Very large suspended graphene as an efficient electron-transparent gate electrode

Although a focused electron beam is required in field emission-based various applications, the electron beam is generally diverged in a conventional triode because the gate has a circular aperture through which the electrons are accelerated to reach the anode. To prevent the beam divergence, a suspended multi-layer graphene (MLG) was fabricated on a very large gate aperture to be used as an electron-transparent gate in a field emission triode. The suspended MLG was observed to have several micro-openings with an average diameter of ∼5 μm formed during a transfer. It was observed that the MLG with micro-openings was likely to act as an efficient transparent gate for electrons even with large number of graphene layers, exhibiting a high transmittance of ∼90%. The solid angles of the beams obtained using conventional gate aperture and suspended MLG gate were 0.225 and 0.074 sr, respectively, indicating that the suspended MLG resulted in a focused electron beam. Simulations confirm that the suspended MLG with micro-openings suppresses the beam divergence in a given triode configuration because the MLG results in the flattened electric field profiles between gate and cathode whereas a distorted potential distribution causing beam divergence occurs around the aperture in a conventional triode.

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