{"id":1601,"date":"2013-07-25T18:30:31","date_gmt":"2013-07-25T18:30:31","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/?p=1601"},"modified":"2013-08-23T22:20:15","modified_gmt":"2013-08-23T22:20:15","slug":"controlled-placement-of-colloidal-quantum-dots-in-sub-15-nm-clusters","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/controlled-placement-of-colloidal-quantum-dots-in-sub-15-nm-clusters\/","title":{"rendered":"Controlled Placement of Colloidal Quantum Dots in Sub-15-nm Clusters"},"content":{"rendered":"

Semiconductor colloidal quantum dots (QDs) are electronically quantized systems with promising applications in optoelectronic devices[1<\/a>]<\/sup>. A key aspect of such systems is the fine control of optical properties in the synthesis process[2<\/a>]<\/sup>. These QDs are predominantly used in thin-film arrangement, deposited by spin casting or dip coating. Single QD patterning is one of the major challenges to designing a system that takes advantage of individual properties of QDs[3<\/a>]<\/sup>. Here we present a templated self-assembly technique to control the position of individual QDs through electron-beam lithography (EBL). This optimized top-down lithographic process is a step towards the integration of individual QDs in optoelectronics systems for industrial applications.<\/p>\n

The fabrication process for QD placement occurred in four steps. First, a poly(methylmethacrylate) (PMMA) resist was spin coated on a silicon substrate to a thickness of 12 nm. Then, EBL was performed to obtain an array of holes (templates). The QD solution (6-nm-diameter CdSe or 5-nm-diameter CdSe\/CdZnS) was spin cast or drop cast on top of the PMMA holes, and the remaining resist was removed by dissolution in acetone for 3 min[4<\/a>]<\/sup>. This process resulted in QD clusters attached to the substrate, as shown in Figure 1. For the application of patterned QDs in excitonic or nano-optical devices, optical characterization is required. We investigated the resilience of the photoluminescence (PL) following the patterning process. The samples were observed with confocal scanning microscopy. Figure 2 shows PL signal of a sub-15-nm diameter QD cluster. Thus, the placed QD clusters may be used for further experiments and applications.<\/p>\n\n\t\t