Measurement Of On-surface Rapid Dynamic Processes

The author investigated two kinds of surface dynamic processes in surface science:surface diffusion and surface chemical reaction.The measurement of tracer diffusion behavior relies on atomic-resolved surface measurement methods,therefore,scanning tunneling microscopy(STM)is the best choice.There are several methods for measuring surface tracer diffusion using STM,in which the tunnel current/time spectrum(I-t)method can exploit the measurement limits of STM devices for high frequency diffusion.In order to measure higher-frequency surface diffusion,we proposed two methods.The first is to analyze the signal with a high-re solution spectrum analyzer without making major changes to the device.To this end,we have studied the aperiodic random square wave signal exhibited in the I-t spectrum.We have obtained the power spectral density calculation method of the random signal,and made an appropriate approximation to obtain the analytical expression.Therefore,we realized fast and accurate extraction of hopping rate data.However,experimental tests have found that it is difficult to break the 100 kHz limit Therefore,we have designed a solution to transform the high-frequency signal transmission and amplification capabilities inside the device.Due to the limited of time,the program was designed but not yet implemented.In the study of surface diffusion,the author also explored the possibility of quantum diffusion ofLi atoms on Si(111)-7×7 surface.Our data suggest that Li has the potential to exhibit measurable quantum diffusion behavior,but further confirmation is needed.The second part is related to surface chemical reactions.We have studied the stability of two-dimensional materials MoTe2 and ZrTes in water or oxygen environments.Experiments indicate that ZrTes is highly stability to oxygen,while the 5×10-7 mbar water vapor can dramatically change its properties within 30 min.MoTe2 is also highly stability in oxygen environment of 1×10-6 mbar and in a water vapor environment of 5×10-7 mbar.However,an energy gap opening is observed under latm of Oxygen within 3min.Combined with transport experiments,it can be shown that the appearance of the MoTe2 energy gap is due to surface oxidation.The results of surface chemical reactions provide a basis for the experimental research and application of two two-dimensional materials.