high-work-function contact. For the same reason, electrons are extracted from C60 at the CalMEH-PPV:C,, interface. The result, then, is that separated carriers are not "wasted": thev are automaticallv collected by the prope; electrode so that external work can be done.The substantial enhancement in n ' C achieved with the bicontinuous D-A network material results from the large increase in the interfacial area over that in a D-A bilayer and from the relatively short distance from any point in the polymer to a charge-separating interface. Moreover, the internal D-A junctions inhibit carrier recombination and thereby improve the lifetime of the photoinduced carriers (6), so that the separated charge carriers can be efficiently collected by the built-in field from the asymmetric electrodes. Similar effects have been observed in MEH-PPV:Cyano-PPV polymer blends (10 , 1 1).The device efficiencies are not yet optimized. Because only -60% of the incident power was absorbed at 430 nm in the thinfilm devices used for obtaining the data in u Fig. 3, the internal carrier collection efficiency and energy conversion efficiency are approximately 1.7 times larger; that is, qc.= 90% e/ph and qr;-5.5% at 10 p,W/cm2. Although nearly 100% absorption can be achieved"by using thicker films, qc is currently limited in thick-film devices by internal resistive losses. Further imorovements in device efficiencies are expected when the blend com~ositionand the network morphology are optimized. SCIENCE VOL. 270 15 DECEMBER 1995

No abstract

Methanolysis of {t-Bu2In[μ-P(SiMe3)2]}2 (1) in aromatic solvents gives polycrystalline InP fibers (dimensions 10−100 nm × 50−1000 nm) at 111−203 °C. The chemical pathway consists of a molecular component, in which precursor substituents are eliminated, and a nonmolecular component, in which the InP crystal lattices are assembled. The two components working in concert comprise the solution−liquid−solid (SLS) mechanism. The molecular component proceeds through a sequence of isolated and fully characterized intermediates:  1 → [t-Bu2In(μ-OMe)]2 (2) → [t-Bu2In(μ-PHSiMe3)]2 (3) → 2 → [t-Bu2In(μ-PH2)]3 (4). Complex 4, which is alternatively prepared from t-Bu3In and PH3, undergoes alkane elimination, the last steps of which are catalyzed by the protic reagent MeOH, PhSH, Et2NH, or PhCO2H. In the subsequent nonmolecular component of the pathway, the resulting (InP) n fragments dissolve into a dispersion of molten In droplets, and recrystallize as the InP fibers. Important criteria are identified for crystal growth of covalent nonmolecular solids from (organic) solution. The outcomes of other solution-phase semiconductor syntheses are rationalized according to the functioning of molecular and nonmolecular pathway components of the kind identified here.

Efficient materials for recording volume holograms are described that could potentially find application in archival data storage. These materials are prepared by mixing photopolymerizable vinyl monomers with a liquid epoxy resin and an amine hardener. A solid matrix is formed in situ as the epoxy cures at room temperature. The unreacted vinyl monomers are subsequently photopolymerized during hologram recording. A key feature of these materials is the separation of the epoxy and vinyl polymerizations. This separation allows for a large index contrast to be developed in holograms when components are optimized. The standard material described in this work consists of a low index matrix (n = 1.46), comprised of diethylenetriamine and 1,4-butanediol diglycidyl ether, and a high index photopolymer mixture (n = 1.60) of N-vinylcarbazole and N-vinyl-2-pyrrolidinone. This material is functional in thick formats (several millimeters), which enables narrow angular bandwidth and high diffraction efficiency. A dynamic range (M/#) up to 13 has been measured in these materials. Holographic performance is highly dependent on the amount of amine hardener used, as well as on photopolymer shrinkage.