Determination of Nanocrystal Sizes:  A Comparison of TEM, SAXS, and XRD Studies of Highly Monodisperse CoPt₃ Particles

Abstract

One of the most fundamental tasks in nanoscience is the accurate determination of particle sizes. Various methods have been developed to elucidate the mean particle diameter and the standard deviation for an ensemble of nanocrystals. However, good agreement between the results from different methods is not always encountered in the literature. In this study, we investigate colloidally prepared, highly monodisperse CoPt3 nanoparticles by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and powder X-ray diffraction (XRD). The results are compared in order to examine to which extent agreement is obtained by the different techniques when applied to small nanocrystals in the size range below 10 nm. In particular, the applicability of the simple Scherrer formula for size determination from the broadening of XRD reflections is checked. When the different techniques are correctly applied, the results from all methods are in good agreement.

The Concept of Delayed Nucleation in Nanocrystal Growth Demonstrated for the Case of Iron Oxide Nanodisks

“…When Fe(CO) 5 is decomposed under the same conditions reported above except for the absence of oxidizer, the formation of a dark colloid occurs with the same induction time measured for the preparation of the iron oxide nanoparticles. On the other hand, the thermal decomposition of Fe(CO) 5 in the presence of oxidizer without surfactant takes place in the time scale of less than 1 minute. These results indicate that the mCPBA does not play a determinant role in reaction kinetics.…”

“…Iron Pentacarbonyl (Fe(CO) 5 , 99.5%) and tridecanoic acid (C 13 H 26 O 2 , 98%) were purchased from Alfa Aesar and Aldrich, respectively, and were used without further purification. 3-chloro peroxybenzoic acid (or meta-chloro peroxybenzoic acid, mCPBA) (C 7 H 5 O 2 Cl, 77% Aldrich) was dehydrated with a procedure including extraction with dichloromethane and dehydration with phosphorous anhydride, followed by vacuum drying.…”

“…The effect of iron precursor concentration on the reaction rate was studied by varying the initial amount of Fe(CO) 5 , while keeping all other synthetic parameters constant. Figure 4C …”

“…In the typical synthesis, monodisperse nanoparticles were first formed by the reaction described previously, i.e. adopting a Fe(CO) 5 : tridecanoic acid: mCPBA molar ratio of 1:3:1.5. One minute after the solution turns dark, an ether solution of mCPBA (mCPBA/ Fe(CO) 5 =1.5) was injected.…”

“…It has been reported that amines bind less strongly than carboxylic acids of the same carbon chain length. 36,37 We have therefore performed the decomposition of Fe(CO) 5 in the presence of dodecylamine as surfactant, recording an induction time of a few minutes.…”