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Title: Investigation of crystal lattice strain in multilayers via microdiffraction
Author: Aitchison, P. R.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1997
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The fabrication of SiGe layers with ingrown crystal lattice strain allows engineering of the electronic properties of the alloy. This phenomenon is of scientific and ultimately commercial interest (Meyerson 1994). In this work the information available via the microdiffraction technique developed on a VG HB501 Scanning Transmission Electron Microscope (STEM) is investigated by analysing the strain information retrievable from nanometer scale Si/Si1-xGex multilayers. Deficit Higher Order Laue Zone (HOLZ) line patterns are recorded from localised lattice positions within strained Si/SiGe superlattices. It is shown that by employing a simple model for the production of the HOLZ lines, direct measurement of the crystal lattice strain and lattice parameter can be achieved by measuring displacement of the HOLZ lines. The two main problems concerned with the determination of lattice strain by electron microscopy have been addressed. The first is due to the fact that strained materials which are thinned down to electron transparency may undergo varying degrees of bulk and surface relaxation which are difficult to predict. This has been observed as a splitting and blurring of deficit HOLZ lines or by significant deviation of line positions from that predicted by CBED simulations. Investigations of the relaxation of materials prepared with different specimen geometries have been investigated. The second problem is the possibility that the pattern changes observed in the two dimensional diffraction plane of the microscope could be caused by more than one possible displacement in the 3D reciprocal lattice. This uniqueness problem results from the fact that it is impossible to separate out which displacements of a single deficit line in the 2D microdiffraction plane have been caused by the three possible different displacements in the 3D lattice. A rigorous geometrical description of the movement of the HOLZ lines is developed and inter-relationships between the straining of the lattice along the different lattice axes are used to solve a unique solution to the strain tensor.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available