With the summer ending, it is crazy how quickly ten weeks pass by. I joined Professor Crowther’s lab after taking a year of organic chemistry and a semester of quantitative analysis, which is not very related to what we do in lab. Sure, we go over spectroscopy in general chemistry and quantitative analysis, but I have never heard of micro-Raman spectroscopy before this summer. Now, I take Raman spectra every other day. The first few weeks of the summer I felt like I was at a disadvantage not having taken Quantum or Spectroscopy Lab. It took a while for me to get the hang of things and feel comfortable taking measurements alone. I have made a lot of progress since the first day of research this summer. Now, when I align the laser to take a measurement, I am very efficient because it has become second nature.
The amount of knowledge I gathered this summer became obvious this past week when I was explaining my research to an incoming first-year who was shadowing our lab. I remember the second day of work when one of my lab mates taught me how to make graphene samples and identify single-layered pieces of graphene in the microscope. It felt very different when I taught the incoming first-year how to make graphene samples. It was one of those great moments in life when the student becomes the teacher. Not only that, but when observing the samples under the microscope, I was able to locate a several pieces of single-layered graphene that I can potentially use for experiments in the fall. As I mentioned in my first blog-post, identifying single-layered pieces of graphene on samples is not easy. There is a luck component when making the samples. Sometimes I am not able to locate a piece of useful single-layer graphene in a batch of samples. It is almost a bit weird because after making many samples at the beginning of the summer, I spent the latter half focused on conducting experiments and analyzing data. Therefore, I had not spent a lot of time lately feeling frustrated about sample-making. However, going back to it during the last week and obtaining some useful samples means that I developed some sample-making skills, maybe more than I realized in the beginning when I would make eight samples each day. This experience was also incredibly beneficial because all the samples I made in the beginning of the summer had been photochlorinated, so now I have more that I can use in the fall semester. So I will not be as stressed in the beginning of the new semester about making more samples and can instead focus on the chemical reaction part of the project which is much more exciting.
Working with Professor Crowther this summer has undoubtedly made me a better scientist. Besides learning new experimental techniques and how to operate different equipment, I also learned how to think about my experiments to a certain extent. In a teaching lab like organic chemistry and general chemistry, the experiments are designed to expose student to different techniques. The procedures have already been written and there are expected results. If a student gets a different result than what is expected, there are ways to understand what went wrong.
In contrast, in research a procedure is designed to obtain a certain data set, but sometimes that procedure is not as efficient as possible. For example, this summer when conducting the initial photochlorination experiments, it would take around five hours to see significant results. Eventually we decided to mount spacers on the sample so the graphene would not directly touch the cuvette face. In other words, we had to modify the procedure. Even now when it comes to determining the length of the irradiation period, there is no written procedure on the best time length. Instead we choose it based on the previous spectra. Before doing research, when something did not occur like I expected it to, I would be uncertain and not know what to do to solve the problem. Now, I feel more comfortable evaluating the problem, thinking about it, and developing a strategy to fix it. I almost always need to discuss my next step of action with Professor Crowther. However, in the beginning of the summer, he would often just tell me what I should do differently, while now it is more of a conversation which I really appreciate. I like looking at my results and being able to give Professor Crowther my interpretation of the data and hearing his opinion about it.
With the summer coming to an end, I do not necessarily feel a sense of closure with my project since I am continuing it during the fall semester. I never went into this experience expecting to start and finish a project in the ten weeks I would be here during the summer. I am excited to return in the fall semester and gather more data. When I return in September, I will work on conducting more experiments and coming up with a mathematical approach to quantify my data. I read a paper where the authors calculated uniaxial strain and hole doping in annealed graphene samples. I used the paper as a reference when analyzing my data, but Professor Crowther and I agreed that we should try to come up with our own method to quantifying the data. That means that when the fall starts I’m going to have to spend some time looking at my notes from multivariable calculus. I think it will be a challenging task, but I am excited to attempt it.
In summary, I learned a lot this summer: I learned how to think like a research scientist, some quantum chemistry, and a whole lot about the photochlorination of graphene. I always knew I wanted to do research at some point in my undergraduate career, but I was not expecting to enjoy it as much as I did and to care about my project as much as I do. I am genuinely ecstatic to return in the fall and continue working on my project. Hopefully classes will not get in the way too much!
Half the summer has passed at this point, and I can barely believe how much I have learned. Since the last blog post, I have learned a lot more. As a reminder, for my project this summer I am collecting graphene samples to measure its behavior when chlorinated using Raman spectroscopy which I discussed on my last blog post.
In addition to taking a single Raman spectrum of a sample, I have started measuring Raman spatial maps of my graphene samples. When I shine the laser on a sample to take its Raman spectrum, the spectrometer only obtains a measurement at that specific location. A map measures multiple Raman spectra at each specific location on the sample using a computer program that automatically shifts the translation stage one step at a time. Programming the stage so it moves the number of steps I want is another process I learned since the last blog post. It requires a few simple calculations and visually determining the area where the map should be taken to encompass the entire graphene sample. The spectrometer is programed to take a spectrum every 60 seconds, so if I program the stage so it moves 15 steps on the x-axis and 20 steps on the y-axis, the spectrometer will take 336 spectra (16 x 21). At 60 seconds a spectrum, it will take approximately 5.5 hours for the map to finish. For that reason, maps are usually measured overnight.
Once the map data has been collected, I upload it into the data analysis program Igor. Igor is very convenient because it analyzes all the spectra at once as opposed to me having to manually analyze them, which is especially useful when I measure a map with 336 spectra. We already have several Igor macros that were written to perform the desired functions like loading multiple files and fitting peaks. However, as part of my training, Professor Crowther taught me how to edit the macros to only display the one layer graphene sample of interest as opposed to also including other spectra of surrounding graphite or multi-layered graphene. As a result, I can now edit several mapping programs. I was delighted when the codes I wrote worked especially because learning how to code was something I always wanted to pick up and the fact that it improved the data processing was exciting.
After taking the initial map of a graphene sample, I run an experiment on it. For my project, I am conducting photochlorination experiments. I begin by exposing the silicon substrate where the graphene sample is located to chlorine gas. Chlorine gas is highly toxic, so for this part of the experiment I work in a fume hood using appropriate safety equipment. Because of the toxicity of the gas, the setup for the chlorination experiment uses a manifold to control the exposure. The sample is placed in a cuvette which is attached to the system. The whole system is evacuated and tested for leaks before the chlorination experiment can begin. Once the setup is deemed safe, the sample is exposed to chlorine gas for less than two minutes. Chlorine gas has a distinct yellow color, so once the cuvette obtains that color, it is sealed, trapping the gas with the sample. The remaining chlorine gas is pushed out of the system using nitrogen gas into a wash bottle where it is converted to harmless Cl-. Nitrogen gas continues running through the system for about ten minutes to ensure no more toxic chlorine gas is present before the cuvette can be removed and the equipment can be turned off. What makes this experiment complicated and dangerous if not done carefully is that everything must be turned on and off in the correct order.
With the sample successfully exposed to chlorine, it is time to irradiate it with a 405 nm laser which has a nice purple color. For the irradiation step, I must first find the graphene in the sample on the cuvette on an elevated stage which restricts how much the translation stage can move making it harder to find the graphene sample than if it was in a slide. Once I have found the sample and aligned both the 405 nm laser and the 532 nm laser onto the sample, I can begin irradiation. I typically irradiate the sample for prolonged time varying from 30 minutes to maybe an hour. Once the time has passed, I take a Raman spectrum of the sample. I repeat this process for a total of 5 or 6 hours.
When I take all the different Raman spectra at different time intervals, the important feature that I am observing is the change in peak intensity ratios. As I mentioned previously, a typical graphene spectrum has 2 distinguishing peaks: A G and a 2D peak. Upon photochlorinating a sample, the 2D peak lowers in intensity until it is relatively flat. Another peak also appears at around 1350 cm-1, which was not previously observed before the experiment. This peak is called the D peak. While the 2D peak decreases in intensity the longer the sample is irradiated, the D peak increases in intensity. In order to measure the effect of the irradiation on the graphene sample, the intensity of the D peak and the G peak are observed. The longer the sample is irradiated, the larger the ratio of the D peak to G peak intensity. When the photochlorination process is finished, I measure another Raman spatial map of the graphene sample to determine how the location and the intensity of the peaks changed after the experiment.
Besides working on this project, this past week I helped Professor Crowther give a talk to the students in the Pre-College Program. Professor Crowther gave a brief summary of the Barnard Chemistry Department as well as an overall explanation of the research we do in our lab. We then took the students on a department tour showing them the teaching labs as well as our own lab. Upon entering the lab, I spoke to the students about the research I am conducting this summer. I later did a Q&A explaining to them what it is like to do research and study at Barnard. It was pretty exciting because I have never really given a presentation on my research before even though this was relatively informal. Next week, I will again talk about my research during group meeting to keep my lab mates updated on what I have done this summer so far.
Overall, I feel good about the data I have gathered so far. I hope in the next few weeks to collect more data and perform more photochlorination experiments on graphene samples.
After working for two weeks in Professor Crowther’s lab, I have learned a number of skills and techniques. Before joining Professor Crowther’s lab, I had taken two years of Barnard College chemistry classes including general, organic, and quantitative analytical chemistry. Although these classes have shaped me into the chemist I am today, Professor Crowther’s research is in the subfield of physical chemistry and materials chemistry based in part on quantum chemistry - a class I will take in Fall 2017. Beginning research without this course was very intimidating, especially during the first few days. A lot of the information seemed to go over my head. However, Professor Crowther patiently and calmly explained the theory behind the research, and my understanding of the work has increased significantly.
My project in Professor Crowther’s lab involves investigating how chemical reactions affect the electronic properties of graphene. Graphene is a two-dimensional carbon material, making it the thinnest material that exists. It is made up of carbons connected in a honeycomb lattice. Despite being over a million times thinner than hair, graphene is also stiffer than steel. I will be investigating graphene’s potential as an electronic material by performing reactions on graphene samples and observing how these reactions change its electronic properties.
The first few weeks are memorable due to the amount of knowledge I have gained. I have learned a lot of the theory behind my project and many experimental techniques I will use. I learned how to make graphene samples using graphite flakes and Scotch tape. The fact that the material I will be conducting experiments on can be made with Scotch tape is incredible. After preparing these samples, I analyze them under an optical microscope to identify graphene that I will be able to conduct experiments on. This part is rather frustrating because I still have difficulty finding one-layer graphene in the microscope due to its faint purple color. In order for a sample to be useful, the piece of graphene must be not only single-layer, but also must be large enough for subsequent experiments and stand alone as opposed to being near a graphite flake or a piece of graphene that is two or more layers. According to Professor Crowther, obtaining single-layer graphene is 67% skill and 33% luck. Despite making a plethora of samples, only one piece of one-layer graphene was found so far. Most of the graphene that I found was bilayer, which is useful for some experiments, but my work will focus mainly on one-layer graphene. After finding a piece of graphene, I obtain its Raman spectrum.
Raman spectroscopy, unlike IR absorption spectroscopy, is a scattering process. A laser strikes a sample and the scattered light is measured by a detector. The instrument is complex because the laser cannot hit the sample directly, but must first go through several optics, irises, and mirrors. As a result, the process of aligning the laser to take the measurements has many steps. I have spent the last two weeks being trained by Professor Crowther to use the equipment. I must first find the piece of graphene on the sample using a different microscope. Then, I must check the power of the laser before focusing the laser beam on the sample to ensure it strikes in the right position. When that is done, the alignment of the laser must be checked on the pinhole, so it enters the spectrometer slit. After checking all of the alignment, I can then begin measuring the spectra. Although, at first trying to remember all the steps was overwhelming, a few days ago I was able to successfully take Raman spectra of seven different samples. I am excited because I am now able to take these spectra faster and more confidently. Every time I align the Raman spectrometer and measure a spectrum, I go to Professor Crowther with fewer and fewer questions.
Although I have definitely learned a lot these last few weeks, I am also aware that I am nowhere near done with the training and learning necessary concepts and experimental techniques. I feel confident about operating the Raman spectrometer at this point, but next week Professor Crowther will teach me how to take spatial maps of the graphene samples. The laser hits the sample at one specific location so I can generate a Raman map of a graphene sample by taking spectra across the surface of the entire sample. This data will be particular useful for determining the homogeneity of graphene reactants.
In order to successfully obtain the data I need, I must first prepare more graphene samples. As previously mentioned, most of the samples I made had bilayer graphene which is not particular useful for the experiments I will be performing. Therefore, I hope to increase my sample library in the next few days. After doing so, I will take the initial Raman spectrum of each sample. I will also measure an initial Raman map of the graphene sample. After doing so, I will perform chemical reactions on the graphene. I will then measure a second Raman spectrum and map to observe the results of my experiments. Since it is still early in the summer, my goal for the next few weeks is to make many more samples to guarantee that I have a large number of one-layer graphene samples and start running some graphene reactions.
Additionally, I hope to further my knowledge of quantum chemistry. Every day I learn something new, including the theory behind spectroscopy or potential energy diagrams. These concepts prepare me for the class I will take in the fall and allows me to understand my work more completely. When I measure a Raman spectrum, I am aware of how the instrument works by scattering the light as it interacts with the sample. Understanding this interacting, makes me a better scientist.
Overall, I am satisfied with what I have achieved so far. While the lack of one-layer graphene samples is rather frustrating, the fact that I feel confident using the Raman spectrometer is gratifying. Before joining Professor Crowther’s lab, I had never seen a Raman spectrometer. The first time I used it, I was nervous that I would break something because I did not have a clear sense of what I was doing, but with more practice, I became more comfortable with it. Taking seven spectra without needing to go ask Professor Crowther many questions shows a huge improvement. I am excited to measure more spectra in the next few days and become more comfortable with the Raman spectrometer to the point where I can operate it independently.
In terms of STEM education, the information I have gathered from these last two weeks has definitely helped my understanding of science and technology due to different computer programs used to calibrate and analyze the Raman spectra. By understanding the theory behind the research, I will be able to explain and teach the material to someone else. Although I feel good about what I have learned so far, I recognize that I still have a long way to go!