Nanoparticle Imprint Lithography: From Nanoscale Metrology to Printable Metallic Grids.

Large scale and low-cost nanopatterning of materials is of tremendous interest for optoelectronic devices. Nanoimprint lithography has emerged in recent years as a nanofabrication strategy that is high-throughput and has a resolution comparable to that of electron-beam lithography (EBL). It is enabled by pattern replication of an EBL master into polydimethylsiloxane (PDMS), that is then used to pattern a resist for further processing, or a sol-gel that could be calcinated into a solid material. Although the sol-gel chemistry offers a wide spectrum of material compositions, metals are still difficult to achieve. This gap could be bridged by using colloidal nanoparticles as resist, but deep understanding of the key parameters is still lacking. Here, we use supported metallic nanocubes as a model resist to gain fundamental insights into nanoparticle imprinting. We uncover the major role played by the surfactant layer trapped between nanocubes and substrate, and measure its thickness with subnanometer resolution by using gap plasmon spectroscopy as a metrology platform. This enables us to quantify the van der Waals (VDW) interactions responsible for the friction opposing the nanocube motion, and we find that these are almost in quantitative agreement with the Stokes drag acting on the nanocubes during nanoimprint, that is estimated with a simplified fluid mechanics model. These results reveal that a minimum thickness of surfactant is required, acting as a spacer layer mitigating van der Waals forces between nanocubes and the substrate. In the light of these findings we propose a general method for resist preparation to achieve optimal nanoparticle mobility and show the assembly of printable Ag and Au nanocube grids, that could enable the fabrication of low-cost transparent electrodes of high material quality upon nanocube epitaxy.

Biomineralization in living hypercalcified demosponges: toward a shared mechanism?

Massive skeletons of living hypercalcified sponges, representative organisms of basal Metazoa, are uncommon models to improve our knowledge on biomineralization mechanisms and their possible evolution through time. Eight living species belonging to various orders of Demospongiae were selected for a comparative mineralogical characterization of their aragonitic or calcitic massive basal skeleton. The latter was prepared for scanning and transmission electron microscopy (SEM and TEM), selected-area electron diffraction (SAED) and X-ray diffraction (XRD) analyses. SEM results indicated distinctive macro- and micro-structural organizations of the skeleton for each species, likely resulting from a genetically dictated variation in the control exerted on their formation. However, most skeletons investigated shared submicron to nano-scale morphological and crystallographical patterns: (1) single-crystal fibers and bundles were composed of 20 to 100nm large submicronic grains, the smallest structural units, (2) nano-scale likely organic material occurred both within and between these structural units, (3) {110} micro-twin planes were observed along aragonitic fibers, and (4) individual fibers or small bundles protruded from the external growing surface of skeletons. This comparative mineralogical study of phylogenetically distant species brings further evidence to recent biomineralization models already proposed for sponges, corals, mollusks, brachiopods and echinoderms and to the hypothesis of the universal and ancestral character of such mechanisms in Metazoa.

Efficient NIR-light emission from solid-state complexes of boron difluoride with 2'-hydroxychalcone derivatives.

This article describes a series of nine complexes of boron difluoride with 2'-hydroxychacone derivatives. These dyes were synthesized very simply and exhibited intense NIR emission in the solid state. Complexation with boron was shown to impart very strong donor-acceptor character into the excited state of these dyes, which further shifted their emission towards the NIR region (up to 855 nm for dye 5 b, which contained the strongly donating triphenylamine group). Strikingly, these optical features were obtained for crystalline solids, which are characterized by high molecular order and tight packing, two features that are conventionally believed to be detrimental to luminescence in organic crystals. Remarkably, the emission of light from the π-stacked molecules did not occur at the expense of the emission quantum yield. Indeed, in the case of pyrene-containing dye 4, for example, a fluorescence quantum yield of about 15 % with a fluorescence emission maximum at 755 nm were obtained in the solid state. Moreover, dye 3 a and acetonaphthone-based compounds 1 b, 2 b, and 3 b showed no evidence of degradation as solutions in CH(2) Cl(2) that contained EtOH. In particular, solutions of brightly fluorescent compound 3 a (brightness: ε×Φ(f) =45,000 M(-1) cm(-1)) could be stored for long periods without any detectable changes in its optical properties. All together, these new dyes possess a set of very interesting properties that make them promising solid-state NIR fluorophores for applications in materials science.

Multi-scale mineralogical characterization of the hypercalcified sponge Petrobiona massiliana (Calcarea, Calcaronea).

The massive basal skeleton of a few remnant living hypercalcified sponges rediscovered since the 1960s are valuable representatives of ancient calcium carbonate biomineralization mechanisms in basal Metazoa. A multi-scale mineralogical characterization of the easily accessible Mediterranean living hypercalcified sponge belonging to Calcarea, Petrobiona massiliana (Vacelet and Lévi, 1958), was conducted. Oriented observations in light and electron microscopy of mature and growing areas of the Mg-calcite basal skeleton were combined in order to describe all structural levels from the submicronic to the macroscopic scale. The smallest units produced are ca. 50-100nm grains that are in a mushy amorphous state before their crystallization. Selected area electron diffraction (SAED) further demonstrated that submicronic grains are assembled into crystallographically coherent clusters or fibers, the latter are even laterally associated into single-crystal bundles. A model of crystallization propagation through amorphous submicronic granular units is proposed to explain the formation of coherent micron-scale structural units. Finally, XRD and EELS analyses highlighted, respectively, inter-individual variation of skeletal Mg contents and heterogeneous spatial distribution of Ca ions in skeletal fibers. All mineralogical features presented here cannot be explained by classical inorganic crystallization principles in super-saturated solutions, but rather underlined a highly biologically regulated formation of the basal skeleton. This study extending recent observations on corals, mollusk and echinoderms confirms that occurrence of submicronic granular units and a possible transient amorphous precursor phase in calcium carbonate skeletons is a common biomineralization strategy already selected by basal metazoans.

The 2C putative helicase of echovirus 30 adopts a hexameric ring-shaped structure.

The 2C protein, which is an essential ATPase and one of the most conserved proteins across the Picornaviridae family, is an emerging antiviral target for which structural and functional characterization remain elusive. Based on a distant relationship to helicases of small DNA viruses, piconavirus 2C proteins have been predicted to unwind double-stranded RNAs. Here, a terminally extended variant of the 2C protein from echovirus 30 has been studied by means of enzymatic activity assays, transmission electron microscopy, atomic force microscopy and dynamic light scattering. The transmission electron-microscopy technique showed the existence of ring-shaped particles with ∼12 nm external diameter. Image analysis revealed that these particles were hexameric and resembled those formed by superfamily 3 DNA virus helicases.

Dye-adsorption-induced gelation of suspensions of spherical and rodlike zinc oxide nanoparticles in organic solvents.

The adsorption of amphiphilic Ru(II) complex Z907 onto the surface of ZnO nanospheres and nanorods causes the gelation of organic solvents, such as THF and acetone. The gels are thermally stable at very low concentration (nanoparticle volume fraction phi = 0.009) but mechanically fragile, with the behavior being dependent on the nature of the solvent, nanoparticle concentration, and the Z907/ZnO mole/weight ratio. Rheological experiments confirmed that the solid component built up a network to give a viscoelastic gel-phase material with a weak value of storage modulus G'. However, TEM and SEM experiments did not give evidence that nanoparticle long-range ordering occurred under the experimental conditions investigated. Moreover, time-dependent SAXS measurements pointed to a decrease in the nanoparticle aggregate size upon gelation. All together, the data obtained might be rationalized in terms of the aggregate-to-aggregate transition in solution, with the primitive large aggregates giving rise to smaller ones upon reaction with Z907. The resulting smaller hybrid aggregates could be the active species that act as self-assembling components in the gelation process. Given the interesting electronic and photonic properties of zinc oxide nanoparticles, such hybrid organic-inorganic gels could open new directions in materials science, low-cost electronics, and photovoltaics.

Carbon nanotubes in macrophages: imaging and chemical analysis by X-ray fluorescence microscopy.

X-ray fluorescence microscopy (microXRF) is applied for the first time to study macrophages exposed to unpurified and purified single-walled (SW) and multiwalled (MW) carbon nanotubes (CNT). Investigating chemical elemental distributions allows one to (i) image nanotube localization within a cell and (ii) detect chemical modification of the cell after CNT internalization. An excess of calcium is detected for cells exposed to unpurified SWCNT and MWCNT and related toxicological assays are discussed.

Self-assembled lamellar structures with functionalized single wall carbon nanotubes.

Highly ordered self-assembled multi-layer structures with denatured collagen wrapped single wall carbon nanotubes and surfactant systems were obtained through bioinspired methodology.