title: Conformal and atomic characterization of ultrathin CdSe platelets with a helical shape.
abstract: Currently, ultrathin colloidal CdSe semiconductor nanoplatelets (NPLs) with a uniform thickness that is controllable up to the atomic scale can be prepared. The optical properties of these 2D semiconductor systems are the subject of extensive research. Here, we reveal their natural morphology and atomic arrangement. Using cryo-TEM (cryo-transmission electron microscopy), we show that the shape of rectangular NPLs in solution resembles a helix. Fast incorporation of these NPLs in silica preserves and immobilizes their helical shape, which allowed us to perform an in-depth study by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Electron tomography measurements confirm and detail the helical shape of these systems. Additionally, high-resolution HAADF-STEM shows the thickness of the NPLs on the atomic scale and furthermore that these are consistently folded along a ⟨110⟩ direction. The presence of a silica shell on both the top and bottom surfaces shows that Cd atoms must be accessible for silica precursor (and ligand) molecules on both sides.
authors.affiliation: Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science, Utrecht University , Princetonplein 1, 3584 CC Utrecht, The Netherlands.
authors.forename: Eline M
authors.initials: EM
authors.lastname: Hutter
authors.forename: Eva
authors.initials: E
authors.lastname: Bladt
authors.forename: Bart
authors.initials: B
authors.lastname: Goris
authors.forename: Francesca
authors.initials: F
authors.lastname: Pietra
authors.forename: Johanna C
authors.initials: JC
authors.lastname: van der Bok
authors.forename: Mark P
authors.initials: MP
authors.lastname: Boneschanscher
authors.forename: Celso
authors.initials: C
authors.lastname: de Mello Donegá
authors.forename: Sara
authors.initials: S
authors.lastname: Bals
authors.forename: Daniël
authors.initials: D
authors.lastname: Vanmaekelbergh
keywords: 2D semiconductor nanocrystals; CdSe nanoplatelets; nanohelices; silica coating