Seoul National University Researchers Develop Graphene Solutions for Use with Photolithographic Techniques to Make Graphene Semiconductor Devices

Seoul National University (Seoul, KR) researchers have developed a method for manufacturing a graphene structure solution and a graphene semiconductor device using nano photolithographic techniques. A uniform graphene nanostructure solution is produced by applying anisotropic etching on multi-layered graphene using an oxide nanowire as a mask.
A graphene device is manufactured by dipping a substrate with a pattern of a molecule layer in a graphene nanostructure solution so that graphenes are aligned with the pattern on the substrate say inventors Biophysics and Chemical Biology, College of Natural Sciences  Professor Seunghun Hong and Koh Juntae in U.S. Patent 20100035186. The molecule layer pattern is formed by utilizing a photolithography process
Graphene shows stable characteristics and high electric mobility, and has accumulated considerable interest as a material for use in next generation semiconductor devices. However, in order to show semiconductor characteristics, the graphene is typically required to be formed as a channel having a nanoscale line width. This is because the graphene basically has a metallic characteristic.

Graphene nanostructures are typically synthesized in a form of a solution or powder. Therefore, in order to manufacture a device using a graphene nanostructure, a process of aligning a graphene nanostructure on a solid surface with a desired directivity is required.

Recently, in order to commercialize a device utilizing a graphene nanostructure, techniques for selectively adhering graphene nanostructures on a substrate at desired positions have been widely studied. Among them, a technique in which a solution with dispersed graphenes is spread on a silicon substrate so that graphenes may be adhered on the substrate is being studied.

However, when a nanoscale graphene device is manufactured using a graphene-dispersed solution according to conventional schemes, including the aforementioned schemes, it is difficult to fabricate devices having uniformly good characteristics since the nanostructure graphenes dispersed in the solution are not uniform in their widths. In addition, a technique that positions graphenes at desired positions for mass production has not yet been developed.

Techniques for manufacturing a graphene device and a graphene nanostructure solution were developed by Hong and Juntae to overcome the above problems. One of their methods of manufacturing a graphene nanostructure solution comprises: forming a target nanostructure on a multi-layered graphene; forming a multi-layered graphene nanostructure by performing anisotropic etching using the target nanostructure as a mask; and forming a solution having graphene nanostructures dispersed therein by dispersing the multi-layered graphene nanostructure in a dispersion solvent.
For a dispersion solvent o-dichlorobenzene is used. However, other materials such as 1,2-dichloroethane or poly(m-phenylenevinylene-co-2,5-dioctoxy-p-phenylenevinylene) may also be used as dispersion solvent.
A hydrophilic molecule layer may help adhesion of the graphene nanostructure to the substrate by increasing affinity between them. In further detail, graphene nanostructures may be adhered to the hydrophilic molecule layer by applying a positive voltage to the substrate after forming the hydrophilic molecule layer in the region where the graphene is adhered.  
Aminopropyltriethoxysilane (APTES), 3-mercaptopropyl trimethoxysilane (MPTMS), etc., may be used for the hydrophilic molecule layer.

As shown in FIGS. 1(A) and 1(B), an oxide nanowire (20) having a diameter of several nanometers is adhered on a multi-layered graphene (10)  utilizing a van der Waals force. In the present example embodiment, highly oriented pyrolytic graphite (HOPG) that is currently commercially available is used as the multi-layered graphene that includes a plurality of graphene layers (11). 

A a van der Waals force is utilized to attach the oxide nanowire (20) to the graphene (10). However, it is notable that the oxide nanowire may be adhered to the graphene in various other ways, for example by utilizing an electrostatic force. A vanadium oxide nanowire, by way of example, may be used as the oxide nanowire. FIG. 2 is a flowchart that shows a method of manufacturing a dispersion solution of graphene nanostructure.

International Team of Researchers Cure Osteoporosis in Mice and Rats

An international team led by researchers from Columbia University Medical Center was able to cure osteoporosis in mice and rats through a daily dose of an experimental compound that inhibits serotonin synthesis in the gut.
Recent research has already shown that serotonin in the gut stalls bone formation. This latest finding could lead to novel therapies that build new bone; most current osteoporosis drugs can only prevent the breakdown of old bone. The research results were published in the Feb. 7 issue of Nature Medicine.
“New therapies that inhibit the production of serotonin in the gut have the potential to become a novel class of drugs to be added to the therapeutic arsenal against osteoporosis,” said Gerard Karsenty, M.D., Ph.D., chair of the Department of Genetics and Development at Columbia UniversityCollege of Physicians and Surgeons, lead author of the paper.
Osteoporosis is a disease in which bones become fragile and porous, increasing the risk of breaks. It is diagnosed when bone mass drops below a certain level. It is a growing health concern that affects tens of millions of people worldwide given the aging population, and a particular issue for women because of the rising incidence of post-menopausal osteoporosis.
Bone constantly undergoes renovation, with some cells responsible for removing old material and other cells responsible for creating new bone. In humans, the balance between bone formation and breakdown tips toward breakdown after age 20, and bone mass starts to decline. The rate of decline for women increases after menopause, when estrogen levels drop and cells that tear down old bone become overactive.
“There is an urgent need for new treatments that not only stop bone loss, but also build new bone,” Karsenty said. “Using these findings, we are working hard to develop this type of treatment for human patients.”
The Nature Medicine paper follows on another major discovery by Karsenty’s group in 2008 (and published in the journal Cell) that serotonin released by the gut inhibits bone formation, and that regulating the production of serotonin within the gut affects the formation of bone. Prior to that discovery, serotonin was primarily known as a neurotransmitter acting in the brain. Yet, 95 percent of the body’s serotonin is found in the gut, where its major function is to inhibit bone formation.
Based on their findings reported in the Cell paper, the Karsenty team postulated that an inhibitor of serotonin synthesis should be an effective treatment for osteoporosis. Shortly thereafter, they read about an investigational drug, known as LP533401, which is able to inhibit serotonin in the gut. “When we learned of this compound, we thought that it was important to test it as proof of principle that there could be novel ways to treat osteoporosis with therapies that can be taken orally and regulate the formation of serotonin,” said Karsenty.
Karsenty and his team tested their theory by administering a small daily dose of the compound orally for up to six weeks to rodents experiencing post-menopausal osteoporosis. Results demonstrated that osteoporosis was prevented from developing, or if present, could be fully cured. Of critical importance, levels of serotonin were normal in the brain, which indicated that the compound did not enter the general circulation and did not cross the blood-brain barrier, thereby avoiding many potential side effects.
“There is an urgent need to identify new, safe therapies that can increase bone formation on a long term basis and to such an extent that they compensate for the increase in bone resorption caused by menopause,” said Karsenty. “Furthermore, it is important to note that since this study was conducted in rodents, it will need further confirmation in human subjects.”
This research was supported by grants from the National Institutes of Health and a Gideon and Sevgi Rodan fellowship from the International Bone and Mineral Society.
Co-authors on this paper include Vijay K. Yadav from the Department of Genetics and Development at Columbia University Medical Center (CUMC); Santhanam Balaji and Marc Vidal, Department of Genetics, Harvard Medical School; P.S. Suresh and R. Medhamurthy, Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, India; X. Sherry Liu, Xin Lu andEdward Guo, Department of Biomedical Engineering (Columbia); Zhishan Li and Michael D. Gershon, Department of Cell Biology (CUMC); J. John Mann, Department of Psychiatry (CUMC); Anil K. Balapure, Tissue and Cell Culture Unit, Central Drug Research Institute, India; and Patricia Ducy, Department of Pathology (CUMC).

German Team Treats Nanoparticle Surfaces to Achieve Organic Solar Cell Record 2% Efficiency with CdSe Quantum Dots

A German team of scientists has developed a technique to treat nanoparticle surfaces. This treatment boosts the efficiency of organic solar cells. Presented in the journal Applied Physics Letters, the work shows how 2% efficiency was obtained by using so-called quantum dots made up of cadmium selenide.

The researchers from the Institute of Microsystem Technology (IMTEK) and the Freiburg Materials Research Center (FMF), both at the University of Freiburg in Germany, succeeded in breaking the previously held efficiency ratings of between 1% to 1.8%. The method is protected by patent.

The ‘Dye and Organic Solar Cells’ research group at Fraunhofer Institute for Solar Energy Systems in Germany confirmed the measurements made by the Freiberg scientists.

According to the team, hybrid solar cells are protected by a layer containing a mixture of inorganic nanoparticles and an organic polymer. From a theoretical perspective, the new technique can be used on many nanoparticles, and could further fuel the efficiency of this type of solar cell.

Still in the developmental phase, organic solar cells are part of the third generation of solar cells, the scientists said. Latest data show that the world record for purely organic solar cells stands at 7% for layers created through wet chemical methods. The photoactive layer of these organic solar cells is made up of organic materials.

The energy market would benefit immensely from organic solar cell use. Energy producers commonly use conventional silicon cells, but solar cells are significantly thinner, more flexible, cheaper and quicker to produce.

The scientists said organic solar cells can be used to strengthen everyday devices and systems that are not used consistently including electrical appliances. Ultimately, organic solar cells could be used to significantly decrease people’s dependence on batteries and cables.

‘The interdisciplinary orientation of the group is a clear advantage and has led to rapid progress on the project,’ explained IMTEK’s Dr Michael Krüger, who led the group. ‘We were able to carry out all of the steps on our own: from the synthesis of the nanoparticles to the modification of their surface and integration into composite materials.’

The research group comprises physicists, chemists and engineers. They are currently applying the technique to other materials with a lot of potential so as to refine them further and get them ready for a technology market launch. Commercialisation of the technique is dependent on better efficiency, improved durability of the materials, and cheaper production costs.

For more information, please visit:

IMTEK:
http://www.imtek.de/

Freiburg Materials Research Center:
http://www.fmf.uni-freiburg.de/index_en.html

Nanolithographic Process Precisely Produces Reliable Quantum Dot Active Layers for LEDs at Lower Costs

The light emitting diode (LED) is a kind of semiconductor component. Compared to the general light bulb, the service life of the LED is longer than that  by 50 to 100 times; the power consumption of the LED is only 1/3.about.1/5 that of the general light bulb. Owing to the many advantages of LEDs as a lighting source, it will probably dominate the future lighting market. It will become a new lighting source with benefits in energy savings and environmental protection and will eventually replace conventional tungsten and mercury lighting sources in 21st century.  The world lighting market is believed to exceed $71 billion annually. 
Ming-Nung Lin (Pingtung City, Pingtung County, TW) garnered U.S. Patent 7,659,129 for an efficient method for manufacturing quantum dot active layers for LEDs by nano-lithography.”  Nano-lithography permits fabrication of new active layers of LEDs with a nano quantum dot structure in a more miniature, reliable and precise manner than that permitted by current fabrication methods.  The LEDs resulting from nano-lithography are high quality and feature longer light wavelengths, brighter luminance and lower forward bias voltage.   .
The dimensional size of each nano quantum dot and the respective distance among all the nano quantum dots can be completely controlled in 100% precise manner so that the performance and the optical properties are very stable.  The process can be further employed to create an effective and reliable montage effect as well as considerably improve various LED photoelectrical effects The fabrication method “is very valuable” in industrial applications,” says Lin.
Lin ‘s fabrication method for quantum dot active layer of LED by nano-lithography” includes  the process steps:
(a): Firstly, deposit a sealant of gas molecule or atom state on top-opening of a nano cylindrical pore on an epitaxy substrate so that the diameter of top-opening gradually reduce to become a reduced nano-aperture, whose opening diameter is smaller than that of the top-opening;
(b): Secondly, firmly place the epitaxy substrate on a tilt-rotary console having capability of 3-D tilt with rotation in horizontal direction and directly pass a deposit material of gas molecule or atom state perpendicularly through the reduced nano-aperture so that a nano quantum dot of nano structure with diameter being same as that of the reduced nano-aperture is directly formed on the surface of the epitaxy substrate, which being laid beneath the bottom of the nano cylindrical pore;
 (c): Thirdly, tilt rightwards the epitaxy substrate together with the tilt-rotary console in a right tilt angle by the reduced nano-aperture as center and re-pass the deposit material of gas molecule or atom state through the reduced nano-aperture in same direction as the previous direction so that another nano quantum dot of nano structure with diameter being same as that of the reduced nano-aperture is directly formed on the surface of the epitaxy substrate with position at right side of the previous nano quantum dot;
d): Fourthly, tilt leftwards the epitaxy substrate together with the tilt-rotary console in a left tilt angle by the reduced nano-aperture as center and re-pass the deposit material of gas molecule or atom state through the reduced nano-aperture in same direction as the previous direction so that another nano quantum dot of nano structure with diameter being same as that of the reduced nano-aperture is directly formed on the surface of the epitaxy substrate with position at left side of the previous nano quantum dot;
 (e): Fifthly, properly rotate the epitaxy substrate together with the tilt-rotary console in a rotation angle by the reduced nano-aperture as center and re-pass the deposit material of gas molecule or atom state through the reduced nano-aperture in same direction as the previous direction so that a further nano quantum dot of nano structure with diameter being same as that of the reduced nano-aperture is directly formed on the surface of the epitaxy substrate with position at front side of the previous nano quantum dot;
(f): Finally, by means of solution rinsing (i.e. wet etching) or gas etching (i.e. dry etching), remove all the nano cylindrical pores on the epitaxy substrate, many active layers of nano quantum dots in same dimension for the LED are fabricated on the epitaxy substrate in high density and even distribution manner.

Arizona State University Scientists Develop Faster and Cheaper Way to Read the DNA Genetic Code

Arizona State University scientists have come up with a new twist in their efforts to develop a faster and cheaper way to read the DNA genetic code. They have developed the first, versatile DNA reader that can discriminate between DNA’s four core chemical components, the key to unlocking the vital code behind human heredity and health.
Led by ASU Regents’ Professor Stuart Lindsay, director of the Biodesign Institute’s Center for Single Molecule Biophysics, the ASU team is one of a handful that has received stimulus funds for a National Human Genome Research Initiative, part of the National Institutes of Health, to make DNA genome sequencing as widespread as a routine medical checkup.
The broad goal of this “$1000 genome” initiative is to develop a next-generation DNA sequencing technology to usher in the age of personalized medicine, where knowledge of an individual’s complete, 3 billion-long code of DNA information, or genome, will allow for a more tailored approach to disease diagnosis and treatment. With current technologies taking almost a year to complete at a cost of several hundreds of thousands of dollars, less than 20 individuals on the planet have had their whole genomes sequenced to date.
Figure: As a single chemical base of DNA (blue atoms) passes through a tiny, 2.5nm gap between two gold electrodes (top and bottom), it momentarily sticks to the electrodes (purple bonds) and a small increase in the current is detected. Each of the chemical bases of the DNA genetic code, abbreviated A, C, T or G, gives a unique electrical signature as they pass between the electrodes
.Image Credit: Biodesign Institute at Arizona State University
To make their research dream a reality, Lindsay’s team has envisioned building a tiny, nanoscale DNA reader that could work like a supermarket checkout scanner, distinguishing between the four chemical letters of the DNA genetic code, abbreviated by A, G, C, and T, as they rapidly pass by the reader. To do so, they needed to develop the nanotechnology equivalent of threading the eye of a needle. In this case, the DNA would be the thread that could be recognized as it moved past the reader ‘eye.’ During the past few years, Lindsay’s team has made steady progress, and first demonstrated the ability to read individual DNA sequences in 2008—but this approach was limited because they had to use four separate readers to recognize each of the DNA bases. More recently, they demonstrated the ability to thread DNA sequences through the narrow hole of a fundamental building block of nanotechnology, the carbon nanotube.
Lindsay’s team relies on the eyes of nanotechnology, scanning tunneling- (STM) and atomic force- (ATM) microscopes, to make their measurements. The microscopes have a delicate electrode tip that is held very close to the DNA sample. In their latest innovation, Lindsay’s team made two electrodes, one on the end of microscope probe, and another on the surface, that had their tiny ends chemically modified to attract and catch the DNA between a gap like a pair of chemical tweezers. The gap between these functionalized electrodes had to be adjusted to find the chemical bonding sweet spot, so that when a single chemical base of DNA passed through a tiny, 2.5 nanometer gap between two gold electrodes, it momentarily sticks to the electrodes and a small increase in the current is detected. Any smaller, and the molecules would be able to bind in many configurations, confusing the readout, any bigger and smaller bases would not be detected.
What we did was to narrow the number of types of bound configurations to just one per DNA base,” said Lindsay. “The beauty of the approach is that all the four bases just fit the 2.5 nanometer gap, so it is one size fits all, but only just so!”
At this scale, which is just a few atomic diameters wide, quantum phenomena are at play where the electrons can actually leak from one electrode to the other, tunneling through the DNA bases in the process. Each of the chemical bases of the DNA genetic code, abbreviated A, C, T or G, gives a unique electrical signature as they pass between the gap in the electrodes. By trial and error, and a bit of serendipity, they discovered that just a single chemical modification to both electrodes could distinguish between all 4 DNA bases.
“We’ve now made a generic DNA sequence reader and are the first group to report the detection of all 4 DNA bases in one tunnel gap,” said Lindsay. “Also, the control experiments show that there is a certain (poor) level of discrimination with even bare electrodes (the control experiments) and this is in itself, a first too.”
“We were quite surprised about binding to bare electrodes because, like many physicists, we had always assumed that the bases would just tumble through. But actually, any surface chemist will tell you that the bases have weak chemical interactions with metal surfaces.”
Next, Lindsay’s group is hard at work trying to adapt the reader to work in water-based solutions, a critically practical step for DNA sequencing applications. Also, the team would like to combine the reader capabilities with the carbon nanotube technology to work on reading short stretches of DNA.
If the process can be perfected, DNA sequencing could be performed much faster than current technology, and at a fraction of the cost. Only then will the promise of personalized medicine reach a mass audience.
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The authors on the Nano Letters paper are: Shuai Chang, Shuo Huang, Jin He, Feng Liang, Peiming Zhang, Shengqing Li, Xiang Chen, Otto Sankey and Stuart Lindsay
The Nano Letters research article can be accessed online at URL: http://pubs.acs.org/doi/pdfplus/10.1021/nl1001185
(open sponsored access)