Metallic liquid crystals

A new class of materials formed by combining liquid crystals and metal clusters glow intensely red in the infra-red region of the electromagnetic spectrum when irradiated over a broad range of wavelengths. The materials, dubbed clustomesogens, could be used in analytical instrumentation and potentially in display technologies.

Liquid crystals are well known in display technologies from digital watches to flat panel televisions. As their name suggests, they are at once liquid and can flow, but their molecules can also be oriented into something akin to a crystal state, usually under the influence of an electric field.

A second class of materials of interest to the optoelectronics field is metal clusters. Clusters are aggregates of just a few atoms, and so their properties are not those of individual atoms nor of the bulk metal, but somewhere in between. Indeed, metal clusters show some rather unusual electronic, magnetic, and optical properties because of the presence of the particular types of bonds that form between metals when just a few are present.

Now, Yann Molard, of the University of Rennes, in France, and colleagues there and at the University of Bucharest have united the two classes in clustomesogens to create metal clusters that exist in a liquid-crystalline phase.

Liquid crystals containing bonds between metal atoms are rare and usually limited to compounds in which just two metal atoms are connected in each unit. Molard and colleagues have produced liquid crystals that contains octahedral clusters made of six molybdenum atoms. Eight bromide ions sit on the eight surfaces of the octahedron, six fluorides and an aromatic organic group, or ligand, is at each vertex of the octahedron. These aromatic ligands each have three long hydrocarbon chains also ending in a pair of aromatic rings.

Yann Molard
Yann Molard

Simple warming these materials initiates a process of self-organization in which the clusters stretch out to form long, narrow units arranged in what is known as a lamellar, plate-like, structure. The flat rings at the ends of the ligands of neighbouring layers are interleaved and the structure has liquid-crystalline properties.

“The association of mesomorphism with the peculiar properties of metallic clusters should lead to clustomesogens that offer great potential in the design of new electricity-to-light energy conversion systems, optically based sensors, and displays,” the team says.

Links

Angew Chem Int Edn, 2010, 49, 3351-3355
Yann Molard homepage

Spotting carboot bombers

Improvised explosive devices are the weapon of choice for suicide bombers and have been a major cause of military and civilian casualties in Iraq, Afghanistan, and elsewhere in the world. Now, a group in engineering at the University of Michigan have developed a novel approach to detection of such devices that might allow security forces to intervene in a situation before a device is detected.

A team of undergraduate students at Michigan have developed a palm-sized metal detector based on a magnetometer explains team member Ashwin Lalendran who graduated in May 2009.

The device could be hidden in rubbish bins, under tables or in flowerpots, that are linked together using a wireless sensor network connected to a peripatetic command centre. The inexpensive low-power devices have a long transmission range and outperform all other devices on the market according to Nilton Renno, the team’s supervisor.

“We built it entirely in-house – the hardware and the software,”
explains Lalendran. “Our sensors are small, flexible to deploy, inexpensive and scalable. It’s extremely novel technology.”

The technology has already earned recognition with the Michigan team recently winning a competition sponsored by the US Air Force in conjunction with Ohio State University. The Air Force Research Laboratory at Wright Patterson Air Force Base and other bases across the US sponsor similar contests on a regular basis with the aim of getting a rapid technological reaction to ongoing issues that can be highly innovative.

The team has tested its system in Dayton, Ohio, at a mock outdoor sale event – a simulated carboot sale – secreting detectors across the site.
The organisers then hid simulated explosive devices among the crowd in backpacks and handbags and among the goods “on sale”.

“We had an excellent turnout in technology,” Tenning said. “Regardless of the competition results, often successful ideas from each student team can be combined into a product which is then realized for Department of Defence use in the future.”

Their success demonstrated sound engineering skills and a lot of imagination to the solution of an extremely difficult real-world problem, said Bruce Block, an engineer in the Space Physics Research Laboratory, who worked with the team. He adds that, “they worked well together and never gave up when the going got rough.” The students will continue to work on this project through the summer.

Team member Michael Shin discussing the development of a wireless network for detecting suicide bombers (Credit: UMich)

Podcast from The University of Michigan

13.73 Billion years BCE

Science doesn’t have a lot to say about what happened before the Big Bang, but researchers have now developed microwave detectors that will let them take a look at the first trillionth of a trillionth of a trillionth of a second after that primordial cosmic event.

A collaboration between scientists at the National Institute of Standards and Technology (NIST), Princeton University, the University of Colorado at Boulder, and the University of Chicago has yielded super-sensitive microwave detectors that were revealed at the American Physical Society (APS) April meeting held in Denver during May.

Cosmic microwave temperature fluctuations fill the sky and are an echo of the first moment after the Big Bang (Credit: NASA/WMAP Science Team)

Cosmic microwave temperature fluctuations fill the sky and are an echo of the first moment after the Big Bang (Credit: NASA/WMAP Science Team)

The cosmic microwave background (CMB) is often referred to as the afterglow of creation. This remnant, or echo of the Big Bang fills the universe and various projects have obtained snapshots of the CMB stretching back closer and closer to the Big Bang. The new project will use a large array of the sensors mounted on a telescope mounted in the Chilean desert. They will look for subtle fingerprints of the CMB from primordial gravitational waves, ripples in the fabric of the spacetime continuum. Theory has it that these waves will have left an imprint on the direction of the CMB’s electric field, called the B-mode polarization.

This is one of the great measurement challenges facing the scientific community over the next twenty years, and one of the most exciting ones as well, says Kent Irwin, the NIST physicist leading the project.

Prototype NIST detector that will be used to spot signature of rapid inflation immediately after the Big Bang. (Credit: NIST)

Prototype NIST detector that will be used to spot signature of rapid inflation immediately after the Big Bang. (Credit: NIST)

If found, these waves would be the clearest evidence yet in support of the inflation theory, which suggests that all of the currently observable universe expanded rapidly (within the first tiny fraction of a second) from a subatomic volume, leaving in its wake the telltale cosmic background of gravitational waves.

The B-mode polarization is the most significant piece of evidence related to inflation that has yet to be observed, explained NIST’s Ki Won Yoon, at the APS meeting. A detection of primordial gravitational waves through CMB polarization would go a long way toward putting the inflation theory on firm ground.

These types of experiments can only be done by treating the universe as a whole as a cosmic laboratory. The particles and electromagnetic fields that exist immediately after the Big Bang are billions of times more energetic than those available even with the most powerful particle colliders on Earth today. On this energy scale, three of the fundamental forces of nature but excluding gravity, are predicted to merge into a single unified force.

At the energy scale at which inflation occurred, which is the GUT or Grand Unified Theory energy scale, only 3 out of the 4 fundamental forces are predicted to merge into a single unified force – electromagnetism, the strong nuclear force, and the weak nuclear force, Irwin told Spotlight.

The final force of nature, gravity, is not predicted to merge with the other three until a much higher energy scale referred to as the Planck scale, which would have occurred before inflation, and would not have been related to the primordial gravity waves. A theory that correctly incorporates gravity into a unified field is humorously referred to as a TOE or Theory of Everything, he adds.

Further reading

APS April 2009 Meeting
http://www.aps.org/meetings/april/

National Institute of Standards and Technology homepage
http://www.nist.gov/index.html

Suggested searches

Big Bang
cosmology
cosmic microwave background