Low Secondary Electron Emission 2D Surfaces

The secondary electron emission is the feedback mechanism of the resonant avalanche of electrons or Multipactor discharge in high- power RF devices onboard satellites. The multipactor discharge is a severe problem which limits the maximum power of RF instrumentation in space missions, it can cause RF signal loss and distortion and it can increase the noise figure or bit-error-rater even total mission failure. The search for surfaces with a low secondary electron emission yield (SEY) is considered one of the main research areas to reduce the multipactor effect in high-power RF devices used in spacecraft and other important technological fields such as high-energy particle accelerators. In this study, RF devices were made using aluminum alloy AA6061. The RF insertion losses of the devices were improved, meaning they were reduced, when AA was silver-coated. However, the SEY of silver, although lower than that of AA, still needs to be reduced to prevent multipactor. The SEY of silver exposed to air is greater than 2. The aim of this study was to deposit a 2D MoS2 layer on silver coatings that are suitable for reducing SEY and preventing multipactor discharge. Prior to the deposition of the silver coating, the aluminum alloy of the RF devices was zincated, followed by the deposition of intermediary layers of Ni and Cu. We used deep eutectic ionic liquids (2:1 ethylene glycol-choline chloride) instead of water to deposit these coatings. Finally, the MoS₂ was deposited on the external silver coating using an optimized electroless process. As a result, we have developed an electroless plating process for growing 2D nanostructures with a high aspect ratio. The characterization was performed in an ultra-high vacuum (UHV) system composed of three interconnected chambers at a pressure of less than 10-9 hPa, while the fast entry chamber remained at 2x10-7hPa. SEY is defined as the number of emitted electrons per incident electron, that is, SEY = Ie/Ip, where Ie is the emitted current and Ip is the primary or incident current. SEY was measured in the primary electron energy range from 0 to 1000 eV. The samples were also analyzed by x-ray photoemission spectroscopy (XPS) and field-emission scanning electron microscopy (FESEM).<br/>In this study, we report an extremely low SEY of this multi-layer coating. The SEY as a function of primary electron energy curves show a maximum value close to 0.8. Furthermore, a linear translation of the SEY curve towards the region where SEY &gt;1 for oxygen content &gt;0.3% is observed. The energy distribution curves (EDC) or energy spectra of secondary electrons also exhibit a significant decrease in the signal for kinetic energies &lt;50eV, which is consistent with the SEY results.