The extinction coefficient per mole of nanocrystals at the first exitonic absorption peak, ε, for high-quality CdTe, CdSe, and CdS nanocrystals was found to be strongly dependent on the size of the nanocrystals, between a square and a cubic dependence. The measurements were carried out using either nanocrystals purified with monitored purification procedures or nanocrystals prepared through controlled etching methods. The nature of the surface ligands, the refractive index of the solvents, the PL quantum yield of the nanocrystals, the methods used for the synthesis of the nanocrystals, and the temperature for the measurements all did not show detectable influence on the extinction coefficient for a given sized nanocrystal within experimental error.

Size dependent thermal conductivity of single-walled carbon nanotubes J. Appl. Phys. 112, 013503 (2012) Inter-tube thermal conductance in carbon nanotubes arrays and bundles: Effects of contact area and pressure Appl. Phys. Lett. 100, 261908 (2012) The thermal flash technique: The inconsequential effect of contact resistance and the characterization of carbon nanotube clusters Rev. Sci. Instrum. 83, 054904 (2012) Thermal stability of wetting layer in quantum dot self-assembly J. Appl. Phys. 111, 093526 (2012) Additional information on Appl. Phys. Lett.

We have produced nanotube-in-oil suspensions and measured their effective thermal conductivity. The measured thermal conductivity is anomalously greater than theoretical predictions and is nonlinear with nanotube loadings. The anomalous phenomena show the fundamental limits of conventional heat conduction models for solid/liquid suspensions. We have suggested physical concepts for understanding the anomalous thermal behavior of nanotube suspensions. In comparison with other nanostructured materials dispersed in fluids, the nanotubes provide the highest thermal conductivity enhancement, opening the door to a wide range of nanotube applications.

Controllable reactivity of Cd precursors in the growth of CdS nanocrystals was achieved by varying the concentration of stabilizing ligand with a noncoordinating solvent. Such tunable reactivity is critical for developing the synthesis of semiconductor nanocrystals to the level of that of CdSe nanocrystals. The high quality of the CdS nanocrystals is indicated by the sharpness of the UV/Vis and photoluminescence spectra (see diagram, A=absorbance, IPL=photoluminescence intensity).

The formation of nearly monodisperse CdTe nanocrystalsdots (either zinc blende or wurtzite crystal structure), rods, and tetrapodsin a noncoordinating solvent was studied. Several strong ligand effects were observed, and the ligand effects on the monomers were found to play a more important role than the ligand effects on the nanocrystals. Experimental results suggest that, instead of monomer concentrations, monomer activities is a more relevant term for understanding the formation of nanocrystals because strong ligands always exist in the reaction solutions. The bonding strength and the steric effects of ligands dramatically affect the reactivity of monomers and are considered as contributors to the activity coefficients of monomers. The overall optical properties of the as-prepared CdTe nanocrystals are better than those reported in the literature and comparable to the standard CdSe nanocrystal system. The configuration of the hydrocarbon chains of the ligands on the surface of each nanocrystal also plays a critical role in determining the stability of CdTe nanocrystals.

Magnetic separations at very low magnetic field gradients (<100 tesla per meter) can now be applied to diverse problems, such as point-of-use water purification and the simultaneous separation of complex mixtures. High-surface area and monodisperse magnetite (Fe3O4) nanocrystals (NCs) were shown to respond to low fields in a size-dependent fashion. The particles apparently do not act independently in the separation but rather reversibly aggregate through the resulting high-field gradients present at their surfaces. Using the high specific surface area of Fe3O4 NCs that were 12 nanometers in diameter, we reduced the mass of waste associated with arsenic removal from water by orders of magnitude. Additionally, the size dependence of magnetic separation permitted mixtures of 4- and 12-nanometer-sized Fe3O4 NCs to be separated by the application of different magnetic fields.

A white light-emitting diode (0.33, 0.33) is fabricated using perovskite quantum dot/silica composites. It is shown to have greatly improved stability.

High-quality nanocrystals formed in organic solvents can be completely solubilized in water using amphiphilic copolymers containing poly(ethylene glycol) or PEG. These copolymers are generated using a maleic anhydride coupling scheme that permits the coupling of a wide variety of PEG polymers, both unfunctionalized and functionalized, to hydrophobic tails. Thermogravimetric analysis, size exclusion chromatography, cryogenic transmission electron microscopy, and infrared spectroscopy all indicate that the copolymers effectively coat the nanocrystals surfaces. The composite nanocrystal-polymer assemblies can be targeted to recognize cancer cells with Her2 receptor and are biocompatible if their surface coatings contain PEG. In the particular case of semiconductor nanocrystals (e.g., quantum dots), the materials in water have the same optical spectra as well as quantum yield as those formed initially in organic solutions.