直接合成石墨烯於絕緣基板上之磁阻特性

Magnetoresistance Properties in Direct Synthesis of Graphene on Insulator Substrates

我們成功利用常壓化學氣相沉積法直接成長鎳催化石墨烯於二氧化矽(SiO2)基板上。根據拉曼光譜的量測和大範圍(10×10μm2)的拉曼影像的分析，本實驗的鎳催化之免轉移石墨烯是具有低缺陷且大部分(~90%)都是單層結構。在不同溫度下(300 K到10 K)的I-V量測中(-20 V至20 V)，鎳催化之免轉移石墨烯的阻抗隨溫度降低而增加，顯示出鎳催化之免轉移石墨烯是具有半導體特性。經由真空環境(10-6 torr)下退火處理(375 K)去除殘留物(水分子與氣體分子)，可進一步強化鎳催化之免轉移石墨烯的磁阻(Magnetoresistance, MR)特性。在變溫(6 K至150 K)測量磁阻特性時，發現鎳催化之免轉移石墨烯的負磁阻轉變成正磁阻的臨界溫度範圍落在20~30 K之間，同時也觀察到弱局域化效應(Weak localization)，此現象是量子傳輸現象中量子干涉效應的一種。以上這些結果展示了鎳催化之免轉移石墨烯可能有望實際應用在磁場感測。

Ni-catalyzed graphene was grown directly on SiO2 successfully via atmospheric pressure chemical vapor deposition (APCVD). According to Raman spectrum and large area Raman mapping (10×10μm2), Ni-catalyzed transfer-free graphene in this study is mostly single-layer structure (~90%) with low defects. Under different temperature (300 K to 10 K), the I-V measurements show the resistance of Ni-catalyzed transfer-free graphene increased with decreasing temperature, indicating the semiconductor property of Ni-catalyzed transfer-free graphene. By annealing process (at 375 K) in vacuum environment (10-6 torr), the magnetoresistance (MR) of Ni-catalyzed transfer-free graphene could be enhanced further due to removing the residues (H2O and gas molecules) on the graphene surface. With MR measurement at different temperature (from 10 K to 150 K), the critical temperature range of Ni-catalyzed transfer-free graphene for the converting from negative MR to positive MR is between 20 K and 30 K. At the same time, the weak localization effect also be observed, which is one kind of quantum interference effects in quantum transport. These above results demonstrate that Ni-catalyzed transfer-free graphene may be promising for the practical applications of magnetic sensing.