Bimetallic nanostructures (NSs), with utility in catalysis, are typically prepared using galvanic exchange (GE), but the final catalyst morphology is dictated by the dynamics of the process. In situ single nanoparticle (NP) optical scattering spectroscopy, coupled with ex situ electron microscopy, is used to capture the dynamic structural evolution of a bimetallic NS formed in a GE reaction between Ag and [PtCl₆]²⁻. We identify an early stage involving anisotropic oxidation of Ag to AgCl concomitant with reductive deposition of small Pt clusters on the NS surface. At later stages of GE, unreacted Ag inclusions phase segregate from the overcoated AgCl as a result of lattice strain between Ag and AgCl. The nature of the structural evolution elucidates why multi-domain Ag/AgCl/Pt NSs result from the GE process. The complex structural dynamics, determined from single-NP trajectories, would be masked in ensemble studies due to heterogeneity in the response of different NPs.

Bimetallic nanostructures (NSs), with utility in catalysis, are typically prepared using galvanic exchange (GE), but the final catalyst morphology is dictated by the dynamics of the process. In situ single nanoparticle (NP) optical scattering spectroscopy, coupled with ex situ electron microscopy, is used to capture the dynamic structural evolution of a bimetallic NS formed in a GE reaction between Ag and [PtCl₆]²⁻. We identify an early stage involving anisotropic oxidation of Ag to AgCl concomitant with reductive deposition of small Pt clusters on the NS surface. At later stages of GE, unreacted Ag inclusions phase segregate from the overcoated AgCl as a result of lattice strain between Ag and AgCl. The nature of the structural evolution elucidates why multi-domain Ag/AgCl/Pt NSs result from the GE process. The complex structural dynamics, determined from single-NP trajectories, would be masked in ensemble studies due to heterogeneity in the response of different NPs.

Although inert in its bulk form, nanostructured gold supported on oxides has been found to be catalytically active. In many cases, the oxide promotes the activity of Au. It is now shown that in turn, nanoscale Au particles can chemically activate the solid oxide. Specifically, it was discovered that 4 nm Au nanoparticles deposited on zinc oxide catalyze the transformation of the oxide into the sulfide in the presence of an organosulfur species. Contact of the oxide with Au nanoparticles lowers the activation barrier for the solid-state reaction by approximately 20 kJ mol⁻¹, allowing the reaction to be achieved closer to ambient temperatures. Electron transfer from oxygen vacancies to Au nanoparticles is proposed to generate acidic sites on the surface of the zinc oxide, resulting in the enhanced reactivity of the oxide. Knowledge of such electronic interactions between the noble metal and oxide can be exploited for engineering reactive heterostructures for low-temperature pollutant sorption and hydrocarbon processing.

Although inert in its bulk form, nanostructured gold supported on oxides has been found to be catalytically active. In many cases, the oxide promotes the activity of Au. It is now shown that in turn, nanoscale Au particles can chemically activate the solid oxide. Specifically, it was discovered that 4 nm Au nanoparticles deposited on zinc oxide catalyze the transformation of the oxide into the sulfide in the presence of an organosulfur species. Contact of the oxide with Au nanoparticles lowers the activation barrier for the solid-state reaction by approximately 20 kJ mol⁻¹, allowing the reaction to be achieved closer to ambient temperatures. Electron transfer from oxygen vacancies to Au nanoparticles is proposed to generate acidic sites on the surface of the zinc oxide, resulting in the enhanced reactivity of the oxide. Knowledge of such electronic interactions between the noble metal and oxide can be exploited for engineering reactive heterostructures for low-temperature pollutant sorption and hydrocarbon processing.

The realization of common materials transformations in nanocrystalline systems is fostering the development of novel nanostructures and allowing a deep look into the atomistic mechanisms involved. Galvanic corrosion is one such transformation. We studied galvanic replacement within individual metal nanoparticles by using a combination of plasmonic spectroscopy and scanning transmission electron microscopy. Single-nanoparticle reaction trajectories showed that a Ag nanoparticle exposed to Au³⁺ makes an abrupt transition into a nanocage structure. The transition is limited by a critical structural event, which we identified by electron microscopy to comprise the formation of a nanosized void. Trajectories also revealed a surprisingly strong nonlinearity of the reaction kinetics, which we explain by a model involving the critical coalescence of vacancies into a growing void. The critical void size for galvanic exchange to spontaneously proceed was found to be 20 atomic vacancies.

The realization of common materials transformations in nanocrystalline systems is fostering the development of novel nanostructures and allowing a deep look into the atomistic mechanisms involved. Galvanic corrosion is one such transformation. We studied galvanic replacement within individual metal nanoparticles by using a combination of plasmonic spectroscopy and scanning transmission electron microscopy. Single-nanoparticle reaction trajectories showed that a Ag nanoparticle exposed to Au³⁺ makes an abrupt transition into a nanocage structure. The transition is limited by a critical structural event, which we identified by electron microscopy to comprise the formation of a nanosized void. Trajectories also revealed a surprisingly strong nonlinearity of the reaction kinetics, which we explain by a model involving the critical coalescence of vacancies into a growing void. The critical void size for galvanic exchange to spontaneously proceed was found to be 20 atomic vacancies.

We review the discovery of localized surface plasmon resonances (LSPRs) in doped semiconductor quantum dots (QDs), an advance that has extended nanoplasmonics to materials beyond the classic gamut of noble metals. The initial demonstrations of near-infrared LSPRs in QDs of heavily self-doped copper chalcogenides and conducting metal oxides are setting the broad stage for this new field. We describe the key properties of QD LSPRs. Although the essential physics of plasmon resonances are similar to that in metal nanoparticles, the attributes of QD LSPRs represent a paradigm shift from metal nanoplasmonics. Carrier doping of quantum dots allows access to tunable LSPRs in the wide frequency range from the THz to the near-infrared. Such composition or carrier density tunability is unique to semiconductor quantum dots and not achievable in metal nanoparticles. Most strikingly, semiconductor quantum dots allow plasmon resonances to be dynamically tuned or switched by active control of carriers. Semiconducting quantum dots thus represent the ideal building blocks for active plasmonics. A number of potential applications are discussed, including the use of plasmonic quantum dots as ultrasmall labels for biomedicine and electrochromic materials, the utility of LSPRs for probing nanoscale charge dynamics in semiconductors, and the exploitation of strong coupling between photons and excitons. Further advances in this field necessitate efforts toward generalizing plasmonic phenomena to a wider range of semiconductors, developing strategies for achieving controlled levels of doping and stabilizing them, investigating the spectroscopy of these systems on a fundamental level, and exploring their integration into optoelectronic devices.