1 September 2012
Reflect on this: a gentle push is all it takes to turn the blackest material in the world into a shiny mirror. What’s more, combining the two extremes in one substance could open up applications in optical sensors and bendy electronics.
The dark material is a “forest” of vertical carbon nanotubes that absorb more than 99 per cent of incoming light. Kenichi Takahata, Alireza Nojeh and their and colleagues at the University of British Columbia in Vancouver, Canada, discovered they could make the nanotubes reflective by bending a few “trees”.
Slowly pulling a vertical tungsten rod through the deep dark forest turned the plowed regions into a smooth, polished surface, capable of reflecting 10 to 15 per cent of visible and infrared light (Applied Physics Letters, doi.org/h64). While not a high shine compared to normal mirrors, it does create useful contrast when reflective patterns are etched into the forest.
Walter Lubeigt, a physicist at the University of Strathclyde in Glasgow, UK, says it is impressive that the team increased the forest’s reflectivity by a factor of 100. But the polished surfaces cannot match existing micro-mirrors, which can be up to 99.9 per cent reflective.
Takahata points out that the reflective nanotubes are bendable, unlike other micro-mirrors, so they might find a use in flexible electronics or in computer memories based on optics. Patches of bent tubes could represent 1s and erect ones 0s, say, and light would be used to read out the data.