Sensitivity of Micro-Raman Spectrum to Crystallite Size of Electrospray-Deposited and Post-Annealed Films of Iron-Oxide Nanoparticle Suspensions

Abstract

This paper demonstrates the sensitivity of the Raman spectra of electrospray-deposited iron-oxide nanoparticle films to their grain size. The grain size in the films was controlled using the temperature of annealing. The position and width of the bands at ∼ 225, 612, 660, and 1317 Δcm⁻¹ were investigated for their sensitivity to both grain size and laser-induced heating, using 532 nm excitation. The parameter most sensitive to grain size was found to be the difference between the band position of the 660 Δcm⁻¹ LO and 225 Δcm⁻¹ TO bands (X₆₆₀ - X₂₂₅). The distance between the two bands narrowed with increasing annealing temperature of the films, suggesting that, as grain size increases, these two bands become closer. The 660 Δcm⁻¹ band position was very stable regardless of variation in laser power and, thus, laser-induced heating effects. The films were prepared by electrospray deposition of a commercial maghemite (γ-Fe₂O₃) nanoparticle suspension onto a silicon wafer followed by post-annealing in a temperature range of 600–1000 °C for 15 min in an air atmosphere.