Molecular Electronics (2)

Lunchlecture VVTP by Jan van Ruitenbeek

Technical University Delft 15-1-2015

A smartphone or tablet that you can bend without breaking it? Large scale production of cheap solar cells? Electronic circuits of which the components are single molecules? These are the topics that concern Professor Jan van Ruitenbeek, who works at the Leiden Institute of Physics. Invited by the VVTP, he came to share some knowledge on Molecular Electronics, which is his main research area. Molecular Electronics is the field of research that deals with electronics made of organic molecules. It promises to be very useful in the future, mainly because organic components are cheaper and easier to manipulate than metal components. Before you can use organic molecules as a substitute of metal in electronics, you must first find a way to transform the generally insulating molecules into conducting molecules. The reason molecules (read: organic molecules, from now on) do not conduct electricity whereas metals do, is that they have a very large band gap. This means that there is a large difference of energy between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The reason metals conduct electricity so well, is that they have small band gaps and metal atoms are closely together, so that the electrons orbiting the metal nuclei can reach the conducting band quite easy and when this conducting band is reached, the higher energy electron can already interfere with neighboring molecules. Organic molecules however, do not have such an organized and closely packed structure as metals do, and together with the large bandgap, conduction of electricity is much more harder to induce. There are however two ways to overcome this problem, resulting in ways you can use organic molecules in electric circuits:

  • Use the large band gap
  • Reduce the large band gap

A beautiful example of using the large band gap is the realization of photovoltaic cells: solar cells containing organic molecules with high band gaps. In these solar cells, organic molecules absorb sunlight. This absorption of sunlight causes an electron to jump from the HOMO to the LUMO, and this allows the electron to transfer to an atom nearby that has a lower LUMO than the electron, and this means that a current is running.

It is also possible to reduce the large band gap. This can be done using a fairly simple technique, for which Alan Heeger, Alan MacDiarmind and Hideki Shirakawa received the 1977 Nobel Prize in Chemistry. It basically comes down to oxidising a chain of polyacetylene  with halogens resulting in a molecule that can conduct electricity as good as copper does! The principle is shown below.Conducting PolyacetyleneIn conclusion, Professor Ruitenbeek told us that our economy as well as our technology is going to be more and more based on light and light-based technologies. It is therefore that 2015 is declared international year of light. For those who are interested in what this means, please visit:

http://www.light2015.org/

I want to encourage you all to visit this website and see what the year of light can mean to you, and see what you can do.

Kasper Spoelstra – wkspoelstra@hotmail.nl

Quantum Entanglement and Teleportation

Seminar Department of Quantum Nanoscience by Ronald Hanson

Technical University Delft 14-1-2015

Of all the implications of today’s quantum theory, quantum entanglement might be one of the weirdest. The basic idea of quantum entanglement is that it is possible that two particles are in some way linked, without being close to each other. This implies that it is theoretically possible to have, for example, two electrons entangled, while holding them light-years apart from each other. The important and extremely weird feature of this entanglement is, that if you then measure the state of only one of the electrons, the state of the entangled electron is automatically determined. Using this, you could “send” information to the other end of the universe, in fact you could actually teleport information instantaneously through space! A physicist familiar with the concept of special relativity might now be concerned that Einstein’s second postulate* is violated, but that is in fact not the case, since the information has not travelled through the space in between the two entangled particles.

At the Department of Quantum Nanoscience TU Delft, the team of Ronald Hanson is investigating the technology associated with practical applications of this quantum teleportation. The Ronald Hanson lab was actually the first team in the world to teleport information between quantum bits of different computer chips. They did this over a distance of 3 meters, using diamonds that contained Nitrogen-Vacancy centers. These NVs are like atomic prisons in the diamond structure, containing an isolated Nitrogen atom and a lattice vacancy. In normal diamonds, these NVs would be imperfections, but they might come out perfect to us if we will learn to use them to our advantage, like the Hanson lab. An additional benefit to this great technology is that it happens with 100% certainty. This means that the information being sent is 100% sure to end up at the receiver (and nowhere else). One can only imagine in how many ways this technology can and will be exploited in future applications. One of the applications, that might not be as far away as we think right now, is a Quantum Computer. This is basically a computer that exists of bits that do not necessarily have the value 0 or 1, but have a blurry value in between. Together with Leo Kouwenhoven (from my last post), Ronald Hanson is taking important steps towards the future with this research.

For more and more detailed information about this specific research topic, see also:

[1] http://hansonlab.tudelft.nl/teleportation/

[2] http://phys.org/news/2014-05-team-accurately-teleported-quantum-ten.html

Kasper Spoelstra – wkspoelstra@hotmail.nl

* Einsteins second postulate says that the speed of light is the same in all inertial reference frames and that nothing can exceed the speed of light.

Molecular electronics

Speaker:      Jan van Ruitenbeek (Head of the Casimir Research Group and Professor of Experimental Physics, Leiden)

Subject:       Molecular Electronics

Location:    Lecture room TNW, TU Delft

Date:            Thursday, January, 13:45-14:45

Author: Jasper Veerman 

In the past 30 years, the sizes of electronic components have been reduced in size. From a few micrometer in size, more recent transistors have sizes in the order of nanometers.  This development creates interest in the future of these components: will it be possible to generate single molecules, properly functioning as diodes and transistors? Jan van Ruitenbeek spoke about a number of developments in the field of molecular electronics.

Currently, organic material is being studied for application in electrical components. Despite the high energy-gap often encountered in organic molecules, organic light emitting diodes (OLEDs)  allow for production of flexible displays. The above-mentioned energy-gap can also be used to generate organic conducting materials, like RF-ID chips for theft protection.

On a smaller scale, mechanically controlled break junctions provide a relatively simple means to experiment with single molecules as electrical components. In Figure 1 below, it can be seen that a wire, fixed to a plate, can be put under enough stress to break.

Figure 1
Figure 1: Mechanically controlled break junctions

The two tips – ends of the broken wire – are still very close. They can be brought so close, that only a single molecule can fit in between. If the black container is then filled with a solution, one of the molecules in the solution will fill the gap. The properties , f.e. conductance, of this single molecule can now be measured. This has been done numerous times, allowing for evaluation of interesting molecules to be implemented in future, single molecule electronics.

The professor also touched upon a last interesting experiment he is involved in. Looking at the scale researchers are starting to operate in, it is desired to build structures with the precision of a single atom. For this purpose, a low temperature scanning tunneling microscope (STM) was built. The tip of this microscope, only one atom in size, was used to drag individual gold atoms along a golden surface. The atoms could be placed anywhere with the help of a Wii-inspired controller, showing the promise of true sub-nanoscale engineering.