The Journal of Physical Chemistry Letters最新文献

Ionic liquids are promising solvents for batteries, biomassprocessingand critical mineral recovery, but their viscosities can exceed thoseof conventional molecular solvents by several orders of magnitude,impeding mass and charge transport and complicating process design.Using complementary neutron spin echo spectroscopy and nuclear magneticresonance diffusometry, we probe local and long-range dynamics ofthree protic ionic liquids over time scales from 10^–12 to 10^–3 seconds. We identify a fast relaxationwith closely corresponding self and collective time scales, indicatingcooperative rearrangement of the surrounding molecular network. Itscharacteristic time scale correlates with bulk viscosity, while itstemperature dependence reveals distinct Arrhenius activation energiesdepending on whether extended networks are dominated by hydrogen bondingor electrostatic interactions. These results link cooperative networkrelaxation to macroscopic viscosity and show how molecular structurecan tune the energetic cost of structural relaxation through networkconnectivity.

Strong light–matter coupling in optical cavitiesis beingwidely explored as a strategy for modifying molecular dynamics andenhancing coherence. At the same time, structured vibrational environmentscan exhibit non-Markovian memory that promotes information backflowand coherence revival. We investigate the competition between theseeffects in a vibronic molecular system strongly coupled to a lossyoptical cavity. Using hierarchical equations of motion to treat structuredvibrational baths, we quantify both system coherence and non-Markovianityvia the l₁ norm of coherence and the Breuer–Laine–Piilomeasure, respectively. We find that cavity coupling enhances coherencein overdamped environments but can suppress memory-assisted coherencein resonant underdamped regimes, even in the absence of significantphoton loss. This suppression arises from hybridization-induced modificationof system–bath information flow. We demonstrate that cavitycoupling does not universally protect coherence but establishes limitsgoverned by the competition between vibrational recurrence time scalesand polaritonic hybridization.

Understanding how pyrimidine nucleobases form in spaceis centralto prebiotic chemistry, yet the pathways assembling these heterocyclesremain unresolved. Carbonisocyanatidic amide (H₂NC(O)NCO),an acyclic intermediate with heteroatom connectivity relevant to uraciland thymine, has not been detected in interstellar ice analogs. Here,we show that carbonisocyanatidic amide is formed in low-temperatureisocyanic acid (HNCO) ices exposed to energetic electrons and is identifiedduring the desorption phase by synchrotron vacuum ultraviolet photoionizationreflectron time-of-flight mass spectrometry combined with high-levelquantum chemical calculations. A plausible, product-constrained networkinvolves hydrogen abstraction and addition steps that generate radicalintermediates, followed by radical–radical recombination andcarbon–nitrogen bond formation. These results establish anexperimental link between simple interstellar volatiles and nitrogen-richmolecular architectures relevant to pyrimidine nucleobases, supportingan astrochemical route to prebiotic intermediates in icy grains andtheir possible delivery to early Earth.

Two-dimensional (2D) vertical transistors, featuringatomicallythin channels and an inherent vertical architecture, hold extensivepromise for ultrascaled electronics. However, achieving reliable polaritycontrol in such devices has remained a persistent challenge over thepast decade. Here, we demonstrate a vertical MoTe₂ transistorwith highly controllable polarity. By implementing van der Waals (vdW)integration for both contacts, the carrier injection barrier can beeffectively modulated via the work functions of the electrodes. Leveragingthe favorable band alignment with graphene and the narrow bandgapof MoTe₂, we achieve selective n-type and p-type operationusing Ag and Pt top contacts, respectively. Furthermore, through graphenework-function engineering, we optimize the switching performance,realizing an on/off ratio exceeding 10⁴ in a ∼5nm p-type MoTe₂ vertical transistor, surpassing all previouslyreported p-type 2D vertical transistors based on graphene/TMD/metalarchitectures. Finally, we integrate two vertical transistors of oppositepolarities, fabricated from graphene/MoTe₂ heterostructurewith different top contacts, to demonstrate a complementary inverteron a single chip. Our work not only provides a viable strategy forpolarity control in vertical heterostructures but also suggests apotential pathway toward complementary circuits based on 2D verticaltransistors.

Formation and evolutionof ice nanocrystals in rapidlyfrozen sugarsolutions were investigated using spin-contrast-variation small-angleneutron scattering (SCV-SANS). As the sugar concentration decreased,the SCV-SANS signal from nanocrystalline ice plates decreased relativeto that from micrometer-sized ice crystals, while the diffractionpeaks became sharper. These results indicate that the micrometer-sizedcrystals formed predominantly through Ostwald ripening, which dependedprimarily on sugar concentration and secondarily on sugar species.Regardless of the initial sugar concentration, ice crystal growthwas arrested when the sugar concentration in the freeze-concentratedamorphous ice reached 66–71 wt % for trehalose and sucroseand 62–63 wt % for glucose. Despite its lower glass-transitiontemperature, glucose showed growth arrest at a lower degree of freezeconcentration than trehalose and sucrose. However, the water activityat these growth-arrest concentrations converged to 0.80–0.82under the present rapid-freezing conditions, indicating that wateractivity determines ice nanocrystal evolution until vitrificationarrests further growth.