The applications of electron microscopy analysis are diverse, as this class of imaging techniques can be used for particle analysis, material characterization, industrial failure analysis, quality control purposes and much more. As clean technology products continue to advance and emerge, there remains a pressing need for researchers in this area to have access to reliable and precise ways to evaluate the performance of these tools. Electron microscopy, particularly transmission electron microscopy (TEM) and scanning electron microscopy (SEM), have emerged as useful techniques for this purpose.
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TEM
Conventional transmission electron microscopes (TEM) analyze an ultra-thin specimen by irradiating it with an electron beam that exhibits a uniform density. As the energy of the electron beam passes through the sample, it interacts with it to form an image that represents its electron-intensity distribution. As compared to light microscopes, TEM have been shown to produce images of a significantly higher resolution to provide users to minute detail on the sample.
Scanning/TEM (S/TEM) and Green Technology
The development and advancements that have been made for both nanomaterials and nanostructures have largely been made in an effort to improve the efficiency of energy conversion systems, automobiles and other transportation modalities, food production methods and how natural resources are used. The analysis of these nanomaterials therefore often requires detailed characterization on the relationship that exists between its structure and unique properties.
Atomic-scale scanning/TEM (S/TEM) has emerged as a powerful tool for the characterization of nanomaterials. The most notable attributes of S/TEM for this purpose include its spatial resolution within the sub-nanometer range, energy resolution capabilities within the sub-eV range and the sensitivity to detect single atoms. Furthermore, S/TEM can be used to visualize the size and shape, as well as the specific bulk, surface and interface structures of nano-objects, as well as analyze their electronic properties and elemental distributions at the nanometer level.
Evaluating Gas-Solid Interaction in Nanomaterials
When utilized in gaseous environments, nanomaterials can undergo a gas-solid interaction that has serious implications to their property and performance capabilities. Since the variance in how nanomaterials respond to this condition is unpredictable upon initial examination, especially when high vacuum conditions are considered, in situ characterization techniques are highly sought-after.
Various studies have been published in an effort to evaluate the application of an environmental S/TEM to determine the size, shape and structural changes that catalyst nanoparticles experience when exposed to high vacuum gaseous conditions. For example, Hansen et al. demonstrated that high-resolution TEM images provided information regarding the dynamic reversible shape changes experienced by active copper (Cu) nanocrystal catalysts when present in a gaseous environment. As the field of ETEM continues to improve, researchers are hopeful that this technique will provide them with the ability to directly study functional nanomaterials that play a significant role in challenges associated with the development of clean technologies.
Solar Cell Analysis
Like TEM, SEM imaging provides researchers with important information on the fine structure of samples. When used to analyze solar cells, even when these catalyzing structures are present in large commercial devices, SEM has allowed researchers to visualize a higher depth of field, which would otherwise be impossible if an optical microscope were used. SEM has also proven useful in the detection of defect clusters in multicrystalline solar grade silicon solar cells, thereby providing clean technology researchers with a highly specific method of analyzing and understanding the propagation mechanisms of these defects to determine overall cell efficiency.
Other electron microscopy techniques that have been successfully used in the characterization of thin-film solar cells include focused ion-beam microscopy, time-resolved cathodoluminsence and aberration-correction.
References
- “Transmission Electron Microscope” – CAS-TWAS Centre of Excellence for Green Technology
- Reimer, L. (2013). Transmission Electron Microscopy: Physics of Image Formation and Microanalysis.
- Jinschek, J. R. (2014). Advances in the environmental transmission electron microscope (ETEM) for nanoscale in situ studies of gas-solid interactions. Royal Society of Chemistry Chemistry Communications 50; 2696-2706. DOI: 10.1039c3cc49092k.
- “SEM and EBIC” – PVEducation.org
- MEndis, B. G., & Durose, K. (2012). Prospects for electron microscopy characterization of solar cells: Opportunities and challenges. Ultramicroscopy 119; 82-96. DOI: 10.1016/j.ultramic.2011.09.010.
- Berthod, C., Odden, J. O., & Saetre, T. O. (2014). Scanning electron microscopy analysis of defect clusters in microcrystalline solar grade silicon solar cells. Proceedings from the 2014 IEEE 40th Photovoltaic Specialist Conference. DOI: 10.1109/PVSC.2014.6925549.
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