Viscoelastic Flows in Simple Liquids Generated by Vibrating Nanostructures

Newtonian fluid mechanics, in which the shear stress is proportional to the strain rate, is synonymous with the flow of simple liquids such as water. We report the measurement and theoretical verification of non-Newtonian, viscoelastic flow phenomena produced by the high-frequency (20 GHz) vibration of gold nanoparticles immersed in water-glycerol mixtures. The observed viscoelasticity is not due to molecular confinement, but is a bulk continuum effect arising from the short time scale of vibration. This represents the first direct mechanical measurement of the intrinsic viscoelastic properties of simple bulk liquids, and opens a new paradigm for understanding extremely high frequency fluid mechanics, nanoscale sensing technologies, and biophysical processes

Gold Bipyramid Nanoparticle Dimers

An aqueous synthesis of gold bipyramid dimers is presented. The methodology, its selectivity, and the characterization of the resulting structures with optical dark-field and scanning electron microscopy are presented and discussed. In the bowtie orientation, the dimers exhibit a 20% red shift in their plasmon resonance as compared to the individual particles, with a weak dependence on the interparticle separation. From the analysis, it was found that the in situ absorption peaks that develop during the assembly can be assigned to specific dimer structures, which has not been shown previously. Last, the kinetics of the assembly are analyzed

Scalable Ligand-Mediated Transport Synthesis of Organic–Inorganic Hybrid Perovskite Nanocrystals with Resolved Electronic Structure and Ultrafast Dynamics

Colloidal perovskite nanocrystals support bright, narrow PL tunable over the visible spectrum. However, bandgap tuning of these materials remains limited to laboratory-scale syntheses. In this work, we present a polar-solvent-free ligand-mediated transport synthesis of high-quality organic–inorganic perovskite nanocrystals under ambient conditions with photoluminescence quantum yields up to 97%. Our synthesis employs a ligand-mediated transport mechanism that circumvents the need for exquisite external control (<i>e</i>.<i>g</i>., temperature control, inert-gas protection, dropwise addition of reagents) required by other methods due to extremely fast reaction kinetics. In the ligand-mediated transport mechanism, multiple equilibria cooperatively dictate reaction rates and enable precise control over NC size. These small nanocrystals exhibit high photoluminescence quantum yields due to quantum confinement. Nanosecond transient absorption spectroscopy experiments reveal a fluence-independent PL decay originating from exciton recombination. Two-dimensional electronic spectroscopy resolves multiple spectral features reflecting the electronic structure of the nanocrystals. The resolved features exhibit size-dependent spectral positions, further indicating the synthesized nanocrystals are quantum-confined