Compound semiconductor nanocrystals (quantum dots) exhibit unique size-dependent optoelectronic properties that make them attractive for a variety of applications, including ultrasensitive biological detection, high-density information storage, solar energy conversion, and photocatalysis. There is presently a great need for development of scalable processes that allow efficient synthesis, size control, and functionalization of such materials, without loss of the desirable optical properties. Vapor-phase synthesis techniques have several advantages over the commonly used liquid-phase techniques for quantum dot production, including better scalability, high throughput, higher purity of the final product, elimination of organic solvents from the process, and better compatibility with existing microelectronic processing operations.

In previous work, the synthesis and surface passivation of ZnSe Quantum Dots in a counterflow jet recator have been reported [1,2]. Crystalline ZnSe nanoparticles were synthesized at room temperature by reacting vapors of dimethyl zinc with hydrogen selenide gas, using hydrogen as the carrier gas. The two reactants were supplied from opposite inlets of the counterflow jet reactor and initiated particle nucleation in a region near the stagnation point of the reactor.

A model describing the particle formation process has been developed and used to identify operating conditions leading to formation of ZnSe nanoparticles with sizes below the quantum confinement threshold (<8nm). The model describes flow of the hydrogen carrier gas in the counterflow jet reactor, mass transfer of the two precursors, particle nucleation by a spontaneous and irreversible reaction, particle diffusion, and growth by particle-particle coalescence. Finite element simulations have been performed to identify optimal reactor designs and operating conditions leading to narrow particle size distributions and average sizes below the confinement threshold. The model predictions are compared to experimental data from a laboratory-scale reactor.

References

1. D. Sarigiannis, J.D. Peck, G. Kioseoglou, A. Petrou and T.J. Mountziaris, Applied Physics Letters 80(21), 4024-4026 (2002).

2. C. Sarigiannidis, M. Koutsona, A. Petrou and T.J. Mountziaris, J. Nanoparticle Research 8, 533-542 (2006).

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