1 Center for Electron Nanoscopy, Technical University of Denmark2 Department of Micro- and Nanotechnology, Technical University of Denmark3 Molecular Windows, Department of Micro- and Nanotechnology, Technical University of Denmark
This work focuses on creating tools for imaging liquid samples at atmospheric pressure and room temperature in two different electron microscopes; the scanning electron microscope (SEM) and the transmission electron microscope (TEM). The main focus of the project was the fabrication of the two systems; the electrochemical scanning-electron-microscopy cell (EC-SEM cell) and the TEM chip (version 1 and 2), and verifying that they can be used, for liquid phase experiments, in SEM and TEM. These systems allow imaging of liquids and of objects in the liquid. They also include electrical connection to the liquid allowing measurement of electrical signals or the application of a voltage to the liquid during imaging. In a SEM, where there is a comparatively large chamber to work with, a polycarbonate holder with micro-fluidic channels was fabricated to contain the liquid. The EC-SEM chip with an electron-transparent window and built-in electrodes was placed above a reservoir, sealing off the liquid from the vacuum, but allowing imaging through the window in the chip. In-situ electrochemical experiments have been performed with this setup: imaging the electron beam (e-beam) deposition of nickel on the window, electrolysis of H2SO4 and measureing a CV of K3Fe(CN)6. In a TEM the volume to work with is far smaller and a monolithic micro-fabricated chip was designed and fabricated for this microscope. The chip includes a microchannel which contains the liquid and runs over an electron-transparent membrane. The channel keeps the liquid in a well defined area and reduces the volume increase from bulging in vacuum. Special windows are defined where the channel wall is thinned down to reduce the mass-thickness in these areas and retain the mechanical stability of the rest of the chip. Electrical connection to the liquid can be achieved with platinum electrodes lithographically defined on the chip. The TEM chip has been used to image liquids in the TEM and to perform proof-ofconcept experiments of holography of liquid. Furthermore, in SEM, preliminary work has been completed to integrate graphene windows in the EC-SEM cell. In TEM, holography of graphene multi-layer sheets has been performed and the phase change per sheet has been determined as a step towards in-situ holography of liquid through graphene.