奈米碳管场发射特性之改善与其侧向元件之研究4.pdf

Chapter 2 Improvement of Field-Emission Characteristics of Carbon Nanotube Field- Emission-Arrays by Oxide Capping Layer The density distribution of CNTs is one of the crucial parameters dominating the field-emission characteristics of CNTs. To effectively control the density of CNTs, an oxide capping layer is deposited on a catalyst. The results show that improved field emission property can be obtained with a thin SiO layer on the catalyst layer as the x precursor. Microwave plasma-enhanced chemical vapor deposition (MPCVD) and thermal chemical vapor deposition (TCVD) are used to grow nanotubes. For 3.5 nm Fe and 3.5 nm SiOx on 3.5 nm Fe as catalysts to grow nanotubes in MPCVD, the turn-on field can be decreased from 3.7 V/µm. to 2.2 V/µm and the field-emission -6 2 -3 2 current density increases from 3.8x10 mA/cm to 1.5x10 mA/cm when the applied field was 3.5 V/µm. The threshold field which is defined as the field at which an 2 emission current density of 10 mA/cm is generated is about 5.32 V/µm. For 5 nm Fe and 1.5 nm SiO on 5 nm Fe as a catalyst to grow nanotubes in TCVD, the turn-on x electric field reduced from 3.8 V/µm to 1.8 V/µm and the emission current density increased from 7 x 10-8 mA/cm2 to 1.77mA/cm2 at an applied electric field of 3.5 V/µm. 28 2.1 Introduction Carbon nanotubes have attracted considerable attention owing to their excellent electronic and structural properties, enabling their use in a broad range of applications [2.1-2.2]. Due to their hig