室溫下雷射退火快速成長二維材料

Ultrafast Two-Dimensional Materials Growth at Room Temperature by Laser Irradiation Process

黃杞智(Huang, Chi Chih)

指導教授 ： 闕郁倫

國立清華大學/工學院/材料科學工程學系/碩士(2015年)

摘要

二維材料是層狀結構材料，每層厚度為原子等級 (~0.7奈米)，其中以石墨烯最為人所知，石墨烯為最早被人製備且穩定之二維材料，擁有許多優異性質，例如高強度，高熱傳導率，和高電子遷移率。而最近Transition Metal Dichalcogenides(TMDs)因其特殊性質而漸漸受研究者矚目，TMDs中的二硫化鉬以及二硫化鎢擁有半導體特性，且為直接能隙，可成為有效的光電元件，因而成為TMDs的研究重點。
現今得到二維材料的方式主要為兩種: (1) 機械剝離(exfoliation) (2) 化學氣象沉積 (CVD)，但第一種方式生產效率極低，而CVD製程雖可得到大面積的材料，卻需要高溫以及轉移基板的步驟，造成基板的選擇有限，以及轉移步驟後的有機物殘留會嚴重影響材料性質。因此本文將介紹以雷射輔助加熱製備石墨烯和TMDs材料，改善上述之問題並維持高品質。
在石墨烯部分，拉曼光譜及穿透式電子顯微鏡(TEM)影像顯示出此方式可得到多層石墨烯(小於8層)，並可利用不同厚度之金屬層定義石墨烯圖型用以製備電子元件，例如場效電晶體，並得到其電洞及電子遷移率分別為500 與950 cm2 V −1 s −1。
TMDs材料除上述之製備問題，二硫化鉬以及二硫化鎢在先前的研究中已知其光電性質在大氣中會因吸收水氣或氧氣而改變。因此本實驗可用一步驟在氧化物保護層下生成雙層二硫化鎢，可直接生成於所需基板不需轉移步驟且可利用上層之氧化物保護二硫化鎢與大氣接觸而變質。並於文末介紹將此二硫化鎢應用於光感測元件。

關鍵字

雷射 ； 石墨烯 ； 二維材料 ； 電晶體 ； 光感測元件 ； 過渡金屬二硫族化物

並列摘要

Two-dimensional(2D) materials have attracted a great attention due to their high performancefor several applications. Graphene with ultra high mobility, excellent conductivity and strength at few atomic layers, made it the first and the most well-known 2D material. Further development in other layered materials also reported interesting results upon electron confinement in 2D materials while the thickness is approaching to single atomic layer. In particular, transition metal dichalcogenides (TMDs) based on Mo and W as transition metal, displaya transition to direct-gap for potential applications in optoelectronicsand energy harvesting. Despite that Chemical Vapor Deposition (CVD) is the most common way to synthesize 2D materials, several obstacles should beovercome. The high temperature and the required transfer process are the major issues to be addressed. The high temperature induces damage and limit the number of possible substrates used for the operation and the transfer process creates wrinkles and marks in the transferred film. Novel methods to grow and pattern graphene and TMDs with atomic thickness are an important step to pursue. In this study the use of laser was explored as a novel method for the synthesis of graphene and MS2 (M=W, Mo) with atomic thickness.
In the first part, a layer structure to directly synthesize few layer graphene on insulating substrates by laser irradiation, inducing local heating, is suggested.Tuning the metal layer thickness and laser power at different scanning rates, the number of graphene layers can be tuned. In order to overcome the limitation the resolution of the laser beam, submicrometer resolution of graphene can be achieved by patterning the intermediate metal layer usingstandard lithography methods. Furthermore, hole and electronmobilities of 500 and 950 cm2 V −1 s −1were measured. Laser annealing provides a one step process to directly grow graphene on insulators without required transfer.
In the second part, two kinds of TMDs-WS2 and MoS2 were synthesized successfully underneath an oxide layer, acting as a protective layer. Raman, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were applied to validate the presence and the numbers of layers. In addition, the simple structure of photo-sensing devices made of the WS2 denotes potential for mass-production. Additionally, this approach may apply to other kinds of TMDs materials by choosing the corresponding precursors.

並列關鍵字

laser ； graphene ； two dimensional materials ； transistor ； photo sensor ； transition metal dichalcogenide

參考文獻

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