| Complementary metal-oxide-semiconductor (CMOS) device scaling beyond 22-nm technology node (i.e. minimum feature size <10 nm) is expected to be very difficult or even impractical. In the search for newer technologies that could be integrated with CMOS or even replace it, molecular electronics has shown initial promise. In the recent past, many novel devices such as molecular rectifiers, carbon nanotube transistors and molecular switches have been demonstrated on a research scale. However, there are no clear solutions for patterning substrates at the nanometer scale, which is essential for integrating these molecular devices into circuits. Also, the substrates suited for molecular components may be organic in nature, e.g. self-assembled monolayers.; In this research, a novel technique to generate reactive aryl amine patterns on aryl azide self-assembled monolayers using II-VI semiconductor quantum dots (Qdots) was demonstrated. CdS and CdSe Qdots of 2-5 nm diameter were successfully synthesized in both aqueous and organic solvents. Tightly packed, well-ordered aryl azide-terminated self-assembled monolayers were assembled on smooth gold substrates from a novel disulfide precursor. These monolayers were reduced, at least partially, to aryl amines in an aqueous environment using ∼2 nm aminethiol-capped US Qdots as photocatalysts. The same Qdots were selectively adsorbed onto a freshly assembled aryl azide monolayer in a predefined pattern either by dispensing from a micropipette or using a pre-patterned poly(dimethylsiloxane) stamp. Illumination of these substrates resulted in selective reduction of azide to amine only in areas with adsorbed Qdots, resulting in aryl amine patterns (100 mum-1 mm). To attempt chemical patterning at the nanoscale, the Langmuir-Blodgett (LB) technique was used to deposit a two-dimensional array of dodecanethiol-capped Qdots on an aryl azide SAM, and the SAM was subsequently subjected to Qdot-catalyzed photolysis. Azide-to-amine reduction was observed not to be as efficient as previously observed with aminethiol Qdots, as a result of which no nanopatterns could be discerned. A separate stability study was conducted to determine the parameters (size, capping ligand, etc.) that yield the most stable Qdot LB films. Larger Qdots formed more stable LB films than smaller ones. Capping ligands studies showed that trioctylphosphine oxide (TOPO) capped Qdots resulted in the most stable LB films. |
