Thermionic emission from phosphorus (P) doped diamond nanocrystals supported by conical carbon nanotubes and ultraviolet photoelectron spectroscopy study of P-doped diamond films

• We present novel hybrid structure of phosphorous (P) doped diamond crystals supported by Conical Carbon Nanotubes (CCNT)
• We report reduced work function 2.23 eV (Thermionic Emission method) of the P doped diamond crystals supported by CCNT
• Ultraviolet Photoelectron Spectroscopy (UPS) measurements of the P doped diamond films yielded a work function value of 1.8 eV
• This is the first report on the work function of phosphorus doped diamond polycrystalline films measured by UPS

Materials with low work function values (< 2 eV) are highly in demand for low temperature thermionic electron emission, which is a key phenomenon for waste heat recovery applications. Here we present the work function reduction of phosphorus (P) doped (i) diamond nanocrystals grown on conical carbon nanotubes (CCNTs) and (ii) diamond films grown on silicon substrates. Thermionic emission measurements from phosphorus doped diamond crystals on CCNTs resulted in a work function value of 2.23 eV. The CCNTs provide the conducting backbone for the P-doped diamond nanocrystals and the reduced work-function is interpreted as due to the presence of midband-gap state and no evidence for negative electron affinity was seen. However, ultraviolet photoelectron spectroscopy studies on phosphorus doped diamond films yielded a work function value of ~ 1.8 eV with a negative electron affinity (NEA) value of 1.2 eV. Detailed band diagrams are presented to support the observed values for both cases.