Tailoring the Electron Affinity and Electron Emission of Diamond (100) 2 x 1 by Surface Functionalization Using an Organic Semiconductor

We present here a synchrotron-based photoemission spectroscopy (PES) study of the organic functionalization of bare single crystalline diamond C(100) 2 x 1 surface with an organic semiconductor-copper phthalocyanine (CuPc). Our results reveal that CuPc undergoes chemical reactions with the bare diamond surface by covalently bonding to diamond dimers. The functionalizing molecules induce an interface dipole layer that increasingly reduces the work function and electron affinity of diamond with increasing CuPc coverage, transforming bare diamond from a positive electron affinity to a negative electron affinity (NEA) surface. Meanwhile, a significantly enhanced secondary electron emission yield accompanied the reduced electron affinity, as a result of the lowered electron emission barrier and enhanced electron conduction from diamond to vacuum through the grafted molecules. The work function and electron affinity modulation contributed by the induced interface dipole is estimated to be 0.7 eV, on top of the band bending contributions. Our results highlight the utilization of organic semiconductor molecular functionalization as a means to tailor the Surface electronic properties of diamond and other conventional inorganic semiconductors. The unique combination of NEA, high electron emission, and organic semiconductor functionality on diamond could lead to the integration of molecular electronic function with diamond devices.