Hafnium–zirconium oxide (HZO) thin films are of interest due to their ability to form ferroelectric (FE) and antiferroelectric (AFE) oxide phases. Density functional theory is employed to elucidate the stabilization mechanisms of both FE HZO thin films and AFE ZrO2 films. The FE orthorhombic phase is primarily stabilized by in-plane tensile strain, which spontaneously occurs during the synthesis process, and this is more effective for HZO than HfO2. Layer-by-layer stack models and core-matrix three-dimensional models of the polymorphs reveal that the electrostatic component of interfacial free energy can play a critical role in the formation of the AFE tetragonal phase in ZrO2 and the “wake-up” effect for FE HZO.

Silicon (Si) is one of the most extensively studied materials owing to its significance to semiconductor science and technology. While efforts to find a new three-dimensional (3D) Si crystal with unusual properties have made some progress, its two-dimensional (2D) phases have not yet been explored as much. Here, based on a newly developed systematic ab initio materials searching strategy, we report a series of novel 2D Si crystals with unprecedented structural and electronic properties. The new structures exhibit perfectly planar outermost surface layers of a distorted hexagonal network with their thicknesses varying with the atomic arrangement inside. Dramatic changes in electronic properties ranging from semimetal to semiconducting with indirect energy gaps and even to one with direct energy gaps are realized by varying thickness as well as by surface oxidation. Our predicted 2D Si crystals with flat surfaces and tunable electronic properties will shed light on the development of silicon-based 2D electronics technology.

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We developed a model template method mimicking the nanocasting process by introducing cylindrical templates during the quenched molecular dynamics process [Y.