ABSTRACT
If we can keep a constant electrical signal, we will get a constant gap of probe-specimen. In addition, if we can increase the tunneling current when we are on the top of an atom by lowering the tip a little, the attractive force between the tip and the atom would then increase, allowing us to “drag” atoms around. For example, an atom of iron can stick on the copper surface. The other iron atoms can then be dragged along the copper surface to form a circle. 17.4 Strong and Weak PointsSTM has some strong and weak points, as summarized in Table 17.1. Table 17.1 Strong and weak points of STM
K m
µ -
=
exp( )2
2 F where d is the tip-sample distance, K is the decay rate, m is the electron mass, F is the barrier height, and ħ is Planck’s constant. Assume the local barrier height to be 4 eV. Discuss the electrical sensitivity on the gap of the probe-specimen if the current is kept within 2%. 2. Write the one-dimensional potential diagram for STM. 3. Give some examples of STM feedback circuits. 4. Explain the typical piezoscanner.
