Experimental Physics/Electron- and Ion-Nanooptics

Strain Fields in Heterostructures

Distortion Measurements on a GaAs Mesa Structure with a Buried AlOx Current Aperture

An interesting derivative of off-axis electron holography is dark-field electron holography developed by Hytch [1] to measure distortion fields. Here, a diffracted beam from an unstrained crystalline reference surface is made to interfere with the corresponding reflection originating from a strained surface. The resulting phase gradient is a measure of local variations in geometric phase. By repeating the experiment with a second non-collinear reflection, the full 2D distortion field can be easily evaluated by simple matrix algebra. This method is applied to the example of a GaAs mesa structure with a buried AlOx aperture, where in-plane tensile strain promotes the selective nucleation of InAs quantum dots in the center of the aperture [2]. A quantitative comparison with corresponding calculations (Dr. Andrei Schliwa/IFKP) based on linear elasticity theory clearly shows that strain relaxation in a TEM lamella must be taken into account in the simulation even at a thickness of a few 100 nm. [3]

[1] M. Hytch et al., Nature 453 (2008) 1086.
[2] F. Kießling et al., Phys Rev. B 91 (2015) 075306.
[3] The work was funded within the CRC 787.