Growth of Cr on Ir(111) studied by scanning tunneling microscopy

摘要

We have studied the room-temperature growth of Cr on Ir(111) by scanning tunneling microscopy. Even in the low-coverage regime, up to a total coverage of 2 monolayers (ML), Cr does not grow in the layer-by-layer mode. Instead, we observe islands with local coverages Θ between 1 ML and 5 ML. While the 1st layer growth is pseudomorphic, sporadic defect lines are observed in the 2nd layer. For Θ ≥ 3 ML periodic one-dimensional dislocation lines appear indicating the onset of strain relief. Scanning tunneling spectroscopy reveals that islands with Θ = 1 ML exist in two modifications. Though their tunneling spectra are qualitatively rather similar, direct comparison shows that the main peak is shifted by about 15 mV, resulting in peak positions of -0.255 V and —0.270 V. We interpret these two modifications as regular fcc Cr and Cr which exhibits a faulted hcp stacking on Ir(111), respectively. The assignment of fcc to areas directly attached to substrate steps together with the evolution of the ratio of the different ML-areas with coverage leads to the conclusion that hcp is the more favorable stacking.