磁控溅射铂抑制镀银表面的二次电子发射

Suppressing secondary electron emission from silver-plated surface by magnetron sputtered platinum

降低表面的二次电子产额是抑制微波部件二次电子倍增效应和提升功率阈值的有效途径之一,目前主要采用在表面构造陷阱结构和沉积非金属薄膜的方法降低二次电子产额,其缺点是会改变部件的电性能.针对此问题,采用在表面沉积高功函数且化学惰性的金属薄膜来降低二次电子产额.首先,采用磁控溅射方法在铝合金镀银样片表面沉积100 nm铂,测量结果显示沉积铂后样片的二次电子产额最大值由2.40降至1.77,降幅达26%.其次,用相关唯象模型对二次电子发射特性测量数据进行了拟合,获得了在40-1500 eV能量范围内能够准确描述样片二次电子产额特性的Vaughan模型参数,以及在0-50 eV能量范围内能够很好地拟合二次电子能谱曲线的Chung-Everhart模型参数.最后,将获得的实验数据和相关拟合参数用于Ku频段阻抗变换器的二次电子倍增效应功率阈值仿真研究,结果表明通过沉积铂可将部件的功率阈值由7500 W提升至36000 W,证实了所提方法的有效性.研究结果为金属材料二次电子发射特性的研究提供实验数据参考,对抑制大功率微波部件二次电子倍增效应具有参考价值.

The multipactor effect has to be dealt with seriously when designing and manufacturing high power microwave devices used in space, as it will cause inreversible damage to devices and hence the whole system fails to work. Lowering the secondary electron yield of device surface is an effective way to suppress multipactor effect, which can be realized by creating trapping structure or depositing nonmetallic materials with low secondary electron yield on the surface.However, these treatments will result in electrical performance changing even to an unacceptable extent in some cases.To solve this problem, the deposited materials with conductivity as good as metals＇ should be used, besides, they should be chemically inactive in air. Taking the above into account, the method of suppressing the secondary electron yield of silver plated surface of device by magnetron sputtering platinum is proposed and investigated in the present paper.Firstly, platinum film with a thickness of 100 nm is deposited on silver plated aluminum alloy substrates by magnetron sputtering, and secondary electron yields of substrates with and without deposited platinum film are measured with the bias current method. The experimental results indicate that the maximum value of secondary electron yield and the first cross energy of silver plated aluminum alloy sample are 2.40 and 30 eV, respectively. After depositing platinum film on sample, these values change to 1.77 and 70 eV, a reduction of 26% in maximum of secondary electron yield is achieved. Secondly, universal law, Vaughan model, Furman model and Scholtz model are used to fit the experimental data of secondary electron yield, and the results indicate that only Vaughan model accords well with the property of secondary electron yield in an energy range of 40-1500 eV, and corresponding parameters are also obtained. The Chung-Everhart model is used to fit the secondary electron spectrum curve, and the fitted work function is 9.9 eV.Finally, the simulation of multipactor threshold of Ku-band impedance transformer is carried out by using a software with utilizing the experimental data and fitted results of secondary electron emission of samples. The simulation results indicate that the multipactor thresholds by utilizing the data of samples with and without platinum are 7500 W and36000 W, respectively, which means that the large increase of multipactor threshold of high power microwave device can be achieved by depositing platinum film on the surface. The method proposed and results obtained in the present work provide a reference not only for studying the secondary electron emission of metal, but also for suppressing the multipactor effect of high power microwave device.