The efficiency of spin-to-charge conversion is a key parameter in determining the performance of emerging spintronic devices. In the topological surface state of a topological insulator (TI), the spin-momentum locking effect offers a great possibility for efficient spin-to-charge conversion. Here, we report the relation between the Fermi level position E F and spin-to-charge conversion efficiency in heterostructure Ni80Fe20 (Py)/(Bi1–x Sb x )2Te3. The band structure of (Bi1–x Sb x )2Te3 films becomes tailored by tuning the ratio of bismuth to antimony so that the position of the Fermi level E F varies from the top side of the valence band to the bottom side of the conduction band through the in-gap surface Dirac cone. The result is consistent with the electronic behavior of the majority carriers varying from n-type to p-type. In spin-pumping measurements, we observed that the inverse Edelstein effect length (λIEE) with a tuned E F near the Dirac point is significantly enhanced, indicating that the spin-charge conversion is determined mainly by the topological surface state. These results demonstrate that fine-tuning of E F in a TI-based heterostructure is critical to maximizing the efficiency of spin-to-charge conversion using a spin-momentum locking mechanism.

We fabricate Co/Pt and Co/Pd multilayers and measure magnetoresistance. Our data show clear anisotropic interface magnetoresistance (AIMR) effect, in which the resistance variation shows a different sign from Co films when external magnetic saturation fields are rotated from in-plane transverse to perpendicular direction of the film plane. The AIMR percentages increase with decreasing Co thickness for both multilayers when the Co thickness is larger than 2.5 nm. However, the AIMR decreases in Co/Pt for thinner Co but still increases in Co/Pd, thus, showing inverse dependence to Co thickness.

Tungsten disulfide (WS2) was prepared from W metal and WO3 by ion beam sputtering and sulfurization in a different number of layers, including monolayer, bilayer, six-layer, and nine-layer. To obtain better crystallinity, the nine-layer of WS2 was also prepared from W metal and sulfurized in a furnace at different temperatures (800, 850, 900, and 950 °C). X-ray diffraction revealed that WS2 has a 2-H crystal structure and the crystallinity improved with increasing sulfurization temperature, while the crystallinity of WS2 sulfurized from WO3 (WS2-WO3) is better than that sulfurized from W-metal (WS2-W). Raman spectra show that the full-width at half maximum (FWHM) of WS2-WO3 is narrower than that of WS2-W. We demonstrate that high-quality monocrystalline WS2 thin films can be prepared at wafer scale by sulfurization of WO3. The photoluminescence of the WS2 monolayer is strongly enhanced and centered at 1.98 eV. The transmittance of the WS2 monolayer exceeds 80%, and the measured band gap is 1.9 eV, as shown by ultraviolet-visible-infrared spectroscopy.

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