Science for our
Nation's
Energy Future

Energy Frontier Research Center

Community Website
Frontiers in
Energy Research
Newsletter
September 2013

Real-Time Imaging of Nanomaterials with High Energy X-Rays

Closer to predicting the material properties at the core of the Earth and other planets

Laila Jaber-Ansari

Schematic of Coherent X-ray Diffraction Imaging (CXDI). The high energy X-ray beam from the synchrotron interacts with the electronic structure of the crystal and is diffracted. The diffracted beams carry vital information about the electronic structure of the crystal and are recorded by an X-ray sensitive area detector. A computer modeling system is used to convert this information to three-dimensional images of the nanocrystals.

Three-dimensional strain distribution in a 400-nanometer single crystal gold particle subjected to 1.7 gigapascal pressure. The normal directions of two sets of crystalline planes {111} and {100} are marked by arrows (fat and narrow). The color represents the phase shift (lattice strain) ranged from -π/4 to π/4. (a) Crystal shape and surface truncated (100) and (111) crystal planes, (b) and (c) are the top and bottom views, (d-f) are side views with 120 degrees rotation along the surface normal (111) direction.

When materials are constrained to nanoscale dimensions, they exhibit interesting properties that are different from their bulk counterparts. The reason for this difference is known as the nano-size effect. For example, gold nanocrystals with an average size of 30 nanometers, about 200 times smaller than a typical red blood cell, are 60 percent stiffer than bulk gold. Wenge Yang and a team of scientists at the Center for Energy Frontier Research in Extreme Environments (EFree) devised a new method that allows them to see how high pressures strain a single gold nanoparticle. This breakthrough is key to understanding the properties of materials under extreme conditions, as well as predicting materials' structure and properties at the core of the Earth and other planets, which can lead to designing new materials for energy-based applications.

Published in Nature Communications, this research is one of the first reports that show nanometer-resolution imaging of a material under real conditions and in real time. Other nanometer-resolution imaging techniques, such as transmission electron microscopy, require the measurements to be done in ultra high vacuum because of the scattering of the electron beam in otherwise ambient conditions. The method applied by Yang and coworkers, called Coherent X-ray Diffraction Imaging, uses the high energy, highly coherent X-ray beam at the Advanced Photon Source in Argonne National Laboratory (see first figure).

They used a Diamond Anvil Cell (DAC) to apply pressures up to 6.4 gigapascals, 60,000 times higher than atmospheric pressure. The DACs, which have been around for about half a century, are a refined version of the Opposed Anvil Machine built by P. W. Bridgman, who won a Nobel Prize for his work in high-pressure physics in 1946. In a DAC, the sample is placed between two diamond anvils and a blend of fluids, such as a methanol and ethanol mixture, is used as the pressure-transmitting medium to ensure a uniform hydrostatic pressure around the sample. This design enables the DAC to create in situ pressures up to hundreds of gigapascals, several million times higher than atmospheric pressure.

"When coupled with laser heating, one can simulate the real condition that exists in the core of the Earth and even other planets," said Yang.

High energy X-rays are the only source able to provide nanoscale resolution of a sample under high pressure in the DAC because they can penetrate through the surrounding materials under high pressure. The X-ray beam interacts with the electronic structure of the crystal and is scattered because of a phenomenon called diffraction. The diffracted X-ray beam carries vital information about the electronic structure of the crystal, which is related to its physical properties, such as strain; these data are recorded by an X-ray sensitive area detector. Yang and his team used a computer modeling system to convert this information to three-dimensional images of the nanocrystals (see second figure). They observed the evolution of strain in gold nanoparticles while the applied external pressure was increased, step by step, from 0.8 to 6.4 gigapascals.

Until now, scientists could only observe the nano-size effect in particles smaller than a few tens of nanometers; but this work now shows that the nano-size effect can be observed at a much larger scale -- in 400-nanometer gold particles.

"Nano-size effects do exist in larger crystals. You can see them when you zoom in and do good microscopy," said Yang.

The team's next step will be to look at even more interesting materials like core-shell structures during deformation to understand the properties of interfaces in extreme conditions.

"It took us about two years to develop the coherent diffraction tool to undertake in situ studies at high pressure. It is harder to take the first step; our next steps will be much easier," he said.

More Information

Yang W, X Huang, R Harder, JN Clark, IK Robinson, and HK Mao. 2013. "Coherent Diffraction Imaging of Nanoscale Strain Evolution in a Single Crystal under High Pressure." Nature Communications 2013(4):1-6. DOI: 10.1038/ncomms2661

Acknowledgments

The work by Wenge Yang, Xiaojing Huang, Ross Harder, Jesse N. Clark, and Ho-kwang Mao was supported by EFree, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences; Ian Robinson at University College of London was supported by the European Research Council "nanosculpture" advanced grant 227711.

About the author(s):

  • Laila Jaber-Ansari is a Ph.D. candidate in Materials Science and Engineering at Northwestern University (Illinois), studying with Mark C. Hersam. She is a member of Center of Electrical Energy Storage (CEES). She received her M. Eng. in Materials Science and Engineering from Northeastern University (Massachusetts) in 2009. Her research interests include application of carbon-based nanomaterials in advancing energy storage devices.

How Do Nanoparticles Handle the Strain?

New imaging method shows how crystals react to pressure

In this new imaging method, a high energy X-ray beam interacts with the crystal's electronic structure and is diffracted. By measuring the diffraction and using a complex modeling program, the team gets three-dimensional images of the nanocrystals under extreme pressure.

Particles thousands of times smaller than the width of a human hair react differently to extreme conditions than their larger counterparts. Understanding these reactions could result in designing new materials that benefit energy production and storage technologies. Scientists have studied how the particles deform under pressure. The challenge is getting accurate data inside a pressure vessel. Scientists devised a method that directs a high energy, highly coherent x-ray beam into the crystal inside a pressure cell. The beam interacts with the crystal's electronic structure and provides data on changes in the crystal. The data is turned into three-dimensional high-resolution images. This technique provides accurate images and information that could open doors to new materials for batteries, biofuels and other applications. The Center for Energy Frontier Research in Extreme Environments, led by the Carnegie Institution of Washington, performed the research.

More Information

Yang W, X Huang, R Harder, JN Clark, IK Robinson, and HK Mao. 2013. "Coherent Diffraction Imaging of Nanoscale Strain Evolution in a Single Crystal under High Pressure." Nature Communications 2013(4):1-6. DOI: 10.1038/ncomms2661

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.