K3 IS: Low dose EM meets catalysis

Introduction

In-situ and operando transmission electron microscopy (TEM) enable observation of active catalysts at the nanoscale1. However, observations performed in the TEM have always suffered from various deleterious effects of the electron beam. These effects are not always understood or accounted for and can make it impossible to image certain classes of materials. Efforts to mitigate electron beam effects have traditionally involved limiting electron dose, but this often comes at the expense of limiting spatial/temporal resolution, or the duration of observation.

Recent advances in camera technology have enabled breakthroughs for Cryo-EM – a low electron dose TEM technique commonly used with sensitive biological samples. Today, at low electron doses, nearly every electron that passes through a sample can be individually identified and counted. The ‘counted’ images that result are of unprecedented quality2. This electron counting technology will enable the study of catalyst dynamics while reducing the impact of the electron beam, enabling observation of sensitive materials such as metal-organic frameworks (MOFs), and extending the duration and resolution of continuous observations.

Methods

The data shown in the videos below were acquired with a variety of instrumentation, all using TEMs equipped with Gatan cameras. Video 1 was acquired from a ZIF-8 MOF using a K2® camera in electron counting mode on an FEI Titan 80 – 300 TEM at KAUST3. Video 2 was acquired from a hydroxycancrinite zeolite using K3™ IS electron counting camera and traditional Rio™ 16 IS TEM camera on an FEI Tecnai TEM at Gatan. Video 3 was acquired from a Cu-Sn alloy using a K3 IS electron counting camera on the same FEI Tecnai; a Protochips Fusion holder was used to heat the Cu-Sn sample during imaging.

Results

Video 1 shows the accumulation of electron counts in a single image of a MOF sample over 3 seconds. Using older cameras, it was impossible to image MOFs at high spatial resolution, as they are quickly destroyed by the electron beam. Video 2 shows two videos of a beam-sensitive zeolite sample (Si/Al ratio 1.2). The left video was acquired with a Rio 16 IS camera which is highly sensitive, but does not count electrons, while the right video was collected on the same TEM minutes later with a K3 IS camera in electron counting mode. This counted video displays better detail at high spatial resolution, even at this low dose rate. Video 3 shows a counted in-situ TEM video. A Cu-Sn alloy (10:90) was heated to 600 ⁰C, at which temperature the alloy dissociates, leaving both small and large particles of pure Sn. The video was 2 min long and captured at 20 frames per second, but the dose rate was just 27 e-/Å2/s, and the total electron dose was only 3240 e-/Å2. A traditional TEM camera would likely require at least 5x this dose rate to achieve a similar result.

Video 1: Accumulation of electron counts into a single image of a ZIF-8 MOF using a Gatan K2 Summit camera. The image was acquired with 120 individual frames over 3s, with a dose rate of 1.4 e-/Å2/s and total dose of 4.1 e-/Å2. The K2 was used in electron counting mode on an FEI Titan 80 – 300 TEM operated at 300 kV by KAUST1. The individual frames were aligned before summing to generate the final image. 1Zhu, Y., Ciston, J., Zheng, B., Miao, X., Czarnik, C., Pan, Y., Sougrat, R., Lai, Z., Hsiung, C.-E., Yao, K., Pinnau, I., Pan, M., Han, Y., 2017. Nat. Mater. 16, 532–536. For full resolution video, please download.

Video 2: Comparison of 2 TEM datasets acquired from a hydroxycancrinite zeolite using a K3 IS direct detection electron counting camera and a traditional Rio 16 IS CMOS camera. The left video was acquired with the Rio camera, and the right video was collected on the same TEM minutes later from a new location on the sample with the K3 IS camera in electron counting mode. Both datasets were acquired at 20 frames per second, were collected with a low dose rate of 10 e-/Å2/s, and used a total dose of 175 e-/Å2. The cameras were both installed on an FEI Tecnai TEM operated at 200 kV at Gatan's headquarters. The sample was provided by Shery Chang (Arizona State University) and is a highly beam-sensitive zeolite sample with a Si/Al ratio of 1.2. For full resolution video, please download.

Video 3: Two minute video revealing alloy dissociation acquired with a K3 IS direct detection camera at an electron dose rate of just 27 e-/Å2/s and a total electron dose of only 3240 e-/Å2. A Cu-Sn (10:90) alloy (purchased from USNano) was heated to 600 ⁰C using a Protochips Fusion holder. When the temperature reached 600 ⁰C, the alloy dissociated, leaving both small and large particles of pure Sn. The data was acquired with a K3 IS camera at Gatan’s headquarters using an FEI Tecnai TEM operated at 200 kV. The 2 min dataset was captured at 20 frames per second. A traditional scintillator-based TEM camera would require at least 5x this dose rate to achieve a similar result. The video was drift corrected after acquisition using Gatan Microscopy Suite® 3. For full resolution video, please download.

Significance

Recent advances in electron counting camera technology will improve the study of catalyst dynamics while reducing the impact of the electron beam, and this will enable observation of sensitive materials such as metal-organic frameworks.

 

_______________________________________________________________________

References

  1. Miller, B.K. 2016, Development and Application of Operando TEM to a Ruthenium Catalyst for CO Oxidation, Arizona State University.
  2. Li, X., Mooney, P., Zheng, S., Booth, C.R., Braunfeld, M.B., Gubbens, S., Agard, D.A., Cheng, Y., 2013. Nature Methods 10, 584–590.
  3. Zhu, Y., Ciston, J., Zheng, B., Miao, X., Czarnik, C., Pan, Y., Sougrat, R., Lai, Z., Hsiung, C.-E., Yao, K., Pinnau, I., Pan, M., Han, Y., 2017. Nat. Mater. 16, 532–536.