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Title: | 鉍奈米線陣列的氦離子束微影製備與其能隙分析 Properties of Bismuth Nanowire Arrays Prepared by Helium Ion Beam Lithography |
Authors: | 蔡連晉 Lien-Chin Tsai |
Advisor: | 林浩雄 Hao-Hsiung Lin |
Keyword: | 鉍薄膜,氦離子束微影技術,鉍奈米線,G(T)模型,量子侷限效應, Bismuth thin film,Helium ion beam lithography,Bismuth nanowire,G(T) model,Quantum confinement effect, |
Publication Year : | 2024 |
Degree: | 碩士 |
Abstract: | 本論文於MBE成長之鉍薄膜上,使用氦離子束微影技術(Helium ion beam lithography, HIBL)進行鉍奈米線的製備,並透過Hall bar結構研究其電性。
由於氦離子具有較高的質量,一顆氦離子可激發的二次電子數量約為電子束的5倍,因此HIBL對曝光劑量的靈敏度(Sensitive)很高,文中整理了以PMMA作為光阻,不同曝光劑量下的奈米線製作結果,對氦離子束的鄰近效應進行量化分析,評估鄰近效應的影響以及圖形轉移完整度後選擇使用劑量 8.3 μC/cm^2,並成功製作出最細線寬22 nm的奈米線陣列。 在初期的研究中發現單根的奈米線會在數次IV量測後逐漸劣化,為了解決這個問題,我們將單根奈米線改為10條的奈米線陣列,成功的解決奈米線於量測時劣化的問題。 我們對奈米線陣列進行溫度範圍10 K~300 K的變溫四點霍爾量測,將變溫量測獲得的片電阻數據,使用文獻中的G(T)模型進行擬合分析,擬合結果呈現出奈米線寬度愈細,能隙愈高的趨勢,其中寬度22 nm的奈米線陣列之等效能隙高達360 meV,比同一片樣品上之100 μm Hall bar的能隙75 meV高。我們使用電子背向散射繞射(Electron Backscatter Diffraction, EBSD)反極圖,觀察奈米線為單晶且傳輸方向為[11-20]方向,與實驗室學長進行之二維量子侷限理論模型模擬計算的結果相比,兩者接近,因此我們認為這是鉍奈米線受到二維量子侷限效應影響的效果。 This paper utilizes helium ion beam lithography (HIBL) on bismuth thin films grown by molecular beam epitaxy (MBE) to fabricate bismuth nanowires. The study investigates their electrical properties using a Hall bar structure. Due to the higher mass of helium ions, the secondary electron yield is approximately five times higher than that of an electron beam, making HIBL highly sensitive to exposure doses. The paper presents results of nanowire fabrication using PMMA as a resist at different exposure doses, quantitatively analyzing the proximity effect of helium ion beams. After assessing the impact of the proximity effect and evaluating the fidelity of pattern transfer, a dose of 8.3 μC/cm² is chosen, successfully producing nanowire arrays with a minimum linewidth of 22 nm. In the initial stages of the study, it was observed that individual nanowires degraded gradually after multiple IV measurements. To address this issue, a solution was found by changing from single nanowires to an array of 10 nanowires, effectively resolving the degradation problem during measurements. Temperature-dependent four-point Hall measurements were conducted on the nanowire arrays in the temperature range of 10 K to 300 K. The resistance data obtained from temperature-dependent measurements were fitted using the G(T) model from the literature. The fitting results indicate a trend of higher bandgap with decreasing nanowire width. Notably, the nanowire array with a width of 22 nm exhibits an exceptionally high effective bandgap of 360 meV, compared to the bandgap of 75 meV for a 100 μm Hall bar on the same sample. Electron backscatter diffraction (EBSD) inverse pole figure analysis reveals that the nanowires are single crystals oriented along the [11-20] direction. The simulated results from a two-dimensional quantum confinement model, consistent with the experimental observations, suggest that the effects observed in bismuth nanowires are influenced by two-dimensional quantum confinement effects. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/91764 |
DOI: | 10.6342/NTU202400296 |
Fulltext Rights: | 同意授權(全球公開) |
Appears in Collections: | 光電工程學研究所 |
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ntu-112-1.pdf | 3.5 MB | Adobe PDF | View/Open |
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