Perpendicular magnetic anisotropy in ion beam sputtered Co/Ni multilayers

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 34-35).Co/Ni multilayers display perpendicular magnetic anisotropy and have applications in magnetic devices that could lead to a large increase in the density of magnetic storage. Co/Ni 10-(2 Å Co/ 8Å Ni) and 10-(2 Å Co/ 4 Å Ni) multilayers were deposited with ion beam sputtering on either ion beam sputtered copper or direct current magnetron sputtered gold buffer layers of various thicknesses. The effect of the the roughness and the degree of (1 1 1) texture of the buffer layers and the multilayers on the perpendicular magnetic anisotropy of the deposited multilayers was examined. In addition the effect of the deposition method used to fabricate the samples, ion beam sputtering, was analyzed. The magnetic behavior of the multilayers was examined with alternating gradient magnetometry and vibrating sample magnetometery, the structure of the buffer layers and the multilayers was characterized with X-ray diffraction, and the roughness of the surface of the multilayers was characterized with atomic force microscopy. None of the deposited films showed perpendicular magnetic anisotropy and instead showed parallel magnetic anisotropy which was found to have occurred for every sample due to either a low degree of (1 1 1) texture in the buffer layer and the Co/Ni multilayer, a too high degree of roughness in the buffer layer and the Co/Ni multilayer or a combination of these two factors. In addition it was hypothesized that as the samples were deposited with sputtering, diffusion and alloying at the multilayer interfaces may have contributed to the multilayers having parallel magnetic anisotropy instead of perpendicular magnetic anisotropy.by Boris Rasin.S.B

Lis1–Nde1-dependent neuronal fate control determines cerebral cortical size and lamination

Neurons in the cerebral cortex originate predominantly from asymmetrical divisions of polarized radial glial or neuroepithelial cells. Fate control of neural progenitors through regulating cell division asymmetry determines the final cortical neuronal number and organization. Haploinsufficiency of human LIS1 results in type I lissencephaly (smooth brain) with severely reduced surface area and laminar organization of the cerebral cortex. Here we show that LIS1 and its binding protein Nde1 (mNudE) regulate the fate of radial glial progenitors collaboratively. Mice with an allelic series of Lis1 and Nde1 double mutations displayed a striking dose-dependent size reduction and de-lamination of the cerebral cortex. The neocortex of the Lis1–Nde1 double mutant mice showed over 80% reduction in surface area and inverted neuronal layers. Dramatically increased neuronal differentiation at the onset of corticogenesis in the mutant led to overproduction and abnormal development of earliest-born preplate neurons and Cajal–Retzius cells at the expense of progenitors. While both Lis1 and Nde1 are known to regulate the mitotic spindle orientation, only a moderate alteration in mitotic cleavage orientation was detected in the Lis1–Nde1 double deficient progenitors. Instead, a striking change in the morphology of metaphase progenitors with reduced apical attachment to the ventricular surface and weakened lateral contacts to neighboring cells appear to hinder the accurate control of cell division asymmetry and underlie the dramatically increased neuronal differentiation. Our data suggest that maintaining the shape and cell–cell interactions of radial glial neuroepithelial progenitors by the Lis1–Nde1 complex is essential for their self renewal during the early phase of corticogenesis

Vertical Block Copolymer Cylinder-Nanorod Self-Assembly

The properties of polymer nanocomposites (PNCs) depend on the position and orientation of nanoparticles in the polymer matrix. Improved control over nanoparticle position and orientation in PNCs would result in PNCs with improved properties. A powerful approach to controlling nanoparticle position and orientation in PNCs is nanoparticle-block copolymer (NP-BCP) self-assembly. NP-BCP self-assembly with spherical nanoparticles has been extensively studied. However, NP-BCP self-assembly with anisotropic nanoparticles is less well understood. In this work we study the position and orientation of nanorods in self-assembled nanorod-BCP nanocomposite films. More specifically we study films consisting of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) and gold nanorods (AuNRs) functionalized with P2VP. When the films are solvent annealed the PS-b-P2VP assumes a morphology of vertical P2VP cylinders in a PS matrix. Relatively short AuNRs are found to localize at the base of the vertical P2VP cylinders with their axis parallel to the substrate. Simulations showed that the AuNRs relieved chain stretching at the base of the cylinders. Studies were done with longer 70 nm and 101 nm long nanorods. The 70 nm nanorods were distributed between three states at the film surface. The three states were the bridging state, the centered state and the vertical state. The bridging state is where the AuNR is embedded in the film surface, the AuNR long axis is parallel to the film surface and each end of the AuNR is at the top of nearest neighbor P2VP cylinders. The centered state is where the AuNR is embedded in the film surface, the AuNR axis is parallel to the film surface, and the AuNR is centered over a single vertical P2VP cylinder. The vertical state is where the AuNR is localized within a vertical P2VP cylinder, is vertically oriented and has its tip at the film surface. The 101 nm long AuNRs were distributed between the bridging and vertical states at the film surface. The experimental results were compared to hybrid particle-field theory (HPFT) calculations of the system free energy. Further, HPFT simulations were used to understand the block copolymer morphology when a 101 nm long AuNR was in the bridging state

Three-dimensionally-patterned submicrometer-scale hydrogel/air networks that offer a new platform for biomedical applications

Phase mask interference lithography was employed to fabricate three-dimensional (3D) hydrogel structures with high surface area on neural prosthetic devices. A random terpolymer of poly(hydroxyethyl methacrylate-ran-methyl methacrylate-ran-methacrylic acid) was synthesized and used as a negative-tone photoresist to generate bicontinuous 3D hydrogel structures at the submicrometer scale. We demonstrated that the fully open 3D hydrogel/air networks can be used as a pH-responsive polymeric drug-release system for the delivery of neurotrophins to enhance the performance of neural prosthetic devices. Additionally an open hydrogel structure will provide direct access of neuronal growth to the device for improved electrical coupling.close252

Chilensosides E, F, and G—New Tetrasulfated Triterpene Glycosides from the Sea Cucumber Paracaudina chilensis (Caudinidae, Molpadida): Structures, Activity, and Biogenesis

Three new tetrasulfated triterpene glycosides, chilensosides E (1), F (2), and G (3), have been isolated from the Far-Eastern sea cucumber Paracaudina chilensis (Caudinidae, Molpadida). The structures were established based on extensive analysis of 1D and 2D NMR spectra and confirmed by HR-ESI-MS data. The compounds differ in their carbohydrate chains, namely in the number of monosaccharide residues (five or six) and in the positions of sulfate groups. Chilensosides E (1) and F (2) are tetrasulfated pentaosides with the position of one of the sulfate groups at C-3 Glc3, and chilensoside G (3) is a tetrasulfated hexaoside. The biogenetic analysis of the glycosides of P. chilensis has revealed that the structures form a network due to the attachment of sulfate groups to almost all possible positions. The upper semi-chain is sulfated earlier in the biosynthetic process than the lower one. Noticeably, the presence of a sulfate group at C-3 Glc3—a terminal monosaccharide residue in the bottom semi-chain of compounds 1 and 2—excludes the possibility of this sugar chain’s further elongation. Presumably, the processes of glycosylation and sulfation are concurrent biosynthetic stages. They can be shifted in time in relation to each other, which is a characteristic feature of the mosaic type of biosynthesis. The hemolytic action of compounds 1–3 against human erythrocytes and cytotoxic activities against five human cancer cell lines were tested. The compounds showed moderate hemolytic activity but were inactive against cancer cells, probably because of their structural peculiarities, such as the combination of positions of four sulfate groups

Chilensosides E, F, and G—New Tetrasulfated Triterpene Glycosides from the Sea Cucumber <i>Paracaudina chilensis</i> (Caudinidae, Molpadida): Structures, Activity, and Biogenesis

Three new tetrasulfated triterpene glycosides, chilensosides E (1), F (2), and G (3), have been isolated from the Far-Eastern sea cucumber Paracaudina chilensis (Caudinidae, Molpadida). The structures were established based on extensive analysis of 1D and 2D NMR spectra and confirmed by HR-ESI-MS data. The compounds differ in their carbohydrate chains, namely in the number of monosaccharide residues (five or six) and in the positions of sulfate groups. Chilensosides E (1) and F (2) are tetrasulfated pentaosides with the position of one of the sulfate groups at C-3 Glc3, and chilensoside G (3) is a tetrasulfated hexaoside. The biogenetic analysis of the glycosides of P. chilensis has revealed that the structures form a network due to the attachment of sulfate groups to almost all possible positions. The upper semi-chain is sulfated earlier in the biosynthetic process than the lower one. Noticeably, the presence of a sulfate group at C-3 Glc3—a terminal monosaccharide residue in the bottom semi-chain of compounds 1 and 2—excludes the possibility of this sugar chain’s further elongation. Presumably, the processes of glycosylation and sulfation are concurrent biosynthetic stages. They can be shifted in time in relation to each other, which is a characteristic feature of the mosaic type of biosynthesis. The hemolytic action of compounds 1–3 against human erythrocytes and cytotoxic activities against five human cancer cell lines were tested. The compounds showed moderate hemolytic activity but were inactive against cancer cells, probably because of their structural peculiarities, such as the combination of positions of four sulfate groups