Molecular inorganic clusters, which are stable under ambient conditions, can be used as convenient single-source precursors for controlled preparation of 2-9-nm CdSe and CdSe/ ZnS nanocrystals and 2-5-nm nanocrystals of ZnSe. The use of a cluster-based single-source precursor allows nanomaterial growth to be initiated at low temperature without the pyrolytic step for nucleus formation traditionally required for lyothermal growth processes. The elimination of the pyrolytic step allows greater synthetic control, slow thermodynamic growth at lower temperatures, high crystallinity, and reaction scalability (>50 g/L) while maintaining size dispersity at ∼5%.

Development of synthetic strategies that allow the formation of controlled 3-dimensional architectures composed of discrete ensembles of nanoparticles is a challenging goal. We present a synthetic strategy that allows the preparation of a macroscopic 3-D metal−semiconductor assemblage composed of 6.0-nm Au and 6.0-nm CdSe nanoparticles cross-linked by a bifunctional organic spacer. Optical absorption and electron microscopy imaging, coupled to electron diffraction and energy-dispersive X-ray analysis, indicate a 1:6 Au−CdSe composite that appears to be uniform over a micrometer scale. The 1:6 structure is believed to be a close-packed structure which arises from a combination of soft-sphere packing forces due to van der Waals and steric forces, and thermodynamic forces due to an acid/base controlled selective interaction of the organic headgroup moieties with the nanoparticle surfaces.

Because of their small size, Cryptosporidium oocysts cannot be easily filtered from water. This study evaluated the use of surrogates for measuring the microbial treatment performance of two point‐of‐use devices incorporating filtration with electrostatic charge interaction mechanisms. Both systems were challenged with Cryptosporidium oocysts (4‐6 μm), Bacillus subtilis (B. subtilis) spores (~1.2 μm), polystyrene latex (PSL) beads (~ 3 μm), Escherichia coli, and MS2 bacteriophage. The target biological contaminants were more effectively removed than the PSL beads, and the smaller B. subtilis spores mimicked Cryptosporidium oocyst removal more closely than the ~ 3‐μm PSL beads. Thus, surface charge appears to be an important factor for microorganism attachment, and B. subtilis spores should be considered a more appropriate surrogate than PSL beads for evaluating Cryptosporidium movement through charged media. For noncharged devices, PSL beads may still be useful as a surrogate for Cryptosporidium.

2002 nanotechnology nanotechnology V 1505 -263Inorganic Clusters as Single-Source Precursors for Preparation of CdSe, ZnSe, and CdSe/ZnS Nanomaterials.-Nanomaterials of the title semiconductors are prepared from Li 4 [M 10 Se 4 (-S-Ph) 16 ] or (Me 3 NH)[M 10 Se 4 (-S-Ph) 16 ] (M: Cd, Zn) cluster compounds in hexadecylamine (220-280 • C). The samples are characterized by absorption and emission spectroscopy and TEM. 2-9 nm CdSe and CdSe/ZnS nanocrystals and 2-5 nm crystals of ZnSe are obtained. The use of a cluster-based single-source precursor allows nanomaterial growth to be initiated at low temperature without a pyrolytic step for nucleus formation. The elimination of the pyrolytic step allows greater synthetic control, slow thermodynamic growth at lower temperatures, high crystallinity, and reaction scalability (¿50 g/L) while maintaining size dispersity at approximately 5%. -(CUMBERLAND, SCOTT L.; HANIF, KHALID M.; JAVIER, ARTJAY; KHITROV, GREGORY A.; STROUSE, GEOFFREY F.; WOESSNER, STEPHEN M.; YUN, C. STEVEN; Chem.