title: Nanocrystal film patterning by inhibiting cation exchange via electron-beam or X-ray lithography.
abstract: In this Letter we report patterning of colloidal nanocrystal films that combines direct e-beam (electron beam) writing with cation exchange. The e-beam irradiation causes cross-linking of the ligand molecules present at the nanocrystal surface, and the cross-linked molecules act as a mask for further processing. Consequently, in the following step of cation exchange, which is performed by directly dipping the substrate in a solution containing the new cations, the regions that have not been exposed to the electron beam are chemically transformed, while the exposed ones remain unchanged. This selective protection allows the design of patterns that are formed by chemically different nanocrystals, yet in a homogeneous nanocrystal film. Spatially resolved compositional analysis by energy-dispersive X-ray spectroscopy (EDS) corroborates that the selective exchange occurs only in the nonirradiated regions. We demonstrate the utility of this lithography approach by fabricating conductive wires and luminescent patterns in CdSe/CdS nanocrystal films by converting nonirradiated regions to Cu2-xSe/Cu2-xS. Furthermore, we show that X-ray irradiation too can lead to protection from cation exchange.
authors.affiliation: Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Karol
authors.initials: K
authors.lastname: Miszta
authors.forename: Fanny
authors.initials: F
authors.lastname: Greullet
authors.forename: Sergio
authors.initials: S
authors.lastname: Marras
authors.forename: Mirko
authors.initials: M
authors.lastname: Prato
authors.forename: Andrea
authors.initials: A
authors.lastname: Toma
authors.forename: Milena
authors.initials: M
authors.lastname: Arciniegas
authors.forename: Liberato
authors.initials: L
authors.lastname: Manna
authors.forename: Roman
authors.initials: R
authors.lastname: Krahne