二維磁性材料身為二維材料的家族成員之一，具有單層厚度依然保持長程磁序，因為天生的低尺寸而層與層之間以凡得瓦爾力鍵結，並具有自旋耦合的效應。二維磁性材料具有非常多種的組合類型，其中CrTe2為過渡金屬二硫屬化物(Transition Metal Dichalcogenides ,TMDCs)[1]中的一員，被理論預測具有室溫鐵磁性的二維磁性材料。本實驗以分子束磊晶系統(Molecular Beam Epitaxy, MBE)成長二維鐵磁性材料CrTe2薄膜，調整相關成長參數如Cr/Te的分壓比和成長溫度得到好的結構晶向以及平坦表面的薄膜樣品，並研究其磁特性。在結構與成份分析方面，以臨場(in-situ)反射高能電子繞射儀(Reflection high-energy electron diffraction ,RHEED)以及原子力顯微鏡Atomic Force Microscope, AFM)觀察確認表面平整度，以X光繞射儀分析晶格結構與薄膜樣品厚度，並且利用穿透式電子顯微鏡(Transmission Electron Microscope, TEM)確認剖面層狀結構以及薄膜厚度，並對照於X光量測的厚度來推估成長的薄膜厚度。透過拉曼光譜(Raman spectroscopy)以及X射線光電子能譜 (X-ray Photoelectron Spectroscopy, XPS)定性定量分析樣品組成的元素比例。
在磁性方面，探討改變CrTe2薄膜厚度其磁性與磁光特性的變化。由超導量子干涉 儀(Superconducting Quantum Interference Device, SQUID)量測不同厚度的薄膜磁化率及磁滯曲線，在低於居禮溫度後(Curie temperature,Tc)時CrTe2薄膜呈現鐵磁性且Tc隨著厚度增加而下降，利用磁圓二色性光譜儀(Magnetic Circular Dichroism,MCD)量測時，CrTe2薄膜的在正負磁場下，MCD磁光訊號分裂，所得到的磁滯訊號與SQUID的結果一致，根據以上的結果可證明成長出來的CrTe2薄膜為二維鐵磁性材料。

Recently, CrTe2 2D material had been theoretically predicted to be the transition metal dichalcogenides with room temperature ferromagnetic properties. In this study, CrTe2 thin films on the sapphire (0001) substrates were grown using molecular beam epitaxy (MBE) system. We optimized the Cr/Te beam flux ratio and growth temperature to achieve high-quality and single-phase CrTe2 thin films. The quality and structure of CrTe2 thin films were characterized with in-situ the reflective high energy electron diffraction(RHEED), X-ray diffraction (XRD) and atomic force microscope(AFM), which indicated the flat surface and well-order structure. The thickness of CrTe2 thinfilm were confirmed by both X-ray reflectometry (XRR) and high-resolution transmission electron microscopy (HRTEM). Moreover, the stoichiometry of the film was estimated using Raman spectra and X-ray photoelectron spectroscopy(XPS) analysis, which showed that Cr : Te was 1 : 2 which is consistent with the chemical formula of compound CrTe2.
The magnetic properties of CrTe2 thin film with different thickness were measured by superconducting quantum interference device (SQUID), which reveal the out-of-plane ferromagnetic behavior and the Curie temperature (Tc) decrease with increasing the CrTe2 thickness from 210 K to around 195 K. From the magnetic circular dichroism (MCD) spectra results, the magnet-optical signals as a function of the magnetic field in CrTe2 thin films had been observed. The hysteresis loop results were obtained from MCD spectra, consistent with the SQUID results. Based on our results, the CrTe2 grown thinfilm is the 2D magnetic material.

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