#Arrays of tiny conical tips that eject ionized materials could fabricate nanoscale devices cheaply Luis Fernando Velsquez-Garca's group at MIT's Microsystems Technology Laboratories (MTL) develops dense arrays
depositing or etching features onto nanoscale mechanical devices; spinning out nanofibers for use in water filters body armor and smart textiles;
or propulsion systems for fist-sized nanosatellites. In the latest issue of the IEEE Journal of Microelectromechanical systems Velsquez-Garca his graduate students Eric Heubel and Philip Ponce de Leon and Frances Hill a postdoc in his group describe a new prototype
array that generates 10 times the ion current per emitter that previous arrays did. Ion current is a measure of the charge carried by moving ions
The same prototype also crams 1900 emitters onto a chip that's only a centimeter square quadrupling the array size and emitter density of even the best of its predecessors.
because scaling down emitters implies less power consumption less bias voltage to operate them and higher throughput says Velsquez-Garca a principal research scientist at MTL.
Surface tension wicks the fluid up the side of the emitters to the tip of the cone whose narrowness concentrates the electrostatic field.
But in the new work they instead used carbon nanotubes atom-thick sheets of carbon rolled into cylinders grown on the slopes of the emitters like trees on a mountainside.
and height of the nanotubes the researchers were able to achieve a fluid flow that enabled an operating ion current at very near the theoretical limit.
We also show that they work uniformly that each emitter is doing exactly the same thing Velsquez-Garca says.
That's crucial for nanofabrication applications in which the depth of an etch or the height of deposits must be consistent across an entire chip.
To control the nanotubes'growth the researchers first cover the emitter array with an ultrathin catalyst film
which is broken into particles by chemical reactions with both the substrate and the environment. Then they expose the array to a plasma rich in carbon.
The nanotubes grow up under the catalyst particles which sit atop them until the catalyst degrades.
Increasing the emitter density the other improvement reported in the new paper was a matter of optimizing existing manufacturing recipe Velsquez-Garca says.
The emitters like most nanoscale silicon devices were produced through photolithography a process in which patterns are transferred optically to layers of materials deposited on silicon wafers;
a plasma then etches the material away according to the pattern. The recipe is the gases power pressure level time
and the sequence of the etching Velsquez-Garca says. We started doing electrospray arrays 15 years ago
Velsquez-Garca believes that using arrays of emitters to produce nanodevices could have several advantages over photolithography the technique that produces the arrays themselves.
and don't require a vacuum chamber the arrays could deposit materials that can't withstand the extreme conditions of many micro-and nanomanufacturing processes.
In my opinion the best nanosystems are going to be done by 3-D printing because it would bypass the problems of standard microfabrication Velsquez-Garca says.
which requires a high level of training to operate and everything is defined in planes. In many applications you want the three-dimensionality:
3-D printing is going to make a big difference in the kinds of systems we can put together
and not a beam of droplets says Herbert Shea an associate professor in the Microsystems for Space technologies Laboratory at the cole Polytechnique Fdrale de Lausanne.
Using their nanotube forest they're able to get the devices to operate in pure ion mode
#Creating nanostructures using simple stamps Nanostructures of virtually any possible shape can now be made using a combination of techniques developed by the MESA+Institute for Nanotechnology of the University of Twente.
Especially the unique properties of so-called perovskites can be exploited further: their crystal structure is influenced not by the process.
The UT scientists present their#findings in the journal Advanced Functional Materials. Perovskites are materials with special properties especially at their interfaces.
At the interface between two nonconducting perovskites for example a conducting'path'can arise. The magnetic properties of perovskites are unique as well.
Within the group Inorganic Materials science UT scientists have gained a lot of experience with these materials: earlier the group developed the Pulsed laser deposition technique (PLD)# for this building the materials one atomic layer at a time.
PLD is combined now with another technique for creating patterns within these ultra thin layers. This was a problem until now
because other patterning techniques have the risk of damaging the crystal structure and orientation and thus influence the properties of the material.
The new combination of techniques does not show this disadvantage. The solution that UT researchers publish in Advanced Functional Materials is combining PLD with so-called soft lithography.
The mold used for creating patterns can be made relatively easy and consists of PDMS#a rubber like polymer with silicon in it.
Via this mask a pattern of zinc oxide can be placed on the perovskite for example. Using PLD a sandwich of different materials can be made.
The properties of each layer are secured. The new structures can lead to sensors and chips for future devices like smartphones computers and medical equipment.
They are also suitable for fundamental research in physics and materials science. Research has been done within the Inorganic Materials science group part of the MESA+Institute for Nanotechnology at the University of Twente.
The paper'Patterning of epitaxial perovskites from micro and nano molded stencil masks'by Maarten Nijland Antony George Sean Thomas Evert Houwman Jing Xia Dave Blank Guus Rijnders Gertjan Koster
en Andr#ten Elshof#will appear#in Advanced Functional Materials. The paper is#online as an#'Early View
'and will appear in one of the coming issues. Explore further: Seeking the ability to design control
J. E. 2014) Patterning of Epitaxial Perovskites from Micro and Nano Molded Stencil Masks. Adv. Funct.
#Researcher develops optically traceable smart 2-D nanosheet that responds to ph Nanoparticles have the potential to revolutionize the medical industry
so that doctors and researchers can track the particles. Finally they need to perform their function at the right moment ideally in response to a stimulus. The Nanoparticles By design Unit at the Okinawa Institute of Science
and Technology Graduate University is trying to develop new particles with unprecedented properties that still meet these requirements.
Recently Dr. Jeong-Hwan Kim took one step forward when he experimented with a new type of nanomaterial:
the nanosheet. Specifically he designed a strong stable and optically traceable smart 2-D material that responds to ph or the acidity or basicity of its surrounding environment.
The American Chemical Society published his findings on August 12 2014 in their journal#Applied materials & Interfaces.
Nanosheets are unusual amongst nanotechnology because they do not exactly conform to nanoscale. The sheets that Kim produced are just a few nanometers thick thin enough to earn the nano prefix.
But their length and width can be measured in microns sometimes with surface areas that can be measured in centimeters;
much larger than typical nanostructures.##Nanosheets'structure gives them the ability to change shape from a flat surface to a scroll.
Unfortunately most nanosheets roll and unroll spontaneously. If researchers can design a nanosheet to change form in response to a stimulus they can use it for a number of new applications.
Kim tried adding different polymers to his nanosheets to make them responsive. For this experiment he incorporated a relatively simple polymer that responds to ph. He found that the resulting nanosheet would always curl in basic high ph conditions
and always flatten in acidic low ph conditions. Kim also made his nanosheets responsive to near-infrared light a wavelength of light that is harmless to humans.
Depending on the shape of the nanosheet the near-infrared radiation bounces back with a different wavelength.
In this way Kim can noninvasively track the nanosheets even though he can't see them. Using these optical properties to characterize the nanosheets Kim determined that he could approximate ph. Kim envisions biomedical engineers wrapping drugs inside of scrolled nanosheets
so that when the sheet unrolls it releases the medicine. PH responsive nanosheets for example could prove useful for targeting different parts of the human digestive tract
which changes ph between the acidic stomach and basic intestines. Yet this is only the beginning;
creating a responsive nanosheet is just a matter of adding the right polymer. A nanosheet is like pizza dough Kim said.
Whatever you like to put on it#one topping two toppings anything#you can. A nanosheet with a heat-sensitive polymer could burn surrounding tumors to destroy them functioning as a kind of super-specific chemotherapy.
It's easy to get the nanosheets to the cancer cells explains Kim. Targeting specific tissues is simply a matter of adding the appropriate biomarker
so that the body sends the nanosheet where it belongs. The advantage of the rolling means that this nanosheet can entrap many markers
or drugs securely inside the body said Kim. By encapsulating a dangerous substance such as a cancer-treating drug into a nanosheet doctors can attack very specific parts of the body.
This would decrease the amount of the drug necessary and minimize side effects. There are tons of smart polymers
and metals Kim said explaining the many properties he hopes to incorporate into nanotechnology. This new structure is composite
which means it allows us to mix all different kinds of components. Now Kim just needs to build the right nanosheet for each purpose.
Explore further: Like cling wrap new biomaterial can coat tricky burn wounds and block out infection More information:
Smart Composite Nanosheets with Adaptive Optical Properties Jeong-Hwan Kim Murtaza Bohra Vidyadhar Singh Cathal Cassidy and Mukhles Sowwan Applied materials & Interfaces2014.
American Chemical Society DOI: 10.1021/am504170
#New nanomaterial introduced into electrical machines Lappeenranta University of Technology in Finland has constructed the world's first prototype electrical motor using carbon nanotube yarn in the motor windings.
The new technology may significantly enhance the performance. Engineers of LUT have constructed the world's first electrical motor applying a textile material;
carbon nanotube yarn. The presently most electrically conductive carbon nanotube yarn replaces usual copper wires in the windings.
The motor prototype is built by the LUT Electrical engineering group as a start towards lightweight efficient electric drives.
The test motor output power is 40 W it rotates at 15000 rpm and has almost a 70%efficiency.
In the near future carbon nanotube fibers have potential to significantly enhance the performance and energy efficiency of electrical machines.
The new technology may revolutionize the whole industry. Researchers are constantly searching for opportunities to upgrade the performance of electrical machines;
to this end one of the objectives is to find higher-conductivity wires for the windings.
The best carbon nanotubes (CNTS) have demonstrated conductivities far beyond those of the best metals. Thus future windings made of CNTS may have a double conductivity compared with the present-day copper windings.
In order to make CNTS easy to manipulate they are spun to form multifiber yarn. If we keep the electrical machine design parameters unchanged and only replace copper with future carbon nanotube wires it is possible to reduce the Joule losses in the windings to half of the present-day machine losses.
Carbon nanotube wires are significantly lighter than copper and also environmentally friendlier. Therefore replacing copper with nanotube wires should significantly reduce the CO2 EMISSIONS related to the manufacturing
and operating of electrical machines. Furthermore the machine dimensions and masses could be reduced. The motors could also be operated in significantly higher temperatures than the present ones says Professor Juha Pyrh nen who has led the design of the prototype at LUT.
No definite upper limit for the conductivity Traditionally the windings in electrical machines are made of copper which has the second best conductivity of metals at room temperature.
Despite the high conductivity of copper a large proportion of the electrical machine losses occur in the copper windings.
For this reason the Joule losses are referred often to as copper losses. The carbon nanotube yarn does not have a definite upper limit for conductivity (e g. values of 100 MS/m have already been measured.
According to Pyrhnen the electrical machines are so ubiquitous in everyday life that we often forget about their presence.
In a single-family house alone there can be tens of electrical machines in various household appliances such as refrigerators washing machines hair dryers and ventilators.
In the industry the number of electrical motors is enormous: there can be up to tens of thousands of motors in a single process industry unit.
All these use copper in the windings. Consequently finding a more efficient material to replace the copper conductors would lead to major changes in the industry tells Professor Pyrh nen.
The prototype motor uses carbon nanotube yarns spun and converted into an isolated tape by a Japanese-Dutch company Teijin Aramid
which has developed the spinning technology in collaboration with Rice university the USA. The industrial applications of the new material are still in their infancy;
scaling up the production capacity together with improving the yarn performance will facilitate major steps in the future believes Business Development Manager Dr. Marcin Otto from Teijin Aramid agreeing with Professor Pyrhnen.
There is a significant improvement potential in the electrical machines but we are now facing the limits of material physics set by traditional winding materials.
Superconductivity appears not to develop to such a level that it could in general be applied to electrical machines.
Carbonic materials however seem to have a pole position: We expect that in the future the conductivity of carbon nanotube yarns could be even three times the practical conductivity of copper in electrical machines.
In addition carbon is abundant while copper needs to be mined or recycled by heavy industrial processes.
Explore further: Carbon nanotube fibers outperform coppe e
#New absorber will lead to better biosensors Biological sensors or biosensors are like technological canaries in the coalmine.
By converting a biological response into an optical or electrical signal they can alert us to dangers in our external and internal environments.
They can sense toxic chemicals and particles in the air and enzymes molecules and antibodies in the body that could indicate diabetes cancer and other diseases.
An optical biosensor works by absorbing a specific bandwidth of light and shifting the spectrum
when it senses minor changes in the environment. The narrower the band of absorbed light is the more sensitive the biosensor.
Currently plasmonic absorbers used in biosensors have a resonant bandwidth of 50 nanometers said Koray Aydin assistant professor of electrical engineering and computer science at Northwestern University's Mccormick School of engineering and Applied science.
It is significantly challenging to design absorbers with narrower bandwidths. Aydin and his team have created a new nanostructure that absorbs a very narrow spectrum of light#having a bandwidth of just 12 nanometers.
This ultranarrow band absorber can be used for a variety of applications including better biosensors. We believe that our unique narrowband absorber design will enhance the sensitivity of biosensors Aydin said.
It's been a challenge to sense very small particles or very low concentrations of a substance.
This research was described in the paper Ultranarrow band absorbers based on surface lattice resonances in nanostructured metal surfaces published in the July 29 issue of ACS Nano.
Typical absorber designs use two metal sheets with a nonmetallic insulating material in between. By using nanofabrication techniques in the lab Aydin's team found that removing the insulating layer#leaving only metallic nanostructures#caused the structure to absorb a much narrower band of light.
The absorption of light is also high exceeding 90 percent at visible frequencies. Aydin said this design can also be used in applications for photothermal therapy thermophotovoltaics heat-assisted magnetic recording thermal emission and solar-steam generation.
The beauty of our design is that we found a way to engineer the material by using a different substrate Aydin said.
Explore further: Researchers seek broadband/multiband electromagnetic absorbers based on plasmonic and metamaterial structure r
#'Stealth'nanoparticles could improve cancer vaccines Cancer vaccines have emerged recently as a promising approach for killing tumor cells before they spread.
But so far most clinical candidates haven't worked that well. Now scientists have developed a new way to deliver vaccines that successfully stifled tumor growth
when tested in laboratory mice. And the key they report in the journal ACS Nano is in the vaccine's unique stealthy nanoparticles.
Hiroshi Shiku Naozumi Harada and colleagues explain that most cancer vaccine candidates are designed to flag down immune cells called macrophages and dendritic cells that signal killer T cells to attack tumors.
The problem is that approaches based on targeting these generally circulating immune cells have not been very successful.
But recent research has suggested that a subset of macrophages only found deep inside lymph nodes could play a major role in slowing cancer.
But how could one get a vaccine to these special immune cells without first being gobbled up by the macrophages
and dendritic cells circulating in the body? Shiku's team wanted to see if stealthy nanoparticles they had developed
and clinically tested in patients might hold the answer. The researchers injected the nanoparticles into mice.
They found that the particles which have no electric charge or surface molecules that would attract the attention of circulating immune cells were able to enter the mice's lymph nodes.
But once inside the lymph nodes'core the special kind of macrophage engulfed the particles. When molecules for signaling killer T cells were put inside the nanoparticles they hindered tumor growth far better than existing vaccines.
Explore further: Hitchhiking vaccines boost immunity More information: Nanogel-Based Immunologically Stealth Vaccine Targets Macrophages in the Medulla of Lymph node
and Induces Potent Antitumor Immunity ACS Nano 2014 8 (9) pp 9209#9218. DOI: 10.1021/nn502975r Because existing therapeutic cancer vaccines provide only a limited clinical benefit a different vaccination strategy is necessary to improve vaccine efficacy.
We developed a nanoparticulate cancer vaccine by encapsulating a synthetic long peptide antigen within an immunologically inert nanoparticulate hydrogel (nanogel) of cholesteryl pullulan (CHP.
After subcutaneous injection to mice the nanogel-based vaccine was transported efficiently to the draining lymph node and was engulfed preferentially by medullary macrophages
but was sensed not by other macrophages and dendritic cells (so-called immunologically stealth mode). Although the function of medullary macrophages in T cell immunity has been unexplored so far these macrophages effectively cross-primed the vaccine-specific CD8+T cells in the presence of a Toll-like receptor (TLR) agonist as an adjuvant.
The nanogel-based vaccine significantly inhibited in vivo tumor growth in the prophylactic and therapeutic settings compared to another vaccine formulation using a conventional delivery system incomplete Freund's adjuvant.
We also revealed that lymph node macrophages were highly responsive to TLR stimulation which may underlie the potency of the macrophage-oriented nanogel-based vaccine.
These results indicate that targeting medullary macrophages using the immunologically stealth nanoparticulate delivery system is an effective vaccine strategy e
#Nanoparticles accumulate quickly in wetland sediment (Phys. org) A Duke university team has found that nanoparticles called single-walled carbon nanotubes accumulate quickly in the bottom sediments of an experimental wetland setting an action they say could indirectly damage the aquatic food chain.
The results indicate little risk to humans ingesting the particles through drinking water say scientists at Duke's Center for the Environmental Implications of Nanotechnology (CEINT.
But the researchers warn that based on their previous research the tendency for the nanotubes to accumulate in sediment could indirectly damage the aquatic food chain in the long term
if the nanoparticles provide Trojan horse piggyback rides to other harmful molecules. The results appear online in the journal Environmental science:
Nano. Carbon nanotubes are rapidly becoming more common because of their usefulness in nanoelectric devices composite materials and biomedicine.
The Duke study was done using small-scale replications of a wetland environment called mesocosms that include soil sediments microbes insects plants and fish.
These ecosystems-in-a-box are closed semi meaning they get fresh air and rainwater but don't drain to their surroundings.
While not perfect representations of a natural environment mesocosms provide a reasonable compromise between the laboratory and the real world.
The wetland mesocosms we used are a much closer approximation of the natural processes constantly churning in the environment said Lee Ferguson associate professor of civil and environmental engineering at Duke.
Although it's impossible to know if our results are fully accurate to natural ecosystems it is clear that the processes we've seen should be considered by regulators and manufacturers.
Ferguson and his colleagues dosed the mesocosms with single-walled carbon nanotubes and measured their concentrations in the water soil and living organisms during the course of a year.
They found that the vast majority of the nanoparticles quickly accumulated in the sediment on the pond floor.
However they found no sign of nanoparticle buildup in any plants insects or fish living in the mesocosms.
While this is good news for humans or other animals drinking water after a potential spill or other contamination event the accumulation in sediment does pose concerns for both sediment-dwelling organisms
and the animals that eat them Previous research has shown that carbon nanotubes take a long time to degrade through natural processes
if they do at all and any chemical that binds to them cannot easily be degraded either.
These nanoparticles are really good at latching onto other molecules including many known organic contaminants said Ferguson.
Coupled with their quick accumulation in sediment this may allow problematic chemicals to linger instead of degrading.
The nanoparticle-pollutant package could then be eaten by sediment-dwelling organisms in a sort of'Trojan horse'effect allowing the adsorbed contaminants to accumulate up the food chain.
The big question is whether or not these pollutants can be stripped away from the carbon nanotubes by these animals'digestive systems after being ingested continued Ferguson.
That's a question we're working to answer now. Explore further: Biodistribution of carbon nanotubes in the body More information:
Fate of single walled carbon nanotubes in wetland ecosystems. Schierz A. Espinasse B. Wiesner M. R. Bisesi J. H. Sabo-Attwood T. Ferguson P. L. Environmental science:
Nano Sept. 2014. DOI: 10.1039/c4en00063 3
#All directions are created not equal for nanoscale heat sources Thermal considerations are rapidly becoming one of the most serious design constraints in microelectronics, especially on submicron scale lengths.
A study by researchers from the University of Illinois at Urbana-Champaign has shown that standard thermal models will lead to the wrong answer in a three-dimensional heat-transfer problem
if the dimensions of the heating element are on the order of one micron or smaller."
"As materials shrink, the rules governing heat transfer change as well, "explained David Cahill, a professor of materials science and engineering at Illinois."Our current understanding of nanoscale thermal transport isn't nuanced enough to quantitatively predict
when standard theory won't work. This can impact the design of high-power RF devices that are used widely in the telecommunication industryor example, 4g wireless infrastructure.
The transistor spacing in RF devices is rapidly approaching length-scales where theory based on the diffusion of heat won't be valid,
and the engineering models currently used won't accurately predict the operating temperature of the device.
The temperature is a key factor for predicting mean-time to failure.""""Our research focuses on understanding the physics of thermal transport on submicron length-scales in the presence of an interface,
"explained Richard Wilson, lead author of the study published in Nature Communications.""Our study focused on a variety of crystals that have controlled differences in thermal transport properties, such as Si, doped Si,
and Sige alloys,"Wilson said.""We coated these crystals with a thin metal film, heated the surface with a laser beam,
and then recorded the temperature evolution of the sample.""On length-scales shorter than the phonon mean-free-paths of the crystal,
heat is transported ballistically, not diffusively. Interfaces between materials further complicate the heat-transfer problem by adding additional thermal resistance."
"Researchers found that when the radius of the laser beam used to heat the metal coated crystals was above ten microns,
the predictions made by assuming heat is transported diffusively matched the experimental observations. However, when the radius neared one micron,
diffusive theory over-predicted the amount of energy carried away from the heated surface.""We discovered fundamental differences in how heat is transported over short versus long distances.
Fourier theory, which assumes heat is transported by diffusion, predicts that a cubic crystal like silicon will carry heat equally well in all directions.
We demonstrated that on short length-scales heat is carried not equally well in all directions.
By measuring the temperature of the sample surface as a function of distance from the center of the heated region,
we were able to determine how far heat was traveling parallel to the surface, and deduce that,
when heater dimensions are small, significantly less heat is carried parallel to the surface than Fourier theory predicts,"Wilson stated.
Wilson and Cahill also studied the effect of interfaces on nanoscale thermal transport.""It's been well known for 75 years that the presence of a boundary adds a thermal boundary resistance to the heat-transfer problem,
but it's always been assumed that this boundary resistance was localized to the interface and independent of the thermal transport properties of the underlying material,"Cahill added."
"Our experiments show that these assumptions aren't generally valid. In particularly for crystals with defects, the boundary resistance is distributed and strongly dependent on the defect concentration."
"Wilson and Cahill also provided a theoretical description of their results that can be used by device engineers to better manage heat and temperature in nanoscale devices c
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