Study Of AFM Probe Contamination Control And Its Effects On The Measurement Of PZC Of Al₂O₃ Single Crystal

In view of the high melting point,high hardness and high thermal conductivity of sapphire,it was widely used in the areas of advanced ceramics,LED,compound materials and catalysis.The point of zero charge(PZC)was a key parameter of sapphire,which showed the acidic or basic property of the surface,were vary from pH=3 to pH=8 in the references.The main problem lieed in that although researchers realized that PZC was a surface sensitive parameter,surface structure and the contamination control of the measurement system were neglected,which affected the reproducibility and accuracy of PZC measurement greatly.AFM colloidal probe microzone measurement method has been widely used to characterize the charging state of the surface,in this dissertation,it was used to obtain the PZC of sigle sapphire(0001),due to the lack of effeicient method in eliminating contaminants on the surface of AFM probe,regular ways to clean the probe were studied systematically,and a new method was proposed.The ex situ AFM measurement was also improved.On the basis of improving the contamination control of probe and sapphire crystal,along with the degas process towards solution with inert gas,the point of zero charge of sapphire crystal(0001)was obtained.Three areas of the AFM colloidal probe microzone measurement method were improved in this dissertation.First,the cleaning effect of various wet and dry cleaning methods were critically evaluated using comprehensive surface analysis techniques including the optical microscope(OM),scanning electron microscope(SEM),atomic force microscopy(AFM),XPS and contact angle measurements(CA).Furthermore,a new UP cleaning method was designed to properly clean the probes,which showing outstanding cleaning performance and without causing any damage to the probe.Second,in situ measurements of surface imaging,colloidal probe reverse imaging and force curve were obtained together under the same test system,and the systematic error was reduced.Third,according to the bibliography,single sapphire was cleaned rigorously,“step-terrace” structure was obtained to make sure the interaction happened between colloidal probe and intrinsic surface.By injecting inert gas into the solution,the stability of the pH value was improved.On the basis of these improvements,the PZC of sapphire was obtained.Furthermore,the surface imaging and force curve measurement were realized based on the “silica sphere-silica sphere” system,which provided reliable surface potential benchmark to “silica spheresapphire plane” system.The reliablility and reproducibility were both improved by adopting the optimized system,and the results showed that PZC was between pH=7.3~7.5.The results could be explained by the improved Bickmore model with pKa=7.9~11.6 replaced by pKa=7.3~7.5.