Publications

We are analysing late-time (older than about 150 d past explosion) optical spectra of Type II-Plateau (IIP) supernovae (SNe), which are H-rich SNe that come from red supergiant (RSG) progenitors. The dataset includes nearly 100 spectra of about 40 objects, making this the largest sample of SN IIP nebular spectra ever investigated. Quantitative criteria from within the spectra themselves are employed to determine if an observation is truly nebular, and thus should be included in the study. We present the temporal evolution of the fluxes, shapes, and velocities of various emission lines (see, for example, Fig. 1). These measured values are also compared to photometric data in order to search for correlations that can allow us to gain insight into the diversity of RSG progenitors and learn more about the details of the explosion itself.

Pentacene’s extraordinary photophysical and electronic properties are highly dependent on intermolecular, through-space interactions. Macrocyclic arrangements of chromophores have been shown to provide a high level of control over these interactions, but few examples exist for pentacene due to inherent synthetic challenges. In this work, zirconocene-mediated alkyne coupling was used as a dynamic covalent C-C bond forming reaction to synthesize two geometrically distinct, pentacene-containing macrocycles on a gram scale and in four or fewer steps. Both macrocycles undergo singlet fission in solution, with rates that differ by an order of magnitude while the rate of triplet recombination is approximately the same. This independent modulation of singlet and triplet decay rates is highly desirable for the design of efficient singlet fission materials. The dimeric macrocycle adopts a columnar packing motif in the solid state, with large void spaces between pentacene units of the crystal lattice.

Abstract : This final report summarizes the Caltech Plasmonics MURI program accomplishments. It is no exaggeration to say that the FY04 Plasmonics MURI catalyzed a worldwide research effort in which MURI investigators were research leaders of the plasmonics field from 2004-2010. In the MURI program, a large number of new concepts and devices were conceived, designed and demonstrated, including subwavelength waveguides, negative refractive index materials at visible frequencies, a far-field hyperlens, a plasMOStor plasmonic modulator, deep subwavelength plasmon lasers as well as larger plasmon lasers; laser antennas, plasmonic hyperspectral infrared detectors, to name a subset of achievements. Under MURI support, a total of 65 journal publications were published, including 2 papers in Nature, 2 in Nature Materials, 4 in Nature Photonics, and 2 in Science.

\n We have conducted a systematic and comprehensive monitoring programme\nof the type Ia supernova 2000cx at late phases using the VLT and\nHST. The VLT observations cover phases 360 to 480 days past maximum\nbrightness and include photometry in the BVRIJH bands, together with a \nsingle epoch in each of U and Ks. While the optical\nbands decay by about 1.4 mag per 100 days, we find that the\nnear-IR magnitudes stay virtually constant during the observed\nperiod. This means that the importance of the near-IR to the\nbolometric light curve increases with time. The finding is also in\nagreement with our detailed modeling of a type Ia supernova in the\nnebular phase. In these models, the increased importance of the\nnear-IR is a temperature effect. We note that this complicates\nlate-time studies where often only the V band is well monitored. In\nparticular, it is not correct to assume that any optical band follows\nthe bolometric light curve at these phases, and any conclusions based\non such assumptions, e.g., regarding positron-escape, \nmust be regarded as premature.\nA very simple model where all positrons are trapped\ncan reasonably well account for the \nobservations. The nickel\nmass deduced from the positron tail of this light curve is\nlower than found from the peak brightness, providing an estimate of the \nfraction of late-time emission that is \noutside of the observed wavelength range.\nOur detailed models show the signature of an infrared catastrophe at these \nepochs, which is not supported by the observations. \n\n\n

MgCl2 and C2H5OH form complexes over a wide range of C2H5OH to MgCl2 molar ratios. MgCl2(C2H5OH)x adducts prepared over a wide composition range, x = 0.47 to 6, have been studied by ultraviolet Raman spectroscopy. These studies indicate the breaking of the Mg−Cl bonds at x ≥ 2. The Raman shift of the O−H stretch shifts in the 3230−3480 cm-1 range as the C2H5OH to MgCl2 molar ratio is altered and thus, it can be used to monitor the MgCl2(C2H5OH)x composition. It is suggested that the presence of the peak at 683 cm-1 may be attributed to the totally symmetric breathing mode of Mg−O octahedra, reinforcing the structure analysis of MgCl2(C2H5OH)6.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

This paper describes an 'environmentally friendly,' water castable, water developable photoresist system. The chemically amplified negative-tone resist system consists of three water-soluble components: a polymer, poly(methyl acrylamidoglycolate methyl ether), [poly(MAGME)]; a photoacid generator, dimethyl dihydroxyphenylsulfonium triflate and a crosslinker, butanediol. Poly(MAGME) was synthesized by solution free radical polymerization. In the three-component resist system, the acid generated by photolysis of the photoacid generator catalyzes the crosslinking of poly(MAGME) in the exposed regions during post-exposure baking, thus rendering the exposed regions insoluble in water. Negative tone relief images are obtained by developing with pure water. The resist is able to resolve 1 micrometer line/space features (1:1 aspect ratio) with an exposure dose of 100 mJ/cm<SUP>2</SUP> at 248 nm. The resist can be used to generate etched copper relief images on printed circuit boards using aqueous sodium persulfate as the etchant. The crosslinking mechanism has been investigated by model compound studies using <SUP>13</SUP>C NMR. These studies have revealed that the acid catalyzed reaction of the poly(MAGME) with butanediol proceeds via both transesterification and transacetalization (transaminalization) reactions at low temperatures, and also via transamidation at high temperatures.