Experiments have suggested that particles in a colloidal suspension tend to form layers close to confining walls but this conjecture is difficult to prove unambiguously. Recently, we carried out an experiment on OFFSPEC with a charge-stabilzed colloidal suspension of 180-nm-diameter silica nanoparticles in contact with a specially fabricated silicon diffraction grating with 5-micron-deep rectangular grooves with parallel walls separated by about 300 nm. We found that the colloidal particles form a single close-packed layer in each groove. We now wish to determine how the layering changes with groove width and whether any particular structure (such as a 2-d perfect crystal) develops as a function of depth in the grooves.