二維材料的新穎奈米元件

Two-dimensional materials for novel nanodevices

陳俊宏(Jyun-Hong Chen)

指導教授 ： 鐘元良

中原大學/理學院/物理研究所/博士(2015年)

https://doi.org/10.6840/cycu201500957

摘要

近來二維奈米材料因為豐富的物性和極具應用潛力成為近年來熱門的研究題目。我們研究高電導的石墨烯和具有半導體特性的二硫化鉬之材料製作、光學分析、電性研究。藉由膠帶以物理剝離的方式成功製作出單層石墨烯和二硫化鉬，並使用拉曼光譜判斷層數。另外我們研究數層石墨烯在不同二氧化矽厚度的矽基底上的光學對比值可讓我們預測石墨烯在各種基底上的光學影像，計算多層干涉模型的結果與實驗一致，另外我們也發現其拉曼光譜會受到基底影響而有光強變化。修正多層干涉模型計算拉曼光強，計算分成兩部分，為材料吸收光強和拉曼散射光強，最後計算結果與實驗相近。我們使用化學氣相沉積法(CVD)製作大面積石墨烯並轉置在二氧化矽/矽基底上，再藉由電子束微影製作限制寬度的石墨烯緞帶以觀察磁電阻和緞帶寬度的關係。在溫度2K的環境中從四種寬度(50、75、245、705奈米)石墨烯緞帶之磁電阻觀察到弱局域現象和普式電導漲落，分析弱局域效應改變的電阻大小可得到寬度與電導改變比例之關係，電導增加比例從寬度低於245奈米出現非線性的增加。另外寬50奈米的石墨烯緞帶在溫度2K時發現庫倫阻斷的現象。
二硫化鉬為直接能隙的n型半導體二維材料。我們使用CVD法製作二硫化鉬並製作成有背閘極和側閘極的場效電晶體元件，研究單層CVD二硫化鉬的材料電性。在室溫時場效電子遷移率(μ)約為1.2cm2 V-1 S-1，在300K~170K溫度區間背閘極和側閘極的場效電子遷移率分別為正比於T-1.73和T-1.63，這與聲子散射限制的結果正比於T-1.69相近。另外從電導與溫度的關係圖中可分析出三個熱激發傳輸溫度區間，其中低溫傳輸的機制仍是一個未知的問題。另外CVD二硫化鉬可成長成zigzag邊緣的三角外形，我們在三個角上製作金屬電極和側閘極，發現非對稱整流現象。這可能與金屬接觸有關。另外在CVD二硫化鉬樣品上也出現壓電特性。我們使用原子力顯微鏡的探針使二硫化鉬型變，由於樣品的三角外形和zigzag的邊界，使得CVD成長的三角外形單層二硫化鉬受到等向形變進而產生壓電現象，並證實了應力誘導極化電荷在元件的zigzag邊緣。

關鍵字

石墨烯 ； 二硫化鉬 ； 光學干涉 ； 拉曼光譜 ； 量子干涉 ； 電子傳輸 ； 壓電效應

並列摘要

Two dimensional nanomaterials (TDNM) has recently become a hot research topic in recent years, because of the rich features and great potential. We study highly conductive graphene and semiconductor characteristics molybdenum disulfide material about device fabrication, optical analysis and electrical research. Graphene and molybdenum disulfide are exists in the form of bulk in nature, we successfully produce monolayer graphene and molybdenum disulfide by the physical peeling bulk, and identify by Raman spectrum. The atomic layer material is not easy to find by optical microscope, we calculate the contrast of graphene on top of SiO2/Si substrate by classical electromagnetic in multi-interference model and agree with experimental optical images results. The contrast of TMNM is function of incidence wavelength and substrate thickness, so the TDNM is visible on top of special thickness substrate. Not only optical images but also Raman spectrum of TDNM is to follow classical electromagnetic, it can calculate intensity factor by multi-interference model. We transfer large area chemical vapor deposition (CVD) graphene sheet to top of SiO2/Si substrate. We fabricated graphene ribbon (GR) device by electron beam lithography and study the relationship between wide and electron properties. We find weak localization and universal conductance fluctuation in GR that wide are 50nm, 75nm, 245nm, 705nm at temperature down to 2K. The weak localization effect is nonlinear when the wide of GR is smaller than 245nm. In addition we find Coulomb oscillation at 50nm width GR.

Molybdenum disulfide (MoS2) is a direct energy gap and n type semiconductor 2D material. We fabricated CVD MoS2 filed effect transistor with back gate and side gate, to research monolayer MoS2 electron properties. At room temperature, the filed effect mobility is about 1.2cm2 V-1 S-1, at 300~170K the back and side gate filed effect mobility are proportional to T-1.73 and T-1.63 respectively, this is similar to phonon-limited electron mobility T-1.69. We find three thermally activated transport at three temperature ranges from conductance as a function of temperature, but the electron transport at low temperature range is still unknown issue. The monolayer single crystal MoS2 is triangular ship with zigzag edge, we fabrication three electrode on MoS2’s corners and side gate. In the triangular transistor, we are observed the phenomenon of asymmetric rectifier. This may be related to metal contact. In addition, we are observed piezoelectric properties in CVD MoS2. Using AFM probe to make MoS2 deformation, because sample have triangular ship and zigzag edge, the samples were subjected to isotropic deformation and produce a piezoelectric phenomenon and confirm the force induced polarized charges in zigzag edge of MoS2.

並列關鍵字

Graphene ； molybdenum disulfide ； optical interference ； Raman spectroscopy ； quantum interference ； electronic transmission ； piezoelectric effect

參考文獻

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