Electrostatic Force Microscopy with the Nano-R™ AFM

Procedure

Mount EFM cantilever to tip holder using conductive adhesive.
Insert EFM cantilever and sample into standard positions.
Connect sample to the power supply.
Connect the tip to the power supply.
Choose contact imaging mode.
With the power supply off, collect a topographic image of the sample surface of interest.
To collect an EFM image you will need to raise the tip above the surface of the sample to remove the topography component. The simplest way is to use the motors on the AFM coarse approach motors to withdraw the tip from the sample surface. The forces involved with EFM are typically larger than those with MFM (since we can control the applied voltage to some extent) which allows more freedom with the tip sample spacing. We typically raised the tip approximately 800 nm above the sample surface (one step of the stepper motor).
Turn off the PID (by using Settings/PID ON/Off menu option) or decrease the gain settings to 1. This will prevent the AFM from trying to go into feedback when a deflection of the cantilever is recorded.
Start scanning the sample while slowly increasing the applied bias on the tip and/or substrate (we were able to record EFM images with a bias of less than 3 V on a conducting gold substrate).
The image will appear by recording the error (deflection) signal.
A quick check can be performed to determine if the measured signal is an EFM image by reversing the applied bias which should invert your image. Depending on your sample, this may not be possible.
We were able to collect EFM images gold patterned substrate within 5 minutes of imaging.

Figure 1: Optical image of gold fingers on a glass substrate.

Figure 2: 91 × 91 чm scans of gold fingers on a glass substrate. The fingers alternate in applied bias. A) Topographic, contact, image. B) EFM images where + 17 V is applied to the tip. C) -17 V applied to the tip. In both B and C, the fingers with the same bias appear dark.

Figure 3: Screen capture of the data collected in figure 2 halfway through the scan while changing the bias. This effect can clearly bee seen in the Z(ERR) window where a reverse of contrast is evident. The gain is set to 1 with the PID on.

Figure 4: 76 × 76 чm scans of the ends of gold fingers on a glass substrate. The fingers alternate in applied bias. A) Topographic, contact, image. B) EFM images where + 17 V is applied to the tip. C) -17 V applied to the tip.

Figure 5: 3D reconstruction of figure 4B. This image shows how the electric field dissipates over the surface. It is interesting that the electric field is higher on the arms further away from the base, even though they are at the same bias.