Electrochemistry
5
Keysight 5500 SPM User’s Guide
5-8
Troubleshooting
The most frequently encountered problem is leakage from around the
bottom of the liquid cell. It is generally more of a problem with solvents
that “wet” the substrate well, such as methanol. This causes leakage
current and erratic imaging. Make sure that the sample is flat and large
enough to fit underneath the liquid cell without gaps. Check that the
O-ring is clean and pliable. Tightening the sample plate screws will
increase pressure on the cell. Do not overtighten as this may crack the
liquid cell.
Electrochemistry Definitions
1
In STM Mode the tip is always virtual ground. Virtual ground means
that the potential of the probe is actively kept at ground by the
operational amplifier, but the tip itself is not connected physically to
ground.
2
In AFM Mode the potential of the tip is determined by the setting of
the switch on the back of the Head Electronics Box (for conductive
cantilevers):
a
If the switch is set to
WE
then the cantilever is biased to the same
potential as the working electrode (sample substrate).
b
If the switch is set to
Tip
then the cantilever is tied to the tip bias
DAC output. This is typically ground unless the bias setting is
configured so that the probe is biased instead of the sample.
c
If the switch is set to
BNC
then the cantilever potential is the
same as the Cantilever BNC potential. This can be driven
externally or will float if nothing is connected to the BNC.
3
Sample Bias = WE.
4
Sample Potential = WE - RE.
5
Probe Potential = - RE.
a
Sample Potential = Sample Bias + Probe Potential.
b
The only two independently-controlled potentials are WE and
RE.
6
VEC = WE - RE
7
IEC = Current into or out of the working electrode. Positive is
flowing into the working electrode.
