Advanced Materials

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Materials Characterization


graphitic layers viewed at 2 nmCharacterization of materials is a key capability enabling the structure and functionality of materials to be understood, as well as the chemical processes occurring at interfaces, such as those that occur in catalysis, corrosion, and fluid transport. ORNL develops and applies a broad range of electron microscopy and electron spectroscopy techniques to provide insight into the structure and composition of materials at the atomic level. Transmission electron microscopy approaches probe functionalities (electronic structure, magnetism, etc.) and explore materials in operando, using a variety of controlled environments. A variety of scanning probe modalities have been developed to provide both atomic and nanoscale information on materials, including electronic and magnetic behaviors. Chemical imaging, which includes specialized scanning probes combined with optical and mass spectrometry techniques, can provide a wealth of information on chemistry occurring at surfaces. Another area of specializion, atom probe tomography, yields a complete three-dimensional atom-by-atom reconstruction of a specimen. Many of these capabilities are available to the scientific community through the Center for Nanophase Materials Sciences (CNMS) and the Shared Research Equipment (ShaRE) program, both of which are DOE Basic Energy Sciences user facilities. ORNL has state-of-the-art capabilities for examining a range of materials—from geological to biological materials—using nuclear magnetic resonance and mass spectrometry.

In addition to atomic and nanoscale characterization, ORNL has a comprehensive suite of mechanical materials characterization tools, ranging from routine stress/strain testing to specialized nanoindentation techniques used to examine the effects of defects in materials. ORNL also has developed a a suite of characterization techniques specially designed for use in post-irradiation examination of materials. Finally, ORNL is home to two major neutron sources that are utilized for a wide range of different neutron-based materials characterization measurements: the High Flux Isotope Reactor (HFIR) and the Spallation Neutron Source (SNS). These resources are used to study structure of a variety of materials, such as superconductors, advanced alloys and polymers. In addition, many neutron scattering techniques combined with isotopic labeling allow detailed insight into dynamics observed in catalysis, water transport through membranes and lithium transport at battery electrode surfaces. Thus, ORNL has a comprehensive set of characterization tools allowing materials to be understood from the atomic to system level.

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Guidelines Clarify Origins of Ferroelectric Signals
— Recent developments in piezoresponse force microscopy (PFM) and spectroscopy revealed the presence of electromechanical hysteresis loops in a variety of materials including inorganic oxides, polymers and bio systems. This behavior is often (mis)interpreted as evidence of ferroelectricity.

Electron Beam Guides Engineering of Functional Defects
— The electron beam of a scanning transmission electron microscope was applied to generate Se vacancies in a semiconducting monolayer of MoSe2, provide energy to drive the formation and growth of inversion domains and metallic 60˚ grain boundaries, and track the dynamics.

True structure of pnictide 122 superconductors revealed
— High-resolution microscopy revealed an unexpected room-temperature crystal structure of the ‘122’ Ba(Fe1-xCox)2As2 superconductors, with domains similar to those in ferroelectrics but with nanometer size.

Atomic-Scale Observations Aid Mesoscale Catalyst Design
— Two phases of Mo-V-O–based oxides, M1 and M2, are promising catalysts for direct conversion of propane to acrylonitrile and are believed to act synergistically. Researchers engineered the mesoscale structure of M1- and M2-phase oxides to amplify these effects, greatly improving selectivity for propane ammoxidation.

Technique Recovers Atomic Resolution in Spectrum Images
— Researchers have demonstrated a technique for obtaining atomic-resolution information from spectrum images of thick specimens of MnFePSi compounds, which are promising for ecofriendly refrigeration. This technique allows the quantitative examination of specimens for which atomic-resolution spectroscopic analysis was previously impossible.

 
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