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Cvd synthesis of intermediate state-free, large-area and continuous mos2 via single-step vapor-phase sulfurization of moo2 precursor
(2021-10-01)
Chiawchan, Tinna
;
Ramamoorthy, Harihara
;
Buapan, Kanokwan
;
Somphonsane, Ratchanok
The low evaporation temperature and carcinogen classification of commonly used molybdenum trioxide (MoO3) precursor render it unsuitable for the safe and practical synthesis of molybdenum disulfide (MoS2). Furthermore, as evidenced by several experimental findings, the associated reaction constitutes a multistep process prone to the formation of uncontrolled amounts of intermediate MoS2−yOy phase mixed with the MoS2 crystals. Here, molybdenum dioxide (MoO2), a chemically more stable and safer oxide than MoO3, was utilized to successfully grow cm-scale continuous films of monolayer MoS2. A high-resolution optical image stitching approach and Raman line mapping were used to confirm the composition and homogeneity of the material grown across the substrate. A detailed examination of the surface morphology of the continuous film revealed that, as the gas flow rate increased by an order of magnitude, the grain-boundary separation dramatically reduced, implying a transition from a kinetically to thermodynamically controlled growth. Importantly, the single-step vapor-phase sulfurization (VPS) reaction of MoO2 was shown to suppress intermediate state formations for a wide range of experimental parameters investigated and is completely absent, provided that the global S:Mo loading ratio is set higher than the stoichiometric ratio of 3:1 required by the VPS reaction.
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Fabrication of tungsten carbide–diamond composites using SiC-coated diamond
(2019-12-01)
Kitiwan, Mettaya
;
Goto, Takashi
Tungsten carbide (WC) and SiC-coated diamond composites were prepared by spark plasma sintering at 1473–1873 K for 300 s under 130 MPa under vacuum. The diamond particle surface was coated with silicon carbide (SiC) via rotary chemical vapor deposition to improve the interfacial bonding of the WC–diamond composites. The relative density of the WC–20 vol% diamond (SiC) composite increased from 61% to 94% with increasing sintering temperature. Raman spectroscopic analysis showed that the diamond-to-graphite transition did not occur at any of the investigated sintering temperatures. The WC–20 vol% diamond composite sintered at 1773–1873 K exhibited high hardness (30.5 GPa) and fracture toughness (12.3 MPa m1/2). The high hardness resulted from the SiC coating functioning as an interlayer to improve the bonding between the diamond and WC body. The improvement in fracture toughness was attributed to the presence of diamond, which effectively blocks crack propagation and promotes crack deflection.
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Facile growth of carbon nanaotube electrode from electroplated Ni catalyst for supercapacitor
(2015-01-01)
Yordsri, Visittapong
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Wongwiriyapan, Winadda
;
Thanachayanont, Chanchana
A facile growth of carbon nanotubes (CNTs) was facilitated by the use of direct-current plating technique for catalyst preparation. Ni nanoparticles (NPs) were deposited on Cu foil at different applied voltages of 1.0, 1.5 and 2.0 V. The Ni-deposited foil was subsequently used as catalyst for CNTs synthesis by chemical vapour deposition (CVD) method. CVD was carried out at 800 °C using ethanol as carbon source. A voltage of 1.5 V was the optimum condition to deposit uniform Ni NPs that had a narrow size distribution of 55±3 nm, which in turn, yielded synthesized CNTs with a uniform diameter of approximately 60±5 nm with graphitic layers parallel to the CNTs axis. On the other hand, electroplated Ni at 1.0 V produced CNTs with graphitic layers at an angle to the CNTs axis, while electroplated Ni at 2.0 V produced curly CNTs with a wide distribution of diameters. These results show that Ni NPs size distribution could be controlled by electroplated voltage. Our observation was that Ni NPs with a narrow distribution of sizes and a uniform diameter is a key to uniform CNT synthesis. Furthermore, the synthesized CNTs electrode shows a faradic pseudo capacitance property, which can be attributed to the existence of oxidized Ni NPs. These results propose that the synthesized CNTs are promising materials for future super capacitor application. The optimization of ratio of Ni NPs and CNTs may improve the supercapacitors performance.
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Plasma impedance tuning effect on nanostructure of diamond films
(2013-10-25)
Thowladda, Warawoot
;
Khlayboonme, S. T.
The morphology and structure of nanocrystalline diamond films as well as the plasma chemistry were studied by altering the plasma impedance. These impedances related to electron density were altered via the matching system. Two films were grown by the microwave plasma under different values of the plasma impedance, resulting in low and high electron densities in the plasma. By the use of measurements of plasma impedance and optical emission, the lowering of an inductive component of the impedance, indicating an increasing electron density, encouraged H-radical concentration present in the plasma. As the plasma was changed to the high electron density, Raman spectra of the films showed the sp3 Raman peak shifted from 1325 to 1328.5 cm-1 with narrower broadening. This behavior arose from an increase in grain size, corresponding to images from a field emission scanning electron microscope. Raman spectra of G-peak position and white light reflectometry showed a reduction in sp2 carbon content of the film. The G-peak shifted from 1564 to 1541 cm-1 and refractive index increased from 1.84 to 2.16. The formation of the films related to the concentrations of H and CH3 radicals. The plasma impedance affected the radical concentrations. © (2013) Trans Tech Publications, Switzerland.
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Nanocrystalline diamond films deposited by two-step approach from CH4/H2 microwave plasma: The influence of reactor pressure
(2013-08-30)
Khlayboonme, S. T.
;
Thowladda, W.
The morphology, growth rate and atomic-bonding structure of nanocrystalline diamond films deposited on Si substrates were investigated under various pressures of the reactor. The films were deposited by CH<inf>4</inf>/H<inf>2</inf> microwave plasma with two-step deposition and H<inf>2</inf>-plasma cleaning processes. The pressures of 1, 2, 5, 9, and 25 kPa were used for deposition. In situ gas-phase species, including electron density, were monitored by an optical spectrometer and impedance analyzer. The films were characterized by SEM, Raman microscope, and white light reflectrometer. When the pressure increased, the surface smoothness and diamond grain size increased, amorphous carbon content decreased, and the intensity ratio of CH/H<inf>β</inf> for the growth step increased. The growth rate was in proportional to the ratio of CH/H<inf>β</inf> for the nucleation step but in inverse proportion to the electron density. The growth rates decreased from 370 nm/h for 1 kPa to 320 nm/h for 2 kPa. After that, the growth rate rapidly increased to 460 nm/h for 9 kPa, but it gradually decreased to 450 nm/h for 25 kPa. The film refractive indices were 2.16 for 5 kPa, 2.21 for 9 kPa, and 2.38 for 25 kPa. The films grown under 1 and 2 kPa showed highly light absorption. © (2013) Trans Tech Publications, Switzerland.
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Synthesis of carbon nanotube and carbon nanofiber in nanopore of anodic aluminum oxide template by chemical vapor deposition at atmospheric pressure
(2012-10-15)
Kasi, Jafar Khan
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Kasi, Ajab Khan
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Wongwiriyapan, Winadda
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Afzulpurkar, Nitin
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Dulyaseree, Paweena
Carbon nanotube (CNT) is one of the most attractive materials for the potential applications of nanotechnology due to its excellent mechanical, thermal, electrical and optical properties. We demonstrated the fabrication of carbon nanotube and carbon nanofiber (CNF) inside the pore and at the surface of anodic aluminum oxide (AAO) membrane by chemical vapor deposition method at atmospheric pressure. Ethanol was used as a hydrocarbon source and Co-Mo as catalyst. CNT was synthesized at different temperature. High graphitic multiwall carbon nanotube (MWCNT) was found at 750°C, while CNF was found at 800oC and above temperature analyzing by Raman spectroscopy. © (2012) Trans Tech Publications, switzerland.

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