Surface and Interface Properties

Many applications for quasiscrystals use, or would use, them in the form of low-dimensional solids (coatings, powders, small inclusions) where the surface area-to-volume ratio is high. Hence, surface and interface properties are important in these applications. For instance, properties which make them potentially attractive as coatings include low coefficients of friction, good wear-resistance, and good corrosion-resistance. This motivates basic studies of surface phenomena. We are addressing issues in the following areas.


1. Structure and composition of the clean surface

Is the surface of a bulk sample quasicrystalline? If so, under what preparation conditions? Is it smooth or rough? On what length scales? How does surface composition compare with bulk composition--is there surface segregation?

These are fundamental questions whose answers will contribute to our basic understanding of quasicrystalline surfaces.

Techniques being employed:

Low-energy ion scattering
Low-energy electron diffraction
X-ray photoelectron spectroscopy
Scanning Auger electron microscopy and spectroscopy
Scanning tunneling microscopy


2. Surface and interface chemistry of corrosion, friction, fracture, and adhesion

Does the surface form a passivating oxide layer, and is this layer responsible for friction at "dry" (unlubricated) surfaces? What is the role of grain boundaries in oxidation at polygrain and multiphase materials? How well do clean and oxidized quasicrystals adhere to other materials?

Techniques being employed:

Transmission and scanning electron microscopies
Thermogravimetric analysis
Tribometry in ultrahigh vacuum
X-ray photoelectron spectroscopy
Scanning Auger electron microscopy and spectroscopy
Temperature-programmed desorption


3. Uniqueness of quasicrystals

Which of the interesting properties are due to quasicrystallinity, and which are due simply to chemical composition? The answers are provided by comparisons in the above areas between crystalline and quasicrystalline materials.