Study On The Conductivity Of Surface-modified Diamond Film

By different surface modification,the diamond films would show various surface conductivities.This makes it have a broad application prospect in the development of in-plane micro-electronics and micro-electrochemical devices.So,it is of great significance to study the surface modification of diamond films and conducting mechanisms in the field of electricity and electrochemistry.By means of first principles methods and experiment,the effect of adsorbed active particles on the electrical conductivity of diamond films with different surface modification was investigated.On the aspect of theoretical study,by means of first principles method based on density functional theory,models corresponding to hydrogenated,oxygenated and ammoniac diamond?100?surfaces with various active adsorbates were built up.Their equilibrium geometry and density of states were investigated.Firstly,on the adsorption system of H₃O⁺ ion and H₂O molecule,after adsorption with H₃O⁺ ion on hydrogenated diamond?100?surface,shallow acceptors appear near Fermi level,which arises from charge transfer from hydrogenated diamond surface to adsorbed H₃O⁺ ion.Therefore,it exhibits p-type conductivity.When mixed adsorption with H₃O⁺ ion and H₂O molecule,no significant effects on its conductivity is detected,though its surface energy band structure alters.For the ammoniac diamond?100?surfaces,the charge transfer is weaker than that of hydrogenated surface when adsorption with H₃O⁺ ion.And in the rest of the adsorption systems,ammoniac diamond showed similar results.However,the adsorbates containing H₂O molecule and H30+ ion on oxygenated diamond?100?surfaces would not exist stably.H₃O⁺ ion would decompose.All the oxygenated diamond surfaces with various adsorbates exhibit electric insulativity.Secondly,on the adsorption system of NO2 molecule and H₂O molecule,H₂O molecule in the adsorbate could weaken the interactions between the adsorbates and hydrogenated diamond surface significantly.Compared with H₂0 molecule,NO2 molecule relaxes more dramatically when adsorbed on hydrogenated diamond surface.After adsorption with NO2 molecule on hydrogenated diamond?100?surface,shallow acceptors appear near Fermi level,which arises from charge transfer from hydrogenated diamond surface to adsorbed NO2 molecule.Therefore,it exhibits a p-type conductivity.Similarly,the ammoniac diamond film adsorption system also showed similar conductivity.However,oxygenated diamond?100?surfaces with various adsorbates containing different NO2 and H₂O molecules on it exhibit an insulating property.The above results provide a basis for further exploring the conductive mechanism of diamond films and the development of the electronic and electrochemical devices with high quality.Compared with other modified methods,electrochemical method has many advantages,such as no damage to diamond surface and easy preparation.On the aspect of experimental study,by using electrochemical methods,hydrogen-,oxygen-and ammonia-terminated diamond films were prepared under various conditions.Then,their surface morphologies,phase structures,chemical composition,water wettability and conductivity are characterized.Firstly,hydrogenation and oxygenation have no effects on the surface morphology of diamond film.At the same time,hydrogen,oxygen and ammonia terminations impact its surface phase structure little.And hydrogen terminations show hydrophobic property,while oxygen and ammonia terminations show hydrophilicity.By using cathode immersion under the voltage of-5V,diamond film exhibits the best hydrogen termination.Secondly,in the NO2 and humid atmosphere,hydrogen and ammonia terminations show high electrical conductivity,while oxygen terminations still show insulation.The experimental results are in agreement with the theoretical results.The above results provide electrochemical methods for preparation of diamond films with different surface modification.