of AlAs/GaAs grown by MBE at 500 C [3]. The thickness of the cap

The near-field photoluminescence (NPL) spectra were taken in collectionillumination mode at 10 K under excitation of the 514.5 nm Ar-laser line. The spectra were measured using a CCD detector together with a 280 mm focal length monochromator. The excitation power was below the emission threshold of QD excited states (<20 W/cm2). An Oxford Instruments CryoSXP cryogenic positioning system was used for 3D scanning. We used 50-300 nm diameter tapered fiber tips with anAl coating of 50-200 nm thickness (see Fig.lc) and transmission 10-4-10-2•

Contact of the tip to a sample surface (zero vertical tip position-z) was controlled by a tuning fork and further increase of the z position produces pressure on the sample. We used 7 nm steps and total vertical displacement up to 70 nm. The damage threshold of