Materials Structure and Data Group

Our group combines expertise in all major methods of structure determination, including X-ray and neutron total (Bragg plus diffuse) scattering, various derivations of X-ray and neutron small-angle scattering, X-ray absorption fine structure spectroscopy, diffraction and imaging tools available in a modern transmission electron microscope, spatially-resolved electron energy loss and X-ray energy dispersive spectroscopies, and electron paramagnetic resonance spectroscopy. Experimental measurements are supplemented by first principles calculations of material structure and properties. A strong emphasis is placed on the development of data analysis and structure modeling tools that integrate inputs from multiple measurement techniques and theory to obtaining a comprehensive structural solution across the length scales ranging from sub-nanometer to several nanometers to macroscopic. Additionally, the group develops and maintains the widely used crystallographic and phase equilibria databases.

Software and Data Products

Recent Group Publications

Group Post Doctoral Research Opportunities

The National Research Council sponsors a 2-year fellowship to work at NIST.

Base stipend is $78,592 per year plus benefits and relocation expenses
Application deadlines are Feb. 1 and Aug. 1 of each year
Open to US citizens only

Projects and Programs

Measurement and Prediction of Local Structure

Our goal is to provide analytical tools that allow measurement and prediction of local structure to enable the development of ceramic materials for electronic applications. Under this project, we develop data analysis methods for quantitative determination of local structure from multiple experimental techniques, and theoretical methods for prediction of local atomic configurations from first principles.

Additive Manufacturing of Ceramics

The NIST program seeks to facilitate the commercialization of the ceramics additive manufacturing via the concurrent development of: (1) New measurement approaches to characterize AM processes relevant to ceramic materials, and (2) Computational methods for predictive modeling of an AM workflow, from feedstock to a printed part.

Measurements of Point-Defect Chemistry in Complex Oxides

Project Goal: To develop magnetic resonance, x-ray absorption, electron diffraction, and electrical conductivity measurements to better characterize dilute concentrations of point defects in oxide materials and effectively correlate electro-mechanical properties to measured defect chemistry.

Inorganic Phase Equilibrium Data

Compile and evaluate phase equilibrium data for NIST Standard Reference Database 31 (Phase Equilibria Diagrams); disseminate the data in a readily accessible and searchable format in partnership with the American Ceramic Society.

Ab initio theoretical modeling for predicting structure and properties in advanced materials

We develop first-principles-based methods for prediction of atomic arrangements and properties in advanced materials and develop tools for the prediction and interpretation of experimental x-ray absorption spectra, microscopy images, etc.

Electron-Solid Interactions

This project will develop innovative models and data to validate and guide microscopy measurement accuracy. Fundamental understanding of electron-solid interactions is key to interpreting electron microscopy images for quantitative metrology. Scanning electron microscopy (SEM) is a workhorse in microelectronics manufacturing and development. SEM is used for critical dimension, contour, and roughness metrology and for defect and failure analysis. However, the limitations of today’s physical models for electron-solid interactions directly affect microscopy measurement accuracy.

Sub-nanoscale electron microscopy of complex nanostructures

The aim of this project is to develop robust, quantitative measurement methods utilizing transmission electron microscopy methods for complex, nanostructured devices with nanometer and sub-nanometer spatial resolution.

Multiscale Modeling and Validation of Semiconductor Materials and Devices

A comprehensive understanding of how current and next-generation materials impact the performance of semiconductor devices is critical to U.S. Semiconductor Manufacturing. This project will develop qualitative and quantitative models for advanced semiconductor heterostructures, including material properties and the impact of the interface quality via multi-scale, multi-fidelity computational approaches.

Crystallographic Databases

Components and devices used in a broad spectrum of technology sectors such as health care, communications, energy and electronics are manufactured from crystalline materials. The objective of this project is to provide critically evaluated, comprehensive crystal-structure databases that enable phase identification required for the development of advanced inorganic materials and devices depending on them. NIST designs, populates, evaluates and disseminates NIST Standard Reference Databases SRD 3 (NIST Inorganic Crystal Structure Database, ICSD).

Advanced Analytical Electron Tomography for Materials Development and Failure Analysis in Semiconductor Devices

This project will develop quantitative, atomic-resolution methods for the three-dimensional characterization of complex semiconductor devices via electron tomography. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) are widely used in industry for identifying structural and morphological characteristics in process development, control, and failure analysis. Existing TEM and STEM imaging methods struggle with complex semiconductor device architectures.

Images depicting an advanced analysis of HR-EBSD data

Strain Measurement for Semiconductor Devices and Packages

Mechanical strain impacts the performance of semiconductor devices. Manufacturing processes must be carefully controlled for strain to achieve high-yield and high-performance products. However, measuring strain in nanoscale devices remains a metrology challenge for manufacturers. This project will advance techniques to measure strain, advance techniques, improve accuracy, and supply new reference materials to ensure capabilities for future-generation devices.

Multiscale structure and dynamics in advanced technological materials

This project develops and applies metrologies and standards for characterizing microstructure and dynamics in advanced functional materials of technological importance, including heterogeneous or porous materials, over multiple length scales in situ and operando.

Software

GSAS_USE (Bayesian Statistics Approach to Accounting for Unknown Systematic Errors)

GSAS_USE addresses the effects of systematic errors in Rietveld refinements. The errors are categorized into multiplicative, additive, and peak-shape types. Corrections for these errors are incorporated into using a Bayesian statistics approach, with the corrections themselves treated as nuisance parameters and marginalized out of the analysis. Structural parameters refined using the proposed method represent probability-weighted averages over all possible error corrections.

BBEST Bayesian Estimation of Incoherent Neutron Scattering Backgrounds

We implemented a Bayesian-statistics approach for subtraction of incoherent scattering from neutron total-scattering data. In this approach, the estimated background signal associated with incoherent scattering maximizes the posterior probability, which combines the likelihood of this signal in reciprocal and real spaces with the prior that favors smooth lines.

NANOP

This software package implements functions to simulate spherical, ellipsoid and cubic polyatomic nanoparticles with arbitrary crystal structures and to calculate the associated pair-distribution function and X-ray/neutron total-scattering signals. It also provides a target function that can be used for simultaneous fitting of small- and wide-angle total scattering data in real and reciprocal spaces. The target function can be generated either as a sum of weighted residuals for individual datasets or as a vector of residuals suitable for optimization using multi-criteria algorithms (e.g. Pareto methods).

RMCPROFILE

RMCProfile is a free software package (developed as a collaborative effort between scientists at several institutions including NIST), that can fit simultaneously different types of diffraction and spectroscopy data using a Reverse Monte Carlo (RMC) algorithm to determine both local and average atomic arrangements in a broad range of materials. The NIST team focuses on the development of multi-technique aspects of this analysis and on the optimization of the software’s computing speed to enable handling of larger atomic configurations.

gppois

gppois is a Bayesian tool for learning about a smooth function based on noisy measurements of its values. Users train a model of the true function on the noisy datapoints, then use that model to make predictions at whatever points they desire to know.

RMCProfile Utility Programs

RMCProfile is a free software (www.rmcprofile.org), developed at ISIS, that can fit simultaneously atomic pair-distribution function, total scattering function S(Q), and Bragg profile under various geometric and bond valence sum constraints. Recently, an extension to RMCProfile that enables a simultaneous fit of neutron/X-ray total scattering data, Extended Absorption Fine Structure (EXAFS) (real space), and a geometric shape of diffuse scattering in electron/X-ray single-crystal diffraction was developed at NIST.

Tools and Instruments

Analytical Electron Microscope

The Titan 80-300 is a transmission electron microscope (TEM) equipped with spectroscopic detectors to allow chemical, elemental, and other analytical measurements to be performed at high spatial resolution. The Titan operates between 80 keV and 300 keV electron beam energy, and uses a thermal (Schottky) field emission electron source to illuminate the sample. It can be used in full-field imaging mode as both a conventional TEM and a phase-contrast high resolution TEM for imaging the atomic scale lattice in many materials.

$Divergent Beam Diffractometer$

The Divergent Beam Diffractometer Laboratory

The Divergent Beam Diffractometer is the primary instrument at NIST used to certify powder SRMs for their X-ray diffraction properties. It is a custom-built instrument which provides a very highly-characterized angular scale in a well-controlled environment. It is a Bragg-Brentano instrument, usable with either open beam from a fine-focus copper X-ray tube, or using monochromated beam from a Ge(111) Johansson optic.

Awards

2019 - Bronze Medal Award---Thomas Gnaupel-Herold, Carelyn Campbell, Michael Katz, Eric Lass, Lyle Levine, Mark Stoudt, Maureen Williams, Fan Zhang, Thien Phan

For identifying improved post-processing treatments for additive manufacturing metal alloys that resolve a critical issue of mechanical part failure.

2016 - Silver Medal Award---Andrew Allen, Lyle Levine

For establishing a revolutionary new technique for measuring materials microstructure and dynamics over multiple scales and under working conditions.

News and Updates

$Diagram shows X-rays diffraction during 3D printing, with colorized microscopic image showing the orientation of different grains within the material.$