Scientists view the atomic structure of the crystal under the optical microscope

Scientists from the University of Sheffield have analysed the microscopic structure of widely used crystal materials for the first time to reveal their detailed atomic properties.

The experts from the University's Department of Physics and Astronomy have been able to shed new light on the inter-atomic bonding in semiconductor crystals using optical microscopy. Inter-atomic bonding is crucially important for crystal properties and, for example, can explain why the exact same carbon atoms can be a pencil lead and diamonds depending on the atomic structure.

Creating a technique similar to an MRI scanner, the team analysed the samples of several types of semiconductor quantum dots to show that the nature of the microscopic structure can be extracted by simply looking at the properties of the light emitted by the crystal.

Researchers placed samples containing semiconductor quantum dots under an optical microscope to analyse the light emitted which enabled them to investigate the magnetic coupling of different atoms – known as hyperfine interaction – and, for the first time, unexpectedly reveal the details of electronic band structure of crystals.

This is a considerable improvement compared to previous sophisticated techniques that require bombardment of the sample with X-rays or high-energy electrons.

Dr Evgeny Chekhovich, of the University of Sheffield who worked in the group of Dr Alexander Tartakovskii and in collaboration with a theorist Dr Mikhail Glazov from Ioffe Institute in St Petersburg, Russia, said: "Crystalline materials have a myriad of applications in modern technology, including a broad class of materials used as light emitters and detectors, computer chips, microwave sources and more."

Dr Chekhovich added: "The family of solid state materials is very large and used widely in modern technology. The way the atoms bond to each other and align inside the crystal largely defines the properties of the material: how well it can conduct heat and electrical current; whether it may be applied for light emission useful in lasers and LEDs or light absorption useful for solar cells; how robust its structure is and whether it may be good for making devices’ parts capable of operating for many thousands of hours.

"The effect of inter-atomic ordering, or microscopic structure of the crystal, on its properties is of great importance in material sciences. For example, it is well known that, depending on the nature of the inter-atomic bonding, the same carbon atoms can form completely different materials: graphite of a pencil lead and diamond."

Initially the team set out on a quest for a reliable hardware implementation of a qubit, a computing bit to be used in quantum computation, before their work took on a new and unexpected direction allowing them to gain new insights into microscopic internal structure of macroscopically large crystals.

The findings, which are published in the journal Nature Physics, also have long-reaching consequences for a large area of research related to quantum information processing.

Additional information The University of Sheffield

With nearly 25,000 students from 125 countries, the University of Sheffield is one of the UK’s leading and largest universities. A member of the Russell Group, it has a reputation for world-class teaching and research excellence across a wide range of disciplines. The University of Sheffield was named University of the Year in the Times Higher Education Awards 2011 for its exceptional performance in research, teaching, access and business performance. In addition, the University has won four Queen’s Anniversary Prizes (1998, 2000, 2002, and 2007). These prestigious awards recognise outstanding contributions by universities and colleges to the United Kingdom’s intellectual, economic, cultural and social life. Sheffield also boasts five Nobel Prize winners among former staff and students and many of its alumni have gone on to hold positions of great responsibility and influence around the world. The University’s research partners and clients include Boeing, Rolls-Royce, Unilever, Boots, AstraZeneca, GSK, ICI, Slazenger, and many more household names, as well as UK and overseas government agencies and charitable foundations. The University has well-established partnerships with a number of universities and major corporations, both in the UK and abroad. Its partnership with Leeds and York Universities in the White Rose Consortium has a combined research power greater than that of either Oxford or Cambridge.