Ultrafast Carrier Dynamics in Nanostructured Materials: From Charge Transfer to Lasing Action
Nanostructured materials have emerged as new building blocks for future innovative devices. The size-tunable properties exhibited across a wide variety of nanostructures, ranging from quantum confinement to optical confinement, can have a direct impact on how efficiently energy is transferred, stored, and utilized. Two distinct types of nanostructured materials in different size regimes are described in this dissertation: Pt-tipped CdSe/CdS nanorods and ZnO tetrapods.
Charge separation dynamics are investigated in Pt-tipped and non-tipped CdSe (quantum dot)/CdS nanorods by ultrafast white light transient absorption spectroscopy. Charge transfer is observed from the CdS and CdSe regions, with evidence for electron transfer to the Pt tip occurring over both sub-ps and sub-100 ps timescales. By exciting the CdSe quantum dot directly at 550 nm and probing the quantum dot directly at 580 nm, electron transfer to the Pt tip is monitored from a local region of the nanorod that is separated from the CdS-Pt interface.
To investigate the lasing action in nanostructured cavities in detail, single ZnO tetrapod structures are isolated with a home-built confocal microscope and excited with a sub-ps UV pump pulse (267 nm). The lasing thresholds are observed to be in the range of ~50- 200 J/cm2. To characterize the Fabry-Pérot-type cavities further, micro-Raman studies are performed and rate equations for microcavity lasers are numerically solved to investigate the near-threshold lasing dynamics.