Micropositioning and tilting systems based on thermoelectric actuation.
Systems for micropos i t ion ing and tilting (to "--1 p m or 0.001 °, respectively) are usually based on piezoelectr ic actuat ion. These systems are indispensable for high dynamic appl icat ions (fast posi t ioning). For s lower m o v e m e n t s ('-,0.1 p m s -1) we have deve loped a very low cost system based on thermoelec t r ic ac tuat ion that has comparab le posi t ion resolut ion and stiffness (Meyer , 1995; Meyer e t a l . , 1996). Hea t ing and /or cooling of the ac tua tor is p e r f o r m e d by a Pel t ier e lement . For accurate operat ion, one side of the Pei t ier e l emen t mus t be thermal ly stabilized, i .e. held at a prese t or known tempera tu re . The p ro to type of such a micropos i t ion ing system provides a m a x i m u m transit of 15 pm with a resolut ion be t te r than 0.1 pm (l imited by the pos i t ion-measur ing system). precisions are l imited by the accuracy of the electric cur ren t for the Pelt ier e lement , and are suitable for a DAFS (diffraction anoma lous fine s t ructure) expe r imen t at an epitaxic single-crystal layer [1.9 gm ( G a l n ) P on [001] GaAs] . To hold the peak posi t ion of a Bragg reflection dur ing an energy scan (up to 1 keV in the vicinity of an absorp t ion edge) , the coarse pos i t ioning of gonio m e t e r angles (20 angle posi t ion of the de tec tor , o) incidence angle of synchro t ron radia t ion to the reflecting plane of the