We have designed a series of combinatorial pulsed laser deposition (PLD) systems. The deposition chambers are similar to traditional PLD chambers except for the addition of movable masks close to the sample surface. We describe three different masking geometries, involving a carousel design and linear masks. The masking accuracy has been determined by measuring the film thickness variation at the edge of a cell in a combinatorial thin film library. Compositional variation has been observed at the cell edge using a scanning microwave microscope. It was found that a transition region, up to 200 mum in width, is unavoidable at cell edges using the present masking system. This puts a limit of 256 cells in a library chip fabricated on a typical 15 mm x 15 mm single crystal substrate. The problem can be avoided when composition spread samples are used instead of isolated cells. In that case the effective library density is determined by the spatial resolution of the analysis equipment. (C) 2002 Elsevier Science B.V. All rights reserved.