MoS2 and related metal dichalcogenides (MoSe2, WS2, WSe2) are layered two-dimensional materials that are promising for nanoelectronics and spintronics. For instance, large spin-orbit coupling and spin splitting in the valence band of single layer (SL) MoS2 could lead to enhanced spin lifetimes and large spin Hall angles. Understanding the nature of the contacts is a critical first step for realizing spin injection and spin transport in MoS2. Here, we have investigated Co contacts to SL MoS2 and find that the Schottky barrier height can be significantly decreased with the addition of a thin oxide barrier (MgO). Further, we show that the barrier height can be reduced to zero by tuning the carrier density with back gate. Therefore, the MgO could simultaneously provide a tunnel barrier to alleviate conductance mismatch while minimizing carrier depletion near the contacts. Such control over the barrier height should allow for careful engineering of the contacts to realize spin injection in these materials.

The gradient of the Casimir force between a Si-SiO 2 -graphene substrate and an Au-coated sphere is measured by means of a dynamic atomic force microscope operated in the frequency shift technique. It is shown that the presence of graphene leads to up to 9% increase in the force gradient at the shortest separation considered. This is in qualitative agreement with the predictions of Lifshitz theory using the dielectric permittivities of Si and SiO 2 and the Dirac model of graphene.

We review our recent work on spin injection, transport and relaxation in graphene. The spin injection and transport in single layer graphene (SLG) were investigated using nonlocal magnetoresistance (MR) measurements. Spin injection was performed using either transparent contacts (Co/SLG) or tunneling contacts (Co/MgO/SLG). With tunneling contacts, the nonlocal MR was increased by a factor of ~1000 and the spin injection/detection efficiency was greatly enhanced from ~1% (transparent contacts) to ~30%. Spin relaxation was investigated on graphene spin valves using nonlocal Hanle measurements. For transparent contacts, the spin lifetime was in the range of 50-100 ps. The effects of surface chemical doping showed that for spin lifetimes on the order of 100 ps, impurity scattering (Au) was not the dominant mechanism for spin relaxation. While using tunneling contacts to suppress the contact-induced spin relaxation, we observed the spin lifetimes as long as 771 ps at room temperature, 1.2 ns at 4 K in SLG, and 6.2 ns at 20 K in bilayer graphene (BLG). Furthermore, contrasting spin relaxation behaviors were observed in SLG and BLG. We found that Elliot-Yafet spin relaxation dominated in SLG at low temperatures whereas Dyakonov-Perel spin relaxation dominated in BLG at low temperatures. Gate tunable spin transport was studied using the SLG property of gate tunable conductivity and incorporating different types of contacts (transparent and tunneling contacts).Consistent with theoretical predictions, the nonlocal MR was proportional to the SLG conductivity for transparent contacts and varied inversely with the SLG conductivity for tunneling contacts. Finally, bipolar spin transport in SLG was studied and an electron-hole asymmetry was observed for SLG spin valves with transparent contacts, in which nonlocal MR was roughly independent of DC bias current for electrons, but varied significantly with DC bias current for holes. These results are very important for the use of graphene for spin-based logic 3 and information storage applications.

Abstract:Graphene is an attractive material for spintronics due to theoretical predictions of long spin lifetimes arising from low spin-orbit and hyperfine couplings. In experiments, however, spin lifetimes in single layer graphene (SLG) measured via Hanle effects are much shorter than expected theoretically. Thus, the origin of spin relaxation in SLG is a major issue for graphene spintronics. Despite extensive theoretical and experimental work addressing this question, there is still little clarity on the microscopic origin of spin relaxation. By using organic ligand-bound nanoparticles as charge reservoirs to tune mobility between 2700 and 12000 cm 2 /Vs, we successfully isolate the effect of charged impurity scattering on spin relaxation in SLG. Our results demonstrate that while charged impurities can greatly affect mobility, the spin lifetimes are not affected by charged impurity scattering. Keywords:graphene; spintronics; spin relaxation; mobility; charged impurity scattering 2 Single layer graphene (SLG) is a promising material for spintronics due to theoretical predictions of long spin lifetimes based on its low intrinsic spin-orbit and hyperfine couplings [1][2][3][4][5] . However, spin lifetimes measured in SLG spin valves are much shorter (0.05 -1.2 ns) 6-9 than predicted (100 ns -1 s) [1][2][3][4][5] . Thus, the origin of spin relaxation in SLG has become a central issue for graphene spintronics and has motivated intense theoretical and experimental studies. Theoretical studies of spin relaxation include impurity scattering 10 , ripples 5 , spin orbit domains 11,12 , and substrate effects 13 , while experimental studies have investigated contact-induced spin relaxation 7, 9, 14 , ripples 15 , band structure effects 6,14,16 , edge effects 7 and charged impurity scattering 6, 8 .However, apart from recognizing the requirement for high quality tunneling contacts to suppress contact-induced spin relaxation 9 , there is little clarity regarding the origin of spin relaxation. To address the situation, it is crucial to develop experimental techniques that systematically isolate the various microscopic sources of spin relaxation.In this work, we successfully isolate the effect of charged impurity scattering on spin relaxation in SLG by exploiting the novel tunable mobility imparted by organic ligand-bound nanoparticles on the SLG surface 17 . The nanoparticles act as charge reservoirs that freely transfer charge with graphene at room temperature. At low temperature, the frozen charge distribution on the nanoparticles results in SLG mobility ranging from 2700 to 12000 cm 2 /Vs. This approach is able to isolate the effect of charged impurity scattering on spin relaxation more clearly than previous investigations based on adatom deposition 8 . This is because depositing adatoms to the graphene surface could introduce additional effects such as short-range scattering, lattice deformation, and/or spin-orbit coupling, whereas such effects should be minimized in the current approach. Additionally, we utilize tunne...

We report the experimental demonstration of a magnetologic gate built on graphene at room temperature.This magnetologic gate consists of three ferromagnetic electrodes contacting a single layer graphene spin channel and relies on spin injection and spin transport in the graphene. We utilize electrical bias tuning of spin injection to balance the inputs and achieve "exclusive or" (XOR) logic operation. Furthermore, simulation of the device performance shows that substantial improvement towards spintronic applications can be achieved by optimizing device parameters such as device dimensions. This advance holds promise as a basic building block for spin-based information processing. 1Spintronics is an approach to electronics that utilizes the spin of the electron for information storage and processing [1][2][3]. By providing the ability to integrate logic with nonvolatile storage in ferromagnetic data registers, spintronics could greatly reduce the power consumption in logic circuits and go beyond traditional CMOS architectures. The demonstration of spin injection into semiconductors [4,5] prompted a variety of proposals for spintronic devices taking advantage of the tunable nature of semiconductors [6][7][8][9][10][11]. Among these was a proposal by Dery and Sham [12] for an "exclusive or" (XOR) gate based on spin accumulation in a semiconductor channel contacted by three ferromagnetic (FM) electrodes (see Fig. 1(a)). In this device, the magnetization directions of the first two FM electrodes represent the logic inputs ('0' and '1'), and spin injection from these input electrodes generates a current through the third FM electrode which represents the logic output. Subsequently, a more general proposal was developed that combines two such XOR gates to form a universal reconfigurable magnetologic gate (MLG) [8]. This MLG consists of five FM electrodes and the logic operation is represented by OR(XOR(A, B), XOR(C, D)), where A, B, C and D are the four logical input states and the fifth FM electrode reads the output. This can also be utilized as a universal two-input gate, where B and D define the gate operation (e.g. NAND, OR) and A and C represent the two inputs. The experimental discoveries of room temperature spin transport [13] and efficient spin injection into graphene [14] provided an ideal materials platform to realize such MLG devices. Motivated by these advances, the theoretical performance of graphene-based MLG was analyzed and novel spintronic circuits for rapid parallel searching were developed [15]. However, despite these extensive advances in the device modeling and spintronic circuit design, the experimental demonstration of the proposed three-terminal XOR and fiveterminal universal MLG has been lacking.In this Letter, we experimentally demonstrate the proposed three-terminal XOR magnetologic gate operation in a graphene spintronic device at room temperature. By carefully tuning the bias current between the two input electrodes, and an offset voltage in the detection loop, a clear non-ze...

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The KIF3 subunit KIF3B was proved to be associated with mitosis. It has been known to be engaged in intracellular transport of neurons. To elucidate the certain expression and biological function in central nervous system, we performed an acute spinal cord contusion injury model in adult rats. Western blot analysis indicated a marked upregulation of KIF3B after spinal cord injury (SCI). Immunohistochemistry revealed wide distribution of KIF3B in spinal cord, including neurons and glial cells. Double immunofluorescent staining for proliferating cell nuclear antigen and phenotype-specific markers showed increases of KIF3B expression in proliferating microglia and astrocytes. Our data suggest that KIF3B may be implicated in the proliferation of microglia and astrocytes after SCI.