Si nanowires are magnetic: New materials for Spintronics

Taiwan scientists first discovered ferromagnetism at room temperature in Si nanowires with ion implants. Lih Chen's team and colleagues at the National University of Qinghua (Taiwan) have successfully built this material and can reach applications for nanoscale spintronics technology - technology to harness the spin of electricity. death.

Mn-implanted silicon also known as magnetic dilute semiconductor combines magnetic transport properties of semiconductors and memory properties of magnetic materials. They play an extremely important role in the development of spin-controlled electronic components and magnetic components. Indeed, a team of researchers conducted on III-V semiconductors (compounds A3B5) and II-VI (A2B6) showed that they could be used as spin-sort materials in emitting diodes optical optical spin. These results lead to the search for magnetic diluted semiconductors based on Class IV substances that have a high Curie temperature (Curie temperature at which the temperature of ferromagnetism disappears) because they are very compatible. Technical side with existing integrated circuits.

Si is a class IV substance in the periodic table, which is one of the most important semiconductors and Si-based components have dominated most integrated circuits over the past few decades. The researchers also know that Si with additional Mn or Co ions can produce ferromagnetism at room temperature, but this is the first time this property has been observed on additional nanowires.

Figure 1. Nanowires observed with electron microscopy.

Chen and colleagues made single-crystal Si nanowires. Initially, they coated a 2 nm-thick gold film (Au) on the substrate of clean Si by electron beam evaporation technology (ie, using a beam of electrons to bombard beer to evaporate materials). The Mn + ion is then implanted on the substrate from a high-energy arc plasma source. Next, the sample is incubated at 600oC and 800oC for half an hour. By electron microscopy (SEM and TEM), it was observed that the implantation process did not change the size or appearance of the nanowires (Figure 1), with a diameter of 30 to 80 nm. Magnetization measurements show that the saturation level increases with Mn concentration. However, ferromagnetism disappears at an incubation temperature of 800oC because Mn atoms are removed from the surface of the nanowires (Figure 2).

Figure 2. Measured hysteresis curves at 10 K in different heat treatment modes.

Both the electrical and magnetic properties of Si nanowires are important because they are all used for spintronics applications. A new point here is that Mn atoms act as a magnetic doped, but still retain the properties as electrons (n-type doping). The researchers say one thing is certain that Si nanowires are easy to doped both p and n type, unlike nanowires that were still made before, such as ZnO. This is extremely important because of the ability to generate pn contacts, a basic element of all transistors and components present in all integrated circuits.

The research team in Taiwan (This is the group at Tsinghua University, Taiwan, don't be confused with Tsinghua University in Beijing, the People's Republic of China) currently studying microstructure, electrical properties as well. as the properties of bonding between Mn and Si atoms in Mn Si nanowires. This will help researchers prove the properties needed for applications. These results have just been published in Applied Physics Letter ( Appl. Phys. Lett. 90, 043121 2007 ).

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