Analysis of graphene via atomic moire interferometry

moire patternsIn a groundbreaking series of experiments, scientists in the United States managed to develop a new method of analyzing how graphene sheets are stacked on top of each other. The technique is also suitable for determining which areas of the compound are subjected to most strain, when the material is placed inside more complex structures. All of this can be inferred using moire patterns, which are interference patterns that appear at an atomic scale, when two layers of atoms are placed on top of each other imperfectly, as in slightly askew (image courtesy of NIST).

The research team that conducted the new investigation features physicists from the US National Institutes of Standards and Technology (NIST) and the Georgia Institute of Technology (Georgia Tech). The experts say that the moire patterns can also be used on multiple grids or atom arrays, not only on two. They add that using “atomic moire interferometry” can also help scientists determine the rotational orientation of the graphene sheets used in a variety of technological applications. Their work is published in the Physical Review B journal.

Given that one of the most complex areas of graphene research today is figuring out how the material changes its properties when stacked in multiple layers, being able to obtain a map of the strains that develop within it is extremely important. The electronic and transport properties of the single-atom-thick carbon compound can now be analyzed and determined with a much higher degree of accuracy than ever before, the NIST/Georgia Tech team says. Due to its revolutionary semiconducting properties, graphene is now hailed as the material of the future, at least in the electronics industry.

For the new experiments, Georgia Tech experts developed sheets of graphene on a silicon carbide substrate. After the samples were transferred at NIST, scientists here used a custom-built scanning tunnelling microscope (STM) to look at the graphene samples. The high resolve power on this instrument allows the experts to peer deep within the sample, past the topmost layer. It was through this method that the moire patterns became visible. Distinguishing them is fairly easy because of the hexagonal arrangement of carbon atoms in graphene. Any layers that are misplaced on top of others are immediately clear.

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