Manufacturing Bits: June 2

X-raying chocolate
X-ray scattering is a next-generation metrology technology. Using an X-ray source, the technology can be used for imaging complex structures and films in three dimensions. It can be used in various applications, such as biology and semiconductors.

Here’s another surprising application: chocolate. Using X-ray scattering, Deutsches Elektronen-Synchrotron (DESY) has helped improve the quality of chocolate. Hamburg University of Technology (TUHH) and food giant Nestlé were also part of the research.

With the technology, researchers discovered new insights into the formation of fat bloom. This is an unwanted white layer that sometimes forms on chocolate.

Microscope view of fat bloom on chocolate. (Credit: Svenja Reinke/TUHH)

Using DESY’s X-ray technology, researchers can observe the underlying processes of fat bloom in real time. “For the first time, we have been able to track in detail the dynamic mechanisms that lead to the creation of fat bloom,” said DESY scientist Stephan Roth on the organization’s Web site. “The method used is known as small-angle X-ray scattering and is precisely adapted to real-time investigations of this kind, and to observing the structural changes caused by the moving lipids. The joint study has supplied important information as to how we can study structural changes in such ‘everyday’ multi-component systems.”

The technology, in turn, could help reduce fat bloom. “One consequence might, for example, be to reduce the porosity of the chocolate during manufacture, so that the fat migrates more slowly,” said Svenja Reinke of TUHH. “Another approach is to limit the amount of fat that is present in a liquid form by storing the product in cool, but not too cold, conditions. 18 degrees Celsius is ideal.”

Super microscopes
In a separate move, DESY has devised a new X-ray lens that could one day lead to the development of a super microscope.

Researchers have devised a high numerical aperture multilayer Laue lens. Using the lens technology, DESY tested the lens using its X-ray source, which produced a focus just 8nm wide. The technology could one day enable imaging at 1nm resolutions.

The X-ray source, dubbed PETRA III, is DESY’s third-generation synchrotron radiation source. With a circumference of 2.3 kilometers, the source is said to be the biggest and brightest storage ring light source in the world.

The lens itself was constructed using a new deposition technique. It was made using 5,500 alternating layers of silicon carbide and tungsten. The final lens was 40 x 17.5 x 6.5 micrometers.

SEM image of the novel X-ray lens (Source: DESY)

X-rays have wavelengths of about 1nm to 0.01nm, as compared to 400nm to 800nm for visible light, according to DESY. X-ray technology can be used for three-dimensional imaging in various applications.

In conventional lenses, X-rays cannot be bent. One way to bend them is to graze them from the surface of a mirror. But in this application, the X-ray mirrors themselves are limited.

Another way to bend X-rays is by using crystals. Crystal lattices diffract X-rays, enabling the multilayer Laue lens (MLL), according to researchers. “However, conventional Laue lenses are limited in their converging power for geometric reasons,” said Saša Bajt of DESY on the organization’s Web site. “To gain the maximum power, the layers of a MLL need to be slightly tilted against each other.”

With the technology, X-ray imaging could compete more favorably with the scanning electron microscope (SEM). The SEM has a resolution down to 4nm.

Revisiting charge pumping
The National Institute of Standards and Technology (NIST) has devised a new version of an old technology called charge pumping.

Charge pumping was a viable technique for characterizing the interface charge in MOSFETs. But chipmakers abandoned this technique about a decade ago. This technology had issues due to scaling.

Now, NIST has created a new version of the technology, dubbed frequency-modulated charge pumping (FMCP). In FMCP, researchers transform the quasi-DC charge pumping measurement into an AC measurement. “The AC detection scheme is highly resistant to gate leakage currents and extends the usefulness of charge pumping as a defect monitoring tool for future technologies,” according to NIST.

FMCP is similar to charge pumping. “Researchers alternately fill and drain the interface traps with electrons by applying a gate voltage (MHz or kHz) to a transistor at two or more different frequencies,” according to NIST. “But instead of applying multiple gate voltage waveforms to the device one frequency at a time, taking direct current measurements, and analyzing them offline, in FMCP a single gate voltage waveform is applied to the transistor, and that single waveform is modulated back and forth between two or more frequencies. Alternating between different frequencies hundreds of times per second allows for a more precise measurement of a small signal by transforming charge pumping into an alternating current measurement.”