structural characterizations of films have been studied by X-ray diffraction. X-ray diffraction pattern prove crystallinity of the deposited films that crystallize in the cubic phase of CdS. The films show high absorption and band gap value which were found to be 2.58 eV. The specific conductivity of the film was found to be in the order of 10^?7 (Ω cm)^?1.     

Fabrication and optical properties of gallium phosphide nanoparticulate thin film

The gallium phosphide (GaP) nanoparticulate thin films were fabricated by colloidal suspensions deposition with GaP nanoparticles dispersed in N,N-dimethylformamide (DMF). The microstructure and optical properties of the film have been studied by scanning electron microscopy, high resolution transmission electron microscope, and optical absorption and fluorescence spectra. The morphology of the film was found to be composed of nanoparticle aggregates, and with an irregularly rough surface. From the result of fluorescence, it can be established that the film not only retains the violet and blue light emissions which ascribed to transition from conduction band to valence band of gallium phosphide particles, but has an excellent luminescence property. The correlation between the optical properties and the microstructure of the thin film is discussed.     

Asymmetric electrochemical capacitor microdevice designed with vanadium nitride and nickel oxide thin film electrodes

Vanadium nitride thin film has been coupled with electrodeposited nickel oxide in order to design an electrochemical capacitor microdevice. VN has been used as negative electrode while NiO was used as the positive one in 1 M KOH electrolyte. VN exhibits a pseudo-capacitive behavior while NiO shows a faradaic behavior. This asymmetric microdevice has been operated between 0.5 and up to 1.8 V in aqueous based electrolyte (1 M KOH). Long term cycling ability (10,000 charge/discharge cycles) has been demonstrated with interesting energy (1.0 μW h cm^− 2) and power (40 mW cm^− 2) densities.     

Fabrication and optical property of silicon oxide layer coated semiconductor gallium nitride nanowires

Quasi one-dimensional GaN-SiO(2) nanostructures, with a silicon oxide layer coated on semiconductor GaN nanowires, were successfully synthesized through as-synthesized SiO(2) nanoparticles-assisted reaction. The experimental results indicate that the nanostructure consists of single-crystalline wurtzite GaN nanowire core, an amorphous SiO(2) outer shell separated in the radial direction. These quasi one-dimensional nanowires have the diameters of a few tens of nanometers and lengths up to several hundreds of micrometers. The photoluminescence spectrum of the GaN-SiO(2) nanostructures consists of one broad blue-light emission peak at 480 nm and another weak UV emission peak at 345 nm. The novel method, which may results in high yield and high reproducibility, is demonstrated to be a unique technique for producing nanostructures with controlled morphology.     

Spectroscopic study of a D.C. discharge in an argon-silane-nitrogen gas mixture under silicon nitride thin film deposition conditions

A detailed experimental investigation of a D.C. discharge in an argon-silanenitrogen gas mixture is undertaken using mainly spatially resolved spectroscopy. Discharge parameters are studied as functions of the gas mixture composition, and the influence of nitrogen concentration on the dissociation phenomena of SiH₄ and on dehydrogenation mechanisms of the growing film surface is particularly discussed.     

Mechanical properties of hydrogenated nanocrystalline silicon thin film with different indentation depths

Hydrogenated nanocrystalline silicon thin films were prepared on Corning 7059 glasses by plasma enhanced chemical vapor technique with radio frequency and direct current bias stimulation. The surface topography and microstructure of sample were characterized with atomic force microscopy and X‐ray diffraction. The mechanical properties of the samples were investigated by TriboIndenter nanosystem. The elastic modulus E and hardness H of samples were calculated by means of Oliver and Pharr analysis method. The results show that with increasing the indentation depth from 70 to 180 nm, the maximum applied load P_max increases from 500 to 2000 µN, while the elastic modulus E dives to 25 from 45 GPa, and the hardness H decreases from 4.9 to 3.8 GPa. After complete unloading, some plastic deformations occur on the films' surface and with the increase of the indentation depth, they become more obvious. This phenomenon is mainly connected with the film's growth mechanism. In this paper, we did an investigation and a discussion in detail about this phenomenon. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of trace metals in thin silicon nitride films by total-reflection X-ray fluorescence

The validity of a matrix withdrawal method for the analysis of trace metals in silicon nitride films on silicon wafers by total-reflection X-ray fluorescence has been evaluated with samples contaminated with diluted standard solutions of eight metals (Ca, V, Cr, Fe, Ni, Cu, Ta, W). The nitride matrix was removed by a decomposition step with HF vapor at ambient conditions followed by the vaporization of the product at a temperature higher than 240°C. The recovery of added metals was determined first directly after vaporization and secondly after preconcentration by the droplet collection (DC) method. The recovery of metals after vaporization at a temperature of 300±50°C was generally close to 100%, except for Cu whose recovery was approximately 40%. The efficiency of the DC step was approximately 50% for most metals but only 10–20% for Cu and Cr. Thus for most metals the total recovery was close to 50%, which is acceptable for analytical purpose. The recovery of Cu and Cr was studied in more detail considering the influence of the thickness of the nitride film, the vaporization temperature, and the composition of the DC solution. The total recovery of Cu increased from approximately 10 to 40% by lowering the temperature of the vaporization step and using a more concentrated DC solution. The recovery of Cr by DC was markedly influenced by the thickness of the nitride film with no great benefit of using a more concentrated DC solution.     

Fabrication of submicron scale patterned plastic thin film fluidic devices with controllable thickness

We present a soft-lithography based method to fabricate plastic thin film fluidic devices on glass and plastic substrates. Principles of soft-lithography and spin casting were used to generate the films. The thickness of these films is controllable and the patterns we have generated have submicron scale dimensions. By using commercially available compact disc (CD) components as molds, we have been able to generate parallel line and cross patterns on these thin films. These patterned films could be lifted from the substrates and further folded into rolls.     

Ellipsometric characterization of inhomogeneous non‐stoichiometric silicon nitride films

Variable‐angle spectroscopic ellipsometry is employed for the optical characterization of non‐stoichiometric silicon nitride thin films exhibiting inhomogeneity formed by refractive index and extinction index changes through the film thickness. For all the film samples, the best fit of the experimental data is achieved if, in addition to the inhomogeneity, an overlayer or roughness of the upper boundary is included. However, distinguishing of these two defects is found not to be possible. The influence of working gas ratio, deposition temperature and on/off time on the film properties is studied. The refractive index and extinction coefficient is found to increase with increasing working gas ratio and less significantly with decreasing deposition temperature. It is also found that the inhomogeneity increases with decreasing deposition temperature, and the deposition rate of the films decreases with increasing working gas ratio. The influence of the on/off time on the film properties is practically unimportant. Copyright © 2013 John Wiley & Sons, Ltd.     

Deposition of silicon nitride thin films by reaction of SiH4 in a nitrogen post-discharge

Silicon nitride thin films are deposited on silicon wafers at room temperature when silane gas is injected in a nitrogen flowing post-discharge. Reactive processes involving siane molecules and long-lifetime nitrogen species are studied, pointing out the nonreactivity of the N₂(A³ _u ⁺ ) metastable state, the low contribution of the vibrationally excited nitrogen ground-state molecules, and the high reactivity of N(⁴S) atoms. Spectroscopic observations performed in the reaction region are correlated with thin-film characteristics.     

Multi-element characterization of silicon nitride powders by atomic and mass spectrometric solution methods

A sample pretreatment technique for silicon nitride involving digestion and matrix/traces separation was developed by means of radiotracers and applied to analysis of this material by inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry and graphite furnace atomic absorption spectrometry. The results obtained for a high purity silicon nitride material by these methods are compared each with the other and with those obtained by neutron activation analysis. The limits of detection and the capabilities of the methods are compared and discussed.     

Fabrication and characterization of hexagonal boron nitride powder by spray drying and calcining-nitriding technology

Hexagonal boron nitride (hBN) powder was fabricated prepared by the spray drying and calcining-nitriding technology. The effects of nitrided temperature on the phases, morphology and particle size distribution of hBN powder, were investigated. The synthesized powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Fourier transformed infrared spectrum, ultraviolet-visible (UV-vis) spectrum and photoluminescence (PL) spectrum. UV-vis spectrum revealed that the product had one obvious band gap (4.7 eV) and PL spectrum showed that it had a visible emission at 457 nm (λ_ex=230 nm). FESEM image indicated that the particle size of the synthesized hBN was mainly in the range of 0.5-1.5 μm in diameter, and 50-150 nm in thickness. The high-energy ball-milling process following 900 °C calcining process was very helpful to obtain fully crystallized hBN at lower temperature.