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(PhysOrg.com) -- Most of the invisibility cloaks that have been demonstrated to date conceal objects at frequencies that are not detectable by the human eye. Designing invisibility cloaks that can conceal objects from visible light has been more challenging due to the strict material requirements. But in a new study, researchers have fabricated a carpet cloak that can make objects undetectable in the full visible spectrum.

A simple technique for stamping patterns invisible to the human eye onto a special class of nanomaterials has been developed by researchers at Vanderbilt University. The new method works with porous nanomaterials that are riddled with tiny voids, which give them unique optical, electrical, chemical, and mechanical properties. There are nanoporous forms of gold, silicon, alumina, and titanium oxide, among others. The technique involves the creation of pre-mastered stamps using traditional, but complex, clean room processes and then using the stamps to create patterns using a new process called direct imprinting of porous substrates (DIPS). DIPS can create a device in less than a minute, regardless of its complexity. The smallest pattern the researchers have made to date has features of only a few tens of nanometers (about the size of a single fatty acid molecule). They have also succeeded in imprinting the smallest pattern yet reported in nanoporous gold, one with 70-nanometer features. The first device the group has created is a "diffraction-based" biosensor that can be configured to identify a variety of different organic molecules, including DNA, proteins and viruses. The researchers envision a wide range of applications including drug delivery, chemical and biological sensors, solar cells, and battery electrodes.

Physicists have created a "hole in time" using the temporal equivalent of an invisibility cloak.

In a paper published in Nature Photonics, University of Toronto researchers report the first efficient two-layer solar cell based on colloidal quantum dots (CQD) to capture both visible and near-infrared rays. CQDs are nanoscale materials that can be tuned to respond to specific wavelengths of the visible and invisible spectrum. By capturing such a broad range of light waves - wider than normal solar cells - tandem CQD solar cells can in principle reach up to 42 per cent efficiencies. The best single-junction solar cells are constrained to a maximum of 31 per cent efficiency. (In reality, solar cells that are on the roofs of houses and in consumer products have 14 to 18 per cent efficiency.) The researchers expect that in five years, solar cells using the graded recombination layer paper will be integrated into building materials and mobile devices.