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Exploratory Development of Theoretical Methods

FWP/Project Description: 
Project Leader(s):
 
Principal Investigators:
Vladimir Antropov, Viatcheslav Dobrovitski, Bruce Harmon, Kai-Ming Ho, Costas Soukoulis

The scope of this project is to generate new theories, models, and algorithms that will be beneficial to the research program at Ames Laboratory and to the mission of DOE. The need to make quantitative theoretical predictions and to obtain detailed agreement between theory and experiment are crucial for the design, characterization, and control of complex materials. This project focuses on the development of theoretical tools which will be used to study a broad range of problems in physics, materials science, and chemical as well as biological systems.

Research subtasks in this project will include:

  • Methods for accurate calculation of strongly correlated electron systems.
  • Methods for large scale atomistic simulation of complex structures & materials.
  • Methods for studying the dynamics of non-equilibrium or nonlinear systems.

Extraordinary Responsive Rare Earth Magnetic Materials

FWP/Project Description: 
Project Leader(s):
 
Principal Investigators:
Scott Chumbley, Karl Gschneider, Jr.

A major goal of this research is to uncover the underlying electronic, atomic and microscopic interactions that result in an extraordinarily strong coupling between the magnetic and crystal lattices and remarkable responsiveness to both strong (temperature and pressure) and weak (magnetic field) stimuli in some rare earth intermetallic materials. It will be achieved by focusing on the state-of-the-art synthesis, processing and characterization, combined with theory, modeling and computations gauged and refined against reliable experimental data.

The following systems have been selected as model candidates: GdNi and other equiatomic RM compounds (R is a rare earth metal and M is a 3d transition metal or a main Group 14 element), RCo2, La(Fe1‑xSix)13 and hydrides La(Fe1‑xSix)13Hy, and R5T4 compounds (T is a main Group 14 element). These materials exhibit a number of diverse and unique properties associated with magnetic ordering alone, magneto-volume, itinerant electron metamagnetic, and magnetic-martensitic transformations, respectively, which may or may not be driven by a reversible breaking and reforming of specific chemical bonds.

Development and validation of phenomenological models of transformations that range from magneto-volume to magnetic-martensitic is another goal, thus guiding future discoveries of material systems exhibiting strong reactions to small changes of magnetic field, with temperature and pressure providing additional sources of stimulation.

Innovative & Complex Metal-Rich Materials

FWP/Project Description: 
Project Leader(s):
 
Principal Investigators:
Qisheng Lin, Srinivasa Thimmaiah

The goal of this project is the discovery and understanding of new, complex metal-rich solids. The effort brings together two solid-state chemists (Corbett, Miller) and a surface chemist (Thiel) to address fundamentals of designing and perfecting atom- and energy-efficient synthetic methods for new, complex metal-rich materials. These materials provide rich potential for new thermoelectrics, magneto-responsive processes, molecular storage, and coatings. This research team combines expertise in high-temperature synthesis, diffraction and structural analysis, ultra-high vacuum science, electronic structure theory, and surface characterization to study complex bulk and surface structures. The strength of the scientific components is demonstrated by past work on bulk structure and surfaces of quasicrystals, and on bulk Zintl phases. If successful, this project will uncover a wealth of new solid-state phases, and develop general principles for understanding their stability and properties, both bulk and surface.

The highly-interwoven topics in this project are:

  • To discover and design new materials. Our strategy is to combine experiment, viz. exploratory synthesis and temperature-dependent structure determinations, with electronic structure theory to uncover and ultimately design new families of intermetallic phases and to understand the factors that stabilize both new and known phases. In the next three years, for example, we will elucidate precise atomic distributions in complex intermetallic phases, e.g., gamma-brass structures incorporating 3d elements, e.g., Pd-Zn-Al and Mn-Ga-Sn, and quasicrystal approximants, that will establish chemical guidelines for designing new ternary systems, especially those showing quasiperiodicity and potentially interesting itinerant magnetism. We will also investigate how relativistic effects influence and control structure, bonding, and stabilities of intermetallic phases that incorporate 6th period elements, e.g., distinguishing Hg from Tl in BaHg2Tl2 and the new families of gold cluster networks (J. Corbett, G. Miller).
  • To understand surface stability and surface properties of complex metal-rich solids. We will experimentally investigate microscopic and mesoscopic morphology, atomic locations, interfacial growth, friction, and chemical reactivity of Pd-Zn-Al quasicrystals. We will apply the tools developed for the bulk phases, to obtain and understand the surfaces. As an example, theoretical aids for understanding stability, structural features and chemical bonding of complex intermetallic systems will be developed. (P. Thiel, J. Corbett, G. Miller).
  • To establish structure-property relationships. We will establish these for complex metal-rich materials in the bulk and at their surfaces as related to both fundamental as well as practical issues, e.g., thermoelectrics, magnetocalorics, hydrogen storage, tribology, and structural behavior. In the next three years, we will study insertion of interstitial atoms, e.g., hydrogen in La-Al phases, or lattice substitution of selected heteroatoms. (J. Corbett, P. Thiel).

Metamaterials

FWP/Project Description: 
Project Leader(s):
 
Principal Investigators:
Thomas Koschny, Jigang Wang

The objective of this project is to obtain a better understanding of the physics of metamaterials, particularly left-handed materials. This project collectively has been, and continues to be, a prime mover and initiator of the development of left-handed materials, characterized by a negative index of refraction. This revolutionary concept originally prompted objections, based on perceived violations of causality, momentum conservation, and Fermat’s principle. This controversy is now settled, mainly through the work of this project, clearing the way for the following objectives to be addressed.

  • Modeling and simulation tools
  • Three-dimensionality
  • Chirality
  • Losses
  • Gain and nonlineraity

The work in this project will have deep impact on the BES Grand Challenge "how do we design and perfect atom- and energy-efficient syntheses of revolutionary new forms of matter with tailored properties?" and in current optical technologies, such as nanophotonics, optical communications, optical imaging, and optical circuitry. In addition, the novel nanofabrication and advanced characterization techniques involved in this program can be readily transferred to other DOE-related programs.

Magnetic Nanosystems: Making, Measuring, Modeling and Manipulation

FWP/Project Description: 
Project Leader(s):
 
Principal Investigators:
Viatcheslav Dobrovitski, Xikui Fang, Bruce Harmon, Myron Hupalo, Yongbin Lee, Michael Tringides, David Vakin, Jigang Wang
 
This effort is concerned with magnetism as manifested and controlled at the meso- and nano-scale.  The program engages in basic research to discover new magnetic materials with unique, useful and controllable/tunable properties. There are comprehensive efforts in synthesis, characterization as well as theory and computation.  The focus is on detection, interrogation, control, and applications of spins in confined geometries at and out of equilibrium. The effort ranges from growth and characterization of complex magnetic molecules, magnetic islands on surfaces, to studying individual defects and solids where spatially - limited spin degrees of freedom can have profound consequences on bulk properties, as in the FeAs superconductors.  The major goals are to discover the magnetic material suitable for control and interrogation at the nanoscale, in order to gain both fundamental new knowledge, and also to exploit that knowledge.  A major effort is put on establishing novel measurement techniques, such as nitrogen-vacancy-centers – based optical magnetometry, magneto-optics, ultrafast optics and spin-polarized low - temperature STM capable of measuring the transport properties at the nano- and meso-scales.
 
Subtasks in this project are:
  • Development of “NV – nanoscope”
  • Growth, characterization and functionalization of magnetic nanostructures
    • Magnetic nanoislands on graphene
    • Quantum size effects (QSE) in magnetic systems
    • X-ray spectroscopy of magnetic nanoislands
    • Correlating nanoisland magnetization with growth mode
    • ​​Ultrafast spin dynamics in uniform height metal islands
    • Metallic islands as electronic junctions in molecular spintronics
  • Chemical Synthesis and Functionalization
    • Hybridization of carbon nanotubes and polyoxometalate-based molecular magnets
    • Deposition of magnetic molecules onto metal/metal oxide surfaces
    • Magnetic molecules in ultra–high magnetic field
  • Theoretical effort
    • Studies of quantum dynamics and decoherence in few- and many-spins systems. Application of quantum spins, such as nitrogen-vacancy centers in diamond, for advanced sensing at nanoscale.
    • Density functional theory to study magnetic properties of magnetism in confined geometries

Novel Materials Preparation & Processing Methodologies

FWP/Project Description: 
Project Leader(s):
 
Principal Investigators:
Lawrence Jones, Evgenii Levin, Yong Liu, Thomas Lograsso, R. William McCallum, Qingfeng Xing (Sam)

The growth, control and modification of novel materials in single crystal and polycrystalline form, represent a national core competency that is essential for scientific advancement within and across traditional disciplinary boundaries, and are critical components of the Basic Energy Sciences’ mission. In support of this mission, the Novel Materials Preparation and Processing Methodologies FWP focuses on developing synthesis protocols for energy-relevant materials that contain volatile, reactive or toxic components such as the rare earth metals, Mg-based and RE containing thermoelectric alloys and Fe-As based superconductors.  The objective of Novel Materials is to advance the ability to synthesize and characterize high purity, high quality materials, primarily in single crystal form; to quantify and control processing-structure-property relationships between chemical inhomogeneities and structural defects and  functionality of highly responsive materials; to develop unique capabilities and processing knowledge in the preparation, purification, and fabrication of metallic elements and alloys. Single crystals are often required to achieve scientific understanding of the origin of various phenomena, whether from intrinsic or extrinsic origins, to elucidate its properties as well as to evaluate a material’s full functionality.

FY 2014 Major Program Achievements:  

  • We developed an inverted-temperature-gradient method to grow large and high-quality single crystals of Ba1-xKxFe2As2. When setting the upper zone as the cold zone, on cooling the nucleation initiates from the surface layer of the liquid melt. The crystallization, proceeding from the top of a liquid melt, helps to expel impurity phases during crystal growth compared to the growth inside the flux.  High vapor pressure of K and As elements at the soaking temperature is also an important factor in the growth of single crystals of Ba1-xKxFe2As2. By allowing crystallization of the free surface first, evaporative losses are minimized eliminating large macrosegregation along the crystal and ensuring control of target compositions. High soaking temperature, fast cooling rate, and an adjusted temperature window of the growth are necessary to obtain single crystals of heavily K-doped crystals (0.65< x<0.92) with sharp transition. Findings were published: Y. Liu, M.A. Tanatar, W.E. Straszheim, B. Jensen, K.W. Dennis, R.W. McCallum, V.G. Kogan, R. Prozorov, and T.A. Lograsso, Physical Review B, 89, 134504 (2014). http://dx.doi.org/10.1103/PhysRevB.89.134504
  • In the efforts on studying solidification behaviors and phase space of potential thermoelectric materials made of earth-abundant and non-toxic elements, Mg-Si based materials have been selected.  While finest microstructure on nanometer scale can be achieved by fast cooling, the microstructure is thermally instable.  The phase space of pseudo binary Mg2Si-Mg2Sn system has been elucidated. A method to prepare single crystalline diffusion couples of air-sensitive materials by hot-pressing has been established.

  • Utilizing the high pressure Bridgman furnace we have for the first time synthesized single crystals of Zn-bearing Fe-Ga alloys. We have grown bcc Fe-Ga-Zn single crystals up to 4.6% Zn in a Bridgman furnace under elevated pressure (15 Bar) in order to overcome the high vapor pressure of Zn and obtain homogeneous crystals. Single-crystal measurements of magnetostriction and elastic constants allow for the direct comparison of the magnetoelastic coupling constants of Fe-Ga-Zn with other magnetoelastic alloys. The partial substitution of Ga with Zn (see figure) yields comparable values for the magnetoelastic coupling factor, –b1, to those of the binary Fe-Ga alloys.

Photonic Systems

FWP/Project Description: 
Project Leader(s):
 
Principal Investigators:
Rana Biswas, Viatcheslav Dobrovitski, Kai-Ming Ho, Costas Soukoulis

The goal of this project is to learn to control the flow of light and the conversion of light energy into other forms of energy (and vice versa). This project is fundamental physics research that supports the mission of DOE in the areas of energy-efficient lighting, efficient solar energy utilization, and thermophotovoltaics. Research in this Project can be grouped into two sub-tasks.

Photonic Crystal Physics
Photonic band gap materials are artificially designed periodic dielectric or metallic structures with high refractive-index contrast that can be used to control light (photons) in a manner similar to that used by semiconductors to control electrons. Although this research project originated from theoretical work, its emphasis now is on physical manifestations and tests of the theory. Over the next three years research goals within this subtask will focus on:

  • Wide area fabrication of photonic crystal and polymer waveguide structures using reasonable-cost soft lithography techniques. (K. Constant, W. Leung, K.-M. Ho)
  • Study of fundamental photonic crystal properties including tailored thermal emission, beam steering and focusing. (R. Biswas, K. Constant, C. Soukoulis, W. Leung, K.-M. Ho)
  • Development of highly efficient algorithms for design and study of devices using photonic crystals. Extension of techniques to study non-linear systems or systems with gain as well as the effects of disorder/fabrication defects on the performance of photonic crystal structures. (C. Soukoulis, K.-M. Ho)

Organic Semiconductor Physics
The goal of this subtask is to provide the fundamental physics underpinning necessary to understand and optimize the performance of organic light-emitting devices (OLEDs) at both low and high brightness. More specifically, the goal is to elucidate the interactions (particularly the spin-dependent interactions) between singlet excitons (SEs), triplet excitons (TEs), polarons, bipolarons, and trions, as they impact the optical and transport properties of these materials and devices. For example, our past experimental work has revealed the central role of TEs and polarons in quenching the SEs, thus decreasing the photoluminescence quantum yield of the films and the internal quantum efficiency of OLEDs. Indeed, these quenching processes are now recognized as the source of the decreasing efficiency of OLEDs at high injection current.

Over the next three years research within this subtask will focus on fundamental studies on novel OLED structures, including n-stacked (tandem) OLEDs, graded junction OLEDs, and hybrid polymer/small molecular OLEDs. (J. Shinar)

Structures and Dynamics in Condensed Systems

FWP/Project Description: 
Project Leader(s):
 
Principal Investigators:
Alan Goldman, Kai-Ming Ho, Andreas Kreyssig, Mikhail Mendelev, Ralph Napolitano, Ryan Ott, Xueyu Song, Cai-Zhuang Wang

This project concentrates on developing quantitative, self-consistent structural descriptions of liquid and amorphous states in metallic systems. Our research moves beyond static structural descriptions towards a detailed thermodynamic understanding of liquid and amorphous states, consistent with structural models. Binary alloys are emphasized to more accurately describe local structure. Moreover, the capabilities of the Materials Preparation Center are utilized to synthesize high-purity alloys having precise composition control. Experimental methods, atomistic simulations, and fundamental theoretical predictions are integrated for the measurement of structure, chemistry, and macroscopic thermodynamic properties in selected liquid and amorphous Al- and Zr-based model systems.

This project utilizes DOE-supported x-ray and neutron sources to capture structural- and chemically-specific details about short- and medium-range order in disordered systems. In addition, targeted scattering data are used to support efforts to develop highly accurate inter-atomic potentials. Simulation approaches include ab initio, constrained reverse Monte Carlo, and classical molecular dynamics using both pair-wise and, more importantly, many-body inter-atomic potentials, including tight-binding and embedded-atom method approaches. A new "embedded-cluster" method for ab initio calculations is pursued to mitigate the artifacts created by periodic boundary conditions of conventional first-principles methods. Combined with experimental data, simulations ultimately allow us to predict—e.g., changes in temperature, strain, or composition—alterations in local and long-range atomic ordering, leading to different disordered structures or perhaps highly-correlated phase transformations.

Surface Structures Far-from-Equilibrium

FWP/Project Description: 
Project Leader(s):
 
Principal Investigators:
Kai-Ming Ho, Myron Hupalo, Patricia Thiel, Cai-Zhuang Wang

This project focuses on low dimensional surface structures (ultrathin metallic films, islands, wires, etc.), especially in systems exhibiting quantum size effects (QSE). Since such structures are metastable and grown far from equilibrium, it is important to identify the optimal kinetic pathways. In turn, this requires a better understanding of many atomistic processes (e.g. surface diffusion, nucleation, coarsening) that define the kinetic pathway. In addition the properties of the grown structures (e.g. band structure, density-of-states) depend on the structure dimensions. This opens the possibility to control their potential uses in chemical reactivity and energy storage.

This interdisciplinary effort (physics, chemistry) is built upon a close interaction between theorists (Wang, Ho) and experimentalists (Tringides, Thiel, Hupalo). The scientists with the project have a strong background in film growth, coarsening, diffusion, nucleation, and overlayer structure analysis.

This projects objectives include:

  • Kinetics of growth. Certain systems with QSE exhibit anomalously fast aggregation kinetics, i.e. deposited atoms assemble very quickly into islands. We study and model the “window” in temperature and coverage parameter space where QSE-driven self organization is possible. These data are modeled to extract the controlling barriers. This understanding will be used to search for other systems where height uniformity exists.
  • QSE and chemisorption. We test the effect of QSE on chemisorption in several systems, using both experiment (STM/STS, XPS, HRLEED) and theory. These systems include oxygen and hydrocarbons on Ag nanostructures on Si(111); and oxygen and hydrogen on Pb and Mg nanostructures.

Development of an AccuTOF-DART™ Database of Potential Toxins, Drugs and Other Substances for Use by Forensic Laboratories

FWP/Project Description: 

This project has three phases.  The first will seek to determine the needs for the database and what data already exist.  The second will work to build the database and begin to populate the database.  The third will seek to test the database in a larger population of DART-TOF users and to disseminate the database to these users.  As DART-TOF is a very new technology, the field is very dynamic, necessitating that all involved with the project be flexible and consider other as yet unknown applications and needs.

FUNDING SOURCE:

Research Triangle Institute

FOR MORE INFORMATION:

John McClelland

E-mail: mcclelland@iastate.edu

Phone: (515) 294-7948

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