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Showing posts with label Nanotechnology. Show all posts
Showing posts with label Nanotechnology. Show all posts

Wednesday, 17 July 2019

Researchers have discovered that a bacterium can be used to produce graphene

The study of the exposure of graphite to a species of bacteria has shown that the latter is capable of converting this material into graphene. The industrial application of this discovery could provide substantial savings in the production of this material.

Produced and extracted for the first time only 15 years ago, graphene is a material consisting of a single layer of carbon, which is in nature the main component of graphite. It is particularly used for its very light weight and strength, as well as for its conductive properties in electronics. But it could have been used in more areas if its cost of production had not been a major drag (about 100 euros per gram).

Since 2004, scientists have been trying to develop new methods to make their production cheaper. The first method used was very rudimentary because it was sticking tape to the surface of the graphite to extract it. Chemical methods have then emerged, but the latest, explained in a paper published this month, uses biological processes and could significantly lower the cost of production.

Researchers from Delft University of Technology in the Netherlands and Rochester, New York, have shown that Shewanella oneidensis is capable of producing graphene when mixed with graphite oxide. and thanks to a reaction called in chemistry "reduction", where oxygen molecules are removed from the latter, leaving only conductive graphene. This natural method has the advantage of avoiding the use of chemicals currently used by industries, and is less expensive. Its development on a larger scale (than the laboratory) could allow its application in more computing or medical devices.

The production of a large quantity is difficult and usually gives thicker and less pure graphene. That's where our work comes in, "says Anne Meyer, a biologist at the University of Rochester.

Indeed, not only have the researchers discovered a new way to obtain the material, but the final product is also thinner, more stable, and has a better longevity than graphene chemically produced.

 The production of graphene by the bacterium also has the advantage of not removing all oxygen groups, which could be exploited for their properties to attach to certain molecules. This opens new paths in the design of biomedical devices such as field-effect transistor biosensors, which are devices that detect specific biological molecules, one of the best known being the glucose meter (measuring glucose levels in diabetics).

Many analyzes have yet to be done before considering the wider use of this technique, which could significantly reduce the price of many electronic devices. But given the quality of the graphene obtained and the absence of chemical compounds, the production of this material promises to increase in the future.

" Our graphene produced by bacteria will significantly improve the overall development of this product, " says Meyer.


Creation of Conductive Graphene Materials by Bacterial Reduction Using Shewanella Oneidensis
Benjamin A. E. Lehner Vera A. E. C. Janssen Dr. Ewa M. Spiesz Dominik Benz Dr. Stan J. J. Brouns Dr. Anne S. Meyer Prof. Dr. Herre S. J. van der Zant

First real-time images of molecules that change their electric charge

Just like an atom, a molecule can lose or gain electrons , thus altering its overall electrical charge. These phenomena of modification of the electric charge play a crucial role in the transfer of molecular energy governing certain catalytic and biochemical processes. For the first time, chemists have been able to observe in real time the structural modification of molecules due to electric charge transitions. Results that should help to better understand various essential biological processes.

Using some of the most advanced microscopy technologies in the world, chemists have captured images of molecules that change their electrical charge in real time. To do this, they added and removed electrons , directly observing the changes in the structure of four molecules. The results were published in the journal Science.

Molecular changes in electrical charge have been known for a long time, but this is the first direct observation of the phenomenon. This could help us better understand several molecular processes, including chemical reactions, catalysis and charge transport, and even biological processes.

" We were able to solve the structural changes of individual molecules with unprecedented resolution, " says chemist Leo Gross of IBM Research-Zurich. " This new understanding unveils some of the mysteries of molecular charge-function relationships in how biology converts and transports energy ."

An atomic force microscope to observe molecular charge transitions

The team used atomic force microscopy. The laser tip scans the surface of the structures to be studied, detecting all structural changes, even the weakest ones. These are recorded to create an image of what the probe is scanning. In this way, scientists can get an image of the elements too small to be seen by optical means.

Thus, four types of molecules - azobenzene, pentacene, tetracyanoquinodimethane (TCNQ) and porphine - were examined under a microscope in a cold vacuum chamber to ensure that no external influence would alter the results. A single molecule was placed on a sodium chloride film, and then a small voltage was sent through the probe to transfer electrons to the molecule, one at a time.

The atomic force microscope allowed researchers to image the structure of four different molecules, depending on their state of charge. Credits: IBM

Gross and his colleagues had already developed this load control technique and described it in a study in 2015. They also described their imaging technique in 2009. In this new work, however, the team found a way to combine the two techniques to image the molecules and control the charge at the same time.

They imaged the four molecules in at least two of these four states: positive (minus one electron), neutral (the same number of protons and electrons), negative (plus one electron) and double negative (plus two electrons). The four molecules reacted differently to changes in charge.

This video shows how the porphine molecule transforms as it loses electrons under these controlled conditions:

Molecular charge transition and fundamental biological processes

The azobenzene molecule has become physically twisted. With pentacene, the areas of the molecule became more reactive because of the extra electrons. The change in charge resulted in a change in the type of bond between the TCNQ atoms, which moved physically on the film. And in the porphine, it was not only the type of links, but also their length that changed.

Atomic force microscopy images of each type of molecule, for four different states of electrical charge. Credits: Shadi Fatayer et al. 2019

These results will help to better understand the molecular energy transfer. Specifically, examining porphine molecules so closely may help us better understand some fundamental biological processes, because porphine is the parent compound of porphyrins, a group of organic compounds that make up both chlorophyll and hemoglobin.

" The charge transitions of these molecules are essential to life. Thanks to our new technique, we can better understand how the charge modifies the structure and function of molecules, which play an essential role in many ways, such as photoconversion and the transport of energy in living organisms "concludes Gross.


Molecular structure elucidation with charge-state control
Shadi Fatayer1,*, Florian Albrecht1, Yunlong Zhang2, Darius Urbonas1, Diego Peña3, Nikolaj Moll1, Leo Gross1,*
Science 12 Jul 2019:
Vol. 365, Issue 6449, pp. 142-145
DOI: 10.1126/science.aax5895

Tuesday, 16 July 2019

Physicists reveal the very first image of quantum entanglement between two particles

Among the many phenomena arising from quantum mechanics, quantum entanglement is certainly one of the strangest. When two particles are entangled, they cease to be objects in their own right to become one and the same physical system of solidarity; any modification of one has instantaneous repercussions on the other, regardless of the distance that separates them. For the first time, researchers from the University of Glasgow provided the very first image of a pair of entangled photons, thus demonstrating the violation of Bell's inequalities.

This particular photo shows the entanglement between two photons - the boson of the electromagnetic interaction. Paul-Antoine Moreau, lead author of the study, states that the image is " an elegant demonstration of a fundamental property of nature ". The study was published in the journal Science Advances.

To capture this phenomenon, Moreau and a team of physicists have created a system that sends entangled photon fluxes on what they have described as "unconventional objects." The experiment consisted of capturing four photon images under four different phase transitions.

The researchers succeeded in imaging the entanglement of photon pairs crossing series of four-phase transitions. Credits: Paul-Antoine Moreau et al. 2019

It is actually a composite image of several images of photons that pass through a series of four-phase transitions. Basically, physicists have divided the entangled photons and sent a beam through a liquid crystal material known as barium β-borate, triggering four-phase transitions. At the same time, they captured photos of the entangled pair passing through the same phase transitions, even though it had not crossed the liquid crystal.

Scheme of experimental protocol used by researchers. The entangled photon beam is from the bottom left, half of the entangled pair splits to the left and passes through the four phase filters. The others that go straight have not gone through the filters, but have undergone the same phase changes. Credits: Paul-Antoine Moreau et al. 2019

The violation of Bell's inequalities in images

The camera was able to capture the images of these different sequences of events at the same time, showing that the two photons had changed in the same way despite their spatial remoteness.

Physicists first obtain a raw image from the four-phase filter (left). Then, thanks to a special treatment (de-scanning), they get a clearer picture of the entanglement, which confirms the violation of Bell's inequalities. Credits: Paul-Antoine Moreau et al. 2019

The physicist John Stewart Bell has defined a series of conditions called "Bell inequalities". The latter characterize relations that must be respected by measurements on entangled states, in the context of a local deterministic theory with hidden variables. Demonstrating the entanglement between two particles amounts to violating these inequalities.

" We report here an experiment demonstrating the violation of a Bell inequality in the observed images. This result paves the way for new quantum imaging schemes ... and suggests promising perspectives for quantum information schemes based on spatial variables "concludes the team.


Imaging Bell-type nonlocal behavior
Paul-Antoine Moreau*, Ermes Toninelli, Thomas Gregory, Reuben S. Aspden, Peter A. Morris and Miles J. Padgett*
Science Advances 12 Jul 2019:
Vol. 5, no. 7, eaaw2563
DOI: 10.1126/sciadv.aaw2563

Wednesday, 3 July 2019

Discovery. These quantum particles are basically "immortal"

In the late 1950s, the Soviet physicist Lev Landau developed the theory of Fermi liquids - the state of matter observed at low temperatures for crystalline solids - and introduced the concept of quasiparticles. The latter make it possible to describe complex physical systems in terms of particle groups and interactions, taking the form of vibrations and excitations. Recently, physicists have discovered that unlike ordinary particles that eventually disintegrate and disappear, quasiparticles can escape this inexorable fate, becoming "immortal".

The second law of thermodynamics is clear: the Universe systematically evolves towards disorder, entropy being brought to continually grow in any isolated system. Disintegrated objects can not reform. However, quantum mechanics is known to contravene certain well-established physical rules. In an article published in the journal Nature Physics , physicists have shown that quasiparticles that disintegrate can "be reborn from their ashes".

" Until now, the hypothesis was that the quasiparticles of interacting quantum systems decay after a while, " says physicist Frank Pollman of Munich Technical University. " We now know that the opposite is happening: strong interactions can even completely stop disintegration ." 

Three examples of quasiparticles: a) A polaron, that is to say an electron in a solid interacting with the crystal lattice; b) an exciton, that is, an electron-hole bound state; c) An angulon, that is to say a quantum rotor formed by a phonon field. Credits: Mikhail Lemeshko

Quasiparticles are not ordinary particles, like electrons and quarks. Rather, it is the disturbances or excitations in a solid caused by electrical or magnetic forces that collectively behave like particles. Phonons - discrete units of vibratory energy in a crystal lattice, for example - are classified as quasi-particles, as are polarons, electrons trapped in a network surrounded by a polarization cloud.

Quasiparticles: they disintegrate ... then reform

The researchers involved in this latest study have developed numerical methods to compute the complex interactions of these quasiparticles and have run simulations on a powerful computer to observe their disintegration.

" The result of the simulation: of course, the quasiparticles disintegrate, but new entities of identical particles emerge from the debris, " says physicist Ruben Verresen from the Technical University of Munich and the Max Planck Institute for Complex Systems Physics . " If this degradation occurs very quickly, a reverse reaction will occur after a while and debris will converge again. This process can be repeated at infinity and a sustained oscillation between disintegration and rebirth appears.

This does not violate the second law of thermodynamics because oscillation is a wave transformed into matter, which is covered by the concept of quantum mechanics of the wave-particle duality. Their entropy does not decrease but remains constant. In fact, the discovery solved two other puzzles. For example, there is a magnetic compound, Ba3CoSb2O9, used in experiments whose unexpected stability had previously been found.

It now seems that the key lies in the quasi-magnetic particles it contains, called magnons. According to the simulation, they reorganize after the degradation. Helium is another potential example: it becomes a superfluid without resistance at a temperature close to absolute zero, and this particular property could be explained by the fact that this gas is filled with quasi-particles called rotons.

For the moment, the work only concerns theory, but researchers believe that this immortality of quasi-particles offers a strong potential for sustainable data storage in quantum computing systems.


 Avoided quasiparticle decay from strong quantum interactions
Ruben Verresen, Roderich Moessner, Frank Pollmann
 Nature Physics 
DOI: 10.1038 / s41567-019-0535-3

Monday, 24 June 2019

Researchers break quantum limit in precision of force and position measurements

The technique is unprecedented, but very simple, which will facilitate its practical use in other experiments and laboratories. [Image: Mason et al. - 10.1038 / s41567-019-0533-5]

Precision limit

The precision of the force and position measurements has been raised to a new level thanks to a collaboration of researchers from the University of Copenhagen and the Niels Bohr Institute in Denmark.

The experiment is the first to overcome the so-called "Standard Quantum Limit", or SQL ( Standard Quantum Limit ), which imposes itself as a barrier in the most common and most successful optical techniques for ultra-precise position measurements.

In 2014, a US team detected the smallest force already measured , coming very close to SQL, but did not win. In fact, physicists and engineers have been trying to overcome the Quantum Limit for more than 50 years, using a variety of techniques - but unsuccessfully so far.

David Mason and his colleagues broke the barrier by making a simple modification to the most commonly used approach, which allowed them to cancel the quantum noise in the measurement well enough to push the limit.

The result - and the experiment itself - has important implications for gravitational wave astronomy techniques, atomic force microscopy, various nanotechnology techniques, and the entire field of quantum sensors that have detonated the boundaries of precision in several areas.

Uncertainty and inaccuracy

Quantum actions have quantum consequences. In the context of measurements, this usually means that the very act of measuring a system disturbs you. This effect is called reverse action, or feedback ( backaction ), and is a consequence of the fundamental uncertainties of the systems at the atomic scale, encompassed by the uncertainty principle of Heisenberg .

In many cases, this uncertainty sets a limit to the accuracy with which a measure can be obtained because, in addition to a certain number of figures after the comma, everything is uncertain.

Gravitational wave telescopes, such as LIGO and Virgo, reflect the laser light in a mirror to measure their position in an optical configuration known as an interferometer. The imprecision of this measurement can be improved by increasing the laser power, but eventually the random reflections of the laser photons will disturb the position of the mirror, leading to a less sensitive measurement that will leave astronomical objects weak or distant outside the field of detection.

The Standard Quantum Limit (SQL) is established when an optimal balance between the feedback and the noise responsible for imprecision is achieved. This minimum noise level defines, for example, the best possible accuracy obtained by any interferometer.

A thin silicon nitride membrane (white) is stretched along a silicon (blue) frame. The membrane contains a pattern of holes, with a small island in the center, whose vibrations were measured in the experiment. [Image: Niels Bohr Institute]

Overcoming the Standard Quantum Limit

Mason and his colleagues were able to break the SQL through an ingenious combination of optical and nanomechanical techniques, allowing you to perform the first measurement of an object's position with a precision that exceeds the limit.

Like the LIGO, the new approach uses a laser interferometer to measure a position, in this case the position of a membrane made of ceramic silicon nitride. Although very thin (20 nanometers), the membrane is several millimeters wide and is easily visible to the naked eye.

The trick to going beyond SQL involves doing a double measurement of the light reflected by the membrane. In this configuration, the detector is capable of simultaneously measuring inaccuracy and feedback in a manner that allows those noise sources to mutually cancel each other. In other words, what remains is a "clean" measure.

Using this technique, team measured the position of their membrane with almost 30% better precision than the "allowed" by SQL.

"We are using quantum effects that emerge in the measurement setup itself, so the extra technological effort is really very small. That's good news for possible practical applications," Mason said.


 Continuous force and displacement measurement below the standard quantum limit
David Mason, Junxin Chen, Massimiliano Rossi, Yeghishe Tsaturyan, Albert Schliesser
Nature Physics
DOI: 10.1038 / s41567-019-0533-5