Division Of Medical Sciences Research Articles

(Invited) Electrocatalysis of Ammonia Oxidation Reaction on Pt(100) in Alkaline Solutions

The oxidation of ammonia is an essential process in the nitrogen cycle, with important applications in energy conversion ("ammonia electrolysis"), environmental protection (removal of ammonia from waste streams), electrosynthesis (hydroxylamine production via nitrate or nitric oxide reduction) or sensors (ammonia sensors for a wide range of applications). The conversion of ammonia to nitrogen gas, which is the desirable process in most of these applications, is typically difficult to achieve even though N2 is thermodynamically the most favorable product. Among the three basal planes of platinum, Pt(100) is unique in converting ammonia selectively to nitrogen. This presentation deals with the mechanism of the ammonia oxidation on the Pt(100) single-crystal electrode in alkaline solutions, investigated by basic electrochemical methods coupled with in-situ infrared spectroscopy and online electrochemical mass spectrometry. Our study particularly focuses on the nature of the adsorbed intermediate species and thereby on their role in the N-N coupling and in the observed deactivation. Acknowledgments This research was supported by a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme to Ioannis Katsounaros under Award IOF-327650, and by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division.

Complications of transcatheter aortic valve implantation (TAVI): how to avoid and treat them

Motor neurone disease (MND) is a disorder with a complex aetiology, marked phenotypic variability and malignant progression. Our research program is multidisciplinary and takes place within the Division of Medical...

A Synoptic Review of the 1968 National Research Council Progress Report on Forensic Pathology

In 1968, a “Committee on Pathology” existed within the National Academy of Sciences/National Research Council, Division of Medical Sciences. This group appointed an “ad hoc Committee on Forensic Pathology.” The Committee on Pathology prepared a progress report in April of 1968, and the ad hoc Committee on Forensic Pathology prepared a report in November of 1968. James Luke retained copies of these documents, which were reviewed to prepare this summary article of their content. Many of the issues and concerns raised in these reports remain today. Legal medicine and forensic pathology education in medical school is severely lacking. Exposure of pathology residents to a quality rotation in forensic pathology is deficient in many areas. Affiliations between death investigation offices and medical schools is highly variable and in need of improvement. Research and publication in forensic pathology occurs but needs to be bolstered. There are not enough forensic pathologists to meet the needs of the justice, public health, and public safety communities. Forensic pathology salaries remain non-competitive in many areas. It is difficult to recruit and retain forensic pathologists in the field. There remain practicing forensic pathologists who are not board-certified. Although television shows and movies have increased awareness about death investigation, they have not resulted in significant public or governmental appreciation and support for what forensic pathologists contribute to society. Progress has been made, but forensic pathology still has a long way to go.

The truth in complexes: perspectives on ion channel signaling nexuses in the nervous system.

Leigh A. Swayne*, Christophe Altier and Gerald W. Zamponi 1 Island Medical Program, Division of Medical Sciences, University of Victoria, Victoria, BC, Canada 2 Department of Biology, University of Victoria, Victoria, BC, Canada 3 Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada 4 Department of Physiology and Pharmacology, University of Calgary, Calgary, AB, Canada *Correspondence: lswayne@uvic.ca

All is about Medicinal Product Dictionary

a Department of Pharmacy, Geneva University Hospitals, Geneva, Switzerland b School of Pharmaceutical Sciences, University of Geneva, University of Lausanne, Geneva, Switzerland c International Organization for Standardization Technical Committee 215, Working Group 6 (Pharmacy and Medicines Business) d GS1 Healthcare e Division of Medical Information Sciences, Geneva University Hospitals and University of Geneva, Switzerland

HVPE로 성장된 GaN의 용융 KOH/NaOH 습식화학에칭

Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea*UNIMO Photron, Seoul 137-063 Korea(Received June 10, 2014)(Revised July 7, 2014)(Accepted July 18, 2014)Abstract The hydride vapor phase epitaxy (HVPE) grown GaN samples to precisely measure the surface characteristicswas applied to a molten KOH/NaOH wet chemical etching. The etching rate by molten KOH/NaOH wet chemical etchingmethod was slower than that by conventional etching methods, such as phosphoric and sulfuric acid etching, which may bedue to the formation of insoluble coating layer. Therefore, the molten KOH/NaOH wet chemical etching is a betterefficient method for the evaluation of etch pits density. The grown GaN single crystals were characterized by using X-raydiffraction (XRD) and X-ray rocking curve (XRC). The etching characteristics and surface morphologies were studied byscanning electron microscopy (SEM). From etching results, the optimum etching condition that the etch pits were wellindependently separated in space and clearly showed their shape, was 410

Higher-K Formation in Atomic Layer Deposited Hf1-XAlxOy

As Si metal oxide semiconducting field effect transistors have continued to scale, SiO2-based gate dielectric and polySi gates have been successfully replaced by high-k dielectrics and metal gate at the 45nm technology node and beyond. In order to continue scaling, improvements of key film properties of the high-k dielectric, such as k-value and leakage current, are needed. The electrical properties of HfO2-based dielectrics may be enhanced by structural modifications, since the k-value is dependent on the crystalline phase (monoclinic k=16, tetragonal k=70 and cubic =29) [1]. HfO2 films typically crystallize into the monoclinic phase, which is its most thermodynamically stable phase [2,3]. Alloying HfO2 with other oxides such as ZrO2, TiO2, Al2O3offer a viable option towards engineering the crystalline phase.In this regards, we have deposited 40 cycles of Hf1-xAlxOy films by atomic layer deposition with Al/(Hf+Al)% ranging from 0 to 25%. A set of samples were annealed under N2 at temperatures ranging from 680 oC to 800oC and compared to the as deposited samples. To investigate the crystallinity of the films, we performed grazing incidence in-plane X-ray diffraction (GIIXRD) on the annealed films and in-situ XRD during an anneal process using synchrotron radiation was used to determine the crystallization temperature (Tc) for the unannealed films. The GIIXRD measurements revealed the presence of non-monoclinic peaks which was also confirmed by the in-situ anneal XRD measurements. The crystallization temperature of the non-monoclinic phase obtained from the in-situ anneal XRD is plotted in Fig.1, where it is shown that higher Al/(Hf+Al)% results in higher Tc. In order to resolve the non-monoclinic phase, extended X-ray absorption fine structure (EXAFS) at was utilized. The EXAFS measurement combined with GIIXRD showed the ALD Hf1-xAlxOy films crystallize into a mixture of the tetragonal and monoclinic phases. The electrical properties were investigated by MOS capacitors with ALD TiN as the metal gate. The electrical measurements show a reduction in EOT after post deposition anneal (PDA). In addition, the leakage current was also reduced by a factor of 10 while maintaining a flat-band voltage that is comparable to PDA HfO2 films under identical conditions. The C-V plots of the as deposited samples and annealed samples are shown in Fig. 2 and Fig.3 respectively. We also investigated the effect of different thermal budgets on the Hf1-xAlxOy films. A ~2Å EOT reduction with lower gate leakage was obtained for devices with post deposition anneal near the crystallization temperature of the Hf1-xAlxOyfilms. However, the electrical performance is degraded for devices with higher or lower post deposition anneal temperature than the films’ crystallization.In summary, we have successfully deposited ALD Hf1-xAlxOy. The crystal phase was confirmed to be a mixed phase of tetragonal with monoclinic. The data shows an enhancement in electrical properties near the crystallization temperature of the Hf1-xAlxOyfilms. Acknowledgements Diffraction measurements were carried out at NSLS (X20A and X20C), BNL, which is supported by the DOE, Division of Materials Sciences and Division of Chemical Sciences, under Contract No. DE-AC02-98CH10886.

Pt Monolayer Shell on Hollow Pd Core Electrocatalysts: Scale up Synthesis, Structure, and Activity for the Oxygen Reduction Reaction

The rapidly increasing demand for fossil fuels used in transportation and power generation, and their detrimental environmental effects, have resulted in a wide-spread challenge for the development of renewable energy technologies. Fuel cells are one of the most promising clean energy technologies, particularly attractive for automobile applications, due to their high efficiency, high energy density, and low or zero emissions. The most challenging problem of their application is the slow kinetics of oxygen reduction reaction (ORR) at fuel cell cathodes, even on Pt - the best single element electrocatalyst, which causes a large loss of the cell voltage, resulting in significant efficiency loss. In addition, Pt dissolves under certain operating condition of fuel cells. To mitigate these two drawbacks, catalysts containing large amounts of expensive Pt are required. This is one of the main reasons for the slow commercialization of fuel cells.To address these drawbacks, the use of Pt monolayer (PtML) electrocatalysts was proposed to reduce the cost of Pt while attempting to enhance their ORR activity and stability [1, 2]. Such catalysts, consisting of a monolayer of Pt on a substrate of another material, minimize the amount of Pt while ensuring that all Pt atoms are available at the surface for catalytic activity [1, 2]. Additionally, through geometric and electronic interactions with the substrate [3, 4], a PtMLcan change its electronic properties and be more active and durable than pure Pt electrocatalysts.Several single crystal surfaces, including Pd (111), Ru (0001), Ir (111), Rh (111), and Au (111) have been investigated as supports for PtML catalysts for the ORR [5]. Variations in ORR activity could be accounted for by the oxygen binding energy, which must be tuned to intermediate strength. This leads to a classic catalysis ‘volcano plot’ of ORR activity vs. oxygen binding energy with PtMLon Pd(111) on the top of the volcano plot having higher ORR activity than Pt(111) [5].Since oxygen binding energy appears to be the major descriptor of the ORR kinetics, DFT calculations suggests that further enhancement in ORR activity of PtML on Pd could be accomplished by weakening the O and OH binding energies [5]. This could be achieved by additional contraction of the PtML shell. A hollow core is an interesting structure to investigate geometric interaction between the PtML shell and the core because a hollow core may induce a desirable lattice contraction of a PtML, leading to improved ORR activity by reducing the oxygen binding energy.In this contribution, the synthesis, characterization and kinetics of the ORR of a PtMLshell on Pd(hollow), or Pd-Au(hollow) core electrocatalysts are reported. Comparisons between the ORR catalytic activity of the electrocatalysts with hollow cores and those of Pt solid and Pt hollow nanoparticles were obtained using the rotating disk electrode technique. Hollow nanoparticles were made using Ni or Cu nanoparticles as sacrificial templates. The Pt ORR specific and mass activities of the electrocatalysts with hollow cores were found to be considerably higher than those of the electrocatalysts with solid cores, Fig. 1. This enhanced Pt activity is attributed to the smooth surface morphology and hollow-induced lattice contraction. In addition, the hollow particles have a mass-saving geometry.AcknowledgmentWork at Brookhaven National Laboratory is supported by US Department of Energy, Division of Chemical Sciences, Geosciences and Biosciences Division, under the Contract No. DE-AC02-98CH10886. The work at BNL was supported by the US Department of Energy, Office of Basic Energy Science, Division of Materials Science and Engineering, under Contracts No. DE-AC02-98CH10886. DB thanks the MICINN, Spain (MAT2010-20442 and MAT2011-28673-C02-01) for FPU grant.

Magnetic Excitations in the Kondo Insulator SmB6

SmB6 is a Kondo insulator with surface conductivity that was recently proposed to be topologically protected. I shall describe an inelastic neutron scattering experiment probing magnetic excitations over a wide energy range in a single crystal of SmB6 at low temperatures. Consistent with previous findings by Alekseev et al., a resonant mode near 14 meV is observed at low temperatures near the X and R points of the Brillouin zone. The overall dispersion of the excitation is less than 1 meV. The intensity falls of rapidly in higher Brillouin zones as the 5d electron form factor. The comprehensive inelastic scattering data provide indirect information about the underlying, putative topological, hybridized band structure. Work at IQM was supported by the U.S. Department of Energy, office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-08ER46544. Work at ORNL was supported by LDRD 06576.

Magnetic quasicrystals: Current Status and Open Questions

The magnetic properties of quasicrystals have been the subject of intense theoretical and experimental interest since Dan Shechtman's discovery of icosahedral quasicrystals in 1982 [1]. The first generation of Al-TM (TM = 3d transition metal) quasicrystals with moment bearing elements, such as Al-Mn and Al-Pd-Mn, provided some insight into the fate of magnetism in quasiperiodic systems: only a small fraction of the Mn ions carry a moment and these moments appear to be distributed randomly on the quasilattice. The discovery of the Zn-Mg-R and Cd-Mg-R (R = rare earth) quasicrystals with sizeable local moments that interact via indirect exchange (i.e. the RKKY interaction) reinvigorated the search for long-range magnetic order in the icosahedral phase. However, to date, all of the known quasicrystals with moment bearing elements exhibit frustration and spin-glass-like behavior at low temperature. The recent discovery of binary magnetic quasicrystals in the R-Cd system [2] is particularly exciting because their closely related crystalline approximants, RCd6, exhibit long-range antiferromagnetic order at low temperature [3] permitting a detailed investigation of the effects of aperiodicity on magnetic interactions in this system. Here, I will describe the status of investigations of the R-Cd quasicrystals and RCd6 approximants with regard to their structural and magnetic properties. This research was supported by the Office of the Basic Energy Sciences, Materials Sciences Division, US Department of Energy (DOE).

Materials and Physics Challenges for Spin Transfer Torque Magnetic Random Access Memories

Spin transfer torque (STT) is a process by which a dc current of spin polarized electrons exerts a torque on the magnetization density in a magnetic medium [1]. STT can make the magnetization in a patterned structure unstable and switch between two stable magnetization states. The basic principle behind STT random access memories (STT-MRAM) is to use magnetic tunnel junctions (MTJs) with two thin magnetic layers separated by a thin insulating layer. In one magnetic layer, (the fixed layer) the magnetization has a fixed direction. In the other layer, the free layer or storage layer, the magnetization can be switched between parallel and antiparallel with the magnetization in the fixed layer with corresponding low and high resistance through the tunneling magnetoresistive effect.It has long been recognized that STT-MRAMs can be used as storage-class memory [2]. By using STT to write, stray fields causing unwanted writes on neighboring devices are eliminated. There is nothing that fundamentally prohibits MTJs to be scaled down to below 20 nm size, and the processing is compatible with Si technology. 64 Mbyte STT-MRAM chips are indeed now manufactured by Everspin [3], but there are great challenges that need to be overcome to realize STT-MRAM storage-class memories. The purpose of this talk is to highlight some of these challenges from a materials and physics perspective.One challenge is related to the current that is needed to write. Enough current has to be supplied by a Si-MOSFET transistor. As the current scales with the channel width, a large current requires a large transistor, which sets a lower limit on the footprint of the device. A large write current also impacts the reliability of the device: a moderately large write current degrades the device over time, while a much larger current still may cause a dielectric breakdown in the thin insulating barrier in the MTJ [4]. Therefore, a substantial effort has gone into either device designs or materials development that may allow for a low enough write current that the device can operate reliably while writing with certainty. As an example, dual-MTJs consisting of two insulating barriers have been proposed as means of reducing the required write current [5]. An issue here is that it is very difficult to manufacture arrays of dual MTJs with sufficiently narrow distributions of resistance in both high and low resistance states because of the way the materials in an MTJ grow on one another, and the restrictions on materials sets and crystallinity required for sufficiently high magnetoresistive ratios.Current available STT-MRAM use shape anisotropy – elliptical devices – with the magnetization in the plane of the ellipse to produce stable magnetization states along the long axes of the ellipse. This leads to large variabilities due to process variations. One way to decouple the energy barrier that gives stability from process variation is to use perpendicular anisotropy [6,7], in which the magnetization points out of the plane of the layers (Fig. 1). This gives rise to other challenges such as finding materials with sufficient anisotropy that can be manufactured, are stable, and give rise to high enough tunneling magnetoresistance.In addition to these, and other, materials challenges, there are issues that are beginning to emerge for small magnetic elements. The required write current is in a simple theory proportional to the intrinsic magnetic damping, so reducing the damping reduces the write current. Recent research [8] has shown that damping in nanoscale magnetic elements is highly dependent on size and the dynamical mode of the magnetization. This necessitates a fundamental understanding of the actual inhomogeneous and incoherent motion of the magnetization during reversal, and in addition also a better understanding of the fundamental coupling between spin-polarized conduction electrons and inhomogeneous magnetization motion or spin wave modes.Part of this work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division. Argonne National Laboratory is operated under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC.

Electrocatalytic Pathways for Oxygen Reduction and Evolution in Aqueous and Non Aqueous Electrolytes

Oxygen reduction (ORR) and evolution reaction (OER) at an electrochemical interface has important connotations with several key technologies ranging from the use of oxygen depolarized cathodes in chlorine generation to fuel cells, electrolyzers, water treatment, hybrid batteries (including Li/Air) and even life support. In all the decades of research conducted in a wide range of pH (aqueous) and non aqueous electrolytes some very interesting threads have emerged pointing to revolutionary materials development. For example, recent advances in our understanding of alternative active sites for oxygen reduction has provided for the basis of its molecular design. This presentation will put these developments in the context of more than two decades of effort devoted to engendering such non noble metal electrocatalysts. In this presentation we will present our latest data on the most active analogs which comprise of a FeNx coordinated active site in close concert with Fe nano-particles either present in some polymer composite or more ideally as edge defects close to the Fe-Nx coordinated structure. We will show how these active sites evolve on carbon supports as graphene defect structures. Such active site determinations are made with the use of a special in situ synchrotron x-ray absorption method using the near edge spectra referred to as x-ray absorption near edge structure (XANES), in a subtractive mode wherein the signal contribution from the bulk is successfully subtracted from the effect of the surface adsorbed species. When combined with our ability to simulate the same signatures using models with specifically adsorbed moieties, a powerful tool emerges to study electrochemical interfaces under actual in situ and operando conditions. This technique, commonly called the ‘Delta Mu (Dμ) Technique’ has been applied to a wide variety of transition metal surfaces and alloys[i],[ii] including non-Pt based metal electrocatalysts with element specificity. EXAFS data taken concurrently provide information on the changes in short range atomic order around the absorber atom thereby providing structural information such as bond distances and coordination numbers (thereby information on average cluster size, homogeneity and surface segregation etc.). In this presentation among other things we will provide a picture of the electrocatalytic pathways in aqueous (at both the extreme edges of the pH scale) and non-aqueous environments. In the latter, our prior efforts to understand the effect of electrolyte both in terms of solvent[iii] and choice of salt will be presented in terms of engendering inner our outer sphere charge transfer[iv] during ORR and OER reactions. The technological consequence of such materials in power generation, electrolysis and energy storage will be described. Acknowledgement. The authors deeply appreciate the financial assistance from the Army Research Office (Single Investigator award, W911NF-09-1) and the Department of Energy (EERE, DE-EE-000459). Authors also express their thanks to the Department of Energy, Materials Science Division for building and maintaining the National Synchrotron Light Source, in Brookhaven National Laboratory, Upton, NY.[i] Contrast to Metal Ligand Effects on PtnM Electrocatalysts with M equal to Ru vs. Mo and Sn as Exhibited by in situ XANES and EXAFS Measurements in Methanol’, F. C. Scott, S. Mukerjee, and D. E. Ramaker, J. Phys. Chem. C., 114, 442 (2010). [ii] ‘Electrochemical Kinetics and X-ray Absorption Spectroscopic Investigation of Oxygen Reduction on Chalcogen-Modified Ru Catalysts in Alkaline Medium’, N. Ramaswamy, R. J. Allen and S. Mukerjee, J. Phys. Chem. C., 115, 12650 (2011).[iii] ‘Oxygen Reduction Reactions in Ionic Liquids and the Formulation of General ORR Mechanism for Li-Air Batteries,’ C. J. Allen, H. Hwang, R. Kautz, S. Mukerjee, E. J. Plichta, M. A. Hendrickson and K. M. Abraham, J. Phys. Chem. C., 116, 20755 (2012). [iv] Influence of Inner and Outer Sphere Electron Transfer Mechanisms during Electrocatalysis of Oxygen in Alkaline Medium’, N. Ramaswamy and S. Mukerjee, J. Phys. Chem. C., 115, 18015 (2011).

Understanding Individual Defects in CdTe Solar Cells: From Atomic Structure to Electrical Activity

1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA 2 Department of Chemistry, Vanderbilt University, Nashville, TN, USA 3 Department of Physics and Astronomy, The University of Toledo, Toledo, OH, USA 4 Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, USA 5 Department of Materials, University of Oxford, Oxford, OX13PH, UK 6 SuperSTEM Laboratory, Daresbury, WA44AD, UK 7 School of Materials, University of Manchester, Manchester, M139PL, UK

Influence of Hydrocarbon and CO2 on the Reversibility of Li-O2 Chemistry: An in Situ Ambient Pressure X-Ray Photoelectron Spectroscopy Study

Influence of Hydrocarbon and CO2 on the Reversibility of Li-O2 Chemistry: An in Situ Ambient Pressure X-Ray Photoelectron Spectroscopy Study

“Brick-and-Mortar” Self-Assembly Synthesis of Electrode Architectures

Carbonaceous materials usually have a better electronic conductivity than metal oxides for meeting requirements in high-rate capability applications. However, both carbonaceous and metal-oxide materials suffer slow lithium diffusion rates within the corresponding electrode materials. This deficiency limits the high-rate capability for a number of electrode materials. Herein, we report an one-step “brick-and-mortar” self-assembly synthesis of carbon and oxide composites as anode materials for lithium ion batteries. The objective of this work is to demonstrate that mesoporous carbons and oxides derived from soft-template synthesis not only entail a high storage capacity but also, most importantly, can be made through a “brick and mortar” self-assembly synthesis to have a significantly enhanced electronic conductivity. This enhanced electronic conductivity in 3D architectures is the key to providing high rate capability.The main part of this work was supported by the U.S. Department of Energy’s Office of Basic Energy Science, Division of Materials Sciences and Engineering, under contract with UT-Battelle, LLC.

Invited Presentation: Probing Local Ionic Dynamics in Functional Oxides: From Nanometer to Atomic Scales

Vacancy-mediated electrochemical reactions in oxides underpin multiple applications ranging from electroresistive non-volatile memory and neuromorphic logic devices memories, to chemical sensors and electrochemical gas pumps, to energy conversion systems such as fuel cells. Understanding the functionality in these systems requires probing reversible (oxygen reduction/evolution reaction) and irreversible (cathode degradation and activation, formation of conductive filaments) electrochemical processes. In this talk, I summarize recent advances in probing and controlling these transformations locally on nanometer level using scanning probe microscopy. The localized tip concentrates the electric field in the nanometer scale volume of material, inducing local transition. Measured simultaneously electromechanical response (piezoresponse) or current (conductive AFM) provides the information on the bias-induced changes in material. Here, I illustrate how these methods can be extended to study local electrochemical transformations, including vacancy dynamics in oxides such as titanates, La x Sr1-x CoO3, and Y x Zr1-x O2. The formation of electromechanical hysteresis loops and their bias-, temperature- and environment dependences provide insight into local electrochemical mechanisms and can be directly linked to the defect chemistry. In materials such as lanthanum-strontium cobaltite, mapping both reversible vacancy motion and vacancy ordering and static deformation is possible, and can be corroborated by post mortemSTEM/EELS studies. In ceria, a broad gamut of electrochemical behaviors is observed as a function of temperature and humidity. The possible strategies for elucidation of origins of ionic motion at the electroactive interfaces in oxides using high-resolution electron microscopy and combined ex-situ and in-situ STEM-SPM studies are discussed. In the second part of the talk, probing electrochemical phenomena on in-situ grown surfaces with atomic resolution is illustrated.Research supported (SVK) by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division and partially performed at the Center for Nanophase Materials Sciences, a DOE-BES user facility.

Elucidation of Electrode-Electrolyte Interfaces Using Neutrons

This presentation will describe experimental characterization of the thickness and composition of the reaction products on silicon anode materials and aluminum current collectors measured using neutron reflectometry. NR is a neutron scattering technique highly sensitive to morphological and compositional changes occurring across surfaces and interfaces, including buried interfaces. It can be used to study such changes over lengths scales extending 1 nm to hundreds-of-nanometers. Neutrons, by virtue of their nature, are deeply penetrating and therefore ideally suited as a probe to study materials in complicated environments, such as electrochemical cells. Unlike x-rays, neutrons interact with the nuclear potential of constituent element and are sensitive to light elements like Li and H.We will show that the SiOx surface of silicon materials react irreversibly with the electrolyte 1.2M LiPF6-3:7 wt% ethylene carbonate:dimethyl carbonate. The reaction product is a complex mixture of Si-O-F-C species. It is dense and homogenous and has a thickness of about 3.5 nm. Similar reaction chemistry is observed for Al current collectors. Insights from these measurements will provide a framework to understand capacity losses with cycling of high energy density materials.Acknowledgement: This research was supported by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy under contract with UT-Battelle, LLC (LB, GMV). This Research at Oak Ridge National Laboratory's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U. S. Department of Energy.

Dopant Based Stabilization of LiCoO2: Insight from First-Principles Calculations

LiCoO2 is widely used as cathode material for Li-ion batteries (1). However, the usable specific capacity of LiCoO2 is limited to approximately half of its theoretical capacity. This limitation comes from the mechanical failure of the cathode when more than 50% of Li is deintercalated. The stability of LiCoO2 and its electrochemical performance can be improved by coating its surface with inner metal oxides (2). Such approach has been used for different cathode materials, but the origin of the stabilization effect is poorly understood. The enhanced stability of the cathodes has been rationalized invoking many effects, e.g., i) the inner metal oxides act as a physical barrier to prevent cathode-electrolyte reactions (3), and ii) the layered structure of the cathode material is stabilized by the migration of metal ions from the coating oxides (1). To have a better understanding of the stabilization mechanism, we have performed Density Functional Theory calculations of LiCoO2doped with inner metal ions (Figure 1). Such calculations allow us to study how the migration of metal ions from the coating oxides modify the structure of the cathode materials. Acknowledgments.Research supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. Reference: 1. H. Li, Z. Wang, L. Chen, and X. Huang, Adv. Mater., 21, 4593–4607 (2009).2. Z. Chen, Y. Qin, K. Amine, and Y.-K. Sun, J. Mater. Chem., 20, 7606–7612 (2010).3. J.-S. Kim et al., J. Electrochem. Soc., 151, A1755–A1761 (2004). Figure 1. Schematic of some possible sites for metal dopants in LiCoO2: the left and central panels show the dopant on Li and Co sites, respectively, and the right panel shows substitution on both Li and Co sites.

First Principles Modeling of Metal Nanoislands on Metal Substrates

The catalytic activity of metal-supported metal nanoparticles and overlayers is known to differ from that of the corresponding bulk surfaces (1, 2). Moreover, metal-supported metal nanoparticles exhibit a higher reactivity than their overlayer counterparts (1). Differences in reactivity between bulk and overlayered surfaces arise from lattice strain and ligand effects. Yet, these effects do not suffice for rationalizing the high reactivity of such systems. Thus other aspects of metal-supported nanoparticles are often invoked, e.g., particle size, the density of low-coordinated atoms, and the direct involvement of the substrate in a catalytic cycle. However, a concise rationalization of these aspects has been inhibited, in part, due to the lack of systematic computational studies on metal-supported metal nanoparticles.Recently, we explored geometric, energetic, and electronic properties of metal-supported Pd and Pt clusters employing small triangular model species (3, 4). Such small clusters are far from realistic metal-supported metal nanoparticles that feature diameters of a few nanometers (1). Yet, comparison of Au- and Cu-supported Pt3 and Pd3 clusters with the corresponding monoatomic overlayers brought insights into the electronic properties of larger metal-supported planar metal clusters, i.e., monolayer nanoislands. We found the d-band centers, relative to the Fermi energy, of Au-supported Pt3 and Pd3 clusters to be similar to those of the corresponding overlayers. In contrast, the d-band centers of the same clusters on Cu are ~1 eV closer to the Fermi energy than those of the corresponding overlayers (3). The difference arises from a compensation of counteracting effects in Au-supported Pt3 and Pd3clusters and the corresponding overlayers: lateral interactions (intra-layer coordination) vs. strain due to the support (3). These effects result in downward and upward shifts, respectively, of the d-band centers of monolayer nanoislands on Au surfaces as the size of the islands increases. For similar systems on Cu, both lateral interactions and compressive strain effects shift the d-band centers of nanoislands downward only (3).We have extended our calculations to study nanoislands of hexagonal shape and nanoscale diameters (Figure 1). We systematically explore how geometric and energetic properties of these systems behave as function of size. The results will help, on the one hand, in rationalizing the observed high reactivity of metal-supported metal nanoparticles, and on the other hand, in assessing the accuracy of full overlayers as models of supported nanoparticles. Acknowledgments. J.A.S. work was supported by a research fellowship of the Alexander von Humboldt Foundation and in part by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. Reference: 1. H. Wolfschmidt, O. Paschos and U. Stimming, in Fuel Cell Science: Theory, Fundamentals, and Biocatalysis, A. Wieckowski and J. K. Nørskov Editors, p. 1, Wiley, Chichester, U.K. (2010).2. L. A. Kibler, Electrochimica Acta, 53, 6824 (2008).3. J. A. Santana and N. Rösch, Journal of Physical Chemistry C, 116, 10057 (2012).4. J. A. Santana and N. Rösch, Physical Chemistry Chemical Physics, 14, 16062 (2012). Figure 1. Planar models of metal-supported nanoislands with increasing diameter.

Sovent-Free Synthesis of Lithium Intercalated Graphites Using Thermal or Mechanical Reactors

The intercalation of lithium into graphite is an important process for energy storage devices. The industrial route of intercalation is electrolysis in pre-assembled Li-ion batteries with excess Li loading in the cathode. This has a number of disadvantages: increased battery processing time, mass and volume (from needing excess Li loading), and parallel formation of a solid-electrolyte interphase (SEI). The later is difficult to control and is a major factor in the battery's overall performance and cost. An alternative is to prepare the anode with partially lithiated graphite prior to electrolyte contact. As far as we know this has not been demonstrated. Each step – lithiation of graphite followed by making slurry with binder – presents added complications with the reactive anode powder, but it offers compelling advantages such as, increase in "usable" Li, control of SEI formation, and decreased battery processing time. These advantages may also lead to battery performance and lifetime. Also, it would also allow for investigations into spontaneous formation of SEI, which may provide insight into producing an effective artificial SEI.As reported in the literature, LiC x has been chemically synthesized viacontact with lithium vapor and compression with lithium metal. Both of these has a flaw: graphite reaction with Li vapor is kinetically unfavored due to the low vapor pressure of Li and it is difficult to control the stoichiometry; the compression method has been shown to produce the important stages (I–IV) but it is slow, taking 24 h. Here we present two solvent-free and compression-free methods that can produce stage I or stage II lithiated graphites. The thermal method heats graphite and lithium powders to ca. 300 °C under ultrahigh vacuum (UHV) for 24 h. The mechanical method involves ball-milling the two powders together under ultra-high purity Ar(g) atmosphere for 1 h.Both processes work with different types of graphite sources and we compare the two synthetic methods using a battery-grade mesophase graphite. The products were characterized by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). We show that while the mechanical reactor seems to lithiate the graphite more quickly, it may affect the morphology. Hard carbon fibers were also lithiated using the mechanical reactor. We compare the stability of the LiC6made using mesophase graphite and carbon fiber.XRD and NMR are used to follow the delithiated of the products when in contact with a non-zero moisture environment. It was found that a surface passivation layer is formed that protects intercalated lithium. We also report open-circuit potential (OCP) and electrochemical impedance spectroscopy measurements of the products in contact with standard Li-ion battery electrolyte. These results are used to discuss the spontaneous formation SEI at the LiC6interface. Figure 1: SEM images of a) stabilized lithium metal powder; b) carbon fiber, Pyrograf I; c) MGPA; d) ball-milled lithiated-MGPA. e)X-ray diffractogram of mechanically synthesized lithiated MGPA. Inset is log-scaled expansions of regions in green boxes. (o) raw graphite; (*) LiC12; (†) LiC6.Research was supported by the Fluid Interface Reactions, Structures, and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (RLS, NJD). XPS analysis was done with support of the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division (GMV). The authors thank Applied Science, Inc. for samples of the Pyrograf I carbon fibers and Pred Materials International for the MGPA.