Twisted stacking of two-dimensional van der Waals (vdW) semiconductors creates moiré superlattices, which provides unprecedented control over quantum states and their light-matter interactions. We demonstrate that a simple twist interface between two single-crystalline bulks of hexagonal boron nitride (hBN) creates moiré quantum wells (QWs) embedded in a three-dimensional vdW structure. hBN moiré QWs strongly confine charge carriers under both optical excitation and electrical injection. Despite their indirect bandgap, they emit intense deep-ultraviolet luminescence in the extreme wavelength bands from 215 to 240 nanometers, exceeding that of state-of-the-art conventional aluminum gallium nitride (AlGaN) multiple QWs by more than an order of magnitude. Furthermore, the twist angle control allows wide tunability of luminescence energy and efficiency in moiré QWs.

Antimony (Sb) is an intriguing material for advanced electronics, with thickness-dependent properties at the nanoscale offering new functionalities. However, conventional methods for depositing Sb thin films cannot produce continuous ultrathin films with conformality in complex nanoscale structures. This study introduces a novel sacrificial atomic layer deposition (s-ALD) approach that overcomes these limitations by using chemical substitution between the antimony precursor and the pre-deposited Sb₂Te₃. The structural similarity between Sb₂Te₃ and Sb enables local epitaxial growth of a uniform, (00l)-oriented Sb film with exceptional surface smoothness (root-mean-squared roughness << 1 nm) at a 4-nm thickness. Highly pure Sb films with excellent wafer-scale uniformity and conformality are achieved on high-aspect-ratio structures. The mechanism involves substitution reactions driven by the preferential Te-(CH₃)₃Si bonding, along with enhanced atomic diffusion through the aligned crystal structure. Phase change memory devices using 5-nm-thick s-ALD Sb films demonstrate ultrafast switching with femtosecond laser pulses (≈220 fs) with high device-to-device uniformity (coefficient of variation < 5 %) and ultralow drift coefficients (0.0013 for the on state and 0.0073 for the off state). This s-ALD technique offers a promising pathway for depositing ultrathin, uniform Sb films, enabling full utilization of Sb's unique nanoscale properties.