Nat. Nanotechnol.: Double graphene becomes diamond under pressure

Carbon can form different types of materials, from diamond to graphite, as well as recent fullerenes, nanotubes and graphenes These materials exhibit various special properties due to different carbon bond structures It has always been a challenge to make thin-layer materials with the same or better hardness than diamond For the reasons of science and technology, the transformation of graphite into diamond is still one of the most fascinating and studied solid-solid transformation in materials science Recently, there have been many researches on the chemical functionalization of the surface of multilayered graphene to change the structure of diamond-like carbon However, although some success has been achieved, there is no experimental evidence to prove that this kind of thin film has the mechanical properties similar to diamond TEM images and experimental hardness curves of multilayer epitaxial graphene and SiC buffer layer (source: Nat Nanotechnol.) are from the research team of City University of New York With the efforts of the experimental team led by ELISA Riedo and the theoretical team led by Angelo Bongiorno, it is found that extrusion of double-layer graphene under extremely high pressure can transform it into ultra-thin diamond films This interesting phenomenon has not been found in the case of single-layer or multi-layer graphene, only in the case of double-layer graphene Maybe one day, it can be used to develop ultra-thin protective coatings, or for some sophisticated electronic components The experimental hardness measurement of double-layer graphene (source: Nat Nanotechnol.) a group led by ELISA Riedo found an interesting phenomenon when measuring the surface hardness of the AFM tip by pressing it into the bare silicon carbide and the silicon carbide covered with a variety of graphene layers A single layer of graphene will slightly reduce the surface hardness, while three or more layers will significantly reduce the surface hardness Strangely, however, a double-layer graphene coating makes the surface harder Even a diamond indenter cannot be marked on a surface covered with double-layer graphene, which is at least as hard as diamond Riedo's team is confused For a year, they repeated the experiment and thought they were wrong Finally, the theoretical team led by Angelo Bongiorno pointed out that, as predicted in previous theoretical studies, graphene can be converted into diamonds Subsequently, the experimental team and the theoretical team carried out a number of tests on the obtained hardened film According to the density functional theory, the lattice mismatch between diamond and silicon carbide makes the first layer of graphene on the surface produce a retaining ring These distortions reduce the energy barrier of the first two sp 2-hybrid graphene sheets to sp 3-hybrid diamond lattice However, when there are more than two layers, the combination with these additional layers hinders the transformation "Now we are learning more about the importance of interfaces," Riedo said Microhardness and C-AFM measurement (source: Nat Nanotechnol.) the results of this study show that double-layer graphene on the surface is an interesting candidate for the manufacture of pressure activated adaptive ultra-thin coatings and force controlled dissipation switches A new approach has been developed to study the graphite diamond phase transition in the low dimensional system at room temperature Finally, this work provides a new way for the formation of monolayer diamond in graphene For example, the diamond-like phase can be changed into a more stable state by combining local pressure with temperature, passivation gas or local heating These nanostructures have very promising optical and electronic properties, and the impact on the future materials is difficult to measure DFT and indentation calculation (source: Nat Nanotechnol.) paper link: https://www.nature.com/articles/s41565-017-0023-9 brief introduction of corresponding author: Dr ELISA Riedo http://riedo.gatech.edu/riedo.html