Simultaneous low-dose imaging is delivered by the K3® IS, via real-time electron counting, a large field of view and fast continuous data capture.
The 652 model - a furnace-type holder - is designed to observe microstructural phase changes, catalysis, nucleation, growth and dissolution processes directly in 3 mm transmission electron microscope (TEM) samples at elevated temperatures.
There are many potential applications for MoS2 where void or pit formation plays an integral role in determining material properties. The nucleation and growth of pits may be impacted by adventitious carbon (a thin layer of carbon usually present on materials exposed to air) in real-world synthesis.
An extremely valuable technique for studying this adventitious carbon layer, along with its behavior at high temperatures and its subsequent effects on the formation of pits in MoS2, can be found in in-situ TEM.
It is possible to use low-dose, low-voltage continuous imaging alongside infrequent high-resolution imaging to minimize the impact of the electron beam while observing these processes.
Methods and Materials
In order to reduce beam damage, the MoS2 sample was imaged in a Titan ETEM at 80 kV. A model 652 heating holder was used to heat the sample from room temperature up to 300 °C at 10 °C per minute.
A K3 IS camera was used to record in-situ TEM video over the entire ramp, resulting in a counted video approximately 30 minutes long. A relatively large area was captured by the video (595 x 423 nm) with 1 Å pixels, allowing the simultaneous observation of over 20 carbon nanoparticles.
With its high detective quantum efficiency (DQE) and counted acquisition, the K3 IS camera facilitated a low dose rate of just 8 e-/Å2/s to further limit beam damage. The entire video, comprising of over 8,000 frames, yielded a total dose of just 13,200 e-/Å2. This is a figure comparable to a mere few single atomic-resolution TEM images captured using a traditional TEM camera.
The OneView image in Figure 2c of [1], for example, has a total dose of 3,200 e-/Å2 in a 0.32 second exposure.
Figure 1. Frames from a ~30 min low-dose in-situ video showing formation of carbon nanoparticles during heating in a Gatan heating holder. Note that this sequence starts 11 minutes into the video, but most particles first appear between 14 and 17 minutes (165 – 195 °C). This indicates that heating and not the electron beam was primarily responsible for the carbon agglomeration. The dose rate during acquisition was just 8 e-/Å2/s. Each frame shown here is a sum of 10 original frames, with 16 e-/Å2 total dose. Image Credit: Gatan Inc.
Summary
Though the K3 IS camera captured and counted raw frames internally at 1,500 fps, the framerate of the original video saved to disk was 5 frames per second (fps). The beginning 11 minutes of the video were unexceptional and left unprocessed. The remaining dataset comprised some 4,913 frames, each of which was 5,760 x 4,092 pixels in size, to create a total of 107 GB of data.
The data was binned by a factor of 4, drift corrected, cropped and every 10 frames summed to facilitate a final video dataset after the acquisition. The final dataset was 492 frames, each of which was 812 x 444 pixels in size, resulting in a total of 790 MB of data in *.dm4 format.
Gatan Microscopy Suite® (GMS) was used to process this data and to produce a *.mp4 video of this processed dataset, which was just 93 MB (a 99.9% reduction in data volume). Several frames from the video are depicted in Figure 1.
An in-situ video of MoS2 with relatively minor beam damage was achieved by the 80-kV accelerating voltage, and the low dose rate enabled by the K3 IS camera. Observation of the agglomeration of adventitious carbon into carbon nanoparticles was facilitated through heating the sample using a Gatan heating holder up to 300 °C.
A 93 MB *.mp4 video resulted from processing over 100GB of data with GMS, which can be viewed in the referenced video in the paragraph above.
As evidenced by the data, most particles first appear around 170 – 180 °C. At the same time, it was additionally observed (thanks to in-situ observations made on the same TEM in the presence of O2 gas) that these particles were linked with the formation of pits in the MoS2.1
Credit(s)
Gratitude is owed to Stanford University, including Sangwook Park, Joonsuk Park, Taeho Roy Kim, Robert Sinclair and Xiaolin Zheng.
Reference
- Park, S. et al. Effect of Adventitious Carbon on Pit Formation of Monolayer MoS2. Adv. Mater. 2003020 (2020) doi:10.1002/adma.202003020.
This information has been sourced, reviewed and adapted from materials provided by Gatan Inc.
For more information on this source, please visit Gatan Inc.