Oct. 12, 2006

	In This Issue:
	Fossilized Liquid Assembly: Nanomaterials Research Tool
	Molecular Spintronic Action Confirmed in Nanostructure
	New Fertilizer SRM Can Help Control Heavy Metal Content
	NIST Issues Four-Pack of Computer Security Pubs
	Quick Links
	NIST Releases New Standard for Semiconductor Industry

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Fossilized Liquid Assembly: Nanomaterials Research Tool

Optical microscope image (lower plane) shows spheres at mutiple size scales self-arranging in complex "super-assemblies" in NIST's hierarchical topology modeling system. Atomic-force microscopy (detail) shows the textured surface formed by the spheres. Credit: NIST View hi-resolution image

From a butterfly’s iridescent wing to a gecko’s sticky foot, nature derives extraordinary properties from ordinary materials like wax and keratin. Its secret is hierarchical topology: macroscale structures assembled from microscale components of varying sizes. Borrowing a page from nature’s playbook, researchers at the National Institute of Standards and Technology (NIST) have developed a novel platform for the self-assembly of experimental hierarchical surfaces in a fluid. Their work offers diverse industries a new way to generate and measure self-assembly at the nano-scale.

A butterfly’s wings shimmer because light plays upon tiny rows of scales, like tiles on a Spanish roof. The gecko sticks to surfaces because its feet are patterned with microscopic hairs, each hair tipped with hundreds of even tinier projections. Beads of water roll off the lotus’s leaf because its surface is streaked with microscopic peaks, each with a finer structure, that makes the surface “super hydrophobic.” These enhanced properties—other possibilities include super adhesion and low friction—have attracted the attention of design engineers for applications from bioengineered tissues to photonic crystals to submarines that slice through water with minimal drag.

Creating these topologically complex, self-assembled surfaces for study has been a challenge. If the components are mixed on a surface, that substrate affects how they assemble; if mixed in a solvent and dried, the drying process similarly distorts the results. In a recent paper*, the NIST team detailed a much simpler and faster system they dubbed “fossilized liquid assembly” to create experimental models of hierarchical topologies in which the components are allowed to mix and assemble freely in a fluid, and then quickly “frozen” in place for study. The key is the use of solutions of water and a special monomer that polymerizes—links together—when exposed to ultraviolet light. Like an oil-water mixture, the fluid forms liquid interfaces that can be manipulated to create a desired hierarchical structure and then suddenly solidified with a burst of UV light.

Lead researcher and physicist Alamgir Karim estimates that it takes about five minutes to make a sample of self-assembling particles using NIST’s approach. Other methods, he notes, not only are more complicated and costly, but also do not allow the structures to form as freely. With the new technique, engineers also will be able to build complex dynamic structures and freeze them into solid form, studying self-assembly under the microscope. “How do you take a snapshot of shampoo in action?” asks physicist Jason Benkoski, first author of the paper. “We can now directly observe these small, mobile, delicate structures.”

The researchers also are using the new platform to better understand the fundamental physics behind the formation of hierarchical topology, studying, for example how different forces dominate at different scales of length. Looking ahead, the NIST team plans to build on this study, expanding the technology as a 3D imaging platform.

The work was supported by NIST and a National Research Council Fellowship.

* J.J. Benkoski, H. Hu, and A. Karim. Generation of hierarchical topologies from photocrosslinkable, particle-stabilized emulsions. Macromolecular Rapid Communications. Aug. 2, 2006

Media Contact:
Mark Bello, mark.bello@nist.gov, (301) 975-3776

 

Molecular Spintronic Action Confirmed in Nanostructure

NIST researchers made the first confirmed "spintronic" device incorporating organic molecules using a nanoscale pore test structure, which consisted of self-assembled molecules (shown in white within the middle blue layer in the illustration) sandwiched between nickel and cobalt electrodes (gray top and bottom layers). The pore structure, less than 40 nanometers in diameter, confines the molecules to a very small area, thus enabling good molecule-metal contacts and limiting defects. View .avi file (requires Realplayer or Windows Media Player) Credit: D. DeLongchamp/NIST View hi-resolution image

Researchers at the National Institute of Standards and Technology (NIST) have made the first confirmed “spintronic” device incorporating organic molecules, a potentially superior approach for innovative electronics that rely on the spin, and associated magnetic orientation, of electrons. The physicists created a nanoscale test structure to obtain clear evidence of the presence and action of specific molecules and magnetic switching behavior.

Whereas conventional electronic devices depend on the movement of electrons and their charge, spintronics works with changes in magnetic orientation caused by changes in electron spin (imagine electrons as tiny bar magnets whose poles are rotated up and down). Already used in read-heads for computer hard disks, spintronics can offer more desirable properties—higher speeds, smaller size—than conventional electronics. Spintronic devices usually are made of inorganic materials. The use of organic molecules may be preferable, because electron spins can be preserved for longer time periods and distances, and because these molecules can be easily manipulated and self-assembled. However, until now, there has been no experimental confirmation of the presence of molecules in a spintronic structure. The new NIST results are expected to assist in the development of practical molecular spintronic devices.

The experiments, described in the October 9 issue of Applied Physics Letters,* used a specially designed nanoscale “pore” in a silicon wafer. A one-molecule-thick layer of self-assembled molecules containing carbon, hydrogen and sulfur was sandwiched in the pore, between nickel and cobalt electrodes. The researchers applied an electric current to the device and measured the voltage levels produced as electrons “tunneled” through the molecules from the cobalt to the nickel electrodes. (Tunneling, observed only at nanometer and atomic dimensions, occurs when electrons exhibit wave-like properties, which permit them to penetrate barriers.)

The pore structure stabilized and confined the test molecules and enabled good molecule-metal contacts, allowing the scientists to measure accurately temperature-dependent behavior in the current and voltage that confirm electron tunneling through the molecular monolayer. Some electrons can lose energy while tunneling, which corresponds to vibration energies unique to the chemical bonds within the molecules. The NIST team used this information to identify and unambiguously confirm that the assembled molecules remain encapsulated in the pore and are playing a role in the device operation. In addition, by varying the magnetic field applied to the device and measuring the electrical resistance, the researchers identified magnetic switching in the electrodes from matching to opposite polarities.

This work was supported in part by the Defense Advanced Research Projects Agency.

* W. Wang and C.A. Richter. Spin-polarized inelastic electron tunneling spectroscopy of a molecular magnetic tunnel junction. Applied Physics Letters. Oct. 9, 2006.

 

Media Contact:
Laura Ost, laura.ost@nist.gov, (301) 975-4034

 

New Fertilizer SRM Can Help Control Heavy Metal Content

A new reference material developed by the National Institute of Standards and Technology (NIST) can help the agriculture industry and state regulators monitor the concentrations of several potentially hazardous heavy metal contaminants in fertilizers.

Modern multi-nutrient fertilizers produced for home and agricultural use are formulated from multiple sources to provide significant amount of nitrogen, phosphorus and potassium, the major plant nutrients, and lesser or even trace amounts of other nutrients needed by different crops, such as boron, calcium, iron and zinc.

 

Until relatively recently, fertilizers were tested and certified for their nutrient content, but little attention was paid to the possibility of  heavy metal contaminants introduced by the mineral sources used to prepare the fertilizer. However, in response to incidents of heavy metal contamination of cropland, several states have enacted regulations in the past seven years that limit the amounts of some potentially hazardous non-nutritive elements in fertilizers. Several countries, including Japan, China, and Australia, and the European Union, also limit the amount of selected elements in fertilizers.

 

While fertilizer manufacturers and state regulatory authorities have needed to develop analytical methods to implement these regulations, until now there have been no certified reference materials available that they could use to validate the accuracy of their measurements. It can be difficult to measure accurately trace levels of some metals in a chemically complex mixture like fertilizer.

 

NIST’s Standard Reference Material, SRM 695, “Trace Elements in Multi-Nutrient Fertilizer,” was developed in collaboration with members of the Association of American Plant Food Control Officials (AAPFCO) and The Fertilizer Institute (TFI) to help meet this need. SRM 695 is a typical multi-nutrient fertilizer certified for the content of both major elements and trace elements, including calcium, iron, magnesium, manganese, sodium, potassium, zinc, arsenic cadmium, chromium, cobalt, copper, mercury, molybdenum, nickel, lead and vanadium. Additional reference values are provided for aluminum, boron, nitrogen, phosphorous and selenium.

 

To order SRM 695, Trace Elements in Multi-Nutrient Fertilizer, see: https://srmors.nist.gov/view_cert.cfm?srm=695.

Media Contact:
Michael Baum, michael.baum@nist.gov, (301) 975-2763

 

NIST Issues Four-Pack of Computer Security Pubs

The National Institute of Standards and Technology recently issued four publications to provide computer security advice on issues ranging from securing Windows XP Home Edition® computers and exercising IT plans to guidance on access control policies, models and mechanisms, and security log management.

• Guidance for Securing Microsoft Windows XP Home Edition: A NIST Security Configuration Checklist (http://csrc.nist.gov/itsec/guidance_WinXP_Home.html) provides advice on securing Windows XP Home Edition computers for home users, in particular telecommuting Federal employees. It explains the need to use a combination of security protections and provides instructions on how to implement the most essential security protections. 
• Guide to Test, Training, and Exercise Programs for IT Plans and Capabilities (http://csrc.nist.gov/publications/nistpubs/800-84/SP800-84.pdf) provides guidance on conducting tests, training sessions, and exercises to maintain contingency and computer security incident response plans for managing adverse IT situations.
• Assessment of Access Control Systems (http://csrc.nist.gov/publications/nistir/7316/NISTIR-7316.pdf) provides background information on access control policies, models, and mechanisms to help organizations secure their computer applications.
• Guide to Computer Security Log Management (http://csrc.nist.gov/publications/nistpubs/800-92/SP800-92.pdf) provides detailed information on developing, implementing, and maintaining effective log management practices throughout an enterprise.

Media Contact:
Jan Kosko, kosko@nist.gov, (301) 975-2767

 

Quick Links

NIST Releases New Standard for Semiconductor Industry

A wide range of optical electronic devices, from laser disk players to traffic lights, may be improved in the future thanks to a small piece of semiconductor, about the size of a button, coated with aluminum, gallium, and arsenic (AlGaAs).

The 1-centimeter square coating, just 3 micrometers thick, is the first standard for the chemical composition of thin-film semiconductor alloys issued by the National Institute of Standards and Technology (NIST).  Standard Reference Material (SRM) 2841 was requested by the compound semiconductor industry to help measure and control thin film composition as a basis for optimizing material and device properties. The SRM can be used to calibrate equipment for making or analyzing these materials. Buyers are expected to include companies that grow or characterize thin films or use them to make devices, as well as government and university laboratories.  

AlGaAs is used as a barrier material to increase conductivity in high-speed circuits for wireless communication; semiconductor lasers for optical disk drives, bar code scanning, xerography, and laser surgery; and light-emitting diodes for remote controls, traffic lights, and medical instruments. The NIST standard is expected to increase the accuracy of chemical characterization of AlGaAs films by an order of magnitude over the current state of the art. Improved accuracy will reduce wasteful duplication of reference wafers, increase the free exchange of thin-film materials between vendors and their customers, and ultimately improve the accuracy of data on relationships between material composition and properties.

SRM 2841 can be ordered at http://ts.nist.gov/ts/htdocs/230/232/232.htm.

 

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Editor: Michael Baum

Date created: 10/12/06
Date updated: 10/12/06
Contact: inquiries@nist.gov