不同扫描速度下的导电原子力显微镜电流测试研究

Study on current test of conductive atomic force microscopy under different scanning velocities

导电原子力显微镜(C-AFM)可在微观尺度下同时检测表征材料表面形貌和导电状态,是重要的材料表面表征设备。针对C-AFM测试过程中电流信号失真的问题,研究了其产生的规律,并提出了解决的措施。首先使用原位纳米力学测试系统在砷化镓(GaAs)表面制作出纳米划痕,再利用C-AFM对GaAs表面的划痕进行形貌和电流信号检测,并与GaAs表面做以对比。实验结果表明:在低偏压未导通的情况下,针尖的扫描方向和扫描速度对电流信号的检测有显著影响,当针尖垂直于划痕扫描时,可得到起伏的电流信号,而平行于划痕方向扫描时,则无明显的电流信号;划痕处电流信号的产生与C-AFM的扫描速度大小有关,速度越大,电流波动越明显;降低速度可有效避免这种形貌起伏(如表面沟槽)所致的电流波动的产生。分析表明,这种电流波动的产生与C-AFM探针悬臂梁在针尖经过材料表面的剧烈起伏时所产生的位移电流有关。研究结果提供了C-AFM扫描过程中避免错误电流信号干扰的方法。

The conductive atomic force microscopy(C-AFM)is an important material surface characterization equipment,which can concurrently characterize the morphology of material surface and test the conduction state from microscopic scale.For the distortion of current signal during C-AFM characterization,the reason of such phenomenon was studied and some solutions were proposed.Firstly,an in-situ nano-mechanical testing instrument was used to generate nano-scratches on(100)surface of GaAs.Then the C-AFM was employed to get the morphology and current information of the scratches and compared with the original GaAs surface.The results show that the scanning direction and velocity have a remarkable influence on the current signal under the condition of low bias and without conduction.Fluctuated current signal can be detected when the scanning direction is vertical to the scratch,but no obvious current signal can be detected when the scanning direction is parallel to the scratch.The generation of current signal at the scratches is related to the scanning velocity.The higher the scanning velocity is,the more obvious is the fluctuation of the current value.This current signal caused by the uneven morphology(e.g.surface groove)can be effectively avoided by decreasing the scanning velocity.Analysis indicates that the current change is related to the displacement current induced by the precipitous fluctuation of the tip while scanning on the uneven sample surface.And a method avoiding the interference of the wrong current signal during C-AFM scanning is provided.