NT-MDT Solver Next - Scanning Tunneling Microscopy; Constant Current Mode; Adjusting the Controller Configuration; Approaching the Sample to the Probe

Chapter 7. Performing Measurements
125
7.4. Scanning Tunneling Microscopy
The Scanning Tunneling Microscopy is capable to study surfaces properties of conductive
materials with resolution down to atomic scale. The tunnel current recorded during
scanning is small enough (0.5 pA ÷ 50 nA) to enable investigating samples with low
conductance, biological objects in particular.
Special modes facilitate acquisition of spatial distributions of various electrical
characteristics, such as work function, local density of electron states, etc.
Interpretation of the collected STM data is rather involved because details of the STM
image are determined not only by the surface topography, but also by its local electrical
characteristics.
7.4.1. Constant Current Mode
Initial state
The following steps are assumed to be done (see Ch. 6 “Preparing for Measurements”
on p. 29):
● Launching the control program;
● Turning the instrument on;
● Mounting the sample;
● Moving the STM measuring head to its working position;
● Initial approach;
● Selecting the scan area.
Procedural Sequence
Measurement in the Constant Current mode is arranged in the following procedural
sequence:
1. Adjusting the Controller Configuration (see i. 7.4.1.1 on page 126).
2. Approaching the Sample to the Probe (see i. 7.4.1.2 on page 126).
3. Adjusting Working Level of the Feedback Gain (see i. 7.4.1.3 on page 131).
4. Adjusting Scanning Parameters (see i. 7.4.1.4 on page 132).
5. Scanning (see i. 7.4.1.5 on page 137).
6. Saving Measurement Data (see i. 7.4.1.6 on page 140).
7. Completing Measurements (see i. 7.4.1.7 on page 140).
These procedures are explained below.