Monolithic Chip System with a Microfluidic Channel for In Situ Electron Microscopy of Liquids

Abstract

Electron microscopy of enclosed liquid samples requires the thinnest possible membranes as enclosing windows as well as nanoscale liquid sample thickness to achieve the best possible resolution. Today liquid sample systems for transmission electron microscopy (TEM) are typically made from two sandwiched microchips with thin membranes. We report on a new microfabricated chip system based on a monolithic design that enables membrane geometry on the scale of a few micrometers. The design is intended to reduce membrane deflection when the system is under pressure, a microfluidic channel for improved flow geometry, and a better space angle for auxiliary detectors such as energy-dispersive X-ray spectroscopy. We explain the system design and fabrication and show the first successful TEM images of liquid samples in the chips.

Opportunities and challenges in liquid cell electron microscopy

“…The spacer may be a solid layer with a channel, or spherical particles. The liquid may be inserted through an entry port etched into one chip (14)(15)(16)(17)(18) or flowed in through the gap between the chips (19). Electrodes can be patterned lithographically inside the closed cell and controlled by an external potentiostat (14).…”

“…The liquid layer is usually thicker than desired, especially toward the center of the window, because the windows bulge outward due to the pressure difference between the interior of the cell and the microscope vacuum. To control the deflection, one can fabricate long thin windows or narrow channels (17); join the windows with posts (16); or use thicker, stiffer membranes with small thin regions for imaging (35). Reducing window separation improves resolution, but we can not decrease the liquid thickness arbitrarily and still expect the liquid cell experiment to be a faithful representation of a "real" phenomenon (9).…”

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

“…In case it is difficult to find an overlap between two small windows, they can be assembled in a crossed configuration using a different base microchip. Alternative configurations largely prevent bulging and consist of a monolithic microchip18 or membrane windows supported by pillars19, but those exhibit disadvantages regarding sample loading. One of the most challenging aspects of the current technology is the lack of precise control over the liquid thickness.…”

Ciscem 2014

“…To allow better control of the encapsulated volume and geometry, we are exploring devices using monolithic chips ( Figure 19) with suspended microfluidic channels made from silicon nitride (Jensen et al, 2014). On the channels, thinned window regions allow higher resolution than in the supporting part of the channel.…”