Dissolving Diamond: Kinetics of the Dissolution of (100) and (110) Single Crystals in Nickel and Cobalt Films

We report a study of the kinetics of dissolution of (100) and (110) single-crystal diamond plates ("D(100)" and "D(110)") in thin films of nickel (Ni) and cobalt (Co). This dissolution occurs at the metal-D(100) or metal-D(110) interface and was studied in the presence and also in the absence of water vapor at temperatures near 1000 degrees C. The single-crystal D(100) dissolves in Ni, and also in Co, in the temperature range 900-1050 degrees C. The dissolution is too slow to measure below 900 degrees C. In an argon (Ar) atmosphere (under an Ar(g) flow at 1000 sccm and 1 atm pressure, with no water vapor present in the reaction chamber) and at any temperature in the range 900-1050 degrees C, the metal film is rapidly saturated with dissolved carbon (C), thin graphite films form on the free metal surface and at the metal-D interface during heating at or above 650 degrees C, and the dissolution of the diamond then stops. For addition of water vapor, its partial pressure was controlled by using a water bubbler immersed in a constant temperature bath and Ar(g) was used as the carrier gas. We discovered two different regimes (I and II) for the kinetics of dissolution of D(100) and D(110), in which the rate-determining step was the removal of carbon atoms on the open metal surface (regime I, lower partial pressure of water vapor) or dissolution of diamond at the metal-diamond interface (regime II, higher partial pressure of water vapor) that yielded different Arrhenius parameters. Time-of-flight-secondary ion mass spectrometry depth profiles show the concentration gradient of C from a certain depth into the metal film surface down to the M-D(100) interface, and residual gas analyzer measurements show that the gas products formed in the presence of water vapor on the metal surface are CO and H2. It was found that the rate of dissolution of diamond in Co was higher than that in Ni for both D(100) and D(110) and for both regimes I and II, and possible reasons are suggested. We also found that D(111) could not be dissolved at the Ni/D(111) and Co/D(111) interface in the presence of water vapor (over the same range of sample temperatures). The reaction paths for dissolution of C at the M-D(100) or M-D(110) interface and for removal of C from the free surfaces of Ni and Co were assessed through density functional theory modeling at 1273 K.