Relaxation of strained Si on 20% linear graded virtual substrates was quantified using high resolution X-ray diffraction and a defect etching technique. The thickness of strained Si was varied between 10 and 180nm. Relaxation was observed in layers below the critical thickness but increased to only 2% relaxation in the thickest layers even with annealing up to 950C. Cross-sectional transmission electron microscopy revealed stacking faults present in layers thicker than 25nm, and nucleated 90° Shockley partial dislocations forming micro-twins in the thickest layer. These features were implicated in the impediment of the relaxation process. Misfit Strain Relaxation and Dislocation Formation in Supercritical Strained Silicon on Virtual Substrates. J.Parsons, E.H.C.Parker, D.R.Leadley, T.J.Grasby, A.D.Capewell: Applied Physics Letters, 2007, 91[6], 063127