A seedless approach to continuous flow synthesis of gold nanorods.

A direct seedless method for the continuous synthesis of gold nanorods has been developed using a sequential rotating tube-narrow channel processing microfluidic configuration, with the stock feed solutions (HAuCl(4)/CTAB/acetylacetone and AgNO(3)/CTAB/carbonate buffer) being stable for weeks.

Direct laser writing of three-dimensional photonic crystal lattices within a PbS quantum-dot-doped polymer material.

We report on the synthesis of an optically homogenous PbS quantum-dot-doped polymer material of thickness up to 100 micrometers. It is shown that high quality micro-void channels of submicrometer diameters can be directly fabricated into this nanocomposite by using an ultrafast femtosecond laser beam. Periodically stacked channels in the form of a three-dimensional photonic crystal woodpile lattices reveals a main stop gaps as well as higher-order gaps that overlaps the near-infrared emission wavelength range of PbS quantum dots. These partial stop gaps are well defined in an angular range from zero to 15 degrees in the stacking direction.

High-temperature seedless synthesis of gold nanorods.

We demonstrate seedless synthesis of gold nanorods at high temperatures up to 97 degrees C. Using the correct silver nitrate concentration is crucial for formation of rod-shaped particles at all temperatures. We observed a decrease of nanorod length with increasing temperature, while the width stays constant throughout the temperature range. From kinetics studies, we show 3 orders of magnitude increase in nanorod growth rate when the temperature is raised from room temperature to 97 degrees C. From the temperature dependence of the growth rate, we obtain a average activation energy for growth on all facets of 90 +/- 10 kJ mol(-1). High-temperature synthesis of gold nanorods presents a more attractive method for scalable flow-based production of gold nanorods.

Phosphine-free synthesis of CdSe nanocrystals.

High quality CdSe nanocrystals have been prepared using elemental selenium as the chalcogenide precursor dispersed in 1-octadecene (ODE). The conditions used to prepare the Se precursor were found to be critical for successful nanocrystal synthesis. Systematic titration of the Se precursor solution with tri-n-octylphosphine (TOP) allowed the Se reactivity to be tuned and the final particle size to be controlled. Band-edge and surface related emission were observed for samples prepared in the presence and absence of added TOP. In the absence of a selenium passivant, the crystal structure of CdSe nanocrystals could be altered from zinc blende to wurtzite by the addition of bis(2,2,4-trimethylpentyl)phosphinic acid (TMPPA).

Two-photon fluorescence scanning near-field microscopy based on a focused evanescent field under total internal reflection.

We present two-photon fluorescence near-field microscopy based on an evanescent field focus produced by a ring beam under total internal reflection. The evanescent field produced by this method is focused by a high-numerical-aperture objective, producing a tightly confined volume that can effectively induce two-photon excitation. The imaging system is characterized by the two-photon-excited images of the nanocrystals, which show that the focused evanescent field is split into two lobes because of the enhancement of the longitudinal polarization component at the focus. This feature is confirmed by the theoretical prediction. Unlike other two-photon near-field probes, this method does not have the heating effect and requires no control mechanism of the distance between a sample and the probe.

Rhenium-Based Hydrosols: Preparation and Properties.

Transmission electron microscope (TEM), ultraviolet-visible (UV/vis), electrospray mass spectrometric (ESMS), and X-ray photoelectron spectroscopic (XPS) studies are presented on a little studied rhenium hydrosol system produced by reduction of aqueous K(2)ReCl(6) with hydrazine in the presence or absence of a gum arabic protecting agent. The studies indicate that hydrazine-generated "rhenium hydrosols" are unstable in water and slowly dissolve over time in aqueous media to form the highly stable perrhenate ion. Copyright 2001 Academic Press.