Research Interests

Nanoscience and Nanotechnology: Basic Science and Applications of Nanoparticles
Semiconductor nanocrystals are molecular-like semiconductor materials composed of hundreds to thousands of atoms, intermediate between a solid and a molecule. In this regime fundamental properties depend on size, composition and shape. Due to the tunable properties of such nanostructures, they show great potential for use as building blocks of devices in nanotechnology. I am interested in preparation, characterization, in the optical and electronic properties of nanocrystals and in developing new applications based on their unique properties. Special attention is devoted to nanostructures of technologically relevant II-VI and III-V semiconductors spanning the range from properties of single nanocrstructures to collective effects in their assemblies. In recent years we focus on development of hybrid nanoparticles, composed of disparate elements such as metal-semiconductor hybrid nanoparticles. Such systems manifest a unique model for the semicoductor-metal interface on the nanoscale. The combination of such diverse materials on one nanoparticle, increases the functionality of the system. For example, metal tips on semiconductor nanorods offer anchor points for self assembly and electrical connections. The high level of control of nanoparticle synthesis and deep understanding of the physico-chemical properties achieved in recent years opened avenues for application of such nanoparticles in solar energy harvesting, which is also of central interest for us.

CdS1. Synthesis and characterization of novel semiconductor nanocrystals and nanostructures and their assemblies:
Developing the bottom-up approach for preparing semiconductor nanocrystals and nanostructures with tailored properties.
Development of multi-component hybrid nanocrystals such as gold-tipped nanorods ('nano-dumbbells').
Synthesis of new semiconductor nanocrystals and nanorods with special focus on III-V semiconductors.
Growth of heterostructured nanorods and and nanocrystals including core/shell nanocrystals and seeded nanorods exhibiting high emission quantum yield.
Studies of self assembly of nanocrystals.

 

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2. Size dependent optical and electronic properties of nanocrystals:
Evolution of the electronic, optical and electrical properties with size from the molecular regime to the solid state.
Study of the size dependent level structure using optical spectroscopy, tunneling spectroscopy and transport spectroscopy.
Development of new methods combining optical and tunneling spectroscopy to investigate semiconductor nanocrystals. 
Single electron tunneling phenomena in nanocrystals and nanorods.
Time dependent electronic spectroscopy of semiconductor nanocrystals.

 

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3. Single nanostructure microscopy and spectroscopy:
Scanning probe microscopy including optical microscopy and atomic force microscopy and their application to study of semiconductor nanocrystals and nanorods.
Developing novel scanning probe methods combining optical and force microscopy to study single nanocrystals.
Apertureless near field spectroscopy and microscopy of nanostructures.

 

Photochemistry

4. Alternative energy solutions using nanoparticles:
Development of solar cells and other applications incorporating nanoparticles to harvest light and transform it to useful work and energy forms such as electrical and chemical energy. Photocatalysis with hybrid nanoparticle systems.

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5. Lasers and optical devices based on colloidal semiconductor nanostructures:
Investigation of optical gain properties of semiconductor nanocrystals and nanorods.  Development and study of microcavity lasers with semiconductor nanocrystals and nanorods. 
Light emitting diodes with nanocrystals and nanorods, in particular in the near IR spectral range.


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6.  Biological, medical and sensing applications of nanocrystals:
Use of nanocrystals as fluorescence labels in biology and medicine. Development of sensors for biomolecular processes using nanoparticles.
Use of bio-chemistry for nanocrystal assembly.

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7. Non linear optical properties of semiconductor nanocrystals and nanorods:
Size, shape and composition dependence of second order non-linear optical properties and second harmonic generation in semiconductor nanocrystals and nanorods.
Surface effects and surface processes in nanocrystals and nanostructures studied using second harmonic generation.



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8. Electrical Transport studies on single nanorods and nanocrystal arrays:
Wiring of single nanorods into electrical circuits by high resolution lithography. Studies of current voltage characteristics and transport mechanisms in single nanorods Metal tips as contact points for electrical wiring. Transport in nanocrystal arrays.