tailieunhanh - Báo cáo hóa học: " Excellent Field Emission Properties of Short Conical Carbon Nanotubes Prepared by Microwave Plasma Enhanced CVD Process"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Excellent Field Emission Properties of Short Conical Carbon Nanotubes Prepared by Microwave Plasma Enhanced CVD Process | Nanoscale Res Lett 2008 3 25-30 DOI s11671-007-9109-x NANO EXPRESS Excellent Field Emission Properties of Short Conical Carbon Nanotubes Prepared by Microwave Plasma Enhanced CVD Process Sanjay Kumar Srivastava Vasant D. Vankar Vikram Kumar Received 15 November 2007 Accepted 22 November 2007 Published online 5 December 2007 to the authors 2007 Abstract Randomly oriented short and low density conical carbon nanotubes CNTs were prepared on Si substrates by tubular microwave plasma enhanced chemical vapor deposition process at relatively low temperature 350-550 C by judiciously controlling the microwave power and growth time in C2H2 NH3 gas composition and Fe catalyst. Both length as well as density of the CNTs increased with increasing microwave power. CNTs consisted of regular conical compartments stacked in such a way that their outer diameter remained constant. Majority of the nanotubes had a sharp conical tip 5-20 nm while its other side was either open or had a cone pear-shaped catalyst particle. The CNTs were highly crystalline and had many open edges on the outer surface particularly near the joints of the two compartments. These films showed excellent field emission characteristics. The best emission was observed for a medium density film with the lowest turn-on and threshold fields of and V m respectively. It is suggested that not only CNT tip but open edges on the body also act as active emission sites in the randomly oriented geometry of such periodic structures. Keywords Carbon nanotubes CVD Microwave plasma CVD Field emission Conical CNTs S. K. Srivastava El V. Kumar Electronic Materials Division National Physical Laboratory Dr. . Krishnan Marg Pusa New Delhi 110012 India e-mail srivassk@ V. D. Vankar Department of Physics Thin Film Laboratory Indian Institute of Technology Delhi Hauz Khas New Delhi 110016 India Introduction Carbon nanotubes CNTs 1 have attracted wide attention both in the research and industrial