(Press-News.org) New York, NY--May 25, 2015--Under the direction of Latha Venkataraman, associate professor of applied physics at Columbia Engineering, researchers have designed a new technique to create a single-molecule diode, and, in doing so, they have developed molecular diodes that perform 50 times better than all prior designs. Venkataraman's group is the first to develop a single-molecule diode that may have real-world technological applications for nanoscale devices. Their paper, "Single-Molecule Diodes with High On-Off Ratios through Environmental Control," is published May 25 in Nature Nanotechnology.
"Our new approach created a single-molecule diode that has a high (>250) rectification and a high "on" current (~ 0.1 micro Amps)," says Venkataraman. "Constructing a device where the active elements are only a single molecule has long been a tantalizing dream in nanoscience. This goal, which has been the 'holy grail' of molecular electronics ever since its inception with Aviram and Ratner's 1974 seminal paper, represents the ultimate in functional miniaturization that can be achieved for an electronic device."
With electronic devices becoming smaller every day, the field of molecular electronics has become ever more critical in solving the problem of further miniaturization, and single molecules represent the limit of miniaturization. The idea of creating a single-molecule diode was suggested by Arieh Aviram and Mark Ratner who theorized in 1974 that a molecule could act as a rectifier, a one-way conductor of electric current. Researchers have since been exploring the charge-transport properties of molecules. They have shown that single-molecules attached to metal electrodes (single-molecule junctions) can be made to act as a variety of circuit elements, including resistors, switches, transistors, and, indeed, diodes. They have learned that it is possible to see quantum mechanical effects, such as interference, manifest in the conductance properties of molecular junctions.
Since a diode acts as an electricity valve, its structure needs to be asymmetric so that electricity flowing in one direction experiences a different environment than electricity flowing in the other direction. In order to develop a single-molecule diode, researchers have simply designed molecules that have asymmetric structures.
"While such asymmetric molecules do indeed display some diode-like properties, they are not effective," explains Brian Capozzi, a PhD student working with Venkataraman and lead author of the paper. "A well-designed diode should only allow current to flow in one direction--the 'on' direction--and it should allow a lot of current to flow in that direction. Asymmetric molecular designs have typically suffered from very low current flow in both 'on' and 'off' directions, and the ratio of current flow in the two has typically been low. Ideally, the ratio of 'on' current to 'off' current, the rectification ratio, should be very high."
In order to overcome the issues associated with asymmetric molecular design, Venkataraman and her colleagues--Chemistry Assistant Professor Luis Campos' group at Columbia and Jeffrey Neaton's group at the Molecular Foundry at UC Berkeley--focused on developing an asymmetry in the environment around the molecular junction. They created an environmental asymmetry through a rather simple method--they surrounded the active molecule with an ionic solution and used gold metal electrodes of different sizes to contact the molecule.
Their results achieved rectification ratios as high as 250: 50 times higher than earlier designs. The "on" current flow in their devices can be more than 0.1 microamps, which, Venkataraman notes, is a lot of current to be passing through a single-molecule. And, because this new technique is so easily implemented, it can be applied to all nanoscale devices of all types, including those that are made with graphene electrodes.
"It's amazing to be able to design a molecular circuit, using concepts from chemistry and physics, and have it do something functional," Venkataraman says. "The length scale is so small that quantum mechanical effects are absolutely a crucial aspect of the device. So it is truly a triumph to be able to create something that you will never be able to physically see and that behaves as intended."
She and her team are now working on understanding the fundamental physics behind their discovery, and trying to increase the rectification ratios they observed, using new molecular systems.
INFORMATION:
The study was funded by the National Science Foundation, the Department of Energy, and the Packard Foundation.
DALLAS, May 26, 2015 -- Drinking two or more alcoholic beverages daily may damage the heart of elderly people, according to research in the American Heart Association journal Circulation: Cardiovascular Imaging.
The study correlated weekly alcohol consumption among 4,466 people -- average age 76 -- to the size, structure and motion of various parts of the heart.
Researchers found:
The more people drank, the greater the subtle changes to the heart's structure and function.
Among men, drinking more than 14 alcoholic beverages weekly (heavy drinking) was linked with ...
DALLAS, May 26, 2015 - A vaccine may one day help lower blood pressure for up to six months, according to new research in the American Heart Association's journal Hypertension.
The study in rats may eventually provide a novel alternative to treat high blood pressure in people, who would not need to take a pill everyday.
"The potential of a vaccine for hypertension offers an innovative treatment that could be very effective for the control of non-compliance which is one of the major problems in the management of hypertensive patients," said Hironori Nakagami M.D., ...
A genetically engineered herpes virus can halt the progression of skin cancer by killing cancer cells and sparking the immune system into action against tumours, a landmark clinical trial has shown.
It is the first time that a phase III trial of viral immunotherapy has definitively shown benefit for patients with cancer.
The trial was led in the UK by researchers at The Institute of Cancer Research, London, and The Royal Marsden NHS Foundation Trust, and involved 64 research centres worldwide including the University of Oxford.
Researchers randomised 436 patients ...
BOSTON -- Carbon monoxide is known by many as a poisonous gas that causes brain injury and other neurological symptoms, including memory loss and confusion. But a new study led by investigators at Beth Israel Deaconess Medical Center (BIDMC) suggests the opposite may be true: When administered in small, carefully controlled amounts, carbon monoxide may actually protect the brain from damage following subarachnoid hemorrhage, a devastating stroke that results from bleeding in the brain.
Published online today in The Journal of Clinical Investigation (JCI), the new findings ...
WASHINGTON (May 26, 2015) -- The American College of Cardiology's National Cardiovascular Data Registry was the source of data for seven studies published in the first four months of 2015, including a study that identified possible overuse of anticoagulants in low-risk atrial fibrillation patients and research that found a relationship between operator experience and outcomes in certain patients after percutaneous coronary intervention or angioplasty.
CathPCI Registry Study Compares Outcomes of Sleep-Deprived vs. Non-Sleep-Deprived PCI Operators
Only a small number of ...
University of Florida researchers have identified a biomarker that shows the progression of Parkinson's disease in the brain, opening the door to better diagnosis and treatment of the degenerative disease.
By comparing brain images of Parkinson's patients to those of a control group over a year, an interdisciplinary team found that an area of the brain called the substania nigra changes as the disease advances. The findings provide the first MRI-based method to measure the disease's progression, which can inform treatment decisions and aid in identifying new therapies, ...
Seasonal influenza vaccination of children is likely to represent good short-term value for money in Thailand, according to a study published this week in PLOS Medicine. The study, led by Aronrag Meeyai of the Health Intervention and Technology Assessment Program and Mahidol University, Thailand, uses an age-structured model to estimate the health benefits and cost-effectiveness of flu vaccination among Thai children aged 2 to 17 years.
Many seasonal influenza vaccination programs target elderly people, who have the highest risk of dying as a result of an influenza infection. ...
Adherence to the Dietary Guidelines for Americans (DGA) is linked to lower death rates in a low-income population in southeastern US.
In a low-income population from the southeastern US, higher adherence to the Dietary Guidelines for Americans (DGA) was linked with 14%-23% lower mortality from cardiovascular disease, cancer, and other diseases, according to a study published by Wei Zheng and colleagues from Vanderbilt University, Nashville, USA, in this week's PLOS Medicine.
The researchers analyzed data from the Southern Community Cohort Study (SCCS), a study including ...
PITTSBURGH, May 26, 2015 - Researchers at the University of Pittsburgh School of Medicine have identified two new classes of RNAs that are closely associated with a protein known to be a prognostic biomarker for breast cancer and could play a role in progression of prostate cancer. Their findings were published in the June issue of the scientific journal RNA.
Levels of human Y-box binding protein 1 (YB-1), which is involved in many cellular functions, have been shown to correlate with drug resistance and poor patient outcomes in a variety of cancers. The observation that ...
CINCINNATI - Maxing out the inherently stressed nature of treatment-resistant breast cancer cells thwarts their adaptive ability to evolve genetic workarounds to treatment, a new study suggests.
Scientists from Cincinnati Children's Hospital Medical Center report their results May 26 in Science Signaling.
"We present an alternative generic strategy for cancer treatment, which is removing cancer cells' defenses against their own intrinsic stress," said Kakajan Komurov, PhD, lead author and a researcher at the Cancer and Blood Disease Institute at Cincinnati Children's. ...
