We use low-temperature scanning tunneling microscopy (STM) to investigate geometric and electronic properties of nanoscale structures. In this presentation, we discuss various aspects of the Ag(111) surface state such as surface state confinement to nanometer-sized islands, its interaction with isolated magnetic impurity atoms, and the first study of lifetimes effects on Shockley surface state electrons using low-temperature STM spectroscopy. Moreover, we report on observations of two-dimensional supramolecular clusters and chains which self-assemble upon deposition of 1-nitronaphthalene (NN) onto Au(111). NN molecules become 2D-chiral upon adsorption. Their handedness is determined from from high-resolution STM images and local density calculations. Modeling shows that hydrogen bonds cause the observed self-assembly. Clusters and chains mutually interact via electrostatic repulsion.