Berlin 2012 – scientific programme
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KR: Fachgruppe Kristallographie
KR 6: 100 years since the Laue experiment: Topical aspects of diffraction and scattering (Joint Session KR, BP, DF, GP, MA, MI, MM; related to SYXD)
KR 6.6: Talk
Tuesday, March 27, 2012, 11:00–11:15, EMH 225
Strain measurement in semiconductor nanostructures by convergent electron nanoprobe diffraction — •Knut Müller1, Andreas Rosenauer1, Marco Schowalter1, Josef Zweck2, Rafael Fritz3, and Kerstin Volz3 — 1Universität Bremen, Germany — 2Universität Regensburg, Germany — 3Universität Marburg, Germany
The fundamental but simple Bragg law is exploited to measure lattice strain with a precision of 7·10−4 and a spatial resolution of 0.5−0.7 nm directly from convergent beam electron diffraction (CBED) patterns. In particular, we present 3 different algorithms for pattern recognition to measure CBED reflection positions accurately: The first detects edges in a patch around each CBED disc and iteratively finds all edge points which lie on the disc boundary by circle fitting. The second takes a rotational average in the patch and maximises the gradient in radial direction by optimising the centre of the rotational average. The third and fastest method exploits cross-correlations between each reflection patch and different types of masks. Besides results for a 350 nm wide InxGa1−xNyAs1−y/GaAs highly strained quantum layer stack with alternating compressive/tensile strain, we present prospects for the operation and acquisition hardware of a TEM, directly deduced from the three algorithms above to allow for a fast strain map acquisition directly at the microscope in future. For the present study we operated an FEI Titan (S)TEM microscope in STEM mode to record a series of energy filtered CBED patterns on CCD.