Publications

2019
Franco VA Camargo, Tetsuhiko Nagahara, Yuval Ben-Shahar, Mattia Russo, Uri Banin, and Giulio Cerullo. 2019. “Exciton relaxation pathways in CdSe nanorods revealed by two-dimensional electronic spectroscopy”. Publisher's Version Abstract

"Colloidal semiconductor quantum dots (QDs) are promising for solar energy harvesting, particularly the excess energy of hot and/or high energy excitons before they relax, which would allow efficiencies beyond the Shockley-Queisser limit.IEEE2019 Going beyond QDs, nanostructured materials such as nanorods (NRs) are attracting significant attention, as their geometrical differences with QDs imply different electronic properties, and their one-dimensional character makes them ideal building blocks for hybrid nanostructures [1,2]. Experimental observation of the charge relaxation pathways in such nanostructured systems is challenging, as high resolution in time (to resolve ultrafast processes) and in excitation energy (to distinguish the relaxation pathways of different excitons) are simultaneously required, which are incompatible with regular transient absorption (TA). Both requirements are met by two-dimensional electronic spectroscopy (2DES), which can be thought as an extension of TA employing two phase-locked pump pulses. Acquiring the data as a function of the delay t 1 between them and using Fourier transform spectroscopy yields a correlation map between signal excitation and signal emission energies for each waiting time t 2 [3]. As it provides resolution in the excitation energy, 2DES is ideal to study systems with spectrally congested electronic transitions and was applied to study many nanostructured systems."

2017
Yuval Ben-Shahar, Ilka Kriegel, Francesco Scotognella, Nir Waiskopf, Stefano Dal Conte, Luca Moretti, Giulio Cerullo, Eran Rabani, and Uri Banin. 2017. “Ultrafast carrier dynamics unravel role of surface ligands and metal domain size on the photocatalytic hydrogen evolution efficiency of Au-tipped CdS nanorods: an ultrafast transient absorption spectroscopy study”. Publisher's Version Abstract

Semiconductor-metal hybrid nanostructures are interesting materials for photocatalysis. Their tunable properties offer a highly controllable platform to design light-induced charge separation, a key to their function in photocatalytic water splitting. Hydrogen evolution quantum yields are influenced by factors as size, shape, material and morphology of the system, additionally the surface coating or the metal domain size play a dominant role.

 

In this paper we present a study on a well-defined model system of Au-tipped CdS nanorods. We use transient absorption spectroscopy to get insights into the charge carrier dynamics after photoexcitation of the bandgap of CdS nanorods. The study of charge transfer processes combined with the hydrogen evolution efficiency unravels the effects of surface coating and the gold tip size on the photocatalytic efficiency. Differences in efficiency with various surface ligands are primarily ascribed to the effects of surface passivation. Surface trapping of charge carriers is competing with effective charge separation, a prerequisite for photocatalysis, leading to the observed lower hydrogen production quantum yields. Interestingly, non-monotonic hydrogen evolution efficiency with size of the gold tip is observed, resulting in an optimal metal domain size for the most efficient photocatalysis. These results are explained by the sizedependent interplay of the metal domain charging and the relative band-alignments. Taken together our findings are of major importance for the potential application of hybrid nanoparticles as photocatalysts.

2005
Dan T Fuchs, Ronen Rapaport, Gang Chen, Ylva K Olsson, Vikram C Sundar, L Lucas, S Vilan, Assaf Aharoni, Uri Banin, and Jonathan S Steckel. 2005. “Making waveguides containing nanocrystalline quantum dots”. Publisher's Version Abstract

A new material platform is described that enables inclusion of nanocrystalline quantum dots into a polymer. This technology is compatible with semiconductor processing and may enable integration of active materials into current waveguide technologies. We describe the steps preformed to fabricate a waveguide chip that contains IR-emitting quantum dots. Optical tests demonstrate guiding and preservation of the quantum dots optical properties through the processing steps. Time resolved optical measurements indicate presence of gain in the InAs quantum dot impregnated polymer.