Size effects on the critical scaling laws in a-axis and c-axis oriented 123 thin films

a-axis (CuO2 planes perpendicular to the substrate) and c-asis oriented hig h T-c films of the 123 family have been grown on (100) SrTiO3 substrates by magnetron sputtering from stoichiometric targets. Critical scaling near th e melting transition has been analyzed from transport measurements. Critica l exponents and the dimensionality of the systems are discussed in terms of structure related size effects and the characteristic superconducting leng ths. The interplay of these parameters govern a change from 3D (c-axis) to 2D (a-axis) behavior.