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

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 similar to 225, 612, 660, and 1317 Delta cm(-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 Delta cm(-1) LO and 225 Delta cm(-1) TO bands (X-660 - X-225)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 Delta cm(-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 (gamma-Fe2O3) nanoparticle suspension onto a silicon wafer followed by post-annealing in a temperature range of 600-1000 degrees C for 15 min in an air atmosphere.