Heteropolyacid-Mediated Self-Assembly of Heteropolyacid-Modified Pristine Graphene Supported Pd Nanoflowers for Superior Catalytic Performance toward Formic Acid Oxidation

The in situ growth of Pd nanoflowers on pristine graphene is achieved using phosphomolybdic acid (HPMo) to mediate self-assembly. The HPMo serves simultaneously as a linker, stabilizer, and structure-directing agent, and the nanoflowers are formed by kinetically controlled growth. When the resulting material, Pd nanoflowers on HPMo-modified graphene (HPMo-G) support, is used to catalyze the formic acid oxidation reaction (FAOR), much higher catalytic activity and durability are found than with HPMo-G supported Pd nanospheres, graphene supported Pd nanoparticles, and commercial Pd/C catalysts. The catalytic activity for Pd nanoflowers on HPMo-G is also among the highest reported for Pd-based catalysts. The superior electrocatalytic performance is attributed to the unique nanoflower shape, a promotion by the HPMo mediator, and the excellent support properties of pristine graphene. The use of HPMo to mediate self-assembly of metals on graphene can be extended to fabricate other hybrid nanostructures promising broad applicability

Azimuthally Polarized, Circular Colloidal Quantum Dot Laser Beam Enabled by a Concentric Grating

Since optical gain was observed from colloidal quantum dots (CQDs), research on CQD lasing has been focused on the CQDs themselves as gain materials and their coupling with optical resonators. Combining the advantages of a CQD gain medium and optical microcavity in a laser device is desirable. Here, we show concentric circular Bragg gratings intimately incorporating CdSe/CdZnS/ZnS gradient shell CQDs. Because of the strong circularly symmetric optical confinement in two dimensions, the output beam CQD-based circular grating distributed feedback laser is found to be highly spatially coherent and azimuthally polarized with a donut-like cross section. We also observe the strong modification of the photoluminescence spectrum by the grating structures, which is associated with modification of optical density of states. This effect confirmed the high quality of the resonator that we fabricated and the spectral overlap between the optical transitions of the emitter and resonance of the cavity. Single mode lasing has been achieved under a quasi-continuous pumping regime, while the position of the lasing mode can be conveniently tuned via adjusting the thickness of the CQD layer. Moreover, a unidirectional output beam can be observed as a bright circular spot on a screen without any collimation optics, presenting a direct proof of its high spatial coherence

Polarization-Resolved Plasmon-Modulated Emissions of Quantum Dots Coupled to Aluminum Dimers with Sub-20 nm Gaps

An aluminum dimer nanoantenna with nanogaps is an ideal platform for enhancing light–matter interaction at the nanoscale for the UV–vis spectrum, but its realization has been hindered by the surface oxidation of aluminum nanostructures, aluminum interband loss, and practical limitations in lithographic patterning. Here, we have overcome these problems and demonstrated the successful fabrication of an aluminum dimer antenna with a ∼10 nm gap, which to the best of our knowledge marks the smallest features of an Al nanoantenna. We present the first in-depth study of strongly polarization-dependent emissions of colloidal quantum dots coupled with Al dimers and elucidate the individual contributions of the excitation intensity, quantum yield, and extraction efficiency enhancements from numerical and experimental perspectives. We estimate the Purcell effect corresponding to a single Al-dimer antenna as ∼104 by taking into account the ensemble averaging effect and the distributions in emitter dipole orientations. This finding brings us a step closer toward a cost-effective realization of bright and ultrafast single emitters