Continuous transition from 3D to 1D confinement observed during the formation of CdSe nanoplatelets

Article abstract of DOI:10.1021/ja110046d

We study the formation of colloidal CdSe nanoplatelets using both tansmission electron microscopy (TEM) and spectroscopic analysis. We show that the platelets form by continuous lateral extension of small (<2 nm) nanocrystal CdSe seeds. The nanoplatelet thickness is fixed by the seed dimension and remains constant during the platelet formation. The nanoplatelet lateral dimensions can be tuned using additional precursor injection. Absorption and fluorescence analysis of the CdSe nanoplatelets as they continuously extend laterally confirms a continuous transition from 3D to 1D confined nanoparticles. The formation of the CdSe platelets is found to be similar for different platelet thicknesses that we control with a precision of one CdSe monolayer.

Full text of DOI:10.1021/ja110046d

Supporting Information
Fluorescence emission and excitation spectra were recorded on a Jobin Yvon Fluoromax 3.
Absorption spectra were recorded on a Varian Cary 50 Probe UV-Vis spectrometer source. TEM
images were acquired on a TEM JEOL 2010 with field electron gun. Powder Xray Diffraction
(PXRD) experiments were realized with a Philips X’Pert diffractometer with Cu K〈 source.
Figure S1: XRD pattern of CdSe platelets emitting at a) 510nm and b) 462nm. The standard
diffraction peak position of ZB CdSe are indicated
Figure S2: Small angle diffraction of nanoplatelets emitting at 462nm. The 2.355° angle correponds
to a distance inter plane equal to 3.75nm. This distance represents the thickness of the nanoplatelets
(1.8nm) plus the ligands (2nm) which are oleic acids.
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Figure S3: Absorption spectra at constant volume during the growth of a population of CdSe
nanoplatelets emitting at 462nm (Protocol 1).
Figure S4: Growth stages of CdSe nanoplatelets emitting around 510nm. Top: Transmission
electron microscope images of the CdSe particles 10s (a), 60s (b), 180s (c) and 1 hour (d) after the
injection of TOP Se. Samples are deposited directly in the TEM grid without washing. Scale bars:
20nm. Bottom : corresponding absorption (plain line) and emission spectra (doted lines) of the
samples. The emission spectra maximum is 494, 497, 507 and 510nm in figures e-h) respectively.
The corresponding platelets smallest lateral dimensions are respectively: 2, 5, 8, and 10 nm.
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