Scanning constant current mode

Figure 26. Constant current mode STM image of isolated (A), self-organized in close-packed hexagonal network (C) and in fee structure (E) of silver nanoclusters deposited on Au(l 11) substrate (scan size (A) 17.1 x 17.1 nm, f/t=—IV, /t=ltiA, (C) 136 X 136 nm, f/t = — 2.5 V, /t = 0.8 tiA, (E) 143 x 143 nm, = —2.2 V, /, = 0.72 nA). I U) curves and their derivatives in the inserts of isolated (B), self-organized in close-packed hexagonal network (D) and in fee structure (F) of silver nanoclusters deposited on Au(l 11) substrate. (Reprinted with permission from Ref. [58], 2000, Wiley-VCH.)...

Fig. 26a. Scanning tunneling microscopic image of a 310nmx310nm area of bare Au film epitaxially grown on a mica substrate (Au mica) measured in air constant current mode bias (Vb) of + 50 mV, tunneling current (I,) of 10 nA. b STM image of a 3.5 nm x 3.5 nm area of a bare Au/mica film constant current mode Vb = 4- 4.9 mV I, = 3.0 nA [219]...

Fig. 27a-d. STM image of a 100 nm x 100 nm a n-oetadecanethiol film coated on Au/mica b same area after 10 s of etching mode (Vb = 10 mV, I, = 10 nA) over a 10 nm x 10 nm area (within area shown by broken line% c same area after 10 min of continuous normal scanning d after 35 min normal scanning. All images were taken in constant current mode, Vb = + 1V, and I, = 1 nA [219]... 

The constant height mode of operation results in a faster measurement. In this analysis, the tip height is maintained at a constant level above the surface and differences in tunneling current are measured as the tip is scanned across the surface. This approach is not as sensitive to surface irregularities as the constant current mode, but it does work well for relatively smooth surfaces. 

The electrolysis of the studied systems was carried out in the same cell as voltammetry measurements under the mode of either constant current or voltage. In the constant current mode, the applied current density was in the range of 0.01 0.2 A/ sm2 with reference to the surface area of the cathode before starting the electrolysis. Semi-immersed glassy carbon plate electrodes (cathode area - 5 sm2, anode area - 10 sm2) were used while electrolysis experiments. A powder product was either settled down onto the crucible bottom or assembled on the cathode in the view of electrolytic pear . The deposit was separated from salts by successive leaching with hot water. Thereafter, the precipitate was washed with distilled water by decantation method several times and dried to a constant mass at 100 - 150 °C. The electrolysis products were analyzed by chemical and X-ray phase analyses, methods of electron diffraction and electronic microscopy (transmission and scanning). 

Two different modes of imaging have been developed the constant current mode and the constant height mode. In the first experiment, the tip is scanned across the surface at constant tunnel current /T, maintained at a pre-set value by continuously adjusting the vertical tip position with the feedback voltage Vz. In the case of an electronically homogeneous surface, constant current essentially means constant tip-sample distance z (Fig. 7). 

On the other side, on surface portions with small unevenness, the tip can be rapidly scanned at constant z-position. Such current images allow much faster scanning than in the constant current mode, but a separate calibration of current/height is required. This mode is presented in Fig. 8. 

The step size is given by the size of the scan area and the pixel resolution of the image . Tire acquired signal - either the voltage needed to move the tip up and down in z direction (constant current mode) or the tunneling current itself (con-... 

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