Changing phase

Sci. Rep. 4, 3955 (2014)

Tun Cao and colleagues from Dalian (China), Bristol (UK) and Singapore have numerically predicted a design of metamaterial structure that should be able to absorb ∼97% of incident visible light. The proposed structure consists of a 25-nm-thick Ge₂Sb₂Te₅ layer sandwiched between two 100-nm-thick gold layers, all on a BK7 glass substrate. The top gold layer is patterned into an array of gold rectangles that are 140 nm wide and deep and have a period of 300 nm. As well as studying the strong overlap between the transverse-electric and transverse-magnetic absorptions in the structure, the team incorporated heat transfer into their simulations to determine the temperature distribution in the structures. They predict that an incident optical intensity of just 95 nW μm⁻² should increase the temperature from room temperature to 474 K within 0.56 ns. This is of interest because Ge₂Sb₂Te₅ is promising as a data storage medium, and it undergoes an amorphous-to-crystalline phase transition at ∼433 K. The metamaterial design may be useful for improving the speed and reducing the power requirements of non-volatile phase-change random-access memory.