이미징 원리 다이어그램 a 현미경
현미경 이미징 원리 다이어그램
작업 원리 의 STM
STM works by utilizing the quantum tunneling effect. if the metal needle tip is used as one electrode and the measured solid sample is used as another electrode, a tunneling effect will occur when the distance between them is about 1nm, and electrons will pass through the spatial potential barrier from one electrode to the other electrode to form a current. And Ub: bias voltage; k: Constant, about equal to 1, Φ 1/2: Average work function, S: Distance.
From the above equation, it can be seen that the tunnel current has a negative exponential relationship with the spacing S between the needle tip samples. Very sensitive to changes in spacing. Therefore, when the needle tip performs a planar scan on the surface of the tested sample, even if the surface has only atomic scale fluctuations, it will cause very significant, or even close to an order of magnitude% 2c changes in the tunnel current. in this way, the fluctuation of atomic scale on the surface can be reflected by measuring the changes in current, as shown on the right side of the following figure. This is the basic working principle of STM, which is called constant height mode (keeping the needle tip height constant).
STM has another operating mode, called constant current mode, as shown on the left side of the figure. At this point, during the needle scanning process, the tunnel current is maintained constant through an electronic feedback loop. To maintain a constant current, the needle tip moves up and down with the fluctuation of the sample surface, thereby recording the trajectory of the needle tip's up and down movement% 2c 및 제공 형태 의 샘플 표면.
The constant current mode is a commonly used working mode for STM, while the constant height mode is only suitable for imaging samples with small surface fluctuations. When the surface of the sample fluctuates significantly, due to the needle tip being very close to the sample surface, using constant height mode scanning can easily cause the needle tip to collide with the sample surface, leading to damage between the needle tip 그리고 샘플 표면.
