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SANDIA LAB NEWS

March 18, 2005

LabNews 03/18/2005PDF (650KB)

Tiny porphyrin tubes may lead to new nanodevices

By Chris Burroughs

Sunlight splitting water molecules to produce hydrogen by devices too small to be seen in a standard microscope. That’s a goal of a research team led by Sandian John Shelnutt (1116) that has captured the interest of chemists around the world who pursue this “Holy Grail of chemistry."

“The broad objective of the research is to design and fabricate new types of nanoscale devices,” John says. “This investigation is exciting because it promises to provide fundamental scientific breakthroughs in chemical synthesis, self-assembly, electron and energy transfer processes, and photocatalysis. Controlling these processes is necessary to build nanodevices for efficient water splitting, potentially enabling a solar hydrogen-based economy.”

The prospect of using sunlight to split water at the nanoscale grew out of John’s research into the development of hollow porphyrin nano-tubes (see “Porphyrin nanotubes versus carbon” on page 4). These light-active nanotubes can be engineered to have minute deposits of platinum and other metals and semiconductors on the outside or inside of the tube.

The key to making water-splitting nanodevices is the discovery by Zhongchun Wang (1116) of nanotubes composed entirely of porphyrins. Wang is a postdoctoral fellow at the University of Georgia working in John’s Sandia research group. The porphyrin nanotubes are micrometers in length and have diameters in the range of 50-70 nm with approximately 20-nm-thick walls. They are prepared by ionic self-assembly of two oppositely charged porphyrins — molecules that are closely related to chlorophyll, the active parts of photosynthetic proteins.

These hollow structures are one member of a new class of nanostructures made of porphyrins that John and his team are developing. The porphyrin building blocks (tectons) can be altered to control their structural and functional properties.

John says these porphyrin nanotubes have “interesting electronic and optical properties such as an intense resonance light scattering ability and photocatalytic activity.” When exposed to light, some porphyrin nanotubes can photocatalytically grow metal structures onto tube surfaces to create a functional nanodevice. For example, when the nanotubes are put into a solution with gold or platinum ions and exposed to sunlight, their photocatalytic activity causes the reduction of the ions to the metal. Using this method the researchers have deposited platinum outside the nanotube and grown a nanowire of gold inside the tube.

The nanotube with the gold inside and platinum outside is the heart of a nanodevice that may split water into oxygen and hydrogen. The research team has already demonstrated that the nanotubes with platinum particles on the surface can produce hydrogen when illuminated with light. To complete the nanodevice that splits water, a nanoparticle of an inorganic photocatalyst that produces oxygen must be attached to the gold contact ball that naturally forms at the end of the tube. The gold nanowire and ball serve as a conductor of electrons between the oxygen- and hydrogen-producing components of the nano device. The gold conductor also keeps the oxygen and hydrogen parts separate to prevent damage during operation.

“Laboratory-scale devices of this type have already been built by others,” John says. “All we are doing is reducing the size of the device to reap the benefits of the nanoscale architecture.”

John says the nanodevice could efficiently use the entire visible and ultraviolet parts of the solar spectrum absorbed by the tubes to produce hydrogen, one of the “Holy Grails of chemistry.”

These nanotube devices could be suspended in a solution and used for photocatalytic solar hydrogen production.

“Once we have functional nanodevices that operate with reasonable efficiency in solution, we will turn our attention to the development of nanodevice-based solar light-harvesting cells and the systems integration issues involved in their production,” John says. “There are many possible routes to the construction of functional solar cells based on the porphyrin nanodevices. For example, we may fabricate nanodevices in arrays on transparent surfaces, perhaps on a masked free-standing film. However, we have a lot of issues to resolve before we get to that point.”

Water-splitting is just one of the possible applications of the nanodevices based on porphyrin nanostructures. John expects the tubes to have uses as conductors, semiconductors, and photoconductors, and to have other properties that permit them to be used in electronic and photonic devices and as chemical sensors. -- Chris Burroughs

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ARM-UAV program makes it to the arctic for first time

By Nancy Garcia

A dozen years after it got off the ground, DOE’s Atmospheric Radiation Measurement – Unmanned Aerospace Vehicle (ARM-UAV) Program carried out a series of high-altitude research flights in the arctic region for the first time in its history, with three weeks of climate change measurement flights over the North Slope of Alaska in October 2004.

The flights were the subject of talks this month in Daytona Beach, Fla., where ARM scientists gathered to discuss that mission along with a broad range of climate-related measurement campaigns. Another topic of discussion was the upcoming February 2006 ARM-UAV deployment to Darwin, Australia, where the airborne data-gathering instruments will be used in conjunction with ground-based, satellite, and ship-based instruments to collect information about the characteristics of tropical clouds at altitudes up to about 50,000 feet above the tropical Western Pacific.

Second stop of a ‘grand tour’

The Alaska flights were the second stop in a “Grand Tour” above ARM climate research sites to answer unsolved issues about the interaction of clouds and solar energy. The improved understanding that will come from these measurements will help improve predictive climate models.

The first series of flights was conducted over north-central Oklahoma in 2002. The third stop in the “Grand Tour” will be in Australia.

The conundrum about clouds is whether they tend to shade and cool the Earth or blanket it, trapping in heat and raising the surface temperature, says Exploratory Systems Technology Dept. 8227 Manager Will Bolton, who is technical director for the program.

To understand their role better, a piloted Proteus aircraft was outfitted with 15 discrete instruments, some mounted on the wings, others carried in a payload pod carried under the aircraft or atop the fuselage. Proteus was built by and is operated by Scaled Composites, in Mojave, Calif. The plane underwent three engineering flights there while the payload was controlled through a low-cost satellite link. Then it was flown up to Alaska, refueling in Seattle, with the payload controlled from up to 2,000 miles away through the satellite link.

From Eielson Air Force Base near Fairbanks, the Proteus flew about 90 minutes to the North Slope, rendezvousing with a Citation aircraft provided by the University of North Dakota that was stationed at Dead Horse, Alaska. With the Proteus flying up to 13 kilometers in altitude and the Citation flying inside the clouds, the planes collected data in flights lasting from 96 minutes to almost six hours. It will take about six months to process and calibrate the data, which is stored in the ARM archive based at Oak Ridge National Laboratory as a public resource available to scientists and universities.

Helping understand cloud physics

The data gathered by the ARM-UAV Program will help guide the way in which cloud physics is embodied in climate models. The models currently differ substantially in how they represent clouds and their effects on the atmosphere.

Whenever possible, the ARM-UAV flights are coordinated with satellite overflights of the ground stations. The coincidence of aircraft-borne and satellite measurements over the ground-based instruments provides a more complete picture of cloud characteristics and offers the advantage of comparing the satellite data with data from more recently calibrated instruments.

Sandia’s mission support includes calibrating the instruments, building or modifying some, handing mechanical and engineering design and integration with the aircraft, coordinating field arrangements such as planning and logistics, retrieving and processing data, and directing flight operations at the deployment site.

The latest deployment was supported by some 15 people from universities, laboratories, and industry, including NASA/Ames, the University of Illinois, Colorado State University, the University of Wisconsin, and the University of Massachusetts. This work was supported by DOE’s Office of Science, Climate Change Research Division. For more information about the program, go -- Nancy Garcia

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Forensic gemology: Stephen Attaway’s research hobby casts new light on origins, history of Hope diamond

By Will Keener

Sandia, UT unveil agreement for close strategic partnership

For an engineer who makes his living doing vulnerability assessments and crunching numerical simulations of crashes and impacts using massively parallel computing, Stephen Attaway knows surprisingly a lot about the Hope diamond.

In fact, Stephen (9134), along with his wife Nancy and local diamond replica expert Scott Sucher, have recently completed a combination of historic and high-tech research that sheds new light on the life of the stone.

“There is a lot of mystery and intrigue about where the Hope came from,” says Stephen. “We closed some gaps in a history that a great many people are interested in. And we were able to create an accurate replica of the Hope and the predecessor stones we think it came from.”

So far the gem detective work, done completely as a hobby project at home, has garnered the attention of the Discovery Channel, which premiered a 30-minute documentary on the project last month, and Lapidary Journal, a key trade publication, which is in the process of publishing a paper authored by Nancy. Locals interested in cut gems in general and the Hope diamond in particular will have a chance to learn more this weekend at a display and show hosted by the Albuquerque Gem and Mineral Club.

Smithsonian cooperation

Stephen, Nancy, and Scott did their research in cooperation with the Smithsonian Institution’s National Museum of Natural History in Washington, D.C. Every year some seven million visitors come to the museum, many of them expressly to see the 45.5-carat Hope diamond. Jeffery Post, Smithsonian curator of gems and minerals, calls the research “exciting.” The work represents new information about the museum’s collection of 375,000 specimens, he says. “We are constantly learning new things about our collections as we apply new high-tech research methods. Even the Hope diamond is grudgingly giving up some of its secrets.”

The researchers used state-of-the-art imaging and computer modeling technology, new measurements of the Hope, and historical records and sketches of two historic diamonds to create accurate virtual models of the three. “We were invited by the Smithsonian to photograph the Hope out of its setting. We even got to hold it in our hands. But we didn’t get to hold it very long,” says Stephen.

A highlight of the trip was a personal tour through the cut gem collection in the Smithsonian vault. “For Nancy, who has a long interest in gems and is an expert gem cutter, this was a once-in-a-lifetime chance,” says Stephen. And the data from the trip proved critical to the result of the project. It supports the theory that the Hope was cut from the French Blue Diamond, stolen from the French crown jewels in 1792.

A ‘sister diamond?’

Many have speculated over the years that a second blue diamond, or “sister diamond,” cut from the same “parent stone,” could still exist in a collection somewhere in the world. To understand this, you have to follow the history, beginning with the Tavernier Blue, named after a gem merchant who sold King Louis XIV of France a 112-carat blue diamond from India in 1668. A court jeweler cut the famous 67-carat French Blue out of the Tavernier. It became part of an ornate item of jewelry worn by European royalty until 1792, when it was stolen.

From here history slips into mystery, although most believe that the Hope came into being in the early 1800s when it was re-cut at 45.5 carats from the French Blue in London. (Henry Philip Hope was a diamond collector who owned the stone, hence the name.)

Collectors, doing the math from 67 to 45 carats, wondered if perhaps there could be a large sister stone to be found after the re-cut.

Stephen and his colleagues approached the problem with the idea of constructing, as accurately as possible, virtual and real models of the three historic diamonds. They used books from Tavernier’s travels in India, historic sketches, articles from a French gemology review, data about the lead molds used in creating Louis XIV’s jewelry, and some modern technology. In the case of the French Blue, Stephen generated 14 different iterations of what the diamond might look like based on known data about it, using CAD software, and finally finding a good match of the known dimensions and weights.

Mystery resolved

Using 30 photos of the Hope from their Smithsonian trip, Stephen applied 3-D photo measurement software to generate an accurate rendition. The model showed that the Hope did fit within the French Blue, tightly and only in one way.

Using the software models, Scott cut a model of the Travernier, and Nancy cut a model of the French Blue, both from dark blue cubic zirconia. These replicas were given to the Smithsonian, where they will eventually be displayed near the Hope diamond. Then, by creating molds of the three diamonds using a lost-wax process, the team demonstrated the unlikelihood of a sister diamond. “We believe the diamond material lost during the re-cutting of the French Blue to the Hope was ground into powder,” says Stephen.

Although this is not what the Discovery Channel wanted to hear, the program’s originators were able to make an interesting 30-minute segment out of the effort. “They were convinced the other half of the Hope was out there and they were hot on the trail of it,” says Stephen. “In fact, we proved the opposite of what they wanted.” A film crew spent three days in Albuquerque, helping to give Stephen, Nancy, and Scott their 15 minutes of fame. “It was an interesting process,” says Stephen, “but I learned that I’m not an actor.” -- Will Keener

 

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