#Tiny terahertz accelerator could rival huge free-electron lasers Physicists in the US, Germany and Canada have built a miniature particle accelerator that uses terahertz radiation instead of radio waves to create pulses of high-energy electrons.
A single accelerator module of the prototype is just 1. 5 cm long and 1 mm thick,
and the technology has the potential to create facilities that are much smaller than current radio-frequency (RF) accelerators.
Potential applications include free-electron lasers, whereby the electrons are used to create coherent pulses of X-rays.
However, the team cautions that much more work is needed to develop the technology so it can be used in medicine,
particle physics and material science. Terahertz radiation falls between the microwave and infrared portions of the electromagnetic spectrum (300 GHZ THZ),
and its production and detection are not without significant technical challenges. However, terahertz technologies have been improving steadily
and some physicists are keen on using the radiation in much the same way that radio waves
and microwaves are used to accelerate charged particles. In this latest work Emilio Nanni and colleagues at the Massachusetts institute of technology (MIT), the Center For free-Electron Laser Science (CFEL) at DESY in Germany and the University of Toronto have created a terahertz accelerator module with the aim
of advancing experiments that use ultrafast electron diffraction to reveal the structure and dynamics of matter.
Their prototype accelerator uses optically generated pulses centred at 450 GHZ and a bandwidth of 20000 GHZ.
The wavelength of this radiation is around 1000 times shorter than the electromagnetic radiation used by current particle accelerators the Large hadron collider uses 400 MHZ microwaves everything else on the terahertz accelerator can also be 1000 times smaller.
Steep gradients The terahertz accelerator module increased the energy of electrons fired into it by 7 kev.
This is a boost of 2. 3 Mev/m, which is compared modest to conventional accelerators that can achieve about 50 times that.
But, it does show that terahertz accelerators are feasible and the researchers say that it should be possible to achieve accelerating gradients of around 1 Gev."
"If we can match the accelerating gradient available with radio-frequency sources (around 100 Mev/m),
terahertz accelerators could be attractive for many applications because they can operate at higher repetition rates
and are more efficient, "explains Nanni.""Terahertz accelerators should be able to achieve much higher accelerating gradients than radio-frequency accelerators,
which will reduce the size and cost of accelerators and improve the quality of the electron beams they produce."
"Steven Jamison of the UK's Accelerator Science and Technology Centre (ASTEC), who wasn't involved in the research,
says"While this demonstration of terahertz-driven acceleration is done with low energy beams and significant challenges remain in scaling to higher energies and longer interaction lengths,
it is an important first step to obtaining relativistic energy electrons with terahertz waves.""More power needed The main barrier to faster accelerating gradients is the power of terahertz pulses that can be generated."
"Considerable development is still necessary"in this area, explains team member Franz Kärtner, whose lab at MIT was used to test the prototype.
The researchers now plan to focus on developing a free-electron laser (FEL) based on terahertz technology,
which they expect to be less than 1 m long. FELS fire high-speed electrons down an undulating path,
which causes them to emit intense flashes of X-ray light. Currently, access to large-scale FELS is limited,
In contrast, their prototype accelerator gets by on 10 J. More powerful sources are available,
QKD uses the laws of quantum mechanics to guarantee complete security when two people exchange a cryptographic key.
and work out how Alice is encoding a series of photons sent to her by Bob that will constitute the secret key.
if Alice sets up a detector to measure the energy of the incoming photons, which sounds an alarm
so rendering the quantum system redundant. Faking states In the case of free-space cryptography Makarov and colleagues showed that they could enable a"faked-state attack".
"Alice and Bob share a key encoded using photon polarization, while Eve inserts a device into the polarized beam that very slightly tilts the beam
which detectors are used to measure which photons, and by doing so to steal the key unnoticed.
At temperatures approaching absolute zero, atoms cease their individual, energetic trajectories, and start to move collectively as one wave.
Superfluids are thought to flow endlessly, without losing energy, similar to electrons in a superconductor. Observing the behavior of superfluids
if atoms cannot be kept cold or confined. The MIT team combined several techniques in generating ultracold temperatures,
the John D. Macarthur Professor of Physics at MIT. e use ultracold atoms to map out
originally co-developed by Ketterle, to cool atoms of rubidium to nanokelvin temperatures. Atoms of rubidium are known as bosons,
for their even number of nucleons and electrons. When cooled to near absolute zero bosons form what called a Bose-Einstein condensate a superfluid state that was discovered first co by Ketterle,
and for which he was awarded ultimately the 2001 Nobel prize in physics. After cooling the atoms,
the researchers used a set of lasers to create a crystalline array of atoms, or optical lattice.
The electric field of the laser beams creates what known as a periodic potential landscape, similar to an egg carton,
which mimics the regular arrangement of particles in real crystalline materials. When charged particles are exposed to magnetic fields,
their trajectories are bent into circular orbits, causing them to loop around and around. The higher the magnetic field, the tighter a particle orbit becomes.
However, to confine electrons to the microscopic scale of a crystalline material, a magnetic field 100 times stronger than that of the strongest magnets in the world would be required.
The group asked whether this could be done with ultracold atoms in an optical lattice. Since the ultracold atoms are charged not,
as electrons are, but are instead neutral particles, their trajectories are unaffected normally by magnetic fields. Instead, the MIT group came up with a technique to generate a synthetic
ultrahigh magnetic field, using laser beams to push atoms around in tiny orbits, similar to the orbits of electrons under a real magnetic field.
In 2013, Ketterle and his colleagues demonstrated the technique, along with other researchers in Germany, which uses a tilt of the optical lattice
and two additional laser beams to control the motion of the atoms. On a flat lattice, atoms can easily move around from site to site.
However, in a tilted lattice, the atoms would have to work against gravity. In this scenario, atoms could only move with the help of laser beams. ow the laser beams could be used to make neutral atoms move around like electrons in a strong magnetic field
added Kennedy. Using laser beams, the group could make the atoms orbit, or loop around, in a radius as small as two lattice squares, similar to how particles would move in an extremely high magnetic field. nce we had the idea,
we were excited really about it, because of its simplicity. All we had to do was take two suitable laser beams
and carefully align them at specific angles, and then the atoms drastically change their behavior,
Kennedy says. ew perspectives to known physics After developing the tilting technique to simulate a high magnetic field,
the group worked for a year and a half to optimize the lasers and electronic controls to avoid any extraneous pushing of the atoms,
which could make them lose their superfluid properties. t a complicated experiment, with a lot of laser beams, electronics,
and magnets, and we really had to get everything stable, Burton says. t took so long just to iron out all the details to eventually have this ultracold matter in the presence of these high fields,
and keep them cold some of it was painstaking work. In the end, the researchers were able to keep the superfluid gas stable for a tenth of a second.
During that time, the team took time-of-flight pictures of the distribution of atoms to capture the topology
or shape, of the superfluid. Those images also reveal the structure of the magnetic field something that been known,
but to add strong interactions between ultracold atoms, or to incorporate different quantum states, or spins.
Ketterle says such experiments would connect the research to important frontiers in material research, including quantum Hall physics
The immune system attacks the invader with a number of reactive molecules designed to neutralize it,
However, these molecules can also cause collateral damage to healthy tissue around the infection site:
This lesion, a damaged form of the normal DNA base cytosine, is caused by the reactive molecule hypochlorous acid the main ingredient in household bleach
#Aluminum olk-and-Shellnanoparticle Boosts Capacity and Power of Lithium-ion Batteries One big problem faced by electrodes in rechargeable batteries,
which use aluminum as the key material for the lithium-ion battery negative electrode, or anode, are reported in the journal Nature Communications, in a paper by MIT professor Ju Li and six others.
Most present lithium-ion batteries the most widely used form of rechargeable batteries use anodes made of graphite, a form of carbon.
This expansion and contraction of aluminum particles generates great mechanical stress, which can cause electrical contacts to disconnect.
which would be ok if not for the repeated large volume expansion and shrinkage that cause SEI particles to shed.
As a result, previous attempts to develop an aluminum electrode for lithium-ion batteries had failed.
but yolk-shell particles feature a void between the two equivalent to where the white of an egg would be.
The aluminum particles they used, which are about 50 nanometers in diameter, naturally have oxidized an layer of alumina (Al2o3).
a better conductor of electrons and lithium ions when it is very thin. Aluminum powders were placed in sulfuric acid saturated with titanium oxysulfate.
if the particles stay in the acid for a few more hours, the aluminum core continuously shrinks to become a 30-nm-across olk,
which shows that small ions can get through the shell. The particles are treated then to get the final aluminum-titania (ATO) yolk-shell particles.
After being tested through 500 charging-discharging cycles, the titania shell gets a bit thicker, Li says,
while allowing lithium ions and electrons to get in and out. The result is an electrode that gives more than three times the capacity of graphite (1. 2 Ah/g) at a normal charging rate
Li says. At very fast charging rates (six minutes to full charge), the capacity is still 0. 66 Ah/g after 500 cycles.
indicating ATO is quite close to being ready for real applications. hese yolk-shell particles show very impressive performance in lab-scale testing,
A defectree layer is also impermeable to all atoms and molecules. This amalgamation makes it a terrifically attractive material to apply to scientific developments in a wide variety of fields, such as electronics, aerospace and sports.
e transferred electrons from the dopant potassium to the surface of the black phosphorus, which confined the electrons
and allowed us to manipulate this state. Potassium produces a strong electrical field which is required what we to tune the size of the band gap. his process of transferring electrons is known as doping
and induced a giant Stark effect, which tuned the band gap allowing the valence and conductive bands to move closer together,
Rare, but widely publicized, incidents of overheating or combustion in lithium-ion batteries have highlighted also the importance of safety in battery technology.
They describe a new approach to the development of solid-state electrolytes that could simultaneously address the greatest challenges associated with improving lithium-ion batteries,
The electrolyte in such batteries typically a liquid organic solvent whose function is to transport charged particles from one of a battery two electrodes to the other during charging
was finding solid materials that could conduct ions fast enough to be useful in a battery. here was a view that solids cannot conduct fast enough,
he says. hat paradigm has been overthrown. he research team was able to analyze the factors that make for efficient ion conduction in solids,
The initial findings focused on a class of materials known as superionic lithium-ion conductors which are compounds of lithium, germanium, phosphorus,
and sulfur, but the principles derived from this research could lead to even more effective materials,
While conventional lithium-ion batteries do not perform well in extreme cold, and need to be preheated at temperatures below roughly minus 20 degrees Fahrenheit,
However, quantum mechanics, the underlying physical rules that govern the fundamental behavior of matter and light at the atomic scale,
says Schwab. e all know quantum mechanics explains precisely why electrons behave weirdly. Here, wee applying quantum physics to something that is relatively big,
a device that you can see under an optical microscope, and wee seeing the quantum effects in a trillion atoms instead of just one.
Because this noisy quantum motion is always present and cannot be removed, it places a fundamental limit on how precisely one can measure the position of an object.
Schwab explains. e showed that we can actually make the fluctuations of one of the variables smallert the expense of making the quantum fluctuations of the other variable larger.
ripples in the fabric of space-time. ee been thinking a lot about using these methods to detect gravitational waves from pulsarsncredibly dense stars that are the mass of our sun compressed into a 10 km radius and spin at 10 to 100 times a second,
In order to do that, the current device would have to be scaled up. ur work aims to detect quantum mechanics at bigger and bigger scales
The team is currently working with industrial partners to create metasurfaces for use in commercial devices such as miniature cameras and spectrometers,
Some have used tiny particles of glass, melded together at a lower temperature in a technique called sintering.
Carbon nanotubes are rolled-up arrays of perfect hexagons of atoms; graphene is a rolled out sheet of the same.
and excel at transmitting electrons and heat. But when the two are joined, the way the atoms are arranged can influence all those properties. ome labs are actively trying to make these materials or measure properties like the strength of single nanotubes and graphene sheets,
Shahsavari said. ut we want to see what happens and quantitatively predict the properties of hybrid versions of graphene and nanotubes.
or lose atoms to neighboring rings, depending on how they join with their neighbors. By forcing five, seven or even eight-atom rings
they found they could gain a measure of control over the hybrid mechanical properties. Turning the nanotubes in a way that forced wrinkles in the graphene sheets added further flexibility and shear compliance,
#Physicists Determine the Three-dimensional Coordinates of Individual Atoms A team of physicists from UCLA have determined the three-dimensional positions of individual atoms for the first time,
Atoms are the building blocks of all matter On earth, and the patterns in which they are arranged dictate how strong,
Now, scientists at UCLA have used a powerful microscope to image the three-dimensional positions of individual atoms to a precision of 19 trillionths of a meter,
for the first time, to infer the macroscopic properties of materials based on their structural arrangements of atoms, which will guide how scientists and engineers build aircraft components, for example.
For more than 100 years, researchers have inferred how atoms are arranged in three-dimensional space using a technique called X-ray crystallography,
X-ray crystallography only yields information about the average positions of many billions of atoms in the crystal,
Because X-ray crystallography doesn reveal the structure of a material on a per-atom basis,
the technique can identify tiny imperfections in materials such as the absence of a single atom.
which a beam of electrons smaller than the size of a hydrogen atom is scanned over a sample
and measures how many electrons interact with the atoms at each scan position. The method reveals the atomic structure of materials
because different arrangements of atoms cause electrons to interact in different ways. However scanning transmission electron microscopes only produce two-dimensional images.
The downside of this technique is repeated that the electron beam radiation can progressively damage the sample.
the researchers were able to slowly assemble a 3-D model of 3, 769 atoms in the tip of the tungsten sample.
The researchers compared the images from the first and last scans to verify that the tungsten had not been damaged by the radiation
thanks to the electron beam energy being kept below the radiation damage threshold of tungsten. Miao and his team showed that the atoms in the tip of the tungsten sample were arranged in nine layers, the sixth
of which contained a point defect. The researchers believe the defect was either a hole in an otherwise filled layer of atoms
or one or more interloping atoms of a lighter element such as carbon. Regardless of the nature of the point defect, the researchersability to detect its presence is significant,
demonstrating for the first time that the coordinates of individual atoms and point defects can be recorded in three dimensions. e made a big breakthrough,
Miao said. Miao and his team plan to build on their results by studying how atoms are arranged in materials that possess magnetism or energy storage functions,
which will help inform our understanding of the properties of these important materials at the most fundamental scale. think this work will create a paradigm shift in how materials are characterized in the 21st century,
a chemical change triggers the generation of oxygen-carrying molecules known as reactive oxygen species (ROS). If a sunscreen agents penetrate the skin,
The nanoparticle hydrophilic layer essentially locks in the active ingredient, a hydrophobic chemical called padimate O. Some sunscreen solutions that use larger particles of inorganic compounds, such as titanium dioxide or zinc oxide,
I developed the idea that there was a natural molecule that must exist and be capable of forcing embryonic stem cells into becoming cones,
COCO, a ecombinationalhuman molecule that is normally expressed within photoreceptors during their development. In 2001, he launched his laboratory at Maisonneuve-Rosemont Hospital
and immediately isolated the molecule. But it took several years of research to demystify the molecular pathways involved in the photoreceptors development mechanism.
The surfactant molecules which carry an electrical charge, can be attracted to, or repelled by, a metal surface by changing the polarity of the voltage applied to the metal.
like a dust particle, to start the process of nucleation, the bubbles formed by boiling water also require nucleation.
when Nili goes on to describe the capability of the newly tuned memristors. e have introduced now controlled faults or defects in the oxide material along with the addition of metallic atoms,
Electrons are able to travel though it without resistance at room temperature, promising a new approach to electronics.
and starting the flow of electrons, thus offering an alternative to silicon in electronics. Despite these properties,
when it doped with lithium atoms. The researchers believe that this new property could lead to a new generation of superconducting nanoscale devices.
In ordinary materials, electrons repel each other, but in superconductors the electrons form pairs known as Cooper pairs,
which together flow through the material without resistance. Phonons, the mechanism that facilitates these electronsalliances are vibrations in lattice crystalline structures.
could contribute a lot of phonons to the graphene electrons. In a research paper available on arxiv, the researchers demonstrated in physical experiments that the computer models were indeed correct in their predictions.
then deposited lithium atoms onto the graphene in a vacuum at 8 K, creating a version of graphene known as ecoratedgraphene.
the researchers found that the electrons slowed down as they travelled through the lattice, which they believe to be the result of enhanced electronhonon coupling.
which the researchers measured by identifying an energy gap between the material's conducting and nonconducting electrons.
The researchers who demonstrated last year the role phonons played in the superconductivity of graphite and calcium, Patrick Kirchmann and Shuolong Yang of the SLAC National Accelerator Laboratory
believe this latest work could usher in the fabrication of nanoscale superconducting quantum interference devices and single-electron superconductor quantum dots u
But new results suggest the atom-thick carbon sheet has one clear advantage: precise but practical calibrations of electrical resistance.
The resulting force on electrons causes them to migrate to the side, which in turn raises a voltage perpendicular to the flow of current.
the fundamental charge of the electron and a quantum mechanical measure dubbed the Planck constant.
Researchers have suspected long that the unique behavior of electrons in graphene, namely the big spacing between electron energy levels when the material is exposed to a magnetic field,
could be exploited to produce precise measurements of resistance under less extreme physical conditions. Several recent results support that idea.
The temperature the graphene device operates at is high enough that a lab could accurately measure resistance without needing liquid helium as a refrigerant. hese results support graphene as the material of choice for the next generation of easy-to-use, helium-free,
this unit of current will be redefined in terms of the fundamental charge of the electron, and quantum electrical standards will play a closer, more integrated role.
of how nanomaterials interact with molecules in their environment by looking at the individual nanoparticle as opposed to looking at many of them at the same time,
which involves exploiting the oscillations in the density of electrons that are generated when photons hit a metal surface.
The researchers applied the experimental spectroscopy technique to examine hydrogen absorption in single palladium nanoparticles.
In that way, the gained fundamental understanding of the reasons underlying the differences between seemingly identical individual particles
or impacting them in some other way that eliminates the ability to observe them accurately. hen studying individual nanoparticles you have to send some kind of probe to ask the particle hat are you doing?
said Langhammer. his usually means focusing a beam of high-energy electrons or photons or a mechanical probe onto a very tiny volume.
You then quickly get very high energy densities, which might perturb the process you want to look at.
In contrast to non-polarized light, in which the electric fields of the photons are oriented in random directions,
One of the distinguishing capabilities of circularly polarized light (CPL) is that it can discern the difference between right-handed and left-handed versions of molecules property known as chirality.
The nanowires create a sea of electrons that produces lasmondensity waves, the oscillations in the density of electrons that are generated
when photons hit a metal surface. These plasmon density waves absorb energy from the photons that pass through the silicon wafer.
The absorption of the energy produces otor energetic electrons, which generate a detectable electrical current.
The researchers found that they could make the zigzag pattern of nanowires with a right-or left-handed orientation.
When they arranged the nanowires in right-handed pattern, the surface absorbed right circularly polarized light
These devices take advantage of the ability of electrons to penetrate barriers, a phenomenon known as quantum tunneling.
The new TFET is made from two atomically-thin layers of semiconducting molybdenum sulfide crystal on top of a substrate of germanium.
#A Particle accelerator the Size of a Sewing needle An international research team has demonstrated a high-performance particle accelerator the size of a 1-millimeter mechanical pencil replacement lead.
Tens of thousands of particle accelerators around the world are used for more than physics research. They are used also to manufacture semiconductors,
A key accelerator parameter is the acceleration gradient, the energy (measured in mega electron volts, Mev) gained per meter of travel.
The amount of energy the accelerator can pump into a cluster of particles electrons, for example,
thus becomes a function of the device gradient and length. And cost, of course, increases with physical size of the accelerator.
Thus, conventional linear accelerators, with acceleration gradients around 300 Mev/m, can grow as big as the 3, 073-meter-long Stanford Linear accelerator in Menlo Park,
These machines accelerate charged particles using either a pulse of radio frequency radiation or a wakefield (using high energy unchesof electrons to blast a tunnel through plasma;
when the tunnel collapses back on itself, following particles accelerate by riding the charged wake of the collapsing front).
RF accelerators can reach energies of a few tens of mega electron volts before the RF energy itself begins to destabilize the mechanism in what called plasma breakdown.
In wakefield approaches, balancing the skittish plasma bubble requires terawatt or petawatt lasers, tricky micromachinging,
a compact device that uses pulses of terahertz (THZ) radiation. The research group includes scientists from the Massachusetts institute of technology (MIT), the University of Toronto,
and the Deutsches Electronen Synchrotron (DESY, the German Electron Syncrotron), the Center For free-Electron Laser Science (CFEL), the Max Planck Institute for Structure and Dynamics,
and accommodate a significant amount of charge per bunch of electrons On the other hand, the frequency is high enough that the plasma breakdown threshold for surface electric fields increases The terahertz approach also allows them to use readily available picoseconds lasers.
The accelerator itself is a quartz capillary about 1. 5 centimeters long and 940 micrometers in diameter
electrons are injected at 60 kev through a pinhole at the left end. When the terahertz pulse reflects off the left wall (around the injection pinhole) it catches the electrons,
accelerating them back towards the right. In the initial experiments, the electrons could ride the wave for just 3 mm before the wave started to spread out.
That short ride however, boosted their energy to 67 kev. A back of the envelope calculation translates this modest energy gain into an acceleration gradient over 2 Mev/m. his is not a particularly large acceleration,
his proof-of-principle terahertz linear accelerator demonstrates the potential for an all-optical acceleration scheme that can be integrated readily into small-scale laboratories providing users with electron beams that will enable new experiments in ultrafast electron diffraction and X-ray production
Overtext Web Module V3.0 Alpha
Copyright Semantic-Knowledge, 1994-2011