Weak bonding of Zn in an Al-based approximant based on surface measurements

Abstract

We have studied two surfaces of a new Al–Pd–Zn approximant using mass spectrometry, X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). Zn is bonded weakly in this approximant, perhaps as weakly as in elemental Zn. This is based upon three observations: (1) the low vapor pressure of Zn above the approximant (detectable in the gas phase at 600 K), (2) preferential sputtering of Zn (contrary to the usual preferential sputtering of Al in Al-rich quasicrystals), and (3) preferential surface segregation of Zn. We further show that preferential segregation – and perhaps incipient evaporation – causes the surface to roughen, preventing it from forming a terrace-step morphology. Finally, our data show that at low O₂ pressures, Al oxidizes. In air, Zn oxidizes as well. All results and conclusions are similar for the two-fold and pseudo-10-fold surfaces.

Keywords:

• quasicrystals
• surface physics

Acknowledgements

This work was supported by the Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division of the US Department of Energy (USDOE). This manuscript has been authorized by Iowa State University of Science and Technology under Contract No. DE-AC02-07CH11358 with the US Department of Energy. We are indebted to Srinivasa Thimmaiah and Gordon Miller for allowing us to collaborate on their newly discovered phase. We thank William Yuhasz, James Anderegg and Srinivasa Thimmaiah for growing and characterizing the bulk samples.

Notes

Note

1. In this paper, the terms “alloy” and “intermetallic” are used to denote multicomponent metallic systems. For some scientists, the two terms denote extrema in the continuum of multicomponent metals, where the chemical identity of an atom occupying any given site is either random (alloy) or fixed (intermetallic). In this sense, quasicrystals and approximants are more similar to intermetallics than to alloys.