#10 Flat Washers – Home Depot part number: 887480024715
Pt/Ir tip wire (50 cm) – nanoScience part number: 20105
Conductive carbon tape or conductive silver glue – Ebay
Prepare a tunneling tip. For initial tests, the tip wire can be regular copper wire, but for the best results a Pt/Ir wire should be used. The tunneling tip wire should be cut using scissors or side cutters held at a 45 degree angle. The cut wire should be about 1 cm long. Load the tunneling tip into the tip holder (the section of DIP socket) using a pair of tweezers.
Prepare a sample to image. For early testing, the circuit board of the sample holder can be used, but the best practice is to use a section of DVD. Cut into a DVD-R disk with a pair of scissors. Try to remove the clear plastic layer from the DVD, leaving the top of the disk with the label and the foil layer on it. Cut a section out just smaller than the #10 washer. Place it, foil side up, on the washer. Attach it down using conductive tape or glue. Make a good electrical connection between the foil and the washer. In the picture below, the DVD section is in the foreground and has been attached with silver paint. The sample in the background has been attached with conductive tape. Load the sample into the microscope where the magnet in the sample holder should hold the #10 washer down tightly.
Start the software. Click on the question mark on the extreme right side of the screen. This will open a program information screen. It will show the electrical connections that the software requires. At the bottom of the window, it will show all NI cards in the system. Look for the 6323 card entry or the 6001 device entries and make a note of the device number(s). Enter the device number(s) in the “Card Number” field in the “Calibrations” group.
Check all electrical connections to the computer shown in the program information screen. Use an oscilloscope to monitor the z-axis voltage and the tunnel current output from the transimpedance amplifier. If you do not have an oscilloscope handy, two multimeters can be used instead. They will not capture the quick changes in voltage but they will register trends. Plug in the batteries for the amplifier and plug in the stepper motor power supply.
Click the “Feedback On” button. If no error messages show up on the status bar at the bottom of the screen, the feedback loop is on. As soon as the feedback loop is turned on, the z-axis voltage monitored on the oscilloscope should move quickly to +10 V or -10 V. The tunnel current output monitored on the oscilloscope should be 0 V. Use the “Closer” and “Further” buttons to verify that the stepper motor can move the sample holder.
Next click the “Auto Approach” button. The sample should begin moving slowly toward the tip. At each motor step, the computer will monitor feedback loop. Once the sample has moving into tunneling range, the stepper motor should stop moving.
Once the motor stops, the z-axis voltage monitored on the oscilloscope should be between +10 V and -10 V but not at either extreme. The tunnel current output monitored on the oscilloscope should be at value given in the “Set Point (V)” edit box in the software. If these voltages are right, press the “Take Image” button and the first image acquisition will start. A typical image of a DVD sample is shown in the picture below for a scan width of about 4000 nm. It should have ridges every 740 nm.
It is best to withdraw the tip for a few seconds before turning off the system. This prevents the tip from crashing into the surface when the feedback loop is turned off. Remember to unplug the batteries and the motor power supply.