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STM Scanner I-V Plots

STM Scanner I-V Plots. I-V curves can be used to show the hardware response to a known current. This information can help diagnose scanner and pre-amp problems. Need to make a resistor wire (Agilent supply proper ones but are unnecessary):

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STM Scanner I-V Plots

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  1. STM Scanner I-V Plots

  2. I-V curves can be used to show the hardware response to a known current. This information can help diagnose scanner and pre-amp problems. Need to make a resistor wire (Agilent supply proper ones but are unnecessary): The resistor wire is a 1 GΩ resistor that has a gold tip soldered to one end.

  3. The tip is placed into the scanner you want to test, which is plugged into the STM head. The other end of the wire is inserted into the middle connection of the sample plate plug – this is where the bias is applied to the sample. Bias Bias – middle connector

  4. Experimental Setup Scanner Electronics Board Controller STM Head Resistor Wire Tip Pre-amp Resistor This set up is designed so that a known current is passed to the pre-amp. This isolates them for testing. 10nA The resistance of the wire is 1 GΩ: V = I × R V = 10-9 A × 109Ω = 1 V We should get a straight line with a gradient of 1: 1 nA results in 1 V. -10V 10V -10nA

  5. Experimental Setup • If you know the current input to the scanner to be ok then the scanner output observed in the software is due to the pre-amp and scanner electronics alone. • The IV curve after the scanner should also be a straight line that passes through the origin. Various factors can alter this response: • The controller and STM head – a good response from a working scanner good enough. • The resistor wire: Resistors aren’t perfect and their rated resistance can be wrong by as much as 10% - If you think the resistor is wrong try another one. • The pre-amp: Converts the current through the tip to a voltage between ±10 V. • Scanner electronics. • The hardware set up will change the gradient – gain switch, conversion coefficient. 1. 2. 3. 4. • Assuming the controller, head and tester wire are functioning properly: • Test different scanners in the same head. • Swap the pre-amps between scanners. Very carefully– need electrostatic protection!!! Resistor Wire

  6. In the software, open the Spectroscopy window and in the mode menu select ‘IV Spectroscopy’. Set the scan range to +10 V and –10 V This will set the software to scan the entire range of the pre-amp. Click ‘Start’

  7. Results My Scanner (1 nA/V, STM1) Faulty 1 nA/V Scanner from STM3 Nicola’s Scanner (1 nA/V, STM2)

  8. 50Hz and 60 Hz Noise Example: 50 Hz noise has a period of 0.02s. On a scan lasting 0.1s, 5 oscillations should be discernable, as exemplified below (probably not to scale): 0.1s

  9. 50Hz and 60 Hz Noise In the event that such noise appears, then shielding is necessary. This in normally achieved by positioning a blank sample plate on the STM. The resistor wire should be between the plate and the scanner. This was not used (or even necessary) for the results on the previous slide. Enough shielding already exists. Any other ‘tuna-can’ size piece of metal should do, as long as it’s positioned close.

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