Investigation On The Synthesis And Field Emission Properties Of Nanodiamond Films And Carbon Nanotubes Composites

Among all the carbon materials, nanodiamond (ND) and carbon nanotubes (CNTs) have attracted much attention because of their outstanding properties, and thus there has been extensive research on the synthesis and properties of ND films and CNT-based nanocomposite recently.ND films exhibit some new excellent properties in addition to the same properties as microdiamond (MD) films, such as high toughness, low roughness, low resistivity and low field emission voltage. On the other hand, different CNT-based nanocomposites have different prominent properties such as rigidity, conductivity, field emission property and abrasion resistance. These unique properties of ND films and CNT-based nanocomposites have attracted intense interests in recent years, especially their prominent field emission property make them have a potential application as field emission cold cathode material. Many investigations have concentrated on how to synthesize ND films and CNT-based nanocomposites which have low turn-on field, uniform and stable field emission current, high field emitters density and longer useful time.Up to now, various methods such as microwave plasma chemical vapor deposition (MPCVD), hot filament chemical vapor deposition (HFCVD), direct current arc method, sputtering method, flame method, etc. have been used for the synthesis of diamond films. Although all of the methods are also employed to synthesize ND films, among these methods, MPCVD and HFCVD methods are the most commonly used approaches. However, the deposition using MPCVD and HFCVD usually needs high synthesis power. The key points to obtain ND films is to using the high nucleation density and high second nucleation rate to restrain the growth of diamond crystalline. Substrate pretreatment is the common way for obtaining a high nucleation density.The syntheses of CNTs composite mainly include in-situ polymerization, solution mixing, melt eutectic and Sol-Gel. These methods cannot synthesize CNTs composite directly. In-situ polymerization method utilizes functional group on CNTs surface to participate polymerization, or employs initiator to openпbonding of CNTs for making it to participate polymerization. Solution mixing is another common technique to synthesize CNT-based nanocomposites, in which the matrix material is dissolved into the solvent after dispersing CNTs into it, subsequently the material is processed and the solvent is eliminated to acquire CNTs composite. While in the melt eutectic approach, matrix material is melted above its melting point first and CNTs is put into it directly to mix equably follows, accordingly the composite is achieved. Sol-Gel is the method applying the heat treat with low temperature to the metal organic or inorganic compound solidified after solution, sol and gel in order, and as a result oxide or other solid is made.The aim in this work is to prepare ND films and CNT-based nanocomposites using RF-PECVD with an excellent field electron emission property. Through characterizing the obtained samples, we can have conclusions as follows: 1. ND films on silicon substrates via appropriate nucleation pretreatment scheme can be synthesized by RF-PECVD with a low power. Meanwhile, we can also synthesize CNTs-ZnO composite and CNTs-NCD composite by RF-PECVD via a straightforward method.2. The pretreatment and the H2/CH4 ratio has a significant influence on the grain size, nucleation density and microstructure for obtained samples. 3. Most of the ZnO nanoparticles have about 4 nm in the average size (diameter) in the CNTs-ZnO composite, being the smallest average size of the ZnO nanoparticles coated on the CNTs that has been reported so far.4. For ND films, CNTs-ZnO composite and CNTs-NCD composite all the samples have excellent field emission property, which may have potential applications as cold-cathode electron sources. Their values of turn-on field are 1.5V/μm, 0.6V/μm and 1.2V/μm respectively.5. CNTs-ZnO composite has a better field emission property than CNTs, while CNTs-NCD composite has a better field emission property than CNTs and ND particles.In this work we successfully synthesize ND films and CNT-based nanocomposites using RF-PECVD with a low power. It should be noted that CNTs-ZnO composite and CNTs-NCD composite can be synthesized via the straight method,which offers a promising way to form self-assembled carbon nanostructures.