Construction of a Self-Contained Liquid/Gaseous Measurement Platform for Transmission Electron Microscopy – An In Situ Measurement Platform for Energy Materials and Devices
M. Tanase1,2, R. Sharma1, V. Aksyuk1, G. Holland1, and A.Liddle1
1Center For Nanoscale Science and Technology, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899; 2 Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742
Except in a very few special cases, liquids are incompatible with the vacuum environment of the transmission electron microscope. However, many scientifically interesting and industrially important processes take place in liquids: electrochemistry and catalysis are two that are vital in many applications, not least energy generation and storage. Understanding the processes that, for example, lead to loss of storage capacity in batteries, or loss of reactivity due to catalyst agglomeration, sintering or poisoning is critical. There is thus a growing need for developing metrologies where the system components can be studied in their reactive environments. Although we can perform in situ nanoscale measurements of catalytic processes in gaseous environments using an environmental scanning/transmission electron microscope (ESTEM), comparable measurements in liquids are much more challenging.
We present a new MEMS-based measurement platform for studying systems in liquid/gaseous environments inside the Transmission Electron Microscope (TEM). The platform takes advantage of the high spatial resolution of the TEM, and allows the application and measurement of electrical signals and the possibility of working in controlled gaseous or liquid environments, in situ in the TEM. The platform consists of disposable liquid and environmental cells mounted on a specimen insertion holder with the ability to control a microfluidic flow and the ability to apply and measure electrical signals in the pA range. The cell has an electron-transparent investigation area consisting of liquid confined between silicon nitride membranes, an electron-transparent electrode, reference and current collectors. The cell also contains an interfacing system to an external microfluidic circuit controlled by a syringe pump, and to a sub-nA electrical signal processing system, both supported by the specimen insertion holder, which also provides an air-vacuum interface and an X-ray screening shield compatible with conventional, high-vacuum transmission electron microscopes. Our design addresses issues raised by already-existing encapsulation solutions for TEM in that it provides a fine control of the liquid thickness across the entire electron-transparent area, thus making imaging and quantization using analytical techniques such as EELS and EFTEM possible; it provides simultaneous microfluidic flow control and application/measurement of electrical signals; and it is much less prone to contamination, a major issue in TEM. The platform is self-contained and maintains compatibility with other investigation techniques such as STEM, FESEM, FIB and XRD. It will allow a suite of metrologies already available in the TEM to be coupled with electrical measurements in controlled environments, in order to characterize dynamic processes relevant to energy materials and devices, in situ and with nanoscale spatial resolution.