On the role of the gas environment, electron-dose-rate, and sample on the image resolution in transmission electron microscopy

Abstract

The introduction of gaseous atmospheres in transmission electron microscopy offers the possibility of studying materials in situ under chemically relevant environments. The presence of a gas environment can degrade the resolution. Surprisingly, this phenomenon has been shown to depend on the electron-dose-rate. In this article, we demonstrate that both the total and areal electron-dose-rates work as descriptors for the dose-rate-dependent resolution and are related through the illumination area. Furthermore, the resolution degradation was observed to occur gradually over time after initializing the illumination of the sample and gas by the electron beam. The resolution was also observed to be sensitive to the electrical conductivity of the sample. These observations can be explained by a charge buildup over the electron-illuminated sample area, caused by the beam-gas-sample interaction, and by a subsequent sample motion induced by electrical capacitance in the sample.

Role of Electron Illumination on the Image Resolution and Sensitivity of Catalysts Immersed in Gas Environments

“…Specifically, the resolution degrades for high dose-rates in the presence of gas while resolution is maintained under high vacuum conditions. Interestingly, Figure 1 shows that the inherent 1 Å resolution of the host microscope can be maintained as long as the electron dose-rate is kept sufficiently low [2][3][4]. Detailed measurements of the image resolution as a function of time, sample temperature and gas pressure suggest that the electron dose-ratedependent resolution is caused by a sample charging, induced by the beam-gas interaction, that eventually leads to sample motion and hence contrast smearing [4].…”

“…While these instrumental advances have opened up for impressive TEM studies of catalyst dynamics at the atomicscale, it has also become evident that the electron beam can substantially alter the catalyst and gas phase and, in turn, the chemical processes under inspection. It therefore becomes crucial to address the impact of electron illumination on in situ TEM observations and to suppress the electron-induced alterations to enable chemical relevant observations [2][3][4].…”

“…The measurements were done using the most common types of gas cells including a differentially pumped electron microscopy (FEI Titan 80-300 ETEM) operated at gas pressures of up to 20 mbar [2][3], and a micro-electromechanical-system-based nanoreactor (Thermo Fisher Scientific), operated at gas pressures up to 1 bar [5][6]. The image sensitivity was defined as the signal-to-noise ratio detected by the CCD camera and the image resolution was measured as the shortest transferred lattice vector for a Au/C sample in the differentially pumped gas cell and for Pt nanocrystals in the nanoreactor (Figure 1) [2,4].…”

“…Interestingly, Figure 1 shows that the inherent 1 Å resolution of the host microscope can be maintained as long as the electron dose-rate is kept sufficiently low [2][3][4]. Detailed measurements of the image resolution as a function of time, sample temperature and gas pressure suggest that the electron dose-ratedependent resolution is caused by a sample charging, induced by the beam-gas interaction, that eventually leads to sample motion and hence contrast smearing [4]. For the nanoreactor, similar measurements indicate that the inherent microscope resolution can be preserved even for gas atmospheres at the 1 bar level [5][6].…”

Visualizing Redox Chemistry in Oxide Surfaces at Atomic-Resolution

“…A systematic variation of the electron illumination demonstrates that low dose-rates are needed for alleviating beam-induced alterations in the oxide catalysts. Correspondingly, the HRTEM image signal reaches levels at the detection limit but can beneficially be recovered using low dose-rates in conjunction with in-line holography in order to maintain atomic-resolution and -sensitivity of the oxide surface structures (Figure 1) [2][3][4][5][6]. Second, we employ this concept of dose-fractionating electron detection to uncover redox properties of vanadium oxide supported on anatase titanium dioxide nanoparticles (VOx/TiO2) (Figure 2) [6].…”