On the Impact of Light on Nanoindentations in ZnSe

The (111Zn) surface of single-crystalline ZnSe was subject to nanoindentations in darkness and under illumination using white light. A positive photoplastic effect was observed in the load range from 200 μN to 2 mN: a reduction of the penetration depth by about 5%, resulting in a reversible hardness increase by 10% under illumination. The effect was found to saturate already at 30 mW/cm2, comparable to daylight intensity. There is also a photoplastic after-effect for some seconds, i.e. a reduced hardness increase was found after having turned off the light some seconds before performing the indent.