Supersonic Electrons Could Produce Future Solar fuel


Artificial Fuels id39251

Researchers from institutions including Lund University have taken a step closer to producing solar fuel using artificial photosynthesis. In a new study, they have successfully tracked the electrons’ rapid transit through a light-converting molecule.
The ultimate aim of the present study is to find a way to make fuel from water using sunlight. This is what photosynthesis does all the time – plants convert water and carbon dioxide to energy rich molecules using sunlight. Researchers around the world are therefore attempting to borrow ideas from photosynthesis in order to find a way to produce solar fuel artificially.
electrons’ rapid transit through a light-converting molecule
Researchers from institutions including Lund University have taken a step closer to producing solar fuel using artificial photosynthesis. In a new study, they have successfully tracked the electrons’ rapid transit through a light-converting molecule. (Image courtesy of Lund University)
“Our study shows how it is possible to construct a molecule in which the conversion of light to chemical energy happens so fast that no energy is lost as heat. This means that all the energy in the light is stored in a molecule as chemical energy”, said Villy Sundström, Professor of Chemical Physics at Lund University.
Thus far, solar energy is harnessed in solar cells and solar thermal collectors. Solar cells convert solar energy to electricity and solar thermal collectors convert solar energy to heat. However, producing solar fuel, for example in the form of hydrogen gas or methanol, requires entirely different technology. The idea is that solar light can be used to extract electrons from water and use them to convert light energy to energy rich molecules, which are the constituent of the solar fuel.
“A device that can do this – a solar fuel cell – is a complicated machine with light-collecting molecules and catalysts”, said Villy Sundström.
In the present study, Professor Sundström and his colleagues have developed and studied a special molecule that can serve as a model for the type of chemical reactions that can be employed in a solar fuel cell. The molecule comprises two metal centres, one that collects the light and another that imitates the catalyst where the solar fuel is produced. The researchers have managed to track the path of the electrons through the molecule in great detail. They measured the time it took for an electron to cross the bridge between the two metal atoms in the molecule. It takes half a picosecond, or half a trillionth of a second.
“In everyday terms, this means that the electron flies through the molecule at a speed of around four kilometres a second, which is over ten times the speed of sound”, said Villy Sundström.
The researchers were surprised by the high speed. Another surprising discovery was that the speed appears to be highly dependent on the type of bridge between the atoms. In this study, the speed was 100 times higher than with another type of bridge tested.
“This is the first time anyone has managed to track such a complex and rapid reaction and to distinguish all the stages of the reaction”, said Villy Sundström about the study, which has been published in the journal Nature Communications (“Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses”).
The study is a collaboration between researchers from several departments at Lund University and from Denmark, Germany, Hungary, Japan and the USA. The measurements were performed in Japan at the SACLA X-ray FEL in Harima, Japan, one of only two operating X-ray free-electron lasers in the world.
Source: Lund University

Read more: Supersonic electrons could produce future solar fuel

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Research discovery could revolutionise semiconductor manufacture


28 November 2012

A completely new method of manufacturing the smallest structures in electronics could make their manufacture thousands of times quicker, allowing for cheaper semiconductors. The findings have been published in the latest issue of Nature.

Instead of starting from a silicon wafer or other substrate, as is usual today, researchers have made it possible for the structures to grow from freely suspended nanoparticles of gold in a flowing gas.

 

technologyImage: Aerotaxy production process

Behind the discovery is Lars Samuelson, Professor of Semiconductor Physics at Lund University, Sweden, and head of the University’s Nanometre Structure Consortium. He believes the technology will be ready for commercialisation in two to four years’ time. A prototype for solar cells is expected to be completed in two years.

 

“When I first suggested the idea of getting rid of the substrate, people around me said ‘you’re out of your mind, Lars; that would never work’. When we tested the principle in one of our converted ovens at 400°C, the results were better than we could have dreamt of”, he says.
“The basic idea was to let nanoparticles of gold serve as a substrate from which the semiconductors grow. This means that the accepted concepts really were turned upside down!”
Since then, the technology has been refined, patents have been obtained and further studies have been conducted. In the article in Nature, the researchers show how the growth can be controlled using temperature, time and the size of the gold nanoparticles.

Recently, they have also built a prototype machine with a specially built oven. Using a series of ovens, the researchers expect to be able to ‘bake’ the nanowires, as the structures are called, and thereby develop multiple variants, such as p-n diodes. A further advantage of the technology is avoiding the cost of expensive semiconductor wafers.
“In addition, the process is not only extremely quick, it is also continuous. Traditional manufacture of substrates is batch-based and is therefore much more time-consuming”, adds Lars Samuelson.
At the moment, the researchers are working to develop a good method to capture the nanowires and make them self-assemble in an ordered manner on a specific surface. This could be glass, steel or another material suited to the purpose. The reason why no one has tested this method before, in the view of Professor Samuelson, is that today’s method is so basic and obvious. Such things tend to be difficult to question.
However, the Lund researchers have a head start thanks to their parallel research based on an innovative method in the manufacture of nanowires on semiconductor wafers, known as epitaxy – consequently, the researchers have chosen to call the new method aerotaxy. Instead of sculpting structures out of silicon or another semiconductor material, the structures are instead allowed to develop, atomic layer by atomic layer, through controlled self-organisation.
The structures are referred to as nanowires or nanorods. The breakthrough for these semiconductor structures came in 2002 and research on them is primarily carried out at Lund, Berkeley and Harvard universities.
The Lund researchers specialise in developing the physical and electrical properties of the wires, which helps create better and more energy-saving solar cells, LEDs, batteries and other electrical equipment that is now an integrated part of our lives.
The article ‘Continuous gas-phase synthesis of nanowires with tuneable properties’ can be found by entering “I 10.1038/nature11652” here: http://dx.doi.org/.

Besides Lars Samuelson, the other authors of the article are: Magnus Heurlin, Martin Magnusson, David Lindgren, Martin Ek, Reine Wallenberg and Knut Deppert, all employed at Lund University, except for Martin Magnusson, who works at start-up company Sol Voltaics AB.

aerotaxy work group

 

 

 

 

 

 

 

The research has been funded by the Swedish Research Council, the Swedish Foundation for Strategic Research (SSF), the Knut and Alice Wallenberg Foundation and Vinnova.

For more information, contact Lars Samuelson,+46 46 222 76 79 , +46 703 17 76 79

Lars.Samuelson@ftf.lth.se.

Contact details for the other authors can be found by searching on www.lunduniversity.lu.se.

Lund University Nanometre Structure Consortium, nmC@LU: www.nano.lth.se.

About semiconductors Semiconductors are materials that neither conduct electricity as well as metals, nor stop a current as effectively as insulators – silicon and germanium are two examples. These properties may not sound attractive, but in actual fact they are excellent. The reason is that we can influence the conductive capacity of the materials, for example by introducing impurity atoms, known as doping. Materials with different types of doping can be combined to manufacture products such as transistors, solar cells or LEDs.