We use self-consistent-field calculations and scaling arguments to determine the behavior of AB diblock copolymers that are tethered to a surface. While the surrounding solution is assumed to be a poor solvent for both components, the B block is considered to be less soluble than the A. The solvophobic interactions within the system drive the chains to self-assemble into micelles that have an "onion-" or "garliclike" structure. The specific morphology and dimensions of the micelles depend on the relative block lengths and whether the chains are grafted by the more or the less soluble component. At sparse grafting densities, the layer contains an ordered array of such micellar structures and the film forms a distinct pattern. The size and spacing of the patterns can be manipulated by varying the molecular weights of the copolymers. Thus, the results provide guidelines for fabricating well-defined patterned films.