二維材料介面導致鐵薄膜磁耦合分離現象
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2018
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本實驗旨在於探討鐵磁薄膜沉積在單層二硫化鉬(MoS2)與二氧化矽基板(SiO2 /Si(100))兩種不同表面上產生的矯頑場(coercivity)差異，其鐵薄膜具有不連續的磁耦合分離性質，並分析推測此現象的可能來源。
我們利用自製的化學氣相沉積系統(Chemical Vapor Deposition)合成大量二硫化鉬單層薄膜於二氧化矽基板，並以原子力顯微鏡(Atomic Force Microscope)、拉曼光譜儀(Raman spectrum)驗證其大多為單層的厚度結構。其後於超高真空環境(10-9 torr)蒸鍍鐵薄膜於其上，再以磁光科爾顯微鏡(magneto optical kerr mi-croscope)量測之。結果上，我們發現樣品表面的磁滯曲線(hysteresis loop)呈現非方正的鐵磁曲線，呼應我們對於鐵膜微觀表面上具有許多磁性粒子團的預測，且異質介面導致鐵薄膜在不同介面上有著相異的矯頑場，是為鐵薄膜磁耦合分離現象，此現象伴隨著鐵薄膜厚度提升而逐漸消失。
In this study, we deposited Fe films on MoS2 flakes, and investigated the microscopic magnetic behavior on individual flake. The MoS2 flakes were fabricated on SiO2/Si(100) substrates using chemical vapor deposition. Fe coverage was deposited on the MoS2 flakes by e-beam evaporation with a thin Pd capping for the protection. Investigations by atomic force microscope and Raman spectroscopy confirmed that the MoS2 flakes were of the lateral size: 10-20 µm and mostly single layer thick. Af-ter depositing 3.6-7.0 nm Fe on MoS2/SiO2, clear hysteresis loops were observable with the in-plane magnetic field. From the investigation using a magneto-optical Kerr microscope, we measured the hysteresis curves of individual MoS2 flakes. Alt-hough the Fe coverage was much thicker than the MoS2 atomic step height (∼0.66 nm) and the direct connection and strong ferromagnetic coupling between Fe/MoS2 and Fe/SiO2 was expected, the magnetic decoupling between the magnetic domains of Fe/MoS2 and Fe/SiO2 was surprisingly observed. For 3.6 nm Fe/MoS2, the magnetic coercivity (Hc) was 28±5 Oe, while in contrast, the Hc of 3.6 nm Fe/SiO2 ranged 58±5 Oe. With a thicker Fe coverage, the Hc of interface converged and the magnetic de-coupling became vague to observe. The distinct interface magnetic anisotropy of Fe on different substrates could be responsible for the observed magnetic decoupling across the MoS2 atomic step between Fe/MoS2 and Fe/SiO2 domains. These observa-tions will be valuable in combining a magnetic coverage with a single layer MoS2 for the future spintronic applications.
In this study, we deposited Fe films on MoS2 flakes, and investigated the microscopic magnetic behavior on individual flake. The MoS2 flakes were fabricated on SiO2/Si(100) substrates using chemical vapor deposition. Fe coverage was deposited on the MoS2 flakes by e-beam evaporation with a thin Pd capping for the protection. Investigations by atomic force microscope and Raman spectroscopy confirmed that the MoS2 flakes were of the lateral size: 10-20 µm and mostly single layer thick. Af-ter depositing 3.6-7.0 nm Fe on MoS2/SiO2, clear hysteresis loops were observable with the in-plane magnetic field. From the investigation using a magneto-optical Kerr microscope, we measured the hysteresis curves of individual MoS2 flakes. Alt-hough the Fe coverage was much thicker than the MoS2 atomic step height (∼0.66 nm) and the direct connection and strong ferromagnetic coupling between Fe/MoS2 and Fe/SiO2 was expected, the magnetic decoupling between the magnetic domains of Fe/MoS2 and Fe/SiO2 was surprisingly observed. For 3.6 nm Fe/MoS2, the magnetic coercivity (Hc) was 28±5 Oe, while in contrast, the Hc of 3.6 nm Fe/SiO2 ranged 58±5 Oe. With a thicker Fe coverage, the Hc of interface converged and the magnetic de-coupling became vague to observe. The distinct interface magnetic anisotropy of Fe on different substrates could be responsible for the observed magnetic decoupling across the MoS2 atomic step between Fe/MoS2 and Fe/SiO2 domains. These observa-tions will be valuable in combining a magnetic coverage with a single layer MoS2 for the future spintronic applications.
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二硫化鉬, 磁性, 二維材料, 磁耦合分離, MoS2, magnetism, two-dimensional material, magnetic decoupling