A scanning tunneling microscope (STM) is extremely delicate. A measuring needle with an atomically sharp apex is positioned just a few angstroms away from a sample. This is roughly the diameter of an atom, so the vibrations between the needle and the sample have to be extremely small. As a reference, the tip of Mount Everest would be allowed to vibrate less than the size of a bacterium. Additionally, [Ph.D candidate Irene] Battisti aimed to make a cryogenic microscope with a temperature around 4 Kelvin – almost absolute zero. These ultra-low temperatures are needed for spectroscopic visualization of the electronic properties of materials down to the atomic scale. “This greatly complicates things, as the mechanics of regular STMs are not suited for such low temperatures,” Battisti explains. Therefore, she worked with sapphire. “This material is not only expensive, but its toughness also makes it very difficult to process,” she says.
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