Functionalized diblock copolymers, polystyrene-block-polybutadiene, are adsorbed from solution onto silicon wafers. The much smaller block of polybutadiene is functionalized for adsorption, and the copolymers might be envisaged to be quite similar to end-functionalized polystyrene chains. The amount of adsorbed polymer in dilute toluene solutions and the corresponding grafting density are determined in situ by means of null ellipsometry. After the polymer is dried, the lateral surface structure of grafted brushes is studied in air by means of atomic force microscopy. The two techniques supplement each other in an ideal way, one revealing information on grafting density and mean film thickness and the other on lateral surface structures and topography. The grafted polymers of different molecular weights show surface grafting densities sigma in the range from 0.002 to 0.21 chains/nm(2). Three different structural phases are observed : (i) at high surface coverage (0.21 chains/nm(2)) a homogeneous layer is found, (ii) at intermediate a values (0.065 chains/nm(2)) the formation of laterally inhomogeneous structures (dimples) on the surface is observed, and (iii) at low values of sigma (0.002 chains/nm(2)) isolated islands of clusters of chains are observed. The dimensions of the isolated islands correspond to the radius of gyration of a polymer chain under Theta conditions. These experimental findings are in agreement with recent theoretical predictions.