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Hee Jin Jeong,Laurent Eude,Manoharan Gowtham,Bernd Marquardt,Sung Hun Lim,Shaïma Enouz,Costel Sorin Cojocaru,Kyung Ah Park,이영희,디디에르프리밧 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2008 NANO Vol.3 No.3
The effects of an atomic hydrogen (Hat) pretreatment of the catalyst layer on the low temperature growth of single-walled carbon nanotubes (SWCNTs) have been investigated using a modified catalytic chemical vapor deposition system. Well-defined and isolated individual Fe nanoparticles as a catalyst are successfully formed on the defects with high trapping energy which are created on the Al2O3 surface by Hat pretreatment, yielding highly dense SWCNTs. The pretreatment mechanism of Hat, compared to H2, is also discussed. It was also found that the quality of SWCNTs can be enhanced when Hat is flowed with CH4 during nanotubes growth at low temperature. In this case, the undesired carbon products and defects on catalyst seeds and nanotubes walls can be selectively removed by Hat. Therefore, it is essential to use Hat in pretreatment stage for increasing catalytic activity and keep the size of nanoparticles in the nm range. Hat can also be employed in growth stage for enhancing SWCNTs quality and density at low temperature.
Somnats Ghosh,이준신,Dhiraj Bora,Jinsu Yoo,Manoharan Gowtham,Suresh Kummar Dhungel 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.5I
The present work is an experimental study of the various parameters of a high density plasma produced by using helicon waves in a toroidal structure using ordinary Langmuir probe and an RF compensated Langmuir probe. Helicon breakdown and the parameters were investigated in the toroidal vessel was observed with a right helical antenna (m = +1) at a frequency of 32 MHz. During the experiment, transition from a capacitive mode to a helicon mode of discharge was observed. This work also takes a step toward a realization of the necessity for a compensated Langmuir probe in the study of an RF plasma, especially in the frequency range of tens of MHz. A toroidal magnetic field of 600G (max) is applied at the central axis of a toroidal vessel with an aspect ratio equal to 3. The plasma is generated by using a helical antenna to form and sustain a plasma using hydrogen gas. The power is delivered from an RF generator at 32 MHz via an L-Type matching network. A comparative study has been done using compensated and uncompensated Langmuir probes to measure various plasma parameters. A nonlinear increase in the plasma density with input RF power and with the magnetic field is observed.
Uttam Manna,이준신,Hiranmoy Saha,Jinsu Yoo,김경해,Manoharan Gowtham,Suresh Kumar Dhungel,Utpal Gangopadhyay 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.2
The absorption loss in the n/Al interface of a p-i-n thin- film solar cell is high due to the higher extinction coefficient of the Al used as a back reflector. The insertion of a thin ZnO layer in the n-a-Si : H/Al interface of a solar cell with Glass/textured SnO2 : F/p-a-SiC : H/buffer layer/i-a-Si : H/na- Si : H/Al structure minimizes the absorption loss as ZnO has a lower extinction coefficient (less than 0.5) at longer wavelengths. In this article, the dependence of various electrical characteristics, such as the resistivity, the carrier concentration, the mobility and the optical transmittance, of ZnO : Al films on the thickness and the impact of the thickness of a ZnO : Al film used as a back reflector on the performance of solar cells are reported. The ZnO:Al films are prepared by using a rf magnetron sputtering system. For a 140-nm-thick ZnO : Al layer, the short-circuit current (Isc) increases by 12.7 % in comparison to that for the pure Al-metal back-reflector case. Isc further increases by 23 % when a 180-nm ZnO : Al layer is used, and the conversion efficiency of the solar cell is around 10.26 % for the 180-nm-thick ZnO : Al. The cell efficiency depends on the film thickness. The crystal quality of the deposited film is improved as the film thickness is increased.