Khachatur V. Manukyan

Irradiation-Enhanced Reactivity of Multilayer Al/Ni Nanomaterials

We have investigated the effect of accelerated ion beam irradiation on the structure and reactivity of multilayer sputter deposited Al/Ni nanomaterials. Carbon and aluminum ion beams with different charge states and intensities were used to irradiate the multilayer materials. The conditions for the irradiation-assisted self-ignition of the reactive materials and corresponding ignition thresholds for the beam intensities were determined. We discovered that relatively short (40 min or less) ion irradiations enhance the reactivity of the Al/Ni nanomaterials, that is, significantly decrease the thermal ignition temperatures (Tig) and ignition delay times (τig). We also show that irradiation leads to atomic mixing at the Al/Ni interfaces with the formation of an amorphous interlayer, in addition to the nucleation of small (2-3 nm) Al3Ni crystals within the amorphous regions. The amorphous interlayer is thought to enhance the reactivity of the multilayer energetic nanomaterial by increasing the heat of the reaction and by speeding the intermixing of the Ni and the Al. The small Al3Ni crystals may also enhance reactivity by facilitating the growth of this Al-Ni intermetallic phase. In contrast, longer irradiations decrease reactivity with higher ignition temperatures and longer ignition delay times. Such changes are also associated with growth of the Al3Ni intermetallic and decreases in the heat of reaction. Drawing on this data set, we suggest that ion irradiation can be used to fine-tune the structure and reactivity of energetic nanomaterials.

Microstructure-reactivity relationship of Ti + C reactive nanomaterials

The influence of short-term (≤10 min) high energy ball milling (HEBM) on the microstructure and reactivity of a titanium-carbon powder mixture is reported. It is proved that the mechanism of microstructural transformation in a Ti-C mixture during HEBM defines the reaction mechanism in the produced Ti/C structural energetic materials. More specifically, it is shown that after the first two minutes of dry milling (DM) in an inert (argon) atmosphere the initially crystalline graphite flakes were almost completely amorphized and uniformly distributed on the surface of the deformed titanium particles. A subsequent “cold-welding” leads to formation of Ti-(C-rich/Ti)-Ti agglomerates. TEM studies reveal that the (C-rich/Ti) composite layers consist of nano-size (20 nm) Ti particles distributed in the matrix of the amorphous carbon and thus are characterized by extremely high surface area contacts between the reagents. A rapid self-ignition of the material during DM occurs just after 9.5 min of mechanical treatmen...

Photoactive porous silicon nanopowder.

Bulk processing of porous silicon nanoparticles (nSi) of 50-300 nm size and surface area of 25-230 m(2)/g has been developed using a combustion synthesis method. nSi exhibits consistent photoresponse to AM 1.5 simulated solar excitation. In confirmation of photoactivity, the films of nSi exhibit prompt bleaching following femtosecond laser pulse excitation resulting from the photoinduced charge separation. Photocurrent generation observed upon AM 1.5 excitation of these films in a photoelectrochemical cell shows strong dependence on the thickness of the intrinsic silica shell that encompasses the nanoparticles and hinders interparticle electron transfer.

Mechanochemical synthesis of methylammonium lead iodide perovskite

A mechanically induced solid-state reaction method for the synthesis of organic–inorganic hybrid perovskites, such as methylammonium lead iodide (CH3NH3PbI3) is reported. The perovskites were synthesized both in bulk and Al2O3-supported forms. The phase- and structural-formation mechanisms of such perovskites are also investigated. The experiments suggest that diffusion of PbI2 into CH3NH3I crystals is a rate-limiting step of the reaction process. It is also shown that water (humidity) significantly influences the reaction kinetics. UV–Vis–NIR absorption and photoluminescence spectroscopies indicate that the band edge and emission characteristics of the as-fabricated materials strongly depend on their particle size.

Multiscale X-ray fluorescence mapping complemented by Raman spectroscopy for pigment analysis of a 15th century Breton manuscript

We present complementary multiscale X-Ray Fluorescence (XRF) mapping and Raman spectroscopy to analyze pigments in a rare medieval Breton manuscript. Once a codex of 129 parchment leaves in the Bergendal Collection (olim MS 8), the manuscript was sold at auction and then subsequently dismembered page-by-page. The leaves were then disseminated on the open market by the biblioclast. The analysis was performed on 12 illustrated leaves (samples) out of the 92 which were recovered by Rare Books and Special Collections at the University of Notre Dame. The combination of elemental mapping with molecular spectroscopy permits an unprecedented analysis of the illuminations in the manuscript. XRF scanning provides both elemental analysis of large-scale objects as well as microscopic examination of individual pigment particles. The XRF mapping indicates distinctive elemental distributions within specific regions of interest. Raman spectroscopy of these selected areas identifies the molecular composition of the pigments. This combination of analytical techniques provides an in-depth characterization of the Breton manuscript on the macro, micro- and molecular levels. The results from different leaves confirm that pigments and inks of illustrated leaves belong to the same palette. The results also show the pigments utilized in illustrations, text, and borders are identical indicating that the manuscript was prepared in a single setting, by a single artisan or a small number of artisans working closely.

Shock-induced reaction synthesis of cubic boron nitride

Here, we report ultra-fast (0.1–5 μs) shock-induced reactions in the 3B-TiN system, leading to the direct synthesis of cubic boron nitride, which is extremely rare in nature and is the second hardest material known. Composite powders were produced through high-energy ball milling to provide intimate mixing and subsequently shocked using an explosive charge. High-resolution transmission electron microscopy and X-ray diffraction confirm the formation of nanocrystalline grains of c-BN produced during the metathetical reaction between boron and titanium nitride. Our results illustrate the possibility of rapid reactions enabled by high-energy ball milling possibly occurring in the solid state on incredibly short timescales. This process may provide a route for the discovery and fabrication of advanced compounds.Here, we report ultra-fast (0.1–5 μs) shock-induced reactions in the 3B-TiN system, leading to the direct synthesis of cubic boron nitride, which is extremely rare in nature and is the second hardest material known. Composite powders were produced through high-energy ball milling to provide intimate mixing and subsequently shocked using an explosive charge. High-resolution transmission electron microscopy and X-ray diffraction confirm the formation of nanocrystalline grains of c-BN produced during the metathetical reaction between boron and titanium nitride. Our results illustrate the possibility of rapid reactions enabled by high-energy ball milling possibly occurring in the solid state on incredibly short timescales. This process may provide a route for the discovery and fabrication of advanced compounds.

Combustion Synthesis of Ni-SiO2 Nanoscale Materials

Fabrication of metallic nanoparticles is of high interest for many industrial applications [1-2] including energy conversion and storage, electronics, and heterogeneous catalysts. However, it seems to be a challenging task because the metallic nanoparticles tend to agglomerate and grow into larger crystallites. The successful fabrication methods involves special strategies, for example, adding an organic ligand or inorganic capping agent, and creating of core-shell nanoparticles, in order to prevent the coalescence and growth of the metallic nanoparticles into larger aggregates [3]. The other approach employs the deposition of metal nanoparticles onto a porous solid to inhibit their aggregation and growth. Here we report the use of porous supports in conjunction with metal nanoparticles allows tailoring the textural properties of resulting materials.

TEM Analysis of Structural Transformation in Al/Ni Nanomaterials under High Energy Ion Irradiation

The paper addresses the effect of irradiation by accelerated ion beam on the structural transformation of Al/Ni multilayer nanomaterials studied by Transmission Electron Microscopy (TEM). The Al/Ni multi-layered nanomaterials are promising nanostructured energetic composite materials [1-2] that exhibit tunable ignition properties to a variety of external excitation methods including friction, shock waves, electrical sparks, and local heating. Because the ignition of such materials depends on their atomic structure and composition, irradiation may provide a novel approach for modification of the reactivity of the nanostructured energetic composite materials. Here we study the structural transformation in Al/Ni layers under irradiation. Magnetron sputtering and electron beam evaporation have been used to fabricate free-standing reactive multilayer nanostructured foils [3]. High energy carbon and aluminum ion beams with different charge states and intensities were used to irradiate the samples. The samples were analyzed by TEM using both high resolution TEM (HRTEM) and High Angle Annual Dark Field (HAADF) scanning TEM (STEM) modes at FEI Titan 80-300 electron microscope. The microscope was operated at 300 keV and equipped with an Oxford Inca EDX detector. A TEM cross-sectional sample that included the NiO-Ni interface was prepared from the top surface by Focus Ion Beam (FIB) using FEI Helios SEM/FIB dual beam equipment. It has been demonstrated that a significant enhancement of reactivity of Al/Ni materials after relatively short-term (40 min) high energy (20 MeV) irradiation by C ions (below the ignition threshold), is associated with structural transformations that lead to a decrease in the thermal selfignition temperature and ignition delay time. Indeed x-ray diffraction (Fig. 1) indicates that defect formation in the samples under irradiation leads to a decrease of the diffraction peak intensities of Al and Ni in irradiated materials as compared to the original foils. At the same time, the full width at half maximum (FWHM) of the Al and Ni peaks (not shown) exhibits different trends with irradiation time indicating that longer irradiation can facilitate the growth of Al crystallites while decreasing Ni crystallite size. This observation agrees well with TEM/STEM analysis (Figs. 1 and 2) that evidences the intermixing of Al and Ni at layer interfaces. Both high resolution TEM and electron diffraction indicate that formation of amorphous materials at the interfaces with small (2-3 nm) crystals of the Al3Ni intermetallic phase occur in the amorphous regions. It can be seen that the nuclei of Al3Ni crystals are distributed in the Al-rich phase close to every other Al/Ni interface for the 40 min irradiated foil (Fig. 2). It is interesting that these nuclei line-up perpendicular to the direction of the incident beam. Such structures confirm that the beam induces solid-state diffusion of Ni into the Al layer, where nucleation of Al3Ni phase takes place. Thus, the enhancement of multilayer energetic nanomaterial reactivity is shown to be associated with Paper No. 0292 583 doi:10.1017/S1431927615003712

TEM/STEM Analysis of NiO Reduction to Ni during Annealing in H 2 Atmosphere

1 Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA 2 Department of Chemistry, Yerevan State University, Yerevan, 0025, Armenia 3 Laboratory of Kinetics of SHS processes, Institute of Chemical Physics, Yerevan, 0014, Armenia 4 Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA 5 Notre Dame Integrated Imaging Facility, University of Notre Dame, Notre Dame, Indiana 46556, USA 6 Department of Chemical and Bio-molecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA