August 2009

Researchers in the University of Washington say that they have been able to train tiny semiconductor crystals, called nanocrystals or quantum dots, to display new magnetic functions at room temperature using light as a trigger.

Silicon-based semiconductor chips incorporate tiny transistors that manipulate electrons based on their charges. Scientists also are working on ways to use electricity to manipulate the electrons' magnetism, referred to as "spin," but are still searching for the breakthrough that will allow "spintronics" to function at room temperature without losing large amounts of the capability they have at frigid temperatures.

The team led by Daniel Gamelin, a UW chemistry professor, has found a way to use photons – tiny light particles – to manipulate the magnetism of semiconductor nanocrystals efficiently, even up to room temperature.

The team used nanocrystals of a cadmium-selenium semiconductor called cadmium selenide, but replaced some nonmagnetic cadmium ions with magnetic manganese ions. The crystals, smaller than 10 nanometers across (a nanometer is one-billionth of a meter), were then suspended in a colloid solution, like droplets of cream suspended in milk.

Beams of photons were used to align all of the manganese ions' spins, creating magnetic fields as much as 500 times more powerful than in the same semiconductor material without manganese. The magnetic effects were strongest at low temperatures, but remained remarkably strong up to room temperature, Gamelin said.

In a second paper published Sunday (Aug. 16) in the online edition of Nature Nanotechnology, Gamelin's group reported related effects in semiconductor nanocrystals made of zinc oxide but also containing small amounts of manganese impurities.

QuantumWise A/S is announcing a new release of its software package for atomic-scale simulations of nanoscale electronic and spintronic devices, Atomistix ToolKit (ATK). This code is able to compute electronic structure and transport properties (e.g. I-V characteristics) of nanoscale structures such as nanotubes, graphene, molecular electronics devices, magnetic tunnel junctions and other magnetic system, interface structures, nanowires, etc.

Based on semi-empirical methods, the newly released package extends the company's modeling platform, which already comprises a density-functional theory (DFT) method, to allow faster simulations of larger structures (>1,000 atoms). The new model also offers a better description of semiconducting materials.

Moreover, a new electrostatic model is introduced, which supports inclusion of an arbitrary configuration of dielectric and metallic regions. These gates are described fully self-consistently electrostatically, and this allows for a realistic multi-scale simulation of nanoscale transistor structures.

The QuantumWise platform is based on an open architecture which integrates a Python-based scripting language, NanoLanguage, with a graphical user interface, Virtual NanoLab. The new release extends this platform by including support also for GPAW, an external grid-based DFT code specifically designed for applications within catalysis and surface science.