Research Of Discharge In Micro-gap Based On Scanning Probe Microscope

Scanning probe microscope is often used to characterize the surface structure and properties of micro and nano-scale samples with high spatial resolution of the morphology.By analyzing and processing the various interactions between the micro-probes and the sample,Accurately study the electrical and mechanical properties of the sample.Micro-discharge is a form of gas discharge that limits the discharge to a limited space.At atmospheric pressure,when the electrode size is reduced to a certain extent,the air discharge mechanism is significantly different from the long-gap air discharge.Using the scanning probe microscope to conduct the micro-discharge test at atmospheric pressure,not only the electrode structure can be easily constructed,but also the in-situ characterization of the morphology and the property of the discharge micro-area can be realized,which is favorable for the research on the micro-gap air discharge mechanism.The classical discharge theory can reasonably explain the macro discharge phenomenon and provide theoretical support for the corresponding discharge application.However,the Thomson discharge theory,which is usually used to explain the small gap discharge phenomenon under low pressure,cannot reasonably explain the phenomenon of mesoscopic scale air discharge.Therefore,in order to further explore the characteristics of micro-gap air discharge and determine the role of field emission and micro-discharge mechanism and mechanism to provide a theoretical basis for the application of micro-discharge plasma.Two sets of discharge test systems using manual precision stage and scanning probe microscope which can realize the control of the distance of the micro gap were designed.The phenomenon and mechanism of the micro-gap discharge when the DC voltage is applied under atmospheric pressure and the voltage of the two kinds of electrode structures are studied respectively.The precise positioning and in situ morphological characterization of pinhole electrode micro-regions were achieved by SPM.The experimental results of the first set of discharge test system show that the micro-gap discharge mechanism is very different from the long gap: when the gap length is about 15?m,the electrode of the needle plate can glow discharge under atmospheric pressure,the shape of the glow area is consistent with the shape of the cathode electrode,and the glow discharge damages the electrode more than Other forms of discharge.SPM-based needle plate electrode structure does not glow discharge,the cathode field emission discharge causes the negative breakdown voltage is lower than the same gap positive breakdown voltage.The analysis of the breakdown voltage and the pre-breakdown current shows that the negative polarity breakdown voltage and distance has no connection.The trend of the prebreakdown current value when the gap is less than 2?m is consistent with that described by the Fowler-Nordheim equation.It can be proved that the field emission is the dominant factor of the electric field discharge with very nonuniform micro-gap.SPM test results show that after discharging,the work function of plate electrode in discharge area will change.