A method for measuring the local gas pressure within a gas-flow stage in situ in the transmission electron microscope

Abstract

Environmental transmission electron microscopy (TEM) has enabled in situ experiments in a gaseous environment with high resolution imaging and spectroscopy. Addressing scientific challenges in areas such as catalysis, corrosion, and geochemistry can require pressures much higher than the ∼20 mbar achievable with a differentially pumped environmental TEM. Gas flow stages, in which the environment is contained between two semi-transparent thin membrane windows, have been demonstrated at pressures of several atmospheres. However, the relationship between the pressure at the sample and the pressure drop across the system is not clear for some geometries. We demonstrate a method for measuring the gas pressure at the sample by measuring the ratio of elastic to inelastic scattering and the defocus of the pair of thin windows. This method requires two energy filtered high-resolution TEM images that can be performed during an ongoing experiment, at the region of interest. The approach is demonstrated to measure greater than atmosphere pressures of N2 gas using a commercially available gas-flow stage. This technique provides a means to ensure reproducible sample pressures between different experiments, and even between very differently designed gas-flow stages.

Water without windows: Evaluating the performance of open cell transmission electron microscopy under saturated water vapor conditions, and assessing its potential for microscopy of hydrated biological specimens

“…These gas t/λ values, in the saturation regime, compare favorably with reported values for solid state windows (e.g. t/λ ∼ 0 (monolayer graphene sandwich) to t/λ ∼ 0.6 [ 27 ]) and 100 nm thick amorphous ice (t/λ ∼ 0.3 [ 28 ]). This suggests that open cell water vapor can exhibit comparable scattering performance to these established methods.…”

“…Therefore, we have explored different experimental beam optics configurations and data analysis methodologies (all of which are included in S3 Appendix ). The summary result, following this evaluation, is shown in Fig 6 (some reference values from the literature have also been overlaid, for comparison [ 27 , 28 ]). In this case, we have employed a very well-characterized collection angle geometry for data acquisition [ 29 ], and calculated the effective thickness as a function of pressure using: All variables are explicitly defined in S3 Appendix .…”

“…For comparison purposes, we have also included the equivalent thickness of amorphous ice (assuming an inelastic mean free path of 330 nm at 300 kV [ 28 ]. We indicate (*) a literature value for the effective thickness of enclosing SiN membranes in a conventional closed liquid cell, from [ 27 ]. We have also marked ( # ) the effective water vapor thickness corresponding to saturation vapor pressure at 277 K (0.32 at 729 Pa).…”

Achieve atomic resolution in in situ S/TEM experiments to examine complex interface structures in nanomaterials

“…Great technology progress has been made here as well: either a dedicated environmental S/TEM for confinement of a gaseous environment [52,53,56,65,99,149] or again MEMS cartridge-based holder solution for confining a gaseous [8,[25][26][27]124,166,159,170] and even for confining a liquid environment [48,67,68,127,162,167,176] inside an electron microscope can nowadays be used. Humidity/water vapour experiments have been carried out in ETEM as well [172,179].…”