Molecular attachment to oxidised (100) CVD diamond surfaces

Abstract

The unique bulk and surface properties of diamond coupled with the development of CVD techniques to produce wide area, high quality thin film single crystal diamond films make it an attractive substrate to fulfil the demanding requirements of future device fabrication. Methods by which to modify the diamond surface with an organic functional group, either to impart some property of the organic species to the diamond surface, or to modify the properties of the diamond substrate, are required. Commercial CVD single crystal (100) diamond substrates have been treated by hydrogen plasma to maximise the (100) terrace width and provide high quality surfaces. Thermal oxidation, under controlled conditions, introduced one complete monolayer of oxygen to the (100) diamond surface. The majority of the oxygen was present in a carbonyl-like configuration. Studies of the (100) diamond surface morphology after extended periods suggested oxidation took place by anisotropic etching of steps present on the (100) diamond surface and caused eventual roughening of the surface. A small organic ketone, 2-adamantanone, was used as a molecular mimic of the oxidised (100) diamond surface due to its structural similarity to a small section of the surface. Kinetic studies elucidated the mechanism of reversible imine formation by nucleophilic attack of amines upon 2-adamantanone. Variation from the standard literature reaction mechanism was attributed to steric hindrance around the carbonyl group in 2-adamantanone, and best conditions under which to attempt extension of the reaction to the structurally hindered carbonyl-functional (100) diamond surface were established. The fluorinated amine 4-trifluoromethylbenzylamine has been introduced to the oxidised (100) diamond surface. Covalent binding of 4-trifluoromethylbenzylamine to the (100) diamond surface via an imine bond was strongly supported by XPS evidence. Reductive amination of oxidised (100) diamond introduced 4- trifluoromethylbenzylamine to the diamond surface which could not be removed by washing in water, consistent with in-situ reduction of the imine bond to a water stable amine linkage.