Field Emission Mechanism Of Diamond-like Carbon Films Deposited By The Electrochemical Method

A field emitter serves as a cold source of electrons. It has practical applications in various fields such as field emission flat panel displays, multiple electron-beam lithography, ion propulsion/micro-thrusters, radio frequency source, information storage technology, and electronic cooling.The emission of electrons from the surface of diamond and diamond-like carbon(DLC) films is currently of much interest due to potential applications in cold cathode devices.The negative electron affinity(NEA) of certain hydrogenated diamond surfaces plays an important role.In recent years, various kinds of diamond and DLC films have been prepared by physical vapor deposition(PVD) or chemical vapor deposition(CVD).In these cases the substrate temperature during deposition is kept at 200-400℃ and 600-900℃ for PVD and CVD, respectively.From the standpoint of an application of diamond and DLC films, a reduced substrate temperature is desired to avoide the internal stress of the film or damage of the low melting substrate.The research work is concerned with the preparation of DLC films by electrochemical deposition and the analysis of their field emission properties.At ambient pressure, DLC films were deposited on Si substrate by electrolysis in a methanol solution by controlling experimental parameters(voltage and temperature).The microstructure, morphology, and properties of the resulting DLC films were analyzed by means of FTIR and SEM. The results show that our samples are hydrogenated diamond-like carbon films with sp~2 and sp~3 carbon.The field emission characteristics of the films were tested using a diode configuration.During testing, it was found necessary to ramp the voltage up several times in order for the I —V curves to stabilize and become reproducible. This conditioning effect is often accompanied by morphological changes on the film surface.Depending upon the construction of the electrical circuit, there are manydifferent mechanisms involved as the electrons travel from the negative end of the power supply to the film surface, then tunnel through the potential barrier, such as FN, Schottky, SCLC and SCLC+PF models. By careful analysis of the mathematical form of the current-voltage dependence of the emission, insight into the conduction and emission mechanisms in the liquid-deposited DLC films can be obtained.