Researchers demonstrate quantum dots that assemble themselves

Feb 11, 2013

(—Scientists from the U.S. Department of Energy's National Renewable Energy Laboratory and other labs have demonstrated a process whereby quantum dots can self-assemble at optimal locations in nanowires, a breakthrough that could improve solar cells, quantum computing, and lighting devices.

A paper on the new technology, "Self-assembled Quantum Dots in a Nanowire System for ," appears in the current issue of the scientific journal Nature Materials.

Quantum dots are tiny crystals of semiconductor a few billionths of a meter in diameter.  At that size they exhibit beneficial behaviors of such as forming electron-hole pairs and harvesting excess energy.

The scientists demonstrated how quantum dots can self-assemble at the apex of the /aluminum gallium arsenide core/shell nanowire interface. Crucially, the quantum dots, besides being highly stable, can be positioned precisely relative to the nanowire's center. That precision, combined with the materials' ability to provide for both the electrons and the holes, makes the approach a potential game-changer.

Electrons and holes typically locate in the lowest energy position within the confines of high-energy materials in the nanostructures. But in the new demonstration, the electron and hole, overlapping in a near-ideal way, are confined in the quantum dot itself at high energy rather than located at the lowest energy states. In this case, that's the gallium-arsenide core. It's like hitting the bulls-eye rather than the periphery.

The quantum dots, as a result, are very bright, spectrally narrow and highly anti-bunched, displaying excellent optical properties even when they are located just a few nanometers from the surface – a feature that even surprised the scientists.

"Some Swiss scientists announced that they had achieved this, but scientists at the conference had a hard time believing it," said NREL senior scientist Jun-Wei Luo, one of the co-authors of the study. Luo got to work constructing a quantum-dot-in-nanowire system using NREL's supercomputer and was able to demonstrate that despite the fact that the overall band edges are formed by the gallium Arsenide core, the thin aluminum-rich barriers provide quantum confinement both for the electrons and the holes inside the aluminum-poor quantum dot. That explains the origin of the highly unusual optical transitions.

Several practical applications are possible. The fact that stable quantum dots can be placed very close to the surface of the nanometers raises a huge potential for their use in detecting local electric and magnetic fields. The also could be used to charge converters for better light-harvesting, as in the case of photovoltaic cells.

Explore further: Team reveals molecular structure of water at gold electrodes

More information:… t/full/nmat3557.html

Related Stories

Encouraging quantum dots to emit photons

Aug 05, 2010

( -- One of the fields of great interest to scientists and researchers is that of using the quantum world to enhance various aspects of our lives. Advances in quantum cryptography make headlines, and scientists ...

Single quantum dot nanowire photodetectors

Dec 14, 2010

Moving a step closer toward quantum computing, a research team in the Netherlands recently fabricated a photodetector based on a single nanowire, in which the active element is a single quantum dot with a ...

Short-range scattering in quantum dots

Oct 20, 2010

Chinese researchers, reporting in the Journal of Applied Physics, published by the American Institute of Physics, have described a new breakthrough in understanding the way electrons travel around quantum dots. This might ...

Recommended for you

Quantum effects in nanometer-scale metallic structures

Oct 22, 2014

Plasmonic devices combine the 'super speed' of optics with the 'super small' of microelectronics. These devices exhibit quantum effects and show promise as possible ultrafast circuit elements, but current ...

User comments : 0