Study of WCx and WOx Nanowires Self-Synthesized by Thermal Annealing

• Main Authors: Chin-Hong Wong, 黃展鴻
• Other Authors: Shui-Jinn Wang
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/10933940422209734482

碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 92 === 　　In this thesis, the preparation of tungsten carbide (WCx) and tungsten oxide (WOx) nanowires are studied. SEM, XPS, XRD and TEM are employed for the characterization of WCx films and nanowires prepared in this study. Vacuum I-V measurement is employed to estimate the emission property of the prepared nanowires. 　　The self-synthesis of WCx nanowires by a simple thermal annealing WCx film in nitrogen is proposed in this work. In nitrogen ambient, the optimized annealing temperature and time for the self-synthesis of WCx nanowires are of 700�aC and 30 min, respectively. According to TEM measurements, the diameter and length of the nanowires are found to be about 10-20 nm and 100-180 nm, respectively. Material analysis indicates that the major crystallization of the nanowires consisting of α-W2C. Field emission measurements show that the turn-on electric field of the WCx nanowires prepared under optimum condition is about 1.7 V/�慆, which indicates that the WCx nanowires could be a potential candidate for field emission application as compared to CNTs. The influence of annealing time, temperature, and film thickness on the self-synthesis of nanowires are investigated. 　　An attempt to grow WOx nanowires using sputtered WCx films is also made by two different methods. The first method is the oxidization of self-synthesized WCx nanowires. It is found that nanowires disappeared after oxidation except the samples oxidized at 400�aC for 30 minutes. The obtained nanowires are with an average diameter and length of 7~15 nm and 0.1 �慆 respectively. According to material analysis, it reveals that the major composition of the nanowires is WOx with x in the range of 2.7~2.9. The second method is thermal annealing of WCx film in O2/N2 ambient. Experimental results show that the self-synthesis of WOx nanowires could be achieved under thermal annealing at the temperature range of 500~750�aC for 30 min. The measured turn-on field of WOx nanowires was about 4.8~6 V/�慆. It is found that both the diameter and length of the WOx nanowires are dependent on the annealing temperature and time. 　　In the third part of this thesis, to properly describe the field emission characteristics of nanowires prepared in this work, conventional Fowler-Nordheim equation, F-N parameters by modified Norde method, equation, and mathematical fitting are examined and compared. Employing the measured data obtained from samples annealed at 700�aC for 30 minutes in nitrogen ambient and that annealed at 600　C for 1.5 hours in nitrogen, it is observed that the conventional F-N equation can not be well applied for experimental field emission characteristics of nanowires. On the contrary, equation and mathematical fitting are found to be much more favorable for the simulation of field emission device simulation.