The researchers predict that a family of well-known silicon surfaces, stabilized by small amounts of gold atoms, is intrinsically magnetic despite having no magnetic elements. None of these surfaces has yet been investigated experimentally for magnetism, but the new predictions are already supported indirectly by existing data. The complete findings of the study are published in the August 24, 2010, issue of the journal Nature Communications.
Silicon provides a unique entry point for combining magnetoelectronics based on single spins with standard electronics technology. If a single-spin device can be built on a silicon wafer, input and output electronics can be directly integrated with the magnetic part of the device. This has been an obstacle for current spintronics approaches. For example, spin injection from a metal into silicon is very inefficient unless the metal/semiconductor interface is carefully optimized.
These latest results have the advantage that nature itself guides, by a self-assembly process, the formation of long chains of polarized electron spins with atomically precise structural order. "This integration of structural and magnetic order is crucial for future technologies based on single spins at the atomic level" said Dr. Steven Erwin, a physicist at NRL and lead theorist on the project.
The magnetic silicon surfaces, one of which is illustrated here, naturally form steps which are stabilized by chains of gold atoms (yellow). According to the team's calculations, some of the silicon atoms at the step edges have unpaired electrons that are fully spin polarized and probably magnetically ordered at sufficiently low temperatures.
The atom chains on the Si(553)-Au surface were discovered in the group of co-author Dr. Franz Himpsel at the University of Wisconsin-Madison. Several other groups worldwide have been investigating such "one-dimensional" silicon surfaces in recent years. As Himpsel noted, "The idea of creating magnetism in a nonmagnetic material by manipulating its structure has long intrigued scientists. The hope of realizing this idea in silicon has been widely discussed for decades, but so far none of these speculations has held up under scrutiny."
The work of Erwin and Himpsel suggests several experiments, such as spin-polarized scanning tunneling microscopy, to test their predictions directly. But there is already indirect experimental evidence to support the possibility of magnetism at silicon surfaces. Two research groups, at Yonsei University in Korea and at Oak Ridge National Laboratory in the US, have found that Si(553)-Au develops periodic "ripples" with two different periodicities at low temperatures. One ripple occurs along the silicon step edges with three times the normal periodicity, and the other along the gold chains with two times the normal periodicity. The prediction of Erwin and Himpsel, shown here, reproduces this pattern perfectly. Moreover, this pattern only emerges when magnetism is allowed in the calculation. When magnetism is "turned off" in the theory, the ripples completely vanish. Thus the observation of threefold and twofold ripples offers indirect - if preliminary - confirmation of magnetism.
Linear chains of spin-polarized atoms provide atomically perfect templates for the ultimate memory and logic, in which a single spin represents a bit. One potential application is a "spin shift register" recently proposed theoretically by Gerald D. Mahan, a theoretical physicist at Pennsylvania State University. Another application is the storage of information in single magnetic atoms. Erwin and Himpsel's work also predicts that the magnitude, and even the sign, of the spin coupling can be changed by doping electrons or holes into surface states. The closely related Si(111)-Au surface can be electron-doped by adsorbates (for example, silicon adatoms) on the surface. By varying this adsorbate population one can perform band-structure engineering with extraordinary precision. The possibility of tuning surface magnetism on Si(553)-Au and its relatives using surface chemistry suggests a fascinating new research direction. This work was supported by the Office of Naval Research and by National Science Foundation awards.
Donna McKinney | EurekAlert!
Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst
Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center
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...
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.
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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...
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...
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