Hacking the SEM: Crystal phase detection for nanoscale samples

January 25, 2012, National Institute of Standards and Technology
Top: Transmission electron diffraction pattern from from a segment of an indium gallium nitride (InGaN) nanowire about 50 nanometers in diameter taken with an SEM using the new NIST technique clearly shows a unique pattern associated with crystal diffraction. Bottom: Same pattern but with an overlay showing the crystallographic indexing associated with the atomic structure of the material. Credit: Geiss/NIST

(PhysOrg.com) -- Custom modifications of equipment are an honored tradition of the research lab. In a recent paper, two materials scientists at the National Institute of Standards and Technology describe how a relatively simple mod of a standard scanning electron microscope (SEM) enables a roughly 10-fold improvement in its ability to measure the crystal structure of nanoparticles and extremely thin films. By altering the sample position, they are able to determine crystal structure of particles as small as 10 nanometers. The technique, they say, should be applicable to a wide range of work, from crime scene forensics to environmental monitoring to process control in nanomanufacturing.

The technique is a new way of doing with an SEM. In standard SEM-based electron diffraction, the researcher analyses patterns that are formed by electrons that bounce back after striking atoms in the sample. If the sample is a , with a regular pattern to the arrangement of atoms, these diffracted electrons form a pattern of lines that reveals the particular or "phase" and orientation of the material.

The information, say NIST's Robert Keller and Roy Geiss, can be critical. "A common example is , which can exist in a couple of different crystal phases. That difference significantly affects how the material behaves chemically, how reactive it is. You need to add crystallographic identification to the to completely characterize the material."

SEMs often are outfitted with an instrument for just this task, a device called an EBSD (electron back-scatter diffraction) detector. The problem, they say, is that below a certain size, the usual setup just doesn't work. "You can determine the crystal structure of an isolated particle down to a size of about 100 to 120 nanometers, but below that the crystals are so small that you're getting information about the sample holder instead." A somewhat more exotic instrument, the transmission electron microscope (TEM), does much better, they say, but samples below about 50 nanometers in size show very limited diffraction patterns because the higher-powered electron beam of the TEM just blasts through them.

The novel tweak developed by Keller and Geiss combines a little of each. They moved the SEM sample holder closer to the beam source and adjust the angles so that instead of imaging electrons bouncing back from the sample, the "EBSD" detector is actually seeing electrons that scatter forward through the sample in a manner similar to a TEM. (They also came up with a unique method of holding samples to make this work.)

They have shown that their technique produces reliable crystal phase information for as small as 10 nanometers across, as well as for single crystalline grains as small as 15 nanometers in an ultrathin film.

Electron diffraction in an SEM, says Keller, "in general represents the only approach capable of measuring the atomic structure, defect content, or crystallographic phase of single nanoparticles. This is a critical need in cases of extremely limited sampling of unknown particles. This work pushes electron diffraction to a new frontier by providing spatial resolution that rivals that possible in a TEM, and makes it available to anyone with an SEM. And that's an ubiquitous tool in virtually all fields that require characterization of solids."

Typical applications, the researchers say, include pinpointing ammunition sources from gunshot residue at crime scenes; determining the processing history of confiscated drugs; accurate characterization of nanoparticles for health, safety and environmental impact studies; and optimizing grain structure in high-performance electronics based on and process and quality control in nanomanufacturing.

Explore further: Software for the discovery of new crystal structures

More information: R.R. Keller and R.H. Geiss. Transmission EBSD from 10 nm domains in a scanning electron microscope. Journal of Microscopy, 2011. doi: 10.1111/j.1365-2818.2011.03566.x . Scheduled to appear in the March 2012 issue.

Related Stories

Software for the discovery of new crystal structures

May 11, 2011

A new software called QED (Quantitative Electron Diffraction), which has been licensed by Max Planck Innovation, has now been released by HREM Research Inc., a Japan based company, which is developing products and services ...

New technique to see crystals like never before

November 30, 2011

An international team of scientists led by the Fresnel Institute and the ESRF (European Synchrotron Radiation Facility) in Grenoble has developed a new technique allowing to observe the nanometer-sized structure of crystalline ...

Unveiling the structure of microcrystals

October 4, 2007

Microcrystals take the form of tiny grains resembling powder, which is extremely difficult to study. For the first time, researchers from the European Synchrotron Radiation Facility (ESRF) and the Centre National de Recherche ...

Nano-ruler sets some very small marks

September 22, 2009

The National Institute of Standards and Technology has issued a new ruler, and even for an organization that routinely deals in superlatives, it sets some records. Designed to be the most accurate commercially available "meter ...

FEI Introduces Nova NanoSEM

March 4, 2005

New System is the World's First SEM for Ultra-High Resolution Characterization of Non-Conductive or Contaminating Samples FEI Company released the newest member of its Nova(TM) family of SEM and DualBeam(TM) systems, the ...

Recommended for you

Hauling antiprotons around in a van

February 22, 2018

A team of researchers working on the antiProton Unstable Matter Annihilation (PUMA) project near CERN's particle laboratory, according to a report in Nature, plans to capture a billion antiprotons, put them in a shipping ...

Urban heat island effects depend on a city's layout

February 22, 2018

The arrangement of a city's streets and buildings plays a crucial role in the local urban heat island effect, which causes cities to be hotter than their surroundings, researchers have found. The new finding could provide ...

New quantum memory stores information for hours

February 22, 2018

Storing information in a quantum memory system is a difficult challenge, as the data is usually quickly lost. At TU Wien, ultra-long storage times have now been achieved using tiny diamonds.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.