Week 3

        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.

Week 2

        In all of my years of Winterim so far, this has been my favorite. Don’t get me wrong, I loved the classes I took, (I mean: Cryptography, that was so cool!) but I have not had the chance to get real world experience until now. Not only have I learned great skills, but I have learned more about the college process and have met many amazing people-- even outside the group I have been working with.
        On my first day of this week, I got to building seven-- where the Rosenthal group is located-- early. (In fact, this entire week I got to work about fifteen minutes early and James had to come let me in, much to his dismay.) Part of my arriving early was due to less traffic than expected, but the other part was because I could not wait to get started!
        If I called the first day anything, I would call it a lab day, since that was where I was for the majority of the time. I always enjoy being in the lab because most of the time-- as this is a chemistry-centered group-- there is at least one person working at one of the fume hoods, and it is interesting to hear about what each person is working on.
        The first thing I did on Monday was help Joe make a Type II synthesis in the lab by measuring out the quantities needed of different chemicals. Type II band alignment means that your core and your shell’s energy bands are staggered to separate the charges between the core and the shell so that they cannot recombine.
        After that, I worked with Noah to dilute a sample of white light nanocrystals, and finally I went back to working with Joe on the synthesis we started in the morning. We wanted the sample to be clear at the end of an hour, but it was a light yellow color, so we had to continue heating it. To speed up the process, we used a heating gun-- which is the equivalent to an overzealous blow dryer. In the end, however, the sample was too yellow, so Joe started a new one with a Type I synthesis. Type I band alignment is when the charges are trapped and cannot recombine with anything else.
        On the second day, I knew a bit of what to expect: finishing up the sample Joe and I started and helping Sarah practice for her prelims by critiquing her presentation. That may not make total sense just yet, but bear with me, I will explain it.
        In the lab, Joe had to inject a growth solution and take samples every ten minutes or so for an hour while the synthesis was heating. The growth solution was used to stop something called “Ostwald Ripening” which Joe explained to me on my second day as “Quantum Dot Cannibalism”. Basically, some of the nanoparticles will grow to the point that they will absorb the other nanoparticles.
        Sarah-- who is working in the floor above me, but is still part of the Rosenthal group-- is preparing for her Preliminary PhD Qualifying Exam which is where she presents what she has been researching to a board of professors and shows that she knows what she is doing and what she is going to do. It is a very important step as a graduate student aiming for his or her doctorate.
        The practice is set up just like the actual test, except the board of professors is replaced by a group of her peers. First, Sarah presented everything that she’s been working on-- namely trying to find a way to use quantum dots to make LEDs (Light Emitting Diodes). Second, the group would ask questions about what she has been working on. After that, the questions would turn to general knowledge about nanocrystals, ranging anywhere from basic information that I knew to detailed questions about equations that I have never seen before in my life. Finally, they would go slide by slide and pick out what works and what doesn’t, even to the minor details such as font size-- a particular favorite of James to point out. The entire process took three hours.
        Although the main point of this practice was to show Sarah what she needs to work on before her actual Preliminary PhD Qualifying Exam next Friday, but also to try to trip her up. The group purposefully tried to make it as stressful as they morally could to prepare Sarah for the extent of what the actual presentation is going to be like. This way, she can go in with the thought, “I’ve already done this with the practice, so it won’t be as hard.”
        I personally think that Sarah managed very well, and though she has a few things she needs to fix, she will definitely do well on her Preliminary PhD Qualifying Exam.
        On Wednesday, Joe took me to meet Jay-- a funny coincidence that their names match up like that-- who is working in an analytical chemistry lab. We went because Joe needed to look at his sample on the Mass Spectrometer that their lab uses.
        A Mass Spectrometer, or Mass Spec, works by ionizing a sample (giving it a charge) and then seeing how long it takes for ions to reach the other side of the inside of the Mass Spec. The ions change sides because of how Jay-- or any scientist-- has to calibrate it. If there are more positive ions, then he will make the input side have a positive charge and the other side have a negative charge, and since opposite charges attract, the positive ions will travel to the detection side. If there are more negative ions, it is the same process, but having the input side have a negative charge and the detection side have a positive charge.
        After the detector has noted the ions and when they arrived, the computer uses the equation “KE = ½ mv2” which I learned in Physics class, to find the mass of the different ions compared to known samples. It is a lot of math and I do not think that would interest a lot of my readers. I may or may not write out the math and put it on a new page later.
        After Jay took samples and sent them to Joe, I went back to the eighth floor and worked with Noah in the laser lab for the rest of the day. It seems that his research is coming to a good jumping off point!
        On Thursday, I went to the lab with Joe to prepare for a ligand exchange, which is used to take a charge off of the nanocrystals so that the hole and the electron do not recombine too soon. Afterwards, I went back to the laser lab with Noah, starting to get really great images.
        Friday started off by working on my blog, then helping Noah realign the lasers in the laser lab. Most of the time, because the setup has to be so precise and the equipment is quite expensive (including a camera worth $40,000), I end up watching. I get to help by blocking and unblocking a laser’s path or holding a flashlight or turning on the shutter, which does not seem like I am doing very much, but I really enjoy it. I get to learn how each small piece helps the end result.
        Afterward, I was brought to the TGA (Thermal Gravimetric Analysis) which is a machine on the second floor that helps determine when the organic ligands attached to the nanocrystal core will burn off when the temperature is increased. When we finished the first sample and left the second in the TGA (Thermal Gravimetric Analysis), Joe and I went back to the lab to prepare more samples for analyzing.
        After lunch, Noah and I worked with the white light nanocrystals, attempting to let them grow into blue light. Along the way, we found better white light than before, so we kept those. Sadly, the nanocrystals grew into green light instead of blue light, so the samples-- then useless-- were thrown out. As we were waiting, I asked Noah and Amy some questions about the group, like their ages and their music tastes, which was nice filler conversation.
        As my second week with the Rosenthal group ends, I find myself feeling a bit melancholy because I know that this will end next Friday. I have been enjoying my time very much and I truly do not want to have to leave. Although I will be glad to see the familiar faces of school friends, I will be sad to leave the faces of the people I consider my friends here at Vanderbilt.

Week 1

At the start of this Winterim experience, I had no idea what to expect. I’d be working in a lab under Dr. Sandra Rosenthal of Vanderbilt on something called “Semiconductor Nanocrystals”. I had never heard anything about it in all of my years at school because it is not a part of the normal curriculum for high school students.

Basically, there are certain tiny crystals which emit light when excited by a laser. These crystals, also known as Quantum Dots, are insanely small, to the nanometer scale. A nanometer is 1.0 × 10-9 meters, which is extremely small. Their size is what makes their fluorescence tunable, involving something called Quantum Confinement.

This group shoots lasers through a very intricate process (so that they can tune it to the correct wavelength and energy signature) and finally into the nanocrystals. The core of the nanocrystal (which is Cadmium selenide in the case of the Rosenthal group) is excited and inside, an exciton is created. An exciton is when an electron is excited in the core and orbits around the hole left behind. This orbit is called the Bohr-Exciton Radius, and when the substance’s natural size is smaller than this, it causes Quantum Confinement. When the exciton and the hole recombine, photons are emitted because the energy left over needs to transfer to something. Those photons cause the nanocrystals to glow.

In some situations, when the quantum dots glow, you can see them. They are visible because of changing the nanocrystal structure or size or by tuning the laser to the appropriate settings which cause the quantum dots to glow in the visible spectrum. Sometimes though, the quantum dots can glow in the infrared and ultraviolet spectra, which are not usually visible to the human eye unless close to the visible spectrum and of a very high intensity.

The group I have been working with have been playing around with different ways to excite the nanocrystals and have been trying to figure out why they have certain properties. The lasers aren’t the only way to observe the Quantum Dots, though. They have a lot of equipment in the lab where they create syntheses, as well as the TEM (Transmission Electron Microscope) on the sixth floor of the building to analyze their samples.

Through this experience, I have gotten to see various techniques used to analyze these nanocrystals and have learned about the different possible uses of them, including as biological probes and LEDs. It’s only been a week but I’ve learned so much

This was new to me on Monday: new people, new information, new experiences, so needless to say, I was nervous. As I was waiting in front of Dr. Rosenthal’s office, I actually counted a whole three hundred seconds before going to knock on her door. When we met, she showed me to the place where I would be working.

I was introduced to various graduate students and a research professor, all either aiming for his or her pHd or having already obtained one. The two graduate students who were assigned to show me around were Joe and Noah (who, if they are reading this, are awesome).

For the first part of my first day, Noah walked me around the laser lab, explaining what they have been working on. At first, some of it went over my head, but I kept a few things in mind to look up later. Then, Joe showed me the TEM (Transmission Electron Microscope) with James, the research professor.

It was all very exciting (I even got my own lab coat and goggles!) and I met so many kind people whose IQs are well above mine. I was met with the challenge to learn and understand a field that could take many years for most people to learn. It was hard and I loved it.

The next day, Joe took me around the laser lab for three hours, re-explaining what Noah already taught me, allowing me to solidify the information in my head. Later, I was shadowing Noah while he created substances which he could look at later on his setup in the laser lab. I learned about safety protocols in case of emergencies and got to see syntheses in action.

Wednesday, I stayed with Joe all day-- because a professor who was visiting was working with Noah-- and got to help some with the syntheses of Quantum Dots by using different chemicals of certain quantities in a specific order to balance the core and the shell together. We had to clean the nanocrystals so that they could be viewed on the TEM (Transmission Electron Microscope), which is a difficult process because if there are too few cleaning cycles, the images look oily and are not very useful. However, if there are too many cleaning cycles, you can potentially kick the Quantum Dots out of solution, effectively killing the samples off.

On Thursday, in the beginning of the day, I was following Noah around as he tweaked his laser system and his computer programs to get better resolutions on the pictures of his white light crystals. Next, Joe, James, and I went to the TEM (Transmission Electron Microscope) again, this time looking at the syntheses Joe and I had created the day before. In this case, there were too few cleaning cycles, leaving some not-so-great pictures, but that just meant that Joe had to modify his process some to clean his samples without kicking them out of solution. The rest of the day was spent finding the Quantum Yield, which compares how much light comes out of a substance when photons are shot through it by using the emission and a few other qualities in an equation.

Friday, I made my own synthesis of (hopefully) white light nanocrystals! I was excited and nervous but I do not think I did too terrible of a job for my first try! I had to measure out a certain mass of different chemicals and set up for the heating process. Then, we waited. After a fun group lunch (because it was such a nice day) we had to clean up and prep the samples-- which had been in the centrifuge-- for their cleaning. Until I left, we finished preparing the samples and Joe took me back to the laser lab to explain a bit more about how their setup works. In this session, I learned more about the samples that I was helping to prepare.

White light is important to this group because of some of its properties. White is not a single color, but all colors, so creating this kind of light is difficult. Its emission spans a large portion of the visible spectrum compared to colored light (such as blue light and red light). And the cool thing is when it comes to shooting its emission through a prism. Many people (especially fans of Pink Floyd) know that when white light is shot through a prism, a rainbow comes out. This is because lights of different wavelengths are slowed down to different speeds when shot through. Because they are slowed down, the different wavelengths (which we see as different colors) separate and create what we normally see as a rainbow!

And that is only one example of all of the interesting things I have learned here.This has been a wonderful opportunity because of all of the information and great people I have been introduced to here. I cannot wait for the next two weeks for more to learn!