How to make vanadium dioxide metallic At about 70°C, the material vanadium dioxide (VO 2 ) switches from being a semiconductor to a metal. The switch happens so fast that it may be useful in electronic devices, but it is not clear whether the switch is primarily caused by enhanced interactions between electrons or by a change in the crystal structure. Morrison et al. shone laser light on a sample of VO 2 , initially in a semiconducting state. They used electron diffraction to monitor the changes in the material's crystal structure and simultaneously measured its optical properties to monitor the electronic state. For certain laser powers, VO 2 switched to a long-lived metallic state even though it preserved its initial crystal structure. Science , this issue p. 445