Nanofabrication of cylindrical STEM specimen of InGaAs/GaAs quantum dots for 3D-STEM observation.

We demonstrate the multiazimuth observation (360 degrees in principle) of InGaAs/GaAs quantum dots (QDs) by means of a 300 kV scanning transmission electron microscope (STEM), where both cross-sectional and plan-view observations are performed on a single STEM specimen for the first time. A cylindrical specimen with a diameter of 200-300 nm including the QD layer inside along the rotation axis was fabricated by the focused ion beam (FIB) technique, with the application of a newly developed mesa-cutting method to adjust the position and angle of the QD layer precisely. The 360 degrees STEM observation is realized by mounting the cylindrical specimen on a holder equipped with a specimen-rotation mechanism. High potential of 3D-STEM observation is briefly presented by showing high contrast images of QDs, dark field images, and moire fringes with various incident angles.