Nanocrystal Diffusion Doping

Abstract

A diffusion-based synthesis of doped colloidal semiconductor nanocrystals is demonstrated. This approach involves thermodynamically controlled addition of both impurity cations and host anions to preformed seed nanocrystals under equilibrium conditions, rather than kinetically controlled doping during growth. This chemistry allows thermodynamic crystal compositions to be prepared without sacrificing other kinetically trapped properties such as shape, size, or crystallographic phase. This doping chemistry thus shares some similarities with cation-exchange reactions, but proceeds without the loss of host cations and excels at the introduction of relatively unreactive impurity ions that have not been previously accessible using cation exchange. Specifically, we demonstrate the preparation of Cd(1-x)Mn(x)Se (0 ≤ x ≤ ∼0.2) nanocrystals with narrow size distribution, unprecedentedly high Mn(2+) content, and very large magneto-optical effects by diffusion of Mn(2+) into seed CdSe nanocrystals grown by hot injection. Controlling the solution and lattice chemical potentials of Cd(2+) and Mn(2+) allows Mn(2+) diffusion into the internal volumes of the CdSe nanocrystals with negligible Ostwald ripening, while retaining the crystallographic phase (wurtzite or zinc blende), shape anisotropy, and ensemble size uniformity of the seed nanocrystals. Experimental results for diffusion doping of other nanocrystals with other cations are also presented that indicate this method may be generalized, providing access to a variety of new doped semiconductor nanostructures not previously attainable by kinetic routes or cation exchange.

Absorption and Magnetic Circular Dichroism Analyses of Giant Zeeman Splittings in Diffusion-Doped Colloidal Cd1–xMnxSe Quantum Dots

“…This breakdown highlights the exceptionally large ΔE Z and the high sample quality (narrow absorption bands) that can be achieved by nanocrystal diffusion doping. 29 Finally, the observation that the data from multiple samples all fall upon the same simulated curve in Figure 5B indicates that this is a universal curve, and hence eq 6 can be used to correct ΔE Z (MCD) to recover an accurate ΔE Z . This observation may be useful for future analyses of giant excitonic Zeeman splittings by MCD spectroscopy.…”

“…29 Extremely large excitonic Zeeman splittings (up to ∼ −100 meV) and g eff values (up to ∼ −900 at 1.8 K) were reported. 29 Here, we report that nanocrystals synthesized by this methodology now allow direct observation of their giant excitonic Zeeman splittings by absorption spectroscopy, a first for colloidal QDs. This new capability permits a quantitative assessment of the MCD analysis commonly applied to interpret such Zeeman splittings in these and other colloidal doped QDs.…”

Magnetoresistance of Manganese-Doped Colloidal Quantum Dot Films

“…Nevertheless, the magnitude of g eff is more than an order of magnitude smaller than for excitons in the chalcogenides systems. 8,16,24 This may be due to the assumption of α = 0 in fitting the data. However, a smaller value of g eff for the electron compared to that of the The Journal of Physical Chemistry C Article exciton is expected because exchange coupling of the manganese ions with the electron is weaker than that with the hole.…”

Solution Synthesis and Optical Properties of Transition-Metal-Doped Silicon Nanocrystals

“…11-12 Using CdSe, ZnSe, and their sulfur analogues as model NC systems, a range of dopants (Ag + , Mn 2+ , Cu 2+ ) have been successfully incorporated into these materials giving a high level of control over dopant incorporation and position within the NC. [13][14][15][16][17] Doping of Si NCs with metal dopants in particular has been relatively unexplored. [18][19] Kauzlarich and co-workers reported a multi step process to synthesize Fe and Mn doped Si NCs through use of doped alkali silicides.…”