Deposition and microhardness of SiC from the Si2Cl6-C3H8-H2-Ar system

We obtained SiC coating layers on a graphite substrate using hexachlorodisilane (Si₂Cl₆, boiling point 144° C) as a silicon source and propane as a carbon source. We examined the deposition conditions, contents of carbon, silicon and chlorine in the deposits, and the microhardness. Mirror-like amorphous silicon layers were deposited in the reaction temperature range 500 to 630° C. well-formed silicon carbide layers with good adherency to the substrate were obtained above 850° C. The lowest deposition temperature of SiC was estimated to be 750 to 800° C. The Vickers microhardness of the SiC layer was about 3800 kg mm^–2 at room temperature and 2150 kg mm^–2 at 1000° C.     

Electrochemical corrosion behavior of amorphous carbon nitride thin films

The corrosion behavior along with biocompatibility and mechanical properties plays an important role in determining of biomedical implants feasibility. Diamond-like carbon seems to be the promising material in which all these three requirements can be achieved. In this study nitrogen doped amorphous carbon (a-C:N) films were deposited on silicon and medical CoCrMo alloy substrates by vacuum glow discharge sputtering technique using different deposition conditions from graphite target. Potentiodynamic polarization tests were employed to assess the corrosion performances of the films at room temperature in 0.89 wt. % NaCl solution. The influence of substrate bias on the electrochemical corrosion behavior was investigated. The highest value off E_corr for CoCrMo substrate was measured on the coating deposited with substrate bias around −0.6 kV. The shift of E_corr to more positive values was about 350 mV.     

The Leidenfrost effect during spray pyrolysis of nickel oxide-gadolinia doped ceria composite thin films

NiO-Ce_0.8Gd_0.2O_1.9 − x (CGO) thin films were prepared by air blast spray pyrolysis with precursors containing nickel nitrate, cerium nitrate and gadolinium chloride in ethanol and a high boiling point organic solvent. Precursors containing solvents with boiling points between 120 and 314 °C were sprayed on sapphire, silicon, Foturan^®, yttria stabilized zirconia and CGO at different substrate surface temperatures.A maximum deposition temperature, above which film deposition ceased completely, was observed. The limiting temperature for film formation was correlated with the Leidenfrost phenomenon. At temperatures above the Leidenfrost point of the precursor, the sprayed droplets do not impact and spread on the substrate surface but levitate on a vapour cushion above the substrate and are swept away by the air stream. The Leidenfrost point of a precursor was found to depend on the solvent boiling point, the metal salt concentration and the thermal properties of the substrate expressed as the product of density, thermal conductivity and heat capacity. The maximum deposition temperature increased with increasing solvent boiling point or metal salt concentration and with decreasing product of density, thermal conductivity and heat capacity of the substrate.     

电化学法预处理硅基片提高金刚石成核密度的研究

通过用电化学法预先沉积一层碳膜的方法，利用热丝化学汽相沉积法使金刚石在光滑硅片上的成核密度达到１０７ｃｍ－２左右，与未镀碳膜相比提高了近３个数量级。文中还分析了可能的原因。     

Interface structure of sputter deposited CNx film on silicon substrate

Amorphous carbon nitride (CN_x, x = 0.05) films were reactively sputtered on Si(100) substrate, and the interface structure was studied by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). In cross-sectional TEM a gray interlayer about 5 nm thick between the bulk CN_x film and silicon substrate is observed, and the interface is dense. A little Si impurity (< 1 at.%) is revealed in the films deposited for short time (7 s and 17 s) by XPS measurement. The in-depth XPS analyses indicate that there exists an interlayer with Si impurity above, and a sub-surface layer with C and N below the original surface of silicon substrate. The two layers have different chemical composition and bonding state.     

Formation and characterization of Si5C3 type silicon carbide by carbon ion implantation with a MEVVA ion source

A Si₅C₃ type silicon carbon has been prepared via carbon ion implantation into silicon substrate using a MEVVA ion source. Carbon ions were implanted into silicon substrate at a fluence of 5 × 10¹⁷ ions/cm² and then the as-implanted samples were annealed at 1250 °C for 2 h. The thermal annealing produced a silicon carbide layer on the surface of silicon substrate. The results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirm the existence of Si₅C₃, rather than SiC. The results of Fourier transform infrared reflection (FTIR) and Raman spectroscopy analyses show that the Si–C vibration frequency in crystalline Si₅C₃ is slightly less than that in crystalline β-SiC.     

Si diffusion in magnetron sputtered silicon carbide films deposited on silicon and carbon substrates

Self-diffusion of silicon in magnetron sputtered silicon carbide films deposited on different substrates (crystalline silicon and glassy carbon) is investigated. Since crystallization of amorphous silicon carbide films strongly depends on the substrate, the diffusivity of silicon is expected to depend on the substrate as well. Isotope hetero-structures and secondary ion mass spectrometry were used for analysis. For amorphous samples an upper limit of the diffusivity of 1 × 10^− 21 m²/s is derived at 1100 C°. For crystallized films diffusivities between 1350 °C and 1600 °C are found to be not significantly different for the two types of substrates. For samples deposited on glassy carbon substrates an activation enthalpy ΔH_D = (8.7 ± 0.9) eV was found for the self-diffusion of Si. The consequences of our findings for crystallization are discussed.     

Nanocrystalline SiC films prepared by direct deposition of carbon and silicon ions

The method of direct deposition of carbon and silicon ions was used for preparation of nanocrystalline silicon carbide films. The deposition energy of carbon and silicon ions was 90 eV. The effect of substrate temperature in the range of 500-1150 °C on the structure of SiC films was studied by means of X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD). According to XPS data, the films contained heterobonded Si-C atoms and homobonded Si-Si and C-C atoms, the relation between which varied as the function of substrate temperature. The data of XRD showed a noticeable growth of a nanocrystalline phase of cubic silicon carbide in the films at a temperature of about 700 °C. The content of 3C-SiC nanocrystalline phase reached 80 at.% at 950 °C. There was an established change from cubic polytype to rhombohedral polytype of silicon carbide α-SiC-21R at a substrate temperature higher than 1000 °C. The size of SiC crystal grains depended on the substrate temperature and changed from 4-5 up to 8-10 nm over the range of 700-950 °C. Besides, silicon unbonded with carbon also crystallized in nanocrystalline form with similar sizes of crystal grains. A possible model of the change of the polytypic composition of SiC film under the conditions of direct ion deposition was discussed.     

Structural, electrical, and optical studies on rapid thermally processed ferroelectric BaTiO3 thin films prepared by metallo-organic solution deposition technique

Polycrystalline BaTiO₃ thin films having the perovskite structure were successfully produced on platinum coated silicon, bare silicon, and fused quartz substrate by the combination of the metallo-organic solution deposition technique and post-deposition rapid thermal annealing treatment. The films exhibited good structural, electrical, and optical properties. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) and metal-ferroelectric-semiconductor (MFS) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 255 and 0.025, respectively, and the remanent polarization and coercive field were 2.2 μC cm⁻² and 25 kV cm⁻¹, respectively. The resistivity was found to be in the range 10¹⁰–10¹² Ω·cm, up to an applied electric field of 100 kV cm⁻¹, for films annealed in the temperature range 550–700 °C. The films deposited on bare silicon substrates exhibited good film/substrate interface characteristics. The films deposited on fused quartz were highly transparent. An optical band gap of 3.5 eV and a refractive index of 2.05 (measured at 550 nm) was obtained for polycrystalline BaTiO₃ thin film on fused quartz substrate. The optical dispersion behavior of BaTiO₃ thin films was found to fit the Sellmeir dispersion formula well.     

Preparation and tribological properties of novel carbon nanotube self-assembled composite films

Carbon nanotube (CNT) composite thin films were prepared on a single-crystal silicon substrate by a self-assembling process from a specially formulated solution. Rare earth solution (RES) surface modification and appropriate acid-treatment methods were used to functionalise carbon nanotubes (CNTs). Silane coupling regent (3-mercaptopropyl trimethoxysilane (MPTS)) was prepared first. The terminal thiol groups (–SH) in the film was oxidised to sulphonic acid groups (–SO₃H) in situ to enhance the film with good chemisorption ability. Treated Caron nanotubes were deposited on the oxidised MPTS–SAM by means of chemisorption with the SO₃H group. The surface energy, chemical composition, phase transformation and surface morphology of the films were analysed using contact angle measurements, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atomic force microscopy. As a result, a conclusion could be made that some lanthanum elements react with –SO₃H groups on the surface of the substrate by a chemical bond, which will improve the bonding strength between the films and the CNTs. Since the CNT thin films were well adhered to the silicon substrate, it might find promising application in the surface-modification of single-crystal Si and SiC in microelectromechanical systems (MEMS).     

内嵌叠氮化铜碳纳米管复合含能材料的制备与表征

叠氮化铜是一种绿色环保的高能含能材料，其极高的静电感度限制了它在MEMS火工品微型装药中的应用。碳纳米管优异的导电性可以有效地降低叠氮化铜的静电感度，而且取向一致、高机械强度的碳纳米管可以有效地提高叠氮化铜的安全性和爆轰输出能量。本文中，设计并制备了基于硅基底及多孔氧化铝模板的内嵌叠氮化铜碳纳米管复合含能材料，探究了合适的制备条件，并对样品进行了表征分析。结果表明:在氧化电压45 V、沉积电流密度0.1 mA/cm²条件下制备的复合材料,经72 h叠氮化反应后得到的内嵌叠氮化铜碳纳米管复合含能材料在静电感度仪测试范围（≤25 kV）内均未发火，有望作为一种新型含能装药应用于MEMS器件中。     

Influence of carbide formation on the strength of carbon fibres on which silicon and titanium have been deposited

Silicon or titanium was deposited on the filaments of carbon fibres by chemical vapour depositions and the reactions between the deposited silicon or titanium and the carbon fibres were investigated below 1300° C. Between the silicon and the carbon fibres, -SiC layers formed at rates of 1.5 to 3 nm in 3 h at 1300° C. These rates were 10^–4 times that of the TiC formation by the reaction of titanium with carbon fibre. Furthermore, the effect of the reaction on fibre strength was investigated. By reaction with silicon, the carbon fibre at a carbonized stage decreased in strength at the beginning of the reaction, but afterwards it recovered to the original level. The carbon fibre at a graphitized stage maintained its original strength after heat treatment for several hours at 1300° C. With the TiC-coated carbon fibres, the carbon fibres decreased in strength following the relation _m d ^–1/2, where d is the thickness of the TiC layer.     

Modification of silicon substrate using low-energy proton beam for selective growth of CNTs

A 3 keV low-energy proton beam was used to irradiate a silicon substrate for selective modification. The water contact angle measurement, chemical etching test with HF and the auger electron spectroscopy were used to investigate the chemical properties and the material composition of the proton beam-irradiated silicon substrate. The proton beam-irradiated silicon substrate was covered with a silicon oxide layer of about 60-70 angstroms due to the incorporation of oxygen molecules after exposure to ambient air. The silicon oxide layer produced by the proton beam was highly resistant to HF treatment which typically used to remove the silicon oxide on a substrate, and the surface of it was more hydrophilic than the native silicon oxide removed silicon surface with Si-H surface group. For the selective growth of carbon nanotubes (CNTs), the silicon oxide pattern was easily fabricated via proton beam irradiation when the silicon substrate was covered with a shadow mask. The Fe-Mo bimetallic catalysts for the growth of CNTs were adsorbed onto the silicon oxide layer, which is more hydrophilic than the silicon surface. The CNTs were grown on the patterned substrate using a chemical vapor deposition method, and it was confirmed by scanning electron microscopy.     

Vapor-solid-solid growth of crystalline silicon nanowires using anodic aluminum oxide template

Silicon nanowires (SiNWs) were grown at low temperatures close to metal silicon eutectic point on a silicon substrate using gold catalyst coupled with assistance of the aluminum anodic oxide template. Either a vapor-solid-solid (VSS) growth process below metal silicon eutectic temperature or a vapor-liquid-solid (VLS) process at slightly higher temperatures was observed. The transmission electron microscopy coupled with both the X-ray energy dispersive spectroscopy and the selected area electron diffraction was adopted to characterize the SiNWs. Although the mechanism triggering the VSS process is still not clear, both the geometric and morphological characteristics of the SiNWs grown by the VSS process are discussed and compared with the SiNWs grown by the VLS process. The VSS SiNWs have a much slower growth rate (less than 100 nm/h), a smaller and more uniform diameter (in the range of 15.22 nm) due to a much slower rate of silicon diffusion and much smaller amount of silicon (6.8 wt.%) dissolved in the solid nanocatalyst.     

Preparation of diamond-like carbon films by cathodic micro-arc discharge in aqueous solutions

Diamond-like carbon films (DLC) and silicon doped diamond-like carbon films were deposited on Ni substrate by cathodic micro-arc discharge at room temperature in aqueous solutions. The deposit potential was 130 V. The structure of the films was characterized by a scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Raman spectra and XPS analysis demonstrated that the films were diamond-like carbon clearly. SEM observation showed that the DLC films were uniform and the thickness was about 200 nm. Potentiodynamic polarization curve indicated the corrosion resistance of the Ni substrate was markedly improved by DLC films.     

等离子体源离子注入法制备类金刚石薄膜

用等离子体源注入(PSII)在Si(100)上制备类金刚石膜，放电气体采用CH4，用微波电子回旋共振(ECR)产生等离子体。将-20～-30kV的高压加在衬底上，来提高离子的能量。通过Raman光谱和FT-IR光谱检测了类金刚石膜的化学组成及状态，并对其机械性能和表面形貌进行了检测。结果显示，硅片硬度和摩擦因数得到了改善，用PSII能够制备出性能优良的膜，可以将其应用到微电子器件(MEMS)上去。     

Broad band photoluminescence studies of diamond layers grown by hot-filament CVD

Photoluminescence and Raman spectroscopy were employed to investigate the broad band luminescence in thin diamond films grown on a silicon substrate by the HF CVD technique. The broad band luminescence with a maximum emission at 1.8–2 eV observed for CVD diamonds is characteristic for amorphous carbon with sp²-hybridized carbon bonds. As was shown by the Raman spectroscopy our diamond layer contained certain amounts of amorphous carbon phase and diamond nanocrystals which were the source of an additional energy state within the diamond energy gap. The experimental results precluded the possibility of broad band luminescence being due to the electron–lattice interaction. The amorphous carbon and diamond nanocrystals admixture in polycrystalline diamond layer introduced a defect state in the energy gap not in the form of point defects but rather in the form of a line or extended defects. In consequence these extended defects were responsible for the broad PL spectrum in the CVD diamond films.     

Preparation and R-curve properties of laminated Si/SiC ceramics from paper

Laminated Si/SiC ceramics were synthesized from paper via impregnation with phenolic resin, followed by lamination and carbonization of the paper–resin laminates and subsequent infiltration and reaction with liquid silicon at a temperature of 1550 °C for 10–90 min. Due to the capillarity infiltration and in situ reaction with liquid silicon, intrinsic micro- and macrostructure in the carbon preform was retained within the final ceramics. The XRD, TGA, and microscopy analysis indicated that the final material exhibited a distinguished laminar structure with alternating arrangement of SiC and silicon layers. The thick SiC layer was composed of beta-SiC and a little of free silicon and un-reacted carbon. Studies on the evaluation of R-curves behavior by the indentation-strength method indicated a strong R-curve behavior for the Si/SiC composites.     

Formation of graphene by the thermal annealing of a graphite layer on silicon substrate in vacuum

In this letter we present our preliminary results about the preparation of graphene and carbon nanosheets by thermal annealing of graphite layer on silicon substrate in vacuum and at temperature 900 °C. The surface area of about several tens of micrometers and curved at the ends. The carbon nanosheets are very clean and look like a piece of paper. Investigations with Raman showed three main peaks D, G, G′ and small peak at 2420 cm⁻¹. This method is considered to be a simple and cheap method for preparing the carbon nanosheets directly on the silicon substrate for the application in the electronics.     

Interfacial transformations in the a-SiC/a-Si/6H-SiC structure caused by high-temperature (1500°C) annealing

We have studied the reactions that take place at interfaces in an a-SiC/a-Si/6H-SiC sandwich structure, which was obtained by the sequential deposition of amorphous silicon (a-Si) and amorphous silicon carbide (a-SiC) onto a 6H-SiC substrate by ion sputtering in vacuum and then annealed at 1500°C (i.e., above the melting point of silicon). It is shown that the annealing leads to complete îdissipationî of the silicon film in SiC, probably as a result of the dissolution of carbon in the silicon melt and the diffusion of silicon into SiC.