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The micro-discharge effect limits the development of high-frequency microwave power components to miniaturization and integration. Therefore, it has become a focus of research to effectively suppress the micro-discharge effect, increase the micro-discharge threshold, and strengthen the environmental stability of high-frequency microwave devices. In this study, different elemental ratios of carbon (C)/silver (Ag)/titanium (Ti) composite films were obtained by multi-target magnetron co-sputtering technology and then systematically analyzed for micro-discharge effects. When the doping ratio of C/Ag/Ti was 3.538/1/0.013, the corresponding maximum secondary electron emission coefficient (δmax) decreased to 1.01 owing to the suppression of secondary electron emission by the increase in the content of sp2 hybrid bond. The micro-discharge threshold of Ku band waveguide filters coated with moderate C/Ag/Ti composite films showed an optimal performance of 10 000−12 500 W, which was increased by approximately 20 times. Moreover, the microstructure of the composite films exhibited higher density and flatness with a tiny increase in the titanium doping ratio, representing good environmental stability. Thus, the effective suppression of the secondary electron emission yield, significant improvement in the micro-discharge threshold, and enhancement of the environment stability of microwave components could be realized simultaneously by reasonably controlling the content of titanium in silver and titanium co-doped carbon-based composite films. [ABSTRACT FROM AUTHOR]

The micro-discharge effect is a failure mechanism that often appeared in space microwave devices under vacuum conditions, such as RF (radio frequency) cavity, RF satellite missile, and antenna launching communication system. How to control micro-discharge effectively and simply has become a research hotspot. In this paper, we have prepared a series of doping silver (Ag)/carbon (C) composite films by double target magnetron sputtering technology and have significantly reduced the maximum secondary electron emission coefficient (δmax) from 2.522 to 1.04 when the doping ratio of Ag/C is 1.345. Theoretically, the continuous increase of sp2 hybrid bond content tuned by the existing Ag nanoparticles has a greater contribution to the conductivity and inhibition of secondary electron emission in the Ag/C composite films. Meanwhile, the gradually emerged "multi-trap" surface structure with the increase of Ag doping content has further increased the collision between excited secondary electrons and free electrons, achieving an obvious inhibition effect. The results demonstrate that secondary electron emission can be suppressed effectively by tuning the structural feature of two kinds of compounded materials with low δmax. It is of great significance in physical mechanism analysis and design of the new doping process. [ABSTRACT FROM AUTHOR]

It is known that an appropriate surface structure can suppress the secondary electron emission as a result of the receded multipactor in a spacecraft microwave component. On the other hand, the multiplier effect caused by electron re-entrance in ordinary surface structures can degrade the suppression of secondary electron emission. The present paper concerns our proposition of a new type of two-level nested microtrap structure surface able to effectively inhibit the generation of the secondary electrons inside the trap structure to achieve better suppression of the total secondary electron emission on the surface. The surface of a two-level nested microtrap array structure was obtained by lithography, stripping, dry etching, and Ag sputtering. Experimental tests were conducted on the two proposed nested structures with different sizes. The test results show that inhibition effects of the two structures have been improved by 100% and 144% compared with those of the traditional single-hole trap structure. The secondary electron yield on the bottom surface of the rough nested trap due to Ag sputtering is higher than that of the ideal regular structure simulated by Monte Carlo. In addition, the larger depth-to-width ratio of the nested trap can inhibit the multi-generation multiplication of electrons in the trap more effectively and further improve the inhibition effect on secondary electrons. For an impedance transformer, the proposed two size nested structure surface can increase the multipactor power threshold by about 346% and 386%. This method plus the nested microtrap structure can achieve a better secondary electron emission suppression effect and further improve the multipactor threshold of space microwave components. [ABSTRACT FROM AUTHOR]

The analytical description of dielectric multipactors requires an accurate physical model. In this article, a nonstationary statistical theory for the analysis of single-surface dielectric multipactors is established by defining an emission-to-emission transition rate and involving all the probability densities related to the emitted secondary electrons. Under the same conditions, the fluctuation of electrons in the evolution process of dielectric multipactors was calculated by the proposed theory and simulated by a commercial particle simulation tool developed based on the Monte Carlo analysis. The calculated results comply well with the simulated ones. Our results also indicated that to obtain an adequate accuracy, at least two random variables, the emission velocity and zenith angle, need to be considered. [ABSTRACT FROM AUTHOR]

Secondary electron (SE) yield, δ , is a very sensitive surface property. The values of δ often are not consistent for even identical materials. The influence of surface changes on the SE yield was investigated experimentally in this article. Argon ion sputtering was used to remove the contamination from the surface. Surface composition was monitored by X-ray photoelectron spectroscopy (XPS) and surface topography was scanned by scanning electron microscope (SEM) and atomic force microscope (AFM) before and after every sputtering. It was found that argon sputtering can remove contamination and roughen the surface. An “equivalent work function” is presented in this thesis to establish the relationship between SE yield and surface properties. Argon ion sputtering of 1.5keV leads to a significant increase of so called “work function” (from 3.7 eV to 6.0 eV), and a decrease of SE yield (from 2.01 to 1.54). These results provided a new insight into the influence of surface changes on the SE emission. [ABSTRACT FROM AUTHOR]

In this work, the surface of Al sheet was coated with a fluorocarbon (FC) thin film by radio frequency (RF) sputtering of polytetrafluoroethylene (PTFE) to investigate the influence of dielectric coatings on the secondary electron yield (SEY) behavior of Al sheets. Atomic-force microscopy (AFM) and energy-dispersive spectroscopy (EDS) were employed to identify the surface topographies and elemental contents of the samples with FC coatings. Water contact angle (WCA) measurements were performed to characterize the surface tension as well as the polar and dispersion components of the samples’ surface. The secondary electron- mission (SEE) behavior of the samples was determined by measuring the SEY coefficients in an ultra-high vacuum chamber with three electron guns. The experimental results indicated that the longer sputtering time effectively led to the increase in coating thickness and a higher ratio of F/C, as well as the continued decrease of surface tension. A quite thin FC coating of about 11.3 nm on Al sheet resulted in the value of maximum SEY (δmax) dropping from 3.02 to 1.85. The further increase in coating thickness beneficially decreased δmax down to 1.60, however, at the cost of a ten-fold thicker coating (ca. 113 nm). It is found that increasing the coating thickness contributes to reducing SEY coefficients as well as suppressing SEE. The results are expected to guide the design of dielectric-coating for SEY reduction as well as multipactor suppression on Al. [ABSTRACT FROM AUTHOR]

The secondary electron emission (SEE) characteristics of materials is one of the issues of interest for microwave components used in space, as it has a decisive effect on the multipactor. In the presented work, the SEE characteristics of gold and silver plating widely used in microwave components is systematically investigated as a function of atmospheric exposure time for up to 400 days. The secondary electron yield (SEY) and the first energy crossover point (E 1) increase and decrease non-monotonically with exposure time for gold plating, whereas they decrease and increase non-monotonically for silver plating, respectively. The results of surface characteristics test and analysis indicate that after exposure to the atmosphere, the surface of gold plating has an adsorption layer consisting of C and O elements, which leads to an increase in SEY, while the surface of silver plating becomes rough and a microporous structure is formed on it due to natural chemical reaction, which results in a decrease in SEY. In addition, the analysis results of parallel plate model show that the multipactor voltage is reduced by up to 3 dB for gold plating and increased by up to 3 dB for silver plating after prolonged exposure to the atmosphere. • Secondary electron yield of gold plating increases non-monotonically with exposure time. • Secondary electron yield of silver plating decreases non-monotonically with exposure time. • Variation of secondary electron emission characteristics greatly affects the multipactor voltage. [ABSTRACT FROM AUTHOR]

• Ordered monolayer silver nano-bowl coatings prepared by an electrodeposition method. • Coating structure modulated by altering the deposition time and template diameter. Multipactor leads to the unrepairable damage to high-power microwave devices in the satellite. Restraining the secondary electron yield (SEY) is an effective method to suppress the multipactor of microwave devices. In this work, silver nano-bowl coating was fabricated via electrodeposition in AgNO 3 electrolyte at room temperature on the surface of silver-plated aluminum alloy using the monolayer colloidal crystal of polystyrene (PS) spheres as templates. The scanning electron microscope images show that the surface structure of the silver-plated aluminum alloy sample could be modulated by altering the deposition time and adjusting the size of the PS spheres. And the pore diameter and the aspect ratio of the nano-bowl have a great influence on the SEY of the silver nano-bowl coating. When the size of the PS spheres is 2000 nm and the electrochemical deposition time is 90 min, the maximum value of SEY value of silver nano-bowl coating drastically decreases by 39.3% from 2.44 to 1.48, compared with that of the initial silver aluminum alloy samples. The silver nano-bowl coating shows great multipactor suppression for potential application in a satellite. [ABSTRACT FROM AUTHOR]

• The influence of adsorption of N 2 , O 2 , Ar and air for Ar ion sputtered Cu on the secondary electron emission were researched experimentally. • Different effects of heat treatment on between Ar ion sputtered sample and gas adsorption sample were confirmed. • The relative contents of C and O with different treatment were analyzed by in-situ XPS. • The relationship between the secondary electron yield and secondary electron spectrum was theoretical derivation and experimental validated. Secondary electron (SE) emission is a superficial physical phenomenon. The range of SEs excited in materials which are finally emitted from the surface is generally within a few tens of nanometers. SE emission from materials by electron irradiation has great dependence on surface quality, such as gas adsorption, oxidation, contamination, and morphology. In this paper, the influence of surface adsorption of N 2 , O 2 , Ar and air on SE yield (SEY) and the SE spectrum (SES) of copper was investigated by experiment. The measured SEY and SES were compared before and after the copper surface was sputtered by Ar ions. The results show that gas adsorption could increase SEY, and air adsorption lead to the maximum increase, Ar adsorption the minimum. Meanwhile, the relationship between the SES and the SEY was deduced and validated by the experiment. It was also found in the experiment that the Ar ion sputtering or heating alone can effectively reduce the SEY, while heating the sample after Ar ion sputtering increases SEY. The reasons for the variation of the SEYs with gas adsorption, sputtering and heating are preliminarily explained with the help of in-situ XPS. Accordingly, the research helps to further reveal the mechanism of SEE influenced by complex superficial factors. [ABSTRACT FROM AUTHOR]

• Secondary electron yield of inert metals increases with exposure time. • Surface adsorption layer consisting of carbon and oxygen elements results in the increase. • A two-layers secondary electron yield model is established and parameters of adsorption layer are obtained. • The increase of secondary electron yield can significantly reduce the multipactor threshold. The secondary electron emission (SEE) property of materials is closely related to the multipactor, which is one of the potential risk factors affecting the reliability of high power microwave components for space application. In the presented work, the influence of atmospheric exposure on the secondary electron yield (SEY) of the inert metal is investigated. It is found that the SEY increases gradually with exposing time, and the increase in SEY results from the surface adsorption layer consisting of carbon and oxygen elements. A two-layers SEY model is established to explain this evolution and obtain the corresponding parameters of the adsorption layer. Simulation on a C band impedance transformer shows that 45 days of exposure will result in a 7.5 dB decrease of multipactor threshold. [ABSTRACT FROM AUTHOR]