The structure and adhesion of hydrogenated amorphous carbon (a-C:H) films synthesized on CoCrMo alloy by plasma immersion ion implantation and deposition at different flow ratios of acetylene to argon

Hydrogenated amorphous carbon (a-C:H) film is deposited on CoCrMo alloy by plasma immersion ion implantation and deposition (PIII-D) at different flow ratios of acetylene to argon (C₂H₂/Ar). The results show that Ar fraction in the C₂H₂-Ar gas mixture has an important effect on the structure and the adhesion of the a-C:H films. When Ar fraction in the C₂H₂-Ar gas mixture is less than 50%, the fabricated a-C:H film composition transfer from graphite-like to diamond-like which contains higher sp³ binding thanks to Ar ion bombardment, and the adhesion strength decreased with the increment of Ar fraction. But when Ar fraction in the C₂H₂-Ar gas mixture is beyond 50%, the fabricated film contains more sp² bonding for thermally driven and exhibits higher adhesion strength with the increment of the Ar fraction.     

Characterization of Plasma Enhanced Chemical Vapor Deposition-Physical Vapor Deposition transparent deposits on textiles to trigger various antimicrobial properties to food industry textiles

Textiles for the food industry were treated with an original deposition technique based on a combination of Plasma Enhanced Chemical Vapor Deposition and Physical Vapor Deposition to obtain nanometer size silver clusters incorporated into a SiOCH matrix. The optimization of plasma deposition parameters (gas mixture, pressure, and power) was focused on textile transparency and antimicrobial properties and was based on the study of both surface and depth composition (X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), as well as Transmission Electron Microscopy, Atomic Force Microscopy, SIMS depth profiling and XPS depth profiling on treated glass slides). Deposition conditions were identified in order to obtain a variable and controlled quantity of ~ 10 nm size silver particles at the surface and inside of coatings exhibiting acceptable transparency properties. Microbiological characterization indicated that the surface variable silver content as calculated from XPS and ToF-SIMS data directly influences the level of antimicrobial activity.     

Local structural analysis of a-SiCx:H films formed by decomposition of tetramethylsilane in microwave discharge flow of Ar

Hydrogenated amorphous silicon carbide (a-SiC_x:H) films were prepared by the decomposition of tetramethylsilane (TMS) with microwave discharge flow of Ar. When radio-frequency (RF) bias voltage (− V_RF) was applied to the substrate, the film hardness increased as (2.39 ± 1.12)-(9.15 ± 0.55) GPa for − V_RF = 0-100 V. The a-SiC_x:H films prepared under various − V_RF conditions were analyzed by the carbon-K near edge X-ray absorption fine structure (NEXAFS), by the elastic recoil detection analysis (ERDA), and by the X-ray photoelectron spectroscopy (XPS). From a quantitative analysis of NEXAFS, the sp²/(sp²+ sp³) ratios of C atoms were evaluated as 67.9 ± 2.0, 55.4 ± 2.7, and 51.7 ± 0.7% for − V_RF = 0, 60, and 100 V, respectively. From ERDA, hydrogen content of the film prepared under the condition of − V_RF = 100 V was found to decrease 28% comparing with that under − V_RF = 0 V. It is suggested that the cause of the increase of the film hardness when applying − V_RF is predominantly the growth of the sp³-hybridized structure of C atoms accompanied by the decrease of hydrogen terminations.     

Effect of hydrogen on diffusion bonding of commercially pure titanium and hydrogenated Ti6Al4V alloys

The diffusion bonding of commercially pure titanium and hydrogenated Ti6Al4V alloys was carried out, and the effect of hydrogen was investigated by SEM, XRD, TEM and TG/DSC. The β_H phase increased with the hydrogen content increasing in hydrogenated alloys, and the δ titanium hydride and α′ martensite were found in high hydrogen content. The TG curves of hydrogenated alloys descended between 600 °C and 950 °C, and the DSC curves represented a large endothermic peak correspondingly. Moreover, some voids were observed at the diffusion bonding interface. The amount of voids decreased and diffusion bonding quality improved gradually with the increase of hydrogen content, which was attributed to the increase of soft β_H phase and release speed of hydrogen as well as the occurrence of more dehydrogenation reaction.     

A study of the effects of annealing and outgassing on hydrogenated amorphous silicon

Annealing and outgassing of thin films of hydrogenated amorphous silicon (a-Si:H) are shown to produce major structural changes in the material. Outgassing can occur in three stages with thresholds at 350°C, 450°C and 575°C corresponding to conversion of SiH₃ groups to SiH₂ and SiH; conversion of SiH₂ groups to Si and SiH; and conversion of SiH to Si respectively. Heating to 575°C also appears to remove most of the hydrogen from vacancies and defects in the material. Such heat treatments could be useful for improving the stability of thin film a-Si:H devices.     

Changes of infrared absorption by light soaking and thermal quenching in a-Si : H

The light- and thermal-induced changes of Si---H bonds in undoped a-Si : H have been studied on the infrared absorption of Si---H stretching mode, using the infrared photothermal deflection spectroscopy and the photothermal bending spectroscopy. The results show that the IR absorption of Si---H bonds increases by light soaking of the high power 500 mW/cm². The change of IR absorption of Si---H bonds reoccurs by thermal annealing at 200°C. This change is related to the increase of the dangling bonds under light soaking. Furthermore, we observe the change of the elasticity modulus by light soaking, using the photothermal bending spectroscopy. The structural change in a-Si : H is discussed based on these results.     

Effects of Carbon Black on the Properties of HNBR Reinforced by in-situ Prepared ZDMA

Hydrogenated nitrile rubber (HNBR) filled with carbon black (CB) and in-situ prepared zinc dimethacrylate (ZDMA) was prepared by mechanical mixing method. The effects of carbon black on the vulcanization characteristics, physical and dynamic mechanical properties, thermal stability and the fracture surface morphologies of HNBR reinforced by in-situ prepared ZDMA (HNBR/ZDMA) were investigated. The results showed that, for given ZDMA loading (50 phr), with the increasing CB content, the scorch time extended, tensile strength, tear strength and elongation at break increased at first and then decreased, while the modulus at 100% and hardness increased. The comprehensive properties of the HNBR/ZDMA/CB was optimal, when the content of CB was 10 phr. DMA analysis showed that the addition of CB could enhance the storage modulus (E’) & loss modulus (E”), and decreased the glass transition temperature (Tg) of HNBR/ZDMA. TGA analysis revealed that the addition of CB could improve the thermal stability of HNBR/ZDMA. SEM analysis showed that the CB dispersed well in the HNBR/ZDMA, and the CB could improve the dispersion of ZDMA effectively.     

Towards high-efficiency thin-film silicon solar cells with the “micromorph” concept

Tandem solar cells with a microcrystalline silicon bottom cell (1 eV gap) and an amorphous-silicon top cell (1.7 eV gap) have recently been introduced by the authors; they were designated as “micromorph” tandem cells. As of now, stabilised efficiencies of 11.2% have been achieved for micromorph tandem cells, whereas a 10.7% cell is confirmed by ISE Freiburg. Micromorph cells show a rather low relative temperature coefficient of 0.27%/K. Applying the grain-boundary trapping model so far developed for CVD polysilicon to hydrogenated microcrystalline silicon deposited by VHF plasma, an upper limit for the average defect density of around 2 × 10¹⁶/cm³ could be deduced; this fact suggests a rather effective hydrogen passivation of the grain-boundaries. First TEM investigations on μc-Si : H p-i-n cells support earlier findings of a pronounced columnar grain structure. Using Ar dilution, deposition rates of up to 9 Å/s for microcrystalline silicon could be achieved.     

Effect of hydrogen content in a-C:H coatings on their tribological behaviour at room temperature up to 150 °C

Hydrogenated amorphous carbon (a-C:H) coatings deposited onto steel substrates by plasma assisted CVD, using different precursor gases (1 < H/C ratio < 4) were tested for their tribological behaviour. The H content in these coatings ranged from 25 to 29 at.%. Fretting mode I tests were performed on different couples consisting of coated and/or uncoated first bodies. Some tests were performed after a heat treatment of the coatings. As-deposited a-C:H/corundum couples tested at 23 °C and 50% RH showed lowering of the coefficient of friction at increasing normal load. Graphitisation is taking place in sliding contacts at high normal loads. For a-C:H/corundum couples a clear minimum in the coefficient of friction was noticed at 100 °C for coatings containing 27 at.% H. The coefficient of friction recorded on such couples is high compared to the one recorded on as-deposited a-C:H/a-C:H couples. However for the a-C:H/a-C:H couple, a lowering of the coefficient of friction with increasing fretting test temperature was noticed. The decreasing coefficient of friction was accompanied by an increasing wear. Graphitisation is causing severe degradation of a-C:H coatings at high test temperatures. An energetic analysis of the wear is finally reported. It appeared that the wear volume recorded at RT on as-deposited a-C:H coatings varies linearly with the cumulative dissipated energy. The wear rate coefficient decreases with increasing H-content. A stabilization of the sp³ bonds with increasing H-content might explain this behaviour. Confirmation was found by performing high temperature fretting tests. Interesting is the finding that fretting tests at RT performed after a thermal treatment of a-C:H coatings at either 100 or 150 °C, show a friction and wear behaviour identical to the ones recorded on as-deposited coatings tested at RT.     

MILD combustion of hydrogenated biogas under several operating conditions in an opposed jet configuration

MILD combustion of biogas takes its importance firstly from the combustion process that diminishes significantly fuel consumption and reduces emissions and secondly from the use of biogas which is a renewable fuel. In this paper, the influence of several operating conditions (namely biogas composition, hydrogen enrichment and oxidizer dilution) is studied on flame structure and emissions. The investigation is conducted in MILD regime with a special focus on chemical effects of CO₂ in the oxidizer. Opposed jet diffusion combustion configuration is adopted. The combustion kinetics is described by the Gri 3.0 mechanism and the Chemkin code is used to solve the problem.It is found that oxygen reduction has a significant effect on flame temperature and emissions while less sensitivity corresponds to hydrogen enrichment in MILD combustion regime. Temperature and species are considerably reduced by oxygen decrease in the oxidizer and augmented by hydrogen addition to the fuel. The maximum values of temperature and species are not influenced by the composition of the biogas in MILD regime. Blending biogas with hydrogen can be used to sustain MILD combustion at very low oxygen concentration in the fuel.In MILD combustion regime, the chemical effect of CO₂ in the oxidizer stream reduces considerably the flame temperature and species production, except CO which is enhanced. For high amounts of CO₂ in the oxidizer, the chemical effect of CO₂ becomes negligible.