利用掃描探針顯微鏡分析還原氧化石墨烯之表面結構與電子結構

Abstract

本實驗主要是利用原子力顯微鏡(atomic force microscopy, AFM)與掃描穿隧顯微鏡(scanning tunneling microscopy, STM)來探討還原氧化石墨烯(reduced graphene oxide, rGO)的表面形貌與電子結構，找到rGO規律性結構，並且驗證理論模型。首先，在AFM影像的剖面高度圖中觀察到rGO的單層厚度約為1 nm，且rGO表面含氧官能基與沉積於基板上的應力都會造成其表面佈滿大大小小的皺褶。接著，透過STM進行小範圍的掃描，rGO的表面形貌大致可分為兩種，一種為無序性結構，另一種則為週期性結構。由STS的量測中得知rGO為無序性結構時，其能隙較大；若為週期性結構，其能隙幾乎為零。由此可推測無序區域的氧覆蓋率較高，因而形成無序鍵結；而規律性區域氧覆蓋率極低約為10%左右，此時，氧原子以armchair方向條紋狀鍵結，使得在STM影像中可觀察到週期性條紋。

In this experiment, we explore the surface structure and electronic properties of reduced grapheme oxide (rGO) by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) in order to study the ordered patterns on rGO surface. The AFM images of rGO reveal that the thickness of single layer rGO sheet is 1 nm. Wrinkles induced by the oxidation and deposition process are clearly observed in AFM images. The two kinds of morphology ordered stripes and disordered structure can be observed from the STM images of rGO. Through scanning tunneling spectroscopy (STS), the ordered region has zero band gap, and disordered region has higher band gap about 1~2 eV. Disordered region can be attributed to high oxide coverage. Ordered region is accounted for lower oxide coverage which oxide atoms form the stripe structure along the armchair direction, so we can observe the ordered stripe in STM image.