Tuning thermal expansions of zinc oxide sheets by varying the layer thickness

Employing density functional theory and Grüneisen formalism, the layer dependence of zinc oxide (ZnO) sheet thermal expansion coefficients (TECs) is investigated. The monolayer ZnO sheet contracts significantly across the entire range of temperatures investigated. The negative TEC with maximum absolute value -2.378 × 10-5 K-1 is determined, which implies that the monolayer ZnO sheet's thermal contraction is more remarkable than those of many other 2D atomic layers, such as graphene's negative TEC with maximum absolute value -6.070×10-6 K-1. The bilayer ZnO sheet, similar to the monolayer sheet, contracts with increasing temperature, but its negative TEC absolute value is much smaller. The trilayer ZnO sheet contracts at low temperature, and expands at high temperature, with relatively low absolute values of TECs. The thermal contraction behaviour disappears in four- and five-layer ZnO sheets. These two sheets expand with increasing temperature. The maximum TEC of the five-layer ZnO sheet, 2.243 × 10-5 K-1, is determined at 1100K, the maximum temperature investigated. © EPLA, 2014.