The general study of crystal growth of spherical-like nanoparticles involves monitoring the kinetics during the progress of the reaction. In the case of cadmium sulfide (CdS), cadmium acetate and sodium sulfide are employed as starting reagents that are dissolved in different solvents (ethylene glycol, glyme, diglyme, and trioctylphosphine) to study the solvent effect on monomers, nucleation rates, and the quality of the seeds. Trialkylphosphine oxide (alkyl = ethyl or octyl) is chosen as a surfactant to passivate the surface of CdS nanoparticles. We propose a kinetic approach model to illustrate the unreported time-evolved crystal growth mechanism observed in this case. An experimental value for the diameter of critical volume (V c), a nanosized volume with a relative minimum surface-volume tension and considered a temporal stable stage (r = 5.7 nm in this case), is derived from transmission electron microscopy images. The size of the nanoparticles made by this synthesis route is tunable by variation of the reaction time and control of the reaction temperature; in addition, the resulting sizes are suitable for spectroscopic testing of electron quantum confinement. The X-ray powder diffraction data are consistent with a pure hexagonal CdS lattice and show no evidence for a mixed phase involving cubic symmetry.

Size-tunable CdS nanorods have been synthesized via the reaction at low temperature (25-65 °C) of air-insensitive inorganic precursors cadmium acetate and sodium sulfide in an aqueous phase with surfactant. Nonionic pluronic amphiphilic triblock copolymers, (EO) x -(PO) y (EO) x , were employed as structure-directing agents. The effects of the (EO)/(PO) ratio, surfactant size, and mole ratio between surfactant and precursors in controlling the diameter and the morphology of the final product were investigated. Transmission electron microscopy (TEM) images show that the diameter of the CdS nanorods synthesized by this method can be controlled by varying the surfactant species, the mole ratio between the inorganic precursors and triblock copolymer, and the reaction temperature. However, if the reaction is refluxed in organic solvent (ethylene glycol and glyme) without surfactant, the morphology of the product will change to microrods with flat ends, dumbbell-shaped microrods, and cotton-ball-like microparticles. The hydrophilic poly(ethylene oxide) fraction, (EO) x , of the triblock copolymers plays a decisive role in controlling the morphology of the final product, and the hydrophobic poly(isopropylene oxide) fraction, (PO) y , affects the diameter of the nanocrystallites. The typical size of CdS nanorods synthesized using (EO) 20 (PO) 70 (EO) 20 is about 5.0-7.0 nm in diameter and 30-90 nm in length. The X-ray powder diffraction pattern is consistent with the hexagonal wurtzite crystal structure. This low-temperature aqueous synthesis route can be considered as an environmentally friendly and inexpensive method of producing nearly monodisperse CdS particles and arrays (σ < 10%).

Nanometer-sized tin, Sn/R, and Sn/Si−R (R = n-C4H9), core/shell nanoparticles have been prepared by the reaction of SnCl4 or SiCl4 with Mg2Sn in ethylene glycol dimethyl ether (glyme) and subsequently with n-C4H9Li. Sn/SiO2 core/shell nanoparticles are produced from the reaction of Mg2Sn with SiCl4 and subsequent reaction with H2O2. Fourier transform Infrared (FTIR) spectra are consistent with n-butyl surface termination for the n-butyl-capped tin (Sn/n-butyl) and the silicon-n-butyl capped tin (Sn/Si-n-butyl) core/shell nanoparticles. High-resolution transmission electron microscope (HRTEM) confirms that the core part of Sn/n-butyl and Sn/Si- n-butyl nanoparticles is consistent with the tetragonal structure of tin, exhibiting lattice fringes of the {200} crystal plane (2.92 Å). The FTIR spectrum of Sn/SiO2 confirms the evidence of silica capping and selected area electron diffraction (SAED) is consistent with an amorphous shell (SiO2) and crystalline Sn core. Solid-state nuclear magnetic resonance (NMR) spectra and X-ray powder diffraction (XRD) pattern provide supporting evidence for the tetragonal structure of β-tin as the core part of Sn/SiO2 nanoparticles. The typical size distribution of Sn/n-butyl, Sn/Si-n-butyl, and Sn/SiO2 nanoparticles (diameter) range from 7 to 15 nm derived from TEM micrographs. The average radius ratio (Rr) value, (radius of SiO2/radius of Sn) for Sn/SiO2 derived from 24 individual nanoparticles in TEM images is 0.17 (0.02).

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MgZnO/ZnO two-dimensional electron gas (2DEG) structures with ZnO annealed at various temperatures (600-900 °C) and photodetectors (PDs) with and without a 2DEG structure were fabricated using a radio frequency magnetron sputtering system. It was found that the carrier concentration and mobility increase with the annealing temperature owing to the improved crystalline in ZnO; however, high-temperature (800 °C or higher) annealing can degrade the crystalline of the ZnO layer. Hall measurements showed that compared with that of bulk ZnO, the sheet carrier concentration of the 2DEG sample increased from 1.3 × 10 to 1.2 × 10 cm, and the mobility was enhanced from 5.1 to 17.5 cm/V s. This is because the channel layer is the total thickness (300 nm) in bulk ZnO, whereas the carriers are confined to a 45 nm region beneath the MgZO layer in the 2DEG sample, confirming the 2DEG behavior at the MgZnO/ZnO interface. The PDs with 2DEG structures demonstrate a higher ultraviolet (UV) response and a UV/visible rejection ratio that is six times larger than that of the PDs without a 2DEG structure. The 2DEG structure also induces a photocurrent gain, which results in a 240% quantum efficiency for the 310 nm incident wavelength. The related mechanism is elucidated with a band diagram.