If you need to study a substance in a very small volume (from 1 cubic micrometer to several cubic nanometers), place it between layers of graphene or other two-dimensional materials, hexagonal boron nitride (hBN) or transition metal dichalcogenides. The substance will be cramped there, and it will slightly expand the graphene layers, since they are bound by weak van der Waals forces. The upper layer swells like paint on a car body, and a so-called nanobubble is formed, which can already be studied by transmission electron and atomic force microscopy.
And then you can not do without the help of the guys from the Center for Design, Production Technologies and Skoltech Materials. They developed a numerical model of a nanobubble that predicts its shape, and at the same time describes the molecular structure of the substance captured by the bubble. Here is what one of the developers, a senior researcher Timur Aslyamov, says about this:
“Our new results are devoted to the description of the specific shape of flat nanobubbles, which appears only at subnanometer scales. We found that the vertical size of such nanostructures can take only discrete values that are multiples of the size of the molecules of the trapped substance. In addition, the developed model offers ways to change the size of nanobubbles, controlling the temperature of the system and the physicochemical parameters of the materials. ”
When researching substances in nanobubbles, be prepared for the unexpected. For example, water under such conditions reduces its dielectric constant by an order of magnitude and begins to burn out the surface of the diamond substrate, which is absolutely not typical for it under normal conditions. And liquid at the same pressure and in a large volume, Argon, being in very small nanobubbles with a radius of up to 50 nm, is able to turn into a crystal.
In general, one can benefit from nanobubbles in layers of graphene and other 2D materials. Although most often they are perceived as annoying defects.
“From a practical point of view, bubbles in van der Waals structures are most often a technological defect, and in most cases, experimenters want to get rid of them. On the other hand, the bubbles themselves create a deformation, which can be used in streintronics devices (from English strain - deformation): the effect of deformation on the electronic structure can be used to create practical devices, for example, transistors, logic elements and ROM memory, ”he said. Skoltekh Senior Researcher Petr Zhilyaev.
Model of graphene nanobubble: Combining classical density functional and elasticity theories published in The Journal of Chemical Physics