Abstract

A reversible E-Z-isomerization by absorption of light can be used in solid media to induce motion at a molecular scale. E.g. the distance between the two phenyl rings of the azobenze changes from 0.60 mn in E-conformation to 0.50 mn in the Z- confonnation. Surprisingly this effect can be used to move polymer chains in the solid phase over many 100 mn. Despite many efforts in explaining this phenomenon a comprehensive theory is still missing. Apart from a pure surface grating there is a further orientation grating and a density grating which appears simultaneously. Laser light scattering is not sufficient to distinguish between all gratings. We performed additional to the laser light diffraction simultaneous x-ray diffraction at a synchrotron light source. X-rays have a much shorter wavelength than visible light which lead to an enhanced sensitivity for small surface relief grating heights. In order to get a surface grating a homogeneous flat surface is illuminated with an interference pattern of the writing laser. The virgin film diffracts neither laser light nor x-rays because of the missing grating. This is the starting point of Figure 1 at the time t=0s. For 1800s a grating is inscribed and the visible light diffraction signal (curve on the top) increases monotonic until the writing laser is turned off.

© 2007 IEEE