Agilent Technologies E5500 Series User's Guide download pdf (Page 221)

Electrochemistry 15

Agilent 5500 SPM User’s Guide 221

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.

Software Controls

Potentiostat

The software potentiostat allows control of sample bias. When in

potentiostat mode, the microscope will maintain a constant voltage on

the working electrode, as long as the current required to do so is within

the limits of the hardware. Three potentials can be controlled: sample

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Agilent Technologies E5500 Series User's Guide Page 221