Tag Archives: Eva-Maria Roller

Light-based computation made better with silver

It’s pretty amazing to imagine a future where computers run on light but according to a May 16, 2017 news item on ScienceDaily the idea is not beyond the realms of possibility,

Tomorrow’s computers will run on light, and gold nanoparticle chains show much promise as light conductors. Now Ludwig-Maximilians-Universitaet (LMU) in Munich scientists have demonstrated how tiny spots of silver could markedly reduce energy consumption in light-based computation.

Today’s computers are faster and smaller than ever before. The latest generation of transistors will have structural features with dimensions of only 10 nanometers. If computers are to become even faster and at the same time more energy efficient at these minuscule scales, they will probably need to process information using light particles instead of electrons. This is referred to as “optical computing.”

The silver serves as a kind of intermediary between the gold particles while not dissipating energy. Capture: Liedl/Hohmann (NIM)

A March 15, 2017 LMU press release (also one EurekAlert), which originated the news item, describes a current use of light in telecommunications technology and this latest research breakthrough (the discrepancy in dates is likely due to when the paper was made available online versus in print),

Fiber-optic networks already use light to transport data over long distances at high speed and with minimum loss. The diameters of the thinnest cables, however, are in the micrometer range, as the light waves — with a wavelength of around one micrometer — must be able to oscillate unhindered. In order to process data on a micro- or even nanochip, an entirely new system is therefore required.

One possibility would be to conduct light signals via so-called plasmon oscillations. This involves a light particle (photon) exciting the electron cloud of a gold nanoparticle so that it starts oscillating. These waves then travel along a chain of nanoparticles at approximately 10% of the speed of light. This approach achieves two goals: nanometer-scale dimensions and enormous speed. What remains, however, is the energy consumption. In a chain composed purely of gold, this would be almost as high as in conventional transistors, due to the considerable heat development in the gold particles.

A tiny spot of silver

Tim Liedl, Professor of Physics at LMU and PI at the cluster of excellence Nanosystems Initiative Munich (NIM), together with colleagues from Ohio University, has now published an article in the journal Nature Physics, which describes how silver nanoparticles can significantly reduce the energy consumption. The physicists built a sort of miniature test track with a length of around 100 nanometers, composed of three nanoparticles: one gold nanoparticle at each end, with a silver nanoparticle right in the middle.

The silver serves as a kind of intermediary between the gold particles while not dissipating energy. To make the silver particle’s plasmon oscillate, more excitation energy is required than for gold. Therefore, the energy just flows “around” the silver particle. “Transport is mediated via the coupling of the electromagnetic fields around the so-called hot spots which are created between each of the two gold particles and the silver particle,” explains Tim Liedl. “This allows the energy to be transported with almost no loss, and on a femtosecond time scale.”

Textbook quantum model

The decisive precondition for the experiments was the fact that Tim Liedl and his colleagues are experts in the exquisitely exact placement of nanostructures. This is done by the DNA origami method, which allows different crystalline nanoparticles to be placed at precisely defined nanodistances from each other. Similar experiments had previously been conducted using conventional lithography techniques. However, these do not provide the required spatial precision, in particular where different types of metals are involved.

In parallel, the physicists simulated the experimental set-up on the computer – and had their results confirmed. In addition to classical electrodynamic simulations, Alexander Govorov, Professor of Physics at Ohio University, Athens, USA, was able to establish a simple quantum-mechanical model: “In this model, the classical and the quantum-mechanical pictures match very well, which makes it a potential example for the textbooks.”

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

Hotspot-mediated non-dissipative and ultrafast plasmon passage by Eva-Maria Roller, Lucas V. Besteiro, Claudia Pupp, Larousse Khosravi Khorashad, Alexander O. Govorov, & Tim Liedl. Nature Physics (2017) doi:10.1038/nphys4120 Published online 15 May 2017

This paper is behind a paywall.

A planet-satellite model for nanoparticles

For anyone who visualizes atoms as planets (many of us were taught to think of atoms and their electrons in that way) then, the planet-satellite model for nanoparticles proposed by scientists at the Nanosystems Initiative Munich (NIM) will have a comforting familiarity, Here’s the model as per a Dec. 13, 2013 news item from Nanowerk,

Nanosystems Initiative Munich (NIM) physicists have developed a “planet-satellite model” to precisely connect and arrange nanoparticles in three-dimensional structures. Like photosystems of plants and algae, the model might in future serve to collect and convert energy.

If the scientists‘ nanoparticles were one million times larger, the laboratory would look like an arts and crafts room at Christmas time: gold, silver and colorful shiny spheres in different sizes and filaments in various lengths. For at the center of the nanoscale “planet-satellite model” there is a gold particle which is orbited by other nanoparticles made of silver, cadmium selenide or organic dyes.

A Dec. 2, 2013 NIM press release, which originated the news item, describes the proposed model in detail,

As if by magic, cleverly designed DNA strands connect the satellites with the central planet in a very precise manner. The technique behind this, called “DNA origami”, is a specialty of physics professor Tim Liedl (LMU Munich) and his team. The expertise on the optical characterization of the individual nanosystems is contributed by Professor Jochen Feldmann, Chair of Photonics and Optoelectronics at LMU and Coordinator of the Nanosystems Initiative Munich (NIM).

Large or small, near or far

A distinctive feature of the new model is the modular assembly system which allows the scientists to modify all aspects of the structure very easily and in a controlled manner: the size of the central nanoparticle, the types and sizes of the “satellites” and the distance between planet and satellite particle. It also enables the physicists to adapt and optimize their system for other purposes.

Artificial photosystem

Metals, semiconductors or fluorescent organic molecules serve as satellites. Thus, like the antenna molecules in natural photosystems, such satellite elements might in future be organized to collect light energy and transfer it to a catalytic reaction center where it is converted into another form of energy. For the time being, however, the model allows the scientists to investigate basic physical effects such as the so-called quenching process, which refers to the changing fluorescence intensity of a dye molecule as a function of the distance to the central gold nanoparticle.

“The modular assembly principle and the high yield we obtained in the production of the planet-satellite systems were the crucial factors for reliably investigating this well-known effect with the new methods,” explains Robert Schreiber, lead author of the study.

A whole new cosmos

In addition, the scientists succeeded in joining individual planet-satellite units together into larger structures, combining them as desired. This way, it might be possible to develop complex and functional three-dimensional nanosystems in future, which could be used as directed energy funnels, in Raman spectroscopy or as nanoporous materials for catalytic applications.

The physicists have supplied an image illustrating their model,


[downloaded from http://www.nano-initiative-munich.de/index.php?eID=tx_cms_showpic&file=uploads%2Fpics%2FBasiccover_6_Zeilen_02.jpg&md5=aec790fc11262dc94b41a440fa6788baeacfac97&parameters[0]=YTo0OntzOjU6IndpZHRoIjtzOjQ6IjUwMG0iO3M6NjoiaGVpZ2h0IjtzOjM6IjUw&parameters[1]=MCI7czo3OiJib2R5VGFnIjtzOjI0OiI8Ym9keSBiZ0NvbG9yPSIjZmZmZmZmIj4i&parameters[2]=O3M6NDoid3JhcCI7czozNzoiPGEgaHJlZj0iamF2YXNjcmlwdDpjbG9zZSgpOyI%2B&parameters[3]=IHwgPC9hPiI7fQ%3D%3D] Courtesy NIM

[downloaded from http://www.nano-initiative-munich.de/index.php?eID=tx_cms_showpic&file=uploads%2Fpics%2FBasiccover_6_Zeilen_02.jpg&md5=aec790fc11262dc94b41a440fa6788baeacfac97&parameters[0]=YTo0OntzOjU6IndpZHRoIjtzOjQ6IjUwMG0iO3M6NjoiaGVpZ2h0IjtzOjM6IjUw&parameters[1]=MCI7czo3OiJib2R5VGFnIjtzOjI0OiI8Ym9keSBiZ0NvbG9yPSIjZmZmZmZmIj4i&parameters[2]=O3M6NDoid3JhcCI7czozNzoiPGEgaHJlZj0iamF2YXNjcmlwdDpjbG9zZSgpOyI%2B&parameters[3]=IHwgPC9hPiI7fQ%3D%3D] Courtesy NIM

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

Hierarchical assembly of metal nanoparticles, quantum dots and organic dyes using DNA origami scaffolds by Robert Schreiber, Jaekwon Do, Eva-Maria Roller, Tao Zhang, Verena J. Schüller, Philipp C. Nickels, Jochen Feldmann, & Tim Liedl. Nature Nanotechnology (2013) doi:10.1038/nnano.2013.253 Published online 01 December 2013

It is behind a paywall but you can preview it for free via ReadCube Access.