Over the past two decades, liquid phase transmission electron microscopy (LPTEM) has been used to explore liquid processes in physics, chemistry, materials- and bio- science down to the atomic scale and at micro/millisecond temporal resolution in situ with their native liquid environment.[1]

A conventional liquid cell consists of two 30-50 nm thick silicon nitride (SiNx) windows (∼50um*200um) suspended on two physically separated silicon chips, which enclose a liquid sample layer with a thickness ranging from a few hundred nanometers to a couple of microns.[2] A liquid sample can be drop cast on one silicon chip before assembly, or it can be pumped in through capillary tubes.[3] With such architecture, nanoparticle nucleation, growth, and etching,[3] self-assembly, interactions, and biological structures have been investigated. By integrating electrodes, one can visualize dendrite formation[4] or the lithiation process.[5] Or, one can use the electrodes as a heater[6] or sensor[2] and investigate temperature influences on chemical reactions etc. Nevertheless, the conventional liquid cell is plagued with window bulging in TEM vacuum giving thick liquid layers, and poor liquid flow profiles that limit image and spectroscopic resolution. A bonding technology allows patterning nanochannel structures on suspended SiNx membranes,[7] enabling well-controlled liquid thickness[8,9] from tens of nanometres to a few hundred of nanometres in a liquid cell with membrane thickness down to 10 nm, and with a well-defined flow profile. It is suitable for high resolution, phase contrast, and quantitative spectroscopy analysis in LPTEM. We present studies of mean inner potential (MIP, V₀) of liquid water,[8] and electron inelastic mean free path in liquid water[9] using such nanochannel liquid cell in TEM.

High-energy electron irradiation and external potential biasing may induce charges on the window material SiNx from electron implantation, beam-induced currents, and secondary electron emission. The charge state of the membrane could significantly influence liquid processes. We use electrokinetics and electron holography to investigate the charge status of the membrane in liquid and dry states. Radiolysis: Our understanding of LPTEM radiolysis is currently based on simulations that rely on data collected from measurements at low electron flux intensities, requiring extrapolation by several orders of magnitude to match the intensities utilized in LPEM.[10] We demonstrate direct electrochemical measurements of radiolytic products during in-situ LPEM, which allows us to directly assess the high flux accuracy of low-flux radiolysis models. Using a specially designed liquid cell for electrochemical detection, we quantify the primary expected radiolysis products H₂ and H₂O₂ in a scanning electron microscope (SEM). We find H₂ production is rapid and in reasonable agreement with predictions, but H2O₂ levels are less than expected from the low-flux radiolysis models.