Light Control Mirror Switches Between Transparent and Reflective States

Light Control Mirror Switches Between Transparent and Reflective States

The Sustainable Materials Research Division of AIST is working to achieve a Light Control Mirror, which can switch between transparent and reflective states.

"This device has a magnesium-based metal coating on the surface. This layer is very thin, about 40 nm, and it exhibits a mirror-like state. By contrast, when such a metal layer is in contact with diffuse hydrogen gas, the magnesium reacts with the hydrogen, forming a hydrogen compound. It's been found that when this hydrogen compound is only 40 nm thick, it becomes transparent. And as a result, it's possible to achieve reversible switching between the mirror state and the transparent state."

As well as hydrogen gas, hydrogen ions can be used, to switch electrically between the reflective and transparent states. This method results in higher durability and switching frequency. On the other hand, the method using hydrogen gas enables a simpler structure, so it's easier to use for larger items.

"The starting point for this research was energy-saving window glass. In the method with hydrogen gas, using a metal layer makes the surface into a mirror. So for example, by using the mirror state to reflect direct sunlight in midsummer, infrared rays and heat can be excluded from indoor environments. This makes it possible, for example, to keep homes very cool while people are out. With the method using electricity, we think there might be applications in sensors, optical switching components, electronic devices, optical devices, mobile devices, and digital cameras."

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