Writing on Nanocrystals: Patterning Colloidal Inorganic Nanocrystal Films through Irradiation-Induced Chemical Transformations of Surface Ligands

摘要

In the past couple of decades, colloidal inorganic nanocrystals and, morespecifically, semiconductor quantum dots have emerged as crucial materials forthe development of nanoscience and nanotechnology, with applications in verydiverse areas such as optoelectronics and biotechnology. Films made ofinorganic NCs deposited on a substrate can be patterned by e-beam lithography,altering the structure of their capping ligands and thus allowing exposed areasto remain on the substrate while non-exposed areas are redispersed in asolvent, as in a standard lift-off process. This methodology can be describedas a direct lithography process, since the exposure is performed directly onthe material of interest, in contrast with conventional lithography which usesa polymeric resist as a mask for subsequent material deposition or etching. Afew reports from the late 1990 and early 2000 used such direct lithography tofabricate electrical wires from metallic NCs. However, the poor conductivityobtained through this process hindered the widespread use of the technique. Inthe early 2010, the same method was used to define fluorescent patterns on QDfilms, allowing for further applications in biosensing. For the past 2 ,3years, direct lithography on NC films with e-beams and X rays has gone throughan important development as it has been demonstrated that it can tune furthertransformations on the NCs, leading to more complex patternings and opening awhole new set of possible applications.