Characteristics of carbon nanotubes grown by mesh-inserted plasma-enhanced chemical vapor deposition

Plasma-enhanced chemical vapor deposition (CVD) has the advantages of low temperature and vertical growth in synthesizing carbon nanotubes (CNTs), but has generally produced stubby CNTs, probably due to an ion bombardment effect. To suppress the ion bombardment, a metal mesh with the same electrical potential as that of the cathode was placed just above the substrate on the cathode. The anode was electrically grounded while the cathode and the mesh were both negatively biased, causing no plasma to occur below the mesh. The substrate was therefore separated from the plasma by the mesh so that the ion bombardment was suppressed. CNTs were grown on a 2 nm-thick Invar catalyst with different DC plasma powers of 0–112 W at 500 °C, 3.3 torr for 10 min, using C₂H₂ (28 sccm) and NH₃ (172 sccm). Compared to CNTs grown with no mesh, these CNTs showed smaller diameters and greater lengths. As the plasma power decreased, the CNTs grown with mesh were thinner and longer and resembled those grown at a higher temperature by thermal CVD. Etching these CNTs by N₂ plasma reduced their population density and considerably improved their field emission characteristics.     

Open‐Ended Two‐Strip Meander‐Line Antenna for RFID Tags

A new meander‐line antenna consisting of two open‐ended strips is proposed for a compact and broadband UHF radio frequency identification tag. An equivalent circuit model for the proposed antenna is derived and used to perform a simple and wideband impedance match to an arbitrary complex impedance of a tag chip without any additional matching network. The performance of the proposed antenna is validated by comparing calculated and measured results, which show good agreement.     

Characteristics of fluid flow and heat transfer in a fluidized heat exchanger with circulating solid particles

The commercial viability of heat exchanger is mainly dependent on its long-term fouling characteristic because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various solid particles. The present work showed that the higher densities of particles had higher drag force coefficients, and the increases in heat transfer were in the order of sand, copper, steel, aluminum, and glass below Reynolds number of 5,000.     

Enhancement of the power conversion efficiency for organic photovoltaic devices due to an embedded rugged nanostructural layer

Organic photovoltaic (OPV) cells utilizing a rugged nanostructural layer were fabricated by using a mixed solution method. The charge separation at the heterointerface between the poly(3-hexylthiophene) (P3HT) nanostructural layer with a rugged surface and the C60 layer was increased due to an increase in the interfacial region between the donor and the acceptor layers, resulting in an increase in the short-circuit current density and the power conversion efficiency (PCE) of the OPV cells with a P3HT nanostructural layer. The PCE of the OPV cells with a nanostructural rugged layer is 30% higher than that without a rugged layer.     

Low-temperature adsorption of hydrogen on ion-exchanged Y zeolites

Ion-exchanged Y zeolites with several alkali metal cations and proton have been used to analyze the effect of electrostatic field or basicity on the hydrogen adsorption at low temperature and low pressure. The adsorption capacity per surface area, isosteric heat of adsorption (-Δ_Hads)$(-\mathrm{\Delta }{H}_{\mathrm{ads}})$, surface coverage and micropore occupancy increase with the decreasing electronegativity of the metals that are introduced in the zeolite. Ion-exchanged zeolites also favorably adsorb hydrogen at relatively low pressures when the electronegativity of the metal is low. This work demonstrates that zeolites with strong electrostatic fields or high basicity are beneficial for high hydrogen uptake especially at low pressure and low temperature.     

Improvement of initial vacuum condition along 2008–2010 KSTAR campaign by vessel baking

Korea Superconducting Tokamak Advanced Research (KSTAR) is upgraded for its KSTAR 3rd campaign for new target mission to produce the D-shaped plasma with a target plasma current of 500 kA and/or pulse length of 5 s. New Plasma Facing Components (PFCs) are installed which leads to the increase of the surface area of the vessel by a factor of about 5. The vacuum conditioning such as the vessel baking has been performed in order to remove various kinds of impurities including H₂O, carbon and oxygen for the plasma. The total outgassing rate in the KSTAR 1st campaign was measured as 1.5 × 10^?4 mbar ? s^?1 which is increased by a factor of 3 (6.49 × 10^?4 mbar ? s^?1) in the KSTAR 3rd campaign. Nevertheless, the outgassing rates per unit area have been decreased from 9.31 × 10^?5 mbar ? m^?2 s^?1 to 1.22 × 10^?5 mbar ? m^?2 s^?1 due to the upgrade of baking system and series of baking operation.     

Characterization of transformed and deformed microstructures in transformation induced plasticity steels using electron backscattering diffraction

The microstructure of transformation induced plasticity (TRIP) steels was characterized by means of electron backscattering diffraction (EBSD) technique to identify and quantify their different microstructures such as ferrite, bainite, and retained austenite. Further, the strain distribution in ferrite and retained austenite was analyzed during deformation. The TRIP steels were annealed by austempering for different durations to investigate the effect of the austempering time on the volume fraction change of the microstructural constituents. The quantitative analysis by EBSD coupled with an image contrast analysis revealed that the amount of retained austenite decreased and the amount of bainite increased with increasing austempering time. The mechanical properties of the TRIP steels were also affected by the austempering time. The maximum elongation was obtained in the sample austempered for 5 min, probably because of the good stability of retained austenite. The strain distribution in bcc and fcc phases during tensile deformation was characterized by evaluating the changes in the average local misorientation of the phases.     

The geometrical effect of single walled carbon nanotube network transistors on low frequency noise characteristics

The noise characteristics of randomly networked single walled carbon nanotubes grown directly by plasma enhanced chemical vapor deposition with field effect transistor. Geometrical complexity due to the large number of tube-tube junctions in the nanotube network is expected to be one of the key factors for the noise power of 1/f dependence. We investigated low frequency noise as a function of channel length (2-10 microm) and found that increased with longer channel length. Percolational behaviors of nanotube network that differs from ordinary semiconducting and metallic materials can be characterized by a geometrical picture with electrical homo- and hetero-junctions. Fixed nanotube density provides a test conditions to evaluate the contributions of junctions as a noise center. Hooge's empirical law is applied to investigate the low frequency noise characteristics of single walled carbon nanotube random network transistors. The noise power shows the dependence of the transistor channel length. It is understood that nanotube/nanotube junctions act as a noise center. However, the differences induced by channel length in the noise power are observed as not so significant. We conclude that tolerance of low frequency noise is important property for SWNT networks as an electronic device application.