標題: 探討石墨烯在電場下所造成的橫向電壓
Electric field induced transverse voltage in pure Graphene
作者: 黃光宇
簡紋濱
Huang,Guang-Yu
Jian,Wen-Bin
電子物理系所
關鍵字: 石墨烯;電性量測;電場;非局域性;graphene;electrical measurements;Electric field;nonlocality
公開日期: 2016
摘要: 本實驗使用機械剝離法製備少數層石墨烯於矽基板上,透過原子力顯微鏡確認樣品為少數層石墨烯,經由光學顯微鏡定位、電子束微影及熱蒸鍍系統,完成場效電晶體結構之石墨烯元件。先利用兩點量測法確認樣品電性傳輸,接著改用四點量測法探討其橫向方向之電壓差值變化。 透過兩點量測法,在施加背向閘極偏壓時,可明顯觀察到石墨烯雙極性(bipolar)的物理特性,且樣品電導率約為7-22 e2/h。透過四點量測法,在汲極/源極兩端輸出電流,並在橫向方向量測電壓差值,發現所量測值與石墨烯場效應呈現一致性,透過積分形式去估算樣品不對稱性所造成的電壓差值,且隨著閘極偏壓造成費米能階的改變,載子濃度的上升與下降皆會影響其變化,並定義出△V34(Vg),其為閘極偏壓之函數。 發現當石墨烯樣品本身品質較好時,有機會在正交方向量測到與△V34(Vg)完全相反的逆向偏壓值,且此逆向偏壓值在狄拉克點處達最大值,此現象有別於磁場所造成之霍爾電壓,而是單純透過電場所造成之橫向電壓,可能與石墨烯非局域效應下所產生之電壓差有關,且當石墨烯樣品本身品質較好時,此一現象表現得更明顯。最後從不同電極位置上進行四點正交量測,發現相同元件上,此橫向電壓與電極所在位置相關。
Graphene sheets are dispersed on SiO2 (300±15 nm) / Si substrates. Electron-beam lithography and thermal evaporation are applied to make devices with Au (80 nm) electrodes for four-probe electrical measurements. The device is measured at room temperature. The few-layer graphene sheets show little disorder with resistances and conductivity in the range of 1-3x103 Ω and 7-20 e2 / h, respectively. By applying back gate voltage, graphene field-effect transistors show typical ambipolar features. To probe transverse voltage, two electrodes arranged perpendicular to the source-drain current direction are used to measure the voltage difference. There are two different results as described below. One is that a voltage difference shows up owing to the geometry asymmetry in graphene devices. We call it the edge effect. The other result shows a transverse voltage which is maximum at the Dirac point and is opposite to the edge effect. It is much more evident especially in high-quality graphene devices. This transverse voltage may be related to the nonlocality due to the long-range electron-electron interactions and the linear dispersion relation in graphene. Actually, the difference between the edge effect and nonlocal effect can be separated apart. The nonlocal effect also shows a strong dependency on the position of the two perpendicular, probing electrodes.
URI: http://etd.lib.nctu.edu.tw/cdrfb3/record/nctu/#GT070252049
http://hdl.handle.net/11536/141685
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