First Observation Of 'Persistent Flow' In A Gas

Source:

http://www.sciencedaily.com/releases/2007/11/071127153345.htm

ScienceDaily (Nov. 29, 2007) — Using laser light to stir an ultracold gas of atoms, researchers at the National Institute of Standards and Technology (NIST) and the Joint Quantum Institute (NIST/University of Maryland) have demonstrated the first "persistent" current in an ultracold atomic gas --a frictionless flow of particles. This relatively long-lived flow, a hallmark of a special property known as "superfluidity," might help bring to the surface some deep physics insights, and enable super-sensitive rotation sensors that could someday make navigation more precise.

To carry out the demonstration, the researchers first created a Bose-Einstein condensate (BEC), a gas of atoms cooled to such low temperatures that it transforms into matter with unusual properties. One of these properties is superfluidity, the fluid version of superconductivity (whereby electrical currents can flow essentially forever in a loop of wire). Although BECs in principle could support everlasting flows of gas, traditional setups for creating and observing BECs have not provided the most stable environments for the generally unstable superfluid flows, which have tended to break up after short periods of time.
To address this issue, the NIST researchers use laser light and magnetic fields on a gas of sodium atoms to create a donut-shaped BEC--one with a hole in the center--as opposed to the usual ball- or cigar-shaped BEC. This configuration ends up stabilizing circular superfluid flows because it would take too much energy for the hole--containing no atoms--to disturb matters by moving into the donut--which contains lots of atoms.
To stir the superfluid, the researchers zap the gas with laser light that has a property known as orbital angular momentum. Acting like a boat paddle sweeping water in a circle, the orbital angular momentum creates a fluid flow around the donut. After the stirring, the researchers have observed the gas flowing around the donut for up to 10 seconds. Even more striking, this persistent flow exists even when only 20 percent of the gas atoms were in the special BEC state.
This experiment may provide ways to study the fundamental connection between BECs and superfluids. More practically, the technique may lead to ultraprecise navigation gyroscopes. A BEC superfluid is very sensitive to rotation; its flow would change in fixed steps in response to small changes in rotation. Sound too impractical for airplane navigation" Research groups around the world already have taken the first step by demonstrating BECs on a chip.
Journal reference: C. Ryu, M. F. Andersen, P. Cladé, V. Natarajan, K. Helmerson and W.D. Phillips, Observation of persistent flow of a Bose-Einstein condensate in a toroidal trap. Physical Review Letters. (forthcoming)
Adapted from materials provided by National Institute of Standards and Technology.

Fausto Intilla

www.oloscience.com

Thermoelectric Materials Are One Key To Energy Savings

Source:

http://www.sciencedaily.com/releases/2007/11/071120195658.htm

ScienceDaily (Nov. 27, 2007) — Breathing new life into an old idea, MIT Institute Professor Mildred S. Dresselhaus and co-workers are developing innovative materials for controlling temperatures that could lead to substantial energy savings by allowing more efficient car engines, photovoltaic cells and electronic devices.

Novel thermoelectric materials have already resulted in a new consumer product: a simple, efficient way of cooling car seats in hot climates. The devices, similar to the more-familiar car seat heaters, provide comfort directly to the individual rather than cooling the entire car, saving on air conditioning and energy costs.
The research is based on the principle of thermoelectric cooling and heating, which was first discovered in the early 19th century and was advanced into some practical applications in the 1960s by MIT professor (and former president) Paul Gray, among others.
Thermoelectric devices are based on the fact that when certain materials are heated, they generate a significant electrical voltage. Conversely, when a voltage is applied to them, they become hotter on one side, and colder on the other. The process works with a variety of materials, and especially well with semiconductors -- the materials from which computer chips are made. But it always had one big drawback: it is very inefficient.
The fundamental problem in creating efficient thermoelectric materials is that they need to be very good at conducting electricity, but not heat. That way, one end of the apparatus can get hot while the other remains cold, instead of the material quickly equalizing the temperature. In most materials, electrical and thermal conductivity go hand in hand. So researchers had to find ways of modifying materials to separate the two properties.
The key to making it more practical, Dresselhaus explains, was in creating engineered semiconductor materials in which tiny patterns have been created to alter the materials' behavior. This might include embedding nanoscale particles or wires in a matrix of another material. These nanoscale structures -- just a few billionths of a meter across -- interfere with the flow of heat, while allowing electricity to flow freely. "Making a nanostructure allows you to independently control these qualities," Dresselhaus says.
She and her MIT collaborators started working on these developments in the 1990s, and soon drew interest from the US Navy because of the potential for making quieter submarines (power generation and air conditioning are some of the noisiest functions on existing subs). "From that research, we came up with a lot of new materials that nobody had looked into," Dresselhaus says.
After some early work conducted with Ted Harman of MIT Lincoln Labs, Harman, Dresselhaus, and her student Lyndon Hicks published an experimental paper on the new materials in the mid 1990s. "People saw that paper and the field started," she says. "Now there are conferences devoted to it."
Her work in finding new thermoelectric materials, including a collaboration with MIT professor of Mechanical Engineering Gang Chen, invigorated the field, and now there are real applications like seat coolers in cars. Last year, a small company in California sold a million of the units worldwide.
Potential applications
The same principle can be used to design cooling systems that could be built right into microchips, reducing or eliminating the need for separate cooling systems and improving their efficiency.
The technology could also be used in cars to make the engines themselves more efficient. In conventional cars, about 80 percent of the fuel's energy is wasted as heat. Thermoelectric systems could perhaps be used to generate electricity directly from this wasted heat. Because the amount of fuel used for transportation is such a huge part of the world's energy use, even a small percentage improvement in efficiency can have a great impact, Dresselhaus explains. "It's very practical," she says, "and the car companies are getting interested."
The same materials might also play a role in improving the efficiency of photovoltaic cells, harnessing some of the sun's heat as well as its light to make electricity. The key will be finding materials that have the right properties but are not too expensive to produce.
Dresselhaus and colleagues are now applying nanotechnology and other cutting-edge technologies to the field. She'll describe her work toward better thermoelectric materials in an invited talk on Monday, Nov. 26, at the annual meeting of the Materials Research Society in Boston.
Dresselhaus and colleagues are continuing to probe the thermoelectric properties of a variety of semiconductor materials and nanostructures such as superlattices and quantum dots. Her research on thermoelectric materials is presently sponsored by NASA.
Adapted from materials provided by Massachusetts Institute of Technology.

Fausto Intilla

www.oloscience.com

Neutron Scatter Camera Detects Shielded Radiation To Find Smuggled Nuclear Material

Source:

http://www.sciencedaily.com/releases/2007/11/071123203623.htm

ScienceDaily (Nov. 26, 2007) — In an effort to find an answer to the problem of identifying smuggled special nuclear material (SNM), researchers at Sandia National Laboratories in California say a neutron scatter camera they are developing may be able to detect radiation from much greater distances and through more shielding than current detection instruments.

The neutron scatter camera, says Sandia physicist Nick Mascarenhas, has the capability to count neutrons from a source of SNM and localize it — meaning it doesn’t only indicate there is radiation present, but also where it is emanating from and, under some circumstances, how much.
“This instrument can pinpoint a hot spot in another room through walls, something not typically possible with gamma-ray detectors,” says Mascarenhas.
“Performance-wise, it’s beating the older technologies, but we want to continue to push the limits of sensitivity and detection distance.”
Distance, says Mascarenhas, is a significant benchmark because it means the neutron scatter camera has the potential to detect through various types of shielding, a concern at any border crossing or point of entry.
Results of neutron scatter camera testing have been encouraging. “It’s more penetrating and can detect unambiguously at a greater distance and through more shielding,” says Jim Lund, who manages the Rad/Nuc Detection Systems group at Sandia/California.
Since 9/11, radiation detection has taken on a new immediacy as a means of preventing a nuclear weapon attack within the United States. Gamma-ray and neutron detectors are being deployed at border crossings and ports, with the goal of enabling interdiction of a nuclear weapon or material before it enters the country.
Role in in-transit radiation characterization
The neutron scatter camera project is currently supported by the Office of Nonproliferation R&D in the National Nuclear Security Administration (NNSA). After successful initial development, the technology is being transitioned to both the Defense Threat Reduction Agency (DTRA) and Domestic Nuclear Detection Office (DNDO) to support specific application studies.
Recently, representatives from DNDO sat in on a presentation by Mascarenhas to NNSA. They were sufficiently impressed to inquire how quickly he could modify the camera for shipping to and from Hawaii as part of Sandia’s in-transit radiation characterization project, which has been examining the viability of radiation detection onboard a ship.
The neutron scatter camera will make three round-trips to Hawaii; the first departed from the Port of Oakland in early September. Sandia physicist George Lasche, who leads the project known as Experimental Limits for In-Transit Detection of Radiological Materials, says the camera has the potential to reduce false alarm rates — a critical issue for in-transit radiation detection.
“Our other instruments have told us a lot about the nature of nuclear radiation at sea, but not where it is coming from,” says Lasche. “The neutron scatter camera can tell us where the radiation is coming from and whether it is coming from a small object or not. This information is very helpful in deciding if we have a serious threat on our hands, and can lead to fewer false alarms and a better chance of not missing the real thing,” he said.
DTRA is funding a separate project to use the neutron scatter camera to measure and characterize background neutrons at Sandia/California, Sandia/New Mexico, and in Alameda, Calif.
“There are neutrons all over the place from cosmic radiation, even when you are sitting indoors,” explains Mascarenhas. “Our instrument can measure the energies, rates and angular variation. This is important in understanding standard operating conditions. You can’t really detect anomalies until you understand what’s normal. This data can also be used to improve instruments to better suppress the standard operation conditions.”
The neutron scatter camera has an advantage over traditional neutron detection because it can differentiate low energy neutrons from high energy neutrons.
“It doesn’t have to worry about the low-energy nuisance neutrons that are always all around us because it can only see high energy neutrons, and the high-energy neutrons carry almost all of the imaging information,” says Lasche.
Another advantage is shielding. While some gamma rays can be blocked from detectors, neutrons are much more difficult to conceal. In a lab test, the camera easily detected and imaged a source placed across the hallway, through several walls and cabinets.
Size and feedback time limitations
Lund notes that the neutron scatter camera does have limitations, particular in terms of size and time. “Ideally, we’d use both the neutron scatter camera and a gamma-ray detector,” he says. “The neutron scatter camera is not practical as a handheld detector with immediate feedback.”
The neutron scatter camera consists of elements containing proton-rich liquid scintillators in two planes. As neutrons travel through the scintillator, they bounce off protons like billiard balls. This is where “scatter” comes into play — with interactions in each plane of detector elements, the instrument can determine the direction of the radioactive source from which the neutron came.
The neutron eventually flies off, but not before energizing the protons with which it has interacted. The proton will lose its energy in the scintillator. As that energy is lost, it is converted into light. Photomultiplier tubes coupled to the scintillator detect the light.
Computers record data from the neutron scatter camera, and using kinematics, determine the energy of the incoming neutron and its direction. Pulse shape discrimination is employed to distinguish between neutrons and gamma rays.
The biggest obstacle to the camera becoming widely adopted is the liquid scintillator, which is flammable, hazardous, and requires special handling. According to Mascarenhas, materials exist that could be used as a solid scintillator, but they need to be mass produced and made readily available in the U.S. for this purpose. Solid scintillator material, he says, is not in the scope of the current project but is a logical next step.
The current version of the neutron scatter camera has four elements on one side and seven on the other. To improve sensitivity and direction, all that is required is to add more elements.
Mascarenhas describes scaling up as an engineering challenge rather than a scientific limit. Bigger means more places where things can break down, but this isn’t a physics issue, he says.
“We are not concerned with size at this point — our mission is to understand everything about the performance of this instrument and make it the best it can be,” he says. “Making it portable or compact might be the next steps, but that’s something I’m confident that Sandia, as an engineering laboratory, can solve.”
Adapted from materials provided by Sandia National Laboratories.

Fausto Intilla - www.oloscience.com

New Nanoparticle Technique Captures Chemical Reactions In Single Living Cell With Amazing Clarity

Source:

http://www.sciencedaily.com/releases/2007/11/071119170147.htm

ScienceDaily (Nov. 19, 2007) — Bioengineers at the University of California, Berkeley, have discovered a technique that for the first time enables the detection of biomolecules' dynamic reactions in a single living cell.
By taking advantage of the signature frequency by which organic and inorganic molecules absorb light, the team of researchers, led by Luke Lee, professor of bioengineering and director of UC Berkeley's Biomolecular Nanotechnology Center, can determine in real time whether specific enzymes are activated or particular genes are expressed, all with unprecedented resolution within a single living cell.
The technique could lead to a new era in molecular imaging with implications for cell-based drug discovery and biomedical diagnostics.
The researchers point out that other techniques, such as nuclear magnetic resonance, can at best provide information about a cluster of cells. But to determine the earliest signs of disease progression or of stem cell proliferation, it's necessary to drill down deeper to the molecular dynamics within a single cell.
To study the biochemical processes of a cell, scientists currently cut through its outer membrane to separate and analyze the cellular components. That method can never provide a real-time view of how components function together because the cell is killed in the process of extracting its components.
"Until now, there has been no non-invasive method that exists that can capture the chemical fingerprints of molecules with nanoscale spatial resolution within a single living cell," said Lee, who is also a faculty affiliate of the California Institute for Quantitative Biosciences and the co-director of the Berkeley Sensor and Actuator Center. "There is great hope that stem cells can one day be used to treat diseases, but one of the biggest challenges in this field is understanding exactly how individual cells differentiate. What is happening inside a stem cell as it develops into a heart muscle instead of a tooth or a strand of hair? To find out, we need to look at the telltale chemical signals involved as proteins and genes function together within a cell."
The researchers tackled this challenge by improving upon conventional optical absorption spectroscopy, a technique by which light is passed through a solution of molecules to determine which wavelengths are absorbed. Cytochrome c, for instance, is a protein involved in cell metabolism and cell death that has several optical absorption peaks of around 550 nanometers.
The absorption spectra of a molecule can change based upon the chemical changes that occur as it interacts with other molecules, such as oxygen.
"For conventional optical absorption spectroscopy to work, a relatively high concentration of biomolecules and a large volume of solution is needed in order to detect these subtle changes in frequencies and absorption peaks," said Lee. "That's because optical absorption signals from a single biomolecule are very weak, so you need to kill hundreds to millions of cells to fish out enough of the target molecule for detection."
The researchers came up with a novel solution to this problem by coupling biomolecules, the protein cytochrome c in this study, with tiny particles of gold measuring 20-30 nanometers long. The electrons on the surface of metal particles such as gold and silver are known to oscillate at specific frequencies in response to light, a phenomenon known as plasmon resonance. The resonant frequencies of the gold nanoparticles are much easier to detect than the weak optical signals of cytochrome c, giving the researchers an easier target.
Gold nanoparticles were chosen because they have a plasmon resonance wavelength ranging from 530 to 580 nanometers, corresponding to the absorption peak of cytochrome c.
"When the absorption peak of the biomolecule overlaps with the plasmon resonance frequency of the gold particle, you can see whether they are exchanging energy," said study co-lead author Gang Logan Liu, who conducted the research as a UC Berkeley Ph.D. student in bioengineering. "This energy transfer shows up as small dips, something we call 'quenching,' in the characteristic absorption peak of the gold particle."
A relatively small concentration of the molecule is needed to create these quenching dips, so instead of a concentration of millions of molecules, researchers can get by with hundreds or even dozens of molecules. The sensitivity and selectivity of the quenching dips will improve the molecular diagnosis of diseases and be instrumental in the development of personalized medicine, the researchers said.
The researchers repeated the experiment matching the protein hemoglobin with silver nanoparticles and achieved similar results.
"Our technique kills two birds with one stone," Lee said. "We're reducing the spatial resolution required to detect the molecule at the same time we're able to obtain chemical information about molecules while they are in a living cell. In a way, these gold particles are like 'nano-stars' because they illuminate the inner life of a cellular galaxy."
Other researchers on the UC Berkeley team are Yi-Tao Long, co-lead author and postdoctoral scholar in bioengineering; Yeonho Choi, a Ph.D. student in mechanical engineering; and Taewook Kang, a postdoctoral scholar in bioengineering.
This research is described in the Nov. 18 issue of the journal Nature Methods. The Ministry of Science and Technology in Korea helped support this research.
Adapted from materials provided by University of California - Berkeley.

Fausto Intilla
www.oloscience.com

New Way To Manipulate Light A Million Times More Efficiently

Source:

http://www.sciencedaily.com/releases/2007/11/071116133558.htm

ScienceDaily (Nov. 17, 2007) — Scientists have discovered a new way to manipulate light a million times more efficient than previous methods.

Using a special hollow-core photonic crystal fibre, a team at the University of Bath, UK, has opened the door to what could prove to be a new sub-branch of photonics, the science of light guidance and trapping.
The team, led by Dr Fetah Benabid, reports on the discovery in Science, which relates to the emerging attotechnology, the ability to send out pulses of light that last only an attosecond, a billion billionth of a second.
These pulses are so brief that they allow researchers to more accurately measure the movement of sub-atomic particles such as the electron, the tiny negatively-charged entity which moves outside the nucleus of an atom. Attosecond technology may throw light, literally, upon the strange quantum world where such particles have no definite position,only probable locations.
To make attosecond pulses, researchers create a broad spectrum of light from visible wavelengths to x-rays through an inert gas. This normally requires a gigawatt of power, which puts the technique beyond any commercial or industrial use.
But Dr Benabid’s team used a photonic crystal fibre (pcf), the width of a human hair, which traps light and the gas together in an efficient way. Until now the spectrum produced by photonic crystal fibre has been too narrow for use in attosecond technology, but the team have now produced a broad spectrum, using what is called a Kagomé lattice, using about a millionth of the power used by non-pcf methods.
“This new way of using photonic crystal fibre has meant that the goal of attosecond technology is much closer," said Dr Benabid, of the University of Bath’s Department of Physics, who worked with students Mr Francois Couny and Mr Phil Light, and with Dr John Roberts of the Technical University of Denmark and Dr Michael Raymer of the University of Oregon, USA.
“The greatly reduced cost and size of producing these phenomenally short and powerful pulses makes exploring matter at an even smaller detail a realistic prospect.”
Dr Benabid’s team has not only made an important step in applied physics, but has contributed to the theory of photonics too. The effectiveness of photonic crystal fibre has lain so far in its exploitation of what is called photonic band gap, which stops photons of light from “existing” in the fibre cladding and enabled them to be trapped in the inside core of the fibre.
Instead, the team makes use of the fact that light can exist in different ‘modes’ without strongly interacting. This creates a situation whereby light can be trapped inside the fibre core without the need of photonic bandgap. Physicists call these modes bound states within a continuum.
The existence of these bound states between photons was predicted at the beginning of quantum mechanics in the 1930s, but this is the first time it has been noted in reality, and marks a theoretical breakthrough.
Adapted from materials provided by University of Bath.

Fausto Intilla

www.oloscience.com

Breakthrough Toward Industrial-scale Production Of Nanodevices

Source:

http://www.sciencedaily.com/releases/2007/11/071112105115.htm

ScienceDaily (Nov. 13, 2007) — Scientists in Maryland are reporting an important advance toward the long-sought goal of industrial-scale fabrication of nanowire-based devices like ultra-sensitive sensors, light emitting diodes, and transistors for inexpensive, high-performance electronics products.

In the report, Babak Nikoobakht points out that existing state-of-the-art assembly methods for nanowire-based devices require complicated, multi-step treatments, painstaking alignments steps, and other processing for nanowires , which are thousands of times smaller than the diameter of a human hair.
The goal is to electrically address the coordinates of millions of nanowires on a surface in order to produce the components of electronic circuits.
The study describes a new method in which zinc oxide nanowires are grown in the exact positions where nanodevices later will be fabricated, in a way that involves a minimum number of fabrication steps and is suitable for industrial-scale applications.
"This method, due to its scalability and ease of device fabrication, goes beyond the current state-of-the-art assembly of nanowire-based devices," the report states. "It is believed to be an attractive approach for mass fabrication of nanowire-based transistors and sensors and is expected to impact nanotechnology in fabrication of nonconventional nanodevices."
The article "Toward Industrial-Scale Fabrication of Nanowire-Based Devices" is scheduled for publication in ACS' Chemistry of Materials.
Adapted from materials provided by American Chemical Society.

Fausto Intilla

www.oloscience.com

Large Hadron Collider Installs Its Precision Silicon Detector, VELO

Source:

http://www.sciencedaily.com/releases/2007/11/071112100650.htm

ScienceDaily (Nov. 13, 2007) — One of the most fragile detectors for the Large Hadron Collider beauty (LHCb) experiment has been successfully installed in its final position. LHCb is one of four large experiments at CERN's Large Hadron Collider (LHC), expected to start up in 2008.

For the LHCb collaboration, including UK scientists from the Universities of Liverpool and Glasgow, installing the Vertex Locator (VELO) detector into its final location in the underground experimental cavern at CERN has been a challenging task.
"It was a very delicate operation", said Paula Collins, LHCb-VELO project leader, "With its successful completion, the VELO is now in place and ready for physics."
Professor Themis Bowcock, lead LHCb scientist from the University of Liverpool where the intricate instrumentation was built and assembled said, "This is a big milestone for VELO and marks an end to the construction side of the project. With each one of the 42 modules that make up the instrument taking 1,000 hours to construct the final installation was a nail biting experience."
The VELO is a precise particle-tracking detector that surrounds the proton-proton collision point inside the LHCb experiment. At its heart are 84 half-moon shaped silicon sensors, each one connected to its electronics via a delicate system of more than 5000 bond wires. These sensors will be located very close to the collision point, where they will play a crucial role in detecting b quarks, to help in understanding tiny but crucial differences in the behaviour of matter and antimatter.
The sensors are grouped in pairs to make a total of 42 modules, arranged in two halves around the beam line in the VELO vacuum tank. An aluminum sheet just 0.3 mm thick provides a shield between the silicon modules and the primary beam vacuum, with no more than 1 mm of leeway to the silicon modules. Custom-made bellows enable the VELO to retract from its normal position of just 5 mm from the beam line, to a distance 35 mm. This flexibility is crucial during the commissioning of the beam as it travels round the 27-km ring of the LHC.
"The installation was very tricky, because we were sliding the VELO blindly in the detector," said Eddy Jans, VELO installation coordinator. "As these modules are so fragile, we could have damaged them all and not realized it straight away." However, the verification procedures carried out on the silicon modules after installation indicated that no damage had occurred.
Dr Chris Parkes, scientist from the University of Glasgow LHCb team, who were responsible for testing the modules, adds, "Now that the VELO is in place we can start work on testing the instrument in situ in the lead up to science operations next year."
UK scientists have a major involvement with the Vertex Locator. The individual modules were designed and assembled at Liverpool University and scientists from Glasgow University are responsible for the reception and testing of modules at CERN. NIKHEF provided the special foil that interfaces with the LHC vacuum. Other collaborators are EPFL Lausanne, CERN, Syracuse and MPI Heidelberg.
Adapted from materials provided by Science and Technology Facilities Council.

Fausto Intilla

www.oloscience.com

Line Between Quantum And Classical Worlds Is At Scale Of Hydrogen Molecule

Source:

http://www.sciencedaily.com/releases/2007/11/071109090639.htm

ScienceDaily (Nov. 12, 2007) — The big world of classical physics mostly seems sensible: waves are waves and particles are particles, and the moon rises whether anyone watches or not. The tiny quantum world is different: particles are waves (and vice versa), and quantum systems remain in a state of multiple possibilities until they are measured — which amounts to an intrusion by an observer from the big world — and forced to choose: the exact position or momentum of an electron, say.

On what scale do the quantum world and the classical world begin to cross into each other? How big does an "observer" have to be? It's a long-argued question of fundamental scientific interest and practical importance as well, with significant implications for attempts to build solid-state quantum computers.
Researchers at the Department of Energy's Lawrence Berkeley National Laboratory and their collaborators at the University of Frankfurt, Germany; Kansas State University; and Auburn University have now established that quantum particles start behaving in a classical way on a scale as small as a single hydrogen molecule. They reached this conclusion after performing what they call the world's simplest — and certainly its smallest — double slit experiment, using as their two "slits" the two proton nuclei of a hydrogen molecule, only 1.4 atomic units apart (a few ten-billionths of a meter). Their results appear in the November 9, 2007 issue of Science.
Double slit experiment
"One of the most powerful ways to explore the quantum world is the double slit experiment," says Ali Belkacem of Berkeley Lab's Chemical Sciences Division, one of the research leaders. In its familiar form, the double slit experiment uses a single light source shining through two slits, side by side in an opaque screen; the light that passes through falls on a screen.
If either of the two slits is closed, the light going through the other slit forms a bright bar on the screen, striking the screen like a stream of BBs or Ping-Pong balls or other solid particles. But if both slits are open, the beams overlap to form interference fringes, just as waves in water do, with bright bands where the wavecrests reinforce one another and dark bands where they cancel.
So is light particles or waves? The ambiguous results of early double slit experiments (the first on record was in 1801) were not resolved until well into the 20th century, when it became clear from both experiment and the theory of quantum mechanics that light is both waves and particles — moreover, that particles, including electrons, also have a wave nature.
"It's the wave nature of electrons that allows them to act in a correlated way in a hydrogen molecule," says Thorsten Weber of the Chemical Sciences Division, another of the experiment's leading researchers. "When two particles are part of the same quantum system, their interactions are not restricted to electromagnetism, for example, or gravity. They also possess quantum coherence — they share information about their states nonlocally, even when separated by arbitrary distances."
Correlation between its two electrons is actually what makes double photoionization possible with a hydrogen molecule. Photoionization means that an energetic photon, in this case an x-ray, knocks an electron out of an atom or molecule, leaving the system with net charge (ionized); in double photoionization a single photon triggers the emission of two electrons.
"The photon hits only one electron, but because they are correlated, because they cohere in the quantum sense, the electron that's hit flies off in one direction with a certain momentum, and the other electron also flies off at a specific angle to it with a different momentum," Weber explains.
The experimental set-up used by Belkacem and Weber and their colleagues, being movable, was employed on both beamlines 4.0 and 11.0 of Berkeley Lab's Advanced Light Source (ALS). In the apparatus a stream of hydrogen gas is sent through an interaction region, where some of the molecules are struck by an x-ray beam from the ALS. When the two negatively charged electrons are knocked out of a molecule, the two positively charged protons (the nuclei of the hydrogen atoms) blow themselves apart by mutual repulsion. An electric field in the experiment's interaction region separates the positively and negatively charged particles, sending the protons to one detector and the electrons to a detector in the opposite direction.
"It's what's called a kinematically complete experiment," Belkacem says, "one in which every particle is accounted for. We can determine the momentum of all the particles, the initial orientation and distance between the protons, and the momentum of the electrons."
What the simplest double slit experiment reveals
"At the high photon energies we used for photoionization, most of the time we observed one fast electron and one slow electron," says Weber. "What we were interested in was the interference patterns."
Considered as particles, the electrons fly off at an angle to one another that depends on their energy and how they scatter from the two hydrogen nuclei (the "double slit"). Considered as waves, an electron makes an interference pattern that can be seen by calculating the probability that the electron will be found at a given position relative to the orientation of the two nuclei.
The wave nature of the electron means that in a double slit experiment even a single electron is capable of interfering with itself. Double slit experiments with photoionized hydrogen molecules at first showed only the self-interference patterns of the fast electrons, their waves bouncing off both protons, with little action from the slow electrons.
"From these patterns, it might look like the slow electron is not important, that double photoionization is pretty unspectacular," says Weber. The fast electrons' energies were 185 to 190 eV (electron volts), while the slow electrons had energies of 5 eV or less. But what happens if the slow electron is given just a bit more energy, say somewhere between 5 and 25 eV? As Weber puts it, "What if we make the slow electron a little more active? What if we turn it into an 'observer?'"
As long as both electrons are isolated from their surroundings, quantum coherence prevails, as revealed by the fast electron's wavelike interference pattern. But this interference pattern disappears when the slow electron is made into an observer of the fast one, a stand-in for the larger environment: the quantum system of the fast electron now interacts with the wider world (e.g., its next neighboring particle, the slow electron) and begins to decohere. The system has entered the realm of classical physics.
Not completely, however. And here is what Belkacem calls "the meat of the experiment:" "Even when the interference pattern has disappeared, we can see that coherence is still there, hidden in the entanglement between the two electrons."
Although one electron has become entangled with its environment, the two electrons are still entangled with each other in a way that allows interference between them to be reconstructed, simply by graphing their correlated momenta from the angles at which the electrons were ejected. Two waveforms appear in the graph, either of which can be projected to show an interference pattern. But the two waveforms are out of phase with each other: viewed simultaneously, interference vanishes.
If the two-electron system is split into its subsytems and one (the "observer") is thought of as the environment of the other, it becomes evident that classical properties such as loss of coherence can emerge even when only four particles (two electrons, two protons) are involved. Yet because the two electron subsystems are entangled in a tractable way, their quantum coherence can be reconstructed. What Weber calls "the which-way information exchanged between the particles" persists.
Says Belkacem, "For researchers who are trying to build solid-state quantum computers this is both good news and bad news. The bad news is that decoherence and loss of information occur on the very tiny scale of a single hydrogen molecule. The good news is that, theoretically, the information isn't necessarily lost — or at least not completely."
"The Simplest Double Slit: Interference and Entanglement in Double Photoionization of H2," by D. Akoury, K. Kreidi, T. Jahnke, Th. Weber, A. Staudte, M. Schöffler, N. Neumann, J. Titze, L. Ph. H. Schmidt, A. Czasch, O. Jagutzki, R. A. Costa Fraga, R. E. Grisenti, R. Díez Muiño, N. A. Cherepkov, S. K. Semenov, P. Ranitovic, C. L. Cocke, T. Osipov, H. Adaniya, J. C. Thompson, M. H. Prior, A. Belkacem, A. L. Landers, H. Schmidt-Böcking, and R. Dörner, appears in the 9 November issue of Science.
Adapted from materials provided by DOE/Lawrence Berkeley National Laboratory.

Fausto Intilla

www.oloscience.com

Atomic-level Microscopy At Least 100 Times Faster With New Technique

Source:

http://www.sciencedaily.com/releases/2007/11/071107184753.htm

ScienceDaily (Nov. 9, 2007) — Using an existing technique in a novel way, Cornell physicist Keith Schwab and colleagues at Cornell and Boston University have made the scanning tunneling microscope (STM) -- which can image individual atoms on a surface -- at least 100 times faster.

The simple adaptation, based on a method of measurement currently used in nano-electronics, could also give STMs significant new capabilities -- including the ability to sense temperatures in spots as small as a single atom, and to detect changes in position as tiny as 0.00000000000001 meters: a distance 30,000 times smaller than the diameter of an atom.
The STM uses quantum tunneling, or the ability of electrons to "tunnel" across a barrier, to detect changes in the distance between a needlelike probe and a conducting surface. Researchers apply a tiny voltage to the sample and move the probe -- a simple platinum-iridium wire snipped to end in a point just one atom wide -- just a few angstroms (10ths of a nanometer) over the sample's surface. By measuring changes in current as electrons tunnel between the sample and the probe, they can reconstruct a map of the surface topology down to the atomic level.
Since its invention in the 1980s, the STM has enabled major discoveries in fields from semiconductor technology to nano-electronics.
But while current can change in a nanosecond, measurements with the STM are painfully slow. And the limiting factor is not in the signal itself: It's in the basic electronics involved in analyzing it. A theoretical STM could collect data as fast as electrons can tunnel -- at a rate of one gigahertz, or 1 billion cycles per second of bandwidth. But a typical STM is slowed down by the capacitance, or energy storage, in the cables that make up its readout circuitry -- to about one kilohertz (1,000 cycles per second) or less.
Researchers have tried a variety of complex remedies. But in the end, said Schwab, an associate professor of physics at Cornell, the solution was surprisingly simple. By adding an external source of radio frequency (RF) waves and sending a wave into the STM through a simple network, the researchers showed that it's possible to detect the resistance at the tunneling junction -- and hence the distance between the probe and sample surface -- based on the characteristics of the wave that reflects back to the source.
The technique, called reflectometry, uses the standard cables as paths for high-frequency waves, which aren't slowed down by the cables' capacitance.
"There are six orders of magnitude between the fundamental limit in frequency and where people are operating," said Schwab. With the RF adaptation, speeds increase by a factor of between 100 and 1,000. "Our hope is that we can produce more or less video images, as opposed to a scan that takes forever."
The setup also offers potential for atomic resolution thermometry -- precise measurements of temperature at any particular atom on a surface -- and for motion detection so sensitive it could measure movement of a distance 30,000 times smaller than the size of an atom.
"This STM will be used for a lot of good physics experiments," said Schwab. "Once you open up this new parameter, all this bandwidth, people will figure out ways to use it. I firmly believe 10 years from now there will be a lot of RF-STMs around, and people will do all kinds of great experiments with them."
The finding is described in the Nov. 1 issue of the journal Nature. The research was supported by the National Science Foundation.
Adapted from materials provided by Cornell University.

Fausto Intilla

www.oloscience.com

Large Hadron Collider Ready To Go

Source:

http://www.sciencedaily.com/releases/2007/11/071107160139.htm

ScienceDaily (Nov. 9, 2007) — CERN Director General Robert Aymar sealed the last interconnect in the world’s largest cryogenic system, the Large Hadron Collider (LHC). This is the latest milestone in commissioning the LHC, the world’s most powerful particle accelerator.

The LHC’s cryogenic system has the task of cooling some 36 800 tonnes of material to a temperature of just 1.9 degrees above absolute zero (–271.3°C), colder than outer space. To do this, over 10 000 tonnes of liquid nitrogen and 130 tonnes of liquid helium will be deployed through a cryogenic system including over 40 000 leak-tight welds. Today’s ceremony marks the end of a two year programme of work to connect all the main dipole and quadrupole magnets in the LHC. This complex task included both electrical and fluid connections.
“This is a huge accomplishment,” said Lyn Evans, LHC project leader. “Now that it is done, we can concentrate on getting the machine cold and ready for physics.”
The LHC is a circular machine, 27 kilometres around and divided into eight sectors, each of which can be cooled down to its operating temperature of 1.9 degrees above absolute zero and powered-up individually. One sector was cooled down, powered and warmed up in the first half of 2007. This was an important learning process, allowing subsequent sectors to be tested more quickly.
“Over the coming months, we’ll be cooling down the remaining sectors,” said Evans. “Five sectors will be cooling by the end of 2007, with the remaining three joining them early next year.”
If all goes well, the first beams could be injected into the LHC in May 2008, and circulating beams established by June or July. With a project of this scale and complexity, however, the transition from construction to operation is a lengthy process.
“There is no big red button, and there are inevitably hurdles to be overcome as we bring the LHC into operation,” said Aymar, “Every part of the system has to be brought on stream carefully, with each sub-system and component tested and repaired if necessary.”
“There have been no show-stoppers so far,” added Evans. “For a machine of this complexity, things are going remarkably smoothly and we’re all looking forward to doing physics with the LHC next summer. If for any reason we have to warm up a sector, though,” he cautioned, “we’ll be looking at the end of summer rather than the beginning.”
Adapted from materials provided by CERN.

Fausto Intilla

www.oloscience.com

Heavier Hydrogen On The Atomic Scale Reduces Friction

Source:

http://www.sciencedaily.com/releases/2007/11/071102163021.htm

ScienceDaily (Nov. 6, 2007) — Scientists may be one step closer to understanding the atomic forces that cause friction, thanks to a recently published study by researchers from the University of Pennsylvania, the University of Houston and the U.S. Department of Energy's Argonne National Laboratory.

The research, led by Robert Carpick of the University of Pennsylvania, found a significant difference in friction exhibited by diamond surfaces that had been coated with different isotopes of hydrogen and then rubbed against a small carbon-coated tip.
Scientists lack a comprehensive model of friction on the nanoscale and only generally grasp its atomic-level causes, which range from local chemical reactions to electronic interactions to phononic, or vibrational, resonances.
To investigate the latter, Argonne scientist Anirudha Sumant and his colleagues used single-crystal diamond surfaces coated with layers of either atomic hydrogen or deuterium, a hydrogen atom with an extra neutron. The deuterium-terminated diamonds had lower friction forces because of their lower vibrational frequencies, an observation that Sumant attributed to that isotope's larger mass. They have also observed same trend on a silicon substrate, which is structurally similar to that of diamond.
Previous attempts to make hydrogen-terminated diamond surfaces relied on the use of plasmas, which tended to etch the material.
"When you're looking at such a small isotopic effect, an objectively tiny change in the mass, you have to be absolutely sure that there are no other complicating effects caused by chemical or electronic interferences or by small topographic variations," Sumant said. "The nanoscale roughening of the diamond surface from the ion bombardment during the hydrogen or deuterium termination process, even though it was at very low level, remained one of our principal concerns."
Sumant and his collaborators had looked at a number of other ways to try to avoid etching, even going to such lengths as to soak the films in olive oil before applying the hydrogen layers. However, no method had provided a smooth, defect-free hydrogen layer with good coverage that would avoid generating background noise, he said.
However, while performing work at the University of Wisconsin-Madison, Sumant developed a system for depositing diamond thin films. The technique, called hot filament chemical vapor deposition, involves the heating of a tungsten filament (like those found in incandescent light bulbs) to over 2000 degrees Celsius.
If the diamond film is exposed to a flow of molecular hydrogen while sitting within a centimeter of the hot filament, the heat will cause the molecular hydrogen to break down into atomic hydrogen, which will react with the film's surface to create a perfectly smooth layer. Since this method does not require the use of plasma, there is no danger of ion-induced etching.
"We've proved that this is a gentler method of terminating a diamond surface," Sumant said.
Sumant said that he hopes to use the knowledge gained from the experiment to eventually discover a way to manipulate the friction of surfaces on the atomic level. Such a result would prove immensely valuable to the development of nanoelectromechanical systems, or NEMS, based on diamonds, one of Sumant's primary research interests at Argonne's Center for Nanoscale Materials.
The paper, "Nanoscale Friction Varied by Isotopic Shifting of Surface Vibrational Frequencies," appears in the November 2 issue of Science.
The research was supported by the National Science Foundation, an NSF Graduate Research Fellowship, the Air Force Office of Scientific Research and the Department of Energy's Office of Science, Office of Basic Energy Sciences.
Adapted from materials provided by DOE/Argonne National Laboratory.

Fausto Intilla

www.oloscience.com

How Electrons 'Gain Weight' In Metal Compounds Near Absolute Zero

Source:

http://www.sciencedaily.com/releases/2007/11/071101144954.htm

ScienceDaily (Nov. 5, 2007) — Rutgers University physicists have performed computer simulations that show how electrons become one thousand times more massive in certain metal compounds when cooled to temperatures near absolute zero -- the point where all motion ceases. The models may provide new clues as to how superconductivity works and how new superconducting materials could be fabricated.

In a paper posted to Science Express, a Web site of research reports slated for upcoming print editions of Science, the researchers describe how electrons interact with other particles in these compounds to morph into what physicists call a fluid of "heavy quasiparticles" or a "heavy fermion fluid." While this effect has been previously observed in some materials, the Rutgers work employs new materials to provide a level of detail that has eluded scientists so far.
"In this paper, we essentially track the fate of electrons as we lower the temperature," said Gabi Kotliar, Board of Governors Professor of Physics in the School of Arts and Sciences. "Experimental physicists may have seen different aspects of this behavior, or they may have seen behaviors they did not understand. Our calculations reconcile what they've seen."
The Rutgers researchers based their models on experiments using a new metallic crystalline compound made of the elements cerium, indium and iridium. This and similar compounds that substitute cobalt and rhodium for iridium are excellent test beds for observing heavy electron behavior.
Earlier investigations used high-temperature superconducting materials called cuprates, which failed to give physicists a clear view of electron behavior because of disorders in the crystalline structure caused by doping. The new cerium-based compounds are simpler to study because they are free of dopants.
"The new compounds are for us what fruit flies are for genetics researchers," said Kristjan Haule, assistant professor of physics and astronomy. "Fruit flies are easy to breed and have a simple gene makeup that's easy to change. Likewise, these compounds are easy to make, structurally straightforward and adjustable, giving us a clearer view into the many properties of matter that arise at low temperatures. For example, we can use a magnetic field to kill superconductivity and examine the state of matter from which superconductivity arose."
These compounds are examples of strongly correlated materials, or materials with strongly interacting electrons, that can't be described by theories that treat electrons as largely independent entities. The terms "heavy quasiparticles" refers to how electrons interact with each other and, as a result of those interactions, form a new type of particle called a "quasiparticle."
In explaining how this effect appears at low temperatures and vanishes at higher ones, Haule noted that electrons in f-orbitals are tightly bound to cerium atoms at room temperature. But as the temperature drops, the electrons exhibit coherent behavior, or delocalization from their atoms. At 50 degrees above absolute zero, or 50 degrees Kelvin, the researchers clearly observe quasiparticles as electrons interact with each other and other electrons in the metal known as conduction electrons.
The work done by Haule and his colleagues is in a branch of physics known as condensed matter physics, which deals with the physical properties of solid and liquid matter. Their models of heavy quasiparticles draw from Haule's earlier work merging two theories of atomic modeling, known as local density approximation and dynamical mean field theory, or LDA+DMFT.
Collaborating with Haule and Kotliar was Ji-Hoon Shim, a postdoctoral fellow. The National Science Foundation's Division of Materials Research and the Rutgers Center for Materials Theory supported their research. Shim received postdoctoral research funding from the Korean Research Foundation.
Adapted from materials provided by Rutgers University.

Fausto Intilla

www.oloscience.com

Electron Spin Rotated With Electric Field

Source:

http://www.sciencedaily.com/releases/2007/11/071101144942.htm

ScienceDaily (Nov. 5, 2007) — Researchers at the Delft University of Technology's Kavli Institute of Nanoscience and the Foundation for Fundamental Research on Matter (FOM) have succeeded in controlling the spin of a single electron merely by using electric fields. This clears the way for a much simpler realization of the building blocks of a (future) super-fast quantum computer.

Controlling the spin of a single electron is essential if this spin is to be used as the building block of a future quantum computer. An electron not only has a charge but, because of its spin, also behaves as a tiny magnet. In a magnetic field, the spin can point in the same direction as the field or in the opposite direction, but the laws of quantum mechanics also allow the spin to exist in both states simultaneously.
As a result, the spin of an electron is a very promising building block for the yet-to-be-developed quantum computer; a computer that, for certain applications, is far more powerful than a conventional computer.
At first glance it is surprising that the spin can be rotated by an electric field. However, we know from the Theory of Relativity that a moving electron can 'feel' an electric field as though it were a magnetic field. Researchers Katja Nowack and Dr. Frank Koppens therefore forced an electron to move through a rapidly-changing electric field. Working in collaboration with Prof. Yuli V. Nazarov, theoretical researcher at the Kavli Institute of Nanoscience Delft, they showed that it was indeed possible to turn the spin of the electron by doing so.
The advantage of controlling spin with electric fields rather than magnetic fields is that the former are easy to generate. It will also be easier to control various spins independently from one another - a requirement for building a quantum computer - using electric fields. The team, led by Dr. Lieven Vandersypen, is now going to apply this technique to a number of electrons.
The scientists published their work in Science Express on 1 November, 2007.
Adapted from materials provided by Delft University of Technology.

Fausto Intilla

www.oloscience.com

Revolutionary Laser Technique Destroys Viruses And Bacteria Without Damaging Human Cells

Source:

http://www.sciencedaily.com/releases/2007/11/071101084950.htm

ScienceDaily (Nov. 2, 2007) — Physicists in Arizona State University have designed a revolutionary laser technique which can destroy viruses and bacteria such as AIDS without damaging human cells and may also help reduce the spread of hospital infections such as MRSA.

The research, published on Thursday November 1 in the Institute of Physics' Journal of Physics: Condensed Matter, discusses how pulses from an infrared laser can be fine-tuned to discriminate between problem microorganisms and human cells.
Current laser treatments such as UV are indiscriminate and can cause ageing of the skin, damage to the DNA or, at worst, skin cancer, and are far from 100 per cent effective.
Femtosecond laser pulses, through a process called Impulsive Stimulated Raman Scattering (ISRS), produces lethal vibrations in the protein coat of microorganisms, thereby destroying them. The effect of the vibrations is similar to that of high-pitched noise shattering glass.
The physicists in Arizona have undertaken experiments to show that the coherent vibrations excited by infrared lasers with carefully selected wavelengths and pulse widths do no damage to human cells, most likely because of the different structural compositions in the protein coats of human cells vis a vis bacteria and viruses.
Professor K. T. Tsen from Arizona State University said, "Although it is not clear at the moment why there is a large difference in laser intensity for inactivation between human cells and microorganisms such as bacteria and viruses, the research so far suggests that ISRS will be ready for use in disinfection and could provide treatments against some of the worst, often drug-resistant, bacterial and viral pathogens."
Femtosecond lasers could find immediate application in hospitals as a way to disinfect blood supply or biomaterials and for the treatment of blood-borne diseases such as AIDS and Hepatitis.
Adapted from materials provided by Institute of Physics.

Fausto Intilla

www.oloscience.com

Scientists Discover New Way To Make Water

Source:

http://www.sciencedaily.com/releases/2007/10/071031125457.htm

ScienceDaily (Nov. 1, 2007) — In a familiar high-school chemistry demonstration, an instructor first uses electricity to split liquid water into its constituent gases, hydrogen and oxygen. Then, by combining the two gases and igniting them with a spark, the instructor changes the gases back into water with a loud pop.

Scientists at the University of Illinois have discovered a new way to make water, and without the pop. Not only can they make water from unlikely starting materials, such as alcohols, their work could also lead to better catalysts and less expensive fuel cells.
"We found that unconventional metal hydrides can be used for a chemical process called oxygen reduction, which is an essential part of the process of making water," said Zachariah Heiden, a doctoral student and lead author of a paper accepted for publication in the Journal of the American Chemical Society, and posted on its Web site.
A water molecule (formally known as dihydrogen monoxide) is composed of two hydrogen atoms and one oxygen atom. But you can't simply take two hydrogen atoms and stick them onto an oxygen atom. The actual reaction to make water is a bit more complicated: 2H2 + O2 = 2H2O + Energy.
In English, the equation says: To produce two molecules of water (H2O), two molecules of diatomic hydrogen (H2) must be combined with one molecule of diatomic oxygen (O2). Energy will be released in the process.
"This reaction (2H2 + O2 = 2H2O + Energy) has been known for two centuries, but until now no one has made it work in a homogeneous solution," said Thomas Rauchfuss, a U. of I. professor of chemistry and the paper's corresponding author.
The well-known reaction also describes what happens inside a hydrogen fuel cell.
In a typical fuel cell, the diatomic hydrogen gas enters one side of the cell, diatomic oxygen gas enters the other side. The hydrogen molecules lose their electrons and become positively charged through a process called oxidation, while the oxygen molecules gain four electrons and become negatively charged through a process called reduction. The negatively charged oxygen ions combine with positively charged hydrogen ions to form water and release electrical energy.
The "difficult side" of the fuel cell is the oxygen reduction reaction, not the hydrogen oxidation reaction, Rauchfuss said. "We found, however, that new catalysts for oxygen reduction could also lead to new chemical means for hydrogen oxidation."
Rauchfuss and Heiden recently investigated a relatively new generation of transfer hydrogenation catalysts for use as unconventional metal hydrides for oxygen reduction.
In their JACS paper, the researchers focus exclusively on the oxidative reactivity of iridium-based transfer hydogenation catalysts in a homogenous, non-aqueous solution. They found the iridium complex effects both the oxidation of alcohols, and the reduction of the oxygen.
"Most compounds react with either hydrogen or oxygen, but this catalyst reacts with both," Heiden said. "It reacts with hydrogen to form a hydride, and then reacts with oxygen to make water; and it does this in a homogeneous, non-aqueous solvent."
The new catalysts could lead to eventual development of more efficient hydrogen fuel cells, substantially lowering their cost, Heiden said.
The work was funded by the U.S. Department of Energy.
Adapted from materials provided by University of Illinois at Urbana-Champaign.

Fausto Intilla

www.oloscience.com

Nano-assembly Mimics Origin Of Life? Molecules Organize Themselves Into Patterns

Source:

http://www.sciencedaily.com/releases/2007/10/071030105309.htm

ScienceDaily (Nov. 1, 2007) — The automatic molecular assembly and selection steps exhibited by the molecules, which start as random mixtures, demonstrates a fundamental step in the evolution of life. The organization is activated by instructions which are built-in to the molecules. During assembly, molecules exhibit active selection: those in incorrect positions move to make room for others which fit properly.

The molecular-level observation of such self-selection gives, for the first time, direct insight into fundamental steps of the biological evolution from inanimate molecules to living entities. The resulting nanostructures also hold great promise as an efficient avenue to new catalysts, nanotechnologies, and surface applications.
In the Proceedings of the National Academy of Sciences of the USA, the scientists from the research groups of Klaus Kern at the Max Planck Institute for Solid State Research in Stuttgart (MPI) and of Mario Ruben at the Karlsruhe Institute of Technology (KIT) explain that this observation of molecular organization at surfaces may lead to further insight of how simple, inanimate molecules can build up biological entities of increasing structural and functional complexity, such as membranes, cells, leaves, trees, etc.
"The ability of molecules to selectively sort themselves in highly organized structures is a fundamental requirement for all molecular based systems, including biological organisms," explains Prof. Dr. Klaus Kern, director of the Nanoscale Science Department at the MPI.
Dr. Mario Ruben’s research team at KIT is responsible for designing molecules with built-in instructions, which when read out activate the self-selection process. He comments: "Spontaneous ordering from random mixtures only occurs when built-in instructions are carefully designed and sufficiently strong to initiate successful self-selection."
Scientists at the MPI directly observe the basic step of self-selection by imaging grid-like assemblies of molecules, which have sorted themselves by size. The features of the grid pattern are about one nanometer in size (0.000 000 001 meters), so small that they can only be imaged using state-of-the-art, ultra sensitive microscopy techniques. "Creating such miniscule architectures with features 50 000 times smaller than a hair is not a simple task," according to Dr. Steven Tait of the MPI. "Carving these nanometer structures with current technology would be inefficient and extremely expensive. Our strategy is to utilize instructed building blocks which can arrange themselves into desired structures."
The molecules are placed on ultra-clean metal surfaces and heated gently to enable motion, sorting, and organization. "The molecule movement on the copper surface is restricted to two-dimensions, but is still efficient enough to allow mixing of the molecules. By placing the molecules on a surface, we have the enormous advantage of being able to use specialized microscopes to ‚see’ the nanometer scale structures of the molecular assemblies," explains Alexander Langner, a graduate student at the MPI and first author of the study.
The study was conducted by Alexander Langner, Dr. Steven Tait, Dr. Nian Lin, and Prof. Dr. Klaus Kern of the Max Planck Institute for Solid State Research and Dr. Chandrasekar Rajadurai and Dr. Mario Ruben of the Karlsruhe Institute of Technology (KIT).
Professor Kern is the director of the Nanoscale Science Department at the MPI and leads a large research team conducting a wide range of studies related to the electronic, optical, and chemical properties of novel materials at the nanometer scale. Dr. Ruben is the leader of the research group "Functional Molecular Nanostructures" at the Institute of Nanotechnology in Karlsruhe and has a long-standing competence in the design and synthesis of instructed molecular components.
Adapted from materials provided by Max-Planck-Gesellschaft.

Fausto Intilla

www.oloscience.com