Week+of+3-18-2013

3-20-2013 I came into the lab today and began scanning a sample of Octanethiol on Au(111) with Matt. When I arrived, Matt has just changed the tip and was waiting for the scope to cool back down to -7.5 degrees BO-1000 Å, 50 ms/line, 64 A/D. I zoomed in to the bottom middle of this region following it. BP-500 Å, 50 ms/line, 128 A/D. This is a fairly decent image. It is pretty blurry but the overall structure of the surface molecules is faintly present here. Matt introduced a new type of scanning called Constant Current mode that can be used with this scope because it is able to scan so quickly and well. Normally, the scope changes it's current based on the height of the scope but if a region is flat enough like the one present here, it will be able to scan the image, possibly more accurately than with the regular mode because the tip won't be as subject to lateral movements which typically cause the high levels of blurriness in scanning. BQ- 500 Å, 15.4 ms/line, 128 A/D. This image is almost entirely indistinguishable from the previous one. I changed the scanning mode back to the regular type afterwards. BR-500 Å, 15.4 ms/line, 128 A/D. I'm pretty sure that the reason for this image's blurriness is the elevated surface on the left side and in the upper right corner. I moved the region down and to the right. BS-500 Å, 50 ms/line, 128 A/D- This image is interesting. The domain boundaries between the different groupings of Octanethiol are seen here as the slightly brighter strings of molecules between the larger stacks of molecular structures, which are actually not that clear in this image. I moved the scanning region downward afterwards. BT-500 Å, 50 ms/line, 128 A/D- This image, although a bit blurrier than the previous one, still displays the domain boundaries on its surface which is one of the hallmark features of an Octanethiol monolayer. I moved the scanning region up and slightly to the right following this. BU-500 Å, 50 ms/line, 128 A/D- Here we have an image of similar quality to the last one. There isn't much more to show here about the atomic structure of the surface. I moved it up and to the left. BV is very much similar to this one, mainly cause they are of the exact same region. BV-500 Å, 50 ms/line, 128 A/D-I zoomed out following this region. BW-1000 Å, 50 ms/line, 64 A/D BX-500 Å, 50 ms/line, 64 A/D. I changed the A/D gain and rescanned this region. BY-500 Å, 50 ms/line, 128 A/D- I moved it partially to the right so that I could avoid the large mound on the left side. BZ-500 Å, 50 ms/line, 128 A/D. Following this image, I zoomed out and took a full scan. This image wonderfully displays the formation of domain boundaries between the different groups of Octanethiol molecules. The groups of Octanethiol molecules form in large groups formed in the same direction and the domain boundaries form where these different groups meet. CA- 3898 Å, 50 ms/line, 16 A/D- I zoomed in to the bottom left. CB-900 Å, 50 ms/line, 128 A/D- I zoomed in to the middle region of this image. CC-500 Å, 50 ms/line, 128 A/D. This image, although somewhat blurry, displays a somewhat faint picture of the atomic structure on the surface. I reduced the line time to try to reduce the blurriness and moved the scanning region to the right. CD-500 Å, 25 ms/line, 128 A/D. This image does a great job of showing the domain boundaries but does not very clearly show the atomic structure of the surface monolayer. I zoomed in to the bottom middle. CE-250 Å, 25 ms/line, 128 A/D- This is an incredible image. The domain boundaries in the bottom right corner and in the upper left quadrant are very clear and defined. The rest of the image shows a very clearly packed Octanethiol structure. I used the constant current mode after this image. CF-250, 15 ms/line, 128 A/D. Although a little blurry here, I scanned it a second time to try to get a better image, hoping that the original cause for this lack of definition was the tip simply drifting and adjusting to the new settings. CG-250, 15 ms/line, 128 A/D. I'm fairly certain that this image more distinctly shows the molecules on the surface. The spaces between each one is much more defined than either of the previous two images, which gives credence to our previous belief that the constant current mode could scan more effectively than the regular mode. CH-250, 50 ms/line, 128 A/D CI-250-25 ms/line, 128 A/D. The first half of this image does a better job of showing the discrete molecules on the surface than CG does. Unfortunately, the quality of the second half of the image is much lower for reasons I am not quite sure of. I kept trying to move the scanning region to find a region of similar quality to the top half of this one. CJ-250, 25 ms/line, 128 A/D CK-250, 25 ms/line, 128 A/D Matt took seismometer measurements of the table, floor and the scope afterwards to find out the vibrations of all three. As suspected, the floor had the least vibrations, the table vibrated only slightly more than the floor, and the scope vibrated much more than the other two. The analysis of the table was done with out the air on, which would normally provide better vibration isolation. What we concluded from our analysis is that the scope is built in a way that when it vibrates the whole thing must be vibrating uniformly which allows it to avoid the negative effects of the vibrations. This is why we have been able to have so much success with scanning so far. I resumed scanning and tried to find an image of quality similar to CI and CG CL-1000, 25 ms/line, 32 A/D CM-500, 25 ms/line, 128A/D. This image has a decent level of quality and a high level of potential for its subsequent images. It is fairly blurry but there still is a faint underlying structure. I zoomed in to the top middle of this image. CN-250, 25 ms/line, 128 A/D. I moved the scanning region down and to the right to avoid the large mound on the left side of this image. CO-250, 25 ms/line, 128 A/D CP-250, 25 ms/line, 128 A/D. I moved this region up and to the right to avoid the huge pit in the bottom left. CQ-250, 25 ms/line, 128 A/D, I finally reached a fairly flat region so that I could utilize constant current mode. I did so after this image. CR- 250, 15 ms/line, 128 A/D- I moved the scanning region upwards after this image to the junk on the bottom and scanned again. CS-250, 15 ms/line, 128 A/D. The drift ended up placing the scanned region much closer to the junk on the bottom than I wanted it to. I moved it up again and re-scanned. CT-250, 15 ms/line, 128 A/D, I moved it to the left and then took several images to gather more proof that the constant current mode could produce images of incredibly high quality. CU-250, 15 ms/line, 128 A/D. Following this image, I moved the scanning region up and to the right. CV-250, 15 ms/line, 128 A/D. I took off the constant current mode after this image and took images of the same region in the regular mode to see how this region would compare. CW-250, 15 ms/line, 128 A/D- For the most part, this and the previous image are of almost identical quality. However, the molecules just under the domain boundary in this image have less defined boundaries than the one in the previous one, suggesting that the constant current mode is indeed better. CX-250, 25 ms/line, 128 A/D. The increased blurriness in this image further suggests that the constant current mode is more effective at scanning. The next two images of this same region, CY, and CZ, also suggest that this is true. CY-250, 25 ms/line, 128 A/D CZ-250 25 ms/line, 128 A/D

3-21-2013 Today I came into the lab and began scanning a sample of C-60 on Au(111) that Matt prepared. Matt informed me that his scans of the sample before I arrived were of dubious quality so I had very low expectations about how the images would look. BI-1500 Å, 50.2 ms/line, 64 A/D, I zoomed in to the upper left. BJ-1000 Å, 50 ms/line, 64 A/D. I zoomed into the middle. BK-500 Å, 50 ms/line, 128 A/D, I zoomed out and scanned the whole region

BM-100 Å, 500 ms/line, 64 A/D. I heated the sample for 10 seconds and the tip crashed just after second 9. I waited 10 minutes for it to cool down. The scanning all day was mediocre at best. There was not definition in any of the images and there was no absolutely no insight or clear representation The approach afterwards did not end up working. I took the sample out and changed the tip. Once more, the approach did not work despite the oscilloscope showing that the tip had crashed. We checked the connection between the bias of the scope and the sample and found that they were at the same potential which is what was preventing the scope from actually tunneling. This is because the resistor's plate which physically connected the sample to the other bias input was connected with regular epoxy rather than conductive epoxy. Before I left, I prepared a new resistor and heat dissipation plate then applied the conductive epoxy. It will be ready to work by next week.