In this contribution we present some aspects of why interfaces are important, how interfaces of organic thin films on inorganic substrates can be prepared under optimum conditions, how interfaces can decisively determine the properties of thin films, and how interfaces can be characterized under all relevant aspects. We concentrate on well-defined systems, i.e. model molecules on single-crystal substrates, prepared under optimised conditions in ultrahigh vacuum by sublimation techniques. We will briefly discuss a number of useful surface/interface characterization techniques and how these can contribute to a deeper understanding of the various properties. By means of a few examples we present results, experience, basic understanding, and some general conclusions which actually were derived from a much larger bulk of experiments and data. The main aspects concern the chemical bonding at the interface, the molecular orientation, the interface dipole and band offset, the interface ordering, and the growth properties of thin films.

1. Introduction and motivation

2. Substrates, molecular materials, and preparation techniques

3. Experimental methods for interface studies

4. Chemical bonding at organic/inorganic interfaces

5. Orientation

6. Work function, interface dipole, and band offset tuning

7. Interface ordering

8. Growth of thin organic films

9. Concluding remarks