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Design of a high-speed electrochemical scanning tunneling microscope
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View: Figures


Image of FIG. 1.
FIG. 1.

Models of two geometries considered for the STM: (a) the “standing head” and (b) the “hanging sample.” The part that can be rigidly clamped in a holder is imaged in blue and marked by arrows.

Image of FIG. 2.
FIG. 2.

Simulated frequency response of the relative tip-sample displacement, calculated using FEA, of the two geometries on the piezo tube motion at different frequencies. The “standing head” geometry is represented by the black line and the “hanging sample” geometry is represented by the red line. In these simulations, the piezo was excited with a sine waveform in the x-direction with a peak-to-peak amplitude of 51 V. This corresponds to a scan distance of 180 nm at the end of the tip holder capillary. For a usual tip length of , the scan distance would be . The relative displacement amplitudes minus the non-resonant displacement of the tip in the x-direction (a) and the z-direction (b) are plotted. The x-direction is along the scan direction and the z-direction is perpendicular to the scan plane.

Image of FIG. 3.
FIG. 3.

Photo of the prototype STM. The components are: (1) scanner head; (2) sample plate; (3) STM holder; (4) micrometere screws and springs; (5) piezo tube with the tip holder; (6) connectors for the electrodes on the piezo tube; (7) flow cell, mounted on the sample plate.

Image of FIG. 4.
FIG. 4.

Measured (black line) and calculated (red line) frequency response of the piezo tube (6.35 mm OD, 4.83 mm ID, 12.7 mm L) with the tip holder. The displacement is measured and calculated at the end of a capillary that sticks 3 mm above the ceramic tip holder, which has a height of 3 mm. The piezo tube was excited with a 51 V peak-peak amplitude sine waveform.

Image of FIG. 5.
FIG. 5.

Frequency response of the prototype STM on the vibrations excited by the piezo motion: comparison between the laser vibrometer measurements (black lines) and the FEA calculations (red lines). In (a), the piezo is excited in the x-direction, whereas in (b), it is excited in the z-direction. In both cases, the displacement is measured at the sample position. The piezo tube was excited with a 51 V peak-peak amplitude in the measurements as well as in the calculations. In (c), a schematic representation of the bending vibration mode of the sample plate, resulting in a resonance at about , is shown.

Image of FIG. 6.
FIG. 6.

Two models of the final STM scanner, equipped with (a) a standard sample plate and (b) a reinforced sample plate. Graphs in (c) and (d) show the results of FEA calculations of the displacement amplitude in x-direction and z-direction of the sample as the function of the piezo excitation frequency for the simple (black) and reinforced (red) sample plates. The piezo was excited with a 51 V peak-peak amplitude in the same direction as the direction in which the displacement is “measured.”

Image of FIG. 7.
FIG. 7.

Design of the flow-cell (a) and STM images measured during flow (b)–(c). (1) and (2) are the inlet and the outlet for the electrolyte. (3) is the hole for the sample. (b) Atomically resolved HOPG surface in ultra-pure water with the pump switched on at pumping rate. The image size is . (c) Cu UPD layer on the Au(111) surface imaged with the pump switched on at pumping rate. The image size is . The total height scale (from black to white) is: (b) 0.84 nm, (c) 0.36 nm. The tunneling parameters are: (b) 1.5 nA tunneling current and tip bias; (c) 1.5 nA tunneling current, tip potential, and sample potential.

Image of FIG. 8.
FIG. 8.

Photos of the final STM assembly. The STM scanner holder consists of an aluminium plate (1) that rests on three aluminium legs (2). An Invar ring in the middle of the plate (3) is used for clamping the scanner (4). The holder is connected to the environmental chamber via a Viton ring (not visible). An inert gas is supplied to the chamber via the input (5). The walls of the environmental chamber (6) are made of plexiglas. Please note that the front wall was removed in the photos. The ports in the side walls (7) are used for electrical and tubing connections. The sample plate (8) is mounted on the scanner. Teflon tubes for the electrolyte flow (9) are not connected to the flow cell in these photos. On top of the STM holder, a tunneling current preamplifier (10) and a USB microscope (11) for optical access are located.

Image of FIG. 9.
FIG. 9.

STM images of HOPG in air with atomic resolution. (a) Height image acquired at 1850 Hz line frequency and 7.2 Hz image frequency; (b) and (c) are error signal images measured at 7250 Hz line frequency and 72.5 Hz image frequency. Image (b) was measured from left to right and image (c) from right to left. The size of all images is . The height scale in (a) (from black to white) is 0.02 nm. The tunneling parameters are: tunneling current, and bias voltage.

Image of FIG. 10.
FIG. 10.

STM images of Cu crystallites, electrodeposited on a Au(111) surface from a , , and solution at sample potential vs . (a) Non-processed height image. The average height of the Cu crystallites is . (b) Differentiated image. Cu crystallites as well as atomic steps of the Au(111) substrate are clearly visible. The image was acquired at 2.93 Hz line frequency (175 s per image). The size of the images is . The tunneling parameters are: tunneling current, tip potential, and sample potential. (c) Height profile that was measured along the black line of the STM image in (a).

Image of FIG. 11.
FIG. 11.

Differentiated STM images of a growing Cu step bunch during electrodeposition on a Cu(111) crystallite from a and solution at sample potential vs . The images were acquired at 300 Hz line-rate (0.85 s per image). Every second image of the acquired image sequence is shown here. The images were acquired while flowing the electrolyte. One can clearly distinguish atomic steps of the growing deposit. Also, a weak corrugation is visible on the terraces (see also inset in the last image), which corresponds to the moiré pattern that originates from the formation of a sulfate adlayer. Size of all images is 155 × 200 nm2 and the size of the inset is 60 × 60 nm2. The tunneling parameters are: −5 mV tip potential and ∼500 pA tunneling current.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Design of a high-speed electrochemical scanning tunneling microscope