Self-aligned wet-cell for hydrated microbiology observation in TEM

Abstract

This paper describes a Self-Aligned Wet (SAW) cell suitable for direct-cell or bacteria incubation and observation in a wet environment inside a transmission electron microscope. This SAW cell is fabricated by a bulk-micromachining process and composed of two structurally complementary counterparts (an out-frame and an in-frame), where each contain a silicon nitride film based observation window. The in- and out-frames can be self-aligned via a mechanism of surface tension from a bio-sample droplet without the aid of positioning stages. The liquid chamber is enclosed between two silicon nitride membranes that are thin enough to allow high energy electrons to penetrate while also sustaining the pressure difference between the TEM vacuum and the vapor pressure within the liquid chamber. A large field of view (150 μm × 150 μm) in a SAW cell is favored and formed from a larger sized observation window in the out-frame, which is fabricated using a unique circular membrane formation process. In this paper, we introduce a novel design to circumvent the challenges of charging/heating problems in silicon nitride that arise from interactions with an electron beam. This paper also demonstrates TEM observations of D. Radiodurans growth in a liquid environment within a thicker chamber (20 μm) within a SAW cell.