Browsing by Author "Chuang, P. K."

Now showing 1 - 3 of 3

Effect of substrate bias on growth and properties of carbon nanotubes deposited under no hydrogen introduction by MPCVD
(2006-04-01)
Chuang, P. K.
;
Teng, I. J.
;
Wang, W. H.
;
Kuo, C. T.
;
材料科學與工程學系
In order to examine the consequence of replacing hydrogen gas with high substrate bias, processes were successfully demonstrated to fabricate various carbon catalyst-assisted nanostructures, including carbon nanotubes (CNTs), by microwave plasma chemical vapor deposition (MPCVD), under the pure CH4 as the only source gas and without additional H-2 gas introduction. The Si wafers were first deposited with catalyst by physical vapor deposition (PVD), and then followed by H-plasma pretreatment to obtain the well-distributed catalyst particles on wafer. The pretreated specimens were then deposited in MPCVD to manipulate the various carbon nanostructures. The main process parameters include catalyst material (Co, Ni and Fe), the substrate bias (0 to - 320 V), and deposition time (1 to 20 min). The as-deposited nanostructures were characterized by SEM, HRTEM, Raman spectroscopy, and field emission I-V measurement. The results indicate that the various nanostructures on Si wafers can be manipulated under sufficient high negative substrate bias (>-200 V) without the additional hydrogen introduction. These results also improve our understanding on growth mechanisms of CNTs or other nanostrucrures, where the most of the proposed mechanisms in the literature were too much emphasis on the role of hydrogen. On important process parameters, except the substrate bias, it is interesting to note that effect of deposition time on nanostructures is essentially to extend the more CNTs into the plasma zone, which can result in different purification effect on CNTs, vary the alignment and sizes of CNTs, and expose the more nanostructures near the substrate surface. Under the present deposition 2 conditions, the best nanostructures with the best field emission properties (Turn-on field = 5 V/mu m, maximum current density > 35 mA/cm(2)) are the well-aligned CNTs with proper tube number densities, purities and sizes. (c) 2005 Elsevier B.V. All rights reserved.
Low-temperature growth mechanism of SW-NTs networks by buffer layer-assisted MPCVD
(2006-04-01)
Wang, W. H.
;
Peng, Y. R.
;
Chuang, P. K.
;
Kuo, C. T.
;
材料科學與工程學系
We present the microstructures and growth mechanism of networks of single-walled carbon nanotubes (SWNTs) fabricated by buffer layer-assisted microwave plasma chemical vapor deposition (MPCVD) at relatively low temperatures. The morphologies and bonding structures of carbon nanostructures were characterized by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and Raman Spectroscopy. Additionally, the surface roughness of buffer layer and its bonding structures with catalyst atom are analyzed by atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. Analytical results demonstrate that networks of CNTs are formed by bundles or individual SWNTs. We suggest that the formation of SWNTs networks at low temperature may follow the root-growth mechanism. The differences comparing with previous growth mechanism are that the nuclei formation resulted from the rough surface of the buffer layer, and dissolution of carbon in catalyst will be enhanced due to the surface diffusion of the buffer layer. These unique effects from the buffer layer can provide favorable conditions to grow SWNTs at relatively low process temperatures. (c) 2005 Elsevier B.V. All rights reserved.
One-step growth process of carbon nanofiber bundle-ended nanocone structure by microwave plasma chemical vapor deposition
(2006-11-01)
Teng, I. J.
;
Chuang, P. K.
;
Kuo, C. T.
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In this work, we report a simple one-step growth process to synthesize a novel and distinct carbon nanostructure, called a carbon nanofiber bundle-ended nanocone (CNFNC) structure, by using microwave plasma chemical vapor deposition (MPCVD) method with CH4 and H, as source gases and Fe catalyst. The nanostructures and their properties after each processing step were characterized by FESEM, HRTEM, ED, AES, and Raman spectroscopy. The preliminary results have demonstrated that the CNFNC structures exhibit excellent field emission properties. The results also show that the favored conditions to form the CNFNC structures include a combination of lower CH4/H-2 flow ratio, higher substrate negative bias, and proper working pressure and deposition time. The possible growth mechanism of the CNFNC structures is proposed. (c) 2006 Elsevier B.V. All rights reserved.