First+Semester+Final+Project+Draft+Agostino+Chris

__**First Semester Final Project Draft**__

My research is based on the use of gold surfaces (Au(111)) submerged in Octanethiol solutions, allowing for a layer of the Octanethiol to arrange on the surface of the gold. The goal of my research is essentially to look for changes caused by laser heating to the structure of Octanethiol chains on the surface of the gold. With the capabilities of the Scanning Tunneling Microscope (shown with the silver sides and golden top below), it is possible for us to take scans of the surfaces of these gold samples (Au(111)) covered with Octanethiol. I am essentially looking for differences in the structure of Octanethiol molecules on the surface of gold caused by heat from a laser. The quality of these scans is directly related to the quality and sharpness of the Platinum Iridium (PtIr) Tips that I employ. The lower the area of the tip in possible contact with the sample is, the sharper and more clear the image will be. When I am able to obtain a high enough quality image, I utilize the laser. However, to combat thermal expansion, I use a sample holder specifically created for my research.
 * Overview of my Research**

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 * Scanning Tunneling Microscope and Sample Holder**

This sample holder is a hollow metal tube that has a hole to allow light to reach the backside of the sample and contains a piezoelectric stack on the top of it (the green box-like object in the above picture). Also, the sample puck has a hole in it to allow for light to pass through and hit the back side of the gold. This piezoelectric stack expands and retracts when voltage is applied or lowered. This change in length is so minute and minuscule that it allows for adequate room for thermal expansion but also enough so as to avoid crashing into the tip. Also, because this change is so small, it allows for the possibility of scanning an extremely similar surface after the laser is applied. The piezoelectric stack is powered by fifteen 9-Volt batteries inside a box that can be controlled by two knobs, one for coarse adjustment(ones) and the other for fine adjustment(tenths). The third knob is in place for a possible future need. As of now, it has no use.

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 * Piezoelectric Stack Power Supply Box**

I have found that small amounts of time such as between 30 seconds and one minute are conducive to getting results and maintaining a similar surface between the before image and the after image. Through experience, I have concluded that a decent amount more than a 45.0 V difference of applied electricity between the scanning state and the lasing state is necessary to allow for thermal expansion without crashing the tip. I have not figured out currently what difference is large enough to allow for thermal expansion but to minimize movement between the before image and the after image.Next semester, I hope to find the optimal difference that allows just the right amount through tests involving different changes in voltages. By doing this, I hope to increase the number of before and after images that have the same area and hopefully retain the quality of the tip and of the sample by avoiding crashing. The laser that I use is a blue-violet laser.

media type="custom" key="11942094" As implied above, this box houses the proper circuitry and batteries for properly powering the laser.
 * Laser Power Supply**

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 * Laser Apparatus and Piezoelectric Wires**

It produces light with a wavelength of 405 nm. I may look into the possibility of procuring a lens to perhaps focus the light to create a much steeper increase in temperature in a shorter amount of time, potentially allowing for a greater change in the surface of the gold because of the rapid change in temperature and the new, faster alignment of the Octanethiol molecules on the surface. One consistent problem will be the quality of the tips involved in the scanning. I will attempt to cut sharper tips but the process of getting better tips more often will be a continuous and experimental one. media type="custom" key="11942136" Although this image from June 28, 2011, was before the beginning of my specific research, it accurately depicts the surface of Au(111) covered with Octanethiol. The groups of about five rows all oriented in the same direction display the arrangement that we expect to see for a surface of Au(111) covered with Octanethiol. This helps as a guide for what to look for in future images.
 * Results**
 * 6-28-11AI**

media type="custom" key="11957994" These two images clearly show the piezoelectric stack's ability to retract with such a minor difference that allows for thermal expansion but also allows for the same area to be scanned in both the before and after image. I shot the laser at the sample for fifty seconds then let it cool for two minutes. "A" in these side-by-side images represents the white, elevated surface in both images. This particular region expands from the before image to the after image. It also seemingly eliminates the valley represented by "D" and the one right below and to the left of "D". It seems as if this region expanded and in doing so, heat was transferred and the region became a more level surface as the sample cooled. The hill indicated by "B" helps to show how the two areas of the images are similar. "B" also indicates the region where the hill is located. This region expands from the before to after image, extending to the end of the scan. Perhaps, as the sample cooled, this region also became more level. This could possibly explain the disappearance of the valleys in the black box in the bottom half. The hills inside the white triangle all expand in size and the distance between them increases slightly. The distance between the valleys in the black triangles does not seem to change much at all.However, the three valleys inside all increase in their individual size. "C" is the semi-circular region it is at the center of and shows two important things: a similarity in both areas to help support that they are the same area and a decrease in the quality of the tip between the before and after image. This is clear in the increased amount of streaks in the after image. These streaks are also obvious on the valleys in the black triangle. These images show the possibility of the thermal expansion of the tip resulting in a poorer tip for the after image. It shows that some of the light does travel through the sample and hit the tip., causing it to expand and change. This could pose many problems when faced with before images of much higher qualities. If I were able to scan with atomic resolution and I ended up using the laser, it could damage the quality of the tip and lower the applicability of the after image when it pales in comparison to the quality of the before image. This might need to be looked in to next semester and a means of preventing this would possibly need to be looked into also. This could help keep the quality of tips and prevent the foiling of laser attempts.
 * 9-14AF-AG**

media type="custom" key="11964696" I shot the laser at this sample for one minute and let it cool for five minutes before approaching with the piezoelectric stack. The black boxes show the similar regions between the two images. The hill designated by the letter "A" seems to widen but also seems to have a smoother border in the second images. The valley designated by the letter "B" also becomes wider in the second image but it is too difficult to truly analyze the smoothness of the edges of the valley.The valley designated as "C" looks sort of like a trapezoid in the before image. In the after image, it appears much more circular. The hill designated as "D" appears to form a rectangular shape but it is also too difficult here to tell if the edges of this hill are smoother in the after image than in the before image. Also, the tip in the after image appears to have improved in quality from the before image. This could be due to the light actually sharpening the tip rather than making it dull. The after image simply appears slightly less blurry than the first one. It is not a drastic change but it is possible for it to happen. However it is also possible for the tip to become duller as a result of its own heating and cooling, causing a rearrangement of the atoms on the end of the tip. If possible, I would attempt to have this happen every time that I shoot the laser. I do not see this having a very high probability of success nor do I currently know how I would be able to do this. I may look into this next semester or sometime after.
 * 10-5-11AE-AF**

I have also decided to include a PowerPoint that I have created which shows all the before and after images side-by-side that I have gathered throughout the entirety of my research. Also it gives certain details about the images, the time exposed to the laser, the time the samples cooled, and, beginning September 8, 2011, it includes the parameters used while scanning the samples. media type="custom" key="11977791"

The quality of the scans depends heavily on the quality and sharpness of the tip and I will need to attempt to make better tips. I will also attempt to be more careful seeing as how there were several instances throughout the semester where I could have possibly had a well-defined after image but I messed it up and accidentally bumped into something or moved something causing the sample holder to move and ruining the chances. I will continue to make sure every day when I arrive that the laser is aligned correctly so as to have maximum and proper contact with the sample. I have several goals which I hope to achieve next semester: I wait with exuberant anticipation for the day where I will obtain results worthy of extensive insight and full of revealing information.
 * Conclusions**
 * I hope to find the optimal difference that allows for minimal retraction and movement but also allow for enough room for thermal expansion. By doing this, I hope to increase the number of before and after images that have the same area and hopefully maintain the quality of the tip and of the sample by avoiding crashing. I will accomplish this through tests involving different amounts of voltages.
 * I will attempt to find a way to reduce the amount of thermal expansion of the tip during the Laser process in order to keep the tip from changing too drastically.
 * I hope to avoid mistakes that ruin Laser opportunities such as accidentally moving something or bumping into something, causing the sample to move and mess up the scan.