The concept of hypervalency emerged as a notion for chemical bonding in molecules to explain the atomic coordination in hypervalent molecules that violates the electron-octet rule. Despite its significance, however, hypervalency in condensed phases, such as amorphous solids, remains largely unexplored. Using ab initio molecular-dynamics simulations, we report here the underlying principles of hypervalency in amorphous chalcogenide materials, in terms of the behaviour of hypervalent structural units, and its implicit relationship with material properties. The origin of a material-dependent tendency towards hypervalency is made evident with the multi-centre hyperbonding model, from which its relationship to abnormally large Born effective charges is also unambiguously revealed. The hyperbonding model is here extended to include interactions with cation s² lone pairs (LPs); such deep-lying LPs can also play a significant role in determining the properties of these chalcogenide materials. The role of hypervalency constitutes an indispensable and important part of chemical interactions in amorphous and crystalline chalcogenide solids.

Blue indium phosphide quantum dot (InP QD) is an emerging colloidal semiconductor nanocrystal, considered as a promising next‐generation photoactive material for light‐emitting purposes. Despite the tremendous progress in blue InP QDs, the synthetic method for tailoring InP core size to realize the blue‐emissive QDs still lags behind. This work suggests a synthetic method for blue‐emitting InP QDs by engineering the core size with an incipient ZnS (i‐ZnS) shell. The formation of i‐ZnS complexes, before the tris(trimethylsilyl)phosphine injection (e.g., before core growth process), restrains the overgrowth of InP nuclei by rapidly forming a ZnS shell on its surface, thereby resulting in further dwarfed InP cores. With additional ZnS shell coating, the blue QDs exhibit a photoluminescence quantum yield of ≈52% at 483 nm. The origin of bandgap diminution with the increase of shell thickness, or with the utilization of ZnSe shell is unraveled via the first‐principles density functional theory simulations. Simulational evidence on InP‐core densification with the shell coating, along with accompanying changes in chemical and structural properties, is presented. The blue‐emitting InP QD device shows a maximum luminance of 1162 cd m⁻² and external quantum efficiency of 1.4%.

Amorphous chalcogenide alloys exhibiting crystallization-free Ovonic threshold switching behaviour have gained immense attention as selector materials. While the switching characteristics depend on the chalcogen species, understanding device-level elemental behaviour, particularly for tellurium (Te), remains challenging due to its low crystallization temperature and poor glass-forming ability. Here, we realize an electrothermally induced amorphous Te (a-Te) phase via on-device cryogenic quenching, which rapidly suppresses crystallization in the supercooled liquid at low ambient temperature. The order-to-disorder transition yields a ~ 0.81 V increase in threshold voltage and a ~ 10³ reduction in subthreshold current, attributed to enhanced deep-level trap formation. The a-Te phase exhibits reliable self-regulated oscillations, driven by deep traps, distinguishing it from conventional capacitance-driven effects. These findings support that the threshold switching in Te originates from defect-mediated transitions occurring before melting, rather than solely from thermal phase-change effects. Our results provide insights into chalcogenide switching mechanisms and pave the way for stoichiometry-tuned selector devices, nano-oscillators, and selector-only memory applications.

The origin of chemical ordering in liquid and supercooled liquid Ge₂Sb₂Te₅ (GST) was investigated using ab initio molecular dynamics (AIMD) simulations. Bond dynamics were analyzed via continuous (${\mathrm{\tau }}_{\mathrm{con}}$) and intermittent (${\tau }_{int}$) lifetimes. The intermittent lifetime (${\tau }_{int}$) reveals that chemically ordered Ge-Te and Sb-Te bonds are the most stable, although ${\mathrm{\tau }}_{\mathrm{con}}$ exhibits a stability anomaly. The faster increase of ${\tau }_{int}$ for these bonds upon cooling explains the overall chemical ordering. A novel ordering mechanism was identified through the analysis of bond separation dynamics. Te-Te ‘wrong’ bonds exhibit a unique dynamic instability, breaking and separating much faster than any other bond type, which actively drives the system towards chemical order. A correlation between lifetime and bond strength, as calculated by the Integrated Crystal Orbital Hamilton Population (ICOHP), supports these dynamic findings. Chemical ordering shows a positive correlation with medium-range structural order, evidenced by the instability of 4-fold rings containing wrong bonds. This study provides a detailed dynamic origin for ordering in liquid GST, highlighting the role of Te-Te bond relaxation.

Nonconventional epitaxial techniques, such as van der Waals epitaxy and remote epitaxy, have attracted substantial attention in the semiconductor research community for their capability to repeatedly produce high-quality freestanding films from a single mother wafer. Successful implementation of these techniques depends on creating a robust, uniform two-dimensional (2D) material surface. The conventional method for fabricating graphene on silicon carbide (SiC) is high-temperature graphitization. However, the extremely high temperature required for silicon sublimation (typically above 1500°C) causes step bunching, forming nonuniform multilayer graphene stripes and an unfavorable surface morphology for epitaxial growth. Here, we developed a wafer-scale graphitization technique that allows fast synthesis of single-crystalline graphene at low temperatures by metal-assisted graphitization. In contrast to previous reports, we found annealing conditions enabling SiC dissociation while avoiding silicide formation, producing uniform single-crystalline graphene while maintaining the pristine surface morphology of the substrate. We successfully produce high-quality freestanding single-crystalline III-N (AlN and GaN) membranes on graphene/SiC via the 2D material–based layer transfer technique.