Hadar, I. ; Abir, T. ; Halivni, S. ; Faust, A. ; Banin, U. .
Size Dependent Ligand Layer Dynamics In Semiconductor Nanocrystals Probed By Anisotropy Measurements.
ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 2016,
251.
AbstractColloidal semiconductor nanocrystals (NCs) are promising building blocks for various applications. This is mainly due to the ability to modify their physical and chemical properties by controlling the particles size and shape in the nanometer scale. The inorganic NCs surface is usually covered by an organic ligands shell, which has a crucial role in controlling the size and shape of the NCs during the colloidal synthesis. The properties of the ligand shell also determine the NCs dispersibility in various solvents and matrices and their physical and chemical properties. Although the importance of the ligand shell its exact properties and specifically the effect of the NC size and shape are still not well understood. This is mainly due to the lack of experimental tools that will enable to study the ligand shell in situ. In our research we have uniquely studied the physical properties of the ligand shell on the surface of spherical quantum-dots (QDs), of various sizes. We have utilized dye molecules that are embedded within the organic ligand layer and adopt its properties to optically study the effective viscosity of the ligand shell. Tracing the reorientation times of the dye molecules we were able to calculate the effective viscosity of the shell. We have found that as the size of the QD decreases (and hence the curvature increases), the effective viscosity of the shell is decreasing. Modifying the physical properties of the ligand shell by changing the shape of the surface is a unique property of NCs. Further investigation of the ligand shell will allow rational design of the surface to achieve desired properties, providing an additional important knob for tuning their functionality.
Hadar, I. ; Halivni, S. ; Even-Dar, N. 'ama; Faust, A. ; Banin, U. .
Dimensionality Effects At The Single Nanocrystal Level: Fret Between Semiconductor Nanorods And Multiple Dye Acceptors.
ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 2016,
251.
AbstractColloidal semiconductor nanocrystals are outstanding donors in energy transfer processes due to their unique size and shape dependent optical properties, their exceptional photostability, and chemical processability. In this research we have performed a study of the dimensionality effect in energy transfer between single heterostructure nanocrystals of spherical and rod shape, serving as donors, and multiple organic dye molecules attached to their surface acting as acceptors. Förster resonant energy transfer (FRET) to individual dye molecules attached to a single nanocrystal is identified via step like changes in both acceptor and donor emission, enabling to calculate the efficiency of energy transfer and distance of each acceptor individually. The ability to trace single molecules attached to the surface of a nanocrystal as well as single binding events offers a unique tool to study the surface chemistry of various nanocrystals. Statistical analysis of many single particles allows extracting the geometrical distribution of acceptor dyes on the nanocrystal surface, reflecting its dimensionality. Moreover, the inner geometry of these heterostructures, such as the location of the seed and shell thickness can be studied by analysis of the obtained distance distribution. Additionally, due to their high extinction coefficient, the nanocrystals serve as an optical antenna that enhances the excitation and emission of the dye molecules through the FRET interaction. These measurements enable to gain deeper understanding of the energy transfer process between semiconductor nanocrystals of various geometries and acceptor dye molecules, and promote its utilization for extremely sensitive sensing applications at the single molecule level.
