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Various nanoscale semiconducting superlattices have been generated by direct templating in a lyotropic organic liquid crystal. These include superlattices of CdS, CdSe, and ZnS, templated in a liquid crystal formed by oligoethylene oxide oleyl ether amphiphiles and water. The semiconductor growth process copied the symmetry and characteristic dimensions of the original mesophase by avoiding growth of mineral within regularly spaced hydrophobic regions. The final product was a superlattice structure in which a mineral continuum was featured with hexagonally arranged cylindrical pores 2−3 nm in diameter and 5 nm apart. Most importantly, the superlattice morphology of the nanostructured systems in contact with the mesophase was found to be thermodynamically stable with respect to the solid lacking nanoscale features. We also found that both the morphology of features in the nanostructured solids and their dimension can be controlled through the amphiphile's molecular structure and water content in the liquid crystal. The semiconducting solids CdS, CdSe, and ZnS were all directly templated, while Ag2S, CuS, HgS, and PbS were produced only as nonfeatured solids using identical synthetic methodologies. We propose that interactions of polar segments in template molecules with the precipitated mineral and with its precursor ions are necessary conditions for direct templating. This is based on the absence of templating in the more covalent minerals and also in the presence of salts known to bind precursor ions.

Communications --ADVANCED MATERIALSsis. Incomplete decomposition of the intermediates of pyrolysis was also observed during the generation of silver powder by the spray pyrolysis of silver nitrate. [16] The morphology of spray pyrolyzed particles is often influenced by the reactor temperature, which affects their rate of den~ification.["~'~.''] Scanning electron microscopy (SEM) of gold powders (Fig. 1) showed that the range of particle sizes increased from 0.4-1 pm at 1200°C to 0.4-2 pm at 800°C. The skeletal density of the powders increased from 87% of the theoretical value at 900°C to 95 % at 1000 "C. The smoothness of the particle surfaces also increased with temperature.The increase in skeletal density, the enhanced smoothness of the particle surfaces and the decrease in particle size were direct consequences of the sintering and growth of crystallites within individual particles, which caused increased aerosol-phase densification with increasing temperature. However, the identical values of the minimum particle size (0.4pm) at 800 and 1200°C suggested that aerosol-phase densification of the smaller particles was almost complete, even at 800°C. The spherical and smooth particles obtained at 1200°C were a consequence of the melting of gold above 1064 "C.Phase-pure, micron-scale, spherical gold particles were generated by spray pyrolysis of gold nitrate at temperatures of 800-1200 "C. The phase composition of the powders was unaffected by the carrier gas used. ExperimentalThe experiments were conducted in an apparatus described previously [16]. The precursor solution was prepared by dissolving gold(1rr) oxide powder (Colonial Metals, Inc., Elkton, Maryland, USA) in concentrated nitric acid (70 wt.-% of HN03) in a beaker covered with a glass plate (1 g of oxide per 10 mL of acid). The mixture of powder and acid was warmed (for about 1 h per 10 g of oxide powder) on a hot plate (at less than 80°C) with occasional stirring until the dissolution of the powder resulted in a clear, greenish-yellow solution, which was then decanted. This precursor solution (0.45 M gold(nr) nitrate) was atomized using a modified ultrasonic home humidifier as the aerosol generator [16]. The aerosol droplets were passed through a mullite tube furnace (180 cm long, 8 cm inside diameter) heated by a 3-zone Lindberg furnace. The heated region of the furnace was 90 cm long. The furnace was maintained at 40&1200 "C. The flow rate of the carrier gas was 3-10 slpm. The residence time of the aerosol stream in the furnace, after correction for temperature changes, varied from 13 to 19 s.The powders were collected on a Tuffryn membrane filter (142 m m dia., 0.45 pn pore dia.) supported on a stainless steel filter holder (Gelman, 147 mm dia.). The phase composition of the powders was determined by XRD. The powder morphology was examined by SEM and transmission electron microscopy. The skeletal density of the powder was determined by helium pycnometry.

In an effort to study sequence ordering during annealing in semicrystalline copolyesters, the carbonyl carbon of p-hydroxybenzoic acid was 13 C tagged and then solution polymerized with 2-hydroxy-6-naphthoic acid to form a low molecular weight, 50/50, random copolyester. The random copolyester was annealed at 40 deg below the crystal nematic transition temperature (Tcn). DSC results indicated a large increase in crystallinity; however 13 C NMR analysis showed no change in the benzoic-naphthoic (BN) and benzoic-benzoic (BB) diad sequence peak ratios. When the random copolyester was annealed near the Tcn, DSC results indicated a large increase in the transition temperature, no increase in crystallinity, and a shift in the BN:BB peak ratio indicating a significant increase in alternating sequences. On the basis of these results, the dramatic increase in transition temperature during annealing near Tcn is best interpreted as sequence ordering via interchain transesterification reactions within the existing crystalline regions.

Aqueous gel‐like lyotropic liquid crystals with extensive hydrogen bonding and nanoscale hydrophilic compartments have been used to define the growth of macroscopic nanotemplated CdS and CdTe thin films. These mesoporous semiconductor films contain a hexagonal array of 2.5 nm pores, 7 nm center‐to‐center, that extend in an aligned fashion perpendicular to the substrate. The CdS is deposited on a polypropylene substrate by a reaction between Cd(NO3)2 dissolved in the liquid crystal and H2S transported via diffusion through the substrate. The CdTe is electrodeposited on indium‐tin‐oxide‐coated glass from TeO2 and Cd(NO3)2, both of which are dissolved in the liquid‐crystal template. The porous nature of the CdTe films enables chemical transformations of the entire bulk of the film. As electrodeposited, the CdTe films are Te rich and, in contrast to a non‐templated film, the excess Te could be removed via a chemical treatment, proving the continuity of the pores in the nanotemplated films. These results suggest that liquid‐crystal lithography with hydrogen‐bonding amphiphiles may be a useful approach to create materials with nanoscale features over macroscopic dimensions.