First Principles Calculations of Zinc-Oxide Nanowires
X. Shen, J-C. Zheng, J.W. Davenport, J.T. Muckerman, and P.B. Allen

Nanostructured zinc oxide is a promising material for a new generation of optoelectronic devices [1] and alloys of zinc oxide with gallium nitride have recently been shown to be effective photocatalysts for hydrogen production through water splitting [2]. We have performed first principles calculations of the electronic structure and geometry of ZnO nanowires using a supercell method and the generalized gradient approximation to density functional theory. We used the Quantum Espresso PWscf code [3]. Crystalline ZnO forms in the hexagonal, Wurtzite structure. Our calculations [4] for the lattice constants within the basal plane and along the hexagonal (z) axis differ from experiment by 1.3% and 0.2%, respectively, values which are typical of density functional theory. ZnO wires are naturally formed by cutting out hexagonal shaped fragments with axis along z containing 13 formula units (26 atoms). Figure 1 compares charge density contours in a plane which contains the z axis for the crystal, and for the unrelaxed and relaxed nanowire. We find that that band gap is increased in the nanowire compared to the bulk crystal while improved photocatalytic properties would require a decrease. This shows the importance of alloying as shown experimentally. Further studies on those systems will be undertaken next.

Figure 1. Charge density contours in the x-z plane (z along the hexagonal axis) for (a) bulk ZnO, (b), the unrelaxed nanowire and (c) the relaxed nanowire.

References

• [1] Wang, Z.L. Zinc oxide nanostructures: growth, properties and applications. J. Phys.: Condens Matter 16: R829-R858 (2004).
• [2] Lu, D., Takata, T., Saito, N., Inoue, Y., and Domen, K. Photocatalyst releasing hydrogen from water. Nature 440: 295 (2006).
• [3] Lu, D., Takata, T., Saito, N., Inoue, Y., and Domen, K. Photocatalyst releasing hydrogen from water. Nature 440: 295 (2006).
• [4] Shen, X., Pederson, M.R., Zheng, J-C., Davenport, J.W., Muckerman, J.T., and Allen, P.B. Electronic Structure of ZnO nanowire. condmat/0610002.

Last Modified: January 31, 2008
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