I must admit that I am sad while writing this final blog post. It is my last week here at Vanderbilt with Joe and Noah and all of the others, and in fact, I am writing this post on my last day. I truly will miss everyone I have known while I have been working here and I am glad that I got the opportunity to work here. A month ago, I had no clue that Quantum Dots existed, but now I have knowledge of what they are, how they are created, and why they are important.
On my first day of this week, solemn from knowing that I only had five more days, Joe took me to see the NMR (Nuclear Magnetic Resonance) instruments. These machines use the fact that certain isotopes have a magnetic spin to analyze the structure of a molecule. To use a NMR (Nuclear Magnetic Resonance) machine, you have to put the sample into the machine-- being sure to leave your phone and credit card on a desk because the magnetic field can mess with them and wipe the data off of them. Then, you have to open a program that analyzes the feed that comes from the NMR (Nuclear Magnetic Resonance) machine and turns it into a bumpy line on a graph. The different bumps correlate with parts of the structure that have different chemical environments and neighboring atoms. People who understand what the bumps mean-- like Joe-- can decode it. NMR (Nuclear Magnetic Resonance), though difficult, is primarily helpful in organic chemistry, but it can also be helpful with Quantum Dots by helping figure out what each of the ligands-- organic molecules attached to the nanocrystal-- looks like.
When we came back, my Winterim adviser (Mrs. Perry) stopped by! We showed her around the laser lab and the wet lab upstairs, and it seemed like she was enthused by what she saw. I surely have been having a great time, even if sometimes all of the information can be overwhelming. She only stopped by for a little while, but I think she got a large portion of the information as to what I have been doing.
After she left, I went with Joe to make a synthesis which we used to find the fluorescence using the spectrofluorometer, which shines a light through all possible wavelengths from infrared to ultraviolet and measures how much light is emitted by the sample.
On Tuesday, I started the day working with Noah in the lab upstairs by diluting some white light nanocrystals that he could later view on the camera in his laser setup. Afterward, I shadowed Joe while he completed a ligand exchange.
A ligand exchange-- when the organic molecules on the surface of the nanocrystals are changed for a different ligand-- is needed because the original ligand does not separate the charges in the exciton (if you do not understand that concept, go back to my first blog post) as needed in solution. Because it can be specific to the structure of the molecule, Joe uses a polymer that was made by scientists Oak Ridge National Laboratory not far from Knoxville.
Afterward, I went back to the laser lab with Noah and we were joined by Andrew and Claire, who are rotation students working with Sarah. Sarah-- as I said in my last blog-- has her Preliminary Qualifying Exam coming up soon, so she has been very busy as of late. Noah showed them around the set up in a way similar to what I experienced on my first day, and then we examined some images and data taken from various samples.
On Wednesday, Joe and I were preparing some syntheses he already made to find the Quantum Yield, which compares how much light is emitted from a sample when light is shot through it by using the emission and other qualities in an equation. Then, I went to the laser lab with Noah and Claire, where we attempted to get good images of single quantum dots on a very small grid. A few quantum dots showed up, however because the grid is so small, it is difficult to find where they were, so we could not view them on a TEM (Transmission Electron Microscope).
To counteract this problem, Noah has to add silver nanoparticles to the grid. This is because the silver nanoparticles are much bigger and show up more easily on a TEM (Transmission Electron Microscope). Then, all he has to do is view the grid with the camera in his setup, find the closest silver nanoparticle, and extrapolate where it is. Then he can take the grid with the silver and the quantum dots to James and they can find it on the TEM (Transmission Electron Microscope).
I worked with Joe on Thursday to tune up his laser setup. The beam started out as a beautiful gold color before he tuned it. By changing the distance the beam had to travel and readjusting it, Joe was able to change the beam from the original gold to an equally beautiful deep red color. Afterwards, he changed it back to the gold. It sounds simple enough, but when each piece has to be focused to the nanometer and when many pieces have to be adjusted, it can get extremely complicated.
Joe then used a fluorescent dye to calibrate his system for fluorescence upconversion, which overlaps the energy of two photons in a special crystal to get a single photon with a new energy and wavelength. Joe had to put the blue dye through a tube system which continually pumps the sample in a loop, causing photobleaching-- or the killing of a sample by overexposure to light-- to no longer be an issue because there are always particles replacing the earlier ones. Then, the gold beam travels through a portion of the loop, exciting the dye to a bright red color. The emission is detected and signals are sent to the computer, creating a graph.
The first thing I did on my last day was set up a synthesis with Joe with a gradient core and shell by using certain chemicals to change the reactivity of some of the reactants. We saved the injection to start the nanocrystal growth for after lunch because as a thank you I ordered pizza for everyone.
After lunch, Joe and I finished the synthesis by injecting the growth solution and taking pulls every so often to monitor its growth. Over time, the nanocrystals-- which fluoresce orange-- grew brighter. When we left the wet lab, I stopped by Scott as he explained how he was scanning solar cell devices that he has been working on under a lamp which was specifically designed to create light that looks like it is sunlight. Not long after, Joe and I began the cleaning process of the synthesis.
My day ended with getting an awesome mug that everybody signed to keep as a memory and sitting around the couch talking. It was a great way to end the experience.
I wanted to leave this last paragraph as a thank you to the entire group. Although I may not have mentioned all of you in my blog, I am glad I met every person I did while I have been at Vanderbilt. I have learned so much from all of you, from Quantum Dots to being a graduate student to the conversation about how J. J. Abrams going to direct Star Wars which I am listening to while writing this. From the first day you all accepted me with kindness and enthusiasm and have taught me so much. Each one of you is unique and fun in different ways-- Xochitl’s fantastic t-shirts and mug, Joe’s epic taste in classic rock, James’ rolling chair sound effects, Amy’s K-Pop, and so much more. Thank you all for giving me this opportunity, I know that it has given me skills that will benefit me for years to come.