Preparation Of Titanium Silicide Thin Film And Its Double-layer Capacitance In Ionic Solutions

With the rapid population growth and the speeding up of the industrialization, water pollution is becoming gradually serious. Generally, waste water include acid, base, oxidizing agent, chloride, ammonia, fluoride, the nitro compounds,copper, cadmium, mercury, arsenic compounds and so on. Therefore, the real-time monitoring of ion concentration in waste water is needed increasingly to monitor quality of the water, ensuring that the health of people is not influenced. The electric double layer capacitance works by the adsorption of electrolyte ion on the electrode surface, and its capacitance value increases with the increasing of the electrolyte concentration at low concentration, hence it is hopeful to using double-layer capacitor in real-time monitoring of waste water.Titanium silicide film is a kind of excellent electrode material because of a combination of excellent properties, such as low-resistance, high thermal stability and chemical stability, low surface work function, good match to silicon technology. The preparation conditions, such as the deposition temperature and the ratio of Si/Ti, have great influences on the surface structure of the film. On the other hand, the specific capacitance not only have close relation with porosity of electrode, but also have close relation with the dimension of pore, topological properties of pore and dimension of ions in solutions. Therefore, it is necessary to study the effect of the different preparation conditions and different electrolyte ions on electric double layer capacitors of the titanium silicide film electrode, which will have important scientific significance and application value to improve the application of materials and manufacture devices with high performance.In this paper, the TiSi2thin films with different mole rate of SiH4/TiCl4and different deposition temperature were deposited on glass slide by APCVD. The crystallinity and surface structure of films were studies by XRD, SEM and AFM. The characteristic of the electric double-layer capacitance was researched by cyclic voltammetry and the effects of the surface structure of films, the concentration of electrolyte and electrolyte ion on the electric double-layer capacitance and the shape of curve were analyzed. Also, the theory relationship between surface structure and the electric double-layer capacitance was built.The results indicate that the crystallinity and surface structure of TiSi2thin films which are deposited at different Si/Ti and temperature are affected the Gibbs free energy and the rate of nucleation and growth. The surface structure can be controlled by adjusting the Si/Ti and deposition temperature. The Si/Ti should be controlled at2and deposition temperature should be controlled at680℃and730℃, to obtain thin film with low stack density and high roughness.The titanium silicide thin films and nanowires have excellent electrochemical double-layer capacitance properties and the cyclic voltammetry curves of them are quasi-rectangular. There is a negative correlation between the specific capacitance and stack density of thin film and a positive correlation between the specific capacitance and roughness height. The thin films with different capacitance values can be obtained by adjusting the Si/Ti and deposition temperature, and the thin film with low stack density and high roughness can be obtained at Si/Ti being2and deposition temperature temperature being680℃and730℃.There is a series resistance in actual double-layer capacitance test, which cause the cyclic voltammetry curve deviate standard rectangular. With the increase of series resistance, the rectangularity of curves becomes worse. The series resistance changes with voltage because of the effect of fine structure. The relational expression between series resistance and voltage is shown below: R=R1+[R2-(KV)2]=R0-(KV)2The current peak strengthens with the increase of K and the decrease of Ro. The current peak only appears when the voltage reaches to a certain value, what’s more the current peak strengthens with the increase of scan rate.With the increase of the concentration of electrolyte, specific capacitance values first increase and then reach to saturation value and keep stable. The TiSi2thin film with specific capacitance value being320μF/cm2is obtained successfully, which is22times of the specific capacitance of ITO thin film. The specific capacitance value of titanium silicide nanowires can reach to1308.7μF/cm2, which is90times of the specific capacitance of ITO thin film. The specific capacitance value of TiSi2thin film in0.05mol/LNa2SO4solution is24times of that in deionized water. The equilibration specific capacitance of TiSi2thin film in Na2SO4solution is59times of that in deionized water. The TiSi2thin films show excellent application prospect on monitor of waste water.