Preparation And Field Emission Properties Of Diamond-like Carbon Films By Electrochemical Deposition

Diamond-like carbon (DLC) is a metastable form of amorphous carboncontaining a significant fraction of sp~3 bonds.It can have a high mechanical hardness,chemical inertness,optical transparency,and it is a wide band gap semiconductor.DLC films have widespread applications in many areas,especially as field emissioncathode materials for vacuum microelectronic devices.DLC films have been preparedby physical vapor deposition (PVD) or chemical vapor deposition (CVD).The aboveprocess is still questioned for its scalability and cost-effectiveness.Search forlow-cost and scalable technique for DLC deposition is still on the hot anvil.In recent times,possibility of depositing DLC films from organic liquids byelectrochemical technique was demonstrated by Namba.Electrodeposition techniquehas demonstrated some advantages over vapor phase deposition,such as thesimplicity and low cost of experimental apparatus,possibility of low temperaturesynthesis and ease of experimental control to produce films with diverse properties,etc.Subsequent efforts were devoted to the progress of electrodeposition of DLCfilms.The research work is concerned with the preparation of DLC films byelectrochemical deposition.The field electron emission properties of DLC films werealso investigated.The main research contents of this thesis are shown as follows:1.At ambient pressure,DLC films were deposited on Al substrates by electrolysis ina methanol solution under various voltages.The surface morphology andmicrostructure of the synthesized films were characterized by SEM,FTIR,XPSand Raman spectroscopy.With the increase of deposition voltage,the sp2 phaseconcentration decreased and the surface morphology changed dramatically.Theinfluence of deposition voltage on the field electron emission (FEE) properties ofDLC films was not monotonic due to two adverse effects of deposition voltage onthe surface morphology and compositions.The DLC film deposited under 1200 V exhibited optimum FEE property.2.Nitrogen incorporated diamond-like carbon (DLC:N) films with different Ncontent were deposited on Si(100) substrates by electrolysis of urea/methanolorganic solution with different mole ratios under a constant voltage of 600 V.Analysis by XPS,FTIR,and Raman spectrometry showed that N wasincorporated into the DLC films by sp~3 C-N and sp~2 C=N bonds and inducedgraphitization of the films.The influence of N content on the electronic fieldemission properties of these films was investigated.The turn-on field (Ec) waslowered with increasing N content,and there was a simultaneous rise in the fieldemission current densities under the electric field of 23.5 V/mm.Enhancement infield emission is attributed to the donor activity of nitrogen and the fieldenhancement effect of sp~2 clusters.3.On the basis of the investigation on deposition of DLC films in methanol,byelectrolysis of the N,N-dimethylformamide solution with simple electrochemicalapparatus,an attempt was made to simultaneously deposit DLC films on bothsurfaces of an aluminum Al substrate.Raman spectra showed that the structuresof the DLC film were uniform.The thickness distribution of the film was260-300 nm.A simple model of the sustaining mechanism was proposed forsimultaneous electrodeposition of the DLC film on both surfaces of conductivesubstrates.The simultaneous formation of the DLC film on both surfaces of theAl substrate showed a possibility in the three-dimensional deposition of DLCfilms on complex conductive substrates.