Hydrogen sensing properties of multi-walled carbon nanotubes

The hydrogen sensing properties of multi-walled carbon nanotubes (MWNTs) synthesized by a hot filament CVD process are reported in this paper. The MWNTs were synthesized by a hot filament assisted chemical vapor deposition method using cobalt oxide nanoparticles as the catalyst on SiO₂ surfaces. The MWNTs were characterized with Raman spectroscopy and scanning electron microscopy. Two-terminal test devices were fabricated by depositing a layer of MWNTs between prefabricated gold electrodes on SiO₂ surfaces. The diameter of these MWNTs was in the 5–8 nm range. The sensitivity of carbon nanotubes was measured for different gas concentrations at different temperatures. It was found that the MWNTs were sensitive to H₂ in low temperature regions of 140–350 °C and had a maximum sensitivity (80%) at 230 °C. No sensitivity was observed at a temperature lower than 140 °C or higher than 400 °C. Though bare MWNTs are not sensitive to H₂ at room temperature, they exhibited very good sensing characteristics in the 140–300 °C range.     

Synthesis of nano-carbon (nanotubes,nanofibres, graphene) materials

In the present study, we report the synthesis of carbon nanotubes (CNTs) using a new natural precursor: castor oil. The CNTs were synthesized by spray pyrolysis of castor oil-ferrocene solution at 850°C under an Ar atmosphere. We also report the synthesis of carbon nitrogen (C-N) nanotubes using castor oil-ferrocene-ammonia precursor. The as-grown CNTs and C-N nanotubes were characterized through scanning and transmission electron microscopic techniques. Graphitic nanofibres (GNFs) were synthesized by thermal decomposition of acetylene (C₂H₂) gas using Ni catalyst at 600°C. As-grown GNFs reveal both planar and helical morphology. We have investigated the structural and electrical properties of multi-walled CNTs (MWNTs)-polymer (polyacrylamide (PAM)) composites. The MWNTs-PAM composites were prepared using as purified, with ball milling and functionalized MWNTs by solution cast technique and characterized through SEM. A comparative study has been made on the electrical property of these MWNTs-PAM composites with different MWNTs loadings. It is shown that the ball milling and functionalization of MWNTs improves the dispersion of MWNTs into the polymer matrix. Enhanced electrical conductivity was observed for the MWNTs-PAM composites. Graphene samples were prepared by thermal exfoliation of graphite oxide. XRD analysis confirms the formation of graphene.     

Joining of Cf/SiBCN composite with CuPd-V filler alloy

Two compositions of CuPd-V system filler alloy were designed for joining the Cf/SiBCN composite. Their dynamic wettability on the Cf/SiBCN composite was studied with the sessile drop method. The CuPd-8 V alloy exhibited a contact angle of 57° after holding at 1170℃ for 30 min, whereas for CuPd-13 V alloy,a lower contact angle of 28°can be achieved after heating at 1200 ℃ for 20 min. Sound C_f/SiBCN joints were successfully produced using the latter filler alloy under the brazing condition of(1170-1230)℃for 10 min. The results showed that the active element V strongly diffused to the surface of Cf/SiBCN composite, with the formation of V_2 C/VN reaction layer. The microstructure in the central part of the joint brazed at 1200 ℃ was characterized by the V_2 C/VN particles distributing scatteringly in CuPd matrix. The corresponding joints showed the maximum three-point bend strength of 82.4 MPa at room temperature.When the testing temperature was increased to 600 0 C, the joint strength was even elevated to 108.8 MPa.Furthermore, the joints exhibited the strength of 92.4 MPa and 39.8 MPa at 800 ℃ and 900 ℃, respectively.     

Field emission properties of Fe70Pt30 catalysed multiwalled carbon nanotubes

Multi-walled carbon nanotubes were grown on nanocrystalline Fe₇₀Pt₃₀ film using low-pressure chemical vapour deposition (LPCVD) method. The growth time was varied between 5?min to 30?min. SEM micrograph of this film revealed that the size of nanoparticles varied from 5?nm to 10?nm. The diameter of the carbon nanotubes varied from 20?nm to 50?nm as verified by TEM. HRTEM image confirmed that the carbon nanotubes are bamboo-shaped multiwalled carbon nanotubes (MWNTs). Field emission characteristics of MWNTs at various growth times (5?min, 15?min and 30?min) with working distances (50?µm, 100?µm and 150?µm) were also studied. The carbon nanotubes grown for 30?min with working distance 150?µm exhibited the lowest turn-on field of 2.45?V/µm. The turn-on field increases from 2.45?V/µm to 6.21?V/µm as the growth time decreases from 30?min to 5?min whereas for lower working distances (100?µm and 50?µm), the turn-on field increases from 4.74?V/µm to 6.74?V/µm and from 8.79?V/µm to 14.49?V/µm respectively. The turn-on field (E _to) and field enhancement factor (β) were studied as a function working distance (d) and growth time respectively to see the effect of these parameters on field emission properties. The field enhancement factor (β) was also studied as a function of radius of apex curvature (r) . It was found the field enhancement factor (β) decreases with the increase in radius of apex curvature (r) and growth time whereas the value of field enhancement factor (β) increases as working distance (d) increases. On the basis of the dependence of β on radius of apex curvature (r) a relationship of β?∝?r ^?1/2 is fitted.     

Quaternary co-electrodeposition of the Cu2ZnSnS4 films as potential solar cell absorbers

Cu₂ZnSnS₄ (CZTS) films are successfully prepared on Mo substrate by electrochemical epitaxial method. An electrolyte contains 0.124 M CuSO₄·5H₂O, 0.14 M ZnSO₄, 0.13 M SnCl₂·2H₂O, 0.16 M Na₂S₂O₃·5H₂O, 2.25 M NaOH, 1.36 M C₆H₅Na₃O₇, 1.00 M C₄H₆O₆. The equilibrium potential for quaternary co-electrodeposited solution is set at ?1.1 ～ ?1.20 V. The results show that elements are deposited in the following sequence: Cu/S/Zn/S/Cu/S/Sn/S…. The ternary and quaternary compounds are formed with the increasing temperature during annealing. Finally the CZTS film can be well formed at 550 °C. The resistivity of CZTS is about 5.6 × 10⁴ Ω cm.     

Study on laser-alloyed self-lubricating anti-wear composite coating after ageing treatment

The NiCr/Cr₃C₂-10CaF₂ (wt-%) composite coatings were fabricated on Ti-6Al-4V alloy by laser surface alloying. Ageing treatments were performed at 600°C for 0, 24, 48 and 96?h, respectively. Microstructure and tribological properties of the as-laser-alloyed and aged composite coatings were investigated systematically. Results showed that microstructure became more homogeneous after ageing at 600°C for 48?h. Wear rates and friction coefficients of the aged composite coatings were slightly higher than that of the as-laser-alloyed coating. It indicates that microstructure and tribological properties of the composite coatings present good high-temperature stability.     

Development of nanostructured ZnO thin film sensor for NO2 detection

In this work, we report on the performance of a NO₂ sensor based on nanocrystalline zinc oxide (ZnO) operating at 200°C. The sensor was fabricated using spin coating technique on glass substrates. ZnO film was characterised for their structural as well as surface morphologies and NO₂ response was studied. The XRD analysis showed formation of nanocrystalline ZnO. Morphological analysis using SEM revealed formation of a diffusion free surface. The ZnO film showed selectivity for NO₂ over methanol compared to ethanol, H₂S, Cl₂ and NH₃ (S_NO2 /S_CH3OH?=?18.6, S_NO2 /S_C2H5OH?=?12.4, S_NO2 /S_Cl2 ?=?9.3, S_NO2 /S_H2S?=?3.32 and S_NO2 /S_NH3 ?=?5.32). The maximum NO₂ response of 37.2% with 78% stability for the film annealed at 700°C at gas concentration of 100?ppm at 200°C operating temperature was achieved.     

Artificial Pinning Centers on MgB2 Superconducting Thin Films Coated by FeO Nanoparticles

MgB₂ thin films were fabricated on MgO (100) single crystal substrates. First, deposition of boron was performed by rf magnetron sputtering on MgO substrates and followed by a post deposition annealing at 850?°C in magnesium vapor. In order to investigate the effect of FeO nanoparticles on magnetic properties of MgB₂ thin films, the films were coated with different concentrations of FeO nanoparticles by spin coating process. The magnetic field dependence of the critical current density $J_{\mathrm{c}}$ was calculated from the M?CH loops and also magnetic field dependence of the pinning force density $f_{\mathrm{p}}(b)$ was determined for the films containing different concentrations of FeO nanoparticles. The values of the critical current density $J_{\mathrm{c}}$ in zero field at 5?K was found to be around 1×10⁶?A/cm² for pure MgB₂ film, 1.4×10⁶ for MgB₂ film coated with 25?%, 7.2×10⁵ for MgB₂ film coated with 33?%, 9.1×10⁵ for MgB₂ film coated with 50?% and 1.1×10⁶?A/cm² for MgB₂ film coated with 100?%. It?was?found that the film coated with 25?% FeO nanoparticles has slightly enhanced critical current density and it can be noted that especially the film coated with 25?% FeO became stronger in the magnetic field. The films coated with FeO were successfully produced and they indicated the presence of artificial pinning centers created by FeO nanoparticles. The superconducting transition temperature of the film coated with 25?% FeO nanoparticles was determined by moment?Ctemperature (M?CT) measurement to be 34?K which is 4?K higher than that of the pure film.     

Reduction the leakage current through povidone-SiO<Subscript>2</Subscript> nano-composite as a promising gate dielectric of FETs

In the present study, povidone-SiO₂ nano-composite dielectric film was introduced to replace SiO₂ gate dielectric film. The organic and inorganic particles homogeneously dispersed in nano-composite film. The structure of nano-composite film was affected by annealing temperatures. By increase in annealing temperature up to 200?°C, wt% of carbon, oxygen and nitrogen increased and wt% of silicon decreased. At 240?°C, the organic phase desorbed and nano-composite structure degraded. The annealing temperature of 150?°C was suitable for adhesion between two phases. The cross-linked structure of dielectric film annealed at 150?°C led to decrease in leakage current.     

Synthesis of the oxide NiSb2O6 and its electrical characterization in toxic atmospheres for its application as a gas sensor

In this work, nanoparticles of the trirutile-type oxide NiSb₂O₆ were synthesized for its application as a gas sensor using the colloidal method assisted by microwave radiation. The crystalline evolution of the powders was analyzed by X-ray diffraction, finding the phase NiSb₂O₆ at 600 °C. SEM micrographs revealed the growth of microspheres, microrods, and irregularly shaped particles. Using TEM, the average size of the nanoparticles was calculated at?~?17.1 nm. For dynamic tests, pellets and thick films were made from the powders calcined at 600 °C. For the thick films, alternating current was used at frequencies of 0.1 and 1 kHz in C₃H₈ and CO₂ atmospheres at 360 °C, where the material’s sensitivity magnitude in CO₂ was?~?2.61% (0.1 kHz) and?~?2.97% (1 kHz). In contrast, for C₃H₈, the sensitivity was?~?6.69% (0.1 kHz) and?~?5.12% (1 kHz) on average. For the pellets, direct current signals and volumetric flow rates of 100, 150, and 200 cm³/min of CO at 200 °C were applied, where the sensitivities were?~?24.37,?~?35.33, and?~?40.77%, respectively. In each test, the sensitivity visibly increased when the gases were injected. Likewise, the response and recovery times decreased when the frequency and gas concentration increased. The results obtained for the trirutile-type oxide NiSb₂O₆, which showed good stability, efficiency, and high sensitivity in CO₂, C₃H₈, and CO atmospheres, make it ideal as a toxic gas sensor.

     

Tunable surface hardness and dielectric constant of SiC x O y thin film converted from solution-processed organosilicon compound

Decaphenylcyclopentasilane (DPCPS), a solution-processable precursor, was used to develop inorganic thin films with variable electromechanical properties in terms of their surface hardness and dielectric constant through thermal treatment. By varying the thermal treatment temperature and environmental conditions, the organic covalent bonds in DPCPS disappeared via various chain scission reactions and, consequently, an SiC _x O _y hard-surface coating was achieved by the orbital hybridization of carbon and silicon. The inorganic thin film developed at thermal treatment temperatures over 700?°C in this study reached a pencil hardness of 7H and dielectric constant of around 2.3–2.5, which is lower than that of silica, seemingly because of the carbon atoms incorporated in the atomic lattice structure of SiO₂. The thermal treatment in an air environment gave higher dielectric constants than that in argon at <700?°C, but the ultimate dielectric constants after thermal treatment at temperatures over 700?°C were similar in both environments.     

Production of single and multi-walled carbon nanotubes using natural gas as a precursor compound

In this work, the Catalytic Chemical Vapor Deposition (CCVD) technique was used to synthesize carbon nanotubes (CNT). Natural gas (NG) was employed as a carbon source for the growing of CNT, while magnesium oxide was used as a catalyst support for the nanotubes synthesis. Two systems were utilized. The Fe–Mo/MgO system was obtained by the impregnation technique through the dispersion of iron oxide, which is the catalyst, over magnesia (with molybdenum additions). This system was tested intending to optimize the parameters for the production of single-walled carbon nanotubes (SWCNT). Moreover, Mg_1−x Fe _x MoO₄, which was prepared by the combustion synthesis method, was tested to produce multi-walled carbon nanotubes (MWCNT). The Fe-Mo/MgO tests were carried out under H₂/GN and Ar/GN atmospheres at 950 °C, whereas the Mg_1−x Fe _x MoO₄ was submitted to 1,000 °C under H₂/GN atmosphere. The Fe–Mo/MgO catalyst produced better results regarding number of CNT and their diameters under Ar/NG atmospheres than under H₂/NG atmospheres. The system Mg_1−x Fe _x MoO₄ produced MWCNT according to the expectations.     

Effect of Annealing on Virgin and Recycled Carbon Fiber Electrochemically Deposited with N-type Bismuth Telluride and Bismuth Sulfide

N-type thermoelectric bismuth telluride (Bi₂Te₃) and bismuth sulfide (Bi₂S₃) were deposited on virgin carbon fiber (VCF) and recycled carbon fiber (RCF) substrates by electrodeposition. The effects of annealing on the surface morphology and the Seebeck coefficient of the Bi₂Te₃ and Bi₂S₃ films were investigated. A nearly stoichiometric N-type Bi₂Te₃ was obtained from an electrolyte solution of 8 mM of Bi(NO₃)₃.5H₂O and 10 mM of TeO₂, which displayed the highest Seebeck coefficient of ?20.01 and ?13.0 µV/K for VCF and RCF, respectively. The deposition of Bi₂S₃ was slightly off-stoichiometry, but the improvement was still significant with a Seebeck coefficient of ?16.3 and ?12.4 µV/K for VCF and RCF, respectively. The effect of varying the annealing temperature (275°C and 350°C) and annealing time (2 and 3 hours) was studied on a nearly stoichiometric N-type Bi₂Te₃. The result shows an improvement in the Seebeck coefficient by 1.51–1.24 times at 350°C for 2 hours.     

Properties of Co0.5Ni0.5Fe2O4/carbon nanotubes/polyimide nanocomposites for microwave absorption

High-temperature microwave absorbing materials are of great interest due to their ability to withstand high temperatures. Multi-walled carbon nanotubes (MWNTs) were surface modified by Ar plasma and Co_0.5Ni_0.5Fe₂O₄ nanoparticles were doped onto the surface of the MWNTs by a chemical co-precipitation method. Co_0.5Ni_0.5Fe₂O₄/MWNTs powders were then added to polyimide to prepare nanocomposites for microwave absorption. After plasma modification, the surface of the MWNTs produced carboxyl groups, which are beneficial for interfacial bonding between the MWNTs and PI. The glass transition temperature of the nanocomposites was 261 °C and their thermostability was preserved up to 500 °C. The maximum reflection loss (RL) value of nanocomposites containing 0.75 wt% modified MWNTs was ?24.37 dB and the frequency range where the RL value was less than ?10 dB was 5.1 GHz from 7.8 to 12.9 GHz.     

The growth characteristics of chemical vapour-deposited β-SiC on a graphite substrate by the SiCl4/C3H8/H2 system

Silicon carbide has been grown at 1300–1800°C by chemical vapour deposition using the SiCl₄/C₃H₈/H₂ system on a graphite substrate. The effect of C₃H₈ flow rate and deposition temperature on the growth characteristics and structure of the deposit has been studied. The experimental results show that the degree of film density is changeable from a dense plate to a porous one with increasing C₃H₈ flow rate. The activation energy increases with increasing C₃H₈ flow rate. The grain size of the polycrystalline β-SiC becomes coarser when the C₃H₈ flow rate and the deposition temperature are increased. The preferred orientation of the deposited SiC layers changes from (111) to (220) on increasing deposition temperature from 1300°C to 1400°C. The deposition mechanism is also discussed.     

Oxidation behavior of aluminide coatings on carbon steel with and without electrodeposited Ni–CeO2 film by low-temperature pack cementation

A CeO₂-dispersed aluminide coating was fabricated through aluminizing the electrodeposited Ni–CeO₂ nanocomposite film on carbon steel using pack cementation method at 700 °C for 4 h. The isothermal and cyclic oxidation behavior of the CeO₂-dispersed aluminide coating at 900 °C, including the growth of oxide scale and the microstructure of the coatings, have been investigated comparing with the aluminide coating on carbon steel. The results show enhanced oxidation performance of the CeO₂-dispersed aluminide coating, which is concerned with not only CeO₂ effect on the microstructure and oxidation, but also decreased interdiffusion between the aluminide and the Ni film. The CeO₂ benefit effects and interdiffusion are discussed in detail.     

Thermodynamically Stable Mesoporous C3N7 and C3N6 with Ordered Structure and Their Excellent Performance for Oxygen Reduction Reaction

Carbon nitrides with a high N/C atomic ratio (>2) are expected to offer superior basicity and unique electronic properties. However, the synthesis of these nanostructures is highly challenging since many parts of the C? N frameworks in the carbon nitride should be replaced with thermodynamically less stable N? N frameworks as the nitrogen content increases. Thermodynamically stable C₃N₇ and C₃N₆ with an ordered mesoporous structure are synthesized at 250 and 300 °C respectively via a pyrolysis process of 5‐amino‐1H‐tetrazole (5‐ATTZ). Polymerization of the precursor to the ordered mesoporous C₃N₇ and C₃N₆ is clearly proved by X‐ray and electron diffraction analyses. A combined analysis including diverse spectroscopy and FDMNES and density functional theory (DFT) calculations demonstrates that the N? N bonds are stabilized in the form of tetrazine and/or triazole moieties in the C₃N₇ and C₃N₆. The ordered mesoporous C₃N₇ represents the better oxygen reduction reaction (ORR) performances (onset potential: 0.81 V vs reversible hydrogen electrode (RHE), electron transfer number: 3.9 at 0.5 V vs RHE) than graphitic carbon nitride (g‐C₃N₄) and the ordered mesoporous C₃N₆. The study on the mechanism of ORR suggests that nitrogen atoms in the tetrazine moiety of the ordered mesoporous C₃N₇ act as active sites for its improved ORR activity.     

TiC coatings deposited onto carbon and molybdenum surfaces by electron beam evaporation

TiC coatings were deposited onto graphite and molybdenum substrates by an electron beam evaporation method. A titanium film 1000–10000 Å thick was evaporated onto the graphite substrate which was then heated at 1000 °C for 5 min to form the TiC film by an interdiffusion process. In the case of the molybdenum substrate, a double-layer film consisting of titanium and carbon (Ti/C/Mo) was prepared by evaporation and the subsequent heat treatment was performed at 700 °C or at 1000 °C for 5 min. The properties of the coatings were examined by various surface analysis techniques including Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Rutherford backscattering (RBS). The atomic ratio of carbon to titanium in these coatings was found to be 0.9. The in-depth profiles obtained by XPS examination showed that the coating prepared at 700 °C had a carbon layer between the TiC layer and the molybdenum substrate, while that prepared at 1000 °C had an Mo₂C layer between the coating and the substrate.     

Using “intercalation bridging” to effectively improve the electrothermal properties of sheet graphite / ultrafine carbon powder conductive paste for screen printing

Electrothermal materials can easily and controllably convert electric energy into heat energy, and are widely used in many electrothermal fields. In this paper, a series of conductive pastes were simply prepared by ball milling, and their rheological and electrothermal properties were studied. Phenolic resin was used as curing agent of epoxy resin and rheological modifier, which could make the paste have very good printing applicability. Ultrafine carbon(UC) powder has excellent dispersion effect. Sheet carbon materials such as graphite powder(GP), graphite nanosheet(GS) and graphene(GE) would improve the performance of paste using only UC as conductive filler. It was proved that GE with the smallest thickness has the most obvious lifting effect. UC was gathered around the graphene sheet, as a bridge between graphene sheets. GE could also be connected with each other to build a more effective and denser conductive path. The electrothermal film could reach 199°C under 30 V voltage, increasing by 254.7% compared with the electrothermal film with only UC as conductive filler. The electrothermal film had a short response time, good recyclability and excellent flexibility. The electrothermal film also had certain electromagnetic shielding efficiency. The electromagnetic shielding efficiency SE could reach about 20 dB at 30–1500 MHz, and the ratio of field strength before and after attenuation SE_% could reach 97%?+?. This electrothermal film has simple preparation process, good printing applicability, controllable film resistance, excellent flexibility, fast response speed and good recyclability. It is suitable for large-scale preparation and has broad application prospects in many scenarios.

     

Comparative study on the properties of amorphous carbon layers deposited from 1-hexene and propylene for dry etch hard mask application in semiconductor device manufacturing

Amorphous carbon layers (ACLs) were prepared by plasma enhanced chemical vapor deposition (PECVD) from 1-hexene (C₆H₁₂) and propylene (C₃H₆) as a carbon source at different temperatures for dry etch hard mask of semiconductor devices manufacturing process. The deposition rate of ACL deposited at 550 °C from C₆H₁₂ and C₃H₆ was 5050 Å/min and 6360 Å/min. Although the deposition rate of ACL deposited from C₆H₆ was lower than that from C₃H₆, normalized deposition rate of ACL deposited from C₆H₁₂ was 1.64 times higher than that from C₃H₆. The relative amount of hydrocarbon contents measured by FTIR (Fourier transformation infrared) and TDS (thermal desorption spectroscopy) was decreased with the increase of deposition temperature. Raman results showed that the numbers and size of graphite cluster of ACLs deposited from each source were increased with the increase of deposition temperature. The extinction coefficient of ACL deposited at 550 °C from C₆H₁₂ was 0.51 and that from C₃H₆ was 0.48. The density of ACL deposited at 550 °C from C₆H₁₂ was 1.48 g/cm³ and that from C₃H₆ was 1.45 g/cm³. The dry etching rate of ACL deposited at 550 °C from C₆H₁₂ was 1770 Å/min and that from C₃H₆ was 1840 Å/min. The deposition rate, dry etch rate and the amount of hydrocarbon contents of ACLs deposited from each carbon source were decreased with the increase of deposition temperature but extinction coefficient and density were increased with the increase of deposition temperature. We concluded that the variation behavior of the deposition characteristics and film properties of ACLs from C₆H₁₂ with the increase of deposition temperature was the same as those of ACLs from C₃H₆. The high density and low dry etch rate of ACL from C₆H₁₂ can be explained by less hydrocarbon incorporation during deposition and these properties are more favorable for the dry etch hard mask application in semiconductor device fabrication.