#One step closer to a single-molecule device Researchers have designed a new technique to create a single-molecule diode,
The group, under the direction of Latha Venkataraman, associate professor of applied physics at Columbia Engineering, is the first to develop a single-molecule diode that may have real-world technological applications for nanoscale devices.
Their paper,"Single-Molecule Diodes with High On-Off Ratios through Environmental Control,"is published May 25 in Nature Nanotechnology."
"Our new approach created a single-molecule diode that has a high(>250) rectification and a high"on"current (0. 1 micro Amps),"says Venkataraman."
"Constructing a device where the active elements are only a single molecule has long been a tantalizing dream in nanoscience.
and single molecules represent the limit of miniaturization. The idea of creating a single-molecule diode was suggested by Arieh Aviram
and Mark Ratner who theorized in 1974 that a molecule could act as a rectifier, a one-way conductor of electric current.
Researchers have since been exploring the charge-transport properties of molecules. They have shown that single-molecules attached to metal electrodes (single-molecule junctions) can be made to act as a variety of circuit elements
including resistors, switches, transistors, and, indeed, diodes. They have learned that it is possible to see quantum mechanical effects, such as interference, manifest in the conductance properties of molecular junctions.
Since a diode acts as an electricity valve, its structure needs to be asymmetric so that electricity flowing in one direction experiences a different environment than electricity flowing in the other direction.
In order to develop a single-molecule diode, researchers have designed simply molecules that have asymmetric structures.""While such asymmetric molecules do indeed display some diode-like properties,
they are not effective, "explains Brian Capozzi, a Phd student working with Venkataraman and lead author of the paper."
"A well-designed diode should only allow current to flow in one direction-the'on'direction
They created an environmental asymmetry through a rather simple method-they surrounded the active molecule with an ionic solution
and used gold metal electrodes of different sizes to contact the molecule. Their results achieved rectification ratios as high as 250: 50 times higher than earlier designs.
which, Venkataraman notes, is a lot of current to be passing through a single-molecule. And, because this new technique is implemented so easily,
An illustration of the molecule used by Columbia Engineering professor Latha Venkataraman to create the first single-molecule diode with a non-trivial rectification ratio overlaid on the raw current versus voltage data.
it is absorbed by electrons in the gold arms. The arms are so thin that the electrons are forced to move along the spiral.
Electrons that are driven toward the center absorb enough energy so that some of them emit blue light at double the frequency of the incoming infrared light. his is similar to
what happens with a violin string when it is bowed vigorously, said Stevenson Professor of Physics Richard Haglund,
The electrons at the center of the spirals are driven pretty vigorously by the laser electric field.
because the polarization pushes the electrons toward the center of the spiral. Counterclockwise polarized light,
because the polarization tends to push the electrons outward so that the waves from all around the nano-spiral interfere destructively.
So far, Davidson has experimented with small arrays of gold nano-spirals on a glass substrate made using scanning electron-beam lithography.
#Engineers show how'perfect'materials begin to fail at the nanoscale Crystalline materials have atoms that are lined neatly up in a repeating pattern.
where atoms behave in a more liquid-like way. Their increased mobility makes it more likely they will rearrange themselves into the beginnings of a ine defect,
heye often grown from the bottom up, in an atom-by-atom, layer-by-layer process,
the atoms on the surface comprise a much larger proportion of the total and can control the properties of the nanoscale material.
which provided each atom with the time and energy to move around until it found its preferred spot in the metal crystalline structure.
Gianola said. ur goal was to deduce the point where the first of the nanowire atoms begin to shift out of their original positions
what was driving this process. iffusion of atoms on a surface, Gianola said, s the only mechanism that has this low thermal activation barrier.
Surface diffusion is atoms hopping around, site to site, somewhat chaotically, almost like a fluid.
A palladium atom sitting inside the bulk of the wire has 12 neighbors and has to break most of those bonds to move around.
Velásquez-García and his colleagues use a technique called deep reactive-ion etching. On either face of a silicon wafer, they etch dense arrays of tiny rectangular columns tens of micrometers across
A scanning electron micrograph of the new microfiber emitters, showing the arrays of rectangular columns etched into their sides.
Velásquez-García and his colleagues use a technique called deep reactive-ion etching. On either face of a silicon wafer, they etch dense arrays of tiny rectangular columns tens of micrometers across
A scanning electron micrograph of the new microfiber emitters, showing the arrays of rectangular columns etched into their sides.
the electron temperature is much higher than that of acoustic vibrational modes of the graphene lattice,
but using it in its pure formraphenend at its ultimate size limitne atom thick. he group is currently working to further characterize the performance of these devicesor example,
plants that are exposed to sunlight use carefully organized nanoscale structures within their cells to rapidly separate charges pulling electrons away from the positively charged molecule that is left behind,
The polymer donor absorbs sunlight and passes electrons to the fullerene acceptor; the process generates electrical energy.
because the electrons sometimes hop back to the polymer spaghetti and are lost. The UCLA technology arranges the elements more neatly like small bundles of uncooked spaghetti with precisely placed meatballs.
The fullerenes inside the structure take electrons from the polymers and toss them to the outside fullerene
which can effectively keep the electrons away from the polymer for weeks. hen the charges never come back together,
led the team that created the uniquely designed molecules. e don have these materials in a real device yet;
plants that are exposed to sunlight use carefully organized nanoscale structures within their cells to rapidly separate charges pulling electrons away from the positively charged molecule that is left behind,
The polymer donor absorbs sunlight and passes electrons to the fullerene acceptor; the process generates electrical energy.
because the electrons sometimes hop back to the polymer spaghetti and are lost. The UCLA technology arranges the elements more neatly like small bundles of uncooked spaghetti with precisely placed meatballs.
The fullerenes inside the structure take electrons from the polymers and toss them to the outside fullerene
which can effectively keep the electrons away from the polymer for weeks. hen the charges never come back together,
led the team that created the uniquely designed molecules. e don have these materials in a real device yet;
scientists and engineers have developed many two-dimensional (2d) material innovations layered materials with the thickness of only one atom or a few atoms.
#X-rays and Electrons Join forces To Map Catalytic Reactions in Real-time New technique combines electron microscopy and synchrotron x-rays at Brookhaven Lab to track chemical reactions under real operating conditions.
including single atoms and larger structures, during an active reaction at room temperature,"said study coauthor and Brookhaven Lab scientist Eric Stach."
a focused electron beam passes through the sample and captures images of the nanoparticles within.
"With TEM, we take high-resolution pictures of the particles to directly see their size and distribution,"said Stach,
Particles smaller than a single nanometer were hidden behind what we call the resolution curtain of the technique."
which are measured to identify its chemical composition-in this instance, the distribution of platinum particles.""The XAS and TEM data, analyzed together,
and only the combination of techniques could reveal all catalytic particles.""Versatile micro-reactorthe new micro-reactor was designed specifically
"A relatively straightforward mathematical approach allowed them to deduce the total number of ultra-small particles missing in the TEM data."
which incorporates particles of all sizes, and removed the TEM results covering particles larger than one nanometer-the remainder fills in that crucial subnanometer gap in our knowledge of catalyst size
and distribution during each step of the reaction, "Frenkel said. Added Stach,"In the past, scientists would look at data before and after the reaction under model conditions, especially with TEM,
and complementary x-ray and electron probe techniques over time. NSLS ended its 32-year experimental run in the fall of 2014,
"Through Laboratory Directed Research and development funding, we will be part of the initial experiments at the Submicron Resolution X-ray (SRX) Spectroscopy beamline this summer,
And that's just one of the NSLS-II beamlines where we plan to deploy this technique."
To accomplish this, traditional solar panels can be used to generate an electrical current that splits water molecules into oxygen and hydrogen,
The most famous example of this is Cherenkov radiation, wakes produced as electrical charges travel through liquids faster than the phase velocity of light, emitting a glowing blue wake.
and Cherenkov radiation,"said Patrice Genevet, a lead author, formerly of SEAS, currently affiliated with the Singapore Institute of Manufacturing Technology.
because they have consisted only of a few layers of thermal conductive atoms. When you try to add more layers of graphene,
i e. the addition of a property-altering molecule. Having tested several different additives, the Chalmers researchers concluded that an addition of (3-Aminopropyl) triethoxysilane (APTES) molecules has desired the most effect.
When heated and put through hydrolysis, it creates so-called silane bonds between the graphene and the electronic component (see picture).
and environmentally benign method to combat bacteria by engineering nanoscale particles that add the antimicrobial potency of silver to a core of lignin,
North carolina State university engineer Orlin Velev and colleagues show that silver-ion infused lignin nanoparticles, which are coated with a charged polymer layer that helps them adhere to the target microbes,
The remaining particles degrade easily after disposal because of their biocompatible lignin core, limiting the risk to the environment."
says that the particles could be the basis for reduced risk pesticide products with reduced cost and minimized environmental impact."
We are now working to scale up the process to synthesize the particles under continuous flow conditions
and environmentally benign method to combat bacteria by engineering nanoscale particles that add the antimicrobial potency of silver to a core of lignin,
North carolina State university engineer Orlin Velev and colleagues show that silver-ion infused lignin nanoparticles, which are coated with a charged polymer layer that helps them adhere to the target microbes,
The remaining particles degrade easily after disposal because of their biocompatible lignin core, limiting the risk to the environment."
says that the particles could be the basis for reduced risk pesticide products with reduced cost and minimized environmental impact."
We are now working to scale up the process to synthesize the particles under continuous flow conditions."
and Katsumasa Fujita at Osaka University developed a way to image small, mobile bioactive molecules in living cells,
The method involves tagging bioactive molecules with small alkyne molecules and then imaging them using Raman microscopy technique that detects the vibrations of molecules by exciting them using a microscope-focused laser beam.
Unlike the comparatively large fluorescent tags used in conventional approaches the alkyne tags used in Sodeoka method do not alter the physical properties of bioactive molecules
or impede their motion in cells. One of Sodeoka collaborators, Michio Murata at Osaka University, suggested applying the technique to lipid raftsmall domains in cell membranes that are rich in lipids such as cholesterol
At its most basic level, your smart phone's battery is powering billions of transistors using electrons to flip on and off billions of times per second.
But if microchips could use photons instead of electrons to process and transmit data, computers could operate even faster.
the free electrons on its surface begin to oscillate together in a wave. These oscillations create their own light,
which reacts again with the free electrons. Energy trapped on the surface of the nanocube in this fashion is called a plasmon.
and a thin sheet of gold placed a mere 20 atoms away. This field interacts with quantum dotspheres of semiconducting material just six nanometers widehat are sandwiched in between the nanocube and the gold.
The quantum dots, in turn, produce a directional, efficient emission of photons that can be turned on and off at more than 90 gigahertz. here is great interest in replacing lasers with LEDS for short-distance optical communication,
lack of efficiency and inability to direct the photons, said Gleb Akselrod, a postdoctoral research in Mikkelsen laboratory. ow we have made an important step towards solving these problems. he eventual goal is to integrate our technology into a device that can be excited either optically
The group is now working to use the plasmonic structure to create a single photon source necessity for extremely secure quantum communicationsy sandwiching a single quantum dot in the gap between the silver nanocube and gold foil.
At its most basic level, your smart phone's battery is powering billions of transistors using electrons to flip on and off billions of times per second.
But if microchips could use photons instead of electrons to process and transmit data, computers could operate even faster.
the free electrons on its surface begin to oscillate together in a wave. These oscillations create their own light,
which reacts again with the free electrons. Energy trapped on the surface of the nanocube in this fashion is called a plasmon.
and a thin sheet of gold placed a mere 20 atoms away. This field interacts with quantum dotspheres of semiconducting material just six nanometers widehat are sandwiched in between the nanocube and the gold.
The quantum dots, in turn, produce a directional, efficient emission of photons that can be turned on and off at more than 90 gigahertz. here is great interest in replacing lasers with LEDS for short-distance optical communication,
lack of efficiency and inability to direct the photons, said Gleb Akselrod, a postdoctoral research in Mikkelsen laboratory. ow we have made an important step towards solving these problems.?
is pushing pretty hard for. he group is now working to use the plasmonic structure to create a single photon source necessity for extremely secure quantum communicationsy sandwiching a single quantum dot in the gap between the silver nanocube and gold foil.
The researchers report in Nano Letters that by combining inorganic semiconductor nanocrystals with organic molecules, they have succeeded in pconvertingphotons in the visible and near-infrared regions of the solar spectrum. he infrared region of the solar
The hybrid material we have come up with first captures two infrared photons that would normally pass right through a solar cell without being converted to electricity,
then adds their energies together to make one higher energy photon. This upconverted photon is absorbed readily by photovoltaic cells,
generating electricity from light that normally would be wasted. ardeen added that these materials are essentially eshaping the solar spectrumso that it better matches the photovoltaic materials used today in solar cells.
The cadmium selenide nanocrystals could convert visible wavelengths to ultraviolet photons while the lead selenide nanocrystals could convert near-infrared photons to visible photons.
In lab experiments, the researchers directed 980-nanometer infrared light at the hybrid material, which then generated upconverted orange yellow fluorescent 550-nanometer light,
almost doubling the energy of the incoming photons. The researchers were able to boost the upconversion process by up to three orders of magnitude by coating the cadmium selenide nanocrystals with organic ligands,
but are good at combining two lower energy photons to a higher energy photon. By using a hybrid material,
the inorganic component absorbs two photons and passes their energy on to the organic component for combination.
The organic compounds then produce one high-energy photon. Put simply, the inorganics in the composite material take light in;
the ability to upconvert two low energy photons into one high energy photon has potential applications in biological imaging, data storage and organic light-emitting diodes.
from red to blue, can impact any technology that involves photons as inputs or outputs,
The researchers report in Nano Letters that by combining inorganic semiconductor nanocrystals with organic molecules, they have succeeded in pconvertingphotons in the visible and near-infrared regions of the solar spectrum. he infrared region of the solar
The hybrid material we have come up with first captures two infrared photons that would normally pass right through a solar cell without being converted to electricity,
then adds their energies together to make one higher energy photon. This upconverted photon is absorbed readily by photovoltaic cells,
generating electricity from light that normally would be wasted. ardeen added that these materials are essentially eshaping the solar spectrumso that it better matches the photovoltaic materials used today in solar cells.
The cadmium selenide nanocrystals could convert visible wavelengths to ultraviolet photons while the lead selenide nanocrystals could convert near-infrared photons to visible photons.
In lab experiments, the researchers directed 980-nanometer infrared light at the hybrid material, which then generated upconverted orange yellow fluorescent 550-nanometer light,
almost doubling the energy of the incoming photons. The researchers were able to boost the upconversion process by up to three orders of magnitude by coating the cadmium selenide nanocrystals with organic ligands,
but are good at combining two lower energy photons to a higher energy photon. By using a hybrid material,
the inorganic component absorbs two photons and passes their energy on to the organic component for combination.
The organic compounds then produce one high-energy photon. Put simply, the inorganics in the composite material take light in;
the ability to upconvert two low energy photons into one high energy photon has potential applications in biological imaging, data storage and organic light-emitting diodes.
from red to blue, can impact any technology that involves photons as inputs or outputs,
The attice constantrepresents the distance between the atoms. To produce all possible wavelengths in the visible spectral range you need several semiconductors of very different lattice constants
For the present demonstration, the researchers had to use a laser light to pump electrons to emit light.
Because quantum physics.""You can't measure a quantum state, and expect it to still be explained quantum
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and electron transport at the nanometer scale. Professor Cronin's research spans a broad range of topics including electrical and spectroscopic characterization of carbon nanotubes, graphene,
Ionized oxygen atoms diffuse towards the sample chamber with low kinetic energies. Samples were exposed to the O2 plasma for about three minutes.
While typical plasma cleaners used in semiconductor fabrication operate using a"sputtering"mechanism where the sample is bombarded with ions carrying significant kinetic energy
Analytical techniques including photoluminescence spectroscopy (PL), Raman spectroscopy, atomic force microscopy (AFM), and electron energy loss spectroscopy (EELS) are used to follow the effects of the plasma treatments on a range of samples having different numbers of layers.
The authors successfully demonstrate the generation of an indirect-to-direct bandgap transition in many-layer Mos2 through the use of an easy to use, scalable oxygen induced plasma process.
A new technique invented at Caltech to produce graphene--a material made up of an atom-thick layer of carbon--at room temperature could help pave the way for commercially feasible graphene-based solar cells and light-emitting diodes, large-panel displays, and flexible electronics."
The electrical mobility of a material is a measure of how easily electrons can travel across its surface.
which is important for calculating the amount of energy a single particle of light, or photon, Boyd wondered
if he, like Millikan, could devise a method for cleaning his copper while it was under vacuum conditions.
hydrogen gas that has been electrified to separate the electrons from the protons--to remove the copper oxide at much lower temperatures.
and air molecules in the chamber's atmosphere generates cyano radicals--carbon-nitrogen molecules that have been stripped of their electrons.
Like tiny superscrubbers, these charged molecules effectively scour the copper of surface imperfections providing a pristine surface on
The Sub-ngstrm Low Voltage Electron (SALVE) microscope should improve contrast and reduce damage on biomolecules and two-dimensional nanomaterials, such as graphene March 18th,
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One of the newest methods of synthesis in modern chemistry, click chemistry, works on a similar basis. Here, molecules are combined to form new chemical compounds by means of chemical'snaps'.
'groups of three nitrogen atoms (azides), which in the presence of a catalyst can combine with groups of carbon atoms (terminal alkynes) located at the end of other molecules.
When they are connected, the two groups form stable nitrogen-carbon (triazole) rings. In this study, the azide groups were located on a glassy carbon substrate,
while maintaining an appropriate concentration of copper two ions and supporting electrolyte. In this environment, the production of the right catalyst, complexes of copper one and the bonding of nanoparticles itself to the substrate is very efficient,
Examples of these types of light sources are fluorescent molecules, nanoparticles, and quantum dots. The JQI work uses quantum dots
which are tiny crystals of a semiconductor material that can emit single photons of light.
The Sub-ngstrm Low Voltage Electron (SALVE) microscope should improve contrast and reduce damage on biomolecules and two-dimensional nanomaterials, such as graphene March 18th,
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It is now theoretically possible to remotely control the direction in which magnetic molecules spin,
Lithium-sulfur batteries have recently become one of the hottest topics in the field of energy storage devices due to their high energy density
--which is about four times higher than that of lithium-ion batteries currently used in mobile devices.
the uniform distribution of sulfur in carbon matrix and the strong interaction between carbon and sulfur are two important factors that affect the performance.
According to the researchers, the simultaneous combination of ultrafine grained structure with average particle size of 280 nm
and silicon carbide nanoparticles with aver particle size of 55 nm as strengthening agents results in the production of aluminum-based nanocomposite with a strength of 284 MPA.
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or less accessible to the molecule that reads the genome: the RNA polymerase. Depending on the specialisation of the cells,
An international team of researchers has used infinitely short light pulses to observe ultrafast changes in the electron-level properties of superconductors, setting a new standard for temporal resolution in the field.
whether the electron interactions occurring inside the materials are direct and instantaneous, or mediated by some delayed interaction.
The snap-shot observations, detailed this week in Nature Physics, support the hypothesis that electron interactions are delayed
and mediated by their interaction with the spin and magnetic pull of other electrons. The process took only 10 femtoseconds--something that
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