Single-Crystal Semiconductor Wire Built Into Optical Fiber

An international science team from Penn State University in the United States and the University of Southampton in the United Kingdom has developed a process for growing a single-crystal semiconductor inside the tunnel of a hollow optical fiber. The device adds new electronic capabilities to optical fibers, whose performance in electronic devices such as computers typically is degraded by the interface between the fiber and the device. The research is important because optical fibers -- which are used in a wide range of technologies that employ light, including telecommunications, medicine, computing, and remote-sensing devices -- are ideal media for transmitting many types of signals.

The development of the single-crystal device, which will be described in a paper to be published later this month in the journal Advanced Materials, builds on research reported in 2006, in which the team first combined optical fibers with polycrystalline and amorphous semiconductor materials in order to create an optical fiber that also has electronic characteristics. The group's latest finding -- that a single-crystal semiconductor also can be integrated into an optical fiber -- is expected to lead to even further improvements in the characteristics of optical fibers used in many areas of science and technology.

"For most applications, single-crystal semiconductor materials have better performance than polycrystalline and amorphous materials," says John Badding, associate professor of chemistry at Penn State. "We have now shown that our technique of encasing a single-crystal semiconductor within an optical fiber results in greater functionality of the optical fiber, as well."

The team used a high-pressure fluid-liquid-solid approach to build the crystal inside the fiber. First, the scientists deposited a tiny plug of gold inside the fiber by exposing a gold compound to laser light. Next, they introduced silane, a compound of silicon and hydrogen, in a stream of high-pressure helium. When the fiber was heated, the gold acted as a catalyst, decomposing the silane and thus allowing silicon to deposit as a single crystal behind the moving gold catalyst particle, forming a single-crystal wire inside the fiber.

"The key to joining two technologies lies not only in the materials, but also in how the functions are built in," says Pier Sazio, senior research fellow in the Optoelectronics Research Centre at the University of Southampton. "We were able to embed a nanostructured crystal into the hollow tube of an optical fiber to create a completely new type of composite device."

The research team sees potential to carry the application to the next level. "At present, we still have electrical switches at both ends of the optical fiber," says Badding. "If we can get to the point where the electrical signal never leaves the fiber, it will be faster and more efficient."

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Researchers Develop Darkest Manmade Material

Researchers at Rensselaer Polytechnic Institute and Rice University have created the darkest material ever made by man.

The material, a thin coating comprised of low-density arrays of loosely vertically aligned carbon nanotubes, absorbs more than 99.9 percent of light and one day could be used to boost the effectiveness and efficiency of solar energy conversion, infrared sensors, and other devices. The researchers who developed the material have applied for a Guinness World Record for their efforts.

“It is a fascinating technology, and this discovery will allow us to increase the absorption efficiency of light as well as the overall radiation-to-electricity efficiency of solar energy conservation,” says Shawn-Yu Lin, professor of physics at Rensselaer and a member of the university’s Future Chips Constellation, who led the research project. “The key to this discovery was finding how to create a long, extremely porous vertically-aligned carbon nanotube array with certain surface randomness, therefore minimizing reflection and maximizing absorption simultaneously.”

The research results were published in the journal Nano Letters.

All materials, from paper to water, air, or plastic, reflect some amount of light. Scientists have long envisioned an ideal black material that absorbs all the colors of light while reflecting no light. So far they have been unsuccessful in engineering a material with a total reflectance of zero.

The total reflectance of conventional black paint, for example, is between 5 and 10 percent. The darkest manmade material, prior to the discovery by Lin’s group, boasted a total reflectance of 0.16 percent to 0.18 percent.

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Big Screen TVs, Flexible Electronics, Surfboards Made From Same New Material

There is nothing new about combining two materials to make a composite material with more desirable properties than the originals. Fibreglass has been a mainstay of the marine industry for decades and the construction industry is built on reinforced concrete. Now carbon nanotubes (CNT) are getting in on the act with nanotechnologists working out how to grow nanotube reinforcements for polymers in an ideal manner.

Researchers from Trinity College have developed a scalable inexpensive technique to grow grid patterns of nanotube arrays. To maximize the effect of CNT reinforcement on a polymer thin film, while minimizing nanotube content, a controllable way of varying the volume fraction of CNTs within the composite is needed. In order to do this, the inter-grid spacing can be tailored as required giving a simple method of controlling the volume fraction of nanotubes grown on substrates.

The research work by Werner Blau, Emer Lahiff, Andrew Minett and Kentaro Nakajima is expected to lead to incorporation of CNTs in polymer matrices within flat panel displays, sensors, flexible electronic devices and actuators.

The study has been published in a special edition of the open access journal, AZoJono.

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System Detects Hazardous, Toxic Material in Concealed Packaging

Researchers at Sandia National Laboratories are developing the next generation of screening devices that will identify hazardous and toxic materials even if concealed by clothing and packaging materials.

Working in the underutilized terahertz (THz) portion of the electromagnetic spectrum that lies between microwaves and infrared, a team of Labs scientists is harnessing Sandia’s strengths in a variety of technical areas with the goal of building a highly integrated miniaturized terahertz transmitter-receiver (transceiver) that could make a number of applications possible.

The project, the Terahertz Microelectronics Transceiver Grand Challenge, is in its second of three years of funding through Sandia's internal Laboratory Directed Research and Development program.

Sandia is a U.S. National Nuclear Security Administration (NNSA) laboratory.

“The technology being developed in the Grand Challenge can be used to scan for items such as concealed weapons or materials, explosives, and weapons of mass destruction,” says Mike Wanke, principal investigator. “In addition, we believe it will find applications in advanced communication systems and high-resolution radars. However, the infrastructure needed to move the terahertz technology from the laboratory to the field is unavailable right now. We want to develop that infrastructure and invent the necessary technologies.”

Wanke says over the past three years, “the terahertz situation has begun to change dramatically, primarily due to the revolutionary development of terahertz quantum cascade lasers.”

These tiny lasers are semiconductor sources of terahertz radiation capable of output powers in excess of 100 mW. Previously, such powers could only be obtained by molecular gas lasers occupying cubic meters and weighing more than 100 kg, or free electron lasers weighing tons and occupying entire buildings.

Quantum cascade laser-based systems can be less than the size of a baseball and powered from a nine-volt battery. Sandia has been a leader in developing this new technology and in collaboration with MIT is responsible for several world performance records for the lasers. Also, the Labs and its partners are the only US institutions that have demonstrated the ability to grow the unique semiconductor crystals such that they can be turned into operating terahertz quantum cascade lasers. The crystals are grown by Sandia research scientist John Reno, an expert in molecular beam epitaxy, a method of laying down layers of materials with atomic thicknesses onto substrates.

Sandia researchers spent the first year of the Grand Challenge using Sandia’s unique strengths in integrated microelectronics and device physics to develop components that are now being combined to create an integrated THz microelectronic transceiver, a core enabling element.

The team is currently developing the receiver, doing systems tests and exploring packaging requirements. At the end of three years, the researchers expect to have an actual working prototype capable of detecting the materials and chemicals by reading distinctive molecular spectral “signatures.”

“Most materials and chemicals have their own unique terahertz spectral signatures,” Wanke says. “A terahertz transceiver system would be able to measure, for example, the signature of a gas and determine what it is.”

“Atmospheric scientists and radio astronomers have spent years developing terahertz spectral signature databases to identify chemicals in nebula and planetary atmospheres,” says Greg Hebner, program manager. “Even though the current devices are washing machine-sized, they are located in a few observatories, and one is even flying on a satellite. To address specific national security problems, we are working on reducing the size, weight, and power requirement as well as expanding the existing spectral databases.”

In addition to monitoring for concealed hazardous materials, Mike believes a terahertz system can be used to monitor the air for toxic materials. Using air sampling technology developed at Sandia and other locations, hazardous vapors can be preconcentrated. Shining light from the quantum cascade laser through the concentrated sample provides a direct identification of the vapor. This technology can be used in conjunction with existing mass spectrometer-based systems to reduce false identifications.


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