AVS 50th International Symposium
    Thin Films Thursday Sessions
       Session TF-ThM

Paper TF-ThM9
From Ab-initio Modeling to Experimental Thin Film Synthesis of a Novel Boron-oxygen-yttrium Phase

Thursday, November 6, 2003, 11:00 am, Room 329

Session: Modeling & Fundamentals in Thin Film Deposition
Presenter: D. Music, Linköping University, Sweden
Authors: D. Music, Linköping University, Sweden
V. Chirita, Linköping University, Sweden
J.M. Schneider, RWTH Aachen, Germany
U. Helmersson, Linköping University, Sweden
Correspondent: Click to Email
The B-O based material system is a promising candidate for a wide range of tribological applications. For example, crystalline boron suboxide has been reported to have the elastic modulus of 470 GPa. However, typical requirements to form crystalline boron suboxide include high pressure (5-7 GPa) and temperature (>2000 °C), and are very difficult to achieve with standard thin film synthesis techniques such as reactive sputtering. In this work, we use ab-initio calculations to theoretically design and then experimentally grow polycrystalline boron suboxide based films. A new crystalline boron-oxygen-yttrium (BOY) phase is obtained by alloying with Y. The essential element in the modeling is Y substituting for O in the boron suboxide structure with Y/B and O/B ratios of 0.07. The overall effect of electron doping, induced by the Y substitution, is to shorten the chemical bonds in boron suboxide. This renders the formation of the BOY phase characterized by a 45% volume reduction and consequently a 23% increase in bulk modulus (from 235 to 289 GPa). The calculations predict that the BOY phase is 0.36 eV/atom more stable than crystalline boron suboxide and experiments confirm the formation of crystalline thin films. The BOY phase was synthesized with reactive RF magnetron sputtering and identified with x-ray and selected area electron diffraction. Films with Y/B ratios ranging from 0.10 to 0.32, as determined via elastic recoil detection analysis, were grown over a wide range of temperatures (300-600 °C) and found to withstand 1000 °C. Details of the electronic structure of this new phase will also be presented.