Thermally-induced order-order transition of DNA-cationic surfactant complexes

Polyanionic DNA interacts with cationic amphiphiles to form electrostatic complexes exhibiting rich self-assembled structures. This type of complex has been considered as a nonviral carrier in gene therapy and as a template for nanostructure construction. Here we report a thermally-induced phase transition of the complexes of DNA with the mixtures of a cationic surfactant, dodecyltrimethyl bromide (DTAB), and a neutral lipid, dioleoylphosphatidylethanolamine (DOPE), in fully hydrated state. An order-order transition between a multilamellar (L(c)alpha) phase and an inverted hexagonal (H(c)II) phase was found to occur with the transition temperature adjustable by the DTAB-to-DNA base pair molar ratio (x) and DOPE-to-DTAB molar ratio (m). The stability of the L(c)alpha phase was enhanced at lower m and x, as the L(c)alpha-to-H(c)II transition temperature increased with the decreases of these two parameters. The suppression of -to- transition at lower x was attributed to the lower entropic gain from the counterion release due to the presence of uncomplexed DNA in the bulk solution.     

Spin and orbital magnetic moments of Fe3O4

We present measurements of the spin and orbital magnetic moments of Fe3O4 by using SQUID and magnetic circular dichroism in soft x-ray absorption. The measurements show that Fe3O4 has a noninteger spin moment, in contrast to its predicted half-metallic feature. Fe3O4 also exhibits a large unquenched orbital moment. Calculations using the local density approximation including the Hubbard U method and the configuration interaction cluster-model suggest that strong correlations and spin-orbit interaction of the 3d electrons result in the noninteger spin and large orbital moments of Fe3O4.     

Charge-orbital ordering and Verwey transition in magnetite

Local density approximation + Hubbard U (LDA + U) band structure calculations reveal that magnetite (Fe3O4) forms an insulating charge-orbital-ordered state below the Verwey transition temperature. The calculated charge ordering is in good agreement with that inferred from recent experiments. We found an associated t(2g) orbital ordering on the octahedral Fe2+ sublattice. Such an orbital ordering results primarily from the on-site Coulomb interaction. This finding unravels such fundamental issues about the Verwey transition as the mechanism for the charge ordering and for the formation of the insulating gap, as well as the nonobedience of the Anderson's criterion for the charge ordering.     

Water structure at interfaces: the present situation

This paper discusses the structure of adsorbed water at interfaces. It begins with a review of the development of the research, then examines and compares some of the most important models in this field. The results of recent spectroscopic work, especially those of IR spectroscopy, are discussed and applied to the selection of the most probable model.     

Rate enhancement for nitroxide stable free radical polymerization of n‐butyl acrylate by dodecylbenzenesulfonic acid

Dodecylbenzenesulfonic acid, DDBSA, was chosen as a new rate‐accelerating additive for 2,2,6,6,‐teramethyl‐1‐piperidinyloxy (TEMPO)‐mediated stable free radical polymerization of n‐butyl acrylate (n‐BA) monomers with 2,2′‐azobisisobutyronitrile (AIBN). It was found that the number‐average molecular weight of polymers could reach about ten thousand with a narrow polydispersity index (PDI) of 1.4 in a few minutes, which was faster than other systems reported previously. But, at higher conversion, the molecular weight distribution of polymers became broad, and a bimodal distribution occurred. The macro‐initiators isolated from the former polymers with narrow PDI could be extended by polymerization with monomers by the addition of DDBSA. Furthermore, a proposed kinetic model demonstrated that the decay of the concentration of DDBSA would reduce the living polymer concentration and retard the growth of the polymers, which could be further propagated by the supplement of DDBSA. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 42–49, 2005     

Application of Al/PI composite bumps to COG bonding process

This work demonstrates the probing, testability and applicability of Al/PI (aluminum/polyimide) composite bumps to the chip on-glass (COG) bonding process for liquid crystal display (LCD) driver chip packaging. The experimental results showed that the thickness of Al overlayer on PI core of the bump, the location of pin contact, and the bump configuration affect bump probing testability. The bump with type IV configuration prepared in this work exhibited excellent probing testability when its Al overlayer thickness exceeded 0.8 μm. We further employed Taguchi method to identify the optimum COG bonding parameters for the Al/PI composite bump. The four bonding parameters, bonding temperature, bonding time, bonding pressure and thickness of Al overlayer are identified as 180° C, 10 s, 800 kgf/cm² and 1.4 μm, respectively. The optimum bonding condition was applied to subsequent COG bonding experiments on glass substrates containing Al pads or indium tin oxide (ITO) pads. From the results of resistance measurement along with a series of reliability tests, Al pad is found to be a good substrate bonding pad for Al/PI bump to COG process. Excellent contact quality was observed when the bumps had Al overlayer thickness over 1.1 μm. As to the COG specimens with substrate containing ITO pads, high joint resistance suggested that further contact quality refinement is necessary to realize their application to COG process     

Leakage mechanism in Cu damascene structure with methylsilane-dopedlow-K CVD oxide as intermetal dielectric

This letter investigates the leakage mechanism in the Cu damascene structure with methylsilane-doped low-k CVD organosilicate glass (OSG) as the intermetal dielectric (IMD). The leakage between Cu lines was found to be dominated by the Frenkel-Poole (F-P) emission in OSG for the structure using a 50-nm SiC etching stop layer (ESL). In the structure using a 50-nm SiN ESL, the leakage component through SiN also made a considerable contribution to the total leakage in addition to the bulk leakage from trapped electrons in OSG. An appropriate ESL of sufficient thickness is essential to reduce the leakage for application to a Cu damascene integration scheme