#Aligned carbon nanotube/graphene sandwiches By in situ nitrogen doping and structural hybridization of carbon nanotubes (CNTS) and graphene via a two-step chemical vapor deposition (CVD) scientists have fabricated nitrogen-doped aligned carbon nanotube/graphene (N-ACNT/G) sandwiches
with three-dimensional (3d) electron transfer pathways interconnected ion diffusion channels and enhanced interfacial affinity and activity.
The as-fabricated N-ACNT/G sandwiches described in the journal Advanced Materials on Sep 17 2014 demonstrated high-rate performances in lithium-sulfur (Li-S) batteries.
CNTS and graphene the most highlighted sp2-bonded carbon nanomaterials over the past decades have attracted enormous attention in the area of energy storage heterogeneous catalysis healthcare environmental protection as well as nanocomposites
which are highly dependent not only on their superior intrinsic physical properties such as mechanical strength electrical and thermal conductivity but also on their tunable chemical characters such as functional groups doping and surface modification.
However the heteroatom-containing nanocarbon tends to aggregate due to strong Van der waals interactions and large surface area explosion thereby constantly limiting the demonstration of their intrinsic physical properties and performances in as-fabricated materials and practical devices.
The combination of CNTS and graphene into 3d hybrid composites can usually mitigate the self-aggregation
and restacking of nanocarbon materials and also amplify physical properties at macroscale. Up to now several strategies have been explored to fabricate such CNTS/graphene hybrids including post-organization methods
and in situ growth while integration of high-quality CNTS and graphene without barrier layers is still difficult.
A team from Tsinghua University (China) led by Prof. Qiang Zhang and Fei Wei have fabricated now successfully sandwich-like N-ACNT/G hybrids via a two-step catalytic growth on bifunctional natural materials.
Aligned CNTS were intercalated firstly into the interlayer spaces of the layered catalyst embedded with metal nanoparticles (NPS) through a low-temperature (L-T) CVD
and graphene was deposited sequentially onto the surface of lamellar flakes at the bottom of aligned CNTS through a high-temperature (H-T) CVD.
NH3 was introduced simultaneously during the CVD growth for the incorporation of nitrogen atoms into the carbon framework.
After catalyst removal alternative aligned CNTS and graphene were connected vertically to each other in long-range periodicity thereby forming a sandwich-like structure.
The key issue for the fabrication of the novel N-ACNT/G architecture is that the high-quality aligned CNTS
and graphene were grown on the NPS and lamellar flakes at L -and H-T CVD respectively and conjointly. first-author Cheng Tang explained to Phys.
Org''Thereby the seamless connection of high-quality aligned CNTS and graphene provided 3d electron transfer pathways and interconnected ion diffusion channels.
Also the nitrogen doping induced moderate chemical modulation to the carbon framework whereby enhanced the interfacial affinity and electrochemical activity.
One of the most promising candidates for next-generation power sources Li-S battery is with very high theoretical energy density of 2600 Wh kg-1 natural abundance
of element sulfur and environment friendly as well. We try to enhance the cyclic and rate performances of Li-S batteries for practical application with the N-ACNT/G hybrids as cathode materials. said Prof.
Wei. A high initial reversible capacity of 1152 mah g-1 can be available at 1. 0 C maintaining ca. 880 mah g-1 after 80 cycles
which was about 65%higher than that of sole aligned CNTS. Even at a high current density of 5. 0 C a reversible capacity of ca. 770 mah g-1 can be achieved.
The remarkable cycling capacity and rate capability can be attributed to the novel structural and chemical characteristics of the N-ACNT/G sandwiches Prof.
Zhang elaborated The seamless junction of CVD-grown aligned CNTS and graphene provides rapid electron transfer and mechanical robustness.
The 3d interconnected mesoporous space improves the penetration and diffusion of electrolytes. Additionally the nitrogen-modified interfaces give rise to enhanced interfacial affinity for efficient confinement and utilization of sulfur and polysulfides.
It is expected highly that the N-ACNT/G sandwiches hold various potential applications in the area of nanocomposite energy storage environmental protection electronic device as well as healthcare because of their robust hierarchical structure 3d electron transfer
pathways and ion diffusion channels and enhanced interfacial affinity and activity as well. Prof. Zhang said Because such design
and fabrication strategy is generally applicable we foresee a new branch of material chemistry evolving in the area of advanced hierarchical nanostructures through the 3d topological nanosystems and interfacial modification.
Explore further: Rational hybridization of N-doped graphene/carbon nanotubes for oxygen reduction and oxygen evolution reaction More information:
Tang C Zhang Q Zhao MQ Huang JQ Cheng XB Tian GL Peng HJ Wei F. Nitrogen-Doped Aligned Carbon nanotube
/Graphene Sandwiches: Facile Catalytic Growth on Bifunctional Natural Catalysts and Their Applications as Scaffolds for High-Rate Lithium-Sulfur Batteries.
Advanced Materials 2014 26 (35) 6100-6105. DOI: 10.1002/adma. 20140124 4
#Ceramics don't have to be brittle: Materials scientists are creating materials by design Imagine a balloon that could float without using any lighter-than-air gas.
Instead, it could simply have all of its air sucked out while maintaining its filled shape.
Such a vacuum balloon, which could help ease the world's current shortage of helium,
can only be made if a new material existed that was strong enough to sustain the pressure generated by forcing out all that air
Greer's team has developed a method for constructing new structural materials by taking advantage of the unusual properties that solids can have at the nanometer scale,
the Caltech researchers explain how they used the method to produce a ceramic (e g.,, a piece of chalk or a brick) that contains about 99.9 percent air yet is incredibly strong
and that can recover its original shape after being smashed by more than 50 percent.""Ceramics have always been thought to be heavy and brittle,
"says Greer, a professor of materials science and mechanics in the Division of Engineering and Applied science at Caltech."
"We're showing that in fact, they don't have to be either. This very clearly demonstrates that
if you use the concept of the nanoscale to create structures and then use those nanostructures like LEGO to construct larger materials,
you can obtain nearly any set of properties you want. You can create materials by design."
"The researchers use a direct laser writing method called two-photon lithography to"write"a three-dimensional pattern in a polymer by allowing a laser beam to crosslink
and harden the polymer wherever it is focused. The parts of the polymer that were exposed to the laser remain intact
while the rest is dissolved away, revealing a three-dimensional scaffold. That structure can then be coated with a thin layer of just about any kind of material metal, an alloy, a glass, a semiconductor, etc.
Then the researchers use another method to etch out the polymer from within the structure
leaving a hollow architecture. The applications of this technique are practically limitless, Greer says. Since pretty much any material can be deposited on the scaffolds,
the method could be particularly useful for applications in optics, energy efficiency, and biomedicine. For example, it could be used to reproduce complex structures such as bone,
producing a scaffold out of biocompatible materials on which cells could proliferate. In the latest work, Greer and her students used the technique to produce
what they call three-dimensional nanolattices that are formed by a repeating nanoscale pattern. After the patterning step,
they coated the polymer scaffold with a ceramic called alumina (i e.,aluminum oxide), producing hollow-tube alumina structures with walls ranging in thickness from 5 to 60 nanometers and tubes from 450 to 1, 380 nanometers in diameter.
Greer's team next wanted to test the mechanical properties of the various nanolattices they created.
Using two different devices for poking and prodding materials on the nanoscale, they squished, stretched, and otherwise tried to deform the samples to see how they held up.
They found that the alumina structures with a wall thickness of 50 nanometers and a tube diameter of about 1 micron shattered when compressed.
That was not surprising given that ceramics especially those that are porous, are brittle. However, compressing lattices with a lower ratio of wall thickness to tube diameterhere the wall thickness was only 10 nanometersroduced a very different result."
"You deform it, and all of a sudden, it springs back, "Greer says.""In some cases, we were able to deform these samples by as much as 85 percent,
and they could still recover.""To understand why, consider that most brittle materials such as ceramics, silicon,
and glass shatter because they are filled with flawsmperfections such as small voids and inclusions. The more perfect the material,
when you reduce these structures down to the point where individual walls are only 10 nanometers thick,
"The Greer lab is now aggressively pursuing various ways of scaling up the production of these so-called metamaterials a
#'Human touch'nanoparticle sensor could improve breast cancer detection (Phys. org) niversity of Nebraska-Lincoln scientists have developed a nanoparticle-based device that emulates human touch
and that could significantly enhance clinical breast exams for early detection of cancer. In a newly published article in the journal ACS Advanced Materials & Interfaces, researchers Ravi Saraf and Chieu Van Nguyen describe a thin-film sensor that can detect tumors too small and deep
to be felt with the fingers. In research funded with a grant from the National institutes of health, Saraf and Nguyen perfected a thin film made of nanoparticles and polymers
which when pressed against the skin creates changes in electrical current and light that can be captured by a high-quality digital camera.
The film, just one-60th the thickness of a human hair, is a sort of"electronic skin"able to sense texture and relative stiffness.
Using a silicone breast model identical to those used to train doctors in manual breast exams,
the researchers ued the film to successfully detect tumors as small as 5 millimeters, hidden up to 20 millimeters deep.
Saraf, a professor of chemical and biomolecular engineering said he envisions a stethoscope-like device that a doctor would press across a patient's chest to image the buried palpable structure.
It could be used by family doctors during routine patient examinations or by physicians serving remote regions of the world.
"A tool like this could be interfaced with a laptop to provide high-quality screening capability to save lives in poor countries in remote parts of the world,
is to acquire funding to build a prototype device.""We have enough know-how now. We can start building this device today,
or CBE, doctors manually examine the breast for abnormalities and use their hands to palpate the tissue in search of lumps.
Though it may seem low-tech compared to mammograms, magnetic resonance imaging and ultrasound, CBE is an important cancer-screening tool.
Mammograms, which identify lumps by their density compared to breast tissue, are less effective with young women and those with dense and vascular breasts.
Yet the challenge with CBE is the lack of a visual record to compare with previous examinations to aid in diagnosis. Also,
while the American Cancer Society reports a 94 percent survival rate if breast cancer is diagnosed when tumors are diagnosed at less than 10 millimeters.
Saraf said the thin-film tool would have at least three advantages to a manual breast exam performed by a physician:
#Team uses nanotechnology to help cool electrons with no external sources A team of researchers has discovered a way to cool electrons to#228°C without external means and at room temperature,
an advancement that could enable electronic devices to function with very little energy. The process involves passing electrons through a quantum well to cool them
The team details its research in"Energy-filtered cold electron transport at room temperature, "which is published in Nature Communications on Wednesday, Sept. 10."
"said Seong Jin Koh, an associate professor at UT Arlington in the Materials science & Engineering Department,
The team used a nanoscale structure which consists of a sequential array of a source electrode, a quantum well,
a tunneling barrier, a quantum dot, another tunneling barrier, and a drain electrode to suppress electron excitation
and to make electrons cold. Cold electrons promise a new type of transistor that can operate at extremely low energy consumption."
"Implementing our findings to fabricating energy-efficient transistors is currently under way,"Koh added. Khosrow Behbehani, dean of the UT Arlington College of Engineering, said this research is representative of the University's role in fostering innovations that benefit the society,
such as creating energy-efficient green technologies for current and future generations.""Dr. Koh and his research team are developing real-world solutions to a critical global challenge of utilizing the energy efficiently
and developing energy-efficient electronic technology that will benefit us all every day, "Behbehani said.""We applaud Dr. Koh for the results of this research
and look forward to future innovations he will lead.""Usha Varshney, program director in the National Science Foundation's Directorate for Engineering,
which funded the research, said the research findings could be vast.""When implemented in transistors,
these research findings could potentially reduce energy consumption of electronic devices by more than 10 times compared to the present technology,
"Varshney said.""Personal electronic devices such as smart phones, ipads, etc. can last much longer before recharging."
"In addition to potential commercial applications, there are many military uses for the technology. Batteries weigh a lot, and less power consumption means reducing the battery weight of electronic equipment that soldiers are carrying,
which will enhance their combat capability. Other potential military applications include electronics for remote sensors, unmanned aerial vehicles and high-capacity computing in remote operations.
Future research could include identifying key elements that will allow electrons to be cooled even further.
The most important challenge of this future research is to keep the electron from gaining energy as it travels across device components.
This would require research into how energy-gaining pathways could be blocked effectively
#Molecular self-assembly controls graphene-edge configuration A research team headed by Prof. Patrick Han and Prof.
Taro Hitosugi at the Advanced Institute of Materials Research (AIMR), Tohoku University discovered a new bottom-up fabrication method that produces defect-free graphene nanoribbons (GNRS) with periodic zigzag-edge regions.
This method, which controls GNR growth direction and length distribution, is a stepping stone towards future graphene device fabrication by self-assembly.
Graphene, with its low dimensionality, high stability, high strength, and high charge-carrier mobility, promises to be a revolutionary material for making next-generation high-speed transistors.
Moreover graphene's properties are predicted to be directly controllable by its structure. For example, recent works have demonstrated that the bandgap of armchair GNRS is controlled by the ribbon width.
However, the property-tailoring capabilities of other edge conformations (e g.,, the zigzag edge is predicted by theory to have magnetic properties) have not been tested,
because their defect-free fabrication remains a major challenge.""Previous strategies in bottom-up molecular assemblies used inert substrates,
such as gold or silver, to give molecules a lot of freedom to diffuse and react on the surface,
and the determination of the property-tailoring effects of the GNR edges shown in this work.
#Engineers advance understanding of graphene's friction properties (Phys. org) An interdisciplinary team of engineers from the University of Pennsylvania has made a discovery regarding the surface properties of graphene the Nobel-prize winning material that consists of an atomically thin sheet
However on the nanoscale adding fluorine to graphene had been reported to vastly increase the friction experienced
The research was led by postdoctoral researcher Qunyang Li graduate student Xin-Zhou Liu and Robert Carpick professor and chair of the Department of Mechanical engineering and Applied Mechanics in Penn's School of engineering and Applied science.
They collaborated with Vivek Shenoy a professor in the Department of Materials science and engineering. The Penn contingent also worked with researchers from the Naval Research Laboratory and Brown University.
Besides its applications in circuitry and sensors graphene is of interest as a super-strong coating.
As components of mechanical and electrical systems get smaller they are increasingly susceptible to wear and tear. Made up of fewer atoms than their macroscale counterparts each atom is that much more important to the component's overall structure and function.
Teflon is fluorinated a carbon polymer so we thought fluorinated graphene might be like two-dimensional Teflon.
and are experts in producing samples of the material to specification. This meant we were able to systematically vary the degree of fluorination in our graphene samples
when we tested the friction of these different samples with an atomic force microscope an ultra-sensitive instrument that can measure nanonewton forces.
It turns out that by adding fluorine Liu said we're changing the energy corrugation landscape of the graphene.
which at the nanoscale can act like physical roughness in increasing friction. In fluorinated graphene the fluorine atoms do stick up out of the plane of carbon atoms
but the physical changes in height paled in comparison to the changes of local energy each fluorine atom produced.
At the nanoscale Carpick said friction isn't just determined by the placement of atoms
but also how much energy is in their bonds. Each fluorine atom has so much electronic charge that you get tall peaks
#Doped graphene nanoribbons with potential Graphene is a semiconductor when prepared as an ultra-narrow ribbon although the material is actually a conductive material.
Researchers from Empa and the Max Planck Institute for Polymer Research have developed now a new method to selectively dope graphene molecules with nitrogen atoms.
and undoped graphene pieces they were able to form heterojunctions in the nanoribbons thereby fulfilling a basic requirement for electronic current to flow in only one direction
and electricity it is transparent harder than diamond and extremely strong. But in order to use it to construct electronic switches a material must not only be an outstanding conductor it should also be switchable between on and off states.
This requires the presence of a so-called bandgap which enables semiconductors to be in an insulating state.
The problem however is that the bandgap in graphene is extremely small. Empa researchers from the nanotech@surfaces laboratory thus developed a method some time ago to synthesise a form of graphene with larger bandgaps by allowing ultra-narrow graphene nanoribbons to grow via molecular self-assembly.
Graphene nanoribbons made of differently doped segmentsthe researchers led by Roman Fasel have achieved now a new milestone by allowing graphene nanoribbons consisting of differently doped subsegments to grow.
Instead of always using the same pure carbon molecules they used additionally doped molecules molecules provided with foreign atoms in precisely defined positions in this case nitrogen.
The researchers have shown that these display similar properties to those of a classic p-n-junction
and negative charges across different regions of the semiconductor crystal thereby creating the basic structure allowing the development of many components used in the semiconductor industry.
and collaborators at Rensselaer Polytechnic institute The latter has a direct impact on the power yield of solar cells.
The researchers describe the corresponding heterojunctions in segmented graphene nanoribbons in the recently published issue of Nature Nanotechnology.
Transferring graphene nanoribbons onto other substratesin addition the scientists have solved another key issue for the integration of graphene nanotechnology into conventional semiconductor industry:
Fasel's team and colleagues at the Max-Planck-Institute for Polymer Research in Mainz have succeeded in showing that graphene nanoribbons can be transferred efficiently
Graphene is thus increasingly emerging as an interesting semiconductor material and a welcome addition to the omnipresent silicon.
The semiconducting graphene nanoribbons are particularly attractive as they allow smaller and thus more energy efficient and faster electronic components than silicon.
However the generalized use of graphene nanoribbons in the electronics sector is anticipated not in the near future due in part to scaling issues
and in part to the difficulty of replacing well-established conventional silicon-based electronics. Fasel estimates that it may still take about 10 to 15 years before the first electronic switch made of graphene nanoribbons can be used in a product.
In a second paper published in Nature Communications Pascal Ruffieux also from the Empa nanotech@surfaces laboratory
and his colleagues describe a possible use of graphene strips for instance in solar cells. Ruffieux and his team have noticed that particularly narrow graphene nanoribbons absorb visible light exceptionally well
and are therefore highly suitable for use as the absorber layer in organic solar cells. Compared to normal graphene
and electricity better than any other known materialas potential industrial uses that include flexible electronic displays, high-speed computing, stronger wind turbine blades,
and more-efficient solar cells, to name just a few under development. In the decade since Nobel laureates Konstantin Novoselov and Andre Geim proved the remarkable electronic and mechanical properties of graphene
"said Thomas E. Mallouk, Evan Pugh Professor of Chemistry, Physics, and Biochemistry and Molecular biology at Penn State.
In a paper first published online on Sept. 9 in the journal Nature Chemistry, Mallouk and colleagues at Penn State and the Research center for Exotic Nanocarbons at Shinshu University, Japan, describe a method called intercalation,
in which guest molecules or ions are inserted between the carbon layers of graphite to pull the single sheets apart.
The intercalation of graphite was achieved in 1841 but always with a strong oxidizing or reducing agent that damaged the desirable properties of the material.
One of the most widely used methods to intercalate graphite by oxidation was developed in 1999 by Nina Kovtyukhova, a research associate in Mallouk's lab. While studying other layered materials,
Mallouk asked Kovtyukhova to use her method, which requires a strong oxidizing agent and a mixture of acids,
to open up single layers of solid boron nitride, a compound with a structure similar to graphite.
Mallouk asked her to try a similar experiment without the oxidizing agent on graphite, but aware of the extensive literature saying that the oxidizing agent was required, Kovtyukhova balked."
If the reaction didn't work I would owe her $100, and if it did she would owe me $10.
I have the ten dollar bill on my wall with a nice Post-it note from Nina complimenting my chemical intuition."
"Mallouk believes the results of this new understanding of intercalation in boron nitride and graphene could apply to many other layered materials of interest to researchers in the Penn State Center for Two-dimensional and Layered Materials who are investigating
#Ultra-thin high-speed detector captures unprecedented range of light waves New research at the University of Maryland could lead to a generation of light detectors that can see below the surface of bodies walls and other objects.
Using the special properties of graphene a two-dimensional form of carbon that is only one atom thick a prototype detector is able to see an extraordinarily broad band of wavelengths.
A research paper about the new detector was published Sunday September 07 2014 in Nature Nanotechnology.
Lead author Xinghan Cai a University of Maryland physics graduate student said a detector like the researchers'prototype could find applications in emerging terahertz fields such as mobile communications medical imaging chemical sensing
and low frequencies fall between microwaves and infrared waves. The light in these terahertz wavelengths can pass through materials that we normally think of as opaque such as skin plastics clothing and cardboard.
It can also be used to identify chemical signatures that are emitted only in the terahertz range.
however in part because it is difficult to detect light waves in this Range in order to maintain sensitivity most detectors need to be kept extremely cold around 4 Kelvin or-452 degrees Fahrenheit.
Existing detectors that work at room temperature are bulky slow and prohibitively expensive. The new room temperature detector developed by the University of Maryland team
and colleagues at the U s. Naval Research Lab and Monash University Australia gets around these problems by using graphene a single layer of interconnected carbon atoms.
By utilizing the special properties of graphene the research team has been able to increase the speed
Using a new operating principle called the hot-electron photothermoelectric effect the research team created a device that is as sensitive as any existing room temperature detector in the terahertz range
and more than a million times faster says Michael Fuhrer professor of physics at the University of Maryland and Monash University Australia.
Graphene a sheet of pure carbon only one atom thick is suited uniquely to use in a terahertz detector
because when light is absorbed by the electrons suspended in the honeycomb lattice of the graphene they do not lose their heat to the lattice
but instead retain that energy. The concept behind the detector is simple says University of Maryland Physics Professor Dennis Drew.
Light is absorbed by the electrons in graphene which heat up but don't lose their energy easily.
So they remain hot while the carbon atomic lattice remains cold. These heated electrons escape the graphene through electrical leads much like steam escaping a tea kettle.
The prototype uses two electrical leads made of different metals which conduct electrons at different rates.
The speed and sensitivity of the room temperature detector presented in this research opens the door to future discoveries in this in-between zone.
New'T-ray'tech converts light to sound for weapons detection medical imaging More information: Sensitive Room-temperature Terahertz Detection via Photothermoelectric Effect in Graphene Xinghan Cai et al.
Nature Nanotechnology dx. doi. org/10.1038/nnano. 2014.18
#First graphene-based flexible display produced A flexible display incorporating graphene in its pixels'electronics has been demonstrated successfully by the Cambridge Graphene Centre and Plastic Logic,
the first time graphene has been used in a transistor-based flexible device. The partnership between the two organisations combines the graphene expertise of the Cambridge Graphene Centre (CGC),
with the transistor and display processing steps that Plastic Logic has developed already for flexible electronics.
This prototype is a first example of how the partnership will accelerate the commercial development of graphene,
and is a first step towards the wider implementation of graphene and graphene-like materials into flexible electronics.
and has the potential to revolutionise industries from healthcare to electronics. The new prototype is an active matrix electrophoretic display,
similar to the screens used in today's e readers, except it is made of flexible plastic instead of Glass in contrast to conventional displays, the pixel electronics,
or backplane, of this display includes a solution-processed graphene electrode, which replaces the sputtered metal electrode layer within Plastic Logic's conventional devices,
bringing product and process benefits. Graphene is more flexible than conventional ceramic alternatives like indium-tin oxide (ITO) and more transparent than metal films.
The ultra-flexible graphene layer may enable a wide range of products including foldable electronics. Graphene can also be processed from solution bringing inherent benefits of using more efficient printed
and roll-to-roll manufacturing approaches. The new 150 pixel per inch (150 ppi) backplane was made at low temperatures (less than 100°C) using Plastic Logic's Organic Thin Film Transistor (OTFT) technology.
The graphene electrode was deposited from solution and subsequently patterned with micron-scale features to complete the backplane.
For this prototype, the backplane was combined with an electrophoretic imaging film to create an ultra-low power and durable display.
Future demonstrations may incorporate liquid crystal (LCD) and organic light emitting diodes (OLED) technology to achieve full colour and video functionality.
Lightweight flexible active-matrix backplanes may also be used for sensors with novel digital medical imaging and gesture recognition applications already in development."
"We are happy to see our collaboration with Plastic Logic resulting in the first graphene-based electrophoretic display exploiting graphene in its pixels'electronics,
"said Professor Andrea Ferrari, Director of the Cambridge Graphene Centre.""This is a significant step forward to enable fully wearable and flexible devices.
This cements the Cambridge graphene technology cluster and shows how an effective academic-industrial partnership is key to help move graphene from the lab to the factory floor.""
""The potential of graphene is well-known, but industrial process engineering is required now to transition graphene from laboratories to industry,
"said Indro Mukerjee, CEO of Plastic Logic.""This demonstration puts Plastic Logic at the forefront of this development,
which will soon enable a new generation of ultra-flexible and even foldable electronics"This joint effort between Plastic Logic
and the CGC was boosted also recently by a grant from the UK Technology Strategy Board,
within the'realising the graphene revolution'initiative. This will target the realisation of an advanced, full colour, OELD based display within the next 12 months h
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