Tag Archives: F. Javier García de Abajo

Nanoparticles and strange forces

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An April 10, 2017 news item on Nanowerk announces work from the University of New Mexico (UNM), Note: A link has been removed,

A new scientific paper published, in part, by a University of New Mexico physicist is shedding light on a strange force impacting particles at the smallest level of the material world.

The discovery, published in Physical Review Letters (“Lateral Casimir Force on a Rotating Particle near a Planar Surface”), was made by an international team of researchers lead by UNM Assistant Professor Alejandro Manjavacas in the Department of Physics & Astronomy. Collaborators on the project include Francisco Rodríguez-Fortuño (King’s College London, U.K.), F. Javier García de Abajo (The Institute of Photonic Sciences, Spain) and Anatoly Zayats (King’s College London, U.K.).

An April 7,2017 UNM news release by Aaron Hill, which originated the news item, expands on the theme,

The findings relate to an area of theoretical nanophotonics and quantum theory known as the Casimir Effect, a measurable force that exists between objects inside a vacuum caused by the fluctuations of electromagnetic waves. When studied using classical physics, the vacuum would not produce any force on the objects. However, when looked at using quantum field theory, the vacuum is filled with photons, creating a small but potentially significant force on the objects.

“These studies are important because we are developing nanotechnologies where we’re getting into distances and sizes that are so small that these types of forces can dominate everything else,” said Manjavacas. “We know these Casimir forces exist, so, what we’re trying to do is figure out the overall impact they have very small particles.”

Manjavacas’ research expands on the Casimir effect by developing an analytical expression for the lateral Casimir force experienced by nanoparticles rotating near a flat surface.

Imagine a tiny sphere (nanoparticle) rotating over a surface. While the sphere slows down due to photons colliding with it, that rotation also causes the sphere to move in a lateral direction. In our physical world, friction between the sphere and the surface would be needed to achieve lateral movement. However, the nano-world does not follow the same set of rules, eliminating the need for contact between the sphere and the surface for movement to occur.

“The nanoparticle experiences a lateral force as if it were in contact with the surface, even though is actually separated from it,” said Manjavacas. “It’s a strange reaction but one that may prove to have significant impact for engineers.”

While the discovery may seem somewhat obscure, it is also extremely useful for researchers working in the always evolving nanotechnology industry. As part of their work, Manjavacas says they’ve also learned the direction of the force can be controlled by changing the distance between the particle and surface, an understanding that may help nanotech engineers develop better nanoscale objects for healthcare, computing or a variety of other areas.

For Manjavacas, the project and this latest publication are just another step forward in his research into these Casimir forces, which he has been studying throughout his scientific career. After receiving his Ph.D. from Complutense University of Madrid (UCM) in 2013, Manjavacas worked as a postdoctoral research fellow at Rice University before coming to UNM in 2015.

Currently, Manjavacas heads UNM’s Theoretical Nanophotonics research group, collaborating with scientists around the world and locally in New Mexico. In fact, Manjavacas credits Los Alamos National Laboratory Researcher Diego Dalvit, a leading expert on Casimir forces, for helping much of his work progress.

“If I had to name the person who knows the most about Casimir forces, I’d say it was him,” said Manjavacas. “He published a book that’s considered one of the big references on the topic. So, having him nearby and being able to collaborate with other UNM faculty is a big advantage for our research.”

Here’s a link to and a citation for the paper,

Lateral Casimir Force on a Rotating Particle near a Planar Surface by Alejandro Manjavacas, Francisco J. Rodríguez-Fortuño, F. Javier García de Abajo, and Anatoly V. Zayats. Phys. Rev. Lett. (Vol. 118, Iss. 13 — 31 March 2017) 118, 133605 DOI:https://doi.org/10.1103/PhysRevLett.118.133605 Published 31 March 2017

This paper is behind a paywall.

Nanodiamonds and a broken heart

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Nanowerk’s March 3, 2013 news item highlights some research with biomedical applications taking place in Australia,

Researchers at Macquarie University have been perfecting a technique that may help see nanodiamonds used in biomedical applications. PhD student Jana Say has been working on processing the raw diamonds so that they might be used as a tag for biological molecules.

“We are working with nanodiamonds to process them so that they are stable enough to be used as a probe for single-molecule interactions. As diamonds are made from carbon, they are non-toxic which makes them advantageous for many biological applications over other nanoparticles,” says Say.

The Macquarie University Feb. 13, 2013 news release, which originated the Nanowerk news item, provides more detail,

The processing technique has already contributed to the success of research projects that have used the diamonds. Working with an international team, Say’s diamonds were able to be optically trapped and manipulated in three-dimensions – this first time this has been achieved.

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The diamonds themselves are incredibly small, 5000 times smaller than a human hair, and so the real strength in Say’s technique is her ability to consistently produce stable samples.

“The real challenge is reliably producing the same sample. It’s a very repetitive and involved process to prepare and characterise these diamonds,” she says.

Say, under the supervision of Dr Louise Brown of the Department of Chemistry and Biomolecular Sciecnes, has plans to continue to develop these diamonds and collaborate with other researchers to explore their full potential.

“Jana’s work is incredibly important,” says Dr Brown. “These diamonds were recently used in a project which won a Macquarie University research excellence award for demonstrating that nanodiamonds can be isolated and made to emit light. With this work, we continue to make real breakthroughs in this area and are contributing to the long term goals in ultrasensitive imaging and sensing technologies.”

For anyone who’s interested, here’s a citation and link to the research paper,

Three-dimensional optical manipulation of a single electron spin by Michael Geiselmann, Mathieu L. Juan, Jan Renger, Jana M. Say, Louise J. Brown,  F. Javier García de Abajo, Frank Koppens & Romain Quidant. Nature Nanotechnology (2013) doi:10.1038/nnano.2012.259 Published online 10 February 2013

The article is behind a paywall. One final comment, I very much enjoyed the fanciful title for the news release about this work, Diamonds may mend a broken heart: Researchers perfect nanodiamonds for use in biomedical applications.