Raman spectroscopy and field emission characterization of delafossite CuFeO2

Abstract

Delafossite p-type CuFeO2 (CFO) semiconductors were synthesized by a modified solid state reaction technique and investigated by x-ray diffraction, x-ray photoemission spectroscopy (XPS), energy dispersive x-ray spectroscopy, and scanning electron microscopy, revealing the single-phase nature of CFO with 1:1 Cu/Fe atomic ratio. The valance states of CFO were examined by XPS and suggest Cu and Fe ions are in +1 and +3 valance states with high spin S=5/2. The “turn-on field” which is the macroscopic field needed to get an emission current of 9 nA, was calculated as 5.72 V/μm. Room temperature Raman spectra of CFO displayed two main Raman active modes at Eg∼351 cm−1 and Ag∼692 cm−1 in accord with other delafossite structures. Temperature dependent Raman spectra showed that both the modes shifted to lower frequency with significant decrease in intensity with increase in temperature. Frequency shift and linewidth of both phonon lines matched well with the theoretical damped harmonic oscillator model based on thermal expansion of the lattice and their anharmonicity coupling with other phonons.