Acetylene Gas Flow Research Articles

Enhanced optical and electrical stability of thermally carbonized porous silicon

In the current paper, the intrinsic instability of physical properties of porous silicon (PS) was minimized using a thermal carbonization (TC) method. A typical PS showed an obvious quenching of its photoluminescence (PL) properties under long-term laser radiation. To resolve this problem, an ultra-thin stabilizing layer was grown on the porous structure under an acetylene gas flow. During the TC process at high temperatures, carbon atoms were detached from the acetylene molecules and dissolved in the porous structure. Thermally carbonized PS (TC-PS) layer changed the PL peak position of PS slightly due to the formation of Si–C species on porous surface after acetylene exposure. The effects of TC-PS layer in electrical properties of fabricated photodetectors were studied. The photocurrent of freshly prepared PS decreased under prolonged green laser radiation (532nm, 5mW), but the TC-PS sample showed more stable electrical characteristics under the same conditions.

Effect of acetylene concentration and thermal ramping rate on the growth of spin-capable carbon nanotube forests

Spin-capable multiwalled carbon nanotube (MWCNT) forests that can form webs, sheets, and yarns provide a promising means for advancing various technologies. It is necessary to understand the critical factors to grow spin-capable carbon nanotubes (CNTs) in a repeatable fashion. Here we show how both the spinning capability and morphology of MWCNT forests are significantly changed by controlling the C2H2 concentration and ramp rate of temperature. The acetylene gas flow was varied in the range of 0.25–6.94% by volume. The MWCNTs grown at C2H2 concentrations between 1.47–3.37% are well-aligned and become spin-capable. The well-aligned forests have higher areal density and shorter distance between CNTs. The thermal ramp rate was also changed from 30 °C/min to 70 °C/min. A specific range of thermal ramp rate is also required to have the suitably sized nanoparticles with sufficient density resulting in higher CNT areal density for spinnable MWCNTs. A ramp rate of 50 °C/min forms suitable sized nanoparticles with sufficient density to produce CNT forests with a higher areal density and a shorter tube spacing.

Fabrication of Silicon Carbide Thin Film as a Stabilizing Layer for Improving the Stability of Porous Silicon Photodiodes

This paper investigates the effect of silicon carbide (SiC) thin film as a stabilizing layer on porous silicon (PS) in metal–semiconductor–metal (MSM) photodiodes. Photo-assisted pulsed electrochemical etching method was used to produce the PS layers with large pore density and small crystallite size. As–prepared PS surface was modified with acetylene gas flow in a thermal process (750°C) in order to replace the hydrogen termination by Si–C bonds which is more stable. During the thermal carbonization, carbon atoms penetrated into the silicon lattice forming a thin (~4 nm) SiC layer. Because of high inertness of silicon carbide thin film, thermally carbonized porous silicon layer (TC-PS) was found to be more stable than the freshly prepared PS surfaces. A small reduction in specific surface area was found after carbonization which is due to the small size of acetylene molecules. The FTIR measurements confirmed the presence of SiC bonds in the TC-PS sample. The photocurrent of the fabricated photodiodes based on as-grown PS was lowered under prolonged green laser radiation (532nm, 5mW), but devices based on TC-PS showed more stable I-V characteristics under the same condition even for 120 min of laser exposure.

다구찌 기법을 이용한 용사코팅의 공정 최적화

In the present study, process optimization for thermal-sprayed Ni-based alloy coating has been performed using Taguchi method and analysis of variance(ANOVA). Ni-based alloy coatings were fabricated by flame spray process on steel substrate, and the hardness test and wear test were performed. Experiments were designed as per Taguchi's L9 orthogonal array and tests were conducted with different Oxygen gas flow, Acetylene gas flow, Powder feed rate and Spray distance. Multi response signal to noise ratio (MRSN) was calculated for the response variables and the optimum combination level of factors was obtained simultaneously using Taguchi's parametric design.

니켈기 용사코팅의 스플랫 형성에 관한 연구

Thermal spray coatings developed by deposition of splats, it formed by impacting molten droplets on substrates during thermal spray process. In this study, the Ni-based coatings were fabricated by thermal spray process with two different process parameters, oxygen gas flow and acetylene gas flow, with three different levels of each parameters. The morphology of splats and microstructure were observed by optical microscope. Hardness test were performed on the Ni-based coatings. It was confirmed that process parameters of thermal spray process have effect in morphology of splats. These effects also have important implications on the deposit microstructure and properties of Ni-based coatings.

Room temperature CO and H2 sensing with carbon nanoparticles

We report on a shell-shaped carbon nanoparticle (SCNP)-based gassensor that reversibly detects reducing gas molecules such as CO andH2 at room temperature both in air and inert atmosphere. Crystalline SCNPs were synthesized bylaser-assisted reactions in pure acetylene gas flow, chemically treated to obtain well-dispersedSCNPs and then patterned on a substrate by the ion-induced focusing method. Ourchemically functionalized SCNP-based gas sensor works for low concentrations of CO andH2 at room temperature even without Pd or Pt catalysts commonly used for splittingH2 molecules into reactive H atoms, while metal oxide gas sensorsand bare carbon-nanotube-based gas sensors for sensing CO andH2 molecules can operate only at elevated temperatures. A pristine SCNP-based gas sensorwas also examined to prove the role of functional groups formed on the surface offunctionalized SCNPs. A pristine SCNP gas sensor showed no response to reducing gases atroom temperature but a significant response at elevated temperature, indicatinga different sensing mechanism from a chemically functionalized SCNP sensor.

니켈기 경질 용사코팅의 경도 및 마모율에 미치는 공정조건의 영향

The various process parameters of thermal spray process affects on quality of Ni-based coatings. Thus, there is need to analyze the effect of process parameters on quality of Ni-based coatings. In this paper, the effects of process parameters on hardness and wear rate of Ni-based coatings were investigated using 4 design of experiments. First, the Ni-based coatings were fabricated according to <TEX>$L_9(3^4)$</TEX> orthogonal array. The hardness tests and the wear tests were performed on the Ni-based coatings. The analysis of variance for the hardness and wear rate were carried out. As a results, the acetylene gas flow and the powder feed rate were identified as main factors effected on the hardness and the oxygen gas flow and the acetylene gas flow were identified as main factors effected on the wear rate. The full factorial experiments design with different levels was applied for investigation of effect of these main factors.

Hardness of and stress in tungsten carbide–diamond like carbon multilayer coatings

Hardness of and stress in tungsten carbide–diamond like carbon (WC–DLC) multilayer coatings sputtered in reactive argon/acetylene plasma have been studied as a function of the bilayer thickness. The multilayer structure has been deposited by a periodic modulation of the reactive acetylene gas flow from 0 to 5 sccm, producing a series of pure WC layer and W–C:H amorphous layer. Internal stress and microstructure have been investigated by wafer curvature and transmission electron microscopy whereas hardness was obtained by nanoindentation. In a previous paper on WC–DLC multilayers [Appl. Phys. Letts. 90, 021913 (2007)] we reported an interface stress of 11.12 N/m. By changing the layout of the gas lines in the deposition equipment, a new series of multilayers were produced. Our results show that in this new series of multilayers, the compressive stress exhibits the same dependence on bilayer thickness as reported before and a huge interface stress of 8.5 N/m is still present in the multilayer. In this new series of multilayers, we are reporting a hardness of 18.7 GPa, and contrarily to the observed in the first set of WC–DLC multilayers, the hardness does not depend on the bilayer thickness. These results are discussed in terms of the microstructure of the individual layers and the structure of the interfaces.

Tribological Performance of Reactively Sputtered a-C:H Coatings in Ambient air and Aqueous Environment

Amorphous hydrogenated carbon (a-C:H) films, supported by a layer system consisting of substoichiometric chromium nitride and amorphous carbon, were deposited on case-hardened steel disks using reactive magnetron sputtering of graphite targets in an acetylene-containing atmosphere. The a-C:H film hardness was adjusted between 8 and 19 GPa by varying the acetylene gas flow and the bias voltage. To evaluate friction and wear behaviour, pin-on-disk tests were done in ambient air and deionised water. It could be shown that optimised a–C:H films are suitable to protect steel from sliding wear in ambient air but also in aqueous environment eliminating the problem of insufficient heat removal.

Stress in tungsten carbide-diamond like carbon multilayer coatings

Tungsten carbide-diamond like carbon (WC-DLC) multilayer coatings have been prepared by sputter deposition from a tungsten-carbide target and periodic switching on and off of the reactive acetylene gas flow. The stress in the resulting WC-DLC multilayers has been studied by substrate curvature. Periodicity and microstructure have been studied by transmission electron microscopy. It has been observed that compressive stress in the multilayers decreases when the bilayer thickness is reduced. Results show a minimum compressive stress for bilayer thickness of around 5nm. This behavior is discussed in terms of interface stress and mixing between layers.

Influences of acetylene gas flow rate on mechanical properties and chemical structure of nanocomposite TiC diamond-like carbon films

Nanocomposite TiC diamond-like carbon (DLC) films were prepared on silicon (100) wafer and Ti alloy samples by reactive magnetron sputtering combining with plasma source ion implantation. The hardness of the films was evaluated using nanoindentation. Micro-nick was employed to investigate the critical loading of the films. X-ray photoelectron spectroscopy and X-ray diffraction were used to analyze the chemical structure of the DLC films containing Ti. The results showed that changing acetylene gas flow rate could control Ti concentration in the films. Many nanometer TiC crystalline grains and nanocomposite TiC/DLC structure were formed by choosing proper C and Ti ratio, and the mechanical properties of the films were distinctly improved. In addition, ion implantation formed the transition layer which enhanced the adherence of the films.

Reactive magnetron sputtering deposition and columnar growth of nc-TiC∕a-C:H nanocomposite coatings

Ti C ∕ a - C : H coatings were deposited using closed-field unbalanced reactive magnetron sputtering deposition from Ti targets. Different acetylene gas flow and substrate bias values were employed to vary the coatings’ compositions and microstructures. The application of an external negative substrate bias increased the deposition rate of the plasma-enhanced chemical vapor deposition process from the reactive atmosphere. The sputtering of carbonaceous species from the poisoned targets surface was a minor source of C flux to the substrates. The application of an external substrate bias during deposition yielded films with a featureless cross-sectional structure, but the dominant parameter controlling the columnar growth was the chemical composition of the films. An explanation of this effect was formulated based on the microstructures observed and the deposition technique employed.

Influence of deposition parameters on the structure and mechanical properties of nanocomposite coatings

Nanocomposite coatings based on TiC nanoparticles embedded in an amorphous hydrocarbon (a-C:H) matrix are deposited via reactive closed field unbalanced magnetron sputtering, employing Ti targets and acetylene gas as material precursors. The composition of the coatings is varied by changing the acetylene gas flow during the depositions. Different values of substrate bias are employed. Electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) monitor the variation of composition and the formation of TiC. Nanoindentations with a Berkovich indenter measure the coatings hardness ( H) and effective Young's modulus ( E*), and a cube corner indenter is employed to probe the coatings toughness. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) investigations confirm the formation of TiC nanoparticles and are employed to determine the particle size and size distribution, respectively, both as a function of the applied substrate bias and of the composition. The TiC volume fractions ( V F) and interparticle distances are calculated based on the compositional analysis and the measured particle sizes. As a consequence of the different nanostructures, the coatings exhibit different toughness. The highest toughness is observed for low TiC volume fractions (0.2) and particle size (≈ 2 nm). The evolution of the H/ E and H 3/ E* 2 parameters as a function of the nanostructure is investigated, and opportunities for their optimization are described.

Deformation and failure mechanism of nano-composite coatings under nano-indentation

Two nano-composite coatings based on nc-TiC particles in an a-C:H matrix are deposited via closed-field unbalanced reactive magnetron sputtering. The compositions of the coatings are varied by changing the acetylene gas flow during the depositions. A Cr/Cr–Ti/Ti–TiC graded interlayer is introduced between substrate and coating. Electron probe micro-analyses (EPMA) show that the Ti content of the coatings varies between 31.7 and 11.5 at.%. The coatings exhibit a hardness ( H) of 20.0 and 15.7 GPa, and a Young's modulus ( E) of 229.4 and 136.6 GPa, respectively, as measured through nano-indentations. Cube corner indentations are performed to probe the fracture toughness of the coatings through the determination of critical indentation loads ( L r) at which radial cracks start to propagate. Transmission electron microscopy (TEM) observations and energy-filtered TEM are employed to characterize the coatings nanostructures. The variation in Ti content is accompanied by a variation in TiC particle size and volumetric fraction, as well as a change in the columnar structure of the coatings. A focus ion beam (FIB) slicing technique is employed to prepare samples from nano-indented locations of coated Silicon and stainless steel (SS) substrates. TEM inspection of the FIB sliced samples determines that the most brittle phase in the coating is the C-enriched columnar boundary, and identifies the location of failure within the interlayer. As a consequence of the different nanostructure, the coatings exhibit different elastic recovery properties and toughness.

Molybdenum–carbon film fabricated using metal cathodic arc and acetylene dual plasma deposition

Metal cathodic arc and acetylene dual plasma deposition is used to synthesize molybdenum-containing diamond-like carbon (Mo-DLC) thin films. The Mo contents in the film layer can be controlled by varying the acetylene gas flow rates and the substrate bias voltages. The Mo-doped film prepared by the above technique exhibits small surface roughness. Fine molybdenum carbide grains are found to be embedded inside the amorphous carbon cross-linked structures. In addition, these films are shown to possess high thermal stability after a series of high temperature annealing. The results show that dual plasma deposition is a useful and effective technique to fabricate metal-incorporated carbon thin films with controlled metal contents.

Molybdenum?carbon film fabricated using metal cathodic arc and acetylene dual plasma deposition

Metal cathodic arc and acetylene dual plasma deposition is used to synthesize molybdenum-containing diamond-like carbon (Mo-DLC) thin films. The Mo contents in the film layer can be controlled by varying the acetylene gas flow rates and the substrate bias voltages. The Mo-doped film prepared by the above technique exhibits small surface roughness. Fine molybdenum carbide grains are found to be embedded inside the amorphous carbon cross-linked structures. In addition, these films are shown to possess high thermal stability after a series of high temperature annealing. The results show that dual plasma deposition is a useful and effective technique to fabricate metal-incorporated carbon thin films with controlled metal contents.

Physical–chemical hybrid deposition of DLC film on rubber by T-shape filtered-arc-deposition

Stretchable and bendable diamond-like carbon (DLC) film was fabricated on rubber substrates using T-shape filtered-arc-deposition (T-FAD) with an acetylene (C 2H 2) gas flow, in order to provide a surface sliding property to the rubber. When the C 2H 2 gas was introduced, the deposition rate became higher. The film obtained under C 2H 2 gas was supposed to be deposited physically with cathodic ion and chemically with decomposed particles of the gas. The smoothest surface was obtained at the optimum gas flow rate at which the deposition rate was highest. The DLC film on the rubber was composed of small meshed islands. When the rubber substrate was bent several times, the islands cracked further to form smaller pieces. Hence, the reason for the deformation of the elastic DLC film together with the rubber deformation was the gradual expansion of the small DLC islands in relation to one another as more and more cracks occurred.

Mechanical and tribological evaluation of PVD WC/C coatings

Abstract Five different WC/C coatings deposited by physical vapour deposition (PVD) on high speed-steel (HSS) have been evaluated with respect to their mechanical and tribological properties. For all coatings a chromium layer was deposited first to enhance coating adhesion. The carbide phase (WC) and the carbon (C) phase were deposited simultaneously by direct-current magnetron sputtering of a WC target and plasma-assisted chemical vapour deposition using hydrocarbon gas, respectively. The influence of the chromium interface layer thickness, the amount of WC phase and the flow of hydrocarbon gas on the mechanical and tribological properties of the coatings have been investigated. The coatings have been characterised with respect to their chemical composition (glow discharge optical emission spectroscopy), hardness (Vickers microhardness), morphology (scanning electron microscopy, SEM), roughness (profilometry), residual stress (beam bending), critical load (scratch testing) and abrasive wear resistance (the “dimple grinder test”). Furthermore, a ball-on-plate test was employed to obtain information about the frictional properties and sliding wear resistance of the coatings. The wear mechanisms and wear debris were analysed by SEM, Auger electron spectroscopy and electron spectroscopy for chemical analysis. All WC/C coatings displayed a thickness between 2 and 4 μm and a surface roughness in the range of 10 to 70 nm. The hardness varied between 1500 and 1800 HV. The coating residual stress was found to range from −2.5 to −0.5 GPa. The scratch test revealed a relatively high critical normal load, i.e., a relatively good adhesion of the WC/C coatings to the HSS. The abrasive wear resistance was found to be very high, in fact equally as high as that of PVD TiN. In the sliding wear test it could be seen that the coating containing the lowest amount of carbide phase (WC), i.e., the highest amount of carbon phase (C), and which had the highest compressive residual stress yielded the lowest friction and wear rate against steel. In addition, this coating was also found to yield the lowest wear rate of the counter material. In summary, a WC/C coating with overall good mechanical and tribological properties was obtained provided a relatively thin chromium layer was deposited first and if a relatively high acetylene gas flow was utilised during deposition of the WC/C layer.

ガス切断に関する二,三の実験(第5報)

By using specially made tips with varying numbers and pitch of circle diameter (P.C.D.) of preheating orifices, a cutting test was performed. The results of the cutting was compared on the basis of the maximum cut thickness that has been introduced by the authors as a convenient criterion for determining cutting ability.The cutting ability was found to increase with increasing numbers of preheating orifices surrounding the cutting orifice, if sufficient amount of acetylene gas is used, but the rate of increase in cutting ability decreases with increasing numbers of preheating orifices. The relation is expressed in the following formula :mf=(1-ε-n+1/1.8)⋅m0If insufficient acetylene gas is used, the cutting ability is below that given by the above formula, depending on the acetylene gas flow and P.C.D. of preheating orifices. The formula for this relation is expressed as follows :m=(1-ε-a/F)⋅mfwhere m, mf=a degree of cutting ability proportional to the cutting efficiencym0=the maximum of the above, being peculiar to a size of tipn=nos. of preheating orificesα=acetylene gas flow per one preheating orificeF=a constant depending on n, size of tip and P.C.D.ε=the base of natural logarithmFrom the results it was also found that many flames issuing from many preheating orifices are more efficient than a single flame of the same amount of acetylene gas.In addition, the direction of a preheating orifice relative to the cutting orifice has no great significance so far as no loss of cut happens. The effectiveness of propane gas is by no means less than that of acetylene, if preheating variables are properly chosen.

ガス切断に関する二,三の実験(第1報)

By using specially made tips with varying numbers and pitch of circle diameter (P.C.D.) of preheating orifices, a cutting test was performed. The results of the cutting was compared on the basis of the maximum cut thickness that has been introduced by the authors as a convenient criterion for determining cutting ability.The cutting ability was found to increase with increasing numbers of preheating orifices surrounding the cutting orifice, if sufficient amount of acetylene gas is used, but the rate of increase in cutting ability decreases with increasing numbers of preheating orifices. The relation is expressed in the following formula :mf=(1-e-n+1/1.8)⋅m0If insufficient acetylene gas is used, the cutting ability is below that given by the above formula, depending on the acetylene gas flow and P.C.D. of preheating orifices. The formula for this relation is expressed as follows :m=(1-e-a/F)⋅mfwhere m, mf=a degree of cutting ability proportional to the cutting efficiencym0=the maximum of the above, being peculiar to a size of tipn=nos. of preheating orificesα=acetylene gas flow per one preheating orificeF=a constant depending on n, size of tip and P.C.D.e=the base of natural logarithmFrom the results it was also found that many flames issuing from many preheating orifices are more efficient than a single flame of the same amount of acetylene gas.In addition, the direction of a preheating orifice relative to the cutting orifice has no great significance so far as no loss of cut happens. The effectiveness of propane gas is by no means less than that of acetylene, if preheating variables are properly chosen.