Decreased Secondary Electron Emission from Aluminum Surface by a Fluorocarbon-Titanium Composite Film

Multipactor, a vacuum discharge under microwave conditions triggered by secondary electron emission (SEE), plays a critical role in managing the power level of microwave devices. In this study, we developed a fluorocarbon-titanium composite film on aluminum by cosputtering polytetrafluoroethylene (PTFE) and titanium via a controlled temperature and sputtering power ratio (RF power for PTFE to DC power for Ti) to suppress the SEE of Al. The evolution of microtopography and chemical composition of the composite film was evaluated. An increasing power ratio varying from 0.5 to 3.0 is found to change the film surface from scattered island-like bumps to a prominent peak-valley pattern and eventually to a smooth surface with few flat swellings. Elemental analysis revealed that the fluorine-to-carbon (F/C) mole ratio in samples was more significantly influenced by the sputtering power ratio than by the substrate temperature. The SEE yield indicates that the peak-valley pattern prepared by a power ratio of 2 leads to the maximum of the SEE yield curve reducing steeply from 2.99 to 1.23, which is attributed not only to the roughed pattern but also to the high F/C mole ratio owing to the higher capacity of electron trapping by the fluorine atoms.