Niobium Base Preparation, Doping And Electrochemical Properties Of Cvd Diamond Film Studies

As a novel electrode material, boron-doped diamond (BDD) coatings possess many exceptional electrochemical properties such as wide electrochemical potential window, very low background currents, a very high electrochemical stability and high resistance to fouling. Therefore, BDD films have been considered to be especially interesting and prospective for the destruction of pollutants in water. Many studies on boron-doping and electrochemical characteristics have been reported for BDD films. However, most of the reported doped diamond films were deposited onto silicon wafers, and the low mechanical strength and restricted conductivity of this substrate limit its use in many practical applications. Thus, it is profound work to choose a more favorable substrate on which to grow high quality and excellent adhesion BDD films.The surface morphology, chemical bonding states, phase composition and adhesion of the as-grown diamond films were investigated by means of field emission scanning electron microscope(SEM), atomic force microscope, Raman spectroscope (Raman), X-ray diffractrometry(XRD) and Vickers microhardness tester, respectively. The effects of process parameters (such as substrate temperature, gas composition and reactor pressure) and boron volume concentration (RB/c=VB2H6:VCH4) on diamond growth were systematically studied. Meanwhile, the electrochemical behaviors of the BDD electrodes were studied by the cyclic voltammetry (CV) in lmol/L H2SO4solution and0.lmol/L KC1+0.01mol/L K3Fe(CN)6redox system. Conclusion can be drawn as following:The quality and performance of diamond film is strongly dependent on the deposition parameter. We showed an optimal growth condition being substrate temperature Ts=800℃, CH4volume fraction RC/H (VCH4/VH2)=1%, reaction pressure P=3.5KPa. Besides, the linear growth rate of diamond films can be optimized by choosing proper growth time (4h).Boron-doping can greatly influence the morphology, microstructure, defect density and nondiamond carbon impurity content in diamond film, consequently, influencing the electrochemical response of diamond thin film electrode. The average grain size and growth rate of diamond film decrease as increasing the volum ratio of B/C. There are several drastic changes of heavy doped diamond films compared with the light doped samples. When borane concentration ranges from3%to6%, the actual boron concentration in diamond films maintains1×1021cm-3.The Nb/BDD electrodes have a wide potential window (-3.5V), low background current (<2×10-5A), good activity and obvious quasi-reversible property in CV test. With the increase of the boron dopant level, the potential windows of the electrodes become narrower, the background currents become larger, and the redox reaction rate become faster. In addition, the reactions are controlled by diffusive mass transport.