ERA NANOSCI: Properties and optical response of single hybrid semiconductor-metal nanoparticles
Zusammenfassung der Projektergebnisse
Noble metal nanoparticles exhibit exotic optical properties due to the excitation of the plasmon resonance. This effect is a direct result of the nanoscale dimensions. Taking advantage of the unique optical characteristics of metal nanoparticles - strong plasmon absorption, resonant light scattering and enhanced localized electromagnetic fields - many applications have emerged using nanoparticles as an optical label or as a sensitive nanosensor. Semiconductor nanoparticles also exhibit size dependent electronic properties which result in the ability to tune the band gap energy by altering the size of the nanoparticle. Such control over the band gap energy has strong advantages for various applications with specific or broad requirements. The latter can be simply achieved using a distribution of semiconductor nanoparticles of single composition with a range of sizes. Metal-semiconductor hybrids often exhibit markedly different properties than the individual components, thereby providing a powerful strategy for altering the properties of nanoparticles. For example, previous studies of semiconductor nanocrystals coupled to metals have exemplified the existence of a plasmonic "antenna effect", leading to amplified excitation or increased radiative decay rate of excitons in the semiconductor. Coherent and incoherent interactions between the metal and the semiconductor may lead to broadening and shifting of the excitonic resonance and strong nonlinear effects. Other studies have shown that charges generated by the optical excitation of the semiconductor domain can be transferred efficiently to the metal part, shifting the plasmon frequency and/or promoting redox reactions. The gold tips grown on semiconductor nanorods can also serve as anchoring points for self-assembly to create elaborate superstructures. Moreover, the gold tips can serve as efficient contact points to external electrical circuits. Due to the high sensitivity of the resulting optical properties on the structural properties for metal and semiconductor nanoparticles all applications for the use of metal-semiconductor nanoparticles rely on a reproducible, high-yield synthesis. We have demonstrated that by using a photochemical approach it is possible to increase the size of the metallic domain to ≈15 nm in diameter. This also improves the plasmonic properties with respect to the original metal tips, diameter ≈2 nm, as metal particles of this size experience strong damping of the plasmon resonance. Single particle experiments are the core of our research. By utilizing our ability to increase the plasmonic domain of the hybrid nanoparticles we are now able to overcome the previous size limitation to study single nanoparticles with darkfield spectroscopy. We have developed several experimental systems allowing us measuring several tens of particles at the time. Together with such an experimental approach, we acquire a strong expertise in numerical simulations. This allows us better understanding the hybrid properties of single particles as well as optimizing experimental conditions. An important step prior to many applications of nanoparticles is the ability to functionalize them. Utilizing gold as the metallic domain for the hybrid nanoparticle allows the opportunity to take advantage of numerous procedures for controlling the surface properties. This ability can be used to prevent access to the surface of the nanoparticles, important for biological applications, or the binding of functional groups for further manipulation of their physical and chemical properties. Throughout the course of our research with metal-semiconductor hybrid nanoparticles we have demonstrated a fine control over the geometry and spatial distribution of each component and investigated the origins of the properties exhibited by these systems.
Projektbezogene Publikationen (Auswahl)
- 'Growth of gold tips onto hyper-branched CdTe nanostructures'. Adv. Mater 2008, 20, 588
Y. Khalavka, C. Sönnichsen
- 'Light-controlled one-sided growth of large plasmonic gold domains on quantum rods observed on the single particle level'. Nano Lett. 2009, 9, 3710
L. Carbone, A. Jakab, Y. Khalavka, C. Sönnichsen
- 'Light-controlled one-sided growth of large plasmonic gold domains on quantum rods observed on the single particle level'. Proc. of SPIE, 2010, 7575, 757505
L. Carbone, A. Jakab, Y. Khalavka, C. Sönnichsen
- 'Absorption properties of metal-semiconductor hybrid nanoparticles'. ACS Nano, 2011, 5, 4712
E. Shaviv, O. Schubert, M. Alves-Santos, G. Goldoni, R. Di-Felice, F. Vallee, N. Del-Fatti, U. Banin, C. Sönnichsen
