September+27-28

As I am not allowed to bring home my notebook from the lab, I have to photocopy the pages. I wasn't able to photocopy them on Monday the 27th, as I was in the basement of the Radiation Lab past 5, which is when the room with the photocopier closes. So, I copied the pages today, the 28th, and am updating for both days.

Monday, September 27th: Today I learned how to use a new AFM, in the basement of the Radiation Lab. I'm now working more directly with Valerie Goss, another PhD candidate whose work focuses more on the AFM. Becky and I went over to the basement where Val(erie) showed us the microscope (images to follow next week). This AFM differs slightly from the portable one that I have been using. The most obvious feature is the size. This AFM, which is not portable, is much larger, about two feet tall, and is hooked up to an old computer that doesn't have internet access (this is to prevent viruses, but makes the image recovery more difficult). With the size, a major difference is that the piezo (the part that holds the tip or sample) holds the sample and moves, up and down with slight lateral movement. This is different from the portable, which just has the scan head move, while the sample is on a magnetic puck. To scan a gold sample, you first "aim" with a high-powered optical scope. This scope allows you to align the laser (which reflects off the back of the scan head to create an image) on top of the scan head. First, you position your sample on the piezo, which is magnetic, and align a small dot of light, which represents where the optical microscope is looking. Then you insert a tray that holds the scan head, and align the laser on the back of the head, using the optical scope. You then use the computer to "auto-tune" the tip, which picks up the frequency at which the head is vibrating. This is shown in kHz. You then approach the tip to the gold, similar to the portable AFM. The first sample of the day was half-exposed to Polonium-210 for 24 hours, and was removed by Becky when I arrived at the lab. Because we weren't yet completely familiar with the scope, Val scanned this first piece, including aligning it with the optical scope. When the image wasn't clear, Val made it clear (no pun intended) that an effective thing to do was change the "Amplitude Set point", which adjusts the amplitude of the tip. That had an impact, although it wasn't perfectly clear yet. Valerie decided to change the tip because she was using a tip that was left in the scope by a previous user. The new tip tuned at a higher frequency than the old one, which Val pointed out to me. This is important because the tips aren't all the same, so you have to adjust the scope to suit each tip's need. Also, the higher the frequency, the more force you can use to scan. The feedback controls were: Integral gain: .8 Proportional gain: 1.6 Amplitude set point: 1.573 volts Drive frequency: 146.6 kHz Drive amplitude: 46.03 millivolts I'm still learning exactly what all the figures mean. Also, the z-height of the scan was 30 nanometers. I was in the lab from 3:30 until 6:30.

September 28th: (Images to come next week) Today, I was back in the basement of the Rad Lab without Becky, just Valerie. I learned how to use the AFM by myself, although Val, of course, was there, for help. The first thing I learned was how to change the tip. It is similar to the portable AFM, although a bit more intricate. Both use a clip system to hold down the tip and establish a current, but the tip holder of the basement AFM is larger and separate from the scope, unlike the portable AFM's which is built in. Also, in the portable AFM, the scan head moves to approach the gold. In the basement AFM, the sample holder moves.