The use of organic molecules to impart electrical surface properties has been a subject of intense research not only from a fundamental perspective but for many technological applications. In particular, organic molecules have been proposed as active components for molecular electronics, as surface functioning agents, and as fabrication paradigms (i.e. utilizing molecular recognition to make complex structures). Combining these molecular attributes with silicon is particularly of interest as there is a vast array of expertise and a substantial fabrication infrastructure available that reduces development time and enables rapid integration of molecule-based devices with conventional CMOS technology. Moreover, chemical bonding to silicon is covalent in nature, giving rise to potentially more robust organic layers and less resistive interfacial contacts. However, the ability to make consistent contacts to the monolayer remains one of the largest challenges in fabrication of reliable molecular electronic structures. Instead of the idealized metal-molecule-substrate sandwich structure, traditional metal vapor-deposition often produces multiple metal filaments which diffuse through the organic monolayer and dominate the electrical response. For monolayers on silicon, metal evaporation is even more problematic as evaporated Au has been shown to displace molecules directly attached to Si. We present a novel route to obtain dense monolayers for metal-molecule-silicon molecular electronic junctions which we term flip-chip lamination. We fabricate monolayers covalently bonded to silicon by first self-assembling on ultrasmooth Au substrate and then utilizing nanotransfer printing to bond to the silicon electrode. We have explored the influence of pressure on molecular conformation and interfacial reactions in the Au-molecule-silicon sandwich structure. This versatile approach facilitates the formation of reliable metal-molecule-Si junctions enabling extensive studies of monolayer electrical properties.
Citation: Journal of the American Chemical Society
Pub Type: Journals