News Article | May 27, 2017
A large team of researchers from MIT, Harvard University, and Sandia National Laboratories has scored a major advance toward building practical quantum computers. The work, which is described in the current Nature Communications, offers a new pathway toward using diamonds as the foundation for optical circuits—computer chips based on manipulating light rather than electric current, basically. Pushing beyond the quantum computing hype and, perhaps, misinformation, we're still faced with a largely theoretical technology. Engineering a real quantum computer is hard because it should be hard. What we're attempting to do is harness a highly strange and even more so fragile property of the quantum world, which is the ability of particles to occupy seemingly contradictory physical states: up and down, left and right, is and isn't. If we could just have that property in the same sense that we can have a basic electronic component like a transistor, we'd be set. But maintaining and manipulating qubits, the units of information consisting of simultaneous contradictory particle states, is really hard. Just looking at a quantum system means disrupting it, and, if that system happened to be encoding information, the information is lost. The almost-perfect lattice structure of atoms in a diamond offers a promising foundation for a quantum circuit. Here, a qubit is stored within a "defect" within the diamond. Every so often within the neatly ordered confines of a diamond, an atom will be missing. In this vacancy, another atom might sneak in to replace the missing carbon atom. This diamond defect may in turn have some free electrons associated with it, and it's among these particles that information is stored (while information is transmitted around the diamond as photons, or light particles). Crucially, this little swarm of electrons naturally emits light particles that are able to mirror the quantum superposition (the particle or particle system in multiple states). This is then a way of retrieving information from the qubit without disturbing it. The challenge is in finding and implementing the ideal replacement for the carbon atom in the diamond lattice. This replacement is known as a dopant. This is where the new study comes in. The most-studied dopant for diamond-defect optical circuits is nitrogen. It's stable enough to maintain the requisite quantum superposition, but is limited in the frequencies of light that it can emit. It's like having a perfect encryption system that can nonetheless only represent like a quarter of the alphabet. The dopant explored in the new research is silicon. Silicon atoms embedded into a diamond lattice are able to emit much narrower wavelength bands. It's like they have a higher-resolution. But the cost of being able represent information with more precision are more precarious quantum states. Consequently, the diamonds have to be kept at very near absolute-zero temperature. Nitrogen states, meanwhile, can withstand heat up to about four degrees above absolute zero. In either case, we're not exactly talking about quantum laptops. The researchers were able to implant silicon defects into diamonds via a two-step process involving first blasting the diamond with a laser to create vacancies and then heating the diamond way up to the point that the vacancies start to move around the lattice and bond with silicon atoms. The result is a lattice with an impressively large number of embedded silicon atoms that are exactly where they should be within the structure. The result is a promising pathway toward reliable fabrication of "efficient light–matter interfaces based on semiconductor defects coupled to nanophotonic devices." The stuff of a quantum computer, in other words.
News Article | May 23, 2017
Dennis L. Siebers, PhD, a retired diesel researcher at Sandia National Laboratories, has been named the 2017 recipient of the John Johnson Award for Outstanding Research in Diesel Engines. He was recently presented with the award at the WCX 17: SAE World Congress Experience in Detroit. Established in 2008 and honoring Dr. John H. Johnson, a Presidential Professor with the Department of Mechanical-Engineering Mechanics at Michigan Technological University (MTU), this award recognizes an outstanding leader whose professional career has focused on advancing the field of diesel engines. In addition, the award recognizes technical innovations through experimental studies and modeling research of the engine, fuel and/or after treatment systems. Dr. Siebers, of Livermore, Calif., was a researcher and leader in the engine combustion research program at Sandia’s Combustion Research Facility for 38 years. His research led to new understanding of diesel combustion and the structure and development of diesel fuel jets, and new facilities and techniques for exploring diesel combustion. From 2002-2014, Dr. Siebers managed Sandia’s Engine Combustion Research Program. During his career, Dr. Siebers provided technical management support to DOE’s advanced engine research programs and related university projects, and led a consortium of 15 engine and energy companies and six national laboratories on advanced engine combustion research. He has authored or co-authored more than 80 papers, receiving several best papers awards from SAE International, ASME, and the Combustion Institute Dr. Siebers is a fellow of both SAE International and the American Society of Mechanical Engineers. He was the recipient of the Distinguished Achievement Award from the Department of Energy for lifetime achievement in the field of engine research. He holds a doctorate degree in mechanical engineering from Stanford University. Dr. John Johnson is a fellow of SAE International and the American Society of Mechanical Engineers. His experience spans a wide range of analysis and experimental work related to advanced engine concepts, emissions studies, fuel systems and engine simulation. Prior to joining MTU, he was a Project Engineer at the U.S. Army Tank Automotive Center and Chief Engineer of Applied Engine Research at International Harvester Company. SAE International is a global association committed to being the ultimate knowledge source for the engineering profession. By uniting over 127,000 engineers and technical experts, we drive knowledge and expertise across a broad spectrum of industries. We act on two priorities: encouraging a lifetime of learning for mobility engineering professionals and setting the standards for industry engineering. We strive for a better world through the work of our philanthropic SAE Foundation, including programs like A World in Motion® and the Collegiate Design Series™.
Leung K.,Sandia National Laboratories
Chemistry of Materials | Year: 2017
Density functional theory and ab initio molecular dynamics simulations are applied to investigate the migration of Mn(II) ions to above-surface sites on spinel LixMn2O4 (001) surfaces, the subsequent Mn dissolution into the organic liquid electrolyte, and the detrimental effects on graphite anode solid electrolyte interphase (SEI) passivating films after Mn(II) ions diffuse through the separator. The dissolution mechanism proves complex; the much-quoted Hunter disproportionation of Mn(III) to form Mn(II) is far from sufficient. Key steps that facilitate Mn(II) loss include concerted liquid/solid-state motions; proton-induced weakening of Mn-O bonds forming mobile OH- surface groups; and chemical reactions of adsorbed decomposed organic fragments. Mn(II) lodged between the inorganic Li2CO3 and organic lithium ethylene dicarbonate (LEDC) anode SEI components facilitate electrochemical reduction and decomposition of LEDC. These findings help inform future design of protective coatings, electrolytes, additives, and interfaces. © 2016 American Chemical Society.
Taatjes C.A.,Sandia National Laboratories
Annual Review of Physical Chemistry | Year: 2017
The carbonyl oxide intermediates in the ozonolysis of alkenes, often known as Criegee intermediates, are potentially important reactants in Earth's atmosphere. For decades, careful analysis of ozonolysis systems was employed to derive an understanding of the formation and reactions of these species. Recently it has proved possible to synthesize at least some of these intermediates separately from ozonolysis, and hence to measure their reaction kinetics directly. Direct measurements have allowed new or more detailed understanding of each type of gas-phase reaction that carbonyl oxides undergo, often acting as a complement to highly detailed ozonolysis experiments. Moreover, the use of direct characterization methods to validate increasingly accurate theoretical investigations can enhance their impact well beyond the set of specific reactions that have been measured. Reactions that initiate particles or fuel their growth could be a new frontier for direct measurements of Criegee intermediate chemistry. ©2017 by Annual Reviews. All rights reserved.
Thurmer K.,Sandia National Laboratories |
Nie S.,Sandia National Laboratories
Proceedings of the National Academy of Sciences of the United States of America | Year: 2013
From our daily life we are familiar with hexagonal ice, but at very low temperature ice can exist in a different structure-that of cubic ice. Seeking to unravel the enigmatic relationship between these two low-pressure phases, we examined their formation on a Pt (111) substrate at low temperatures with scanning tunneling microscopy and atomic force microscopy. After completion of the onemolecule- thick wetting layer, 3D clusters of hexagonal ice grow via layer nucleation. The coalescence of these clusters creates a rich scenario of domain-boundary and screw-dislocation formation. We discovered that during subsequent growth, domain boundaries are replaced by growth spirals around screw dislocations, and that the nature of these spirals determines whether ice adopts the cubic or the hexagonal structure. Initially, most of these spirals are single, i.e., they host a screw dislocation with a Burgers vector connecting neighboring molecular planes, and produce cubic ice. Films thicker than ~20 nm, however, are dominated by double spirals. Their abundance is surprising because they require a Burgers vector spanning two molecular-layer spacings, distorting the crystal lattice to a larger extent. We propose that these double spirals grow at the expense of the initially more common single spirals for an energetic reason: they produce hexagonal ice.
Agency: Department of Defense | Branch: Navy | Program: STTR | Phase: Phase II | Award Amount: 911.40K | Year: 2016
During Phase I and Phase II, M4 Engineering, Inc. and Sandia National Laboratories have created a unique bonded joint analysis methodology and associated software. During Phase II.5, the developed techniques will be further enhanced and a fully functional commercial analysis code (SIMULIA/Abaqus) plug-in will be created. The software plug-in will make the advanced technology accessible to all levels of practicing engineers via integrated pre- and post-processing modules. The technology is based upon a world class nonlinear constitutive equation for polymers developed over a decade at Sandia. A two-pronged approach consisting of concise surrogate models (i.e., traction-separation interface models) for design and analysis and high fidelity models that can be used along with experimental data for surrogate model parameterization will provide the Navy a comprehensive bond modeling method. During Phase I and Phase II, ductile and brittle adhesives for metal bonding have been studied. The upcoming Phase II.5 work will include looking at an additional adhesive, as well as composite substrates. Hence, a key part of this work will also include an experimental program to populate the high fidelity models and validate the surrogate traction-separation models.
Stavila V.,Sandia National Laboratories |
Talin A.A.,Sandia National Laboratories |
Allendorf M.D.,Sandia National Laboratories
Chemical Society Reviews | Year: 2014
Metal-organic frameworks (MOFs) are a class of hybrid materials with unique optical and electronic properties arising from rational self-assembly of the organic linkers and metal ions/clusters, yielding myriads of possible structural motifs. The combination of order and chemical tunability, coupled with good environmental stability of MOFs, are prompting many research groups to explore the possibility of incorporating these materials as active components in devices such as solar cells, photodetectors, radiation detectors, and chemical sensors. Although this field is only in its incipiency, many new fundamental insights relevant to integrating MOFs with such devices have already been gained. In this review, we focus our attention on the basic requirements and structural elements needed to fabricate MOF-based devices and summarize the current state of MOF research in the area of electronic, opto-electronic and sensor devices. We summarize various approaches to designing active MOFs, creation of hybrid material systems combining MOFs with other materials, and assembly and integration of MOFs with device hardware. Critical directions of future research are identified, with emphasis on achieving the desired MOF functionality in a device and establishing the structure-property relationships to identify and rationalize the factors that impact device performance. This journal is © the Partner Organisations 2014.
Sheps L.,Sandia National Laboratories
Journal of Physical Chemistry Letters | Year: 2013
We present the time-resolved UV absorption spectrum of the B̃ ( 1A′) ← X̃ (1A′) electronic transition of formaldehyde oxide, CH2OO, produced by the reaction of CH2I radicals with O2. In contrast to its UV photodissociation action spectrum, the absorption spectrum of formaldehyde oxide extends to longer wavelengths and exhibits resolved vibrational structure on its low-energy side. Chemical kinetics measurements of its reactivity establish the identity of the absorbing species as CH2OO. Separate measurements of the initial CH2I radical concentration allow a determination of the absolute absorption cross section of CH2OO, with the value at the peak of the absorption band, 355 nm, of σabs = (3.6 ± 0.9) × 10-17 cm2. The difference between the absorption and action spectra likely arises from excitation to long-lived B̃ (1A′) vibrational states that relax to lower electronic states by fluorescence or nonradiative processes, rather than by photodissociation. © 2013 American Chemical Society.
Leonard F.,Sandia National Laboratories |
Talin A.A.,U.S. National Institute of Standards and Technology
Nature Nanotechnology | Year: 2011
Existing models of electrical contacts are often inapplicable at the nanoscale because there are significant differences between nanostructures and bulk materials arising from unique geometries and electrostatics. In this Review, we discuss the physics and materials science of electrical contacts to carbon nanotubes, semiconductor nanowires and graphene, and outline the main research and development challenges in the field. We also include a case study of gold contacts to germanium nanowires to illustrate these concepts. © 2011 Macmillan Publishers Limited. All rights reserved.
Leung K.,Sandia National Laboratories
Journal of Physical Chemistry C | Year: 2013
We review recent ab initio molecular dynamics studies of electrode/electrolyte interfaces in lithium ion batteries. Our goals are to introduce experimentalists to simulation techniques applicable to models which are arguably most faithful to experimental conditions so far, and to emphasize to theorists that the inherently interdisciplinary nature of this subject requires bridging the gap between solid and liquid state perspectives. We consider liquid ethylene carbonate (EC) decomposition on lithium intercalated graphite, lithium metal, oxide-coated graphite, and spinel manganese oxide surfaces. These calculations are put in the context of more widely studied water-solid interfaces. Our main themes include kinetically controlled two-electron-induced reactions, the breaking of a previously much neglected chemical bond in EC, and electron tunneling. Future work on modeling batteries at atomic length scales requires capabilities beyond state-of-the-art, which emphasizes that applied battery research can and should drive fundamental science development. © 2012 American Chemical Society.