Organic functionalization of the germanium(100)- 2 x 1 semiconductor interface: Reaction chemistry, selective attachment strategies, and molecular layer deposition

The explosive advancement in microelectronics technology and overall trend toward molecular devices, coupled with the tailorability inherent in organic molecules, have sparked interest in combined inorganic/organic systems. As a result, the attachment of organic molecules to the (100)-2x1 reconstructed, group IV semiconductor surfaces of silicon and germanium has received considerable attention in recent years. The well characterized surface structure and range of attachment configurations possible for the direct, covalent organic functionalization of semiconductor surfaces may uniquely enable the construction of the organic/semiconductor interface with molecular level precision and control.; To develop a fundamental understanding of the chemical principles that govern reactions of carbonyl-containing compounds on these surfaces, carboxylic acids, acyl halides, tertiary amides, and formaldehyde were experimentally and theoretically investigated on Ge(100)-2x1 under ultrahigh vacuum conditions. We found that initial dative bond formation is a common motif observed for these compounds and subsequent surface reaction often leads to products which are analogous to those reported on clean transition metal surfaces. The observation of charge transfer, bidentate surface structures, as well as a catalytic coupling reaction suggests that the semi-metallic character of, and moderate strength bonds formed with, germanium substantially influence the reactivity of this surface.; The controlled deposition of nanoscale organic films with precisely tailored properties and useful functionalities will likely be required for molecular devices, and layer-by-layer reaction of multifunctional molecules appears to be a promising synthetic strategy with which to achieve these layers. An essential prerequisite to this type of deposition is the selective attachment of multifunctional compounds at the semiconductor interface, with retention of at least one reactive moiety. Our studies of amines, nitriles, and carbonyl-containing compounds indicate that narrow product distributions can be achieved with proper control of the reaction kinetics and thermodynamics of competing pathways. Furthermore, the creation of a ultrathin polyurea film on Ge(100)-2x1 at room temperature via the binary deposition of diamines and diisocyanates is demonstrated.