Direct observation of spinodal decomposition phenomena in InAlN alloys during in-situ STEM heating

The spinodal decomposition and thermal stability of thin In(0.72)Al(0.28)N layers and In(0.72)Al(0.28)N/AlN superlattices with AlN(0001) templates on Al(2)O(3)(0001) substrates was investigated by in-situ heating up to 900 °C. The thermally activated structural and chemical evolution was investigated in both plan-view and cross-sectional geometries by scanning transmission electron microscopy in combination with valence electron energy loss spectroscopy. The plan-view observations demonstrate evidence for spinodal decomposition of metastable In(0.72)Al(0.28)N after heating at 600 °C for 1 h. During heating compositional modulations in the range of 2–3 nm-size domains are formed, which coarsen with applied thermal budgets. Cross-sectional observations reveal that spinodal decomposition begin at interfaces and column boundaries, indicating that the spinodal decomposition has a surface-directed component.