Ch. 9. Scanning Tunneling Microscopy Sec. 9.11. Troubleshooting
Material: 80%/20% Platinum Iridium. Wire should be drawn straight. Wire cut from a roll has a small
radius and may not hold tightly into the tube on the STM holder. The tube is bent with a large radius.
This is intentional to help reduce drift due to the stress of bending the probe wire upon insertion into the
holder.
Wire size: 0.01” diameter (0.25mm) , cut approximately .3” long. Longer probes are usable but may
introduce image distortion from drift due to the length. Contact Asylum Research about further tools
and technique required to make the proper cuts.
9.11. Troubleshooting
9.11.1. Testing the STM holder
A 500M Ω resistor is supplied in the STM accessories kit. The resistor is soldered to a short length of
wire terminated by some Pt Ir probe wire.
To test the holder,
1. insert the platinum wire into the tip tube and
2. plug the resistor into the Sample socket in the terminal block.
3. Set the surface bias to 1V and
4. note the measured current. It should be 2nA (1/500e6 Ω).
5. Use the test panel, Email
Support@AsylumResearch.com for details on loading this software.
6. Use the noise tab to measure the current noise of your holder.
7. The typical noise should be ~8mV (~8pA) Adev from 1hz-1kHz with little perceivable periodic
noise in the spectrum.
9.11.2. The Current2 Signal
The initial current to voltage conversion takes place in the first stage of a two channel op amp. The first
gain stage labeled Current2 in the data channels has an output sensitivity of 20nA/V. In most cases this
signal is not suitable for feedback but can be monitored as well as the final 1nA/V final stage if desired.
The reason for this signal is derived from the design of the STM amplifier that is the same basic circuit
as the ORCA - CAFM cantilever holder.
support.asylumresearch.com Page 112
To Next Page
Loading...