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Enhancing the quantum sensing capabilities of diamond: Shooting electrons at diamonds can introduce quantum sensors into them

22/11/2017

Researchers have discovered that dense ensembles of quantum spins can be created in diamond with high resolution using an electron microscopes, paving the way for enhanced sensors and resources for quantum technologies.

Diamonds are made of carbon atoms in a crystalline structure, but if a carbon atom is replaced with another type of atom, this will result in a lattice defect. One such defect is the Nitrogen-Vacancy (NV), where one carbon atom is replaced by a nitrogen atom, and its neighbor is missing (an empty space remains in its place).

If this defect is illuminated with a green laser, in response it will emit red light (fluoresce) with an interesting feature: its intensity varies depending on the magnetic properties in the environment. This unique feature makes the NV center particularly useful for measuring magnetic fields, magnetic imaging (MRI), and quantum computing and information.

In order to produce optimal magnetic detectors, the density of these defects should be increased without increasing environmental noise and damaging the diamond properties.

Now, scientists from the research group of Nir Bar-Gill at the Hebrew University of Jerusalem’s Racah Institute of Physics and Department of Applied Physics, in cooperation with Prof. Eyal Buks of the Technion – Israel Institute of Technology, have shown that ultra-high densities of NV centers can be obtained by a simple process of using electron beams to kick carbon atoms out of the lattice.

This work, published in the scientific journal Applied Physics Letters, is a continuation of previous work in the field, and demonstrates an improvement in the densities of NV centers in a variety of diamond types. The irradiation is performed using an electron beam microscope (Transmission Electron Microscope or TEM), which has been specifically converted for this purpose. The availability of this device in nanotechnology centers in many universities in Israel and around the world enables this process with high spatial accuracy, quickly and simply.

The enhanced densities of the NV color centers obtained, while maintaining their unique quantum properties, foreshadow future improvements in the sensitivity of diamond magnetic measurements, as well as promising directions in the study of solid state physics and quantum information theory.

Nitrogen Vacancy (NV) color centers exhibit remarkable and unique properties, including long coherence times at room temperature (~ ms), optical initialization and readout, and coherent microwave control.

“This work is an important stepping stone toward utilizing NV centers in diamond as resources for quantum technologies, such as enhanced sensing, quantum simulation and potentially quantum information processing”, said Bar-Gill, an Assistant Professor in the Dept. of Applied Physics and Racah Institute of Physics at the Hebrew University, where he founded the Quantum Information, Simulation and Sensing lab.

"What is special about our approach is that it's very simple and straightforward," said Hebrew University researcher Dima Farfurnik. "You get sufficiently high NV concentrations that are appropriate for many applications with a simple procedure that can be done in-house."

CITATION: Farfurnik, D., et al. Enhanced concentrations of nitrogen-vacancy centers in diamond through TEM irradiationAppl. Phys. Lett. 111, 123101 (2017). Publisher's Version

SUPPORT: This work was supported in part by the Minerva ARCHES award, the CIFAR-Azrieli global scholars program, the Israel Science Foundation (Grant No. 750/14), the Ministry of Science and Technology, Israel, the Technion security research foundation, and the CAMBR fellowship for Nanoscience and Nanotechnology.

PHOTO 1: http://media.huji.ac.il/new/photos/hu171114_bar-gill.jpg - Diamond sample illuminated by green light in our home-built microscope. Sample is placed on a special mount, within a printed circuit board, used to deliver microwaves which allow quantum manipulations and magnetic sensing with the NVs. (Credit: Yoav Romach)

PHOTO 2: http://media.huji.ac.il/new/photos/hu171114_bar-gill-cryo.jpg - Cryogenic sample chamber, with diamond sample mounted on copper cold plate. (Credit: Yoav Romach)

PHOTO 3: https://drive.google.com/file/d/1TsGTAKrw1l_dw2X2tUDlbBluwnP_LoGf/view - Hebrew University researchers Nir Bar-Gill and Dima Farfurnik with a diamond magnetic microscope. (Credit: Nir Bar-Gill)

Enhancing the quantum sensing capabilities of diamond: Shooting electrons at diamonds can introduce quantum sensors into them
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Novel technique reveals the intricate beauty of a cracked glass

31/10/2017

Physics, math and special gels explain the formation of fracture patterns in brittle materials

Researchers have long pondered the origin of delicate criss-cross facetted patterns that are commonly found on the surfaces of broken material. Typical crack speeds in glass easily surpass a kilometer per second, and broken surface features may be well smaller than a millimeter. Since the formation of surface structure lasts a tiny fraction of a second, the processes generating these patterns have been largely a mystery.

Now there is a way around this problem. Replacing hard glass with soft but brittle gels makes it possible to slow down the cracks that precipitate fracture to mere meters per second. This novel technique has enabled researchers Itamar Kolvin, Gil Cohen and Prof. Jay Fineberg, at the Hebrew University of Jerusalem’s Racah Institute of Physics, to unravel the complex physical processes that take place during fracture in microscopic detail and in real time.

Their work sheds new light on how broken surface patterns are formed. Surface facets bounded by steps are formed due to a special “topological” arrangement of the crack that cannot easily be undone, much as a knot along a string cannot be unraveled without pulling the whole length of the string through it.

These “crack knots” increase the surface formed by a crack, thereby creating a new venue for dissipating the energy required for material failure, and thereby making materials harder to break. 

“The complex surfaces that are commonly formed on any fractured object have never been entirely understood,” said Prof. Jay Fineberg. “While a crack could form perfectly flat, mirror-like fracture surfaces (and sometimes does), generally complex facetted surfaces are the rule, even though they require much more energy to form. This study illuminates both how such beautiful and intricate patterns emerge in the fracture process, and why the crack cannot divest itself of them once they are formed.”

This physically important process provides an aesthetic example of how physics and mathematics intertwine to create intricate and often unexpected beauty. The research appears in Nature Materials.

The Hebrew University of Jerusalem is Israel’s leading university and premier research institution. Founded in 1918 by innovative thinkers including Albert Einstein, the Hebrew University is a pluralistic institution that advances science and knowledge for the benefit of humankind. For more information, please visit http://new.huji.ac.il/en.

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FUNDING: Fineberg and Kolvin acknowledge the support of the Israel Science Foundation (grant no.1523/15), as well as the US-Israel Bi-national Science Foundation (grant no. 2016950).

CITATION: Itamar Kolvin, Gil Cohen, Jay Fineberg. Topological defects govern crack front motion and facet formation on broken surfaces. Nature Materials, Advance Online Publication October 16, 2017. doi:10.1038/nmat5008. Link: http://dx.doi.org/10.1038/nmat5008

Novel technique reveals the intricate beauty of a cracked glass
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LIGO Confirms 1989 Hebrew University Prediction About Neutron Star Mergers Producing Gamma Ray Bursts

16/10/2017

Prof. Tsvi Piran at Hebrew University's Racah Institute of Physics led a team that published an accurate prediction in 'Nature' that met with skepticism for years

Watch video at https://youtu.be/KhfGqK6st_A 

Two years ago, the LIGO gravitational wave detector stunned the world with the discovery of a merger of two black holes. This past August, LIGO did it again: with the help of a second detector called VIRGO, it discovered a new source of gravitational radiation. Seconds later, NASA’s Fermi satellite detected a gamma-ray burst from the same direction. Several hours later, a telescope in Chile identified the source at a Galaxy located 120 million light years away. While this is an enormous distance for us, on a cosmological scale it is relatively close. 

Since these initial discoveries, most of the telescopes in the world, including the Hubble Space Telescope, have observed this galactic event. The results, which have been kept secret until now (despite a partial leak), are reported today in several scientific papers published in the prestigious journals Physical Review LettersNature, Science and the Astrophysical Journal.

These observations confirm a longstanding prediction made almost thirty years ago by a team headed by Prof. Tsvi Piran at the Hebrew University of Jerusalem. Piran is the Schwartzman Chair for Theoretical Physics at the Hebrew University's Racah Institute of Physics. The prediction, published in Nature in 1989 ("Nucleosynthesis, neutrino bursts and γ-rays from coalescing neutron stars"), suggests that when two neutron star merger they emit, in addition to gravitational waves, a burst of gamma-rays. They also synthesize and eject to outer space rare heavy elements, like gold plutonium and uranium. The merged neutron stars form a black hole in this process.

Neutron stars are rare types of stars that are produced in supernova explosions when a regular star dies. Unlike regular matter that is composed from 50% neutron and 50% protons, neutron stars are made just from neutrons. Due to their strange composition, they are extremely dense: a teaspoon of neutron star matter weights about 100 million tons, and a neutron star of 10 km (smaller than the width of Jerusalem) weights about a million times the mass of Earth. 

The first neutron star was discovered in 1967 by Antony Hewish, who received the 1974 Nobel Prize in Physics. Later a binary pair of neutron stars rotating around each other was discovered by Hulse and Taylor, who were awarded the 1993 Nobel Prize in Physics. (And on October 3, LIGO’s three leading champions were awarded the 2017 Nobel Prize in Physics: Barry Barish and Kip Thorne of Caltech and Rainer Weiss of MIT.)

Shortly after the discovery of a binary neutron star pair in 1975, researchers realized that that such a pair would emit gravitational radiation and eventually merge. The question that Piran and colleagues asked in 1989 was: in addition to the gravitational radiation, what else will be emitted as a result of this merger? They suggested that the merger will produce a burst of gamma-rays — which have the smallest wavelengths and the most energy of any other wave in the electromagnetic spectrum — and at the same time will synthesize and eject into outer space freshly synthesized heavy elements like gold, plutonium and uranium. The ultimate result will be a black hole. This prediction, which Piran and colleagues published in Nature, was met with skepticism and initially ignored. However, Piran continued to work on it, and indirect evidence in its favor mounted over the years. These last observations confirm it without any doubt.

“I am exhilarated by this confirmation of a prediction we made nearly thirty years ago,” said Prof. Tsvi Piran following today’s announcement confirming his prediction. “I also remember how difficult it was to convince the scientific community of our idea: at the time it was against the standard model that was published even in freshman textbooks on astronomy. When we made this prediction in 1989, we did not expect it to be confirmed within our lifetimes. But with continued curiosity and the development of new technologies, we are able learn ever deeper truths about the nature of our Universe."

LIGO’s observations confirmed that the event involved a binary neutron star merger, and the formation of a black hole. The Fermi satellite detected the predicted gamma-rays, and the optical observation confirmed the nucleosynthesis of heavy elements. All of this is published today in multiple research papers, with Piran’s participation in several papers published in the journals Nature, Science and The Astrophysical Journal. These observations solve several puzzles that have bothered astronomers over the years, and open new ways to understand the nature of our Universe.

The Hebrew University of Jerusalem is Israel’s leading university and premier research institution. Founded in 1918 by innovative thinkers including Albert Einstein, the Hebrew University is a pluralistic institution that advances science and knowledge for the benefit of humankind. For more information, please visit http://new.huji.ac.il/en.

A related video can be seen at https://youtu.be/KhfGqK6st_A.

 LIGO Confirms 1989 Hebrew University Prediction About Neutron Star Mergers Producing Gamma Ray Bursts
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Nanoscale chip system measures light from a single bacterial cell to enable portable chemical detection

05/09/2017

Further development could open door to on-chip biological and chemical sensing applications, e.g. detecting chemicals in real-time continuous flow systems and even in an open-air environment

Researchers at the Hebrew University of Jerusalem have created a nanophotonic chip system using lasers and bacteria to observe fluorescence emitted from a single bacterial cell. To fix the bacteria in place and to route light toward individual bacterial cells, they used V-groove-shaped plasmonic waveguides, tiny aluminum-coated rods only tens of nanometers in diameter. The novel system, described in the journal Nano Letters, paves the way for an efficient and portable on-chip system for diverse cell-based sensing applications, such as detecting chemicals in real-time.

The field of on-chip photonic devices for biological and chemical sensing applications presents many powerful alternatives to conventional analytical techniques for applications ranging from “lab on a chip” to environmental monitoring.  However, these sensing schemes rely mainly on off-chip detection and require a cumbersome apparatus, even when measuring only single cells. 

The Hebrew University team looked for ways to integrate all system components, including light sources and detectors, on-chip at the nanoscale. This would result in a lab-on-chip system that is small, portable and can perform sensing in real-time.

To achieve this, they molecularly engineered live bacteria that emit a fluorescent signal in the presence of target compounds. They paired these on-chip with a nanoscale waveguide, which not only served the purpose of guiding light, but also allowed mechanical trapping of individual bacteria within the V-groove.

In three different illumination conditions, they experimentally demonstrated the interrogation of an individual Escherichia coli bacterial cell using a nanoscale plasmonic V-groove waveguide. First, they measured the light emitted from a bacterium flowing on top of the nanocoupler in a liquid environment by allowing the fluorescence from the bacterium to be coupled directly into the waveguide through the nanocoupler. Next, a bacterium was mechanically trapped within the V groove waveguide and was excited by laser directly either from the top or through the nanocoupler. In all cases, significant fluorescence was collected from the output nano coupler into the detector.

The system worked well both in wet environments, where the bacteria are flowing on top of the waveguide, and in dry conditions, where the bacteria are trapped within the waveguide.

The research was led by Prof. Uriel Levy, Director of The Harvey M. Krueger Family Center for Nanoscience and Nanotechnology at the Hebrew University in collaboration with Prof. Shimshon Belkin, at the Hebrew University’s Alexander Silberman Institute of Life Sciences, who genetically engineered the bacterial sensors, and Prof. Anders Kristensen from the Danish Technical University, who was in charge of fabricating the V-groove waveguides. Prof. Levy is the Eric Samson Chair in Applied Science and Technology, and Prof. Belkin is the Ministry of Labor and Social Welfare Chair in Industrial Hygiene, at the Hebrew University.

Unlike the more traditional plasmonic waveguides consisting of either silver or gold, the choice of aluminum was instrumental for being able to guide the fluorescent light emitted from the bacteria all the way to the output nanocoupler. Furthermore, the waveguide dimensions allow for efficient mechanical trapping of the bacteria and the multimode characteristics may become instrumental in gathering more information, e.g., on the specific position and orientation of the bacteria.

The results provide a clear indication of the feasibility of constructing a hybrid bioplasmonic system using live cells. Future work will include the construction of waveguide network, diversifying the system to incorporate different types of bacterial sensors for the detection of various biological or chemical analytes.

The research is a collaboration between scientists at the Department of Applied Physics, the Rachel and Selim Benin School of Engineering and Computer Science, the Harvey M. Krueger Family Center for Nanoscience and Nanotechnology, and the Alexander Silberman Institute of Life Sciences, at the Hebrew University of Jerusalem, Israel; and the Department of Micro- and Nanotechnology, Technical University of Denmark, Kongens Lyngby, Denmark. Additional researchers include Oren Lotan, Jonathan Bar-David, Cameron L.C. Smith, and Sharon Yagur-Kroll.

Support: The researchers acknowledge financial support from the Danish International Network Programme (grant no. 1370-00124B) with Israel. Work in the Belkin lab was partially supported by the Minerva Center for Bio-Hybrid Complex Systems and by the NATO Science for Peace and Security Programme project 985042.

Citation: Oren Lotan, Jonathan Bar-David, Cameron L.C. Smith, Sharon Yagur-Kroll, Shimshon Belkin, Anders Kristensen, and Uriel Levy*. Nanoscale Plasmonic V-Groove Waveguides for the Interrogation of Single Fluorescent Bacterial Cells. Nano Lett., Article ASAP. DOI: 10.1021/acs.nanolett.7b02132. Publication Date (Web): August 3, 2017. http://pubs.acs.org/doi/10.1021/acs.nanolett.7b02132

Videos for Download:

  • http://media.huji.ac.il/new/multimedia/hu170816_nano1.mp4 -A pulsed laser illuminates bacteria which are trapped in a plasmonic waveguide (the waveguide is the dark rectangle seen in the film, bacteria are invisible). The presence of the bacteria causes light coupling into the waveguide. The light then propagates in the waveguide until it is coupled back out by the nano-mirrors and appears as bright pulses on the waveguides' ends.  (Photo credit: Hebrew University)
  • http://media.huji.ac.il/new/multimedia/hu170816_nano2.mp4 - A laser beam excites fluorescent bacteria swimming in a micro-fluidic device. The fluorescent light emitted by these bacteria radiates in all directions, and some of it couples into a plasmonic waveguide and is directed toward the waveguide's end. The direct fluorescence from the bacteria is seen most clearly on the right-hand side, while light which was coupled and propagated in the waveguide appears as a bright spot blinking on the left-hand side. The blinking is a result of the bacteria's changing position, and is correlated to the location of the bacteria relative to the nano-mirror in the waveguide's right side. (Photo credit: Hebrew University)

 

Nanoscale chip system measures light from a single bacterial cell to enable portable chemical detection
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HU Researchers: Simple Method Measures How Long Bacteria Can Wait Out Antibiotics

21/06/2017

The efficient classification of bacterial strains as tolerant, resistant, or persistent could help to guide treatment decisions, and could ultimately reduce the ever-growing risk of resistance

A growing number of pathogens are developing resistance to one or more antibiotics, threatening our ability to treat infectious diseases. Now, according to a study published in Biophysical Journal, a simple new method for measuring the time it takes to kill a bacterial population could improve the ability of clinicians to effectively treat antimicrobial-tolerant strains that are on the path to becoming resistant.

“These findings allow measurement of tolerance, which has previously been largely overlooked in the clinical setting,” says senior study author Prof. Nathalie Balaban, the Joseph and Sadie Danciger Professor of Physics at the Hebrew University of Jerusalem. “Routinely measuring tolerance could supply valuable information about the duration of antibiotic treatments, reducing the chance of both under- and over-treatment. Furthermore, data compiled from such measurements could give an estimate of how widespread the phenomenon of tolerance really is, which is currently a complete unknown.”

According to the World Health Organization, antibiotic resistance is one of the biggest threats to global health and is putting the achievements of modern medicine at risk. Due to selective pressure, pathogens acquire resistance through mutations that make the antibiotic less effective, for example, by interfering with the ability of a drug to bind to its target. Currently, clinicians determine which antibiotic and dose to prescribe by assessing resistance levels using a routine metric called minimum inhibitory concentration (MIC)—the minimal drug concentration required to prevent bacterial growth.

Although resistant strains continue to grow despite exposure to high drug concentrations, tolerant strains can survive lethal concentrations of an antibiotic for a long period of time before succumbing to its effects. Tolerance is often associated with treatment failure and relapse, and it is considered a stepping stone toward the evolution of antibiotic resistance. But unlike resistance, tolerance is poorly understood and is currently not evaluated in healthcare settings.

“The lack of a quantitative measure means that this aspect of the treatment relies largely on the experience of the individual physician or the community,” says first author Asher Brauner, a PhD student in Balaban’s lab at the Hebrew University’s Racah Institute of Physics. “This can lead to treatment being either too short, increasing the risk of relapse and evolution of resistance, or much too long, unnecessarily causing side effects, release of antibiotic waste into the environment, and additional costs.”

To address this problem, Balaban and her team developed a tolerance metric called the minimum duration for killing 99% of the population (MDK99). The protocol, which can be performed manually or using an automated robotic system, involves exposing populations of approximately 100 bacteria in separate microwell plates to different concentrations of antibiotics for varied time periods, while determining the presence or lack of survivors.

The researchers applied MDK99 to six Escherichia coli strains, which showed tolerance levels ranging from 2 to 23 hr under ampicillin treatment. MDK99 also facilitates measurements of a special case of tolerance known as time-dependent persistence—the presence of transiently dormant subpopulations of bacteria that are killed more slowly than the majority of the fast-growing population. Like other forms of tolerance, time-dependent persistence can lead to recurrent infections because the few surviving bacteria can quickly grow to replenish the entire population once antibiotic treatment stops.

“A take-home message from this is that it is important to complete a course of antibiotic treatment as prescribed, even after the disappearance of the symptoms,” Balaban says. “Partial treatment gives tolerance and persistence mutations a selective advantage, and these, in turn, hasten the development of resistance.”

In future studies, Balaban and her team will use MDK99 to study the evolution of tolerance in patients. Moreover, the ability to systematically determine the tolerance level of strains in the lab could facilitate research in the field. “If implemented in hospital clinical microbiology labs, MDK99 could enable the efficient classification of bacterial strains as tolerant, resistant, or persistent, helping to guide treatment decisions,” Balaban says. “In the end, understanding tolerance and finding a way to combat it could significantly reduce the ever-growing risk of resistance.”

###

Scientists involved with this research are affiliated with The Racah Institute of Physics and The Center for NanoScience and NanoTechnology at The Hebrew University of Jerusalem, and The Broad Institute of Harvard University and Massachusetts Institute of Technology (MIT).

FUNDING: This work was supported by the European Research Council (ERC) (grant 681819) and the Israel Science Foundation (ISF) (grant 492/15).

CITATION: Biophysical Journal. Asher Brauner, Noam Shoresh, Ofer Fridman, Nathalie Q. Balaban.: “An Experimental Framework for Quantifying Bacterial Tolerance” http://www.cell.com/biophysj/fulltext/S0006-3495(17)30551-9 / doi: 10.1016/j.bpj.2017.05.014

HU Researchers: Simple Method Measures How Long Bacteria Can Wait Out Antibiotics
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Bacteria Sleep, Then Rapidly Evolve, to Survive Antibiotic Treatments

13/02/2017

Hebrew University biophysicists used quantitative approaches from Physics to understand issues in Biology

Antibiotic resistance is a major and growing problem worldwide. According to the World Health Organization, antibiotic resistance is rising to dangerously high levels in all parts of the world, and new resistance mechanisms are emerging and spreading globally, threatening our ability to treat common infectious diseases. But how these bacterial resistance mechanisms occur, and whether we can predict their evolution, is far from understood.

Researchers have shown (http://new.huji.ac.il/en/article/22060) that one way bacteria can survive antibiotics is to evolve a “timer” that keeps them dormant for the duration of antibiotic treatment. But the antibiotic kills them when they wake up, so the easy solution is to continue the antibiotic treatment for a longer duration.

Now, in new research published in the prestigious journal Science, researchers at the Hebrew University of Jerusalem report a startling alternative path to the evolution of resistance in bacteria. After evolving a dormancy mechanism, the bacterial population can then evolve resistance 20 times faster than normal. At this point, continuing to administer antibiotics won't kill the bacteria.

To investigate this evolutionary process, a group of biophysicists, led by Prof. Nathalie Balaban and PhD student Irit Levin-Reisman at the Hebrew University’s Racah Institute of Physics, exposed bacterial populations to a daily dose of antibiotics in controlled laboratory conditions, until resistance was established. By tracking the bacteria along the evolutionary process, they found that the lethal antibiotic dosage gave rise to bacteria that were transiently dormant, and were therefore protected from several types of antibiotics that target actively growing bacteria. Once bacteria acquired the ability to go dormant, which is termed “tolerance,” they rapidly acquired mutations to resistance and were able to overcome the antibiotic treatment.

Thus, first the bacteria evolved to "sleep" for most of the antibiotic treatment, and then this "sleeping mode" not only transiently protected them from the lethal action of the drug, but also actually worked as a stepping stone for the later acquisition of resistance factors.

The results indicate that tolerance may play a crucial role in the evolution of resistance in bacterial populations under cyclic exposures to high antibiotic concentrations. The key factors are that tolerance arises rapidly, as a result of the large number of possible mutations that lead to it, and that the combined effect of resistance and tolerance promotes the establishment of a partial resistance mutation on a tolerant background.

These findings may have important implications for the development of new antibiotics, as they suggest that the way to delay the evolution of resistance is by using drugs that can also target the tolerant bacteria.

Unveiling the evolutionary dynamics of antibiotic resistance was made possible by the biophysical approach of the research team. The experiments were performed by a team of physicists, who developed a theoretical model and computer simulations that enabled a deep understanding of the reason behind the fast evolution of resistance that were observed.

Researchers involved in the research are affiliated with the Racah Institute of Physics and the Harvey M. Kruger Family Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem, and the Broad institute of Harvard and MIT.

FUNDING: The work was supported by the European Research Council (Consolidator Grant no. 681819) and Israel Science Foundation (492/15). ILR acknowledges support from the Dalia and Dan Maydan Fellowship.

CITATION: Antibiotic tolerance facilitates the evolution of resistance. Irit Levin Reisman, Irine Ronin, Orit Gefen, Ilan Braniss, Noam Shoresh and Nathalie Q. Balaban. Science, February 9, 2017. doi: 10.1126/science.aaj2191. (Paper will be published online at http://science.sciencemag.org/lookup/doi/10.1126/science.aaj2191.)

Bacteria Sleep, Then Rapidly Evolve, to Survive Antibiotic Treatments
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First look inside nanoscale catalysts shows ‘defects’ are useful

11/01/2017

Study in leading science journal Nature validates hypothesis that atomic defects are essential to catalytic reactivity

Using one of the world’s brightest light sources to peer inside some of the world’s smallest particles, scientists have confirmed a longstanding hypothesis: that atomic disorder or “defects” at the edges of nanoparticles is what makes them effective as chemical change agents.

The process by which a change agent, or catalyst, accelerates a chemical reaction is key to the creation of many materials essential to daily life, such as plastics, fuels and fertilizers. Known as catalysis, this process is a basic pillar of the chemical industry, making chemical reactions more efficient and less energy-demanding, and reducing or even eliminating the use and generation of hazardous substances.

Although catalysts have been used in industry for more than a century, scientists have yet to observe how their structure impacts their effectiveness as change agents. That’s because catalysts are typically tiny metallic nanoparticles made of precious metals such as Platinum, Palladium or Rhenium. The extreme smallness that makes nanoparticles such effective catalysts also makes it hard to see how they work.

If scientists could peer inside individual nanoparticles’ chemical reactions at a nanoscopic level, they would gather a treasure of useful knowledge for the design of improved catalysts to address the pressing energy needs of the 21st century.

That type of knowledge may now be close at hand, thanks to new research published January 11 in the journal “Nature”. In the new study — led by Dr. Elad Gross from the Institute of Chemistry and the Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem, and Prof. F. Dean Toste from the College of Chemistry at University of California, Berkeley, and Chemical Science Division at Lawrence Berkeley National Laboratory — researchers directly observed for the first time how metallic nanoparticles, used as catalysts in numerous industrial processes, activate catalytic processes.

Using a light source one million times brighter than the sun, the researchers were able to observe chemical reactivity on single Platinum particles similar to those used as industrial catalysts. What they found is that chemical reactivity primarily occurs on the particles’ periphery or edges, while lower reactivity occurs at the particles’ center.

The different reactivity observed at the center and edges of Platinum particles corresponds to the different properties of the Platinum atoms in the two locations. The atoms are mostly flat at the center, while they’re corrugated and less-ordered at the edges. This disorderly or “defective” structure means that Platinum atoms at the edges are not totally surrounded by other Platinum atoms, and will therefore form stronger interactions with reactant molecules. Stronger interactions can activate the reactant molecules and initiate a chemical reaction that will transform the reactant molecule into a desired product.

The research findings validate a well-known hypothesis in the world of catalysis, which correlates high catalytic reactivity with high density of atomic defects. It also shows, for the first time, that the enhanced reactivity of defected sites can be identified at the single-particle level.

“Our findings provide insights about the ways by which the atomic structure of catalysts controls their reactivity. This knowledge can direct the design of improved catalysts that will make chemical process greener, by decreasing the amount of energy that is consumed in the process and preventing the formation of unwanted, potentially hazardous, products,” said Dr. Elad Gross, from the Institute of Chemistry and the Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem.

To peer into individual nanoparticles, researchers focused a bright infrared beam generated in a synchrotron source (Advanced Light Source, Lawrence Berkeley National Laboratory) into a thin probe with an apex diameter of 20 nanometers. The probe acts as an antenna, localizes the infra-red light in a specific range, and by that provides the capabilities to identify molecules which reside on the surface of the catalytic nanoparticles. By scanning the particles with the nanometric probe while it is being radiated by the infrared light, the researchers were able to identify the locations and conditions in which chemical reaction occurs on the surface of single particle.

The Hebrew University of Jerusalem is Israel’s leading academic and research institution, producing one-third of all civilian research in Israel. For more information, visit http://new.huji.ac.il/en.

PHOTO: http://media.huji.ac.il/new/photos/hu170110_nano.tif - Chemical reactivity was identified on the surface of single Platinum nanoparticles, which are similar to the particles which are used as catalysts in various industrial processes. The chemical reactivity was measured by focusing a bright infrared beam into the apex of a thin tip with a diameter of 20 nm that monitored the chemical reactivity on the particle’s surface. (Credit: Hebrew University of Jerusalem)

CITATION: Chung-Yeh Wu, William J. Wolf, Yehonatan Levartovsky, Hans A. Bechtel, Michael C. Martin, F. Dean Toste, & Elad Gross. High-spatial-resolution mapping of catalytic reactions on single particles. Nature, Advance Online Publication (AOP) on January 11, 2017. doi:10.1038/nature20795. Paper will be online at http://dx.doi.org/10.1038/nature20795.

- Dov Smith

First look inside nanoscale catalysts shows ‘defects’ are useful
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Quantum Leap: Scientists Demonstrate a Compact, Efficient Single Photon Source That Can Operate at Ambient Temperatures On a Chip

04/05/2016

Highly directional single photon source concept is expected to lead to a significant progress in producing compact, cheap, and efficient sources of quantum information bits for future applications

Quantum information science and technology has emerged as a new paradigm for dramatically faster computation and secure communication in the 21st century. At the heart of any quantum system is the most basic building block, the quantum bit or qbit, which carries the quantum information that can be transferred and processed (this is the quantum analogue of the bit used in current information systems). The most promising carrier qbit for ultimately fast, long distance quantum information transfer is the photon, the quantum unit of light.

The challenge facing scientists is to produce artificial sources of photons for various quantum information tasks. One of the biggest challenges is the development of efficient, scalable photon sources that can be mounted on a chip and operate at room temperature. Most sources used in labs today have to be very cold (at the temperature of liquid Helium, about -270C), which requires large and expensive refrigerators. Many sources also emit photons in undefined directions, making efficient collection a hard problem.

Now, a team of scientists from the Hebrew University of Jerusalem has demonstrated an efficient and compact single photon source that can operate on a chip at ambient temperatures. Using tiny nanocrystals made of semiconducting materials, the scientists developed a method in which a single nanocrystal can be accurately positioned on top of a specially designed and carefully fabricated nano-antenna.

In the same way large antennas on rooftops direct emission of classical radio waves for cellular and satellite transmissions, the nano-antenna efficiently directed the single photons emitted from the nanocrystals into a well-defined direction in space. This combined nanocrystals-nanoantenna device was able to produce a highly directional stream of single photons all flying to the same direction with a record low divergence angle. These photons were then collected with a very simple optical setup, and sent to be detected and analyzed using single photon detectors.

The team demonstrated that this hybrid device enhances the collection efficiency of single photons by more than a factor of 10 compared to a single nanocrystal without the antenna, without the need for complex and bulky optical collection systems used in many other experiments. Experimental results show that almost 40% of the photons are easily collected with a very simple optical apparatus, and over 20% of the photons are emitted into a very low numerical aperture, a 20-fold improvement over a freestanding quantum dot, and with a probability of more than 70% for a single photon emission. The single photon purity is limited only by emission from the metal, an obstacle that can be bypassed with careful design and fabrication.

The antennas were fabricated using simple metallic and dielectric layers using methods that are compatible with current industrial fabrication technologies, and many such devices can be fabricated densely on one small chip. The team is now working on a new generation of improved devices that will allow deterministic production of single photons straight from the chip into optical fibers, without any additional optical components, with a near unity efficiency. 

"This research paves a promising route for a high purity, high efficiency, on-chip single photon source operating at room temperature, a concept that can be extended to many types of quantum emitters. A highly directional single photon source could lead to a significant progress in producing compact, cheap, and efficient sources of quantum information bits for future quantum technological applications", said Prof. Ronen Rapaport, of the Racah Institute of Physics, The Department of Applied Physics, and the Center of Nanoscience and Nanotechnology at the Hebrew University of Jerusalem.

The Hebrew University of Jerusalem is Israel’s leading academic and research institution, producing one-third of all civilian research in Israel. For more information, visit http://new.huji.ac.il/en.

FUNDING: The research was supported in parts by the Einstein Foundation Berlin; the U.S. Department of Energy: Office of Basic Energy Sciences, Division of Materials Sciences and Engineering; the European Cooperation in Science and Technology through COST Action MP1302 Nanospectroscopy;  and by the Ministry of Science and Technology, Israel.

REFERENCE: Highly Directional Room-Temperature Single Photon Device. Nitzan LivnehMoshe G. HaratsDaniel IstratiHagai S. Eisenberg, and Ronen Rapaport. Nano Lett., 2016, 16 (4), pp 2527–2532. DOI: 10.1021/acs.nanolett.6b00082. Link: http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.6b00082

Quantum Leap: Scientists Demonstrate a Compact, Efficient Single Photon Source That Can Operate at Ambient Temperatures On a Chip
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