Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Direct electronic readout of 'artificial atoms'

28.02.2011
Bochum physicists are constructing 0-dimensional systems

Through his participation, the research team from Bochum, Duisburg-Essen, and Hamburg now has succeeded in an energy-state occupancy readout of those artificial atoms – using common interfaces to classic computers. This is a big step towards the application of such systems. They report about their findings in Nature Communications.

One million instead of individual atoms

In principle, the spin of electrons in individual atoms can be read-out, but the minuteness of the signals and the difficulty of localising individual atoms limit this technology to highly specialised laboratories. It requires an ultra-high vacuum and costly laser technology. 'It would be considerably more elegant to incorporate atom-like systems into solids,' said Prof. Wieck. In this case, quantum mechanics are helpful: For standard electron densities in semiconductors, the wavelength of electrons (and holes) is several tens of nanometres (nm), which means a distance of 100 atoms. It therefore is not necessary to isolate or insert individual atoms. It suffices to define areas that expand in each direction by about 100 atoms, thus comprising around 1003 = one million atoms. 'But even that is not all that simple, because today's high-level integration controls a resolution that reaches only down to around 50nm,' explained Prof. Wieck.

Trick: Stacking oranges on mandarins

Here is a little useful trick that relates to the inter-atomic distance in the crystal lattice: Electrons prefer residing in indium arsenide (InAs) than in gallium arsenide (GaAs). Since indium is a considerably larger atom than gallium, one can sonsider the compressive stress of an InAs layer on GaAs in the same way as when stacking oranges on top of mandarins. The first layer or oranges (InAs) is arranged so that the oranges on top of the mandarins (GaAs) are 'squeezed', which results in a 'strained' layer. The second orange (InAs) layer must be strained as well, but if several of such layers are placed on top of one another, the orange system 'forgets' its underlying mandarin layer order. The strain 'relaxes', which means it causes defects and gaps and piles up the oranges into individual heaps. Such InAs heaps – InAs quantum dots or 'QD' (derived from the English term 'Quantum Dots') – therefore grow in a self-organised way. They are several 10nm wide and around 5nm high, and therefore are ideally suited for the quantum mechanical charge carrier inclusion. It is just large enough to fit into a wavelength of electrons and/or electron holes. The QDs force the electrons into quantified energies by means of which they can be used as 'artificial atoms' for information processing purposes.

10 million times smaller than a hamburger

For several years now, the Bochum researchers have been producing the most homogenous QD 'ensembles': All produced QDs practically have the same size and, because of their flat bottom, resemble a 'hamburger' top, but are around 10 million times smaller. 'We place a few electrons into each QD of an QD ensemble comprising one million QDs, in which we start with the lightest, namely hydrogen, helium and lithium,' explained Prof. Wieck. So far, the energy levels containing these electrons have been read out only by means of optical methods. 'This may be very elegant, but requires an extensive measuring operation with specialised lasers, detectors and spectrometers', explained Wieck. During the actual work, the researchers adopted quite a different approach: They prepared the QDs on (close to) a conducting layer of electrons and only measured the electric resistance of this layer, which changes with the QD's electron occupation. 'Consequently, this gives us direct electronic access to the occupied states in the QDs and these are capable of being read with the common interfaces of classic computers.'

Title listing

B. Marquardt, M. Geller, B. Baxevanis, D. Pfannkuche, A. D. Wieck, D. Reuter, and A. Lorke: Transport spectroscopy of non-equilibrium many-particle spin states in self-assembled quantum dots. In: Nature Communications, 22.2.2011, doi: 10.1038/ncomms1205

Dr. Andreas Wieck | EurekAlert!
Further information:
http://www.rub.de

More articles from Physics and Astronomy:

nachricht Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst

nachricht Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>