Chemistry Reference
In-Depth Information
Fig. 2.13
Schematic illustration of vertical a and lateral manipulation
moved along predetermined paths of an STM tip [
76
]. This process is illustrated in
Fig.
2.13
b, which is called ''lateral manipulation''. Since the proximity of an STM
tip causes the strong field, the tip gives a finite force on an adsorbate [
77
].
This force involves both van der Waals and electrostatic contributions, which can
be adjusted by controlling the tip-surface separation and the bias voltage. Bartels,
Meyer and Rieder clearly demonstrated several kinds of lateral manipulation
modes depending on tunneling parameters [
78
]. The lateral manipulation also
applied to large molecules including molecular machines [
79
-
82
].
Understanding the force acting between the tip and the adsorbate is funda-
mental importance in STM manipulations. However it is quite hard to measure the
force in STM. Recently, Ternes et al. measured the vertical and lateral forces
exerted on individual adsorbed atoms or molecules by the tip [
83
]. They detected
such forces using the simultaneous operation of STM and atomic force microscope
(AFM). It was found that the force moving cobalt (Co) on Pt(111) and Co on
Cu(111) required a lateral force of 210 and 17 pN, respectively. The emergence of
STM/AFM paves a way to understanding the driving mechanism.
Although the STM manipulation has been well established so far, AFM can also
be used for the manipulation single atoms and molecules. Recent progress of the
non-contact AFM enables to manipulate atoms at semiconducting surfaces [
84
],
even at room temperature [
85
,
86
].
Even though the construction of nano-scale structure using STM manipulation
is inherently quite slow process, it gives fascinating opportunities to investigate
physical and chemical processes in desirable model systems at the single atom/
molecule limit.
