We present the results of our latest work using the spectroscopy of light e
mitted by a sample under the scanning tunneling microscope (STM). For the q
uantum wells in AlGaAs/GaAs layered structures, we have demonstrated that t
he emission spectra from individual wells can be measured by this method an
d that the minority carrier diffusion length can be estimated in real space
. Furthermore, we have discovered that the emission linewidth depends on th
e location even within an individual well. On the reconstructed Au(110)-(2
x 1) surface, the emission from an atomically localized electronic transiti
on in the valley between the atomic rows was found. (C) 2001 Elsevier Scien
ce Ltd. All rights reserved.