Solvent Effects On Cobalt Nanocrystal Synthesis-A Facile Strategy To Control The Size Of Co Nanocrystals

In this paper, revisiting the chemical reduction approach of Co(AOT)(2) (AOT = bis(2-ethylhexyl) sulfosuccinate) precursor by NaBH4, we highlight a novel synthetic strategy based on the change of the solvent to accurately control the size of Co nanocrystals (NCs) from 3.9 to 9.3 nm and their 2D and 3D (supracrystal) ordering. The evolution of the NC size with the solvent is explained by solvent mediated ligand-ligand interactions using Hansen solubility parameters. A formula for the nanocrystal size as a function of the solvent is proposed which predicts its diameter-within 1 nm. Moreover, and to the best of our knowledge, we show the first example of tunable Co NC size while keeping unchanged the chemistry of ligands (combination and proportion) during the growth step. Due to the possibility we have to replace the AOT ligand by the strong-binding dodecanoic acid, Co NCs are characterized by long-term stability against oxidation and coalescence of the metallic NCs, whatever their size. Low-wavenumber Raman spectra are obtained using a triple notch filtered spectrometer under 514.5 nm excitation. Two modes are clearly observed according to Lamb's model of sphere vibrations whenever the excitation laser line is far from plasmon absorption. They shift linearly with inverse particle diameter from similar to 8/17 +/- 0.1 cm(-1) (9.3 nm) to 12.5/23 +/- 0.3 cm(-1) (3.9 nm).