  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. In contrast to a similar 3DES, the 2DES LDOS exhibits
20 times stronger corrugations and rather irregular structures. Both results
are interpreted as a consequence of weak localization. Fourier transforms of
the LDOS reveal that the k-values of the unperturbed 2DES still dominate the
2DES, but additional lower k-values contribute significantly. To clarify the
origin of the LDOS patterns, we measure the potential landscape of the same
2DES area allowing to calculate the expected LDOS from the single particle
Schr"odinger equation and to directly compare it with the measured one.
