Spin Effects in Graphene Progress: From the Metal to the Semiconductor World
June 22, 2016 | HZBEstimated reading time: 2 minutes
Graphene on silicon carbide could be an interesting candidate for future spintronik components. Squeezing gold atoms between the semiconducting substrate and graphene does enhance spin-orbit interaction at hot spots and shows ways to controll the spins. First results at BESSY II are now published in Applied Physics Letters.
In electronic circuits, the charge of the electron is decisive. In a future spintronics, however, the essential role will be taken over by the spin of the electron because it enables a potentially lossless transport of information. This requires the development of materials that can conserve the spin information over long distances but also manipulate it. In this context, graphene has been discussed because of the long distances the electron spin can travel without losing its orientation. A couple of years ago HZB researchers Dr. Andrej Varykhalov and Dr. Dmitry Marchenko demonstrated that also the completely opposite is possible with graphene. Graphene rotates the spin of the electrons when brought in close contact with gold atoms.
No net effect on metal substrate
This finding has led to a number of breakthroughs in the meantime. They had, however, a common disadvantage. In order to get the gold atoms really close to the graphene, graphene was deposited on a metal substrate such as nickel, and the gold could afterwards easily be squeezed between the graphene and the metal. This enhanced the so called spin-orbit interaction in the material by a factor of 10 000. Calculations show that an effect of this order of magnitude is linked to a half rotation (180 °) of spins after traveling about 40 nanometres. This is the length scale where miniaturization of conventional electronic devices has arrived nowadays. Because the substrate is a bulk metal and conducting there are many more electrons flowing with completely random spin orientation which causes something like a short circuit to the spin information.
Pure sample on silicon carbide
This means that the graphene has to be grown on an insulating substrate. The semiconductor silicon carbide is a famous substrate for graphene. The difficult task was to control the charge doping of the sample. Interestingly for small amounts of gold, the graphene charges negatively and for larger amounts it reverses and charges positively. Marchenko, who had employed the trick with the gold on the nickel in his Ph. D. thesis recalls that it was very difficult to produce the pure positively charged phase. After many trials he succeeded and could study it with the method of spin-resolved photoelectron spectroscopy.
Huge spin.orbit interaction at hot spots only
What Marchenko found was a very different behavior as compared to graphene on previous, bulk metallic, substrates. From previous experience, he searched for large spin-orbit effects near hybridization points, so-called hot spots in the band dispersion. He found there a very large splitting of 100 meV, in the same enhancement by 10,000 over pure graphene. However, the effect is only limited to the vicinity of the hot spot - and this is very different from the cases with the metal substrate.
Switching on and off
For the researchers this means that to make use of high spin-orbit effects of graphene on semiconductors they need to dope the system by a second element or use a gate voltage to move the hot spot to the Fermi energy where it can contribute to the transport. "In this case, a rather small gate voltage change should modify the splitting from 0 to 100 meV, working as an on/off switch for spin effects in a graphene based device", Marchenko says.
Suggested Items
Water Management in a Large Printed Circuit Board Manufacturer
04/15/2024 | Charles Nehrig, TTM TechnologiesTTM’s environmental management is grounded in its Environmental Statement and Environmental Policy, which promote measures that make for a more responsible environmental management process. Our management system helps TTM work toward minimizing its environmental footprint and increasing the sustainability of its operations. TTM monitors its environmental performance just as it monitors its operational performance, and provides the resources required to adhere to the Company’s environmental responsibilities.
Happy’s Tech Talk #27: Integrated Mesh Power System (IMPS) for PCBs
04/08/2024 | Happy Holden -- Column: Happy’s Tech TalkA significant decrease in HDI substrate production cost can be achieved by reducing the number of substrate layers from conventional through-hole multilayers and microvia multilayers of eight, 10, 12, and more to only two layers. Besides reducing direct processing steps, the yield will increase as defect-producing operations are eliminated. The integrated mesh power system (IMPS) was invented in the latter years of MCM-D use for thin-film fabrication. Those geometries fit today into our use of ultra HDI.
Trouble in Your Tank: Supporting IC Substrates and Advanced Packaging, Part 5
03/19/2024 | Michael Carano -- Column: Trouble in Your TankDirect metallization systems based on conductive graphite or carbon dispersion are quickly gaining acceptance worldwide. Indeed, the environmental and productivity gains one can achieve with these processes are outstanding. In today’s highly competitive and litigious environment, direct metallization reduces costs associated with compliance, waste treatment, and legal issues related to chemical exposure. What makes these processes leaders in the direct metallization space?
Indium Corporation Experts to Present at SEMI THERM
03/07/2024 | Indium CorporationIndium Corporation Global Account Manager and Senior Thermal Technologist Tim Jensen and Product Development Specialist for Thermal Interface Materials Miloš Lazić will present on thermal interface material (TIM) technology at SEMI-THERM, taking place March 25–28 in San Jose, California, U.S.
Indium Corporation to Showcase Proven EV Products and High-Reliability Alloys at Productronica China
02/28/2024 | Indium CorporationAs a materials pioneer and trusted partner in electric vehicle (EV) and e-Mobility manufacturing, Indium Corporation is proud to showcase its high-reliability alloys and soldering solutions at Productronica China, March 20-22, in Shanghai.