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Illustration of the dual-probe STM unit and STM images. (a) The unit is composed of sample-mounted block, Unit1 with Tip1 and Unit2 with Tip2. The sample-mounted block and Unit1 and Unit2 are mounted on the top plate of the vibration isolation stack. The baseplate of the stack is hung with the three suspension springs and has 12 Cu fins for eddy current damping. The thick arrows on each unit indicate the directions along which the upper parts are moved. (b) and (c) are typical constant current images of a HOPG surface obtained with Tip1 and Tip2, respectively. A parallelogram drawn on each image indicates a unit cell of (0001) plane.
The sequence of probe tip arrangements to the sample surface. (a) The distance between two probe tips is shortened to about . (b) Each probe approaches the sample surface until the tunneling current is detected. (c) Both probes are withdrawn about from the surface. (d) Tip2 is additionally withdrawn from the sample surface, and the feedback loop of Tip1 is turned off. The arrangement of (d) is called the “initial position.”
Illustration of the approach route of Tip2. Tip2 moves at the speed of along a route of the solid arrows (like a rectangular wave) on the upper plane, which is apart from the sample surface. The route has a wavelength of and an amplitude of for and directions, respectively. Tip1 and the sample are biased, while Tip2 is grounded.
Constant current images obtained with (a) Tip1 and (b) Tip2 . Each image shows two identical objects labeled by A and B.
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