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Effects of Thermal and Beta Radiation on Gold(Au(111)) Surfaces Coated with OctanethiolChris Agostino and Guido Caponigri-GuerraEffects of Laser Heating on the Surface of Gold(Au(111)) coated with OctanethiolBy: Chris AgostinoGold Samples (Au(111)) are submerged in Octanethiol Solutions and heated for around 24 hours.The goal of the research is to study the effects of Laser heating on the surface of Gold (Au(111))coated with Octanethiol molecules.The samples are then scanned using a Scanning Tunneling Microscope.The quality of the image taken depends on the sharpness of the Platinum-Iridium tip used and on the solution forming molecules on the Gold surface. If there is not enough time in solution, the molecules can be disorderly on the surface and prevent any useful imaging.The sample holder has a Piezoelectric stack on top of it and is hollow to allow for the light of the laser to hit the sample without removing the sample from the STM.The Piezoelectric stack that sits upon the sample holder is connected to a power box, which houses fifteen 9-volt batteries. When scanning, on average, 40.0-45.0 V are applied to the Piezoelectric stack increasing its length. The reduction of the voltage results in a shortening of the Piezo stack, allowing for a detraction from the Pt-Ir tip that is small enough to minimize movement but allow for thermal expansion.When I take images and find those of high definition or with obvious atomic definition, the retraction method of reducing the voltage is utilized and then the laser is shot at the sample, usually from 35-60 seconds. After this, the sample cools for a few minutes before the same voltage that was used before is once more applied and scanning resumes. This method has proven quite successful throughout the course of the research in its attempt to scan the same area before and after the heat is applied.When I take images and find those of high definition or with obvious atomic definition, the retraction method of reducing the voltage is utilized and then the laser is shot at the sample, usually from 35-60 seconds. After this, the sample cools for a few minutes before the same voltage that was used before is once more applied and scanning resumes. This method has proven quite successful throughout the course of the research in its attempt to scan the same area before and after the heat is applied.This image(right) comes from June 28, 2011. It comes from the beginning days of my work in the Lab and wasactually before I had begun my specific project. This image shows how Octanethiol molecules ideallyarrange themselves on a surface of Gold. They arrange in groups of severalchains as shown in thisimage. I am looking forfeatures similar to those in this image in my own research to investigate theeffects of applied laser heat to the Octanethiol molecules.

These two side-by-side images pictured below are before and after images from September 14, 2011. Although they do not demonstrate clear atomic resolution, they do show the ability of the Piezoelectric stack to retract then increase and continue scanning a verysimilar area. These images show similar features and regions but also show drastic changes in thesurface as seen in the bottom half of the images from the before to the after image. However, the most important aspect of these images isthat the quality of the image decreases drastically from the before to the after image as one can see in the vastly larger amount of streaks in the after image. This reveals the problem of the laser causing thermal expansion in the tip which can possibly decrease or increase the quality of the tip. In this case, the tip decreased in sharpness and therefore in quality.ConclusionsUnfortunately, I have not been able to gain atomic resolution in my scans and this has prohibited me from learning about the effects of the Laser heating on the Octanethiol molecules. Poor samples, dull tips, and high amounts of noise all reduce the quality of the image and it is difficult to ensure the best of all of these three. In a lab with a vacuum pump nearby, it is nearly impossible to rule noise out as a factor in the low quality of the images. I shall still endeavor to cut tips as sharply as possible and do my best to obtain the best possible images.The expansion of the tip during the laser application also creates problems. This can ruin chances of seeing how molecules change from the before to the after image because I would scan with much less certainty.Laser used in scanning pictured belowSTwith sample holder pictured below

Effects of Beta Radiation on the Surface of Gold(Au(111)) coated with OctanethiolBy: Guido Caponigri-GuerraSamples of Gold Au(III) are annealed to smooth and clean surface of gold.Then they are placed in solutions of Octanethiol to be coated.The goal is to look for changes caused by the impace of Carbon-14 Beta Particles I use a Pt-Ir tip to scan on a scanning tunneling microscopeThe samples are exposed to Carbon-14 (beta emitter) for various lengths of time (hours to weeks)They are exposed in nitrogen purge- this ensures that no air molecules disrupt the process.

ResultsMuch of my research has been trial and error, as is expectedBegan with short exposures (less than 1/2 day) and have worked up based on the idea that the more time exposed, the higher the chances of surface impact by particlesThe procedure is to take images of the Au(III) with only Octanethiol and then compare those images to the post-exposure imagesScope reliability and image quality have been two of the most stubborn issues

These images are two of the best Ive gotten so far. In the right one, those mounds are of the octanethiol on the surface of the Au(III). The craters are typical of gold surfaces and not connected to the exposure. (both are post-exposure)

This is the apparatus used to expose the samples to the radiation source. The tube on the left is the nitrogen input. The glove on the right inflates under constant stream of nitrogen (to let us know it is flowing). The dish on the bottom holds the sample and radiation source (Carbon-14 or Polonium-210)

The orange disk is the scan head of the STM. The Pt-Ir tip is at the end of the arrow, under a spring to keep it in place. The silver cylinder is the sample holder, complete with a small magnet on the end to hold the sample disk itself.