Investigations of the Structural and Electron Field Emission Properties of Ultrananocrystalline Diamond Films

Abstract

Growth, microstructural evolution and electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films are investigated in this research work. Initially, we focus on understanding the role of hydrogen in diamond films grown in Ar/H2/CH4 plasma. The factors leading to a transition of diamond grain size from micron to nano- and then to ultranano- size has been investigated when hydrogen concentration is decreased in the plasma. In addition, we have synthesized UNCD films in two different plasma gas mixtures of Ar/CH4 and Ar/1.5% H2/CH4 at various substrate temperatures (TS) (550750 °C) and investigated the effect of TS on the structural modification of UNCD films. A grain growth mechanism is proposed and correlated with the EFE properties of the films. The effect of TS on microstructural evolution of nitrogen incorporated UNCD (N-UNCD) films deposited in N2/CH4 plasma, possessing wire-like morphology with high electrical conductivity is systematically explored. A model for grain growth in the films is proposed and the role played by the TS leading to the growth of grains is discussed. Furthermore, the EFE and plasma illumination characteristics of vertically aligned N-UNCD nanorods fabricated from N-UNCD films by reactive ion etching (RIE) using nanodiamond (ND) particles as a hard etching mask is investigated. In addition to that, the synthesis of a novel core-shell heterostructure with ZnO nanorods as core and ultrananocrystalline diamond needles as shell is investigated. The benefit of these core-shell heterostructures with good EFE properties on exciting the Ar plasma in a device with parallel-plate configuration is also demonstrated. Finally, an in depth investigation on the interface characteristics of UNCD films grown using Au-coated Si substrates and the enhancement in EFE properties of the films is carried out. A highly feasible method of fabricating highly conducting free-standing UNCD films with enhanced EFE properties by using Au-coated Cu substrates at low TS (< 475C) is adopted. The consequence of Au-coatings on the microstructural evolution of the film’s interface characteristics by using transmission electron microscopy (TEM) is inquired. Additionally, the effect of Au and Cu ion implantation to enhance the conductivity and the EFE properties of UNCD films is successfully examined. The modifications to the microstructure of these films due to ion implantation are investigated in detail using TEM.