Manufacturing Bits: May 23

Pushing optical metrology
The University of Illinois at Urbana-Champaign has developed a new way to determine crystal types using optical metrology techniques.

Using an optical-based technique called absorption spectroscopy, researchers have detected tiny nanocrystals down to about 2nm resolutions. Absorption spectroscopy measures the absorption of radiation. It is measured as a function of frequency or wavelength.

Typically, the industry uses X-ray metrology techniques to determine the crystal types in materials. This involves a field called crystallography, which is the science of determining the arrangement of atoms in crystalline solids.

In crystallography, X-ray techniques generally work. At times, though, these techniques produce “ambiguous phase signatures” when the samples are too small, according to researchers from the University of Illinois at Urbana-Champaign. And as before, X-ray metrology is slow and requires large sample quantities, according to researchers.

Hoping to find a new method, the University of Illinois identified the optical signatures of cubic and hexagonal phases in II–VI nanocrystals. To identify the crystals, researchers used absorption spectroscopy and first-principles electronic-structure theory.

The technique enabled the rapid identification of nanocrystals down to about 2nm. “This new ability eliminates the need for slow and expensive X-ray equipment, as well as the need for large quantities of materials that must be extensively purified,” said Andrew Smith, an assistant professor of bioengineering at the University of Illinois at Urbana-Champaign, on the university’s Web site. “These theoretical and experimental insights provide simple and accurate analysis for liquid-dispersed nanomaterials that we think can improve the precision of nanocrystal engineering and also improve our understanding of nanocrystal reactions.”

Advancing X-ray metrology
The National Institute of Standards and Technology (NIST) has developed an X-ray metrology instrument that can make some of the world’s most accurate measurements.

The system could be used for a variety of materials. Initially, with the instrument, NIST took high-precision measurements of the copper alpha spectrum. Researchers took measurements in the regions from 8,000- to 8,100-eV with a precise angular scale.

NIST’s new X-ray machine for high-precision measurement of the copper alpha spectrum. (Credit: James Cline/NIST)

X-ray metrology is not a new technology and is widely used in a number of fields. NIST’s new instrument uses the same techniques as other X-ray systems. For example, in the copper alpha experiment, NIST’s system fires electrons at a copper target.

NIST has advanced the technology, however. The new instrument can make measurements around a sample with more accuracy. The camera within the system provides more information than traditional detectors. It also makes use of a goniometer. This is a part used for the measurement of the angles between the faces of crystals.

The measurement of copper is only a starting point. NIST plans to make measurements with other materials. “The wavelength of an X-ray is a ruler by which we can measure spacings of atoms in crystals,” said Marcus Mendenhall, a researcher at NIST, on the agency’s Web site. “We now know the length of our ruler better, and all kinds of materials can now be measured with improved accuracy.”

Ionic metrology
The U.S. Department of Energy’s (DOE) Brookhaven National Laboratory has demonstrated a new method for observing in real time how the ions of liquids move and reconfigure as different voltages are applied to the electrodes.

Brookhaven used an imaging technique called photoemission electron microscopy (PEEM). “Imaging the whole surface, including the electrodes and the space between them, allows us to study not only the evolution of the structure of the ionic liquid–electrode interface but also to probe both electrodes at the same time while changing various conditions of the system,” said Brookhaven scientist Jerzy (Jurek) Sadowski, on the agency’s Web site.