Week+of+2-4-2013

2-4-2013 I came in today and began scanning the same sample of gold from last week on the new scope. Matt was mostly busy working on his presentation for tomorrow so he had me gain more practice with this new scope setup. The scope I will be using for my heating experiment is very similar to this new one. Matt also wanted me to find an appropriate tip length that can be used as a standard so that the scope can approach quickly. The first approach I did took only 555 steps, a relatively short amount compared to the approaches I used to have when I used the other scopes. AA-1000 Å, 16 A/D, 100 ms/line. I had expected to not be able to get very much but noise and junk with this sample because it has been sitting in air for the past two weeks but surprisingly, I was able to get a half-way decent looking surface of something that is clearly a gold surface. I moved the scanning region up about 3000 Å. AB-1000 Å, 32 A/D, 100 ms/line. There is still definitely some junk on this gold surface but it is also clear from this image that we are indeed looking at a gold surface. I am convinced that I had a very good tip for all of the images of this specific 1000 Å region that I scanned. Matt had told me earlier that this new scope is much more rigid and less susceptible to suffering from vibrations so I tried reducing the line time to see just how fast we could scan while still getting a reasonable image. AC-1000 Å, 32 A/D, 50 ms/line. It seems that the majority of the quality of the previous image was maintained. Speeding up the line time to 50 ms/line did not compromise the image. I decided to see if I could go further and reduced it to 10 ms/line. AD-1000 Å, 32 A/D, 10 ms/line. It is clear from this image that, by scanning at such a high rate, I am losing image quality and amplifying the little low-frequency noise that is present in the table's vibrations. AE-1000 Å, 32 A/D, 25 ms/line. Even after reducing the scanning rate to 25 ms/line, the scan still appears quite blurry and the low frequency noise caused by the table's natural vibrations is able to come through with such a high scanning speed. I've decided that, for this scope at least, I will stick to 100 and 50 ms/line scanning times. AF-1000 Å, 64 A/D, 100 ms/line. Instead of trying to increase the scan speed, I decided to increase the A/D gain to try to improve the image. it appears to have done so to an extent. Prior to this image being taken, Matt had turned on the air tables so that is why it started out a little rough. Otherwise, I think that it was generally an improvement compared to AC. It is still somewhat blurry though and the surface looks to have quite a bit of junk on it. AG-1000 Å, 64 A/D, 50 ms/line. I tried to improve the quality of the image by increasing the scan speed to 50 ms/line yet I don't see that much of a change between the two images. In fact, it looks as if this image is even blurrier than the previous one suggesting that even at 50 ms/line and with the air tables on, the scope is still somewhat susceptible to the vibrations of the table at this relatively high scanning speed. AH-1000 Å,128 A/D, 50 ms/line This image's incredibly high A/D gain coupled with is low line time proved to be a recipe for blurriness. I find this one to be of lower quality than the previous two. Although I believed I had a really good tip, I decided to change the tip because the sample was terrible and the goal for today was to determine a length for tips to be cut so that approaches could be consistently short. The second approach took even less than the first. I was quite surprised. It took 379 steps. AI-1000 Å, 16 A/D, 100 ms/line AJ-1000 Å, 16 A/D, 100 ms/line. This and the previous image are quite blurry, most likely due to the decrease in tip quality. It's harder to tell from these images that I was actually scanning something rather than just junk as opposed to the images done with the previous tip. By time I finished this image, it was time to go. Here is the new scope as viewed from the left side. The silver wires are the high voltage wires that control the different X, Y, and Z offsets. The new scope from the right side. Here is the sample holder and the sample of gold that I used today. The hole in the middle of box houses a tube that keeps the tip in place for scanning.

2-7-2013 I came in today and began adjusting the settings on the new scope to try to make it be able to retract. I first recorded all the settings so that they could be restored at the end of the day. Waveform: Sawtooth Waveform Polarity: Normal Output Channel: DAC 1A Approach Amplitude: 5000 Å Retract Amplitude: 1.00 µm Fast approach: 8 µm Fast Retract: 1.0 µm Period: 1.00 ms Filter period: 0 s Adjust Amplitude: 1000 Å Motion per D/A volt: 1000 Å, Cycle Delay: 15.00 ms At first I tried using the camera set up to visually watch the tip move backwards. I adjusted motion per D/A volt to 2000 Å and the fast retract to 1.5 µm and then 2.0 µm, both without success.l Instead of this, I decided to have the tip approach a sample of gold. After it would tunnel, I would adjust one of the settings or adjust the physical level of the scope. It wouldn't approach for about 20 minutes so I rotated the sample 90 degrees and it was able to approach in 601 steps. I attempted changing the settings I had before and saw the same lack of success I had before. I then tried tilting the scope so that it would need to travel up a slight incline to approach and so that it would be more natural for the scope to retract. This attempt was indeed successful. It was able to use the Retract function but it was still unable to use the Fast Out function. I tried approaching it again afterwards and after about 1600 steps, I stopped the approach and rotated the sample again. After doing so, it approached in 72 steps. I then took two scans of it and utilized the Retract function successfully a second time. Unfortunately, I was once more unable to approach following the retract. Neither scan was particularly great nor had any interesting features. They were mostly just full of junk and were poor scans as I had expected since I had crashed the tip into the old sample so many times in my efforts today. AA-2000 Å, 16 A/D, 100 ms/line AB-2000 Å, 16 A/D, 100 ms/line