Defect free nanocrystal films could enable better led displays, solar cells and biosensors

Nanocrystals could be used in electronic or photonic circuits, detectors for biomolecules, or the glowing pixels on high resolution display screens. However, it's difficult to control their placement on a surface and typical nanocrystal films have cracks that limit their usefulness. "We've been trying to understand how electrons move in arrays of these nanocrystals," commented Marc Kastner, dean of MIT's school of science. This has been difficult with limited control over the formation of the arrays. First, the team built on previous research and produced nanoscale patterns that emit invisible infrared light. Then they succeeded in getting the patterns to glow with visible light, making them visible through an optical microscope and meaning they could greatly speed the development of the new technology. "Even though the nanoscale patterns are below the resolution limit of the optical microscope, the nanocrystals act as a light source, rendering them visible," commented MIT postdoc Tamar Mentzel. The researchers say that the electrical conductivity of their defect free films is roughly 180 times greater than that of the cracked films made by conventional methods. The process also makes it possible to create patterns on a silicon surface that are just 30nm across. According to the researchers, the process is unique in producing such tiny patterns of defect free films. They said the trick was to get the film to be uniform and to stick to the silicon dioxide substrate. This was achieved by leaving a thin layer of polymer to coat the surface before depositing the layer of nanocrystals on top of it. The researchers suggest that tiny organic molecules on the surface of the nanocrystals may help them bind to the polymer layer. Because these nanocrystals can be tuned both to emit and absorb a wide spectrum of colours of light, they could also enable a new kind of broad spectrum solar cell.