IB-1949a

APPLICATIONS:

Berkeley Lab scientists started with anisotropic, branched nanocrystals (top) and added chemical precursors to grow homogeneous shells on these complex structures (bottom), forming Type II charge-separating interfaces.

• Biological Imaging
• Photovoltaics
• Photodetectors
• Photoconductive materials
• Mechanical reinforcement

ADVANTAGES:

• Shells can be grown on complex shapes
• Expands the use of nanocrystals by combining materials with a variety of electronic, optical, and physical properties
• Charges are separated between the core and the shell, providing a conductivity pathway
• Unlike core/shell nanosphere structures, nanorods provide a clear charge direction
• Solution processable

ABSTRACT:

A. Paul Alivisatos, Steven Hughes and Delia Milliron at Berkeley Labs have developed a solution-based method for synthesizing core/shell anisotropic nanocrystal heterostructures so that positive and negative charges are separated between the shell and the core, creating a Type II staggered interface, with a pathway to transport these charges. The Berkeley Lab Type II core/shell invention has been used to fabricate shells on nanorods and tetrapods using two semiconducting materials but can also be used to create even more complex Type II structures using related systems of materials.

Because of their remarkable charge separation and conductive properties, these anisotropic core/shell structures open up new possibilities for biological imaging (quantum dots), photovoltaic devices, photodetectors, photoconductive materials, as well as other electronic and optical devices.

IB-1949b

	TRANSMISSION ELECTRON MICROSCOPE IMAGES OF CONTROLLED BRANCHING IN HETEROSTRUCTURES
	Click on this image for a larger view

APPLICATIONS OF TECHNOLOGY:

• Biological Imaging
• Photovoltaics
• LEDs
• Transistors
• Diodes
• Optical color conversion
• Oriented or ordered nanocrystals
• Memory devices
• Quantum information processing
• Artificial photosynthesis
• Mechanical reinforcement
• Catalysis

ADVANTAGES:

• Enables fabrication of complex nanocrystal geometries
• Each component of the nanocrystal can be independently tuned by varying composition, length, diameter, and crystal phase
• Increases possible points of contact between a nanocrystal and a substrate
• Increases possible number of connections to electrical leads

ABSTRACT:

Berkeley Lab researchers have demonstrated a general approach for fabricating inorganically coupled quantum rods and dots by connecting them epitaxially at branched and linear junctions within single colloidal nanocrystals. The researchers have created branched semiconducting nanorods, nanotetrapods, and other complex geometries where the branching location, branch lengths, and diameters can be controlled and the composition of each rod section may vary. Using the Berkeley Lab method, branching points can be introduced not only at nucleation but also later in the growth process.

The inorganic materials that can be used in this technique have optical, mechanical, electrical, magnetic, catalytic, and other functional properties that can now be controllably combined in a single geometrically complex nanocrystal. This capability invites investigation into new fields such as quantum information processing and artificial photosynthesis and promises improvements to solar cells, LEDs, transistors, and biological imaging (quantum dots).

STATUS:

• Issued Patent # 7,303,628. Available for licensing or collaborative research.

REFERENCE NUMBER: IB-1949

SEE THESE OTHER BERKELEY LAB TECHNOLOGIES IN THIS FIELD:

• Controlled Assembly of Nanocrystal/Organic Composites IB-1941
• Fabrication of Highly Luminescent Graded Core/Shell Nanocrystals and Simple Heterostructures IB-1830