Nucleation in atomic crystallization remains poorly understood, despite advances in classical nucleation theory. The nucleation process has been described to involve a nonclassical mechanism that includes a spontaneous transition from disordered to crystalline states, but a detailed understanding of dynamics requires further investigation. In situ electron microscopy of heterogeneous nucleation of individual gold nanocrystals with millisecond temporal resolution shows that the early stage of atomic crystallization proceeds through dynamic structural fluctuations between disordered and crystalline states, rather than through a single irreversible transition. Our experimental and theoretical analyses support the idea that structural fluctuations originate from size-dependent thermodynamic stability of the two states in atomic clusters. These findings, based on dynamics in a real atomic system, reshape and improve our understanding of nucleation mechanisms in atomic crystallization.
Recent advances in flexible and stretchable electronics have led to a surge of electronic skin (e-skin)–based health monitoring platforms. Conventional wireless e-skins rely on rigid integrated circuit chips that compromise the overall flexibility and consume considerable power. Chip-less wireless e-skins based on inductor-capacitor resonators are limited to mechanical sensors with low sensitivities. We report a chip-less wireless e-skin based on surface acoustic wave sensors made of freestanding ultrathin single-crystalline piezoelectric gallium nitride membranes. Surface acoustic wave–based e-skin offers highly sensitive, low-power, and long-term sensing of strain, ultraviolet light, and ion concentrations in sweat. We demonstrate weeklong monitoring of pulse. These results present routes to inexpensive and versatile low-power, high-sensitivity platforms for wireless health monitoring devices.
A general
problem when designing functional nanomaterials for energy
storage is the lack of control over the stability and reactivity of
metastable phases. Using the high-capacity hydrogen storage candidate
LiAlH4 as an exemplar, we demonstrate an alternative approach
to the thermodynamic stabilization of metastable metal hydrides by
coordination to nitrogen binding sites within the nanopores of N-doped
CMK-3 carbon (NCMK-3). The resulting LiAlH4@NCMK-3 material
releases H2 at temperatures as low as 126 °C with
full decomposition below 240 °C, bypassing the usual Li3AlH6 intermediate observed in bulk. Moreover, >80%
of
LiAlH4 can be regenerated under 100 MPa H2,
a feat previously thought to be impossible. Nitrogen sites are critical
to these improvements, as no reversibility is observed with undoped
CMK-3. Density functional theory predicts a drastically reduced Al–H
bond dissociation energy and supports the observed change in the reaction
pathway. The calculations also provide a rationale for the solid-state
reversibility, which derives from the combined effects of nanoconfinement,
Li adatom formation, and charge redistribution between the metal hydride
and the host.
Two-dimensional
(2D) transition metal dichalcogenide (TMD) layers
are unit-cell thick materials with tunable physical properties according
to their size, morphology, and chemical composition. Their transition
of lab-scale research to industrial-scale applications requires process
development for the wafer-scale growth and scalable device fabrication.
Herein, we report on a new type of atmospheric pressure chemical vapor
deposition (APCVD) process that utilizes colloidal nanoparticles as
process-scalable precursors for the wafer-scale production of TMD
monolayers. Facile uniform distribution of nanoparticle precursors
on the entire substrate leads to the wafer-scale uniform synthesis
of TMD monolayers with the controlled size and morphology. Composition-controlled
TMD alloy monolayers with tunable bandgaps can be produced by simply
mixing dual nanoparticle precursor solutions in the desired ratio.
We also demonstrate the fabrication of ultrathin field-effect transistors
and flexible electronics with uniformly controlled performance by
using TMD monolayers.
Uniformly dispersed palladium species in small-pore zeolite are successfully prepared for catalytic applications, and are investigated by advanced microscopic methods.
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