NIST Tech Beat - October 25, 2007

In the growing catalog of nanoscale technologies, nanowires—tiny rows of conductor or semiconductor atoms—have attracted a great deal of interest for their potential to build unique atomic-scale electronics. But before you can buy some at your local Nano Depot, manufacturers will need efficient, reliable methods to build them in quantity. Researchers at the National Institute of Standards and Technology (NIST) believe they have one solution—a technique that allows them to selectively grow nanowires on sapphire wafers in specific positions and orientations accurately enough to attach contacts and layer other circuit elements, all with conventional lithography techniques. They detailed their results in a recent paper.*

Despite their name, nanowires are more than just electrical connectors. Researchers have used nanowires to create transistors like those used in memory devices and prototype sensors for gases or biomolecules. However working with objects only tens of nanometers wide is challenging. A common approach in the lab is to grow nanowires like blades of grass on a suitable substrate, mow them off and mix them in a fluid to transfer them to a test surface, using some method to give them a preferred orientation. When the carrier fluid dries, the nanowires are left behind like tumbled jackstraws. Using scanning probe microscopy or similar tools, researchers hunt around for a convenient, isolated nanowire to work on, or place electrical contacts without knowing the exact positions of the nanowires. It’s not a technique suitable for mass production.

Building on earlier work to grow nanowires horizontally on the surface of wafers (see “Gold Nano Anchors Put Nanowires in Their Place”), NIST researchers used conventional semiconductor manufacturing techniques to deposit small amounts of gold in precise locations on a sapphire wafer. In a high-temperature process, the gold deposits bead up into nanodroplets that act as nucleation points for crystals of zinc oxide, a semiconductor. A slight mismatch in the crystal structures of zinc oxide and sapphire induces the semiconductor to grow as a narrow nanowire in one particular direction across the wafer. Because the starting points and the growth direction are both well known, it is relatively straightforward to add electrical contacts and other features with additional lithography steps.

As proof of concept, the NIST researchers have used this procedure to create more than 600 nanowire-based transistors, a circuit element commonly used in digital memory chips, in a single process. In the prototype process, they report, the nanowires typical grew in small bunches of up to eight wires at a time, but finer control over the size of the initial gold deposits should make it possible to select the number of wires in each position. The technique, they say, should allow industrial-scale production of nanowire-based devices.

* B. Nikoobakht. Toward industrial-scale fabrication of nanowire-based devices. Chem. Mater., ASAP Article 10.1021/cm071798p S0897-4756(07)01798-X. Web Release Date: October 9, 2007.

A recently completed licensing agreement for two novel National Institute of Standards and Technology (NIST) technologies may help bring affordable graphic reading systems for the blind and visually impaired to market. The two systems bring electronic images to life in the same way that Braille makes words readable.

ELIA Life Technology Inc. of New York, N.Y., licensed for commercialization both the tactile graphic display device and fingertip graphic reader developed by NIST researchers. The former, first introduced as a prototype in 2002, allows a person to feel a succession of images on a reusable surface by raising some 3,600 small pins (actuator points) into a pattern that can be locked in place, read by touch and then reset to display the next graphic in line. Each image—from scanned illustrations, Web pages, electronic books or other sources—is sent electronically to the reader where special software determines how to create a matching tactile display. (For more information, see “NIST ‘Pins’ Down Imaging System for the Blind”.)

An array of about 100 small, very closely spaced (1/10 of a millimeter apart) actuator points set against a user’s fingertip is the key to the more recently created “tactile graphic display for localized sensory stimulation.” To “view” a computer graphic with this technology, a blind or visually impaired person moves the device-tipped finger across a surface like a computer mouse to scan an image in computer memory. The computer sends a signal to the display device and moves the actuators against the skin to “translate” the pattern, replicating the sensation of the finger moving over the pattern being displayed. With further development, the technology could possibly be used to make fingertip tactile graphics practical for virtual reality systems or give a detailed sense of touch to robotic control (teleoperation) and space suit gloves.

The inspiration for both NIST graphic displays came from a “bed of nails” toy found in a novelty store. Watching the pins in the toy depress under fingers and then return to their original state started the researchers thinking about how the principle could be applied to electronic signals.

Persons interested in licensing these or other NIST technologies should contact Terry Lynch, NIST Office of Technology Partnerships, terry.lynch@nist.gov, (301) 975-2691.

“In case of fire use the stairs, not the elevator”— appears on signs posted in elevator lobbies throughout the United States. In the aftermath of Sept. 11, 2001, however, experts are starting to reconsider tall building evacuation strategies. Earlier this year, the National Institute of Standards and Technology (NIST) recommended code changes to increase elevator use in high-rise emergencies in the report of its three-year investigation of the World Trade Center (WTC) collapses, and next April NIST will sponsor a conference to consider the benefits of elevator evacuations, including the advantages for persons with disabilities.

Depending on stairway evacuation alone can be risky, NIST fire prevention engineer Richard Bukowski observed in a recent talk in London.* “The time needed to descend undamaged and smoke-free stairs is about one floor per minute,” he says. “If the fire is on the 60th floor, occupants on that floor or above will spend one hour or more trying to escape the building. Escape from such a height can be exhausting for those in the best shape, let alone those who are elderly or have lower stamina.” However, it would take much more time or even be impossible to evacuate a building by stairs for some persons who need wheelchairs, walkers or crutches; for people with respiratory or cardiac conditions or obesity; and for those with temporary conditions ranging from pregnancy to sprains. Situations in which a person’s wheelchair provides critical life support can also present additional problems. Such chairs are usually quite heavy and difficult for even several people to carry down stairs.

Elevator evacuation, however, would enable people with disabilities to self-evacuate with all the other building occupants. Elevator systems in modern high-rise commercial buildings are designed to move a building’s entire population in or out of the building in one hour or less. In emergencies, elevators could be programmed to move those with the longest distance to go first. Occupants of lower floors (without disabilities) would have a choice to use the stairs. During a total evacuation, elevators would collect occupants from the highest floors first, shuttle them to the exit level and return for another load, working their way down from the top. Pressing a call button would register people awaiting pickup but would not alter the sequence nor would the buttons in the elevator car. People with disabilities would not need to be given any priority since all occupants would be accommodated equally in this system. One elevator should be assigned exclusively to firefighters to provide rapid access to fires on upper floors.

U.S. building codes are currently considering proposals to require such elevators in tall buildings, and regulators in several countries are interested in requiring evacuation elevators as part of their disability regulations. The NIST “Rethinking Egress” conference will be held in Gaithersburg, Md., in April 2008.

* R.W. Bukowski. Emergency egress strategies for buildings. By Richard W. Bukowski. Presented at the International Interflam Conference, London, England. Sept. 3-5, 2007.

Thanks to the polymerase chain reaction (PCR), a method for making multiple copies of DNA fragments, even tiny bits of biological evidence (in the form of hair, tissue, bones, teeth, blood or other bodily fluids) from a crime scene can be used to isolate genetic material that eventually can identify a suspect or victim. A new Standard Reference Material from the National Institute of Standards and Technology (NIST), SRM 2372 (Human DNA Quantitation Standard), is available to help ensure the success of this identification process, known as DNA profiling.

One profiling method popular with forensic experts uses short tandem repeats (STRs are short identical sequences of DNA found in specific regions of a chromosome) to compare samples of DNA from a crime scene to DNA from a suspect or victim. Commercial PCR systems that amplify STRs work best if the amount of DNA—measured in nanograms per microliter of solution—fed into the system is within a narrow range. Too concentrated a solution overwhelms the detection apparatus; too dilute yields poor results or none at all.

DNA quantitation—assessing the amount of DNA present in a crime scene sample—is the necessary precursor to making a suitable solution for profiling. A widely used method to achieve this is quantitative PCR (qPCR); however, current commercial qPCR kits may produce varying values for the DNA concentrations in the kit’s reference samples, rendering these standards less reliable for assaying the quantity of extracted evidential DNA. SRM 2372 can be used by qPCR manufacturers to calibrate their systems in the factory so that measurements made with the kits in forensic laboratories are consistently accurate.

The SRM contains samples of human genomic DNA from three sources—an individual male, multiple female donors and a mix of male and female donors. Each sample has been prepared to yield an optical density (OD) of 1.0 on a spectrophotometer when examined using a 260-nanometer wavelength of light. Scientists have determined that for a solution of double-stranded DNA, an OD of 1.0 at 260 nanometers corresponds to 50 micrograms of DNA per milliliter of solution.

Widely recognized as the engine that drives the U.S. economy, information technology enables the vast majority of organizations to carry out their missions and business operations more efficiently and effectively. Along with their power and usefulness, however, information systems face serious man-made and natural threats that can adversely affect their associated organization’s mission, operations, image and reputation. In order to provide guidelines for addressing these potential threats, the National Institute of Standards and Technology (NIST) has issued a draft of Special Publication 800-39, Managing Risk from Information Systems: An Organizational Perspective, for public comment.

Risk management is a balancing act, requiring explicit management decisions that trade off the utility and convenience of modern information systems against the potential for serious harm if they are misused. Intended for individuals ranging from agency heads to system administrators, NIST’s new guide outlines a top-level process for building and implementing a technically sound and effective information security program within an organization. It ties together various NIST computer security documents and when finalized, it will become the flagship document in a series of NIST documents related to FISMA—the Federal Information Security Management Act.

The draft document is available at http://csrc.nist.gov/publications/PubsDrafts.html. As with all NIST Special Publications, the public review process is an essential part of the document’s development. The public comment period for the document is Oct. 29–Dec. 14, 2007. Comments may be submitted via electronic mail at sec-cert@nist.gov or via regular mail at 100 Bureau Drive (Mail Stop 8930) Gaithersburg, MD 20899-8930.

Four members of the National Institute of Standards and Technology (NIST) staff have been honored in the 2007 Presidential Rank Awards. The awards recognize exceptional long-term accomplishments in public service by career senior government executives. There are two categories of rank awards: Distinguished and Meritorious. This year’s Distinguished category honoree is Charles W. Clark of the NIST Physics Laboratory and the NIST-University of Maryland Joint Quantum Institute (JQI). Honorees in the Meritorious category are Richard F. Kayser Jr., NIST Acting Deputy Director, William J. Boettinger of the NIST Materials Science and Engineering Laboratory, and Paul S. Julienne of the NIST Physics Laboratory and JQI.

Award winners are nominated by their agency heads, evaluated by boards of private citizens, and approved by the President. The evaluation criteria focus on leadership and results. See www.opm.gov/ses/presrankaward.asp.

The American Association for the Advancement of Science (AAAS) has named NIST physicist Paul D. Lett as one of its new fellows. AAAS cites Lett for his work in developing a technique that can be used to measure the forces between atoms cooled very close to absolute zero (–273.15 degrees Celsius or –459.67 degrees Fahrenheit). The technique, known as molecular photoassociative spectroscopy, shines laser light on two slowly colliding atoms in an ultracold gas and gives them energy to join together and form molecules. The colors (frequencies) of the light that allow this to happen provide information on the forces the atoms exert on one another, and yields information on the structure of the molecules and the basic nature of different types of atoms. In their citation, AAAS calls the technique “the single most powerful tool for studying the interactions between ultracold atoms.” Lett, who is also affiliated with the NIST-University of Maryland Joint Quantum Institute, will be presented with an official certificate and a gold rosette pin on Saturday, Feb. 16, 2008, during the 2008 AAAS Annual Meeting in Boston.

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Editor: Michael Baum

Date created: October 25, 2007
Date updated: October 25, 2007
Contact: inquiries@nist.gov