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Schematic drawings of the microscope. Left column: a slider and the lower part of the microscope. Central column: the two main parts of the STM head. Right column: the assembled STM head.
Schematic of the equivalent electric circuit for the piezoelectric positioners. Each piezostack is represented here by a capacitor of C = 1 nF. The voltage signal applied is sawtooth-like.
(a) Schematic of the sample structure. (b) AFM image of a graphene flake presenting a nanogap opened by electroburning and the connecting gold electrodes.
Schematic of the circuit used for detecting the electrodes. The three capacitors represent the capacitances between the tip and the gate and between the tip and each of the two electrodes.
(a) Optical microscope image of the sample. (b) Series of capacitive scans superposed to the optical image. The scan lines are obtained adding the output of the two lock-in amplifiers. The red/yellow dots correspond to lower/higher capacitance. Panels (c) and (d) show the capacitance signal along two of the scans in (b), for each scan we present the output of the two lock-in amplifiers as a function of tip displacement. The blue/red curve corresponds to the capacitance between the tip and the lower/upper electrode.
(a) Composition of STM images of a graphene flake with a nanogap in the middle between the two gold electrodes corresponding to the area shown in Fig. 5 . The distance between the edges of the two Au electrodes is d = 590 nm. (b) STM image of the nanogap in another flake where different layers can be seen. The measured depth of the gap is 11.5 nm.
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