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標題: | 藉由物理性摻雜製備P型/N型石墨烯並研究摻雜石墨烯之電特性 Fabricate p-/n-type graphene via physical doping and Investigate electrical properties of doping graphene |
作者: | Chao-Yu Lee 李兆育 |
指導教授: | 吳志毅(Chih-I wu) |
關鍵字: | 石墨烯,化學氣相沉積法,自組裝層,摻雜,電滯效應, Graphene,Chemical Vapor Deposition,self-assembled layer,Doping,hysteresis, |
出版年 : | 2018 |
學位: | 碩士 |
摘要: | 由於二維材料具有優異的導電性和高度透明的特性,研究和開發二維材料元件一直是科學家的目標。自石墨烯被發現以來,石墨烯快速地發展且其在各個領域都極具前景,並且具有廣泛應用的巨大潛力。本質石墨烯的費米能階切在價帶和導帶的交點,也就是說可傳輸的載子相當得少,若要將其應用,摻雜調整其費米能階,使其成為N型或是P型石墨烯,是不可必免。在本論文中,展示兩種摻雜石墨烯的方法,就其結果進行分析和討論,確認費米能階被調控到適合的位子。
第一種方法利用自組裝層修飾基板,透過自組裝分子摻雜石墨烯。當我們在自組裝層上轉印石墨烯,原本因二氧化矽塊材中及表面缺陷所造成不可控的P型摻雜現象被降低,使石墨烯表現接近本質石墨烯。除此之外,自組裝分子的官能基能對石墨烯進行摻雜。然而,在數據顯示上電性量測的摻雜效果與光譜預期的摻雜效果相反的特性表現,我們認為造成這個現象的原因之一,可能來自石墨烯與自組裝層間的水分子殘留,根據理論上的計算,當水分子的氧基朝向石墨烯時,水分子會傾向於給石墨烯電子;相反地,若是水分子氫基朝向石墨烯,水分子會傾向於從石墨烯上拿走電子,因此,相反的摻雜效果產生。除了非預期的相反摻雜效果,用基板修飾來摻雜還會遇到一個難題,也就是這種方法對石墨烯和基板的品質有一定要求,使得可控的穩定性較低。所以,我們需找一個更為簡單且有效的摻雜方法。 第二種方法則是蒸氣法摻雜,主要流程是將石墨烯置於充滿分子蒸氣腔體中,使石墨烯吸附分子,達到摻雜效果。首先,我們發現吸附的分子,主要利用載子交換的方式對石墨烯進行摻雜,且在一定程度以下的摻雜,能夠提升石墨烯的電性表現;然而,過多的摻雜反而將使石墨烯品質下降。除此之外,N(P)型摻雜物會隨著負(正)閘極電壓增加下,給石墨烯更重的摻雜效果,然而,在正(負)閘極電壓下,摻雜物則不受電壓影響。 最後,我們還研究不同基板上的電滯效應,我們發現不論在二氧化矽或是自組裝層的基板上,電滯效應都存在。在其他研究中指出造成電滯效應的原因,大致可歸咎於兩個原因─水氣、基板缺陷,而他們的機制可能為載子交換和電容效應。這兩種機制在電滯效應上,呈現兩個相反的結果。就我們實驗發現,電性量測的速率與現象的存活時間不匹配,第二則是電容效應產生的效果可能較載子交換來的小。因此,載子交換佔據了主導的地位。 Study and develop 2D-materials devices have been the aim of scientists due to excellent conductivity and highly transparent properties. Since the discovery of graphene, graphene is becoming a rapidly growing and enormously promising field, and have great potential for wide applications. However, conduction band and valance band of intrinsic graphene is meeting at Fermi level, and implies that the carrier for conducting is insufficient. In this thesis, we demonstrate two methods for graphene doping, and analyze the results to make sure that the Fermi level could tune to suitability. The first method is molecular doping from substrate surface by modifying the SiO2/Si substrate surface with self-assembled molecule (SAM). When depositing graphene on SAM layer, the p-doping effect from silicon dioxide would be decreasing. The function groups of SAM would also dope the intrinsic graphene. However, the few H2O molecule between SAM layer and graphene would make serious impression on graphene. In our results, we found the results of SAM layer doping effect by measuring transfer curve are opposite totally of ultraviolet photoelectron spectroscopy. When few H2O molecule adsorb between SAM layer and graphene, the charge would transfer from H2O to graphene while the O atom of H2O head to the graphene surface. On the other hand, the charge would transfer from graphene to H2O when the H atom head to the graphene surface. The unexpected type of doping and high quality requirment of graphene and self-assembled layer make this method worthless. Thus, an easy and efficient method is desirable. Second method is vapor doping. We kept graphene in a place with vapor of dopant fill. Finally, graphene will be doped by adsorbing molecules on its surface. We found that the dominant mechanism of doping could be charge transfer between adsorbate and graphene. Besides, graphene could optimize by doping within certain degree. Finally, we also study the hysteresis of g-FET on different SAM-substrate and vapor doping graphene. In previous reports, the hysteresis of g-FET might originate from transfer and capacitive gating of H2O and SiO2 substrate, and compete with each other. In our study, we found the sweeping rate of measurement is not comparable to the life time of capacitive gating and the influence of capacitive gating is lower than that of charge transfer. For that result, charge transfer dominate the effect. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/70235 |
DOI: | 10.6342/NTU201803565 |
全文授權: | 有償授權 |
顯示於系所單位: | 光電工程學研究所 |
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