Multiscale analysis of Benjamin Franklin's innovations in American paper money.

Benjamin Franklin was a preeminent proponent of the new colonial and Continental paper monetary system in 18th-century America. He established a network of printers, designing and printing money notes at the same time. Franklin recognized the necessity of paper money in breaking American dependence on the British trading system, and he helped print Continental money to finance the American War of Independence. We use a unique combination of nondistractive, microdestructive, and advanced atomic-level imaging methods, including Raman, Infrared, electron energy loss spectroscopy, X-ray diffraction, X-ray fluorescence, and aberration-corrected scanning transmission electron microscopy, to analyze pre-Federal American paper money from the Rare Books and Special Collections of the Hesburgh Library at the University of Notre Dame. We investigate and compare the chemical compositions of the paper fibers, the inks, and fillers made of special crystals in the bills printed by Franklin's printing network, other colonial printers, and counterfeit money. Our results reveal previously unknown ways that Franklin developed to safeguard printed money notes against counterfeiting. Franklin used natural graphite pigments to print money and developed durable "money paper" with colored fibers and translucent muscovite fillers, along with his own unique designs of "nature-printed" patterns and paper watermarks. These features and inventions made pre-Federal American paper currency an archetype for developing paper money for centuries to come. Our multiscale analysis also provides essential information for the preservation of historical paper money.

Switchable wetting of oxygen-evolving oxide catalysts.

The surface wettability of catalysts is typically controlled via surface treatments that promote catalytic performance. Here we report on potential-regulated hydrophobicity/hydrophilicity at cobalt-based oxide interfaces with an alkaline solution. The switchable wetting of single particles, directly related to their activity and stability towards the oxygen evolution reaction, was revealed by electrochemical liquid-phase transmission electron microscopy. Analysis of the movement of the liquid in real time revealed distinctive wettability behaviour associated with specific potential ranges. At low potentials, an overall reduction of the hydrophobicity of the oxides was probed. Upon reversible reconstruction towards the surface oxyhydroxide phase, electrowetting was found to cause a change in the interfacial capacitance. At high potentials, the evolution of molecular oxygen, confirmed by operando electron energy-loss spectroscopy, was accompanied by a globally thinner liquid layer. This work directly links the physical wetting with the chemical oxygen evolution reaction of single particles, providing fundamental insights into solid-liquid interfacial interactions of oxygen-evolving oxides.

Oxygen Evolution Reaction in Ba0.5Sr0.5Co0.8Fe0.2O3-δ Aided by Intrinsic Co/Fe Spinel-Like Surface.

Among the perovskites used to catalyze the oxygen evolution reaction (OER), Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) exhibits excellent activity which is thought to be related to dynamic reconstruction at the flexible perovskite surface due to accommodation of large amount of oxygen vacancies. By studying the local structure and chemistry of BSCF surfaces, in detail, via a range of transmission electron microscopy (TEM) methods, we show that the surfaces of the as-synthesized BSCF particles are Co/Fe rich, and remarkably, adopt a spinel-like structure with a reduced valence of Co ions. Post-mortem and identical location TEM analyses reveal that the Co/Fe spinel-like surface retains a stable chemical environment of the Co/Fe ions, although its structure weakens after electrochemical processing. Further, it is verified that prior to the onset of OER, the Co/Fe spinel-like surface promotes the formation of the highly active Co(Fe)OOH phase, which enhances the OER electrocatalytic properties of the underlying conductive BSCF perovskite. This study provides a detailed understanding of the fundamental transformations that oxide catalysts undergo during electrochemical processes and can aid in the development of novel oxide catalysts with enhanced activity.

Correlative spectroscopy of silicates in mineralised nodules formed from osteoblasts.

Silicon supplementation has been shown to play an important role in skeleton development, however, the potential role that silicon plays in mediating bone formation, and an understanding of where it might localise in the resulting bone tissue remain elusive. An improved understanding of these processes could have important implications for treating pathological mineralisation. A key aspect of defining the role of silicon in bone is to characterise its distribution and coordination environment, however, there is currently almost no information available on either. We have combined a sample-preparation method that simultaneously preserved mineral, ions, and the extracellular matrix (ECM) with secondary ion mass spectroscopy (SIMS) and electron energy-loss spectroscopy (EELS) to examine the distribution and coordination environment of silicon in murine osteoblasts (OBs) in an in vitro model of bone formation. SIMS analysis showed a high level of surface contamination from polydimethysiloxane (PDMS) resulting from sample preparation. When the PDMS was removed, silicon compounds could not be detected within the nodules either by SIMS or by energy dispersive X-ray spectroscopy (EDX) analysis. In comparison, electron energy-loss spectroscopy (EELS) provided a powerful and potentially widely applicable means to define the coordination environment and localisation of silicon in mineralising tissues. We show that trace levels of silicon were only detectable from the mineral deposits located on the collagen and in the peripheral region of mineralised matrix, possibly the newly mineralised regions of the OB nodules. Taken together our results suggest that silicon plays a biological role in bone formation, however, the precise mechanism by which silicon exerts its physicochemical effects remains uncertain. Our analytical results open the door for compelling new sets of EELS experiments that can provide detailed and specific information about the role that silicates play in bone formation and disease.

The origin of long-period lattice spacings observed in iron-carbide nanowires encapsulated by multiwall carbon nanotubes.

Structures comprising single-crystal, iron-carbon-based nanowires encapsulated by multiwall carbon nanotubes self-organize on inert substrates exposed to the products of ferrocene pyrolysis at high temperature. The most commonly observed encapsulated phases are Fe3C, α-Fe, and γ-Fe. The observation of anomalously long-period lattice spacings in these nanowires has caused confusion since reflections from lattice spacings of ≥ 0.4 nm are kinematically forbidden for Fe3C, most of the rarely observed, less stable carbides, α-Fe, and g-Fe. Through high-resolution electron microscopy, selective area electron diffraction, and electron energy loss spectroscopy we demonstrate that the observed long-period lattice spacings of 0.49, 0.66, and 0.44 nm correspond to reflections from the (100), (010), and (001) planes of orthorhombic Fe3C (space group Pnma). Observation of these forbidden reflections results from dynamic scattering of the incident beam as first observed in bulk Fe3C crystals.With small amounts of beam tilt these reflections can have significant intensities for crystals containing glide planes such as Fe3C with space groups Pnma or Pbmn.