Article Review: Visualising Nano-Structure

http://www.nanowerk.com/news/newsid=22791.php

Researchers at Johannes Gutenberg University Mainz have developed a new way to visualize nano-structure and accurately resolve the position of atoms in a variety of substances. Scientists know that the minute structure of a substance determines its physical properties (thermal, optical, mechanical. etc). Structural analyses with X-rays have long been the standard method to determine crystal structures. However, they state that X-rays can only resolve structures down to the micrometer range; nano-particles fall well below this size. Now the scientists have used electron diffraction tomography to establish the location of individual atoms.

The scientists first succeeded in finding the structure of barium sulfate. And have most recently uncovered that of the zeolite ITQ-43. Zeolites are aluminum and silicate based crystals which contain tiny pores that make them useful for catalysis and ion exchange. They are used to filter heavy metals in water treatment, for cracking crude-oil, and are often found in laundry soap. The zeolite studied contained ~100nm sized crystals. The researchers have also used the technique to study color pigments, gemstones and other materials.

The scientists list many advantages of the -new method, including greater accuracy. and speed. Using electron diffraction tomography, structures can be found in a day, in comparison with years for older methods. It can also be used to investigate “beam-sensitive” materials. The method has similarities to computer tomography, including the gradual tipping of the sample to take measurements from different positions.

Analysis: This article states that X-rays can only resolve. micrometer size crystals,’ and makes it seem as if there are no other methods for determining nanostructure. However, I know that xrays can be much less than 1 nm in size, so I don’t know if the first point is completely true. I also know that scanning transmission electron microscopy can resolve nano-scale structures, and I presume that there are at least several other techniques that can perform similarly. The article
should definitely included other such methods and given a comparison of their capabilities. I would also like to learn how electron diffraction tomography is different than electron microscopy in general. In both techniques electrons are directed at an object and diffracted, but I am unclear as to how they differ from there. Furthermore, I think the article should have been more diligent in defining structure. The researchers are determining physical structure, and not chemical structure as far as I can tell, yet no distinction is made, and several passages could be misleading. More information could have been provided on the time scales involved as well; they mention that a single day was all that was needed, but did not specify if this was typical, or whether some substances were more time consuming. Finally, I would like to learn more about "beam sensitive" materials (what they are, why, examples) and how this method alleviates the associated problems.