| Abstract | We have investigated the microstructures and electronic structures of a series of hafnium aluminate (HfAlO) films with Al concentration ranging from 0% to 100%. When the films evolve from pure HfO2 to pure Al2O3 by increasing the aluminum content, we find changes in their radial distribution functions, which disclose the short-range order of the materials, despite the amorphous nature of all films. The HfAlO films (with Al/Hf ratio ranging from 0.25 to 5.8) appear to be a single glassy phase of Hf, Al, and O, instead of simple mixtures of HfO2 and Al2O3. The Hf (Al)舑O, Hf (Al)舑Al, and Hf舑Hf bonds are observed to be insensitive to the amount of Al in the film, except when the Al concentration is large (Al/Hf~5.8), in which case the bonding is similar to that in pure Al2O3. Although the local symmetry of Hf in amorphous HfO2 is suggested by the electron energy-loss spectrum taken at an oxygen K edge, it is largely disrupted when Al is introduced. The valence electron energy-loss spectroscopy reveals three distinct evolving features as the Al content increases, which we discuss in terms of the electronic structure of HfO2. |
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