  The local density of states (LDOS) of the adsorbate induced two-dimensional
electron system (2DES) on n-InAs(110) is studied by low-temperature scanning
tunneling spectroscopy. The LDOS exhibits irregular structures with fluctuation
lengths decreasing with increasing energy. Fourier transformation reveals that
the k-values of the unperturbed 2DES dominate the LDOS, but additional lower
k-values contribute significantly. To clarify the origin of the additional
k-space intensity, we measure the potential landscape of the same 2DES area
with the help of the tip induced quantum dot. This allows to calculate the
expected LDOS from the single particle Schroedinger equation and to directly
compare it with the measured one. Reasonable correspondance between calculated
and measured LDOS is found.
