Energy levels at interfaces between metals and conjugated organic molecules

The fundamental physical and chemical phenomena that can occur at interfaces between conjugated organic molecules and metal surfaces are discussed. The adsorption strength of molecular monolayers on metals covers a wide range from the weak physisorption regime to strong chemisorption, involving charge transfer and/or covalent bond formation. In many cases, molecular conformation changes can be observed, which directly impact the interface electronic structure and charge injection across the organic/metal contact. The energy level positions of organic multilayers are essentially determined by the monolayer/metal interaction, and 'flat-band' conditions prevail for thicker layers of pure organic molecules. Consequently, thermodynamic equilibrium across organic semiconductor films may not always be established.