Liquid Cell Transmission Electron Microscopy

Since its development over fifty years ago, transmission electron microscopy was generally used for thin, solid samples: liquid samples were incompatible with the vacuum inside the microscope. But now we can use microfabrication techniques to enable electron microscopy to provide high spatial and temporal resolution in liquids. The messy device shown here provided an early electron microscopic view of a materials growth process in water.

More recent liquid cells consist of two ultrathin SiN_x membranes that sandwich the liquid when clamped together in a specially designed sample holder. In situ liquid cell experiments can be applied to study a wide range of phenomena. Seeing every step of a reaction gives us a much better chance of understanding what is going on. Our ultimate goal is to understand materials growth and structure in liquids well enough to control the properties of the materials.

Early liquid cell experiments involved measurements of the electrochemical deposition of copper, the process used to fabricate conductive lines in microelectronic circuits. In the image sequence below, copper (dark areas) grows when a voltage is applied and the electrochemical characteristics (here, voltage and current vs. time) are measured simultaneously.

Liquid cell TEM provides a unique window into many other materials reactions. We find electrochemical reactions particularly interesting: batteries as they charge and discharge, corrosion, and growth of compact layers and dendrites. We are also interested in nanobubble dynamics in water and nanoparticle formation from metal ions in solution. To help quantify observations made in the microscope, we also model the effects on the water itself due to irradiation by the high energy electrons.