Probing the Reaction Dynamics of Thermite Nanolaminates

Al/CuO reactive nanolaminate ignition was studied using temperature jump (T-Jump) heating for rates greater than 10⁵ K/s. Multilayer samples were sputter deposited onto thin platinum filaments in alternating layers of Al and CuO. The filaments were resistively heated in a time-of-flight mass spectrometer (ToF-MS), while ignition and reaction were observed with high-speed video. A total deposited thickness of 1800 nm was maintained for all samples, while the number of bilayers was varied from 1 to 12. Increasing this value decreased the diffusion distances and increased the amount of interfacial area across which reaction could occur, while keeping the overall energy of the system constant. From 2 to 6 bilayers, the ignition temperature decreased from 1250 to 670 K and the overall reactivity increased. Past 6 bilayers, the ignition temperature only decreased slightly and there was little impact on the overall reactivity. This behavior is consistent with a mass-transport model where the predominant diffusing species exhibits a low activation energy (50 kJ/mol). Ignition temperature, which depends upon bilayer thickness, is found to be a good predictor of flame speed

Near-Infrared Optical Extinction of Indium Tin Oxide Structures Prepared by Nanosphere Lithography

Indium tin oxide (ITO) has been the most widely studied conducting metal oxide and serves as the best candidate for proof-of-concept experiments in the field of surface plasmon resonance and studies of electric field confinement and manipulation. ITO is chemically stable and relatively easy to sputter. In this report, arrays of ITO nanostructures were produced using nanosphere lithography, which was originally developed for plasmonic applications involving noble metals. However, the experiments presented here show that patterned ITO with similar size and shape to noble metals has an observed extinction that corresponds to the epsilon-near-zero mode. The carrier density of ITO nanostructure can be controlled by the postdeposition annealing process. Thus, one can prove that the optical signals on the surface are those of the ITO nanostructure by reversible on/off switching of the capacitive plasmon resonance by annealing the surfaces successively in forming gas (N₂/H₂) and in air. Thus, using conducting metal oxides confident of the electric field is possible not only along the <i>z</i>-axis perpendicular to the thin film but within the plane of the film as well

New Method for Extracting Diffusion-Controlled Kinetics from Differential Scanning Calorimetry: Application to Energetic Nanostructures

A new expression is derived for interpreting differential scanning calorimetry curves for solid-state reactions with diffusion-controlled kinetics. The new form yields an analytic expression for temperature at the maximum peak height that is similar to a Kissinger analysis, but that explicitly accounts for laminar, cylindrical, and spherical multilayer system geometries. This expression was used to analyze two reactive multilayer nanolaminate systems, a Zr/CuO thermite and an Ni/Al aluminide, that include systematically varied layer thicknesses. This new analysis scales differential scanning calorimetry (DSC) peak temperatures against sample geometry, which leads to geometry-independent inherent activation energies and prefactors. For the Zr/CuO system, the DSC data scale with the square of the bilayer thickness, while, for the Ni/Al system, the DSC data scale with the thickness. This suggests distinct reaction mechanisms between these systems

Epsilon-near-Zero Modes and Surface Plasmon Resonance in Fluorine-Doped Cadmium Oxide Thin Films

In this report we demonstrate fluorine-doped CdO as a model infrared plasmonic material by virtue of its tunable carrier density, high mobility, and intense extreme-subwavelength plasmon–polariton coupling. Carrier concentrations ranging from 10¹⁹ to 10²⁰ cm^–3, with electron mobility values as high as 473 cm²/V·s, are readily achieved in epitaxial CdO films over a thickness range spanning 50 to 500 nm. Carrier concentration is achieved by reactive sputtering in an Ar/O₂ atmosphere with trace quantities of CF₄. Infrared reflectometry measurements demonstrate the possibility of near-perfect plasmonic absorption through the entire mid-IR spectral range. A companion set of reflectivity simulations are used to predict, understand, and optimize the epsilon-near-zero plasmonic modes. In the context of other transparent conductors, CdO exhibits substantially higher electron mobility values and thus sharp and tunable absorption features. This highlights the utility of high-mobility transparent conducting oxides as a materials system for supporting strong, designed light–matter interactions

Supplementary document for Single-peak and narrow-band mid-infrared thermal emitters driven by mirror-coupled plasmonic quasi-BIC metasurfaces - 6827598.pdf

The Supplemental Material contains details of the multipolar decomposition, discussions on the angular dispersion, numerical analysis of the gas detection application, details of simulation and experiment methods and additional discussions

Highly Conductive and Conformal Poly(3,4-ethylenedioxythiophene) (PEDOT) Thin Films via Oxidative Molecular Layer Deposition

This work introduces oxidative molecular layer deposition (oMLD) as a chemical route to synthesize highly conductive and conformal poly­(3,4-ethylenedioxythiophene) (PEDOT) thin films via sequential vapor exposures of molybdenum­(V) chloride (MoCl₅, oxidant) and ethylene dioxythiophene (EDOT, monomer) precursors. The growth temperature strongly affects PEDOT’s crystalline structure and electronic conductivity. Films deposited at ∼150 °C exhibit a highly textured crystalline structure, with {010} planes aligned parallel with the substrate. Electrical conductivity of these textured films is routinely above 1000 S cm^–1, with the most conductive films exceeding 3000 S cm^–1. At lower temperatures (∼100 °C) the films exhibit a random polycrystalline structure and display smaller conductivities. Compared with typical electrochemical, solution-based, and chemical vapor deposition techniques, oMLD PEDOT films achieve high conductivity without the need for additives or postdeposition treatments. Moreover, the sequential-reaction synthesis method produces highly conformal coatings over high aspect ratio structures, making it attractive for many device applications