Metal-semiconductor hybrid heteronanostructures may exhibit not only a combination of properties from the disparate components but also further enhanced property tunability and new synergistic properties that arise from the interactions between the metal and semiconductor components. Here we demonstrate that the Au–Cu2O hybrid core–shell nanoparticles not only combine the optical signatures of Cu2O nanoshells and the plasmonic properties of Au nanoparticles but exhibit further enhanced and expanded plasmonic tunability as well due to the dielectric properties of the Cu2O shells surrounding the Au cores. We have developed a robust wet chemistry approach through which we can fine-control several important geometrical parameters of the Au–Cu2O core–shell nanoparticles, such as Cu2O shell thickness, size of the Au core, and the spacing between the core and shell, to systematically and selectively fine-tune the synergistic light absorption and scattering properties of the particles over a broad spectral range across the visible and near-infrared regions. We have further performed Mie scattering theory calculations to theoretically interpret the correlation between the geometrical parameters and optical characteristics of the Au–Cu2O hybrid nanoparticles. Such optical tunability achieved through the fine-control over core and shell geometries is believed to be important to the optimization of the overall performance of hybrid heteronanostructure-based materials and/or devices for photonic, electronic, and optoelectronic applications.

We report the rational synthesis of dopant-free GaN/AlN/AlGaN radial nanowire heterostructures and their implementation as high electron mobility transistors (HEMTs). The radial nanowire heterostructures were prepared by sequential shell growth immediately following nanowire elongation using metal-organic chemical vapor deposition (MOCVD). Transmission electron microscopy (TEM) studies reveal that the GaN/AlN/AlGaN radial nanowire heterostructures are dislocation-free single crystals. In addition, the thicknesses and compositions of the individual AlN and AlGaN shells were unambiguously identified using cross-sectional high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM). Transport measurements carried out on GaN/AlN/AlGaN and GaN nanowires prepared using similar conditions demonstrate the existence of electron gas in the undoped GaN/AlN/AlGaN nanowire heterostructures and also yield an intrinsic electron mobility of 3100 cm(2)/Vs and 21,000 cm(2)/Vs at room temperature and 5 K, respectively, for the heterostructure. Field-effect transistors fabricated with ZrO(2) dielectrics and metal top gates showed excellent gate coupling with near ideal subthreshold slopes of 68 mV/dec, an on/off current ratio of 10(7), and scaled on-current and transconductance values of 500 mA/mm and 420 mS/mm. The ability to control synthetically the electronic properties of nanowires using band structure design in III-nitride radial nanowire heterostructures opens up new opportunities for nanoelectronics and provides a new platform to study the physics of low-dimensional electron gases.

Noble metal nanoparticles have been of tremendous interest due to their intriguing size- and shape-dependent plasmonic and catalytic properties. Combining tunable plasmon resonances with superior catalytic activities on the same metallic nanoparticle, however, has long been challenging because nanoplasmonics and nanocatalysis typically require nanoparticles in two drastically different size regimes. Here, we demonstrate that creation of high-index facets on subwavelength metallic nanoparticles provides a unique approach to the integration of desired plasmonic and catalytic properties on the same nanoparticle. Through site-selective surface etching of metallic nanocuboids whose surfaces are dominated by low-index facets, we have controllably fabricated nanorice and nanodumbbell particles, which exhibit drastically enhanced catalytic activities arising from the catalytically active high-index facets abundant on the particle surfaces. The nanorice and nanodumbbell particles also possess appealing tunable plasmonic properties that allow us to gain quantitative insights into nanoparticle-catalyzed reactions with unprecedented sensitivity and detail through time-resolved plasmon-enhanced spectroscopic measurements.

An improved structural model for the M1 phase in the Mo-V-Nb-Te-O propane (amm)oxidation catalyst has been refined after accounting for a molybdenumsubstituted-V 2 O 5 impurity and by making adjustments based on aberration-corrected imaging results. The newly refined unit cell has Pba2 symmetry with a = 21.134(1) Å , b = 26.647(1) Å , c = 4.0140(2) Å , and Z = 4, in good agreement with our earlier findings (DeSanto et al. Top Catal 23:23 [20], DeSanto et al. Z Kristallogr 219:152[22]). From the newly refined occupancies, the formula unit is {TeO} 0.86(1) ÁMo 7.48(6) V 1.52(6) NbO 28 . As in the earlier models, V is concentrated in sites that link the pentagonal rings of M1. Careful analysis of bond valences, in combination with the electroneutrality constraint, suggest that the linking sites S3, S4, and S7 all have mixed Mo/V occupancies and valences (d 1 /d 0 ). Furthermore, these sites may contain a mix of Mo 5? and V 5? , which is consistent with the proposed catalytic mechanism in which V 5? plays an important role in propane activation.

While great success has been achieved in fine-tuning the aspect ratios and thereby the plasmon resonances of cylindrical Au nanorods, facet control with atomic level precision on the highly curved nanorod surfaces has long been a significantly more challenging task. The intrinsic structural complexity and lack of precise facet control of the nanorod surfaces remain the major obstacles for the atomic-level elucidation of the structure-property relationships that underpin the intriguing catalytic performance of Au nanorods. Here we demonstrate that the facets of single-crystalline Au nanorods can be precisely tailored using cuprous ions and cetyltrimethylammonium bromide as a unique pair of surface capping competitors to guide the particle geometry evolution during nanorod overgrowth. By deliberately maneuvering the competition between cuprous ions and cetyltrimethylammonium bromide, we have been able to create, in a highly controllable and selective manner, an entire family of nanorod-derived anisotropic multifaceted geometries whose surfaces are enclosed by specific types of well-defined high-index and low-index facets. This facet-controlled nanorod overgrowth approach also allows us to fine-tune the particle aspect ratios while well-preserving all the characteristic facets and geometric features of the faceted Au nanorods. Taking full advantage of the combined structural and plasmonic tunability, we have further studied the facet-dependent heterogeneous catalysis on well-faceted Au nanorods using surface-enhanced Raman spectroscopy as an ultrasensitive spectroscopic tool with unique time-resolving and molecular finger-printing capabilities.