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Superfluous phenomenon conceptual map. The atoms in the molecular chain moving on the surface of the substrate are represented by green spheres, the potential irregularities on the surface of the substrate are indicated by red wavy lines, and the interaction forces are represented by purple spheres.
FIG. A is an image of the observation of the movement of the graphene nanoribbon using a scanning tunneling microscope. The location of the double image indicates the movement. The left side of FIG. B is an image in which the internal structure of the graphene nanoribbon is directly observed by an atomic force microscope.
The Japan Science and Technology Agency (JST) announced on February 26, 2016 that it has succeeded in observing the "superlubrication phenomenon" in which friction has become extremely low due to the effect of graphene, and has ascertained its mechanism. It is said that in the future it is expected to coat the surface with a layer of graphene to reduce the friction between the mechanical parts in order to realize ultra-thin film solid lubricant technology.
The contact surface (interface) between matter and matter, with the flexible movement and alignment of the atoms on the surface, will produce a strong adsorption force, forming friction. The binding force between the carbon atoms constituting the graphene is very strong, and the atoms are almost immobile, so the atoms will not be aligned and the adsorption force generated at the interface will be weak.
To find out the phenomenon of super-lubrication caused by graphene, it is necessary to perform the nano-scale friction characteristic detection on the interface between substrate material and graphene. However, it has heretofore been difficult to arrange graphene having an atom structure of the interface and an arrangement direction of crystal planes on the surface of the substrate. This time, this problem was solved by generating graphene nanoribbons on the surface of a clean gold substrate, and the direct motion was successfully confirmed using a scanning tunneling microscope and an atomic force microscope.
The graphene ribbon formed on the surface of the gold substrate has a width of 7 carbon atoms and a length of 1 n to 50 nm. When using a scanning tunneling microscope, it was observed that the sample inadvertently moved in the longitudinal direction even when the interaction force between the probe and the sample (graphene tape) was extremely reduced. The 27 nm long graphene was only 105 pN when the frictional force was quantitatively measured by an atomic force microscope. This allegedly meant that friction at room temperature was low enough to be less than thermal energy.
In addition, the result of the experiment of picking up the graphene at one end with a probe of a scanning tunneling microscope shows that the frictional force changes in a cycle of 0.28 nm which is equivalent to the distance between gold atoms on the gold surface. This is due to a change in the roughness of the surface of the gold substrate of the hexagonal closest-packed lattice structure (HCP) and the face-centered cubic lattice structure (FCC) called a herringbone structure. It has been confirmed that the results calculated using the molecular dynamics method are consistent with the observations.
This is part of Japan's JST strategic creation research promotion business. It is a joint study with the Dresden University of Technology in Germany, the Swiss Federal Institute for Materials Testing, the Polymer Institute of the German Max Planck Institute, and the University of Basel in Switzerland. The results have been published online in the science magazine Science on February 26th (U.S. time). (Special Contributor: Kudosuke)
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