Barnaby D. A. Levin

Characterization of reactively sputtered c-axis aligned nanocrystalline InGaZnO4

Crystallinity and texturing of RF sputtered c-axis aligned crystal InGaZnO4 (CAAC IGZO) thin films were quantified using X-ray diffraction techniques. Above 190 °C, nanocrystalline films with an X-ray peak at 2θ = 30° (009 planes) developed with increasing c-axis normal texturing up to 310 °C. Under optimal conditions (310 °C, 10% O2), films exhibited a c-axis texture full-width half-maximum of 20°. Cross-sectional high-resolution transmission electron microscopy confirmed these results, showing alignment variation of ±9° over a 15 × 15 nm field of view and indicating formation of much larger aligned domains than previously reported. At higher deposition temperatures, c-axis alignment was gradually lost as polycrystalline films developed.

Rapid electron transfer by the carbon matrix in natural pyrogenic carbon

Surface functional groups constitute major electroactive components in pyrogenic carbon. However, the electrochemical properties of pyrogenic carbon matrices and the kinetic preference of functional groups or carbon matrices for electron transfer remain unknown. Here we show that environmentally relevant pyrogenic carbon with average H/C and O/C ratios of less than 0.35 and 0.09 can directly transfer electrons more than three times faster than the charging and discharging cycles of surface functional groups and have a 1.5 V potential range for biogeochemical reactions that invoke electron transfer processes. Surface functional groups contribute to the overall electron flux of pyrogenic carbon to a lesser extent with greater pyrolysis temperature due to lower charging and discharging capacities, although the charging and discharging kinetics remain unchanged. This study could spur the development of a new generation of biogeochemical electron flux models that focus on the bacteria–carbon–mineral conductive network.

Nanomaterial datasets to advance tomography in scanning transmission electron microscopy

Electron tomography in materials science has flourished with the demand to characterize nanoscale materials in three dimensions (3D). Access to experimental data is vital for developing and validating reconstruction methods that improve resolution and reduce radiation dose requirements. This work presents five high-quality scanning transmission electron microscope (STEM) tomography datasets in order to address the critical need for open access data in this field. The datasets represent the current limits of experimental technique, are of high quality, and contain materials with structural complexity. Included are tomographic series of a hyperbranched Co2P nanocrystal, platinum nanoparticles on a carbon nanofibre imaged over the complete 180° tilt range, a platinum nanoparticle and a tungsten needle both imaged at atomic resolution by equal slope tomography, and a through-focal tilt series of PtCu nanoparticles. A volumetric reconstruction from every dataset is provided for comparison and development of post-processing and visualization techniques. Researchers interested in creating novel data processing and reconstruction algorithms will now have access to state of the art experimental test data.

Direct growth of germanium and silicon nanowires on metal films

We describe the basic thermodynamic and kinetic aspects that govern the growth of Si and Ge nanowires directly on bulk metal films. We illustrate essential differences between the vapour–solid–solid and the conventional vapour–liquid–solid nanowire growth. Ge and Si nanowires were formed on a select set of metal films including Ag, Al, Au, Cr, Cu and Ni. Metals that form silicides or germanides (Cr, Cu, and Ni) generally yield higher quality nanowires compared to nanowires grown on metal films whose equilibrium phases are defined by alloyed phases below eutectic temperatures (Al, Ag, Au). Combinatorial experiments presented here provide new basic insights into nanowire formation in the context of metal germanide and silicide formation rates. The mechanism established from our experiments successfully predicts the nanowire growth under a broad range of conditions and also predicts the nanowire growth on other metals to provide guidance to future progress in nanowire synthesis.

Characterization of Sulfur and Nanostructured Sulfur Battery Cathodes in Electron Microscopy Without Sublimation Artifacts

Lithium sulfur (Li-S) batteries have the potential to provide higher energy storage density at lower cost than conventional lithium ion batteries. A key challenge for Li-S batteries is the loss of sulfur to the electrolyte during cycling. This loss can be mitigated by sequestering the sulfur in nanostructured carbon-sulfur composites. The nanoscale characterization of the sulfur distribution within these complex nanostructured electrodes is normally performed by electron microscopy, but sulfur sublimates and redistributes in the high-vacuum conditions of conventional electron microscopes. The resulting sublimation artifacts render characterization of sulfur in conventional electron microscopes problematic and unreliable. Here, we demonstrate two techniques, cryogenic transmission electron microscopy (cryo-TEM) and scanning electron microscopy in air (airSEM), that enable the reliable characterization of sulfur across multiple length scales by suppressing sulfur sublimation. We use cryo-TEM and airSEM to examine carbon-sulfur composites synthesized for use as Li-S battery cathodes, noting several cases where the commonly employed sulfur melt infusion method is highly inefficient at infiltrating sulfur into porous carbon hosts.

Characterizing Sulfur in TEM and STEM, with Applications to Lithium Sulfur Batteries

The lithium sulfur (Li-S) battery is a promising technology with the potential to provide greater energy density at lower cost than current lithium ion batteries. One of the main challenges to improving the performance of Li-S batteries is the dissolution and loss of sulfur to the electrolyte as the battery is cycled [1]. Recently much effort has focused on nanostructured electrodes that could sequester the sulfur and prevent its loss during battery operation. Analyzing the distribution of sulfur in these electrodes is critical for creating durable Li-S batteries with high energy density.

Systematic Optimization of Battery Materials: Key Parameter Optimization for the Scalable Synthesis of Uniform, High-Energy, and High Stability LiNi0.6Mn0.2Co0.2O2 Cathode Material for Lithium-Ion Batteries

Ni-rich LiNixMnyCo1-x-yO2 (x > 0.5) (NMC) materials have attracted a great deal of interest as promising cathode candidates for Li-ion batteries due to their low cost and high energy density. However, several issues, including sensitivity to moisture, difficulty in reproducibly preparing well-controlled morphology particles and, poor cyclability, have hindered their large scale deployment; especially for electric vehicle (EV) applications. In this work, we have developed a uniform, highly stable, high-energy density, Ni-rich LiNi0.6Mn0.2Co0.2O2 cathode material by systematically optimizing synthesis parameters, including pH, stirring rate, and calcination temperature. The particles exhibit a spherical morphology and uniform size distribution, with a well-defined structure and homogeneous transition-metal distribution, owing to the well-controlled synthesis parameters. The material exhibited superior electrochemical properties, when compared to a commercial sample, with an initial discharge capacity of 205 mAh/g at 0.1 C. It also exhibited a remarkable rate capability with discharge capacities of 157 mAh/g and 137 mAh/g at 10 and 20 C, respectively, as well as high tolerance to air and moisture. In order to demonstrate incorporation into a commercial scale EV, a large-scale 4.7 Ah LiNi0.6Mn0.2Co0.2O2 Al-full pouch cell with a high cathode loading of 21.6 mg/cm2, paired with a graphite anode, was fabricated. It exhibited exceptional cyclability with a capacity retention of 96% after 500 cycles at room temperature. This material, which was obtained by a fully optimized scalable synthesis, delivered combined performance metrics that are among the best for NMC materials reported to date.

Simultaneous Quantification of Electron Transfer by Carbon Matrices and Functional Groups in Pyrogenic Carbon

Pyrogenic carbon contains redox-active functional groups and polyaromatic carbon matrices that are both capable of transferring electrons. Several techniques have been explored to characterize the individual electron transfer process of either functional groups or carbon matrices individually. However, simultaneous analysis of both processes remains challenging. Using an approach that employs a four-electrode configuration and dual-interface electron transfer detection, we distinguished the electron transfer by functional groups from the electron transfer by carbon matrices and simultaneously quantified their relative contribution to the total electron transfer to and from pyrogenic carbon. Results show that at low to intermediate pyrolysis temperatures (400-500 °C), redox cycling of functional groups is the major mechanism with a contribution of 100-78% to the total electron transfer; whereas at high temperatures (650-800 °C), direct electron transfer of carbon matrices dominates electron transfer with a contribution of 87-100%. Spectroscopic and diffraction analyses of pyrogenic carbon support the electrochemical measurements by showing a molecular-level structural transition from an enrichment in functional groups to an enrichment in nanosized graphene domains with increasing pyrolysis temperatures. The method described in this study provides a new analytical approach to separately quantify the relative importance of different electron transfer pathways in natural pyrogenic carbon and has potential applications for engineered carbon materials such as graphene oxides.

Detection of CdS Nanoparticles and Implications for Cadmium Yellow Paint Degradation in Edvard Munch’s The Scream (c. 1910, Munch Museum)

1. School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA. 2. Department of Chemistry and Biochemistry & UD Surface Analysis Facility, University of Delaware, Newark, DE, USA. 3. Cornell Center for Materials Research, Cornell University, Ithaca, NY, USA. 4. The Munch Museum, Tøyen, Oslo, Norway. 5. Department of Conservation, Rijksmuseum, Amsterdam, NL. 6. Department of Materials Science and Engineering, University of Delaware, Newark, DE, USA. 7. Kavli Institute for Nanoscale Science, Cornell University, Ithaca, NY, USA.

Reverse Engineering Cadmium Yellow Paint from Munch’s “The Scream” with Correlative 3-D Spectroscopic and 4-D Crystallographic STEM

1. School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA. 2. Department of Chemistry and Biochemistry & UD Surface Analysis Facility, University of Delaware, Newark, DE, USA. 3. Cornell Center for Materials Research, Cornell University, Ithaca, NY, USA. 4. The Munch Museum, Tøyen, Oslo, Norway. 5. Department of Conservation, Rijksmuseum, Amsterdam, NL. 6. Department of Materials Science and Engineering, University of Delaware, Newark, DE, USA. 7. Kavli Institute for Nanoscale Science, Cornell University, Ithaca, NY, USA.