Taking a new look at carbon nanotubes

Nov. 12, 2013 — Despite their almost incomprehensibly small size -- a diameter about one ten-thousandth the thickness of a human hair -- single-walled carbon nanotubes come in a plethora of different "species," each with its own structure and unique combination of electronic and optical properties. Characterizing the structure and properties of an individual carbon nanotube has involved a lot of guesswork -- until now.

Researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have developed a technique that can be used to identify the structure of an individual carbon nanotube and characterize its electronic and optical properties in a functional device.

"Using a novel high-contrast polarization-based optical microscopy set-up, we've demonstrated video-rate imaging and in-situ spectroscopy of individual carbon nanotubes on various substrates and in functional devices," says Feng Wang, a condensed matter physicist with Berkeley Lab's Materials Sciences Division. "For the first time, we can take images and spectra of individual nanotubes in a general environment, including on substrates or in functional devices, which should be a great tool for advancing nanotube technology."

Wang, who is also a professor with UC Berkeley's Physics Department, is the corresponding author of a paper describing this research in the journal Nature Nanotechnology. Co-authors are Kaihui Liu, Xiaoping Hong, Qin Zhou, Chenhao Jin, Jinghua Li, Weiwei Zhou, Jie Liu, Enge Wang and Alex Zettl.

A single-walled carbon nanotube can be metallic or semiconducting depending on its exact structure. Semiconducting nanotubes can have very different electronic bandgaps, resulting in wildly different electronic or optical properties.

"To fully understand field-effect devices or optoelectronic devices made from single-walled carbon nanotubes, it is critical to know what species of carbon nanotube is in the device," Wang says. "In the past, such information could not be obtained and researchers had to guess as to what was going on."

The physical structure and electronic properties of each individual species of single-walled carbon nanotubes are governed by chirality, meaning their structure has a distinct left/right orientation or "handedness," which cannot be superimposed on a mirror image. As a result, achieving chirality-controlled growth of carbon nanotubes and understanding the physics behind chirality-dependent devices are two of the biggest challenges in nanotube research.

"Polarization-based optical microscopy and spectroscopy techniques are well-suited for meeting these challenges, as polarized light is extremely sensitive to optical anisotropy in a system and has long been exploited to study chirality in molecules and crystals," Wang says. "However, the small signal and unavoidable environment background has made it difficult to use polarized optical microscopy to study single carbon nanotubes."

Difficulties arise from an apparent contradiction in polarization-based optical microscopy. For any optical microscope, a large numerical aperture (NA) objective is crucial for high-spatial resolution, but polarized light passing through a large NA objective becomes strongly depolarized. With their new technique, Wang and his colleagues were able to do what has not been done before and simultaneously achieve both high polarization and high spatial resolution.

"The key to our success was the realization that light illumination and light collection can be controlled separately," Wang says. "We used a large NA objective for light collection to obtain high spatial resolution, but were able to create an effectively small NA objective for illumination to maintain high polarization purity."

In their set-up, Wang and his colleagues collected nanotube-scattered polarized light with a 0.8 NA objective but used a much more narrow incident beam to create illumination light from a supercontinuum laser with a much smaller NA. The result was polarization an order of magnitude higher than what has been achieved with conventional polarized microscopy and spatial resolution at the nanoscale. This enabled them to obtain complete chirality profiles of hundreds of as-grown carbon nanotubes, and to perform in-situ monitoring in active field-effect devices.

"We observed that high order nanotube optical resonances are dramatically broadened by electrostatic doping, an unexpected behavior that points to strong inter-band electron-electron scattering processes dominating the ultrafast dynamics of excited states in carbon nanotubes," Wang says.

In addition to individual single-walled carbon nanotubes, Wang and his colleagues say their technique can also be used to greatly enhance the optical contrast of other anisotropic nano-sized materials that are "invisible" to conventional optical microscopes, including graphene nanoribbons, semiconductor nanowires and nanorods, and nanobiomaterials such as actin filaments.

This research was supported by grants from the National Science Foundation, the Center for Integrated Nanomechanical Systems, and by DOE's Office of Science.

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Drug 'Molly' is taking a party toll in the United States

By Victoria Cavaliere

NEW YORK (Reuters) - Artist and therapy student Anna and her friends marked a birthday in New York recently with a familiar ritual: They pumped up the electronic music, danced, and celebrated with a special guest called Molly.

"It was a group of about 12 people at someone's house and we were all just celebrating," Anna recalled. "Somebody had it and, and you know, it was a pretty electronic music kind of crowd."

Molly, an illegal stimulant frequently sold in pill form, has become prominent in the electronic music scene over the past decade, said Anna, 26, who did not want to give her full name because she is in school and "counseling people to be healthy."

Molly is the street name for a drug that is pushed as the pure powder form of a banned substance known as MDMA, the main chemical in ecstasy. In the last five years, Molly has made its way into popular culture, helped by references to it made by entertainers such as Madonna, Miley Cyrus and Kanye West.

The drug's dangers became more clear after a rash of overdoses and four deaths this summer, including two at a huge annual electronic music festival in New York City.

The parties of the late 1980s and early '90s saw the heyday of ecstasy, but its popularity began to wane a decade ago after a number of deaths and hospitalizations.

That's when Molly made her way onto the scene.

Over the last few years, drugs sold under that name have "flooded" the market, said Rusty Payne, a spokesman with the Drug Enforcement Administration.

In some states, there has been a 100-fold increase - the combined number of arrests, seizures, emergency room mentions and overdoses - between 2009 and 2012, according to DEA figures.

The drug is accessible and marketed to recreational drug users who believe it to be less dangerous than its predecessor, which was often cut with other substances, from Ritalin to LSD.

Like ecstasy, Molly is said to give a lengthy, euphoric high with slight hallucinogenic properties.

In reality, however, the promised pure MDMA experience "doesn't exist," said Payne.

'SOMETHING COMPLETELY DIFFERENT'

Most of the Molly is one of several synthetic designer drugs that have been flooding the U.S. and European marketplace from chemical labs primarily based in China, Payne said.

"A lot of people are missing the boat here," he said. Molly could be anything ... 80 to 90 percent of the time we are given a chemical or substance believed to be Molly, we're finding most of the time it is something completely different."

Four recent deaths attributed to Molly have thrust the club drug into the national spotlight. On August 31, a 23-year-old Syracuse University graduate and a 20-year-old University of New Hampshire student died after taking what they believed to be Molly during an electronic music concert in New York City. The deaths, and several other reported overdoses, prompted the Electric Zoo festival to cancel the final day of the concert.

A University of Virginia student died at a rave in Washington, D.C., the same weekend, after taking what her friends said was Molly. Days earlier in Boston, a 19-year-old woman died in a club and three concert-goers overdosed at the waterfront, police said.

In Atlanta, this weekend's TomorrowWorld music festival organizers warned on its website of zero-tolerance for MDMA use, but noted: "If you or someone around you has taken something that you are concerned about or need help, it is important that you tell our staff. We are here to help and never judge."

The number of visits to U.S. emergency rooms involving MDMA has jumped 123 percent since 2004, according to data compiled by the Drug Abuse Warning Network. In 2011, the most recent year on record, there were 22,498 such visits.

In the New York concert deaths, the medical examiner found lethal mixtures of MDMA and methylone, a synthetic stimulant, the DEA said.

"It's exactly the same phenomenon that occurred with ecstasy a decade ago," said Dr. Charles Grob, a professor of psychiatry and pediatrics at the UCLA School of Medicine and an expert on MDMA. "Ecstasy had terrible reliability and it's the same with Molly. Though it's being marketed as pure MDMA, it's a hoax."

Overdose symptoms can include rapid heart beat, overheating, excessive sweating, shivering and involuntary twitching.

Grob said references in pop culture can fan misconceptions.

Miley Cyrus admitted in July that a lyric in her new dance anthem "We Can't Stop" was a reference to Molly. Last year at a Miami concert, Madonna, the mother of a teenager, asked: "How many people in this crowd have seen Molly?" She later said she was referring to a friend.

The illusion that MDMA is somehow less harmful has been branded with Molly, according to Anna.

"I have definitely heard that people think that it's pure. I have some friends that are like 'I only want to do Molly. I won't do other stuff' because it's marketed as something that's somehow better," said Anna. "But actually no one knows what's in it. All of it is a gamble."

(Editing by Scott Malone and Gunna Dickson)

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Elite Army units to stop taking anti-malarial drug

WASHINGTON (AP) — The top doctor for Green Berets and other elite Army commandos has told troops to immediately stop taking mefloquine, an anti-malaria drug found to cause permanent brain damage in rare cases.

The ban among special operations forces is the latest development in a long-running controversy over mefloquine. The drug was developed by the Army in the 1970s and has been taken by millions of travelers and people in the military over the years. As alternatives were developed, it fell out of favor as the front-line defense against malaria, a mosquito-borne disease that international health officials say kills roughly 600,000 people a year.

The new prohibition among special operations forces follows a July 29 safety announcement by the Food and Drug Administration that it had strengthened warnings about neurologic side effects associated with the drug. The FDA added a boxed warning to the drug label, the most serious kind of warning, saying neurologic side effects like dizziness, loss of balance and ringing in the ears may become permanent.

The drug's other side effects include anxiety, depression and hallucinations — conditions that some military families over the years believe prompted psychotic behavior in their loved ones, including killings and suicides.

Quoting the FDA's July safety warning, the Surgeon General's Office of the Army Special Operations Command sent a message to commanders and medical personnel last Friday ordering a halt in prescribing mefloquine for malaria prevention for the approximately 25,000 Green Berets, Rangers, Civil Affairs and Psychological Operations soldiers, command spokesman Lt. Col. Dave Connolly said.

The message also told commanders and medical workers to assess the possibility that some of their troops have been sickened by the drug but may mistakenly have been thought to be malingering or to have post-traumatic stress disorder or other psychological problems. That's because symptoms of toxic levels of mefloquine in the brain may mimic or be mistaken for other disorders. The message said questions about suspected cases of mefloquine toxicity should be submitted though the War Related Illness and Injury Center of the Veterans Affairs Department, which has been studying the issue.

"What this is is a wake-up call telling troops, 'Look, you've been misinformed,'" said Remington Nevin, a former Army physician and epidemiologist who studies the psychiatric effects of anti-malarial toxicity at the Department of Mental Health at the Johns Hopkins Bloomberg School of Public Health.

Nevin is a critic of military policy on mefloquine, which he says the Pentagon should have stopped using years ago, particularly because it confounds diagnosis of PTSD and traumatic brain injury, two signature health issues of the wars in Iraq and Afghanistan.

Others point out that the drug has been effective in preventing malaria and many people have preferred it because it is less expensive and has to be taken less often than alternatives.

"I take mefloquine when I travel," said Dr. David Sullivan of the Johns Hopkins Malaria Research Institute. "For 80 percent, 90 percent of the people, they have no trouble with it."

Mefloquine is still prescribed to the traveling public and to volunteers in the Peace Corps, which also has reduced its use.

The new prohibition among commando units goes beyond guidance from top Defense Department health officials, who say mefloquine use by the different branches of the military has been dramatically reduced in recent years but is still given to troops who can't use alternatives.

The drug was given to 2,417 uniformed and civilian defense personnel and family members in the first seven months of this year, compared with more than 20,000 in all of 2009.

The Pentagon says it doesn't have data on the number troops who may have suffered ill effects from the drug. But two days after the FDA announcement, the department began a review "of potential neuropsychological effects on service members who were prescribed mefloquine," said Lt. Col. Cathy Wilkinson, a defense spokeswoman.

The review is expected to be finished in January.

Copyright c 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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