  Conformations of partially or fully adsorbed semiflexible polymer chains are
studied varying both contour length $L$, chain stiffness, $\kappa$, and the
strength of the adsorption potential over a wide range. Molecular Dynamics
simulations show that partially adsorbed chains (with "tails", surface attached
"trains" and "loops") are not described by the Kratky-Porod wormlike chain
model. The crossover of the persistence length from its three-dimensional value
$(\ell_p)$ to the enhanced value in two dimensions $(2\ell_p)$ is analyzed, and
excluded volume effects are identified for $L \gg \ell_p$. Consequences for the
interpretation of experiments are suggested. We verify the prediction that the
adsorption threshold scales as $\ell_p^{-1/3}$.
