Environmental Liquid Cell Technique For Improved Electron Microscopic Imaging Of Soft Matter In Solution

Liquid-phase transmission electron microscopy is a technique for simultaneous imaging of the structure and dynamics of specimens in a liquid environment. The conventional sample geometry consists of a liquid layer tightly sandwiched between two Si3N4 windows with a nominal spacing on the order of 0.5 mu m. We describe a variation of the conventional approach, wherein the Si3N4 windows are separated by a 10-mu m-thick spacer, thus providing room for gas flow inside the liquid specimen enclosure. Adjusting the pressure and flow speed of humid air inside this environmental liquid cell (ELC) creates a stable liquid layer of controllable thickness on the bottom window, thus facilitating high-resolution observations of low mass-thickness contrast objects at low electron doses. We demonstrate controllable liquid thicknesses in the range 160 +/- 34 to 340 +/- 71 nm resulting in corresponding edge resolutions of 0.8 +/- 0.06 to 1.7 +/- 0.8 nm as measured for immersed gold nanoparticles. Liquid layer thickness 40 +/- 8 nm allowed imaging of low-contrast polystyrene particles. Hydration effects in the ELC have been studied using poly-N-isopropylacrylamide nanogels with a silica core. Therefore, ELC can be a suitable tool for in situ investigations of liquid specimens.