tate and methyl benzoate (90:10 w/w) and used for the thickness-period library. Different amounts of this mixture were dispensed using a micropipette (Brand Transferpette) in the different columns. Solvent was evaporated under ambient conditions. Thicknesses were characterized using a stylus profilometer (Dektak 3M). The same mixture of solvents was used for the composition-period libraries.The exposure was performed using an USHIO lithographic system (filter at 365 nm, intensity 5 mW cm -2 ). After exposure and heating, all the samples were fully polymerized by flood exposure for 10 min and heating at 80°C for an additional 10 min to fix the relief structure. We checked that this step had a minor influence on the final relief structure. The topography was measured using an automated atomic force microscope (NT-MDT Solver P7 LS, Moscow, Russia) with a motorized Yh-stage. The stage moves automatically to the 44 programmed coordinates on the sample surface corresponding to different processing conditions (e.g., energy-period, temperature-period). In case of the temperature-period library, the sample was virtually divided into 44 samples (11 × 4) and temperatures were estimated using a contact thermometer. All samples were prepared in a clean room (class 100). Recent advances in biotechnology enable us to identify peptides with an affinity for non-biological materials and, in particular, those that mediate the mineralization of inorganic matter. The use of functional peptides is attracting immense interest in the development of bottom-up fabrication procedures of nanometer-scale devices. In biological systems, proteins such as silicatein, [1] silaffins, [2,3] and ferritin [4,5] cause the deposition of inorganic matter inside or around the cell where the nucleation and growth of these materials is controlled. These proteins are being utilized in vitro for the creation of nanostructured materials. [6][7][8] Recently, artificial peptides with an affinity for non-biological inorganic materials have been discovered by means of a combinatorial library approach, [9,10] and these peptides are known to have the potential for mineralization. For example, peptides with an affinity for metals and semiconductors, such as gold, silver, silica, zinc sulfide, and cadmium selenide, can be used to synthesize crystalline nano-to micrometer-sized metal particles.

No abstract

Herein we demonstrate the extra-low-temperature oxygen storage capacity (OSC) of cerium oxide nanocrystals with cubic (100) facets. A considerable OSC occurs at 150 °C without active species loading. This temperature is 250 °C lower than that of irregularly shaped cerium oxide. This result indicates that cubic (100) facets of cerium oxide have the characteristics to be a superior low-temperature catalyst.

This paper describes a method for growing thin polymer films from the surface of a silicon wafer bearing a native oxide (Si/SiO 2 ) by ring-opening metathesis polymerization (ROMP). 1,2 We have prepared norbornenederived polymer films with a wide range of thicknesses (up to 1 µm) and with a control over the chemical composition of the film perpendicular to the surface. Recently, surface-initiated polymerization has become an area of great interest, and several groups have developed approaches to grow thin polymer films on silicon and gold using cationic, anionic, and radical methods. 3 However, these methods often require rigorous reaction conditions and/or an input of thermal energy and have limited abilities to produce films of controlled thickness and chemical composition. Notably, Weck et al. recently reported the use of ROMP in a surface-initiated polymerization. 1b In their work, the polymerization was allowed to occur only at defects within a self-assembled monolayer (SAM) and yielded an extremely small amount of a polymeric material on the surface. Characterizations of the polymerization process and the resulting polymer were not possible. In this paper, we present the use of surface-initiated ROMP as a strategy for offering a high degree of control over a surface polymerization process that occurs at room temperature and demonstrate its use in the facile formation of patterned polymer films on silicon when used with the technique of microcontact printing (µCP).Scheme 1 outlines our three-step procedure: (i) the formation of a self-assembled monolayer (SAM) on silicon that presents norbornenyl groups; (ii) the attachment of a ruthenium catalyst [(Cy 3 P) 2 Cl 2 RudCHPh, Cy ) cyclohexyl] (1) to the surface using the norbornenyl groups; (iii) the polymerization of added monomers to generate the film. 4 In the first step, a SAM of 5-(bicycloheptenyl)trichlorosilane (2) was formed on a Si/SiO 2 surface by immersing a UV-ozone cleaned substrate in a toluene solution of 2 (60 mM) for 6-12 h. The presence of the resulting 0.6 nm thick film of 2 was confirmed by attenuated total reflection (ATR) IR spectroscopy (see the Supporting Information) and ellipsometry. We then attached an immobilized derivative of catalyst 1 to this norbornenyl surface by dipping the substrate into a CH 2 -Cl 2 solution of 1 (17 mM) for 30 min. Subsequent exposure of the substrate to norbornene-based monomers such as 5-(bicycloheptenyl)triethoxysilane (3) or exo-N-methyl-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide (4) (0.01-0.4 M) in CH 2 Cl 2 produced a polymeric film on the surface. Typical polymerization times were 30 min, and the substrate was washed extensively with CH 2 Cl 2 between each step. We characterized the resulting films by transmission IR spectroscopy, ellipsometry, optical microscopy, scanning electron microscopy, and atomic force microscopy (AFM).Parts a and b of Figure 1 show transmission IR spectra of films of poly-3 and poly-4 on silicon, respectively, prepared by the procedure in Scheme 1. In Figure 1a, the str...

Atomic-scale analysis of the cation valence state distribution will help to understand intrinsic features of oxygen vacancies (V ) inside metal oxide nanocrystals, which, however, remains a great challenge. In this work, the distribution of cerium valence states across the ultrafine CeO nanocubes (NCs) perpendicular to the {100} exposed facet is investigated layer-by-layer using state-of-the-art scanning transmission electron microscopy-electron energy loss spectroscopy. The effect of size on the distribution of Ce valence states inside CeO NCs is demonstrated as the size changed from 11.8 to 5.4 nm, showing that a large number of Ce cations exist not only in the surface layers, but also in the center layers of smaller CeO NCs, which is in contrast to those in larger NCs. Combining with the atomic-scale analysis of the local structure inside the CeO NCs and theoretical calculation on the V forming energy, the mechanism of size effect on the Ce valence states distribution and lattice expansion are elaborated: nano-size effect induces the overall lattice expansion as the size decreased to ≈5 nm; the expanded lattice facilitates the formation of V due to the lower formation energy required for the smaller size, which, in principle, provides a fundamental understanding of the formation and distribution of Ce inside ultrafine CeO NCs.

Tailor-made surface-modified metal oxide nanocrystals enable various applications including medical, electronic, magnetic, and photovoltaic devices. Both the synthesis and application of surface-modified metal oxide nanocrystals rely on the interaction between organic molecules and the surface of metal oxides. From this viewpoint, we have focused on the synthesis of metal oxide nanocrystals using supercritical water in the presence of organic molecules as a surface modifier. Here, we describe the use of dicarboxylic acids with various chain lengths as the modifiers of CeO 2 nanocrystals. The morphology and displayed crystallite plane of CeO 2 nanocrystals could be controlled by the length of dicarboxylic acids. Long dicarboxylic acids produced cuboctahedral or cubic CeO 2 nanocrystals, possibly because of the decreased growth rate of the {200} plane. The growth mechanism of the CeO 2 nanocrystals is discussed in detail. Furthermore, dicarboxylic acids on the surface of the CeO 2 nanocrystals changed the isoelectric point of the nanocrystals by displaying carboxyl groups. As a result, we have succeeded in synthesizing water-soluble CeO 2 nanocrystals with various morphologies using dicarboxylic acids.

No abstract

The dynamic behavior of the hydrolysis reaction of Si(OCH3)4 under neutral, basic, and acidic conditions was investigated, for the first time, at the atomic level with short time intervals using a novel tight-binding quantum chemical molecular dynamics program “Colors”. The initial parameters required for the computation were determined completely on the basis of the first principles density functional calculations using Amsterdam density functional program. The simulation results of this study clearly indicate that a flank-side attack mechanism is favored, in all the three cases, for the hydrolysis process, and pentacoordinate silicon intermediates are easy pathways for the displacement of −OCH3 by −OH on silicon. Moreover, the presence of the acid or the base as catalyst promotes the hydrolysis by rapid formation of Si−OH bond in comparison to the hydrolysis under neutral condition. Furthermore, in the case of the latter condition, it was observed that the proton oscillates between −OH and −OCH3 before it migrates to the latter group.