Diamond anvil cells are used to generate high static pressures up to several megabars (hundreds of GPa) in very small volumes of material. We have explored a technique which employs a microwave plasma chemical vapour deposited diamond layer on one side of the rhenium gasket. The high yield strength of the diamond layer prevents excessive thickness reduction of the sample in the gasket hole. As a test case, we show energy dispersive x-ray diffraction data on rare earth metal neodymium to high pressures of 153 GPa using a synchrotron source. The increased sample thickness results in an unambiguous crystal structure determination of a monoclinic phase in neodymium above 75 GPa. © 1999 IOP Publishing Ltd.