Growth and properties of one-dimensional nano-materials

• Main Author: 張志雄
• Other Authors: 陳永芳
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/06333753857753524811

碩士 === 國立臺灣大學 === 物理學研究所 === 89 === The growth and field emission properties of SiCN naonrods, carbon nanotubes and Si nanowires will be presented in this thesis. SiCN is a wide-band gap material (about 4.2 eV). Carbon nanotubes was synthesized by carbon. The electrical properties of CNTs are similar to metallic electrical properties. Si nanowire is the one-dimensional nanostructure of Si, because of the quantum confinement effect the band gap is bigger than that of Si bulk (1.12 eV). The transport and tunnelling of electrons during field emission will be affected by electrical properties as will as band gap of the materials. A two-stage growth strategy was employed for the growth of SiCN nanorods. In the first stage, an electron cyclotron resonance chemical vapor deposition (ECR-CVD) method was employed to deposit nano-crystalline SiCN buffer layers on crystalline silicon substrates. In the second stage, SiCN nanorods were grown rapidly and preferentially along (001) direction in a microwave plasma enhanced chemical vapor deposition (MW-PECVD) system. It will be shown that the density of the nanorods was determined by the density of the nanocrystals in the buffer layer and the field emission enhancement factor β was also related to the buffer layer . The current-voltage characteristics of nanorod samples with different density indicated a strong effect of density of nanorod on the field emission properties. From the simulation of electric field of the sample under diode configurations, we conclude that the optimum ratio of the height of nanorods to the inter-distance between two nanorods should be 1:2.6 for maximum emission. Carbon nanotubes (CNT) are excellent field emitters owing to their small diameters. We first used ion beam sputtering deposition (IBSD) to deposit iron on Si substrate as catalyst, then CNTs were synthesized by MW-PECVD using carbon containing source gases such as methane. Depending on different plasma conditions , the growth temperature can be varied from 500 ℃ to 1300℃ .The Raman spectroscopic studies show that the ratio of the integrated intensity of the D and G band (ID/IG) of CNT decreases with increasing growth temperature. The field emission properties of CNTs produced with various growth temperature are also discussed. Si nanowires (SiNWs) were grown by thermal CVD at 1030℃ with iron catalyst on crystalline silicon wafers. To compare the emission properties of SiNWs with different length, two sets of samples were measured. The I-V curves show that SiNWs of shorter length was exhibited a mush lower turn on field than their longer counterparts. It is likely because the short ones were oriented and had larger field emission enhancement factors than the long ones. SiCN nanorod, carbon, and SiNWs have different energy gap and electrical properties. A thin carbon overcoat layer on SiCN nanorod or Si nanowire was found to improve their field emission properties presumably by decreasing the surface tunnelling barrier. Meanwhile, the substrates type and carrier density can also affect the transport of electrons from the substrate to emitter. Field emission properties of SiCN nanorods, CNTs, SiNWs were thus studied on p-type, n-type and n+-type crystalline Si <100> substrates. For SiCN nanorods, the sample deposited on p-type Si substrate exhibit a higher emission current than that deposited on n-type silicon. As the electron carrier concentration increases for the n-type substrates the turn-on voltage decreases further. In contrast CNTs and SiNW deposited on the n-type substrate produce higher emission than that on the p-type substrate.