Theory of Ferroelectric ZrO2 Monolayers on Si

We use density functional theory and Monte Carlo lattice simulations to investigate the structure of ZrO 2 monolayers on Si(001). Recently, we have reported on the experimental growth of amorphous ZrO 2 monolayers on silicon and their ferroelectric properties, marking the achievement of the thinnest possible ferroelectric oxide [ Dogan, M.; Nano Lett. 18, 2018, 241−246]. Here, we describe the rich landscape of atomic configurations of monocrystalline ZrO 2 monolayers on Si and determine the local energy minima. Because of the multitude of low-energy configurations we find, we consider the co-existence of finite-sized regions of different configurations. We create a simple nearest neighbor lattice model with parameters extracted from density functional theory calculations and solve it numerically using a cluster Monte Carlo algorithm. Our results suggest that up to room temperature, the ZrO 2 monolayer consists of small domains of two low-energy configurations with opposite ferroelectric polarization. This explains the observed ferroelectric behavior in the experimental films as a collection of crystalline regions, which are a few nanometers in size, being switched with the application of an external electric field.