  We have applied a scanning probe method, Subsurface Charge Accumulation (SCA)
imaging, to resolve the local structure of the interior of a semiconductor
two-dimensional electron system (2DES) in a tunneling geometry. Near magnetic
fields corresponding to integer Landau level filling, submicron scale spatial
structure in the out-of-phase component of the tunneling signal becomes
visible. In the images presented here, the structure repeats itself when the
filling factor is changed from nu=6 to nu=7. Therefore, we believe the images
reflect small modulations in the 2DES density caused by the disorder in the
sample.

Mesoscale and Nanoscale Physics