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Kyung Hwan Lee,Lawrence J. Overzet,Gil S. Lee,Duck J. Yang,이병준,장훈식 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.11
Spin-capable multi-walled carbon nanotubes (MWCNTs) were synthesized on a Fe catalyst film in a He environment by using thermal chemical vapor deposition (CVD). The effect of He on the growth behavior of the MWCNTs was investigated. In addition, the variation of the Fe surface during the pre-annealing and MWCNT growth processes was characterized using scanning electron microscopy, X-ray diffraction and atomic force microscopy. It was surmised that the presence of He gas did not help in the formation of Fe nanoparticles on the substrate during the pre-annealing or the growth processes; however, He gas did appear to help activate and/or assist carbon to diffuse into the surface of the Fe nanoparticles. We note that MWCNT forests grew well on the Fe catalyst film even without the pre-annealing process. The characteristic dimension of the MWCNTs was found to be the same as the particle size and the crystallite size of the nanoparticles formed on the substrate. We also found that spin-capable MWCNTs could be grown by controlling the density of nanotubes on the substrate.
Transient effects caused by pulsed gas and liquid injections into low pressure plasmas
Ogawa, D,Chung, C W,Goeckner, M,Overzet, L IOP Pub ; American Institute of Physics 2010 PLASMA SOURCES SCIENCE AND TECHNOLOGY Vol.19 No.3
<P>The fast injection of liquid droplets into a glow discharge causes significant time variations in the pressure, the chemical composition of the gas and the phases present (liquid and/or solid along with gas). While the variations can be large and important, very few studies, especially kinetic studies, have been published. In this paper we examine the changes brought about in argon plasma by injecting Ar (gas), N<SUB>2</SUB> (gas) hexane (gas) and hexane (liquid droplets). The changes in the RF capacitively coupled power (forward and reflected), electron and ion density (<I>n</I><SUB>e</SUB>, <I>n</I><SUB>i</SUB>), electron temperature (<I>T</I><SUB>e</SUB>) and optical emissions were monitored during the injections. It was found that the Ar injection (pressure change only) caused expected variations. The electron temperature reduced, the plasma density increased and the optical emission intensity remained nearly constant. The N<SUB>2</SUB> and hexane gas injections (chemical composition and pressure changes) also followed expected trends. The plasma densities increased and electron temperature decreased while the optical emissions changed from argon to the injected gas. These all serve to highlight the fact that the injection of evaporating hexane droplets in the plasma caused very little change. This is because the number of injected droplets is too small to noticeably affect the plasma, even though the shift in the chemical composition of the gas caused by evaporation from those same droplets can be very significant. The net conclusion is that using liquid droplets to inject precursors for low pressure plasmas is both feasible and controllable.</P>
Carbon Nanotubes Based Methanol Sensor for Fuel Cells Application
Kim, D. W.,Lee, J. S.,Lee, G. S.,Overzet, L.,Kozlov, M.,Aliev, A. E.,Park, Y. W.,Yang, D. J. American Scientific Publishers 2006 Journal of Nanoscience and Nanotechnology Vol.6 No.11
<P>An electrochemical sensor is built using vertically grown multi-walled carbon nanotubes (MWNTs) micro-array to detect methanol concentration in water. This study is done for the potential use of the array as methanol sensor for portable units of direct methanol fuel cells (DMFCs). Platinum (Pt) nanoparticles electro-deposited CNTs (Pt/CNTs) electrode shows high sensitivity in the measurement of methanol concentration in water with cyclic voltammetry (CV) measurement at room temperature. Further investigation has also been undertaken to measure the concentration by changing the amount of the mixture of methanol and formic acid in water. We compared the performance of our micro array sensor built with Pt/CNTs electrodes versus that of Pt wire electrode using CV measurement. We found that our Pt/CNTs array sensor shows high sensitivity and detects methanol concentrations in the range of 0.04 M to 0.10 M. In addition, we found that co-use of formic acid as electrolyte enables us to measure up to 1.0 M methanol concentration.</P>