Gas TEM holder for in‐situ biasing and heating experiments

Abstract

We present our custom designed Gas Transmission Electron Microscopy (TEM) holder for in‐situ electrical, gas and heating experiments. The holder is currently compatible with FEI machines, but it can be easily redesigned for other transmission electron microscopes. The holder has a sliding cassette at the sample position (Figure 1, left side), which can be manually opened and closed through a rotating knob, located at the opposite end of the TEM holder. Closing the cassette will ensure complete gas sealing around the sample, up to a pressure difference of 1 atm (respect to the microscope vacuum). One gas line is used for both inlet and outlet. The beam is blocked when the cassette is closed, meaning that it is not possible to acquire live imaging during the gas flow. However, this configuration is very practical from the point of view of sample loading and unloading, as it only takes a few minutes to replace the sample, without any O‐rings or complicated sealing mechanisms. Moreover, the sample does not need to be exposed to air after the gas reaction, which gives a relevant advantage over ex‐situ measurements. The TEM holder also has 10 electrical feedthroughs, which can be used for in‐situ electrical biasing experiments. Four of these electrical contacts can be used for in‐situ heating, in combination with our custom made MEMS heaters [1] (Figure 1, right side), capable of reaching 1000 K in vacuum and 700 K in 1 atm Argon environment. As a first application of our gas TEM holder, we exposed freestanding multilayer graphene to 1 atm of Hydrogen and simultaneously heated the sample at 550 K for a few minutes. As we can see from Figure 2, this high‐pressure hydrogen annealing resulted in isotropic etching of graphene, with formation of round holes, approximately 80 nm in diameter. Further experiments will be performed to evaluate the etching rate and the isotropicity/anisotropicity as function of temperature, pressure and gas composition.