One-stop Research Shop

Tucked away in the southern corner of Washington, D.C., the Naval Research Laboratory (NRL) stands as one of the U.S.'s less-talked-about national institutions for scientific research. The lab's name may not come up often on the evening news or in family dinner conversations. Yet the discoveries, developments, and inventions coming from NRL during the past three-quarters of a century have led to technology, products, and advances that benefit people everywhere--not just in the military.

"We are the Navy and Marine Corps' corporate laboratory," says Richard L. Thompson, NRL's director of public affairs. "Our primary business here is basic research." Thompson explains that NRL's mission calls for a "broadly based and multidisciplinary research program" to support the Navy and Marine Corps' current needs, as well as those anticipated for the future. NRL also conducts research for the Department of Defense and other government agencies. Indeed, the scope of scientific research carried out at NRL is broad academically and physically. The program encompasses physical and engineering sciences and oceanic, environmental, and space-related investigations.

NRL TRACES its roots to a pre-World War I suggestion by Thomas A. Edison. In response to the growing likelihood that the U.S. would be drawn into war, the famous inventor published a letter in 1915 in the New York Times proposing that "the government should maintain a great research laboratory" in which "could be developed all the technique of military and naval progression." NRL opened its doors officially in 1923.

Since that time, the laboratory has made numerous advances reaching from land to sea, air, and space. In the 1920s, for example, NRL scientists discovered the radar principle. Within a few years, the laboratory developed the detection technology and installed radar units on battleships. The discovery led to various forms of radar detection and widespread use of the technology in military and civilian life.

For more than 50 years, NRL has been deeply involved in rocket programs. The research efforts have led to many firsts including high-altitude measurements of temperature, pressure, and other atmospheric properties, as well as the first high-altitude photos of Earth.

Success in rocket research ushered in a series of satellite programs, which are credited with advancing meteorology and communications and eventually led to a global positioning system that's the forerunner of the systems used today in private automobiles and other consumer equipment. The laboratory has also made key contributions in X-ray, ultraviolet, and radio astronomy; laser technology; sensors; materials; and other areas.

The majority of NRL's roughly 2,500 employees, including more than 550 physicists and chemists, are based at the Washington headquarters. The lab also maintains research facilities in other locations, including a center for oceanographic investigations at Stennis Space Center near Bay St. Louis, Miss.; the marine meteorology division in Monterey, Calif.; and a facility for airborne research programs based at Patuxent River Naval Air Station in Lexington Park, Md. The lab has other facilities in Chesapeake Beach, Md.; Key West, Fla.; and Mobile, Ala.

Research in chemistry, physics, biomolecular sciences, and materials science is conducted within one of NRL's main research units referred to as the Materials Science & Component Technology Directorate. "The materials directorate deals with the entire gamut of science and engineering related to materials," including energetic, biomolecular, electronic, structural, and optical materials, says Bhakta B. Rath, an associate director of research at NRL and head of the materials directorate. The directorate also has research programs that explore magnetism, superconductivity, and the structure of matter, as well as more traditional materials topics, such as metals, ceramics, polymers, and composites.

Rath has no shortage of research topics to draw upon to illustrate the diverse range of problems tackled by NRL scientists. He notes, for example, that in the area of energetic materials, which includes fuels, explosives, and propellants, researchers are studying properties of nitrocubanes. He explains that one of the goals is developing models to determine how best to store the maximum quantity of energy in the smallest volume.

Developing new classes of high-temperature polymers is another NRL focus. Phthalonitrile-based materials prepared at NRL have been shown to withstand temperatures above 600 °C, Rath says. Lightweight, fiber-reinforced composites made from temperature-resistant polymers could be used in a variety of industrial applications, including compressors and structural members on ships and submarines.

Because of the special hazards of fire in maritime operations, fire safety occupies a prominent position among NRL research topics. "People think that if you are in the middle of the sea, you have all the water you need to control on-board fires," Rath remarks. But, in fact, heat and smoke propagate extremely fast in the interior of a ship or submarine, he points out. "It's a very serious problem." Rath adds that the problem is compounded in confined and oxygen-depleted spaces where combustion processes can produce hazardous reactive intermediate species.

A unique part of the fire safety research program is based in Mobile Bay, Ala., where a decommissioned Navy landing ship, the former U.S.S. Shadwell, is permanently moored. The ship is set ablaze regularly under controlled conditions to conduct tests and evaluate fire-fighting techniques. One of the many challenges in that area is finding replacements for halon-based firefighting agents. Rath notes that NRL scientists have had success using sprays consisting of submicrometer-sized water droplets, which, he notes, "have a tremendously high quenching effect."

The 900 or so people working within the materials directorate are grouped into large divisions such as chemistry, electronics, and plasma physics. Divisions are made up of research branches, which in turn are subdivided into smaller research groups referred to as sections. In the chemistry division, for example, the surface chemistry and materials chemistry branches each have a number of research sections that in many ways resemble university research groups.

Leonard J. Buckley heads NRL's materials chemistry branch, which focuses on a number of topics including designing, synthesizing, and characterizing novel materials. "My philosophy has been to perform the best possible research on problems of high interest to the Navy, Department of Defense, and the nation," Buckley says. Regarding the types of research projects best suited to NRL, Buckley contends that "we should do research and development that may not be that easy to perform solely at a university or defense contractor." But because NRL's mission and motivation to conduct research differs from the motivation of defense companies and universities, it's important for NRL to collaborate with those types of institutions, he says.

As a case in point, Buckley describes a project on bioinspired optics that involves a number of collaborations. The overall project is run by the Defense Advanced Research Projects Agency, for which Buckley serves as a program manager. NRL has teamed up with Case Western Reserve University on one aspect of the project with the goal of developing, building, and testing sophisticated lenses made of synthetic materials for use on unmanned air vehicles. One such vehicle, the Dragon Eye, is an NRL-developed flying machine that resembles a model airplane and is used by the Navy to collect information remotely.

Buckley explains that animals' eyes are sophisticated optical systems that are endowed with properties and functions not found in human-made optics. Lenses made from ground glass and other materials, for example, have a particular shape and are characterized by a single index of refraction. In telescope and camera lenses, those characteristics aren't variable--they're fixed.

In contrast, the index of refraction and shape of biological lenses can change in response to an organism's environment. That flexibility provides fish and other animals with very wide and variable fields of view, as well as the ability to focus at far and short distances with high resolution at both extremes. "It's amazing what eyes are capable of doing," Buckley says. Inspired by nature's examples, Buckley and coworkers aim to use synthetic materials to develop simple, lightweight, and high-performance optical systems to improve the capabilities of unmanned aircraft.

ALTHOUGH MUCH of the strategy for making the novel optics is being kept under wraps for now for patent protection purposes, Buckley reveals that a key part involves developing dynamic lenses with graded indices of refraction--meaning an index of refraction that varies spatially across a lens--that can be induced to change. Candidate materials investigated for the application include composite polymers with alternating parallel nanometer-sized domains. Examples of such materials are the polyester/polystyrene and polymethylmethacrylate/polycarbonate composites prepared by the research group of Eric Baer, a professor in Case Western's department of macromolecular science and engineering.

As important as it is for unmanned vehicles to have clear fields of view, it's arguably more important for operators of manned vehicles to be able to see where they're going. Helicopter pilots working in desert areas during Operation Iraqi Freedom were often faced with the dangers of landing their aircraft under brownout conditions, in which visibility is poor because of airborne dust and sand whipped up by the rotors. The flying debris is also harmful to troops on the ground and can damage engines. So NRL scientists were called upon to help out.

James H. Wynne, a staff researcher in the materials chemistry branch, notes that he and his coworkers formulated an aqueous polysaccharide-based solution containing surfactants and other components for use as a dust abatement product. The material, which was shown in desert tests to be effective in holding down dust and sand with a range of particle sizes, solidifies as it is sprayed on the desert floor, thereby preventing brownouts.

Wynne points out that, unlike some commercial dust-control products, the NRL solution is biodegradable, nontoxic, nonflammable, and inexpensive. And in addition to those benefits, the material was developed quickly, Wynne emphasizes.

"We received an e-mail after lunch from Centcom [U.S. military Central Command] describing the problem, and by the end of the day we had a solution ready for testing." Just recently, the product was licensed to a private company for manufacturing.

Elsewhere in the materials chemistry branch, researchers have been developing chemical sensors based on gold nanoclusters modified with a molecular layer of an organic compound. By measuring changes in electrical conductivity between the metal clusters and a microelectrode as analyte molecules bind to the clusters, the sensors can be used to detect some analytes selectively in sub-parts-per-million concentrations. The work has led to a prototype handheld vapor sensor developed in collaboration with Microsensor Systems, Bowling Green, Ky.

In related work, NRL scientists Edward E. Foos, Arthur W. Snow, and their coworkers recently developed a technique for isolating large quantities of trioxyethylene-encapsulated gold nanoclusters labeled with a single strand of DNA [Nano Lett., 4, 737 (2004)]. The new method, which is more straightforward than the established electrophoresis technique, may be useful in a number of applications that rely on DNA recognition to drive molecular-scale self-assembly.

In the surface chemistry branch, which, with about 70 people, is the largest branch within the chemistry division, scientists explore nanoscale surface and interface phenomena, wear and corrosion processes, electrochemistry, and other topics in which molecular layers just a few atoms thick play a central role. Richard J. Colton, who is head of the branch, notes that the scope of surface chemistry research topics is quite broad, "from very fundamental to very applied." For example, some projects focus on basic surface physics and rely on scanning probe analysis and surface spectroscopy methods. Other work involves developing and testing single-molecule biosensors.

THE DIVERSITY of researchers' backgrounds and skills is one of the factors that enables such wide-ranging research to be carried out successfully, Colton says. Equally important is the ease of interacting with scientists in various sections and divisions throughout the lab. According to Colton, the collaborative environment is one of the hallmarks of research at NRL.

One of the more fundamental research thrusts in surface chemistry involves studying the structure and properties of semiconductor surfaces and interfaces. Lloyd J. Whitman, who leads the surface nanoscience and sensor technology section, in which such studies are carried out, explains that probing semiconductors at the atomic scale is crucial for understanding the behavior of military electronic components.

For that reason, Whitman and coworkers in the electronics division use high-vacuum methods and other techniques to relate conditions used for growing semiconductors such as GaSb/InAs to properties of the material. The idea is to be able to correlate material properties with characteristics of an electronic device made from the material. Whitman's group analyzed GaSb/InAs interfaces because III-V semiconductors of this type are of interest to the military for use as long-wavelength infrared detectors for ballistic missile defense applications.

The surface nanoscience group also studies properties of biomolecules and biomolecular interfaces. Atomic force microscopy studies of intermolecular forces conducted by Colton and coworkers several years ago led to a force-discrimination technique in which magnetic microbeads label captured biomolecules and also serve to apply a force that discriminates between specific and nonspecific binding events. Whitman notes that the force-discrimination assays are the basis of a number of biosensor systems that are now being commercialized.

Studying the surface behavior of biomolecules led Whitman and coworkers to a surprising discovery. From competitive adsorption measurements, the group found that the four DNA bases bind to gold with very distinct affinities. Adenine's attraction to gold is sufficiently strong that it displaces other molecules. In contrast, thymine hardly interacts with gold. And the affinities of cytosine and guanine fall between those of adenine and thymine [J. Am. Chem. Soc., 125, 9014 (2003)].

Molecular-scale wear and tear and the effects of friction and lubrication are studied by NRL surface scientists in the tribology section. Staff researcher Kathryn J. Wahl explains that the purpose of the tribology program is to develop the scientific basis for understanding why some materials are endowed with low-friction or low-adhesion surfaces and others are not. The damaging effects of friction and adhesion need to be controlled to maintain engines, aircraft, ships, and other military equipment in peak operating condition.

Examining the interface between two materials--while they are in contact and moving with respect to one another--can be challenging. One strategy used by NRL researchers calls for sandwiching a lubricant between two materials, at least one of which is transparent, in a specially designed laboratory setup. The apparatus enables mechanical forces to be measured while the contact is examined visually with optical microscopy, videography, and other methods, and probed simultaneously via Raman spectroscopy. Using the combination of probes while the materials are in sliding contact, the researchers can monitor the physical and chemical changes as they occur.

In studies using diamond-like carbon films and amorphous Pb-Mo-S as lubricants, Wahl, Irwin L. Singer, and coworkers concluded that the measured friction behavior could be attributed to accumulation, then loss, of a thin layer of material between the lubricant film and the sliding body. The so-called transfer films were determined to consist of graphitelike carbon in one case and MoS₂ in the other.

While some scientists depend primarily on laboratory instruments to conduct research, others rely on computers. In the Center for Computational Materials Science, NRL researchers use computer-based methods to explore properties of known and as-yet-unsynthesized materials.

In one example, Steven C. Erwin and Igor Zutic used computational techniques to explore relationships between electronic and magnetic properties in manganese-doped ferromagnetic semiconductors known as II-IV-V₂ chalcopyrites. The materials may lead to breakthroughs in chip designs for "spintronic" computers. Out of 64 compounds in this class of materials, of which only three have been shown experimentally to be ferromagnetic semiconductors, the team identified a small subset of stable chalcopyrites with excellent prospects for ferromagnetism [Nat. Mater., published online May 16, http://dx.doi.org/10.1038/nmat1127].

In other examples of the center's work, Mark R. Pederson and coworkers use computational techniques to understand properties of Mn₁₂-acetate and other molecular magnets and melanin monomers, which are building blocks of bio-macromolecules. And Alexander Efros studies quantum dots and related systems for use in optoelectronics and quantum computing applications.

With research programs ranging from explosives to X-ray astronomy and from weather prediction to warfare systems, describing NRL's scientific activities as "multidisciplinary" is an understatement. Indeed, as Rath notes, the scope of research efforts at NRL seems to encompass much of science and engineering.