Research On The Secondary Electron Emission Characteristics Of Low Energy Region On The Surface Of Microwave Components

Secondary electron emission is currently an important research topic in the field of surface microanalysis such as scanning electron microscopy(SEM)and Auger electron spectroscopy(AES).It is also an important factor that restricts the performance of electron accelerators,high-power microwave sources,and space microwave devices.Based on the research platform of multifunctional ultra-high vacuum secondary electron emission characteristics built by Xi'an Branch of China Academy of Space Technology,this paper proposes a new measurement method of secondary electron emission coefficient and completes the data collection in low energy region based on the existing testing methods.By comparing the SEY measurements before and after the annealing of more than 10 different types of metals,the common properties of secondary electron emission characteristics affected by temperature were studied,and the corresponding metal SEY database was established.In addition,for the inhibition of surface morphology changes to SEY,design experiments were conducted from the perspective of coating and trap structure respectively.The main contents and research conclusions of this thesis are as follows:1.Improve the existing measurement methods based on the laboratory platform and achieve SEY measurements in the 0-50 e V low energy area.A fixed electron gun cathode voltage was used to adjust the sample bias voltage to achieve precise control of low-energy electrons.Two current meters were used to connect the collector stage and the sample stage,respectively.The difference between the secondary electron current and the incident current and the secondary electron current was measured.To achieve a fast and accurate measurement of the secondary electron emission coefficient in the low energy range.The new method ensures the complete collection of the incident current during measurement and circumvents the experimental error that the original method requires two measurements;Solved the problem of the limitations of the minimum adjustable amplitude of the electron gun of the test platform,and completed the complete measurement of the gold-silver-copper-aluminum low-energy region(0-50 e V)SEY for the first time in China.The experimental results are consistent with the results of R.Cimino et al.It is consistent and provides good data support for the prediction of the micro discharge threshold.2.Common properties of secondary electron emission characteristics of metallic materials are affected by temperature changes.The target metals to be measured are divided into three categories: commonly used metals for microwave(gold,silver,copper and aluminum),magnetic metal materials(iron,nickel and cobalt),and rare metals(platinum palladium,titanium vanadium).A metal coupon with a purity of 99.9999% and a thickness of 0.1 cm was selected.After the SEM observation during the measurement process,the incident energy range was selected to be 40-1200 e V,and the bias current method was used for measurement.Then consider the problem of surface adsorption,in order to accurately determine the effect of temperature heating on the metal surface SEY,ensure that all metal heating conditions are consistent: After heating at 250 degrees Celsius for 10 minutes,the SEY measurement of the corresponding material was performed after the temperature dropped to room temperature.The entire experiment completed the collection of SEY data for multiple metals,and before and after metal annealing,SEY showed a downward trend,and the overall curve area shifted downwards.3.To study the regularity of regular trap structure on the surface SEY of highfrequency microwave components.In order to eliminate the effect of the initial surface roughness on the SEY characteristics,the design experiment was conducted using a heavily doped heavily-doped p-type silicon as the research object.(The roughness of silicon is 0.1-0.15 nm,which is much lower than the roughness of tens of nanometers of ordinary metals.)Using ultraviolet exposure combined with reactive ion etching technology,a circular micro-nano trap structure was designed,and the rule of the regular trap structure on the surface SEY characteristics was systematically studied.Contrasting the experimental results,we found that,compared with the previously known trap structure,SEY has a significant inhibitory effect.In the skin depth scale of high-frequency microwave devices,the regular trap structure does not have an inhibitory effect on the SEY of the sample surface.With the increase of the lateral size of the trap structure,the SEY is on the rise.Based on this additional experiment,the horizontal size of the trap is reduced,and the SEY is significantly reduced after the aspect ratio is increased.The following conclusions have been drawn on the study of the inhibition of the SEY structure on the surface of the sample trap structure: It is of great significance to reduce the lateral size of the trap structure,reduce the trap diameter,and increase the depth-width ratio of the trap.4.Experiments were conducted on Ti N plating on silver surface to qualitatively and quantitatively investigate the inhibitory effect of Ti N structure on SEY.Considering the increase of coating thickness in practical application,the compatibility of the whole system is obtained.In order to obtain a more uniform and reliable surface coating structure,atomic layer deposition method is used to prepare and compare the thicknesses of 1 nm,2 nm,5 nm,and 10 nm as feature thicknesses.The results show that the SEY curve of silver plating on the surface of commonly used microwave components is significantly lower than that of SEY after Ti N coating.The uniformity is very good.With the increase of the thickness of the coating,SEY continuously decreases and stabilizes at about 1.55.