High pressure gold nanocrystal structure revealed

Public release date: 9-Apr-2013
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Contact: Clare Ryan
clare.ryan@ucl.ac.uk
44-020-310-83846
University College London

A major breakthrough in measuring the structure of nanomaterials under extremely high pressure has been made by researchers at the London Centre for Nanotechnology (LCN).

Described in Nature Communications, the study used new advances in x-ray diffraction to image the changes in morphology of gold nanocrystals under pressures of up to 6.5 gigapascals.

Under high pressures, imaging methods such as electron or atomic force microscopy are not viable, making x-ray diffraction imaging the only option. However, until recently, focusing an image created with this method has proved difficult.

Using a technique developed by LCN researchers to correct the distortions of the x-ray beams, the scientists, working in collaboration with the Carnegie Institution of Washington, have now been able to measure the structure of gold nanocrystals in higher resolution than ever before.

Professor Ian Robinson, who led the LCN's contribution to the study, said: "Solving the distortion problem of the x-ray diffraction images is analogous to prescribing eye glasses to correct vision.

"Now this problem has been solved, we can access the whole field of nanocrystal structures under pressure. The scientific mystery of why nanocrystals under pressure are up to 50% stronger than bulk material may soon be unravelled."

To carry out the research, a 400 nm diameter gold nanocrystal was put into a device called a Diamond-Anvil Cell (DAC) which can recreate the immense pressures which exist deep inside the Earth, creating materials and phases which do not exist under normal conditions.

The sample was crushed within the device and the changes were imaged as the pressure, measured by a small ruby sphere, was increased. The study showed that under low pressure, the nanocrystal acted as expected and the edges became strained, however, surprisingly, the strains disappeared under further compression.

The scientists explain this by suggesting that the pressurised material is undergoing "plastic flow", a phenomenon whereby a material will start to flow and become liquid once it reaches a critical pressure. This hypothesis was further supported when the faceted shape of the crystal developed a smoother and rounder shape as the pressure increased.

Professor Robinson added "This development has great potential for exploring the formation of minerals within the Earth's crust, which transform from one phase to another under pressure"

In the future, this technique offers a very promising approach for in-situ nanotechnology development under high pressures.

###

Notes to Editors

1. For more information or to speak to Dr Steven Schofield, please contact Clare Ryan in the UCL Media Relations Office on tel: 44-0-20-3108-3846, mobile: 44-07747-556-056, out of hours 44-0-7917-271-364, e-mail: clare.ryan@ucl.ac.uk

2. 'Coherent diffraction imaging of nanoscale strain evolution in a single crystal under high pressure' is published online in Nature Communications today. Please contact UCL Media Relations for a copy of the paper. DOI: 10.1038/ncomms2661

About UCL (University College London)

Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender and the first to provide systematic teaching of law, architecture and medicine.

We are among the world's top universities, as reflected by our performance in a range of international rankings and tables. According to the Thomson Scientific Citation Index, UCL is the second most highly cited European university and the 15th most highly cited in the world.

UCL has nearly 25,000 students from 150 countries and more than 9,000 employees, of whom one third are from outside the UK. The university is based in Bloomsbury in the heart of London, but also has two international campuses UCL Australia and UCL Qatar. Our annual income is more than 800 million.

http://www.ucl.ac.uk | Follow us on Twitter @uclnews | Watch our YouTube channel YouTube.com/UCLTV

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AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.

Public release date: 9-Apr-2013
[ | E-mail | Share ]

Contact: Clare Ryan
clare.ryan@ucl.ac.uk
44-020-310-83846
University College London

A major breakthrough in measuring the structure of nanomaterials under extremely high pressure has been made by researchers at the London Centre for Nanotechnology (LCN).

Described in Nature Communications, the study used new advances in x-ray diffraction to image the changes in morphology of gold nanocrystals under pressures of up to 6.5 gigapascals.

Under high pressures, imaging methods such as electron or atomic force microscopy are not viable, making x-ray diffraction imaging the only option. However, until recently, focusing an image created with this method has proved difficult.

Using a technique developed by LCN researchers to correct the distortions of the x-ray beams, the scientists, working in collaboration with the Carnegie Institution of Washington, have now been able to measure the structure of gold nanocrystals in higher resolution than ever before.

Professor Ian Robinson, who led the LCN's contribution to the study, said: "Solving the distortion problem of the x-ray diffraction images is analogous to prescribing eye glasses to correct vision.

"Now this problem has been solved, we can access the whole field of nanocrystal structures under pressure. The scientific mystery of why nanocrystals under pressure are up to 50% stronger than bulk material may soon be unravelled."

To carry out the research, a 400 nm diameter gold nanocrystal was put into a device called a Diamond-Anvil Cell (DAC) which can recreate the immense pressures which exist deep inside the Earth, creating materials and phases which do not exist under normal conditions.

The sample was crushed within the device and the changes were imaged as the pressure, measured by a small ruby sphere, was increased. The study showed that under low pressure, the nanocrystal acted as expected and the edges became strained, however, surprisingly, the strains disappeared under further compression.

The scientists explain this by suggesting that the pressurised material is undergoing "plastic flow", a phenomenon whereby a material will start to flow and become liquid once it reaches a critical pressure. This hypothesis was further supported when the faceted shape of the crystal developed a smoother and rounder shape as the pressure increased.

Professor Robinson added "This development has great potential for exploring the formation of minerals within the Earth's crust, which transform from one phase to another under pressure"

In the future, this technique offers a very promising approach for in-situ nanotechnology development under high pressures.

###

Notes to Editors

1. For more information or to speak to Dr Steven Schofield, please contact Clare Ryan in the UCL Media Relations Office on tel: 44-0-20-3108-3846, mobile: 44-07747-556-056, out of hours 44-0-7917-271-364, e-mail: clare.ryan@ucl.ac.uk

2. 'Coherent diffraction imaging of nanoscale strain evolution in a single crystal under high pressure' is published online in Nature Communications today. Please contact UCL Media Relations for a copy of the paper. DOI: 10.1038/ncomms2661

About UCL (University College London)

Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender and the first to provide systematic teaching of law, architecture and medicine.

We are among the world's top universities, as reflected by our performance in a range of international rankings and tables. According to the Thomson Scientific Citation Index, UCL is the second most highly cited European university and the 15th most highly cited in the world.

UCL has nearly 25,000 students from 150 countries and more than 9,000 employees, of whom one third are from outside the UK. The university is based in Bloomsbury in the heart of London, but also has two international campuses UCL Australia and UCL Qatar. Our annual income is more than 800 million.

http://www.ucl.ac.uk | Follow us on Twitter @uclnews | Watch our YouTube channel YouTube.com/UCLTV

---

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AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.

Source: http://www.eurekalert.org/pub_releases/2013-04/ucl-hpg040813.php

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