#Controlling photoluminescence with silicon nanophotonics for better devices Silicon nanowires have a great deal of potential in future high-performance electronic sensing and energy devices.
Red photoluminescence has been reported in silicon nanowires but for many applications this hampers device performance. As Tsuyoshi Okuno from the University of Electro-Communications and his colleagues point out in a recent report
Although the photoluminescence mechanism is discussed often the condition of the appearance and the absence of the red photoluminescence is reported rarely.
Okuno and his colleagues fabricated silicon nanowire arrays by metal-assisted chemical etching an approach that is simple and cost-effective.
They deposited metal nanoparticles on a silicon wafer and etched nanowires using aqueous H2o2. Although the researchers did not have precise control over the nanowire morphology they did observe that higher concentrations of H2o2 led to thicker nanowires.
Photoluminescence studies did not reveal a link between photoluminescence and nanowire diameter or length alone but low aspect ratio nanowires exhibited red photoluminescence.
Further observations of the morphology identified silicon nanocrystals at the nanowire ends which was corroborated by Raman studies of single nanowires.
These nanocrystals disappear on annealing as does the red photoluminescence. The researchers attribute the red photoluminescence to defect states between nanocrystals and surrounding oxide and excitonic transitions.
As the researchers conclude in their report These results of Si nanowire arrays are believed to be useful for future optoelectronic and photovoltaic applications.
Explore further: Mixing silicon with other materials improves the diversity of nanoscale electronic devices More information:
Oda K. Nanai Y. Sato T. Kimura S. & Okuno T. Correlation between photoluminescence and structure in silicon nanowires fabricated by metal-assisted etching.
Physica Status Solidi A 211 (4) 848-855 (2014) DOI: 10.1002/pssa. 20133016 6
#World's smallest reference material is big plus for nanotechnology If it's true that good things come in small packages,
then the National Institute of Standards and Technology (NIST) can now make anyone working with nanoparticles very happy.
NIST recently issued Reference Material (RM) 8027, the smallest known reference material ever created for validating measurements of these man-made, ultrafine particles between 1 and 100 nanometers (billionths of a meter) in size.
RM 8027 consists of five hermetically sealed ampoules containing one milliliter of silicon nanoparticlesll certified to be close to 2 nanometers in diameteruspended in toluene.
To yield the appropriate sizes for the new RM the nanocrystals are etched from a silicon wafer,
separated using ultrasound and then stabilized within an organic shell. Particle size and chemical composition are determined by dynamic light scattering, analytical centrifugation, electron microscopy and inductively coupled plasma mass spectrometry (ICP-MS),
a powerful technique that can measure elements at concentrations as low as several parts per billion."
"For anyone working with nanomaterials at dimensions 5 nanometers or less, our well-characterized nanoparticles can ensure confidence that their measurements are accurate,
"says NIST research chemist Vytas Reipa, leader of the team that developed and qualified RM 8027.
Silicon nanoparticles such as those in RM 8027 are being studied as alternative semiconductor materials for next-generation photovoltaic solar cells and solid-state lighting,
and as a replacement for carbon in the cathodes of lithium batteries. Another potential application comes from the fact that silicon crystals at dimensions of 5 nanometers
or less fluoresce under ultraviolet light. Because of this property silicon nanoparticles may one day serve as easily detectable"tags"for tracking nanosized substances in biological, environmental or other dynamic systems s
#Self-organized indium arsenide quantum dots for solar cells Kouichi Yamaguchi is recognized internationally for his pioneering research on the fabrication and applications of'semiconducting quantum dots'(QDS.
We exploit the'self-organization'of semiconducting nanocrystals by the'Stranski-Krasnov (SK) mode of crystal growth for producing ordered highly dense
and highly uniform quantum dots explains Yamaguchi. Our'bottom-up'approach yields much better results than the conventional photolithographic
or'top-down'methods widely used for the fabrication of nanostructures. Notably electrons in quantum dot structures are confined inside nanometer sized three dimension boxes.
Novel applications of'quantum dots'including lasers biological markers qubits for quantum computing and photovoltaic devices arise from the unique optoelectronic properties of the QDS
when irradiated with light or under external electromagnetic fields. Our main interest in QDS is for the fabrication of high efficiency solar cells says Yamaguchi.
Step by step we have pushed the limits of'self-organization'based growth of QDS and succeeded in producing highly ordered ultra-high densities of QDS.
The realization of an unprecedented QDS density of 5 x 1011 cm-2 in 2011 was one of the major milestones in the development of'self-organization'based semiconducting QDS for solar cells by Yamaguchi
and his colleagues at the University of Electro-Communications (UEC. This density was one of the critical advances for achieving high efficiency quantum dot based photovoltaic devices says Yamaguchi.
Specifically Yamaguchi and his group used molecular beam epitaxy (MBE) to grow a layer of Inas QDS with a density of 5 x 1011 cm-2 on Gaassb/Gaas (100) substrates.
Importantly the breakthrough that yielded this high density of highly ordered QDS was the discovery that Inas growth at a relatively low substrate temperature of 470 degrees Celsius on Sb-irradiated Gaas layers suppressed coalescence
or'ripening'of Inas QDS that was observed at higher temperatures. Thus the combination of the Sb surfactant effect and lower growth temperature yielded Inas QDS with an average height of 2. 02.5 nm.
The potential for photovoltaic device applications was examined by sandwiching a single layer of Inas QDS in a pin-Gaas cell structure.
The resulting external quantum efficiency of these solar cell structures in the 900 to 1150 nm wavelength range was higher than devices with the QD layer.
Theoretical studies suggest QDS solar cells could yield conversion efficiencies over 50%explains Yamaguchi. This is a very challenging target
but we hope that our innovative approach will be an effective means of producing such QD based high performance solar cells.
We have achieved recently Inas QDS with a density of 1 x 1012 cm-2. Explore further:
Resonant energy transfer from quantum dots to graphene More information: Edes Saputra Jun Ohta Naoki Kakuda and Koichi Yamaguchi Self-Formation of In-Plane Ultrahigh-Density Inas Quantum dots on Gaassb/Gaas (001) Appl.
Phys. Express 5 125502 (2012. DOI: dx. doi. org/10.1143/APEX. 5. 125502 Katsuyoshi Sakamoto Yasunori Kondo Keisuke Uchida and Koichi Yamaguchi Quantum dot density dependence of power conversion
efficiency of intermediate-band solar cells J. Appl. Phys. 112 124515 (2012
#Magnetic field opens and closes nanovesicle Chemists and physicists of Radboud University managed to open and close nanovesicles using a magnet.
This process is repeatable and can be controlled remotely allowing targeted drug transport in the body for example.
Nanovesicles for transporting drugs to correct locations in the body-that's the idea. On 24 september chemists and physicists from Radboud University will publish results from a seminal intermediate step in Nature Communications:
they have managed to open the vesicles in a reversible process and close them using a magnet.
The nanovesicles look like minuscule indented balloons. It had already been possible to'load'them with a drug
and open them elsewhere. But this was done using a chemical process for example using osmosis. Researchers at the Nijmegen Institute for Molecules
They have stretched the walls of the vesicles by aligning the molecules in the wall using the strong magnets of the High Field magnet Laboratory (HFML.
Because the strength of the magnetic field is linked precisely to the size of the vesicles the deformation can be controlled more easily.
without the magnetic field the vesicles close and they open when the field is turned on. After switching the field off they return to a closed state.
if we could steer these rockets with magnetic fields but to our surprise the vesicles opened during those experiments.
and medicines then you could transport the vesicle by creating a small opening and only allow the fuel to get out.
They will also experiment with different types of wall molecules. Wilson:''The current bubbles are not suitable for use in the human body
We also hope to find materials for which the same effect occurs in a lower magnetic field-that of an MRI.
Then the technique could be used clinically with MRI SCANNERS. In any case the first step has been made we have demonstrated that the technique works.'
'Explore further: HFML sets world record with a new 38 tesla magnet More information: P. G. van Rhee R. S m. Rikken L. K. E. A. Abdelmohsen J. C. Maan R. J. M. Nolte J
. C. M. van Hest P. C. M. Christianen & D. A. Wilson. Polymersome magneto-valves for reversible capture and release of nanoparticles.
Nature Communications DOI: 10.1038/ncomms601 6
#Fabrication route improves the properties of aluminum-based nanocomposites One challenge in producing strong elastic
and hard-wearing nanocomposites is obtaining an even distribution of the nanoparticles in the metal matrix.
Now researchers at A*STAR have used a process known as friction stir processing (see image) to produce an evenly distributed mix of nanosized aluminum oxide (Al2o3) particles in aluminum.
Their technique is a viable new method for manufacturing nanocomposites and has exciting potential for the car space and defense industries.
Current powder metallurgy or liquid processing methods fail to achieve uniform processing says research leader Junfeng Guo who is from the A*STAR Singapore Institute of Manufacturing Technology.
Guo's team drilled hundreds of 1-millimeter-diameter holes into the surface of a thin sheet of an aluminum alloy.
They then injected a slurry of aluminum oxide nanoparticles into the holes and heated the sheet in an oven.
After cooling the sheet the team plunged a rotating tool into it this is the friction stir processing step.
Placing the nanoparticles in the sheet prior to the friction stir processing step significantly increased the concentration of nanoparticles in the composite.
The team used scanning electron microscopy to check two key properties that influence the strength of nanocomposites.
They first demonstrated that the nanoparticles were dispersed uniformly which means the material has no weak points.
or crystals of the aluminum matrix that recrystallized after being plasticized were extremely small; smaller aluminum matrix grains can flow past each other more smoothly than larger particles enhancing the strength of the material.
and without the Al2o3 nanoparticles the team showed that the nanoparticles contributed to the reduction in grain size.
The best nanoparticle distribution and smallest aluminum alloy grains were obtained after passing the rotating tool through the sheet four times.
The team then demonstrated that the composite made in this way had improved significantly hardness and tensile strength compared to untreated aluminum alloy sheets.
We plan to continue this research to further improve the mechanical and thermal properties as well as the wear resistance of the nanocomposites says Guo.
Eventually we aim to commercialize our technology to aid local industry. Explore further: Scientists use nanoparticles to control growth of materials More information:
Guo J. F. Liu J. Sun C. N. Maleksaeedi S. Bi G. et al. Effects of nano-Al2o3 particle addition on grain structure evolution and mechanical behaviour of friction-stir-processed Al.
Materials science and engineering: A 602 143 149 (2014) dx. doi. org/10.1016/j. msea. 2014.02.02 2
#Gold nanoparticles linked to single stranded-dna DNA create a simple but versatile genetic testing kit Tests for identifying genetic variations among individuals
which can be used to develop precisely targeted drug therapies are a current focus in the emerging field of pharmacogenomics.
A*STAR researchers have developed now and patented a customized and elegant nanoprobe for assessing sensitivity to the drug warfarin.
To develop the nanoprobe Jackie Ying at the A*STAR Institute of Bioengineering and Nanotechnology and co-workers in Singapore Taiwan and Japan devised a relatively simple procedure that uses standard laboratory equipment
and can be adapted easily for other genetic tests. Our method is faster more cost-effective
and more accurate than existing alternatives says Ying. Ying's method detects genetic variations known as single-nucleotide polymorphisms (SNPS) that differ in only a single-nucleotide building block of DNA.
In the case of warfarin#the most frequently prescribed anticoagulant#there are SNP differences in specific parts of the genome that indicate
whether a patient will tolerate the drug or suffer serious side effects. The researchers used gold nanoparticles attached to short sections of DNA that bind to specific complementary sequences of DNA through the base pairing that holds together double-stranded DNA.
These nanoprobes were exposed to fragments of DNA that had been cut out and amplified from a patient's genome.
The nanoprobes are initially pink due to surface plasmonic effects involving ripples of electric charge. When analyzed if the probes do not bind to the DNA fragments they aggregate
and become colorless on exposure to a salt solution. If they do bind to the target they will not aggregate
but will remain pink until heated to a'melting temperature'at which the base pairing is disrupted
and the genome fragments separate. For cases of partial complementarity#in which the fragments are mismatched by a single nucleotide#the melting temperature is lowered by an amount depending on the level of mismatch.
The system can also distinguish between homozygous genotypes (where a person caries the same SNP on each member of a pair of chromosomes)
and heterozygous genotypes (where a person carries different SNPS on each chromosome). The patented warfarin test kit is available for commercialization
and are validating assay kits for several other applications in pathogen detection pharmacogenomics and genetic disease screening.
Using gold nanoprobes to unlock your genetic profile More information: Zu Y. Tan M.-H. Chowbay B. Lee S. C. Yap H. et al.
Nanoprobe-based genetic testing. Nano Today 9 166#171 (2014. dx. doi. org/10.1016/j. nantod. 2014.04.00
#Researchers uncover properties in nanocomposite oxide ceramics for reactor fuel Nanocomposite oxide ceramics have potential uses as ferroelectrics fast ion conductors
A composite is a material containing grains or chunks of several different materials. In a nanocomposite the size of each of these grains is on the order of nanometers roughly 1000 times smaller than the width of a human hair.
In the context of nuclear energy composites have been proposed for the fuel itself as a way for example to improve the basic properties of the material such as the thermal conductivity.
It is the thermal conductivity that dictates how efficiently energy can be extracted from the fuel. Composites have also been created to store the by-products of the nuclear energy cycle nuclear waste where the different components of the composite can each store a different part of the waste.
However composites have much broader applications. The interfaces provide regions of unique electronic and ionic properties
and have been studied for enhance conductivity for applications related to batteries and fuel cells. Using simulations that explicitly account for the position of each atom within the material the Los alamos research team examined the interface between Srtio3
and Mgo demonstrating for the first time a strong dependence of the dislocation structure at oxide heterointerfaces on the termination chemistry.
Srtio3 can be viewed like a layer cake with alternating planes of Sro and Tio2. Thus in principle when matching Srtio3 with another material there is a choice as to
and radiation damage resistance of oxide nanocomposites by controlling the termination chemistry at the interface.
We believe that this discovery that the interface structure is sensitive to the chemistry of the interface will open the door for new research directions in oxide nanocomposites said Blas Uberuaga lead researcher on the effort.
Reactor fuel behavior better understood with phonon insights More information: The research is described in a paper out this week in Nature Communications Termination chemistry-driven dislocation structure at Srtio3/Mgo heterointerfaces s
#Enabling bendable optoelectronics devices: Gallium nitride micro-rods grown on graphene substrates Bendy light-emitting diode (LED) displays
and solar cells crafted with inorganic compound semiconductor micro-rods are moving one step closer to reality thanks to graphene and the work of a team of researchers in Korea.
Currently most flexible electronics and optoelectronics devices are fabricated using organic materials. But inorganic compound semiconductors such as gallium nitride (Gan) can provide plenty of advantages over organic materials for use in these devices#including superior optical electrical and mechanical properties.
One major obstacle that has prevented so far the use of inorganic compound semiconductors in these types of applications was the difficulty of growing them on flexible substrates.
In the journal APL Materials from AIP Publishing a team of Seoul National University (SNU) researchers led by Professor Gyu-Chul Yi describes their work growing Gan micro-rods
on graphene to create transferrable LEDS and enable the fabrication of bendable and stretchable devices.
Gan microstructures and nanostructures are garnering attention within the research community as light-emitting devices because of their variable-color light emission
and high-density integration properties explained Yi. When combined with graphene substrates these microstructures also show excellent tolerance for mechanical deformation.
Why choose graphene for substrates? Ultrathin graphene films consist of weakly bonded layers of hexagonally arranged carbon atoms held together by strong covalent bonds.
It's important to note that for the Gan micro-rod growth the very stable and inactive surface of graphene offers a small number of nucleation sites for Gan growth
To create the actual Gan microstructure LEDS on the graphene substrates the team uses a catalyst-free metal-organic chemical vapor deposition (MOCVD) process they developed back in 2002.
and reliability of Gan micro-rod LEDS fabricated on graphene to the test they found that the resulting flexible LEDS showed intense electroluminescence (EL)
and were reliable#there was no significant degradation in optical performance after 1000 bending cycles noted Kunook Chung the article's lead author and a graduate student in SNU's Physics department.
This represents a tremendous breakthrough for next-generation electronics and optoelectronics devices#enabling the use of large-scale and low-cost manufacturing processes.
By taking advantage of larger-sized graphene films hybrid heterostructures can be used to fabricate various electronics
and optoelectronics devices such as flexible and wearable LED displays for commercial use said Yi. Explore further:
Scientists grow a new challenger to graphene More information: Growth and characterizations of Gan micro-rods on graphene films for flexible light-emitting diodes by Kunook Chung Hyeonjun Beak Youngbin Tchoe Hongseok Oh Hyobin Yoo Miyoung Kim and Gyu
-Chul Yi APL Materials September 23 2014: scitation. aip. org/content/aip/#/9/10.1063/1. 489478 1
#Experts create unique nanoparticles for aerospace industry A development of three universities enables improved thermal and electronic properties on devices with nickel-titanium alloys.
Experts collaborated to produce nanoparticles made of a titanium-nickel alloy used in the development of thermal and electrical sensors that control the operation of high-tech devices such as those used in aerospace,
doctor for the Autonomous University of Nuevo León (UANL), Mexico. Federal Universities of Pernambuco and Campina Grande, both in Brazil, were responsible for obtaining physical media for the shape memory titanium-nickel metal alloy (with the ability to return to its original state after being deformed.
Meanwhile, the team at the UANL manufactured nanoparticles used in the sensors, and after a series of tests confirmed the effectiveness of the titanium-nickel as an electrical and thermal conductor.
With nanoparticles, they produced temperature-sensitive devices that transmit electrical energy to the system but do not cause overheating.
So when it finally reaches 50 degrees Celsius, the sensor stops dilating and enters a paused state;
minutes later, when its temperature and size return to normal it activates again to control the operation of valves,
Manufacturing methods of the alloys are very specific, so the Brazilian universities obtained them by vacuum melting the titanium to make it react with oxygen.
In general, this process is expensive, so the idea was to reduce costs. Then nanoparticles were obtained by thermal evaporation techniques where the molecular bonds of the metals degraded as a powder
and then collected individually. Besides generating nanoparticles for sensors, another goal of this proyect is to train high level human resources in the areas of metallurgy alloys with shape memory,
nanotechnology and improving infrastructure in order to impact scientific and technological production in both countries. Finally, to test the effectiveness of the material,
a special machine in which the sensors are located between two points of electrical contacts, electric power is applied
and removed for some time, whith the purpose of determining how long it takes to return to its original condition i
#Scientists grow a new challenger to graphene A team of researchers from the University of Southampton's Optoelectronics Research Centre (ORC) has developed a new way to fabricate a potential challenger to graphene.
Graphene a single layer of carbon atoms in a honeycomb lattice is increasingly being used in new electronic and mechanical applications such as transistors switches
and light sources thanks to the unprecedented properties it offers: very low electrical resistance high thermal conductivity and mechanically stretchable yet harder than diamond.
Now ORC researchers have developed molybdenum di-sulphide (Mos2) a similar material to graphene that shares many of its properties including extraordinary electronic conduction
and mechanical strength but made from a metal (in this case molybdenum combined with sulphur). This new class of thin metal/sulphide materials known as transition metal di-chalcogenides (TMDCS) has become an exciting complimentary material to graphene.
However unlike graphene TMDCS can also emit light allowing applications such as photodetectors and light emitting devices to be manufactured.
Until recently fabrication of TMDCS such as Mos2 has been difficult as most techniques produce only flakes typically just a few hundred square microns in area.
and related materials rather than just microscopic flakes as previously was the case greatly expands their promise for nanoelectronic and optoelectronic applications.
Dr Huang and his team published their findings in the latest issue of the journal Nanoscale.
They are currently working with several UK companies and universities as well as leading international centres at MIT and Nanyang Technological University (Singapore.
We welcome enquiries from universities and industry who wish to collaborate with us. Explore further:
#Nanotubes help healing hearts keep the beat (Phys. org) Carbon nanotubes serve as bridges that allow electrical signals to pass unhindered through new pediatric heart-defect patches invented at Rice university and Texas Children's Hospital.
A team led by bioengineer Jeffrey Jacot and chemical engineer and chemist Matteo Pasquali created the patches infused with conductive single-walled carbon nanotubes.
The patches are made of a sponge-like bioscaffold that contains microscopic pores and mimics the body's extracellular matrix.
The nanotubes overcome a limitation of current patches in which pore walls hinder the transfer of electrical signals between cardiomyocytes the heart muscle's beating cells
which take up residence in the patch and eventually replace it with new muscle. The work appears this month in the American Chemical Society journal ACS Nano.
The researchers said their invention could serve as a full-thickness patch to repair defects due to Tetralogy of fallot atrial and ventricular septal defects and other defects without the risk of inducing abnormal cardiac rhythms.
The original patches created by Jacot's lab consist primarily of hydrogel and chitosan a widely used material made from the shells of shrimp and other crustaceans.
The patch is attached to a polymer backbone that can hold a stitch and keep it in place to cover a hole in the heart.
That temporary loss of signal transduction results in arrhythmias. Nanotubes can fix that and Jacot who has a joint appointment at Rice
and Texas Children's took advantage of the surrounding collaborative research environment. This stemmed from talking with Dr. Pasquali's lab as well as interventional cardiologists in the Texas Medical center Jacot said.
We've been looking for a way to get better cell-to-cell communications and were concentrating on the speed of electrical conduction through the patch.
We thought nanotubes could be integrated easily. Nanotubes enhance the electrical coupling between cells that invade the patch helping them keep up with the heart's steady beat.
When cells first populate a patch their connections are compared immature with native tissue Jacot said.
The insulating scaffold can delay the cell-to-cell signal further but the nanotubes forge a path around the obstacles.
Jacot said the relatively low concentration of nanotubes 67 parts per million in the patches that tested best is key.
Earlier attempts to use nanotubes in heart patches employed much higher quantities and different methods of dispersing them.
Jacot's lab found a component they were already using in their patches#chitosan#keeps the nanotubes spread out.
Chitosan is amphiphilic meaning it has hydrophobic and hydrophilic portions so it can associate with nanotubes (which are hydrophobic)
and keep them from clumping. That's what allows us to use much lower concentrations than others have tried.
Because the toxicity of carbon nanotubes in biological applications remains an open question Pasquali said the fewer one uses the better.
We want to stay at the percolation threshold and get to it with the fewest nanotubes possible he said.
We can do this if we control dispersion well and use high-quality nanotubes. The patches start as a liquid.
When nanotubes are added the mixture is shaken through sonication to disperse the tubes which would otherwise clump due to Van der waals attraction.
Clumping may have been an issue for experiments that used higher nanotube concentrations Pasquali said. The material is spun in a centrifuge to eliminate stray clumps
and formed into thin fingernail-sized discs with a biodegradable polycaprolactone backbone that allows the patch to be sutured into place.
and for nutrients and waste to pass through. As a side benefit nanotubes also make the patches stronger and lower their tendency to swell
while providing a handle to precisely tune their rate of degradation giving hearts enough time to replace them with natural tissue Jacot said.
If there's a hole in the heart a patch has to take the full mechanical stress he said.
Pasquali noted that Rice's nanotechnology expertise and Texas Medical center membership offers great synergy. This is a good example of how it's much better for an application person like Dr. Jacot to work with experts who know how to handle nanotubes rather than trying to go solo as many do said he.
We end up with a much better control of the material. The converse is also true of course
and working with leaders in the biomedical field can really accelerate the path to adoption for these new materials.
Biocompatible Carbon nanotube#Chitosan Cardiac Scaffold Matching the Electrical conductivity of the Heart. Seokwon Pok Flavia Vitale Shannon L. Eichmann Omar M. Benavides Matteo Pasquali and Jeffrey G Jacot ACS Nano Just Accepted Manuscript DOI:
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