Chapter

Electron Beam (E-Beam) Evaporation

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Abstract

A filament can be raised in temperature to become white-hot using a low-voltage and high-current power supply. The power to the filament can be either AC or DC. With such high currents being used, a magnetic field is created by the current flowing through the wire, and this will affect the electron emission. The quantity of electrons emitted depends on the current passed through the filament, the temperature achieved, and the work function along with other factors. The anode provides the acceleration to the electron (e)-beam. The acceleration voltage can be as high as 35 kV. Once this beam is produced, it can be focused and manipulated in the same way a cathode ray tube operates using electromagnetic sweep coils. The power supply for e-beam guns must be able to do more than supplying a highly stabilized voltage and current. The nature of the power that is involved means that the supplies have to be well protected from arcing. The emission circuit is reliant on a very high stability source and a current-sensing resistor to ensure a constant electron emission current. The acceleration voltage also uses a constant voltage control circuit, thus keeping everything as stable as possible.

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Article
The effects of electropolishing and coating deposition on electrical resistance and chemical stability were studied for the stainless steel bipolar plates in proton exchange membrane fuel cell (PEMFC). A series of 316L stainless steel plates, selected as the substrate for a proton exchange membrane fuel cell (PEMFC) bipolar plate, were electropolished with a solution of H2SO4 and H3PO4 at temperatures ranging from 70 to 110 °C. The surface regions of the two electropolished stainless steel plates were coated with gold and either a titanium or nickel layer using electron beam evaporation. The electropolished stainless steel plates coated in 2-μm thick gold with a 0.1-μm titanium or nickel interlayer showed remarkably smooth and uniform surface morphologies in AFM and FE-SEM images compared to the surfaces of the plates that were coated after mechanical polishing only. The electrical resistance and water contact angle of the deposited stainless steel bipolar plates are strongly dependent on the surface modification treatments (i.e., mechanical polishing versus electropolishing). ICP-MS and XPS results indicate that after electropolishing, the coating layers show excellent chemical stability after exposure to an H2SO4 solution of pH 3. Finally, it was concluded that before coating deposition, the surface modification using electropolishing was very suitable for enhancing the electrical property and chemical stability of the stainless steel bipolar plate.
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