Controlling crystal surface termination by cleavage direction

We have investigated the cleaving behavior of potassium bichromate (K2Cr2O7 ) crystals using atomic force microscopy. This crystal has a double layered AB structure along (001). We find that, upon cleavage along the (001) plan e in he (100) directions, one side is completely A terminated, while the ot her is B terminated. Moreover, the cleavage plane (between an A and a B lay er, or between B and A) depends on the imposed direction of cleavage, i.e.. [100] or [(1) over bar 00]. This means that the molecular layer that termi nates the crystal surface can be controlled by choosing the macroscopic dir ection of the cleavage force. One of the two terminations is metastable and partly reconstructs to the stable termination.