Gareth Wakefield

Trialkylphosphine oxide/amine stabilised silver nanocrystals—the importance of steric factors and Lewis basicity in capping agents

The preparation of specifically passivated silver quantum dots is reported. Investigations into the surface-capping agents have highlighted the importance of both the chain length and bonding strength of the individual ligands. Capping agents traditionally utilised to stabilise semiconductor quantum dots cannot always be used to effectively passivate metal structures, and a dual surfactant system was chosen. Long chain amines, usually weakly binding to a bulk silver surface, were found to be effective passivating agents. The steric properties of weakly bound trialkylphosphine oxides also appear to affect the particle stability. The choice of capping agents highlight the importance of both the Lewis base functionality and steric factors and these may play a key part in the design of future nanostructured materials. It also emphasizes that effective capping agents for nanodispersed metals are not necessarily the optimum ligands for other systems such as semiconductors, metal oxides, etc.

Nanoparticle augmented radiation treatment decreases cancer cell proliferation

UNLABELLED We report significant and controlled cell death using novel x-ray-activatable titania nanoparticles (NPs) doped with lanthanides. Preferential incorporation of such materials into tumor tissue can enhance the effect of radiation therapy. Herein, the incorporation of gadolinium into the NPs is designed to optimize localized energy absorption from a conventional medical x-ray. This result is further optimized by the addition of other rare earth elements. Upon irradiation, energy is transferred to the titania crystal structure, resulting in the generation of reactive oxygen species (ROS). FROM THE CLINICAL EDITOR The authors report significant and controlled cell death using x-ray-activated titania nanoparticles doped with lanthanides as enhancers. Upon irradiation X-ray energy is transferred to the titania crystal structure, resulting in the generation of reactive oxygen species.

Charge injection into porous silicon electroluminescent devices

Abstract Light emitting porous silicon has been studied in a high resolution transmission electron microscope. These studies show that the microstructure is highly dependent on the doping level of the silicon substrate, and on the formation conditions. We have shown that the most efficient light emitting structures are quantum dot like, and that the microstructure consists of silicon dots of size 3–4 nm surrounded by a thin oxide layer. Based on this we have developed a new type of contact in order to inject holes into an electroluminescent device based on an n-type porous silicon layer. Poly(9-vinyl carbazole) is spin coated on a fresh porous silicon layer, and then either indium tin oxide or NiO is used to inject holes. The polymer layer increases the luminescence output by two orders of magnitude, while the use of NiO as a replacement for ITO reduces the switch-on voltage from 55–60 to 10–15 V. These results allow us to propose an energy band model of the device, which is discussed in terms of both the quantum wire and quantum dot models of porous silicon.