A*Star Modeling of Nanowire Transistors Shows that Quantum Effects Must Be Taken Into Account in Their Design

Silicon nanowires are a leading candidate for use in next-generation transistors because they allow for high densities and speeds, as well as low operating power. Numerical modeling is a key part of nanowire transistor design. However, the modeling of capacitance, an important transistor characteristic, has so far been based on semi-classical physics, rather than quantum physics.
Now, Sai Kong Chin of the A*STAR Institute of High Performance Computing and co-workers at A*STAR and the National University of Singapore have developed a rigorous two-dimensional quantum model of the ‘gate-all-around’ nanowire configuration, leading to a better match with experimental data and highlighting the importance of quantum effects1.

Fig. 1: A single nanowire connecting source and drain contacts is wrapped by a cylindrical gate, which controls its current.
Reproduced from Ref. 1 © 2009 IEEE

In nanowire transistors, the nanowire forms a channel through which current flow is controlled by a gate electrode (Fig. 1). The best control has been demonstrated for the gate-all-around configuration, in which the gate wraps around the nanowire. The degree of gate control is critical to transistor function, and is determined in part by the nanowire capacitance.
Accurate modeling of capacitance requires consideration of the quantum behavior of the wave-like electrons inside the nanowire, which Chin and co-workers accomplished by applying the Schrödinger–Poisson equation to the problem. They calculated the capacitance of the nanowire as a function of the gate electrode voltage, and compared the result to experimental measurements for nanowires of 9–10 nanometers in radius.
The capacitances calculated using semi-classical models were 10–20% higher than the experimental observations. The results of the quantum model, however, matched the experiments with good accuracy, demonstrating that quantum effects cannot be ignored at this size scale, serving to reduce the capacitance below what would be expected from purely geometric considerations. Furthermore, the quantum model properly reproduced variations in the capacitance that can be used to determine the energetic spectrum of states inside the nanowire, whereas semi-classical models could not.
The reduction of capacitance due to quantum effects complicates the design of future nanoscale devices. However, these effects give rise to a rich spectrum of states that may lead to new kinds of devices. In either case, modeling of this kind will prove useful. It may also be used in fields such as quantum liquids and strongly correlated systems, which are increasingly being studied as applications of nanowires.
 “Just as the ability to control and characterize two-dimensional electron gases in semiconductor heterostructures spurred advancement in mesoscopic physics in the past, I like to think that our effort in nanowires is part of a broader ‘sharpening of tools’ that may enable future breakthroughs,” says Chin.
The A*STAR affiliated authors in this highlight are from the Institute of High Performance Computing
Reference
  1. Chin, S.K., Ligatchev, V., Rustagi, S.C., Zhao, H., Samudra, G.S., Singh, N., Lo, G.Q. & Kwong, D.-L. Self-consistent Schrödinger–Poisson simulations on capacitance–voltage characteristics of silicon nanowire gate-all-around MOS devices with experimental comparisons. IEEE Transactions on Electron Devices 56, 2312–2318 (2009). | article

University of Western Ontario Developing Nanomaterials and Heat Treatments to Remediate Underground Contamination

University of Western Ontario is proposing underground using smoldering combustion, a slow burn similar to charcoal briquettes to clean contaminated soils.
Through a new Faculty of Engineering group called RESTORE (Research for Subsurface Transport and Remediation), this technology was recently patented to help clean up some of the hundreds of thousands of contaminated industrial and commercial land across North America, also known as brownfield sites.  

RESTORE researchers are also developing reactive nanometals for the remediation of source zone chlorinated solvents with a specific focus on clay permeable media systems.  Further the group is investigating the fate of engineered nanoparticles, including carbon nanotubes, in the subsurface.

Jason Gerhard, with fellow professors Denis O’Carroll, Jose Herrera and Clare Robinson, are moving out of the lab for several field trials this summer in the U.S. and Canada using STAR (Self-sustaining Treatment for Active Remediation).
  
“What we do is locate where the contaminants are in the subsurface and we start a very local and very small smoldering reaction.”
Gerhard speaking at the WORLDiscoveries Research Showcase Feb. 5 at the London Convention Centre, said, “Once that reaction starts it proceeds and can sustain itself, and will travel through the pathway of the contamination, destroying [it] as it goes.”
The process has the remarkable ability to be self-sustaining, self-tracking and once all contamination has been removed, is also self-terminating.
“It has some very unique properties and is a very exciting technology,” he says, noting late last year STAR received the 15th Lord Ezra Award for Innovation in Combustion Engineering from the U.K. Combustion Engineering Association.
With more than 30,000 brownfield sites across Canada, contamination is blocking re-development. These derelict locations hold excellent potential for redevelopment once cleaned up.
Through RESTORE, and with the help of more than two dozen graduate and post-doctoral students, innovative site remediation technologies are being developed to deal with hazardous industrial pollutants in soil and groundwater.
By using less energy, creating less waste, incurring less adverse environmental impact and being less expensive than current strategies, Gerhard is confident the process will reduce contamination and risk to human health.
“We’ve [humans] been making a mess for 80 to 100 years now and over the last 20 years we have been focusing on cleaning them up,” says Gerhard, Canada Research Chair in Environmental Restoration Technology.
“But for most of the major contaminants, we actually haven’t cleaned up perfectly – back to what the natural environment would have been – for one single site.”
Gerhard says many contaminants are highly resistant to natural dispersion and natural processes currently used to clean the sites. With $4.5 million in external funding, RESTORE is focused on “new and innovative technologies to help remediate some of the toughest, most difficult to clean up sites.”
“In engineering we are trying to find innovative ways to clean up these sites without bringing those contaminants to the surface and exposing people to those hazards to a further degree.”
Gerhard estimates that for every $1 spent restoring the environment, $4 will be returned to the economy through new revenue, redevelopment, new jobs, revitalization of urban communities and, most importantly, the health of Canadians.
Learn more about RESTORE ateng.uwo.ca/research/restore.

Yale University Scientists Synthesize New Category of Anti-Cancer Agents

Yale University scientists have streamlined the process for synthesizing a family of compounds with the potential to kill cancer and other diseased cells, and have found that they represent a unique category of anti-cancer agents. Their discovery appears in this week’s online edition of the Journal of the American Chemical Society.

Play video as one of the kinamycin compounds synthesized by Yale researchers destroys ovarian cancer cells (the spherical objects) in less than 48 hours in lab tests


Credit: Gil Mor


The team studied a family of compounds known as the kinamycins, which are naturally produced by bacteria during metabolism and are known for their potent toxicity. For years scientists have guessed that a core structure common to the different compounds within the group was responsible for this toxicity. Until now, chemists could not study the core structure because there was no simple way to create it in the laboratory.
Now the Yale team has developed a new method to recreate this structure that allows them to synthesize the kinamycins with much greater efficiency than previously possible. While scientists have produced kinamycins in the laboratory in the past, the Yale team was able to halve the number of steps required to go from simple, easily obtainable precursors to the complete molecule—from 24 down to 12.
“By shortening the synthesis we can now prepare these molecules in the quantities required for further studies, including animal studies and even clinical trials,” said Seth Herzon, assistant professor of chemistry and lead author of the study.
Working with researchers at the Yale School of Medicine and the Yale Chemical Genomics Screening Facility, the team has begun testing several of the compounds against cancer cells, with promising preliminary results. Next, they will work to understand the exact mechanism that makes the compounds—which are benign on their own—highly toxic once they penetrate cells.
“The key to success will be whether we can develop selectivity—whether we can kill cancer cells in the presence of non-cancerous tissue,” Herzon said. “Based on what we already know about the chemical reactivity of these molecules, I’m optimistic we can do this.”
The reactive core of the kinamycins also plays a key role in another compound the team is studying, called lomaiviticin A, which is even more toxic and could prove even more effective in destroying cancer cells. “Lomaiviticin A is the big fish. It’s more potent than the kinamycins, but it’s also much harder to synthesize,” Herzon said.
Both the kinamycins and lomaiviticin A are unique in their toxicity profiles, Herzon said, representing a new category of anti-cancer agents.
“There’s no close analogy to draw from to predict how these molecules will behave, which will make it especially interesting to see where this research takes us,” Herzon said. “This research involves a lot of exciting chemistry, but it also has real applications in biology and human medicine.”
Other authors of the study include Christina Woo, Liang Lu, Shivajirao Gholap and Devin Smith, all of Yale University.
Funding for this research was provided by Yale University and Eli Lilly.
DOI: 10.1021/ja910769j
PRESS CONTACT: Suzanne Taylor Muzzin 203-432-8555

Dakota County Technical College (DCTC) First College to Offer NanoProfessor Program-Enables 2 Year AAS Degree in Nanoscience

NanoProfessor, a division of NanoInk, Inc.® focused on nanotechnology education, has announced that its NanoProfessor Nanoscience Education Program is currently underway at Dakota County Technical College (DCTC), in Rosemount, MN.
Once completed, students enrolled in the DCTC program, will possess the knowledge and hands-on experience needed to pursue a career in the high-tech world of nanotechnology. DCTC offers a 2-year AAS Degree in Nanoscience and was the first 2-year technical college to offer a multi-disciplinary nanoscience AAS degree.
The NanoProfessor program will provide in depth experimental opportunities for students in the first semester of the program. Comparable hands-on nanotechnology education programs have traditionally only been available at large, prestigious 4-year universities with graduate programs.
“Nanotechnology is a growing aspect of virtually every industry in Minnesota, the U.S. and the world, and it will require a workforce that has a fundamental knowledge of nanotechnology and the hands-on skills to complete the nanotech-oriented jobs of today and the future. Exclusivity to an education in nanotechnology is not the answer,” said Deb Newberry, director of the Nanoscience Technology Program at DCTC. “Together with NanoProfessor, Dakota County Technical College is helping meet this demand by creating opportunities for our students that previously they could only dream about.”
The NanoProfessor program is divided into units alternating between classroom lectures and hands-on lab work. Topics covered include Nanotechnology Basics, NanoPhysics, NanoChemistry, NanoBiology, EHS issues, and the evolution of nanotechnology. During the hands-on lab-work, DCTC students are learning the fundamentals for making custom-engineered, nanoscale structures that are used for applications in the areas of consumer packaging, forensics, medicine and biotechnology.
 Students are using nanotechnology fabrication techniques such as Dip Pen Nanolithography® (DPN®) and working with state-of-art equipment including NanoInk’s NLP 2000 Desktop NanoFabrication System, an Atomic Force Microscope (AFM), an advanced Light Emitting Diode (LED) Fluorescence microscope, and various nano-scale materials used today by nanotechnology experts.
“I am excited to be part of the NanoProfessor Program at Dakota County Technical College, because the curriculum and lab-work are providing me with a great foundation to pursue a career in nanotechnology,” said Kelley McDonald, a student enrolled in DCTC’s AAS Degree program and participating in the NanoProfessor Nanoscience Education Pilot Program. “I’m also gaining valuable hands-on experience using the same equipment that many professionals are currently using, which will help make me more attractive to prospective employers.”
“In order for the United States to remain competitive in the global economy, we need to focus on innovations such as nanotechnology that will help create jobs,” said Dean Hart, executive vice president of NanoInk. “Just as importantly, we need a workforce that will be able to fill these nanotech-focused jobs. Deb Newberry and DCTC are true pioneers in educating and preparing the masses to help secure our Nation’s leadership and competitiveness in the promising field of nanotechnology and NanoProfessor is honored to be a part of their exciting program.”
By 2015, the National Science Foundation has projected that the world will require a skilled workforce of more than two million nanotechnologists. The field of nanotechnology is already pioneering breakthroughs and innovations in the areas of energy, medicine and electronics, which will have a profound impact on lives in the 21st century.
For more information on how the NanoProfessor Nanoscience Education Program can be implemented at your community college, technical school, high school or university, please call (847) 679-NANO (6266) or visit www.NanoProfessor.net.
About Dakota County Technical College (DCTC)
Dakota County Technical College is a public two-year institution of higher education dedicated to the philosophy that there is dignity in all work and value in individual growth and learning. It is the philosophy of the college that all of its students should have access to quality education that prepares them for rewarding careers. DCTC values its role in contributing to economic development by providing a knowledgeable and skilled workforce. The college views itself as a full partner in the higher education community and recognizes its contribution to lifelong learning. More information is available at http://www.dctc.mnscu.edu/index.cfm.
About the NanoProfessor™ Nanoscience Education Program
The NanoProfessor Nanoscience Education Program aims to advance the field of nanoscience and address the growing need for skilled workforce of nanotechnologists. The program utilizes NanoInk’s state-of-the-art NLP 2000 Desktop Nanofabrication System to provide students an interdisciplinary-focused, hands-on approach to quickly and easily build custom-engineered, nanoscale structures in a classroom setting. The NanoProfessor Program, including equipment and an expert-driven curriculum, is available for community colleges, technical schools, high schools and universities nationwide. More information is available at www.NanoProfessor.net.

Tutankhamun Not Murdered Say Scientists Using Genetic Techniques to Reveal Parentage and Illnesses of Ancient Boy King

A team of scientists working in Egypt has used state-of-the-art genetics techniques to reveal the parentage of the famous pharaoh Tutankhamun, the illnesses he suffered from and that he probably was not a victim of murder. The study’s findings are published in the Journal of the American Association (JAMA).

The world has had an enduring fascination with the ‘boy king’ Tutankhamun since his tomb was discovered by the British archaeologist, Howard Carter, in 1922. Questions about Tutankhamun’s short life, the identity of his parents and why he died so early have never been answered – until now.

The research study was led by Dr Zahi Hawass from the Supreme Council of Antiquities in Egypt. The scientists spent 2 years working in a DNA (deoxyribonucleic acid) laboratory in Cairo using the latest DNA research techniques to examine the genetic make-up of 16 mummies.

Their hard work finally paid off – they are now able to reveal that Tutankhamun’s father was the pharaoh Akhenaten, whose mummified body was discovered in a tomb at the Valley of the Kings on the west bank of the Nile. A mummy known as the ‘younger lady’ that was found in a nearby tomb with an older female appears to be boy-king’s mother.

This is the first time that scientists have been able to use extensive genetic, forensic and radiological tests on mummies. Professor Albert Zinc, a member of the research team, and an anthropologist at the Italy-based European Academy of Bozen/Bolzano (EURAC), said: ‘With this project we have opened up a completely new dimension in molecular and medical Egyptology.’

To trace Tutankhamun’s lineage, the scientists took bone tissue samples from 11 mummies related to the pharaoh as well as 5 unrelated ones. The painstaking task of extracting the bone samples, obtaining the DNA and compiling the genetic fingerprints took two years.

‘We repeated our analyses several times and replicated them independently in a second laboratory,’ said Dr Carsten Pusch from Tübingen University, Germany. ‘We did this in order to exclude any possible contamination, any mixing with modern DNA.’

The DNA from the mummies was surprisingly well preserved. The team speculates that the special embalming techniques that were reserved for the pharaohs and royalty were responsible for this.

The DNA enabled the scientists to trace Tutankhamun’s family back five generations and to reveal various illnesses that the king suffered from, including osteonecrosis in his left foot, a rare bone disease which would have made it difficult for him to walk. This discovery explains the number of walking sticks found in the king’s tomb.

Many theories have been posited for Tutankhamun’s early death including murder, but the research team revealed that it is likely that the king died of malaria. ‘Tutankhamun appears to have suffered from the most severe kind of malaria, malaria tropica,’ Dr Pusch pointed out. ‘This affliction, combined with the bone necrosis, may well have brought about his demise.’

Commenting on their work, Professor Zinc and Dr Pusch, both of whom are experts in the study of Egyptian mummies, said: ‘It was our good fortune to be able to carry out these unique experiments which have enabled us to solve the hundred-year-old mystery surrounding the lineage of the world famous pharaoh Tutankhamun. And we shall continue our research: Nefertiti will be our next project. We have moved our research on to a new and so far unexplored level!’

For more information, please visit:

Journal of the American Medical Association (JAMA): http://jama.ama-assn.org/

European Academy of Bozen/Bolzano (EURAC): http://www.eurac.edu/index

Tübingen University: http://www.uni-tuebingen.de/uni/qvr/e-30/m30-01.html