Lu Shi

Phase-change random-access memory (PCRAM) is one of the leading candidates for next-generation data-storage devices, but the trade-off between crystallization (writing) speed and amorphous-phase stability (data retention) presents a key challenge. We control the crystallization kinetics of a phase-change material by applying a constant low voltage via prestructural ordering (incubation) effects. A crystallization speed of 500 picoseconds was achieved, as well as high-speed reversible switching using 500-picosecond pulses. Ab initio molecular dynamics simulations reveal the phase-change kinetics in PCRAM devices and the structural origin of the incubation-assisted increase in crystallization speed. This paves the way for achieving a broadly applicable memory device, capable of nonvolatile operations beyond gigahertz data-transfer rates.

In the present work, the electronic and vibrational properties of both pristine ${\mathrm{V}}_{2}\mathrm{C}$ and fully terminated ${\mathrm{V}}_{2}\mathrm{C}{T}_{2}$ (where $T=\mathrm{F},$ O, OH) two-dimensional monolayers are investigated using density functional theory. First, the atomic structures of ${\mathrm{V}}_{2}\mathrm{C}$-based MXene phases are optimized, and their respective dynamical stabilities are discussed. Second, electronic band structures are computed indicating that ${\mathrm{V}}_{2}\mathrm{C}$ is metallic as well as all the corresponding functionalized systems. Third, the vibrational properties (phonon frequencies and spectra) of ${\mathrm{V}}_{2}\mathrm{C}$-based MXenes are computed with the density functional perturbation theory and reported. Both Raman-active (${E}_{g}$, ${A}_{1g}$) and infrared-active (${E}_{u}$, ${A}_{2u}$) vibrational modes are predicted ab initio with the aim to correlate the experimental Raman peaks with the calculated vibrational modes and to assign them to specific atomic motions. The effect of the terminal groups on the vibrational properties is emphasized, along with the effect on the presence and position of the corresponding Raman peaks. Our results provide insights for the identification and characterization of ${\mathrm{V}}_{2}\mathrm{C}$-based samples using Raman spectroscopy.

Fully targeted mRNA therapeutics necessitate simultaneous organ-specific accumulation and effective translation. Despite some progress, delivery systems are still unable to fully achieve this. Here, we reformulate lipid nanoparticles (LNPs) through adjustments in lipid material structures and compositions to systematically achieve the pulmonary and hepatic (respectively) targeted mRNA distribution and expression. A combinatorial library of degradable-core based ionizable cationic lipids is designed, following by optimisation of LNP compositions. Contrary to current LNP paradigms, our findings demonstrate that cholesterol and phospholipid are dispensable for LNP functionality. Specifically, cholesterol-removal addresses the persistent challenge of preventing nanoparticle accumulation in hepatic tissues. By modulating and simplifying intrinsic LNP components, concurrent mRNA accumulation and translation is achieved in the lung and liver, respectively. This targeting strategy is applicable to existing LNP systems with potential to expand the progress of precise mRNA therapy for diverse diseases.

The reversible and fast phase transitions induced by picosecond electrical pulses are observed in the nanostructured GeSbTe materials, which provide opportunities in the application of high speed nonvolatile random access memory devices. The mechanisms for fast phase transition are discussed based on the investigation of the correlation between phase transition speed and material size. With the shrinkage of material dimensions, the size effects play increasingly important roles in enabling the ultrafast phase transition under electrical activation. The understanding of how the size effects contribute to the phase transition speed is of great importance for ultrafast phenomena and applications.