Enhanced thermal stability of monodispersed silver cluster arrays assembled on block copolymer scaffolds

Oxidation behavior and atomic structural transition of size-selected coalescence-resistant tantalum nanoclusters

Herein a series of size-selected TaN(N = 147, 309, 561, 923, 1415, 2057, 6525, 10 000, 20 000) clusters are generated using a gas-phase condensation cluster beam source equipped with a lateral time-of-flight mass-selector. Aberration-corrected scanning transmission electron microscopy (AC-STEM) imaging reveals good thermal stability of TaNclusters in this study. The oxidation-induced amorphization is observed from AC-STEM imaging and further demonstrated through x-ray photoelectron spectroscopy and energy-dispersive spectroscopy. The oxidized Ta predominantly exists in the +5 oxidation state and the maximum spontaneous oxidation depth of the Ta cluster is observed to be 5 nm under prolonged atmosphere exposure. Furthermore, the size-dependent sintering and crystallization processes of oxidized TaNclusters are observed with anin situheating technique, and eventually, ordered structures are restored. As the temperature reaches 1300 °C, a fraction of oxidized Ta309clusters exhibit decahedral and icosahedral structures. However, the five-fold symmetry structures are absent in larger clusters, instead, these clusters exhibit ordered structures resembling those of the crystalline Ta2O5films. Notably, the sintering and crystallization process occurs at temperatures significantly lower than the melting point of Ta and Ta2O5, and the ordered structures resulting from annealing remain well-preserved after six months of exposure to ambient conditions.

Gas phase fabrication of morphology-controlled ITO nanoparticles and their assembled conductive films

ITO nanoparticles were generated in the gas phase with a magnetron plasma gas aggregation cluster source. Their morphologies were modified by modulating the discharging power of magnetron sputtering. The shape of the nanoparticles changed from rough spheroid formed with a higher discharging power to multi-branch formed with a lower discharging power. With a discharging power of 25 W, the ITO nanoparticles were enriched with tripod and tetrapod-shaped nanoparticles. The formation mechanism of multi-branch nanoparticles was attributed to the oriented attachment of the initially nucleated smaller nanocrystallites. Transparent conductive ITO nanoparticle films were fabricated by depositing the preformed nanoparticles with controlled thickness. The electron conduction in the film was dominated by electron tunnelling and/or hopping in the percolative channels comprised of closely spaced ITO nanoparticle assemblies and could be tuned from highly resistive nonmetal-like to highly conductive metal-like by changing the deposition thickness. The film also displayed a SPR band in the near-IR region. The conductivity of the multi-branch ITO nanoparticle film was significantly superior to that of the spheroidal nanoparticle film. For a 46 nm thick multi-branch ITO nanoparticle film, a surprisingly low specific resistance of 3.09 × 10^-4 Ω cm, which is comparable to the top-class conductivity of bulk ITO films, was obtained after annealing at a mild temperature of 250 °C, with a transmittance larger than 85%.

Released plasmonic electric field of ultrathin tetrahedral-amorphous-carbon films coated Ag nanoparticles for SERS

We have demonstrated the plasmonic characteristics of an ultrathin tetrahedral amorphous carbon (ta-C) film coated with Ag nanoparticles. The simulation result shows that, under resonant and non-resonant excitations, the strongest plasmonic electric field of 1 nm ta-C coated Ag nanoparticle is not trapped within the ta-C layer but is released to its outside surface, while leaving the weaker electric field inside ta-C layer. Moreover, this outside plasmonic field shows higher intensity than that of uncoated Ag nanoparticle, which is closely dependent on the excitation wavelength and size of Ag particles. These observations are supported by the SERS measurements. We expect that the ability for ultrathin ta-C coated Ag nanoparticles as the SERS substrates to detect low concentrations of target biomolecules opens the door to the applications where it can be used as a detection tool for integrated, on-chip devices.

Synthesis and mechanistic study of stable water-soluble noble metal nanostructures

Sodium salt of poly(4-styrenesulfonic acid-co-maleic acid) (PSSMA) has been employed to prepare a series of stable nanosized metal colloids such as silver, gold, palladium, platinum, and silver-gold alloy nanostructures. All of the as-synthesized products are very stable in water. The metal nanostructures have been directly confirmed by ultraviolet-visible spectroscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected area electron diffraction (SAED), and also characterized by techniques such as Fourier transform infrared spectroscopy (FT-IR) and (1)H NMR. Intensive study has found that the metal ions are most probably reduced by organic radicals, generated from the thermal degradation of PSSMA.