What is the difference between the roles of a surfactant and a stabilizer in the process of nanocrystal growth?
CTAB is a cationic surfactant, SDS is an anion surfactant. 

These surfactants act to selectively stabilize ionic faces on the crystal as it grows, causing those faces to grow more rapidly. This leads to a change in geometry or crystal shape. CTAB causes one morphology being cationic, while SDS will cause another, its head ion having the opposite charge. Further, a mixture of the two will cause an intermediary morphology. 

For instance, CTAB will cause an aqueous solution of thioacetamide and Lead(II) acetate to form PbS nanocrystals in a octahedron shape, while SDS will cause them to form a dendritic fern like shape, while a CTAB/SDS mixture (5:1) will cause a stellated octahedron or star shape to form.