Growth behavior, work function, and band gap tuning of nanocrystalline LiMn2O4 thin films

Abstract

We report on the effect of growth (TS) and annealing (Ta) temperatures on structural, morphological, work function mapping, and bandgap properties of nanocrystalline LiMn2O4 thin films grown by the radio frequency sputtering technique. Phase formation in the target material and thin films is confirmed from the presence of all the allowed Raman active modes (A1g + Eg + 3F2g) corresponding to the spinel LiMn2O4 structure. With increasing TS and Ta, the grain size of LiMn2O4 thin films increases exponentially and the activation energy associated with the thermally activated grain growth is observed to be 0.22 eV. The average work function of the LiMn2O4 nanocrystalline thin film grown on stainless steel at 573 K is found to be 5.63 eV. Upon increasing TS and Ta from RT to 973 K, the bandgap increases linearly from 0.58 eV to 1.05 eV and then decreases to 0.89 eV when Ta is 1073 K. The bandgap of LiMn2O4 thin films can be tuned by changing the grain size and the amount of defects present in the films.