In situ Transmission Electron Microscopy (TEM) is a powerful tool for manipulating structures with an electron beam. Recent advancements in in-situ transmission electron microscopy (TEM) allow researchers to gain valuable insights into the formation and design of unique 2D material structures in real-time. This article will provide an overview of in situ TEM for analyzing graphene growth and designing its structural devices.
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Brief Introduction to In Situ TEM
In situ transmission electron microscopy combines the image-capturing abilities of the TEM with real-time observations of how materials react to changes in external conditions such as electric or magnetic field, gas environment, temperature, etc. The transmission electron microscope (TEM) is an observational tool initially intended to capture images of a static sample; however, in situ techniques added experimental capability to TEM, making it a powerful technique for many scientists.
Using MEMS devices and in situ TEM holders, researchers can control the environments in which their samples are observed, allowing them to conduct real experiments within the TEM.
In situ TEM Manipulation of Graphene
Micro-electrical mechanical system (MEMS) technology has made it possible to manipulate graphene at the atomic level using in situ TEM holders. The newly developed in situ TEM sample holders are capable of manipulating graphene structure under a variety of external conditions such as electron beam irradiation.
In situ Electron Beam Irradiation
Electron beam irradiation effects can be used to tailor the structure of samples. For example, the researchers demonstrated that a moderately intense and energetic electron beam could repair defects in monolayer graphene via self-healing of etched holes.
Researchers demonstrated that using a thermal specimen holder in a transmission electron microscope and a combination of electron beam irradiation, it is possible to tailor the size of nanopores in graphene. This research could be very useful for detecting single molecules in gas sensing applications.
Graphene nanoribbons have a wide range of potential applications in the semiconductor industry, where high-intensity, low-energy-consumption circuits are required. Researchers used a focused electron beam to present free-standing graphene's real-time fabrication and characterizing in a transmission electron microscope (TEM). This yielded the narrowest GNR width of about 1.6 nm.
In situ Thermal, Electrical and Mechanical Manipulation
In situ thermal TEM is commonly used to investigate the dynamic evolution of phase transitions and crystal growth, which is critical for thermostability analysis and controllable graphene synthesis. For example, one widely used technique for reducing graphene oxide (GO) is to heat the GO to a high enough temperature to remove the oxygen-containing functional groups present in the GO, thereby converting GO to rGO.
Understanding the processes that occur during this reduction is critical for developing and improving the application potential of rGO. As a result, researchers used in situ thermal in situ TEM to study the effect of thermal annealing on reducing graphene oxide to reduced graphene oxide.
Similar to the in situ thermal holders, if the chips or probes are connected to an electrical measuring system, the response of graphene to an applied electric field can be observed in real-time. In situ mechanical TEM is typically equipped in the sample holder with a piezoelectrically controlled nanotip. By controlling the movement of the nanotip, compression and tension can be applied to the sample.
Liquid Cell In Situ TEM
Graphene is a one-atomic-layer-thin material with high permeability and mechanical tensile strength, making it ideal for enclosing liquid solutions and imaging with in situ TEM. For example, researchers have explored the mechanism of Pt nanocrystals' formation by entrapping a platinum precursor solution between two atomically thin sheets of graphene. The graphene liquid cell enables atomic-level resolution imaging to investigate the real-time growth mechanism of nano crystal formation.
Suppliers and Manufacturers of in-Situ TEM Instruments
In situ TEMs are manufactured by companies such as Zeiss, Jeol, Philips, Amtek and Hitachi. Gatan, Inc. is a member of the Electronic Instruments segment of Amtek. Gatan in-situ TEM comes with a wide range of holders, such as DENSsolutions Wildfire heating holders.
The holders can be used to apply a variety of stimuli to evaluate dynamics caused by electrical, thermal, mechanical strain or simply intense electron beam irradiation.
Using the large field view of the Gatan OneView® IS camera, a change in structure can be captured with good spatial and temporal resolution immediately after heating the sample. At 400 frames per second, it is also possible to see real-time changes in graphene surface caused by an incident electron beam using Gatan's K2® IS camera.
The data management tools built into Gatan IS cameras make it simple to isolate and extract data so that post-processing data analysis can be performed to observe the effects of the stimuli applied to the sample. With Gatan in situ TEM's sub-ms time resolution, it is possible to study reactions that were previously too difficult to capture.
Promises and Challenges of in situ TEM
The use of multifunctional in situ TEM holders increases the ability of TEM to probe and tune interactions between samples and external fields in real-time. An in-situ TEM holder has the advantage of being compatible with the majority of current TEM machines and being simple to install. With its atomic resolution capabilities, transmission electron microscopy (TEM) will undoubtedly contribute to a better understanding of the dynamic structure–property relationship in 2D layered materials.
Even though in situ TEM for the study of 2D layered materials has advanced rapidly in recent years, it still faces several significant obstacles before it can be considered truly useful in the future. Although the relatively high resolution is achievable for in situ TEM, high imaging resolution for the liquid cell is difficult to achieve. The electron detector must be improved in terms of both time resolution and image signal-to-noise ratio to capture the dynamics using TEM.
Continue reading: A Top-Down Approach To Graphene Synthesis.
References and Further Reading
Liu, C., et al. (2022). Current effect on suspended graphene nanoribbon studied using in–situ transmission electron microscopy. Applied Surface Science, 573, 151563. https://www.sciencedirect.com/science/article/pii/S0169433221026118
Lu, N., et al. (2012). In situ studies on the shrinkage and expansion of graphene nanopores under electron beam irradiation at temperatures in the range of 400–1200 C. Carbon, 50(8), 2961-2965. http://dx.doi.org/10.1016/j.carbon.2012.02.078
Wang, Q., et al. (2016). Fabrication and in situ transmission electron microscope characterization of free-standing graphene nanoribbon devices. ACS nano, 10(1), 1475-1480. https://doi.org/10.1021/acsnano.5b06975
Pelaez-Fernandez, M., et al. (2021). Detailed thermal reduction analyses of Graphene Oxide via in-situ TEM/EELS studies. Carbon, 178, 477-487. https://doi.org/10.1016/j.carbon.2021.03.018
Bao, W., et al. (2012). In situ observation of electrostatic and thermal manipulation of suspended graphene membranes. Nano letters, 12(11), 5470-5474. https://doi.org/10.1021/nl301836q
Yuk, J. M., et al. (2012). High-resolution EM of colloidal nanocrystal growth using graphene liquid cells. Science, 336(6077), 61-64. https://doi.org/10.1126/science.1217654
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