The analysis of structural and electronic environments of silicon network in HWCVD deposited a-SiC:H films

Hydrogenated amorphous silicon carbon alloys (a-SiC:H) films were deposited by hot wire chemical vapour deposition (HWCVD) using SiH₄ and C₂H₂ as precursor gases. a-SiC:H films were characterized by Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Solid-state plasmon of Si network shifts from 19.2 to 20.5 eV by varying C₂H₂ flow rate from 2 to 10 sccm. Incorporation of carbon content changes the valence band structure and s orbital is more dominant than sp and p orbital with carbon incorporation.     

Structure and hardness of a-C:H films prepared by middle frequency plasma chemical vapor deposition

a-C:H films were prepared by middle frequency plasma chemical vapor deposition (MF-PCVD) on silicon substrates from two hydrocarbon source gases, CH₄ and a mixture of C₂H₂ + H₂, at varying bias voltage amplitudes. Raman spectroscopy shows that the structure of the a-C:H films deposited from these two precursors is different. For the films deposited from CH₄, the G peak position around 1520 cm⁻¹ and the small intensity ratio of D peak to G peak (I(D)/I(G)) indicate that the C-C sp³ fraction in this film is about 20 at.%. These films are diamond-like a-C:H films. For the films deposited from C₂H₂ + H₂, the Raman results indicate that their structure is close to graphite-like amorphous carbon. The hardness and elastic modulus of the films deposited from CH₄ increase with increasing bias voltage, while a decrease of hardness and elastic modulus of the films deposited from a mixture of C₂H₂ + H₂ with increasing bias voltage is observed.     

Electrochemical corrosion behaviors of a-C:H and a-C:NX:H films

The a-C:H and a-C:N_X:H films were deposited onto silicon wafers using radio frequency (rf) plasma enhanced chemical vapor deposition (PECVD) and pulsed-dc glow discharge plasma CVD, respectively. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize chemical nature and bond types of the films. The results demonstrated that the a-C:H film prepared by rf-CVD (rf C:H) has lower I_D/I_G ratio, indicating smaller sp² cluster size in an amorphous carbon matrix. The nitrogen concentrations of 2.9 at.% and 7.9 at.% correspond to carbon nitride films prepared with rf and pulse power, respectively.Electrochemical corrosion performances of the carbon films were investigated by potentiodynamic polarization test. The electrolyte used in this work was a 0.89% NaCl solution. The corrosion test showed that the rf C:H film exhibited excellent anti-corrosion performance with a corrosion rate of 2 nA cm⁻², while the carbon nitride films prepared by rf technique and pulse technique showed a corrosion rate of 6 nA cm⁻² and 235 nA cm⁻², respectively. It is reasonable to conclude that the smaller sp² cluster size of rf C:H film restrained the electron transfer velocity and then avoids detriment from the exchange of electrons.     

Chemical and morphological difference between TiN/DLC and a-C:H/DLC grown by pulsed vacuum arc techniques

In order to improve the adherence of DLC films, interlayers of amorphous hydrogenated carbon (a-C:H) and titanium nitride (TiN) were deposited by means of the pulsed vacuum arc technique. Bilayers were obtained by using a carbon target of 99.98% of purity in mixtures of (Ar + CH₄) and (Ar + H₂) for producing a-C and DLC, respectively and a target of titanium of 99.999% in a mixture of (Ar + N₂) for growing TiN. After the deposition, chemical and morphological differences between TiN/DLC and a-C:H/DLC bilayers grown on silicon and stainless steel 304 were studied using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and scanning probe microscopy (SPM) techniques. XPS analysis showed a difference in sp³/(sp²+sp³) bonds ratio for each bilayer, being 0.67 for TiN/DLC and 0.45 for a-C:H/DLC bilayers. sp³ and sp² bonds were also observed by the FTIR technique. SPM images, in atomic force microscopy (AFM) and lateral force microscopy (LFM) modes were carried out for illustrating the comparison between TiN/DLC and a-C/DLC morphologic characteristics. Roughness and grain size were studied as a function of the H₂ concentration for both bilayers.     

Structure and elastic recovery of Cr-C:H films deposited by a reactive magnetron sputtering technique

Cr-containing hydrogenated amorphous carbon (Cr-C:H) films were deposited on silicon substrates using a DC reactive magnetron sputtering with Cr target in an Ar and C₂H₂ gas mixture. The composition, bond structure, mechanical hardness and elastic recovery of the films were characterized using energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and nano-indentation. The film tribological behavior was also studied by a ball-on-disc tribo-tester. The results showed that the films deposited at low C₂H₂ flow rate (<10 sccm) presented a feature of composite Cr-C:H structure, which consisted of hard brittle chromium carbide phases and amorphous hydrocarbon phase, and thus led to the observed low elastic recovery and poor wear resistance of the films. However, the film deposited at high C₂H₂ flow rate (40 sccm) was found to present a typical feature of polymer-like a-C:H structure containing a large amount of sp³ C-H bonds. As a result, the film revealed a high elastic recovery, and thus exhibited an excellent wear resistance.     

Effect of H2 dilution on a-CN:H films deposited by hot-wire chemical vapor deposition

Hydrogenated amorphous carbon nitride (a-CN:H) thin films were deposited by hot-wire chemical vapor deposition (HWCVD) using the gas mixture of CH₄, NH₃ and H₂ precursor gases. The structural and electronic environments studies of H₂ diluted a-CN:H films were carried out by Raman spectroscopy and X-ray photoelectron spectroscopy. The nitrogen content increases while the total carbon contents decreases with increase in H₂ flow rate from 0 sccm to 20 sccm in the a-CN:H films. Moreover, the detail analysis of the carbon core orbital, valence band and hole states of a-CN:H were discussed with different H₂ flow rate.     

Local chemical transformations in poly(dimethylsiloxane) by irradiation with 248 and 266 nm

Poly(dimethylsiloxane) (PDMS) has been irradiated with a frequency quadrupled Nd:YAG laser and a KrF^*-excimer laser at a repetition rate of 1 Hz. The analysis of ablation depth versus pulse number data reveals a pronounced incubation behavior. The thresholds of ablation (266 nm: 210 mJ cm⁻², 248 nm: 940 mJ cm⁻²) and the corresponding effective absorption coefficients α_eff (266 nm: 48900 cm⁻¹, 248 nm: 32700 cm⁻¹, α_lin = 2 cm⁻¹) were determined. The significant differences in the ablation thresholds for both irradiation wavelengths are probably due to the different pulse lengths of both lasers. Since the shorter pulse length yields a lower ablation threshold, the observed incubation can be due to a thermally induced and/or a multi-photon absorption processes of the material or impurities in the polymer.Incubation of polymers is normally related to changes of the chemical structure of the polymer. In the case of PDMS, incubation is associated with local chemical transformations up to several hundred micrometers below the polymer surface. It is possible to study these local chemical transformations by confocal Raman microscopy, because PDMS is transparent in the visible. The domains of transformation consist of carbon and silicon, as indicated by the appearance of the carbon D- and G-bands between 1310 and 1610 cm⁻¹, a band appearing between 502 and 520 cm⁻¹ can be assigned to mono- and/or polycrystalline silicon.The ablation products, which are detected in the surroundings of the ablation crater consist of carbon and amorphous SiO_x (x ≈ 1.5) as detected by infrared spectroscopy.     

The reaction of allyl radicals with oxygen atoms—rate coefficient and product branching

The primary product formation of the C₃H₅ + O reaction in the gas phase has been studied at room temperature. Allyl radicals (C₃H₅) and O atoms were generated by laser flash photolysis at λ = 193 nm of the precursors C₃H₅Cl, C₃H₅Br, C₆H₁₀ (1,5-hexadiene), and SO₂, respectively. The educts and the products were detected by using quantitative FTIR spectroscopy. The combined product analysis of the experiments with the different precursors leads to the following relative branching fractions: C₃H₅ + O → C₃H₄O + H (47%), C₂H₄ + H + CO (41%), H₂CO + C₂H₂ + H (7%), CH₃CCH + OH and CH₂CCH₂ + OH (<5%). The rate of reaction has been studied relative to CH₃OCH₂ + O and C₂H₅ + O in the temperature range from 300 to 623 K. Here, the radicals were produced via the fast reactions of propene, dimethyl ether, and ethane, respectively, with atomic fluorine. Laser-induced multiphoton ionization combined with TOF mass spectrometry and molecular beam sampling from a flow reactor was used for the specific and sensitive detection of the C₃H₅, C₂H₅, and CH₃COCH₂ radicals. The rate coefficient of the reaction C₃H₅ + O was derived with reference to the reaction C₂H₅ + O leading to k(C₃H₅ + O) = (1.11 ± 0.2) × 10¹⁴ cm³/(mol s) in the temperature range 300-623 K. The C₃H₅ + O rate and channel branching, when incorporated in a suitable detailed reaction mechanism, have a large influence on benzene and allyl concentration profiles in fuel-rich propene flames, on the propene flame speed, and on propene ignition delay times.     

The influence of H2/(H2 + Ar) ratio on microstructure and optoelectronic properties of microcrystalline silicon films deposited by plasma-enhanced CVD

Hydrogenated microcrystalline silicon films were deposited by glow discharge decomposition of SiH₄ diluted in mixed gas of Ar and H₂. By investigating the dependence of the film crystallinity on the flow rates of Ar and H₂, we showed that the addition of Ar in diluted gas markedly improves the crystallinity due to an enhanced dissociation of SiH₄. The infrared-absorption spectrum reveals that the fraction of SiH bonding increases with increasing the rate ratio of H₂/(H₂ + Ar). The surface roughness of the films increases with increasing the flow rate ratio of H₂/(H₂ + Ar), which is attributed to the decrease of massive bombardment of Ar ions in the plasma. Refractive index and absorption coefficient of the films were obtained by simulating the optical transmission spectra using a modified envelope method. Electrical measurements of the films show that the dark conductivity increases and the activation energy decreases with the ratio of H₂/(H₂ + Ar). A reasonable explanation is presented for the dependence of the microstructure and optoelectronic properties on the flow rate ratio of H₂/(H₂ + Ar).     

Enhanced sonochemical degradation of azure B dye by the electroFenton process

The degradation of azure B dye (C₁₅H₁₆ClN₃S; AB) has been studied by Fenton, sonolysis and sono-electroFenton processes employing ultrasound at 23 kHz and the electrogeneration of H₂O₂ at the reticulated vitreous carbon electrode. It was found that the dye degradation followed apparent first-order kinetics in all the degradation processes tested. The rate constant was affected by both the pH of the solution and initial concentration of Fe²⁺, with the highest degradation obtained at pH between 2.6 and 3. The first-order rate constant decreased in the following order: sono-electroFenton > Fenton > sonolysis. The rate constant for AB degradation by sono-electroFenton is ∼10-fold that of sonolysis and ∼2-fold the one obtained by Fenton under silent conditions. The chemical oxygen demand was abated ∼68% and ∼85% by Fenton and sono-electroFenton respectively, achieving AB concentration removal over 90% with both processes.     

Study on effects of substrate temperature on growth and structure of alignment carbon nanotubes in plasma-enhanced hot filament chemical vapor deposition system

Alignment carbon nanotubes (ACNTs) were synthesized on silicon substrate coated with Ni catalyst film and Ta buffer layer by plasma-enhanced hot filament chemical vapor deposition using CH₄, NH₃, and H₂ as the reaction gas, and they were investigated by scanning electron microscopy and transmission electron microscopy. It is found that the diameter of the bamboo-structured ACNTs is increased from 62 to 177 nm when the substrate temperature was changed from 626 to 756 °C. Their growth rate is enhanced by the substrate temperature in a range of 626-683 °C and it is reversely reduced with the substrate temperature after the substrate temperature is over 683 °C. Beginning with wetting phenomenon, the effects of the substrate temperature on the structure and growth rate of the ACNTs are analyzed.     

Carbon molecular sieves from carbon cloth: Influence of the chemical impregnant on gas separation properties

Carbon materials with molecular sieve properties (CMS) were prepared by pyrolysis of cotton fabrics by chemical activation procedures. To evaluate the changes in the chemical and textural properties, the impregnants AlCl₃, ZnCl₂ and H₃PO₄ were used at 1123 K. The materials were characterized using adsorption of nitrogen and carbon dioxide, TPD, and immersion calorimetry in C₆H₆. Adsorption kinetics of O₂, N₂, CO₂, CH₄, C₃H₈ and C₃H₆ were measured in all the prepared materials to determine their behaviour as molecular sieves. The results confirm that the chemical used as impregnant has a significant effect on the resulting CMS separation properties. All materials exhibit microporosity and low oxygen surface group contents; however, the sample impregnated with zinc chloride, with an immersion enthalpy value of 66.4 J g⁻¹ in benzene, exhibits the best performance in the separation of CH₄-CO₂ and C₃H₈-C₃H₆ at 273 K.     

Intrinsic mechanical properties of ultra-thin amorphous carbon layers

In this work, we extracted the film's hardness (H_F) of ultra-thin diamond-like carbon layers by simultaneously taking into account the tip blunting and the substrate effect. As compared to previous approaches, which did not consider tip blunting, this resulted in marked differences (30-100%) for the H_F value of the thinner carbon coatings. We find that the nature of the substrate influences this intrinsic film parameter and hence the growth mechanisms. Moreover, the H_F values generally increase with film thickness. The 10 nm and 50 nm thick hydrogenated amorphous carbon (a-C:H) films deposited onto Si have H_F values of, respectively, ∼26 GPa and ∼31 GPa whereas the 10 nm and 50 nm thick tetrahedral amorphous carbon (t-aC) films deposited onto Si have H_F values of, respectively, ∼29 GPa and ∼38 GPa. Both the a-C:H and t-aC materials also show higher density and refractive index values for the thicker coatings, as measured, respectively by X-ray reflectometry and optical profilometry analysis. However, the Raman analysis of the a-C:H samples show bonding characteristics which are independent of the film thickness. This indicates that in these ultra-thin hydrogenated carbon films, the arrangement of sp² clusters does not relate directly to the hardness of the film.     

Preparation of ZrC nano-particles reinforced amorphous carbon composite coating by atmospheric pressure chemical vapor deposition

To eliminate cracks caused by thermal expansion mismatch between ZrC coating and carbon-carbon composites, a kind of ZrC/C composite coating was designed as an interlayer. The atmospheric pressure chemical vapor deposition was used as a method to achieve co-deposition of ZrC and C from ZrCl₄-C₃H₆-H₂-Ar source. Zirconium tetrachloride (ZrCl₄) powder carrier was especially made to control accurately the flow rate. The microstructure of ZrC/C composite coating was studied using analytical techniques. ZrC/C coating shows same morphology as pyrolytic carbon. Transmission electron microscopy (TEM) shows ZrC grains with size of 10-50 nm embed in turbostratic carbon. The formation mechanism is that the growth of ZrC crystals was inhibited by surrounding pyrolytic carbon and kept as nano-particles. Fracture morphologies imply good combination between coating and substrate. The ZrC crystals have stoichiometric proportion near 1, with good crystalline but no clear preferred orientation while pyrolytic carbon is amorphous. The heating-up oxidation of ZrC/C coating shows 11.58 wt.% loss. It can be calculated that the coating consists of 74.04 wt.% ZrC and 25.96 wt.% pyrolytic carbon. The average density of the composite coating is 5.892 g/cm³ by Archimedes’ principle.     

Structural, vibrational and dielectric properties of new potassium hydrogen sulfate arsenate: K4(SO4)(HSO4)2(H3AsO4)

A new compound, K₄(SO₄)(HSO₄)₂(H₃AsO₄) was synthesized from water solution of KHSO₄/K₃H(SO₄)₂/H₃AsO₄. This compound crystallizes in the triclinic system with space group P1¯ and cell parameters: a=8.9076(2) Å, b=10.1258(2) Å, c=10.6785(3) Å; α=72.5250(14)°, β=66.3990(13)°, γ=65.5159(13)°, V=792.74(3) Å³, Z=2 and ρ_cal=2.466 g cm⁻³. The refinement of 3760 observed reflections (I>2σ(I)) leads to R₁=0.0394 and wR₂=0.0755. The structure is characterized by SO₄²⁻, HSO₄⁻ and H₃AsO₄ tetrahedra connected by hydrogen bridge to form two types of dimer (H(16)S(3)O₄⁻?S(1)O₄²⁻ and H(12)S(2)O₄⁻?H₃AsO₄). These dimers are interconnected along the [1¯ 1 0] direction by the hydrogen bonds O(3)-H(3)?O(6). They are also linked by the hydrogen bridge assured by the hydrogen atoms H(2), H(3) and H(4) of the H₃AsO₄ group to build the chain S(1)O₄?H₃AsO₄ which are parallel to the “a” direction. The potassium cations are coordinated by eight oxygen atoms with K-O distance ranging from 2.678(2) to 3.354(2) Å.Crystals of K₄(SO₄)(HSO₄)₂(H₃AsO₄) undergo one endothermic peak at 436 K. This transition detected by differential scanning calorimetry (DSC) is also analyzed by dielectric and conductivity measurements using the impedance spectroscopy techniques. The obtained results show that this transition is protonic by nature.     

Solar cell fabrication using edge-defined film-fed growth (EFG) silicon wafers

The insufficient supply of polysilicon is limiting the growth of the segment of the photovoltaic industry using silicon materials. Because it is grown directly in the form of ribbon from a silicon melt, edge-defined film-fed growth (EFG) silicon ribbon is a promising alternative for cutting down wafer costs by reducing the polysilicon consumption and eliminating kerf loss. In this paper, we will discuss the various properties that can be achieved with for low cost and high-efficiency EFG silicon ribbon solar cell fabrication. Boron-doped p-type EFG ribbon silicon wafers with resistivities of 2-4 Ω cm and a size of 125 mm × 125 mm were used. The major fabrication steps we studied were mixed acid (HF, HNO₃, DI water) texturing, phosphorus diffusion with POCl₃, thermal oxide growth for surface passivation, laser process for edge isolation, and PECVD of SiN_x:H for surface passivation and antireflection coating. By optimizing the processing steps, we achieved a conversion efficiency, open circuit voltage, short circuit current, and fill factor as high as 14.5%, 584 mV, 32.1 mA/cm², and 77%, respectively.     

Field emission properties of carbon nanotubes grown on silicon nanowire arrays

Carbon nanotubes are synthesized on the silicon nanowire arrays which are fabricated on silicon substrate by chemical vapor depositing SiCl₄ and H₂ gases in the presence of Au catalysts. The silicon nanowires are single-crystal with lengths up to 100 μm and diameters ranging from 50 to 500 nm. The tangled carbon nanotubes are grown directly from the surface of Si nanowires. The field emission properties of the carbon nanotubes are investigated at the gap of 200 μm. The low turn on and threshold fields are obtained. The stabilization of the emission currents is also presented.     

Surface modification of calcium fluoro and hydroxyapatite by 1-octylphosphonic dichloride

The reactivity of the surface of calcium hydroxyapatite (CaHAp) and fluorapatite (CaFAp) was tested and compared by grafting the 1-octylphosphonic dichloride (C₈H₁₇OPCl₂) using a molar ratio x = 2 or 4, x = n(organic)/n(apatite). Successful synthesis was confirmed by different characterisation techniques such as X-ray powder diffraction patterns, IR spectroscopy, MAS-NMR (¹H and ³¹P) and chemical analysis.The difference between their specific surface area (SSA: 57.46 for HAp and 12.09 m²/g for FAp), the percentage of carbon measured after treatment with (C₈H₁₇OPCl₂) and the intensities of IR bands attributed to the grafted moiety suggests that the surface of hydroxyapatite is more reactive than that of fluorapatite.The ³¹P CP-MAS-NMR spectra of treated fluorapatite show a significant change in isotropic signal due to the protonation and deprotonation of superficial phosphate group. This can be explained by the difference in the nature of inorganic material.     

Structural and luminescence properties of [Ln(ODA)(phen)·4H2O] complexes (Ln=Sm and Dy, ODA=oxydiacetate, phen=1,10-phenanthroline)

Two novel complexes of Sm(III) and Dy(III) with mixed oxydiacetate (ODA) and 1,10-phenanthroline (phen) ligands were synthesized and their structure and luminescence properties were characterized. The complexes of [Ln(ODA)(phen)·4H₂O]Cl·5H₂O [Ln=Sm and Dy] crystallize in the monoclinic space group P2₁/n with Sm: a=12.3401(14) Å, b=16.821(2), c=12.6847(11) Å, β=107.939(10)°, V=2505.0(5) Å³, Z=4 and ρ=1.841 mg/m³, and with Dy: a=12.289(7) Å, b=16.805(6) Å, c=12.705(4) Å, β=108.144(18)°, V=2493.4(19) Å³, Z=4 and ρ=1.786 mg/m³. The complexes of [Sm(ODA)(phen)·4H₂O]⁺ and [Dy(ODA)(phen)·4H₂O]⁺ excited by UV light produce orange red and lightly white emissions, respectively, via the nonradiative energy transfer from phen to the metals. The quantum yield of the sensitized luminescence of [Dy(ODA)(phen)·4H₂O]⁺ (Q=19%) is much greater than that of [Sm(ODA)(phen)·4H₂O]⁺ (Q=1.4%). The luminescence decay times of the complexes were in a few microsecond range and independent of temperature.     

Low-temperature oxidation of SiGe by liquid-phase deposition

Low-temperature silicon dioxide (SiO₂) films were grown on silicon germanium (SiGe) surfaces using the liquid-phase deposition (LPD) method. The growth solutions of LPD-SiO₂ are hydrofluorosilicic acid (H₂SiF₆) and boric acid (H₃BO₃). It was found that the growth rate increases with increasing temperature and concentration of H₃BO₃. The Auger electron spectroscopy profile shows that no pileup of Ge atoms occurs at the interface of SiO₂/SiGe after the LPD-SiO₂ growth. Al/LPD-SiO₂/p-SiGe MOS capacitors were prepared to determine capacitance-voltage (C-V) and current-voltage (I-V) characteristics. In our experiments, a low leakage current density of 8.69 × 10⁻⁹ A/cm² under a 2 MV/cm electric field was observed. Such a value is much smaller than those of plasma- and thermal-oxides as a result of no plasma damage and a lower growth temperature. Moreover, lower oxide charges and interface charge densities of 3.82 × 10¹⁰ cm⁻² and 1.12 × 10¹¹ eV⁻¹ cm⁻², respectively, were achieved in our LPD-SiO₂ compared to direct photochemical-vapor-deposition-SiO₂.