Ming Lin

Site-specific growth of Au-Pd alloy horns on Au nanorods: a platform for highly sensitive monitoring of catalytic reactions by surface enhancement Raman spectroscopy.

Surface-enhanced Raman scattering (SERS) is a highly sensitive probe for molecular detection. The aim of this study was to develop an efficient platform for investigating the kinetics of catalytic reactions with SERS. To achieve this, we synthesized a novel Au-Pd bimetallic nanostructure (HIF-AuNR@AuPd) through site-specific epitaxial growth of Au-Pd alloy horns as catalytic sites at the ends of Au nanorods. Using high-resolution electron microscopy and tomography, we successfully reconstructed the complex three-dimensional morphology of HIF-AuNR@AuPd and identified that the horns are bound with high-index {11l} (0.25 < l < 0.43) facets. With an electron beam probe, we visualized the distribution of surface plasmon over the HIF-AuNR@AuPd nanorods, finding that strong longitudinal surface plasmon resonance concentrated at the rod ends. This unique crystal morphology led to the coupling of high catalytic activity with a strong SERS effect at the rod ends, making HIF-AuNR@AuPd an excellent bifunctional platform for in situ monitoring of surface catalytic reactions. Using the hydrogenation of 4-nitrothiophenol as a model reaction, we demonstrated that its first-order reaction kinetics could be accurately determined from this platform. Moreover, we clearly identified the superior catalytic activity of the rod ends relative to that of the rod bodies, owing to the different SERS activities at the two positions. In comparison with other reported Au-Pd bimetallic nanostructures, HIF-AuNR@AuPd offered both higher catalytic activity and greater detection sensitivity.

High‐Performance Broadband Photodetector Using Solution‐Processible PbSe–TiO2–Graphene Hybrids

Highly sensitive, multicomponent broadband photodetector devices are made from PbSe/graphene/TiO(2). TiO(2) and PbSe nanoparticles act as light harvesting photoactive materials from the UV to IR regions of the electromagnetic spectrum, while the graphene acts as a charge collector for both photogenerated holes and electrons under an applied electric field.

Plasmonic gold nanocrosses with multidirectional excitation and strong photothermal effect.

We report a facile chemical synthesis of well-defined gold nanocrosses through anisotropic growth along both <110> and <001>, whereas gold nanorods grow only along either <110> or <001>. The multiple branching was achieved by breaking the face-centered-cubic lattice symmetry of gold through copper-induced formation of single or double twins, and the resulting gold nanocrosses exhibited pronounced near-IR absorption with a great extension to the mid-IR region. As studied by discrete dipole approximation (DDA) simulations, the entire nanocross gets excited even when one of the branches is exposed to incident light. The above properties make them useful as octopus antennas for capturing near-IR light for effective photothermal destruction of cells. The cell damage process was analyzed using the Arrhenius model, and its intrinsic thermodynamic characteristics were determined quantitatively. Besides effective photothermal treatment and two-photon luminescence imaging, the near- and mid-IR-absorbing gold nanocrosses may also find applications in IR sensing, thermal imaging, telecommunications, and the like.

Toward High Throughput Interconvertible Graphane-to-Graphene Growth and Patterning

We report a new route to prepare high quality, monolayer graphene by the dehydrogenation of graphane-like film grown by plasma-enhanced chemical vapor deposition. Large-area monolayer graphane-like film is first produced by remote-discharged radio frequency plasma beam deposition at 650 °C on Cu/Ti-coated SiO(2)-Si. The advantages of the plasma deposition include very short deposition time (<5 min) and a lower growth temperature of 650 °C compared to the current thermal chemical vapor deposition approach (1000 °C). Near edge X-ray adsorption, Raman spectroscopy, and transmission electron microscopy as well as scanning tunneling microscopy have been applied to characterize the graphane-to-graphene transition for the as-deposited films. The fingerprint quantum hall effect of monolayer graphene can be obtained on the fully dehydrogenated graphane-like film; four fully quantized half-integer plateaus are observed. The interconvertibility between graphane-like and graphene here opens up a possible route for the fabrication of regions with varying conductivity in a single deposition system using maskless, laser writing.

Light-Induced Selective Deposition of Metals on Gold-Tipped CdSe-Seeded CdS Nanorods

We introduce a facile approach for the selective deposition of metals on Au-tipped CdSe-seeded CdS nanorods that exploits the transfer of electrons from CdS to the Au tips upon UV excitation. This light-induced deposition method was used for the deposition of Pd under mild conditions, which produced a Pd/Au alloyed tip while preserving the rest of the semiconductor nanoarchitecture. The highly site-selective deposition method was extended to the deposition of Fe, yielding monodispersed, structurally complex Au core/Fe(x)O(y) hollow shell-tipped semiconductor nanorods. These structurally well-defined rods were found to exhibit magnetic functionality. The synthetic strategies described in this work expand on the range of metals that can be deposited on heterostructured semiconductor nanorods, opening up new avenues for the hierarchical buildup of structural complexity and therefore multifunctionality in nanoparticles.

Room-Temperature Synthesis of Soluble Carbon Nanotubes by the Sonication of Graphene Oxide Nanosheets

The transformation of two-dimensional graphene oxide (GO) nanosheets into carbon nanotubes was achieved by sonicating GO in 70% nitric acid. Through the use of mass spectrometry to track the evolution of molecular fragments during the acid ultrasonication, it was observed that GO can be readily decomposed into polyaromatic hydrocarbons (PAHs). The cavitation-induced condensation of these PAHs results in their molecular reconstruction to form folded carbon nanostructures. UV-emitting, water-soluble carbon nanoparticles as well as carbon nanotubes that exhibit magnetic properties were fabricated under catalyst-free conditions.

Insights into the Oxidation and Decomposition of CO on Au/α-Fe2O3 and on α-Fe2O3 by Coupled TG-FTIR

CO oxidation and decomposition behaviors over nanosized 3% Au/alpha-Fe2O3 catalyst and over the alpha-Fe2O3 support were studied in situ via thermogravimetry coupled to on-line FTIR spectroscopy (TG-FTIR), which was used to obtain temperature-programmed reduction (TPR) curves and evolved gas analysis. The catalyst was prepared by a sonication-assisted Au colloid based method and had a Au particle size in the range of 2-5 nm. Carburization studies of H 2-prereduced samples were also made in CO gas. According to gravimetry, for the 3% Au/alpha-Fe2O3 catalyst, there were three distinct stages of CO interaction with the Au catalyst but only two stages for the catalyst support. At low temperatures (<or=100 degrees C), only the Au catalyst had a rapid weight loss, which confirmed that CO reacted with highly active absorbed oxygen species and/or OH species which were associated with and promoted by the Au nanoparticles. Around 300 degrees C, both the catalyst and support samples experienced the reduction of Fe2O3 to Fe3O4, while above 400 degrees C further reduction to FeO and Fe metal took place. Au played no part in the kinetics of Fe3O4 formation because lattice O mobility was rate-limiting. At higher temperature where Fe3O4 was further reduced to FeO and Fe 0, the initially formed metallic Fe 0 nuclei could decompose CO molecules and release O species. Both this coproduced O species and the lattice oxygen could react with CO molecules. Thus, the CO oxidation was not limited by the mobility of lattice oxygen, and the catalytic function of Au was revealed again. Carburization of metallic Fe, created by prereduction in H 2, revealed a distinct weight gain at 350 degrees C corresponding to Fe 3C formation, as subsequently confirmed by X-ray diffraction (XRD). Sustained carbon deposition ensued at 450 degrees C. In the cases of the 3% Au/gamma-Al 2O 3 and Au/ZrO 2 catalysts prepared by the same method, however, after exposure to CO in the same temperature range, no carbon deposit was observed, indicating that although Au nanoparticles could activate the absorbed oxygen molecules at low temperatures, they were not able to activate the lattice oxygen in the three catalyst supports or to dissociate the CO molecules directly.

Electronic Properties of Nanodiamond Decorated Graphene

The electronic properties of graphene sheets decorated with nanodiamond (ND) particles have been investigated. The chemical fusion of ND to the graphene lattice creates pockets of local defects with robust interfacial bonding. At the ND-bonded regions, the atoms of graphene lattice follow sp(3)-like bonding, and such regions play the role of conduction bottlenecks for the percolating sp(2) graphene network. The low-temperature charge transport reveals an insulating behavior for the disordered system associated with Anderson localization for the charge carriers in graphene. A large negative magnetoresistance is observed in this insulating regime, and its origin is discussed in the context of magnetic correlations of the localized charge carriers with local magnetic domains and extrinsic metal impurities associated with the ND.

Ultrahigh Capacity Due to Multi-Electron Conversion Reaction in Reduced Graphene Oxide-Wrapped MoO2 Porous Nanobelts.

Multivalent transition metal oxides (MOx ) containing redox centers which can theoretically accept more than one electron have been suggested as promising anode materials for high-performance lithium ion batteries (LIBs). The Li-storage mechanism of these oxides is suggested to involve an unusual conversion reaction leading to the formation of metallic nanograins and Li2 O; however, a full-scale conversion reaction is seldom observed in molybdenum dioxide (MoO2 ) at room temperature due to slow kinetics. Herein, a full-scale multi-electron conversion reaction, leading to a high reversible capacity (974 mA h g(-1) charging capacity at 60 mA g(-1) ) in LIBs, is realized in a hybrid consisting of reduced graphene oxide (rGO) sheet-wrapped MoO2 porous nanobelts (rGO/MoO2 NBs). The rGO wrapping layers stabilize the nanophase transition in MoO2 and alleviate volume swing effects during lithiation/delithiation processes. This enables the hybrid to exhibit great cycle stability (tested to around 1900 cycles) and ultrafast rate capability (tested up to 50 A g(-1) ).

Aqueous-Phase Reactions on Hollow Silica-Encapsulated Semiconductor Nanoheterostructures

We introduce a facile and robust methodology for the aggregation-free aqueous-phase synthesis of hierarchically complex metal-semiconductor heterostructures. By encapsulating semiconductor nanostructures within a porous SiO(2) shell with a hollow interior, we can isolate each individual particle while allowing it access to metal precursors for subsequent metal growth. We illustrate this by Pt deposition on CdSe-seeded CdS tetrapods, which we found to be facilitated via the surprising formation of a thin interfacial layer of PtS coated onto the original CdS surface. We took advantage of this unique architecture to perform cation exchange reactions with Ag(+) and Pd(2+), thus demonstrating the feasibility of achieving such transformations in complex metal-semiconductor nanoparticle systems.