Electroluminescence ͑EL͒ and photoluminescence ͑PL͒ from heterostructure thin films made of organic poly ͑phenylene vinylene͒, PPV, and inorganic semiconductor CdSe nanocrystals are investigated. In these devices, the organic PPV structure is built next to an indium tin oxide anode, using the technique of molecular layer-by-layer sequential adsorption, and serves primarily as the hole transport layer. The inorganic layer, adjacent to an Al electrode, is made of spin cast CdSe nanocrystals, passivated with either organic groups or with a wider band gap semiconductor, e.g., ZnS in the present case. We find that the electroluminescence signal is almost exclusively generated within the inorganic layer, with a very weak contribution from the PPV layer at higher applied voltage. The performance of these heterostructure devices is influenced by the thickness of the dot layer. Lifetime tests reveal promising stability, with devices operating continuously over 50-100 h.Values of the external quantum efficiency, ext , as high as 0.1% are reached. The quantum efficiency is not enhanced by the presence of ZnS overcoating, as opposed to the observed increase in the PL quantum yield. This reflects a difference in the efficiency of charge injection into the nanocrystals due to the ZnS overlayer.

Multilayer thin films of sequentially adsorbed polyelectrolytes were utilized as nanoreactors for both metallic (Ag) and semiconductor nanoparticles (PbS). Polyelectrolyte multilayers with a controlled content of free carboxylic acid binding groups were fabricated with weak polyelectrolytes via suitable pH adjustments of the processing solutions. These groups were then used to bind various inorganic ions that were subsequently converted into nanoparticles. Spatial control (at the nanoscale) over the growth of the nanoparticles was achieved via the use of multilayer heterostructures that also contain bilayer blocks that are not able to bind inorganic ions. These “nonbinding” bilayers were fabricated from strong polyacids such as poly(styrene sulfonic acid). TEM imaging of the nanoparticles within the multilayer thin films indicates that the polycation and polyanion layers of these films are highly interpenetrated.

The morphologies of thin, substrate‐free block copolymer films have been examined by cross‐sectional TEM. Two poly(styrene‐b‐butadiene) diblock copolymers were studied: one that forms PS cylinders and the other that forms PB cylinders in the bulk. Films were annealed while supported by metal TEM grids, embedded, and ultramicrotomed in crosssection. We find that at the metal support the film forms a meniscus‐like region, or Plateau border, which exhibits the bulk morphology. Away from the border, the film thickness decreases and regions of terraced in‐plane cylinder domains occur until a minimum thickness is reached. The minimum thickness region of the PB majority copolymer in cross‐section shows a PS interlayer penetrated by a hexagonal array of circular PB channels that connect upper and lower PB surface layers, and a total thickness of 25–27 nm. The minimum thickness region of the PS majority copolymer in plan view shows no image contrast, but in cross‐section reveals a continuous PS interlayer covered by layers of PB, and a total thickness of 20 nm. Comparisons with the chain dimensions suggest a bilayer arrangement for both morphologies with strongly perturbed chain conformations in the surface layers. © 1996 John Wiley & Sons, Inc.

We have observed nanophase-separated structures in rodcoil polymers synthesized in our laboratory. Each polymer consists of a perfectly monodisperse, rodlike segment covalently bonded to a coillike segment of polyisoprene such that both rod and coil share the same molecular backbone. The polyisoprene was prepared by living anionic polymerization, and thus the rodcoil diblock molecules in the systems studied Eire of fairly uniform molar mass. Annealing of solution-cast thin films approximately 5-10 nm thick leads to ordered nanoscale morphologies that depend upon the volume fraction of rod segments in these diblock molecules. We find by transmission electron microscopy that the morphology varies from alternating strips of rod-and coil-rich domains to discrete aggregates of rods arranged in a hexagonal superlattice as rod volume fraction is decreased. At an intermediate volume fraction we see a coexistence of strips and aggregates. This breakup of rod domains may be the result of entropic coil stretching penalties analogous to those postulated recently by Williams and Fredrickson in lamellar assemblies of rodcoils.

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