Surface conductivity on hydrogen-terminated nanocrystalline diamond:: Implication of ordered water layers

The electrical conductivity of hydrogenated diamond surfaces was reported in 1989. Whereas the experimental verification of the conductivity is simple, an Ohmmeter is sufficient, a satisfactory explanation of the effect has not been proposed yet. Existing models attempt to explain the effect on the basis of the semiconductor properties of diamond and a water layer adhering to its surface. The central dogma in them is that it is a surface conductivity. Here we show that the conductivity is not restricted to the surface, leaving room for a new understanding of the effect. Our finding not only represents a new paradigm, but provides a platform for the design of smart biomaterials with adjustable biocompatibility, and the production of biosensors and self-sufficient hygrometers for the exploration of water reservoirs on Mars.