Nanotribological properties of quasicrystals: UHV SF/STM investigation

Quasicrystals are materials with long-range rotational order, but no three-dimensional translational periodicity. It has classically forbidden rotational symmetries as like 5, 8 or 10-fold, which are incompatible with conventional Bravais lattice ordering. Interestingly, this material has several mechanical and tribological properties such as: low friction coefficient, high hardness, low surface energy, good wear-resistance, and good oxidation-resistance. As a result, it is commercially used as a coating material in several products including electrical shavers and fry pans.
However the physical and chemical mechanisms of these intriguing properties are not quite understood. A key question is whether these mechanical properties is linked to the quasicrystallinity or not.
In this project, in collaboration with Prof. Patricia Thiel of the AMES laboratory and Iowa State University, we aim at establishing the basis for the tribological properties of friction, adhesion and wear at surface or interfacial regions of the quasicrystal. We clean the quasicrystal surface in UHV by heating and sputtering, along with surface analysis characterization with LEED and Auger spectroscopy. Further characterization and tribological studies are carried out with AFM/STM. By using a conductive cantilever, the tunneling current and the force between the tip and sample are simultaneously measured. The effect of oxidation on surface passivation and mechanical properties is investigated as a function of adsorbate and coverage. We explore the elastic and plastic regime that depend on the strength of the applied load, and the chemical nature of tip and surface.

The detail of the instrument (pictures and schematic diagrams of UHV AFM/STM system) is found here (pdf file:345KB)
More details are found in the follwoing pdf files:

STM, AFM images of 10-fold decagonal AlNiCo quasicrystal surface (319KB)

Contact AFM images of polymer, graphite, and mica (atomic lattice) (1.1MB)

Researcher: Jeong Young Park