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Measurements of electrical properties of a plastic tape (yellow), taken using a specially designed microwave cavity (the white cylinder at center) and accompanying electrical circuit, change quickly and consistently in response to changes in the tape’s thickness. The setup is inspired by high-volume roll-to-roll manufacturing devices used to mass-produce nanomaterials. The changes in the tape’s thickness spell NIST in Morse code.
Credit: NIST/Nathan Orloff

Manufacturers may soon have a speedy and nondestructive way to test a wide array of materials under real-world conditions, thanks to an advance that researchers at the National Institute of Standards and Technology (NIST) have made in roll-to-roll measurements. Roll-to-roll measurements are typically optical measurements for roll-to-roll manufacturing, any method that uses conveyor belts for continuous processing of items, from tires to nanotechnology components.

In order for new materials such as carbon nanotubes and graphene to play an increasingly important role in electronic devices, high-tech composites and other applications, manufacturers will need quality-control tests to ensure that products have desired characteristics, and lack flaws. Current test procedures often require cutting, scratching or otherwise touching a product, which slows the manufacturing process and can damage or even destroy the sample being tested.

To add to existing testing non-contact methods, NIST physicists Nathan Orloff, Christian Long and Jan Obrzut measured properties of films by passing them through a specially designed metal box known as a microwave cavity. Electromagnetic waves build up inside the cavity at a specific “resonance” frequency determined by the box’s size and shape, similar to how a guitar string vibrates at a specific pitch depending on its length and tension. When an object is placed inside the cavity, the resonance frequency changes in a way that depends on the object’s size, electrical resistance and dielectric constant, a measure of an object’s ability to store energy in an electric field. The frequency change is reminiscent of how shortening or tightening a guitar string makes it resonate at a higher pitch, says Orloff.

The researchers also built an electrical circuit to measure these changes. They first tested their device by running a strip of plastic tape known as polyimide through the cavity, using a roll-to-roll setup resembling high-volume roll-to-roll manufacturing devices used to mass-produce nanomaterials. As the tape’s thickness increased and decreased–the researchers made the changes in tape thickness spell “NIST” in Morse code–the cavity’s resonant frequency changed in tandem. So did another parameter called the “quality factor,” which is the ratio of the energy stored in the cavity to the energy lost per frequency cycle. Because polyimide’s electrical properties are well known, a manufacturer could use the cavity measurements to monitor whether tape is coming off the production line at a consistent thickness–and even feeding back information from the measurements to control the thickness.

Alternatively, a manufacturer could use the new method to monitor the electrical properties of a less well-characterized material of known dimensions. Orloff and Long demonstrated this by passing 12- and 15-centimeter-long films of carbon nanotubes deposited on sheets of plastic through the cavity and measuring the films’ electrical resistance. The entire process took “less than a second,” says Orloff. He added that with industry-standard equipment, the measurements could be taken at speeds beyond 10 meters per second, more than enough for many present-day manufacturing operations.

The new method has several advantages for a thin-film manufacturer, says Orloff. One, “You can measure the entire thing, not just a small sample,” he said. Such real-time measurements could be used to tune the manufacturing process without shutting it down, or to discard a faulty batch of product before it gets out the factory door. “This method could significantly boost prospects of not making a faulty batch in the first place,” Long noted.

And because the method is nondestructive, Orloff added, “If a batch passes the test, manufacturers can sell it.”

Films of carbon nanotubes and graphene are just starting to be manufactured in bulk for potential applications such as composite airplane materials, smartphone screens and wearable electronic devices.

Orloff, Long and Obrzut submitted a patent application for this technique in December 2015.

A producer of such materials has already expressed interest in the new method, said Orloff. “They’re really excited about it.” He added that the method is not specific to nanomanufacturing, and with a properly designed cavity, could also help with quality control of many other kinds of products, including tires, pharmaceuticals and even beer.


Story Source:

The above post is reprinted from materials provided by National Institute of Standards and Technology (NIST). Note: Materials may be edited for content and length.


Journal Reference:

  1. Nathan D. Orloff, Christian J. Long, Jan Obrzut, Laurent Maillaud, Francesca Mirri, Thomas P. Kole, Robert D. McMichael, Matteo Pasquali, Stephan J. Stranick, J. Alexander Liddle. Noncontact conductivity and dielectric measurement for high throughput roll-to-roll nanomanufacturing. Scientific Reports, 2015; 5: 17019 DOI: 10.1038/srep17019

NIST 081115 15CNST009_quantum_dot_finder_LR Life may be as unpredictable as a box of chocolates, but ideally, you always know what you’re going to get from a quantum dot. A quantum dot should produce one, and only one, photon—the smallest constituent of light—each time it is energized. This characteristic makes it attractive for use in various quantum technologies such as secure communications. Oftentimes, however, the trick is in finding the dots.

NIST 081115 15CNST009_quantum_dot_finder_LR[Clockwise from top left] Circular grating for extracting single photons from a quantum dot. For optimal performance, the quantum dot must be located at the center of the grating. Image taken with the camera-based optical location technique. A single quantum dot appears as a bright spot within an area defined by four alignment marks. Electron-beam lithography is used to define a circular grating at the quantum dot’s location. Image of the emission of the quantum dot within the grating. The bright spot appears in the center of the device, as desired.

Credit: NIST
View hi-resolution image

“Self-assembled, epitaxially grown” quantum dots have the highest optical quality. They randomly emerge (self-assemble) at the interface between two layers of a semiconductor crystal as it is built up layer-by-layer (epitaxially grown).

They grow randomly, but in order for the dots to be useful, they need to be located in a precise relation to some other photonic structure, be it a grating, resonator or waveguide, that can control the photons that the quantum dot generates. However, finding the dots—they’re just about 10 nanometers across—is no small feat.

Always up for a challenge, researchers working at the National Institute of Standards and Technology (NIST) have developed a simple new technique for locating them, and used it to create high-performance single photon sources.

This new development, which appeared in Nature Communications,* may make the manufacture of high-performance photonic devices using quantum dots much more efficient. Such devices are usually made in regular arrays using standard nanofabrication techniques for the control structures. However because of the random distribution of the dots, only a small percentage of them will line up correctly with the control structures. This process produces very few working devices.

“This is a first step towards providing accurate location information for the manufacture of high performance quantum dot devices,” says NIST physicist Kartik Srinivasan. “So far, the general approach has been statistical—make a lot of devices and end up with a small fraction that work. Our camera-based imaging technique maps the location of the quantum dots first, and then uses that knowledge to build optimized light-control devices in the right place.”

According to co-lead researcher Luca Sapienza of the University of Southampton in the United Kingdom, the new technique is sort of a twist on a red-eye reducing camera flash, where the first flash causes the subject’s pupils to close and the second illuminates the scene. Instead of a xenon-powered flash, the NIST team uses two LEDs.

In their setup, one LED activates the quantum dots when it flashes (so the LED gives the quantum dots red-eye). At the same time, a second, different color LED flash illuminates metallic orientation marks placed on the surface of the semiconductor wafer the dots are embedded in. Then a sensitive camera snaps a 100-micrometer by 100-micrometer picture.

By cross-referencing the glowing dots with the orientation marks, the researchers can determine the dots’ locations with an uncertainty of less than 30 nanometers. The coordinates in hand, scientists can then tell the computer-controlled electron beam lithography tool to place the control structures in the correct places, with the result being many more usable devices.

Using this technique, the researchers demonstrated grating-based single photon sources in which they were able to collect 50 percent of the quantum dot’s emitted photons, the theoretical limit for this type of structure.

They also demonstrated that more than 99 percent of the light produced from their source came out as single photons. Such high purity is partly due to the fact that the location technique helps the researchers to quickly survey the wafer (10,000 square micrometers at a time) to find regions where the quantum dot density is especially low, only about one per 1,000 square micrometers. This makes it far more likely that each grating device contains one—and only one—quantum dot.

This work was performed in part at NIST’s Center for Nanoscale Science and Technology (CNST), a national user facility available to researchers from industry, academia and government. In addition to NIST and the University of Southampton, researchers from the University of Rochester contributed to this work.

* L. Sapienza, M. Davanço, A. Badolato and K. Srinivasan. Nanoscale optical positioning of single quantum dots for bright and pure
single-photon emission.
Nature Communications, 6, 7833 doi:10.1038/ncomms8833. Published 27 July 2015.

NIST 580303_10152072709285365_1905986131_n The National Institute of Standards and Technology (NIST) has put firm numbers on the high costs of installing pipelines to transport hydrogen fuel–and also found a way to reduce those costs.

Samples of pipeline steel instrumented for fatigue testing in a pressurized hydrogen chamber (the vertical tube). NIST researchers used data from such tests to develop a model for hydrogen effects on pipeline lifetime, to support a federal effort to reduce overall costs of hydrogen fuel. (Image: NIST)
Pipelines to carry hydrogen cost more than other gas pipelines because of the measures required to combat the damage hydrogen does to steel’s mechanical properties over time. NIST researchers calculated that hydrogen-specific steel pipelines can cost as much as 68 percent more than natural gas pipelines, depending on pipe diameter and operating pressure.* By contrast, a widely used cost model** suggests a cost penalty of only about 10 percent.>Samples of pipeline steel instrumented for fatigue testingBut the good news, according to the new NIST study, is that hydrogen transport costs could be reduced for most pipeline sizes and pressures by modifying industry codes*** to allow the use of a higher-strength grade of steel alloy without requiring thicker pipe walls. The stronger steel is more expensive, but dropping the requirement for thicker walls would reduce materials use and related welding and labor costs, resulting in a net cost reduction. The code modifications, which NIST has proposed to the American Society of Mechanical Engineers (ASME), would not lower pipeline performance or safety, the NIST authors say.”The cost savings comes from using less–because of thinner walls–of the more expensive material,” says NIST materials scientist James Fekete, a co-author of the study. “The current code does not allow you to reduce thickness when using higher-strength material, so costs would increase. With the proposed code, in most cases, you can get a net savings with a thinner pipe wall, because the net reduction in material exceeds the higher cost per unit weight.”

The NIST study is part of a federal effort to reduce the overall costs of hydrogen fuel, which is renewable, nontoxic and produces no harmful emissions. Much of the cost is for distribution, which likely would be most economical by pipeline. The U.S. contains more than 300,000 miles of pipelines for natural gas but very little customized for hydrogen. Existing codes for hydrogen pipelines are based on decades-old data. NIST researchers are studying hydrogen’s effects on steel to find ways to reduce pipeline costs without compromising safety or performance.

As an example, the new code would allow a 24-inch pipe made of high-strength X70 steel to be manufactured with a thickness of 0.375 inches for transporting hydrogen gas at 1500 pounds per square inch (psi). (In line with industry practice, ASME pipeline standards are expressed in customary units.) According to the new NIST study, this would reduce costs by 31 percent compared to the baseline X52 steel with a thickness of 0.562 inches, as required by the current code. In addition, thanks to its higher strength, X70 would make it possible to safely transport hydrogen through bigger pipelines at higher pressure (36-inch diameter pipe to transport hydrogen at 1500 psi) than is allowed with X52, enabling transport and storage of greater fuel volumes. This diameter-pressure combination is not possible under the current code.

The proposed code modifications were developed through research into the fatigue properties of high-strength steel at NIST’s Hydrogen Pipeline Material Testing Facility. In actual use, pipelines are subjected to cycles of pressurization at stresses far below the failure point, but high enough to result in fatigue damage. Unfortunately, it is difficult and expensive to determine steel fatigue properties in pressurized hydrogen. As a result, industry has historically used tension testing data as the basis for pipeline design, and higher-strength steels lose ductility in such tests in pressurized hydrogen. But this type of testing, which involves steadily increasing stress to the failure point, does not predict fatigue performance in hydrogen pipeline materials, Fekete says.
NIST research has shown that under realistic conditions, steel alloys with higher strengths (such as X70) do not have higher fatigue crack growth rates than lower grades (X52). The data have been used to develop a model**** for hydrogen effects on pipeline steel fatigue crack growth, which can predict pipeline lifetime based on operating conditions.
Notes
* J.W. Sowards, J.R. Fekete and R.L. Amaro. Economic impact of applying high strength steels in hydrogen gas pipelines. International Journal of Hydrogen Energy. 2015. In press, corrected proof available online. DOI:10.1016/j.ijhydene.2015.06.090
** DOE H2A Delivery Analysis. U.S. Department of Energy. Available online at www.hydrogen.energy.gov/h2a_delivery.html.
*** ASME B31.12 Hydrogen Piping and Pipeline Code (ASME B31.12). Industry groups such as ASME commonly rely on NIST data in developing codes.
**** R.L. Amaro, N. Rustagi, K.O. Findley, E.S. Drexler and A.J. Slifka. Modeling the fatigue crack growth of X100 pipeline steel in gaseous hydrogen. Int. J. Fatigue, 59 (2014). pp 262-271.
Source: NIST

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