As the epitaxial ZrB2(0001) films had been stored in air for some time degreasing was necessary. The epitaxial ZrB2(0001) films investigated were all degreased in an ultrasonic bath in acetone and in ethanol for 3 min each. Following degreasing, the individual buffer layers were inserted in the reactor cell, heated to 1485 °C and then stabilized in 5000 sccm H2 for 3 min and further pre-treated as follows: