Vapor-Phase Synthesis and Surface Functionalization of ZnSe Nanoparticles in a Counterflow Jet Reactor

ABSTRACTCompound semiconductor nanocrystals (quantum dots) exhibit unique size-dependent optoelectronic properties making 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 developing scalable techniques that allow efficient synthesis, size control, and functionalization of quantum dots, without a loss of the desirable optical properties. We report experimental results on the properties and surface modification of ZnSe nanoparticles grown by a continuous vapor-phase technique utilizing an axisymmetric counterflow jet reactor. Luminescent ZnSe nanocrystals were obtained at room temperature by reacting vapors of dimethylzinc:triethylamine adduct with hydrogen selenide, diluted in a hydrogen carrier gas. The two reactants were supplied from opposite inlets of the counterflow jet configuration and initiated particle nucleation in a region near the stagnation point of the laminar flow field. Surface modification of nanoparticles by adsorption of 1-pentanethiol was used to control the rate of particle coalescence. The counterflow jet technique can be scaled up for commercial production and is compatible with other vapor-phase processing techniques used in the microelectronics industry.

Vapor Phase Synthesis of II-IV Semiconductor Nanoparticles in a Counterflow Jet Reactor

The vapor-phase synthesis of polycrystalline ZnSe nanoparticles is reported. The particles were grown at room temperature and at a pressure of 125 torr in a counterflow jet reactor and were collected by impact on a Si watler. The precursors used in this study were vapors of (CH3)2Zn:[N(C2H5)3)]2 and H2Se gas diluted in hydrogen. These precursors have been used in the past for Metalorganic Vapor Phase Epitaxy (MOVPE) of ZnSe thin films. The particles were characterized by Transmission Electron Microscopy (TEM). electron diffraction. and Raman spectroscopy. The reactor was operated in a continuous, steady-state mode using a gas delivery system that is typical flor MOVPII systems.

GAS-Phase Decomposition Kinetics of MOVPE Precursors in a Counterflow Jet Reactor

ABSTRACTA new reactor for studying the purely homogeneous thermal decomposition of organometallic precursors used in the Metalorganic Vapor Phase Epitaxy (MOVPE) of semiconductors is presented. The idea is based on the use of a counterflow jet configuration with one jet being heated and the other unheated. The heated jet contains pure carrier gas (typically hydrogen or nitrogen), while the unheated jet contains vapors of an organometallic species diluted in the same carrier gas. Under appropriate operating conditions, decomposition of the organometallic species takes place near the stagnation plane where the hot jet collides with the cool jet. Since the reactions occur in the gas phase and away from hot walls, purely homogeneous kinetics can be obtained. Such a counterflow jet reactor was designed for studying the thermal decomposition of tertiary-butyl-arsine (TBA), t-C4H9AsH2, a very promising precursor for MOVPE of GaAs films. Two-dimensional finite element simulations of transport phenomena and kinetics have been used to identify optimal operating conditions. An experimental system was constructed and capillary-sampled mass spectroscopy at the stagnation plane was used to study the thermal decomposition of TBA in nitrogen at a total pressure of 252 Torr. Gas-chromatography of the effluent gas stream was employed for positive identification of the hydrocarbon byproducts. The results indicate the existence of two major decomposition routes: (1) A low activation energy pathway producing isobutane AsH, and (2) a higher activation energy, β-hydride elimination pathway producing isobutene and arsine.