Tailoring near-zero-thickness layers (NZTLs) that enhance interfacial adhesion, but inhibit interdiffusion and phase formation, is a critical challenge for fabricating future integrated circuits and MEMS. For instance, < 5-mn-thick barriers (similar to5 times thinner than present ones) that can conformally coat sub-100-mn features with aspect-ratios > 5:1 are needed to fully realize the potential of Cu interconnect technology. Meeting such exacting requirements necessitates new materials and scalable processing methods based on self-assembly. This talk will describe a completely new approach of using similar to0.7 to 5-nmn-thick NZTLs of self-assembled molecular layers (SAMs) and polyelectrolytes to inhibit interfacial diffusion and enhance interfacial adhesion. We will first describe the rationale for using SAMs and polyelectrolytes, and demonstrate that NZTLs inhibit Cu diffusion and effect as musch as similar to5-fold increase in device lifetimes and decrease leakage currents by similar to6 orders of magnitude. It will be shown that the molecular length and terminal functional group of the NZTLs are key factors in determining their efficacy as diffusion barriers. This will be followed by a description of the interfacial adhesion behavior of Cu/SAM/SiO2 and Cu/SiO2 structures measured by a 4-point-bending technique. Our results show that Cu/SiO2 interfacial adhesion can be enhanced by more than a factor of 3 by appropriate choice of SAMs with terminal groups that bond strongly with Cu (e.g., thiol group) on one end and the dielectric surface (e.g., a silane group) on another. We illustrate this concept by using a mercapto-trimethoxy-silane as an example for which electron spectroscopy measurements show that delamination occurs at the SAM/SiO2 interface, leaving the thiol groups on the metal side of the interface. The strong Cu-thiol linkages immobilize Cu, and enables very promising barrier properties (factor of 3-4 higher lifetimes) even for sub-nm-thick SAMs. Our recent studies of Cu/SiO2 with polyelectrolyte NZTLs also show that strong interfacial bonding is critical for superior adhesion and barrier properties. Multilayer formation is not critical for barrier properties, and is deleterious to adhesion in many cases. Based on the above, we will present a model to explain important factors that influence interfacial diffusion and adhesion in Cu/NZTL/dielectric structures.