Scientists shed light on glowing materials

Research could lead to the development of enhanced bio-sensors for healthcare and more efficient solar cells and displays

2012-08-20

(Press-News.org) Researchers at King's College London, in collaboration with European research institutes ICFO (Barcelona) and AMOLF (Amsterdam), have succeeded in mapping how light behaves in complex photonic materials inspired by nature, like iridescent butterfly wings. Scientists have broken the limit of light resolution at the nanoscale and delivered a fundamental insight into how light and matter interact, which could lead to the development of enhanced bio-sensors for healthcare and more efficient solar cells and displays.

Optical measurements of light waves at the nanoscale have always been limited by the resolution of the optical microscope, but researchers were able to break this limit using a new technique which combines electronic excitation and optical detection, to explore the inside of a photonic crystal and study the confinement of light. Working with a spatial resolution of 30 nanometers, scientists examined the structures at a resolution more than ten times smaller than the diffraction limit for light, revealing a greater understanding of how light interacts with matter to create, for example, the visible iridescence phenomena observed in nature on the wings of butterflies.

Dr Riccardo Sapienza, from the Department of Physics at King's, said: 'We were thrilled in the lab to observe the finer details of the photonic crystals that were simply inaccessible before. This is very important as it allows scientists to test optical theories to a new level of accuracy, fully characterise new optical materials and test new optical devices.'

The collaborative research has been published in the journal Nature Materials.

The team constructed an artificial two-dimensional photonic crystal by etching a hexagonal pattern of holes in a very thin silicon nitride membrane. Photonic crystals are nanostructures in which two materials with different refractive indices are arranged in a regular pattern, giving rise to exotic optical properties. Natural photonic crystals can be found in certain species of butterflies, birds and beetles as well as in opal gemstones where they give rise to beautiful shimmering colours.

The photonic crystal inhibits light propagation for certain colours of light, which leads to strong reflection of those colours, as observed when such materials 'catch the light'. By leaving out one hole, a very small cavity can be defined where the surrounding crystal acts as a mirror for the light, making it possible to strongly confine it within a so-called 'crystal defect cavity'.

The scientists based their research methods on a technique used in geology, called cathodoluminescence, whereby a beam of electrons is generated by an electron gun and impacted on a luminescent material, causing the material to emit visible light. Professor Albert Polman and his group in AMOLF modified this technique to access nanophotonics materials. He said: 'In the past few years we have worked hard with several technicians and researchers to develop and refine this new instrument.'

Dr Sapienza said: 'Each time a single electron from the electron gun reaches the sample surface it generates a burst of light as if we had placed a fluorescent molecule at the impact location. Scanning the electron beam we can visualise the optical response of the nanostructure revealing features 10 times smaller than ever done before.'

Professor Niek van Hulst, ICFO, said: 'It is fascinating to finally have an immediate view of the light in all its colours inside a photonic crystal. For years we have been struggling with scanning near-field probes and positioning of nano-light-sources. Now the scanning e-beam provides a local broad-band dipolar light source that readily maps all localised fields inside a photonic crystal cavity.'

With major advances in nanofabrication techniques it has become possible to construct artificial photonic crystals with optical properties that can be accurately engineered. These structures can be used to make high-quality nanoscale optical waveguides and cavities, which are important in telecommunication and sensing applications.

Dr Sapienza said: 'Our research provides a fundamental insight into light at the nanoscale and, in particular, helps in understanding how light and matter interact. This is the key to advance nanophotonic science and it can be useful to design novel optical devices like enhanced bio-sensors for healthcare, more efficient solar cells and displays, or novel quantum optics and information technologies.'

### CONTACT Katherine Barnes
International PR Manager
King's College London
Tel: +44 207 848 3076
Email: katherine.barnes@kcl.ac.uk

NOTES TO EDITORS

AMOLF's full name is FOM Institute AMOLF and it is one of the research laboratories of the Foundation for Fundamental Research on Matter (FOM), part of the Netherlands Organisation for Scientific Research (NWO).

ICFO - the Institut de Ciències Fotòniques - was launched in March 2002 and is an independent, non-profit, permanent research centre established by the Generalitat de Catalunya (Government of Catalonia, Spain), Ministry of Economy and Knowledge and by the Universitat Politècnica de Catalunya. The ICFO's mission is to conduct wide-scope, basic and applied research in several branches of the Sciences and Technologies of Light, at the highest international level.

About King's College London (www.kcl.ac.uk)

King's College London is one of the top 30 universities in the world (2011/12 QS international world rankings), and was The Sunday Times 'University of the Year 2010/11', and the fourth oldest in England. A research-led university based in the heart of London, King's has more than 24,000 students (of whom more than 10,000 are graduate students) from nearly 140 countries, and more than 6,100 employees. King's is in the second phase of a £1 billion redevelopment programme which is transforming its estate.

King's has an outstanding reputation for providing world-class teaching and cutting-edge research. In the 2008 Research Assessment Exercise for British universities, 23 departments were ranked in the top quartile of British universities; over half of our academic staff work in departments that are in the top 10 per cent in the UK in their field and can thus be classed as world leading. The College is in the top seven UK universities for research earnings and has an overall annual income of nearly £525 million (year ending 31 July 2011).

King's has a particularly distinguished reputation in the humanities, law, the sciences (including a wide range of health areas such as psychiatry, medicine, nursing and dentistry) and social sciences including international affairs. It has played a major role in many of the advances that have shaped modern life, such as the discovery of the structure of DNA and research that led to the development of radio, television, mobile phones and radar. It is the largest centre for the education of healthcare professionals in Europe; no university has more Medical Research Council Centres.

The College is in the midst of a five-year, £500 million fundraising campaign – World questions|King's answers – created to address some of the most pressing challenges facing humanity as quickly as feasible. The campaign's three priority areas are neuroscience and mental health, leadership and society, and cancer. More information about the campaign is available at www.kcl.ac.uk/kingsanswers.

ELSE PRESS RELEASES FROM THIS DATE:

Imprisoned molecules 'quantum rattle' in their cages

2012-08-20

Scientists have discovered that a space inside a special type of carbon molecule can be used to imprison other smaller molecules such as hydrogen or water. The nano-metre sized cavity of the hollow spherical C60 Buckminsterfullerene — or bucky ball — effectively creates a 'nanolaboratory', allowing detailed study of the quantum mechanical principles that determine the motion of the caged molecule, including the mysterious wave-like behaviour that is a fundamental property of all matter. Experiments by the international collaboration of researchers, including physicists ...

HIV home testing kits prove their worth

2012-08-20

Thirty years into the HIV epidemic, many people who are at high risk of HIV infection cannot or will not adopt safer sexual practices, such as abstinence and condom use. This means there is room in the market for alternative methods to reduce either exposure to or transmission of HIV among these individuals. One such strategy, HIV home testing (HT), is the subject of a recent study by Alex Carballo-Dieguez and his colleagues at the HIV Center for Clinical and Behavioral Studies at New York. Their work appears online in the journal AIDS and Behavior published by Springer. A ...

Stanford/Intel study details power of new chip to diagnose disease, analyze protein interactions

2012-08-20

STANFORD, Calif. — Researchers at the Stanford University School of Medicine and Intel Corp. have collaborated to synthesize and study a grid-like array of short pieces of a disease-associated protein on silicon chips normally used in computer microprocessors. They used this chip, which was created through a process used to make semiconductors, to identify patients with a particularly severe form of the autoimmune disease lupus. Although the new technology is focused on research applications, it has the potential to eventually improve diagnoses of a multitude of diseases, ...

Spirituality correlates to better mental health regardless of religion, say MU researchers

2012-08-20

Despite differences in rituals and beliefs among the world's major religions, spirituality often enhances health regardless of a person's faith, according to University of Missouri researchers. The MU researchers believe that health care providers could take advantage of this correlation between health – particularly mental health – and spirituality by tailoring treatments and rehabilitation programs to accommodate an individual's spiritual inclinations. "In many ways, the results of our study support the idea that spirituality functions as a personality trait," said ...

American Indian spiritual beliefs influential in spurring youth to avoid drugs and alcohol

2012-08-20

DENVER — New research indicates that urban American Indian youth who follow American Indian traditional spiritual beliefs are less likely to use drugs and alcohol. Arizona State University social scientists will present their findings at the 107th Annual Meeting of the American Sociological Association. The study, "Spirituality and Religion: Intertwined Protective Factors for Substance Use Among Urban American Indian Youth," was recently published in The American Journal of Drug and Alcohol Abuse. The authors are: Stephen Kulis, the study's principal investigator and ...

Couch-potato kids are biggest child health problem in the US, adults say

2012-08-20

ANN ARBOR, Mich. – Adults across the U.S. rate not getting enough exercise as the top health concern for children in 2012, according to a new University of Michigan C.S. Mott Children's Hospital National Poll on Children's Health. In the poll's annual top 10 list, a nationwide sample of adults were asked to identify the top 10 biggest health concerns for kids in their communities. For the first time, not enough exercise was rated by most adults at the top of the list (39 percent). That was followed closely by childhood obesity (38 percent) and smoking and tobacco use ...

Anthrax targets

2012-08-20

A trawl of the genome of the deadly bacterium Bacillus anthracis has revealed a clutch of targets for new drugs to combat an epidemic of anthrax or a biological weapons attack. The targets are all proteins that are found in the bacteria but not in humans and are involved in diverse bacterial processes such as metabolism, cell wall synthesis and bacterial persistence. The discovery of a range of targets might bode well for creating a drug cocktail that could preclude the emergence of drug resistance. Ravi Gutlapalli of the Department of Biotechnology, at Acharya Nagarjuna ...

Ecologist: Genetically engineered algae for biofuel pose potential risks that should be studied

2012-08-20

COLUMBUS, Ohio - Algae are high on the genetic engineering agenda as a potential source for biofuel, and they should be subjected to independent studies of any environmental risks that could be linked to cultivating algae for this purpose, two prominent researchers say. Writing in the August 2012 issue of the journal BioScience, the researchers argue that ecology experts should be among scientists given independent authority and adequate funding to explore any potential unintended consequences of this technological pursuit. A critical baseline concern is whether genetically ...

Drink made from berry wine may provide tasty drug for diabetes

2012-08-20

URBANA – In evaluating the bioactive compounds of Illinois blueberry and blackberry wines, University of Illinois scientists have found compounds that inhibit enzymes responsible for carbohydrate absorption and assimilation. And that could mean a tasty way to help people with diabetes decrease their blood sugar. "We're thinking about a dealcoholized fermented fruit beverage that would optimize the inhibition of the alpha-amylase and alpha-glucosidase enzymes and also make use of the wines' other healthful bioactive components," said Elvira de Mejia, a U of I professor ...

Why do the Caribbean Islands arc?

2012-08-20

The Caribbean islands have been pushed east over the last 50 million years, driven by the movement of the Earth's viscous mantle against the more rooted South American continent, reveals new research by geophysicists from USC. The results, published today in Nature Geoscience, give us a better understanding of how continents resist the constant movement of the Earth's plates – and what effect the continental plates have on reshaping the surface of the Earth. "Studying the deep earth interior provides insights into how the Earth has evolved into its present form," said ...

Scientists shed light on glowing materials

ELSE PRESS RELEASES FROM THIS DATE:

LAST 30 PRESS RELEASES: