3.3. MICROSCOPY
55
STM . Constant Height Mode (Feedback Off)
Tunneling
current
t
STM -Constant Current Mode (Feedback On)
Tunneling
current
4
I
Figure 3.18. Constant-height (top sketch) and constant-current (bottom sketch) imaging mode
01 a scanning tunneling microscope. [From T. Bayburt. J. Carlson. E. Godlrey, M. ShankRetzlaff. and s. G. Sligar. in Nalwa (2000). VoI. 5. Chapter 12, p. 641.1
ncntially with the probe-surface atom separation, depends on the nature of the probe
tip and the composition of the sample surface. From a quantum-mechanical point of
view, the current depends on the dangling bond state of the tip apex atom and on the
orhital states o f the surface atoms.
Figure 3.19. Scanning mechanism for scanning tunneling microscope, showing (1) the piezoelectric baseplate. (2) the three leet of the baseplate and (3) the piezoelectric tripod Scanner
holding the probe tip that points toward the sample. (From R. Wiesendanger. Scanning Probe
Microscopy and Spedroscopy, Cambridge Univ. Press, Cambridge. UK, 1994. p. 81,)