#Researchers find nanowires have pronounced unusually'anelastic'properties Anelastic materials exhibit gradual full recovery of deformation once a load is removed, leading to efficient dissipation of internal mechanical energy.
As a consequence, anelastic materials are being investigated for energy damping applications. At macroscopic scale, however, anelaticity is usually very small or negligible, especially in single-crystalline materials.
Here we show that single-crystalline Zno and p-doped Si nanowires (NWS) can exhibit anelastic behaviour that is up to four orders of magnitude larger than the largest anelasticity observed in bulk materials, with a recovery time-scale in the order
of minutes. In-situ scanning electron microscope (SEM) tests of individual NWS showed that upon removal of the bending load and instantaneous recovery of the elastic strain, a significant portion of the total strain gradually recovers with time.
We attribute the observed large anelasticity to stress-gradient-induced migration of point defects, as supported by electron energy loss spectroscopy (EELS) measurements
and also by the fact that no anelastic behaviour could be observed under tension. We model this behaviour through a theoretical framework by point defect diffusion under high initial strain gradient
and short diffusion distance, expanding the classic Gorsky theory. Finally, we show that Zno single-crystalline NWS exhibit a damping merit index of 1. 13
suggesting crystalline NWS with point defects as potential candidates for efficient energy damping materials. Researchers from North carolina State university and Brown University have found that nanoscale wires (nanowires) made of common semiconductor materials have pronounced a anelasticity-meaning that the wires,
when bent, return slowly to their original shape rather than snapping back quickly.""All materials have some degree of anelasticity,
but it is usually negligible at the macroscopic scale, "says Yong Zhu, an associate professor of mechanical and aerospace engineering at NC State and corresponding author of a paper describing the work."
"Because nanowires are so small, the anelasticity is significant and easily observed --although it was a total surprise
when we first discovered the anelasticity in nanowires.""The anelasticity was discovered when Zhu and his students were studying the buckling behavior of nanowires."
"Anelasticity is a fundamental mechanical property of nanowires, and we need to understand these sort of mechanical behaviors
if we want to incorporate nanowires into electronics or other devices,"says Elizabeth Dickey, a professor of materials science and engineering at NC State and co-author of the paper.
Nanowires hold promise for use in a variety of applications, including flexible, stretchable and wearable electronic devices.
The researchers worked with both zinc oxide and silicon nanowires, and found that -when bent-the nanowires would return more than 80 percent of the way to their original shape instantaneously,
but return the rest of the way (up to 20 percent) slowly.""In nanowires that are approximately 50 nanometers in diameter,
it can take 20 or 30 minutes for them to recover that last 20 percent of their original shape,
"says Guangming Cheng, a Ph d. student in Zhu's lab and the first author for the paper.
The work was done using tools developed in Zhu's group that enabled the team to conduct experiments on nanowires
while they were in a scanning electron microscope. Additional analysis was done using a Titan aberration-corrected scanning transmission electron microscope in NC State's Analytical Instrumentation Facility.
When any material is bent the bonds between atoms are stretched or compressed to accommodate the bending,
but in nanoscale materials there is time for the atoms to also move, or diffuse, from the compressed area to the stretched area in the material.
If you think of the bent nanowire as an arch, the atoms are moving from the inside of the arch to the outside.
When the tension in the bent wire is released, the atoms that simply moved closer or further apart snap back immediately;
this is what we call elasticity. But the atoms that moved out of position altogether take time to return to their original sites.
That time lag is a characteristic of anelasticity.""This phenomenon is pronounced in nanowires. For instance, zinc oxide nanowires exhibited anelastic behavior that is up to four orders of magnitude larger than the largest anelasticity observed in bulk materials,
with a recovery time-scale in the order of minutes,"says Huajian Gao, a professor at Brown University and co-corresponding author of the paper.
Detailed modeling by Gao's group indicates that the pronounced anelasticity in nanowires is because it is much easier for atoms to move through nanoscale materials than through bulk materials.
And the atoms don't have to travel as far. In addition nanowires can be bent much further than thicker wires without becoming permanently deformed or breaking."
"A reviewer commented that this is a new important page in the book on mechanics of nanostructures,
which was very flattering to hear,"Zhu says. The team plans to explore whether this pronounced anelasticity is common across nanoscale materials and structures.
They also want to evaluate how this characteristic may affect other properties, such as electrical conductivity and thermal transport.
The work was done with funding from the National Science Foundation n
#Environmentally friendly lignin nanoparticle'greens'silver nanobullet to battle bacteria Abstract: Silver nanoparticles have antibacterial properties,
but their use has been a cause for concern because they persist in the environment. Here, we show that lignin nanoparticles infused with silver ions
and coated with a cationic polyelectrolyte layer form a biodegradable and green alternative to silver nanoparticles.
The polyelectrolyte layer promotes the adhesion of the particles to bacterial cell membranes and, together with silver ions, can kill a broad spectrum of bacteria,
including Escherichia coli, Pseudomonas aeruginosa and quaternary-amine-resistant Ralstonia sp. Ion depletion studies have shown that the bioactivity of these nanoparticles is limited time because of the desorption of silver ions.
High-throughput bioactivity screening did not reveal increased toxicity of the particles when compared to an equivalent mass of metallic silver nanoparticles or silver nitrate solution.
Our results demonstrate that the application of green chemistry principles may allow the synthesis of nanoparticles with biodegradable cores that have higher antimicrobial activity and smaller environmental impact than metallic silver nanoparticles.
North carolina State university researchers have developed an effective and environmentally benign method to combat bacteria by engineering nanoscale particles that add the antimicrobial potency of silver to a core of lignin,
a ubiquitous substance found in all plant cells. The findings introduce ideas for better, greener and safer nanotechnology and could lead to enhanced efficiency of antimicrobial products used in agriculture and personal care.
In a study being published in Nature Nanotechnology July 13 NC State 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,
effectively kill a broad swath of bacteria, including E coli and other harmful microorganisms. As the nanoparticles wipe out the targeted bacteria,
they become depleted of silver. The remaining particles degrade easily after disposal because of their biocompatible lignin core,
limiting the risk to the environment.""People have been interested in using silver nanoparticles for antimicrobial purposes, but there are lingering concerns about their environmental impact due to the long-term effects of the used metal nanoparticles released in the environment,
"said Velev, INVISTA Professor of Chemical and Biomolecular engineering at NC State and the paper's corresponding author."
"We show here an inexpensive and environmentally responsible method to make effective antimicrobials with biomaterial cores."
"The researchers used the nanoparticles to attack E coli, a bacterium that causes food poisoning; Pseudomonas aeruginosa, a common disease-causing bacterium;
Ralstonia, a genus of bacteria containing numerous soil-borne pathogen species; and Staphylococcus epidermis, a bacterium that can cause harmful biofilms on plastics-like catheters-in the human body.
The nanoparticles were effective against all the bacteria. The method allows researchers the flexibility to change the nanoparticle recipe in order to target specific microbes.
Alexander Richter, the paper's first author and an NC State Ph d. candidate who won a 2015 Lemelson-MIT prize,
says that the particles could be the basis for reduced risk pesticide products with reduced cost and minimized environmental impact."
"We expect this method to have a broad impact, "Richter said.""We may include less of the antimicrobial ingredient without losing effectiveness
while at the same time using an inexpensive technique that has a lower environmental burden. We are now working to scale up the process to synthesize the particles under continuous flow conditions."
"Funding was provided by the U s. Environmental protection agency, the National Science Foundation and NC State. Researchers from the EPA, University of Hull, Wageningen University and University college London participated in the study y
#Nanoscale light-emitting device has big profile University of Wisconsin-Madison engineers have created a nanoscale device that can emit light as powerfully as an object 10,000 times its size.
It's an advance that could have huge implications for everything from photography to solar power.
In a paper published July 10 in the journal Physical Review Letters, Zongfu Yu, an assistant professor of electrical and computer engineering,
and his collaborators describe a nanoscale device that drastically surpasses previous technology in its ability to scatter light.
They showed how a single nanoresonator can manipulate light to cast a very large"reflection."
"The nanoresonator's capacity to absorb and emit light energy is such that it can make itself--and, in applications,
other very small things--appear 10,000 times as large as its physical size.""Making an object look 10,000 times larger than its physical size has lots of implications in technologies related to light,
"Yu says. The researchers realized the advance through materials innovation and a keen understanding of the physics of light.
Much like sound, light can resonate, amplifying itself as the surrounding environment manipulates the physical properties of its wave energy.
The researchers took advantage of this by creating an artificial material in which the wavelength of light is much larger than in a vacuum,
which allows light waves to resonate more powerfully. The device condenses light to a size smaller than its wavelength
meaning it can gather a lot of light energy, and then scatters the light over a very large area,
harnessing its output for imaging applications that make microscopic particles appear huge.""The device makes an object super-visible by enlarging its optical appearance with this super-strong scattering effect,
"says Ming Zhou, a Ph d. student in Yu's group and lead author of the paper.
Much as a very thin string on a guitar can absorb a large amount of acoustic energy from its surroundings
and begin to vibrate in sympathy, this one very small optical device can receive light energy from all around
and yield a surprisingly strong output. In imaging, this presents clear advantages over conventional lenses,
whose light-gathering capacity is limited by direction and size.""We are developing photodetectors based on this technology and, for example,
it could be helpful for photographers wanting to shoot better quality pictures in weak light conditions,
"Yu says. Given the nanoresonator's capacity to absorb large amounts of light energy, the technology also has potential in applications that harvest the sun's energy with high efficiency.
In addition, Yu envisions simply letting the resonator emit that energy in the form of infrared light toward the sky,
which is very cold. Because the nanoresonator has a large optical cross-section--that is, an ability to emit light that dramatically exceeds its physical size--it can shed a lot of heat energy,
making for a passive cooling system.""This research opens up a new way to manipulate the flow of light,
and could enable new technologies in light sensing and solar energy conversion, "Yu says s
#Better memory with faster lasers DVDS and Blu-ray disks contain so-called phase-change materials that morph from one atomic state to another after being struck with pulses of laser light, with data"recorded"in those two atomic states.
Using ultrafast laser pulses that speed up the data recording process, Caltech researchers adopted a novel technique, ultrafast electron crystallography (UEC),
to visualize directly in four dimensions the changing atomic configurations of the materials undergoing the phase changes.
In doing so, they discovered a previously unknown intermediate atomic state--one that may represent an unavoidable limit to data recording speeds.
By shedding light on the fundamental physical processes involved in data storage the work may lead to better, faster computer memory systems with larger storage capacity.
The research, done in the laboratory of Ahmed Zewail, Linus Pauling Professor of Chemistry and professor of physics, will be published in the July 28 print issue of the journal ACS Nano.
When the laser light interacts with a phase-change material, its atomic structure changes from an ordered crystalline arrangement to a more disordered,
or amorphous, configuration. These two states represent 0s and 1s of digital data.""Today, nanosecond lasers--lasers that pulse light at one-billionth of a second--are used to record information on DVDS and Blu-ray disks,
by driving the material from one state to another, "explains Giovanni Vanacore, a postdoctoral scholar and an author on the study.
The speed with which data can be recorded is determined both by the speed of the laser--that is,
by the duration of each"pulse"of light--and by how fast the material itself can shift from one state to the other.
Thus, with a nanosecond laser,"the fastest you can record information is one information unit
one 0 or 1, every nanosecond,"says Jianbo Hu, a postdoctoral scholar and the first author of the paper."
"To go even faster, people have started to use femtosecond lasers, which can potentially record one unit every one millionth of a billionth of a second.
We wanted to know what actually happens to the material at this speed and if there is a limit to how fast you can go from one structural phase to another."
"To study this, the researchers used their technique, ultrafast electron crystallography. The technique, a new development--different from Zewail's Nobel prize-winning work in femtochemistry, the visual study of chemical processes occurring at femtosecond scales--allowed researchers to observe directly the transitioning atomic configuration of a prototypical phase-change
material, germanium telluride (Gete), when it is hit by a femtosecond laser pulse. In UEC, a sample of crystalline Gete is bombarded with a femtosecond laser pulse,
followed by a pulse of electrons. The laser pulse causes the atomic structure to change from the crystalline to other structures
and then ultimately to the amorphous state. Then, when the electron pulse hits the sample, its electrons scatter in a pattern that provides a picture of the sample's atomic configuration as a function of the time.
With this technique, the researchers could see directly, for the first time, the structural shift in Gete caused by the laser pulses.
However, they also saw something more: a previously unknown intermediate phase that appears during the transition from the crystalline to the amorphous configuration.
--and to how fast data can be recorded, regardless of the laser speeds used.""Even if there is a laser faster than a femtosecond laser,
"Despite revealing such limits, the research could one day aid the development of better data storage for computers,
Right now, computers generally store information in several ways, among them the well-known random-access memory (RAM) and read-only memory (ROM.
RAM, which is used to run the programs on your computer, can record and rewrite information very quickly via an electrical current.
whenever the computer is powered down. ROM storage, including CDS and DVDS, uses phase-change materials and lasers to store information.
Although ROM records and reads data more slowly, the information can be stored for decades. Finding ways to speed up the recording process of phase-change materials
and understanding the limits to this speed could lead to a new type of memory that harnesses the best of both worlds.
and then rewrite a DVD. Although these applications could mean exciting changes for future computer technologies,
this work is also very important from a fundamental point of view, Zewail says.""Understanding the fundamental behavior of materials transformation is
#Iranian Scientists Use Gas Sensor to Detect Hydrogen Iranian researchers designed a sensor with the capability of rapidly detecting the amount of hydrogen existing in the environment.
This sensor can detect the leak of hydrogen in hazardous environment which can prevent the explosion.
Hydrogen sensors are convertors that create electrical signal by adsorbing hydrogen molecules, which depends on the concentration of the hydrogen.
In this research, a capacitor MOS sensor was produced that detects the leak of hydrogen at explosive level (4 vol. percent) in less than two minutes.
Capacitor sensors detect any change in the environment through changing the electrical capacity of the capacitor.
The advantages of these sensors over other types of sensors are stability long lifetime and low response time.
For instance, this sensor can be used in the monitoring of hydrogen concentration during the production of ammonia, methanol and hydration of hydrocarbons.
Among other applications of this sensor, mention can be made of desulfurization of petroleum products, production of jet fuel and launching of aircrafts and other aerospace applications.
This research also studies the effect of the thickness of oxide layers in the sensor structure on its properties and performance.
the sensor detects hydrogen in a shorter period of time as the thickness of oxide layer decreases.
Response time has been calculated to be 84 seconds for a capacitor sensor with oxide layer thickness of 28 nanometers.
Results of the research have been published in Sensors and Actuators B: Chemical, vol. 216, issue 1, 2015, pp. 367-373 3
#Nanospheres shield chemo drugs, safely release high doses in response to tumor secretions Scientists have designed nanoparticles that release drugs in the presence of a class of proteins that enable cancers to metastasize.
so that the very enzymes that make cancers dangerous could instead guide their destruction.""We can start with a small molecule
and build that into a nanoscale carrier that can seek out a tumor and deliver a payload of drug,
"said Cassandra Callmann, a graduate student in chemistry and biochemistry at the University of California, San diego,
The system takes advantage of a class enzymes called matrix metalloproteinases that many cancers make in abundance.
The shell fragments form a ragged mesh that holds the drug molecules near the tumor.
The work, led by Nathan Gianneschi a professor of chemistry and biochemisty at UC San diego, builds on his group's earlier sucess using a similar strategy to mark tumors for both diagnosis and precise surgical removal.
To package the drug into the spheres, Callmann had to add chemical handles. As it turns out, a group of atoms essential to the drug molecule's effectiveness,
and also toxicity, made for a good attachment point. That means the drug was inactivated as it flowed through the circulatory system until it reached the tumor.
The protection allowed the researchers to safely give a dose 16 times higher than they could with the formulation now used in cancer clinics,
in a test in mice with grafted in fibrosarcoma tumors. In additional preliminary tests, Callmann and colleagues were able to halt the growth of the tumors for a least two weeks,
using a single lower dose of the drug. In mice treated with the nanoparticles coated with peptides that are impervious to MMPS or given saline,
the tumors grew to lethal sizes within that time. Gianneschi says they will broaden their approach to create delivery systems for other diagnostic and therapeutic molecules."
"This kind of platform is not specific to paclitaxel. We'll test this in other models-with other classes of drug and in mice with a cancer that mimics metastatic breast cancer, for example."
"They'll also continue to modify the shell, to provide even greater protection and avoid uptake by organs such as liver, spleen and kidneys,
he said.""We want to open up this therapeutic window."#"##Additional authors include Matthew Thompson in Gianneschi's chemistry research group and Christopher Barback, David Hall and Robert Mattrey in UC San diego's Moores Cancer Center.
All animal procedures were approved by UC San diego's institution animal care and use committee. Callmann holds a fellowship through the Cancer Researchers in Nanotechnology Program at UC San diego. The National Institute of Biomedical Imaging
and Bioengineering provided financial support. This novel approach to using enzyme-directed assembly of particle theranostics (EDAPT) is patent pending.
Skip Cynar, scynar@ucsd. edu, in UC San diego's technology transfer office can provide information about commercial development t
#Density-near-zero acoustical metamaterial made in China: Researchers create a tunable membrane'metamaterial'with near-zero density,
effectively recreating the quantum tunneling effect for sound waves When a sound wave hits an obstacle and is scattered,
the signal may be lost or degraded. But what if you could guide the signal around that obstacle,
as if the interfering barrier didn't even exist? Recently, researchers at Nanjing University in China created a material from polyethylene membranes that does exactly that.
Researchers have created a tunable membrane'metamaterial'with near-zero density, effectively recreating the quantum tunneling effect for sound waves.
Their final product, described this week in the Journal of Applied Physics, from AIP Publishing, was an acoustical"metamaterial"with an effective density near zero (DNZ).
This work could help to endow a transmission network with coveted properties such as high transmission around sharp corners, high-efficient wave splitting,
and acoustic cloaking.""It's as if the entire interior space is said missing Xiaojun Liu, a professor in the physics department at Nanjing University's Collaborative Innovation Center of Advanced Microstructures."
"We were curious about whether we could make a simple but compact density-near-zero metamaterial from just a few tiny membranes,
"Liu said, "and, if so, can we further manipulate sound and make acoustic invisibility cloaks and other strange functional devices?"
and phononic crystals to create"Dirac cones, "but required large physical dimensions, complex geometric structures,
minimalist realization of their original density-near-zero idea, consisting of 0. 125 mm-thick polyethylene membranes perforated with 9-millimeter-radius holes in a square grid inside of a metal
waveguide, a physical structure for guiding sound waves. The intensive resonances of the membranes significantly reduce the structure's effective mass density
the membranes act as a tunnel for sound, encapsulating the waves into local subwavelength regions. This arrangement allows the sound waves to pass through without accumulating a phase change
or distorting the wavefront--analogous to the quantum tunneling effect, in which a particle crosses through a potential energy barrier otherwise insurmountable by classical mechanics.
the metamaterial would likely be integrated into acoustic circuits and structures. When implemented in a wave splitter,
the researchers found an 80 percent increase in the efficiency of energy transmission, regardless of the wave's incident angle.
Additionally, the researchers are able to tune the frequency of the metamaterial network by altering the membrane's tension and physical dimensions,
This can allow scientists to see fine features of objects such as tumors, or minute flaws within airplane wings in industrial testing, that may otherwise be unobservable due to an instrument's diffractive limit.
Additional planned applications include using smart acoustic structures, such as logic gates that can control acoustic waves by altering their propagation, for communication systems in environmental conditions too extreme for conventional electronic devices and photonic structures."
#Researchers Build a Transistor from a Molecule and A few Atoms A team of physicists from the Paul-Drude-Institut für Festkörperelektronik (PDI) and the Freie Universität Berlin (FUB), Germany, the NTT
Basic Research Laboratories (NTT-BRL), Japan, and the U s. Naval Research Laboratory (NRL), United states, has used a scanning tunneling microscope to create a minute transistor consisting of a single molecule and a small number of atoms.
The observed transistor action is markedly different from the conventionally expected behavior and could be important for future device technologies as well as for fundamental studies of electron transport in molecular nanostructures.
The complete findings are published in the August 2015 issue of the journal Nature Physics. Transistors have a channel region between two external contacts
and an electrical gate electrode to modulate the current flow through the channel. In atomic-scale transistors, this current is extremely sensitive to single electrons hopping via discrete energy levels.
Single-electron transport in molecular transistors has been studied previously using top-down approaches, such as lithography and break junctions.
But atomically precise control of the gate which is crucial to transistor action at the smallest size scales is not possible with these approaches.
The team used a highly stable scanning tunneling microscope (STM) to create a transistor consisting of a single organic molecule and positively charged metal atoms
positioning them with the STM tip on the surface of an indium arsenide (Inas) crystal. Kiyoshi Kanisawa, a physicist at NTT-BRL, used the growth technique of molecular beam epitaxy to prepare this surface.
Subsequently, the STM approach allowed the researchers, first, to assemble electrical gates from the+1 charged atoms with atomic precision and, then,
to place the molecule at various desired positions close to the gates. Stefan Fölsch, a physicist at the PDI who led the team,
explained that he molecule is only weakly bound to the Inas template. So, when we bring the STM tip very close to the molecule
and apply a bias voltage to the tip-sample junction, single electrons can tunnel between template
and tip by hopping via nearly unperturbed molecular orbitals, similar to the working principle of a quantum dot gated by an external electrode.
In our case, the charged atoms nearby provide the electrostatic gate potential that regulates the electron flow
and the charge state of the molecule But there is a substantial difference between a conventional semiconductor quantum dot comprising typically hundreds or thousands of atoms and the present case of a surface-bound molecule:
Steven Erwin, a physicist at NRL and expert in density-functional theory, pointed out that he molecule adopts different rotational orientations,
depending on its charge state. We predicted this based on first-principles calculations and confirmed it by imaging the molecule with the STM This coupling between charge
and orientation has a dramatic effect on the electron flow across the molecule, manifested by a large conductance gap at low bias voltages.
Piet Brouwer, a physicist at FUB and expert in quantum transport theory, said that his intriguing behavior goes beyond the established picture of charge transport through a gated quantum dot.
and orientational dynamics of the molecule This simple and physically transparent model entirely reproduces the experimentally observed single-molecule transistor characteristics.
The perfection and reproducibility offered by these STM-generated transistors will enable the exploration of elementary processes involving current flow through single molecules at a fundamental level.
which they can lead will be important for integrating molecule-based devices with existing semiconductor technologies.
The Paul-Drude-Institut für Festkörperelektronik (PDI) is a German research institute with about 100 employees located in Berlin-Mitte.
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