A first principles study of the properties of Al:ZnO and its adhesion to Ag in an optical coating

作者：Lin, Zheshuai^*; Bristowe, Paul D.

来源：Journal of Applied Physics, 2009, 106(1): 013520.

DOI：10.1063/1.3159651

• adhesion
• adsorption
• aluminium
• compressive strength
• density functional theory
• electron density
• hydrogen
• II-VI semiconductors
• internal stresses
• optical films
• silver
• water
• wide band gap semiconductors
• zinc compounds

A first principles density functional study of the atomistic properties of Al:ZnO and its adhesion to Ag is presented. Optical coatings often contain interfaces between ZnO (0001) and Ag (111) layers whose bonding can be improved by incorporating small amounts of Al into the ZnO but the underlying strengthening mechanism remains unclear. It is assumed that Al relaxes the internal compressive stress in the film but the situation is complicated by the presence of hydrogen and/or water which can adsorb on the ZnO surface during fabrication of the coating. Hydrogen and/or water are known to weaken the Ag/ZnO interface particularly when it is O terminated. In this paper it is shown that aluminum substitutes on Zn sites in ZnO and this does indeed reduce the internal stress in the layer under compression. However, it is also shown that Al segregates to the ZnO surface when it is O terminated (but not Zn terminated) and this reduces the propensity for hydrogen adsorption. Thus by eliminating some of the hydrogen from the ZnO surface which is more likely to be O terminated than Zn terminated under ambient conditions, the strength of the Ag/ZnO interface can be increased. The effect of aluminum incorporation into the ZnO layer is therefore twofold: it relaxes the residual stresses in the coating and also improves the chemical bonding at the metal/oxide interface by removing the weakening effects of gaseous adsorption. The changes in interfacial bonding are explained in terms of an electron redistribution and compensation model.

• 出版日期2009-7-1
• 单位中国科学院理化技术研究所