In This Issue...
JILA Frequency Comb System Detects Gas Impurities to Aid Semiconductor Manufacturing
Purity of ingredients is a constant concern for the semiconductor industry, because a mere trace of contaminants can damage or ruin tiny devices. In a step toward solving a long-standing problem in semiconductor manufacturing, scientists at JILA and collaborators have used their unique version of a “fine-toothed comb” to detect minute traces of contaminant molecules in the arsine gas used to make a variety of photonics devices.
JILA is a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder (CU). The research was conducted with collaborators from NIST’s Boulder campus and Matheson Tri-Gas (Longmont, Colo.).
The research, described in a new paper,* used a NIST/CU invention called cavity-enhanced direct frequency comb spectroscopy (CE-DFCS).** It consists of an optical frequency comb—a tool for accurately generating different colors, or frequencies, of light—adapted to analyze the quantity, structure and dynamics of various atoms and molecules simultaneously. The technique offers a unique combination of speed, sensitivity, specificity and broad frequency coverage.
The semiconductor industry has long struggled to find traces of water and other impurities in arsine gas used in manufacturing of III-V semiconductors for light-emitting diodes (LEDs), solar-energy cells and laser diodes for DVD players. The contaminants can alter a semiconductor’s electrical and optical properties. For instance, water vapor can add oxygen to the material, reducing device brightness and reliability. Traces of water are hard to identify in arsine, which absorbs light in a complex, congested pattern across a broad frequency range. Most analytical techniques have significant drawbacks, such as large and complex equipment or a narrow frequency range.
The JILA comb system, previously demonstrated as a “breathalyzer” for detecting disease***, was upgraded recently to access longer wavelengths of light, where water strongly absorbs and arsine does not, to better identify the water. The new paper describes the first demonstration of the comb system in an industrial application.
In the JILA experiments, arsine gas was placed in an optical cavity where it was “combed” by light pulses. The atoms and molecules inside the cavity absorbed some light energy at frequencies where they switch energy levels, vibrate or rotate. The comb’s “teeth” were used to precisely measure the intensity of different shades of infrared light before and after the interactions. By detecting which colors were absorbed and in what amounts—matched against a catalog of known absorption signatures for different atoms and molecules—the researchers could measure water concentration to very low levels.
Just 10 water molecules per billion molecules of arsine can cause semiconductor defects. The researchers detected water at levels of 7 molecules per billion in nitrogen gas, and at 31 molecules per billion in arsine. The researchers are now working on extending the comb system even further into the infrared and aiming for parts-per-trillion sensitivity.
The research was funded by the Air Force Office of Scientific Research, Defense Advanced Research Projects Agency, Defense Threat Reduction Agency, Agilent Technologies, and NIST.
* K.C. Cossel, F. Adler, K.A. Bertness, M.J. Thorpe, J. Feng, M.W. Raynor, J. Ye. 2010. Analysis of Trace Impurities in Semiconductor Gas via Cavity-Enhanced Direct Frequency Comb Spectroscopy. Applied Physics B. Published online July 20.
** U.S. Patent number 7,538,881: Sensitive, Massively Parallel, Broad-Bandwidth, Real-Time Spectroscopy, issued in May 2009, NIST docket number 06-004, CU Technology Transfer case number CU1541B. Licensing rights have been consolidated in CU.
*** See “Optical ‘Frequency Comb’ Can Detect the Breath of Disease”, in NIST Tech Beat Feb 19, 2008, at www.nist.gov/public_affairs/techbeat/tb2008_0219.htm#comb.
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Beware the Dim Laser Pointer: NIST Researchers Measure High Infrared Power Levels from Some Green Lasers
Green laser pointers have become a popular consumer item, delivering light that’s brighter to the eye than red lasers, but stories have circulated on the Web about the potential hazards of inexpensive models. Now, a team led by physicist Charles Clark at the National Institute of Standards and Technology (NIST) puts some numbers to the problem. In one case, the group found that a green laser pointer emitted almost twice its rated power level of light—but at invisible and potentially dangerous infrared wavelengths rather than green. A new NIST technical note* describes the nature of the problem as well as a home test using an inexpensive webcam that can detect excess infrared light from green lasers.
Late last year, the research team purchased three low-cost green laser pointers advertised to have a power output of 10 milliwatts (mW). Measurements showed that one unit emitted dim green light but delivered infrared levels of nearly 20 mW—powerful enough to cause retinal damage to an individual before he or she is aware of the invisible light. NIST’s Jemellie Galang and her colleagues repeated the tests with several other laser pointers and found similarly intense infrared emissions in some but not all units.
The problem stems from inadequate procedures in manufacturing quality assurance, according to the research team. Inside a green laser pointer, infrared light from a semiconductor diode laser pumps infrared light at a wavelength of 808 nm into a transparent crystal of yttrium orthovanadate doped with neodymium atoms (Nd:YVO4), causing the crystal to lase even deeper in the infrared, at 1064 nm. This light passes through a crystal of potassium titanyl phosphate (KTP), which emits light of half the wavelength: 532 nm, the familiar color of the green laser pointer.
However, if the KTP crystal is misaligned, little of the 1064 nm light is converted into green light, and most of it comes out as infrared. Excess infrared leakage can also occur if the coatings at both ends of the crystal that act as mirrors for the infrared laser light are too thin.
The NIST team says this problem could be solved by incorporating an inexpensive infrared filter at the end of the laser, which could reduce infrared emissions by 100-1000 times depending on quality and cost. Although these filters exist in modern digital cameras and more expensive green laser pointers, they often are left out of the inexpensive models.
The team demonstrates a home test that laser hobbyists could conduct to detect excessive infrared leakage, by using a common digital or cell phone camera, a compact disc, a webcam and a TV remote control. Regardless, they say owners of the devices should never point the lasers at the eyes or aim them at surfaces such as windows, which can reflect infrared light back to the user—a particularly subtle hazard because many modern energy-saving windows have coatings designed specifically to reflect infrared.
The researchers are all members of the Joint Quantum Institute, a collaboration of NIST and the University of Maryland. Co-author Edward W. Hagley is also at Acadia Optronics in Rockville, MD.
* J. Galang, A. Restelli, E.W. Hagley and C.W. Clark, NIST Technical Note (TN 1668), A Green Laser Pointer Hazard (July 2010) Available on-line at www.nist.gov/manuscript-publication-search.cfm?pub_id=906138
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NIST Nanofluidic 'Multi-tool' Separates and Sizes Nanoparticles
A wrench or a screwdriver of a single size is useful for some jobs, but for a more complicated project, you need a set of tools of different sizes. Following this guiding principle, researchers at the National Institute of Standards and Technology (NIST) have engineered a nanoscale fluidic device that functions as a miniature “multi-tool” for working with nanoparticles—objects whose dimensions are measured in nanometers, or billionths of a meter.
First introduced in March 2009 (see “NIST-Cornell Team Builds World’s First Nanofluidic Device with Complex 3-D Surfaces”, the device consists of a chamber with a cascading “staircase” of 30 nanofluidic channels ranging in depth from about 80 nanometers at the top to about 620 nanometers (slightly smaller than an average bacterium) at the bottom. Each of the many “steps” of the staircase provides another “tool” of a different size to manipulate nanoparticles in a method that is similar to how a coin sorter separates nickels, dimes and quarters.
In a new article in the journal Lab on a Chip*, the NIST research team demonstrates that the device can successfully perform the first of a planned suite of nanoscale tasks—separating and measuring a mixture of spherical nanoparticles of different sizes (ranging from about 80 to 250 nanometers in diameter) dispersed in a solution. The researchers used electrophoresis—the method of moving charged particles through a solution by forcing them forward with an applied electric field—to drive the nanoparticles from the deep end of the chamber across the device into the progressively shallower channels. The nanoparticles were labeled with fluorescent dye so that their movements could be tracked with a microscope.
As expected, the larger particles stopped when they reached the steps of the staircase with depths that matched their diameters of around 220 nanometers. The smaller particles moved on until they, too, were restricted from moving into shallower channels at depths of around 110 nanometers. Because the particles were visible as fluorescent points of light, the position in the chamber where each individual particle was stopped could be mapped to the corresponding channel depth. This allowed the researchers to measure the distribution of nanoparticle sizes and validate the usefulness of the device as both a separation tool and reference material. Integrated into a microchip, the device could enable the sorting of complex nanoparticle mixtures, without observation, for subsequent application. This approach could prove to be faster and more economical than conventional methods of nanoparticle sample preparation and characterization.
The NIST team plans to engineer nanofluidic devices optimized for different nanoparticle sorting applications. These devices could be fabricated with tailored resolution (by increasing or decreasing the step size of the channels), over a particular range of particle sizes (by increasing or decreasing the maximum and minimum channel depths), and for select materials (by conforming the surface chemistry of the channels to optimize interaction with a specific substance). The researchers are also interested in determining if their technique could be used to separate mixtures of nanoparticles with similar sizes but different shapes—for example, mixtures of tubes and spheres.
* S.M. Stavis, J. Geist and M. Gaitan. Separation and metrology of nanoparticles by nanofluidic size exclusion. Lab on a Chip, forthcoming, August 2010.
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New NIST Report Advises: Securing Critical Computer Systems Begins at the Beginning
Nothing beats the feeling of starting up a new computer – be it a laptop, desktop or a major, custom-designed computing system. A new system is a blank slate with no worry of botnets, viruses or any other cybersecurity hazards.
Not so, explains computer researcher Marianne Swanson at the National Institute of Standards and Technology (NIST), lead author of a draft report, Piloting Supply Chain Risk Management for Federal Information Systems. Information systems and components are under attack throughout the supply chain from the design phase—including specification and acquisition of custom products—through disposal. "Computer systems are under attack before installation by adversaries enabled by growing technological sophistication and facilitated by the rapid globalization of our information system infrastructure, suppliers and adversaries," Swanson says.
NIST has released a public draft of the new report for comment.
The supply chain report is geared to information systems that are categorized as "high-impact level," systems for which the loss of confidentiality, integrity or availability could be expected to have a "severe or catastrophic adverse effect on organizational operations, organizational assets or individuals."* The report provides an array of practices designed to help mitigate supply chain risk throughout the life cycle, not just on accepting systems and products "as they are" and managing risks after delivery. The practices are based on security procedures found in NIST special publications, and those from the National Defense University and the National Defense Industry Association, and these are expanded to include implementations specific to mitigating supply chain risk.
Typical examples of good practices recommended in the report include integrating information security and supply chain requirements from inception of the project, protecting the supply chain environment, hardening the supply chain delivering mechanisms and configuring the product to limit access and exposure.
NIST is requesting comments on the draft document to be sent to email@example.com by August 15.
The Comprehensive National Cybersecurity Initiative 11, "Develop Multi-Pronged Approach for Global Supply Chain Risk Management," currently is pilot testing many of the practices. To get a more thorough sample, the writers of this draft report are asking readers to consider testing a few of the practices and to provide comments and lessons learned to the same e-mail address by Dec. 30, 2010.
* Categorizing system impact level is described in a NIST document, Standards for Security Categorization of Federal Information and Information Systems (Federal Information Processing Standards Publication 199), available on-line at http://csrc.nist.gov/publications/fips/fips199/FIPS-PUB-199-final.pdf.
** Recommended Security Controls for Federal Information Systems and Organizations (Rev. 3), available on-line at http://csrc.nist.gov/publications/nistpubs/800-53-Rev3/sp800-53-rev3-final_updated-errata_05-01-2010.pdf.
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NIST Seeks New Members for Nine Advisory Committees
The National Institute of Standards and Technology (NIST) is requesting nominations of qualified individuals for its nine existing Federal Advisory Committees. Nominations for all committees will be accepted on an ongoing basis and will be considered as and when vacancies arise. A July 27, 2010, Federal Register notice* details each committee, including the number of members serving on the committee, its objectives and duties, the nomination procedure and committee contacts.
New to the list of NIST advisory committees this year is the NIST Smart Grid Advisory Committee. The Energy Independence and Security Act (EISA) of 2007 charges NIST with primary responsibility to coordinate development of technical protocols and standards necessary for interoperability of smart grid devices and systems. This advisory committee provides guidance to the NIST Director on the overall direction, status and health of the Smart Grid implementation and identifies issues and needs. Input from the committee will be used to help guide Smart Grid Interoperability Panel activities and assist NIST in directing research and standards activities.
The other NIST advisory committees described in the Federal Register notice are: the Board of Overseers of the Malcolm Baldrige National Quality Award, the Judges Panel of the Malcolm Baldrige National Quality Award, the Information Security and Privacy Advisory Board, the Manufacturing Extension Partnership Advisory Board, the National Construction Safety Team Advisory Board, the Advisory Committee on Earthquake Hazards Reduction, the Technology Innovation Program Advisory Board, and the Visiting Committee on Advanced Technology.
* "Request for nominations for members to serve on National Institute of Standards and Technology Federal Advisory Committees," Federal Register Vol. 75, No. 143, p. 43933 (Tuesday, July 27, 2010) See http://www.gpoaccess.gov/fr/.
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Commerce Department Seeks Comments on Cybersecurity and Its Impact on Innovation
The Commerce Department has published a Notice of Inquiry (NOI) on "Cybersecurity, Innovation, and Internet Policy." The department seeks comments from all stakeholders, including the commercial, academic and civil society sectors, on measures to improve cyber security while sustaining innovation.
The Internet has become vitally important to U.S. innovation, prosperity, education, civic activity and cultural life as well as aspects of America's national security. A top priority of the Commerce Department is to ensure that the Internet remains an open and trusted infrastructure, both for commercial entities and individuals.
To support this goal, U.S. Commerce Secretary Gary Locke created the department's Internet Policy Task Force in April. Its mission is to identify leading policy challenges and to recommend possible solutions. The Task Force draws upon expertise across many bureaus at the Commerce Department, including those responsible for cybersecurity standards and best practices, information and communications policy, international trade, intellectual property, business advocacy and export control.
This Notice of Inquiry is one in a series of inquiries from the Task Force. Other reviews examine information privacy, global free flow of information on the Internet, and online copyright protection issues. After analyzing comments on this notice, the department intends to issue a report that will contribute to the Administration's domestic and international policies and activities in advancing both cyber security and the Internet economy.
* "Cybersecurity, Innovation and the Internet Economy," Federal Register Vol. 75, No. 144 , p. 44216. (Wednesday, July 28, 2010) See http://www.gpoaccess.gov/fr/. A copy of the text also is available on-line at http://www.nist.gov/itl/csd/upload/Cybersecurity_NOI_0722101.pdf.
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