The origin of an anomalous, low 2θ peak in x-ray diffraction spectra of MoS₂ films grown by ion beam assisted deposition

The origin of a previously reported anomalous low 2θ x-ray diffraction peak from MoS₂ thin films grown by ion beam assisted deposition was investigated. The anomalous peak, observed in a film grown on Si(100), was removed by ion irradiating the film with 180 keV Ar₊₊ ions to a dose of 1 × 10₁₅ ions/cm². Microstructures of the two films were investigated using x-ray diffraction and cross-section transmission electron microscopy. Diffraction data and bright-field images indicated that the low 2θ peak was due to a local interplanar expansion of the crystal structure normal to MoS₂ basal planes. This expansion was attributed to molecular defects.