Week 1: We listened to professors describe their projects and we got tours of the different laboratories. Then on Wednesday, we selected our projects and met with our mentors on Thursday. I was given a tour of the labs I will be working in this summer, and Frank showed me the ellipsometer. On Friday, I attended my first NIRT meeting.
Week 2: I began working with the ellipsometer, collecting data on a gold-nanoparticle solution of unknown age and concentration. After acquiring the data, I used my Python programs to model a bulk effect and a layer effect. Neither model so far appears to accurately describe the data, but this could simply be due to a phase shift in the data or the fact that the nanoparticle solution is old and therefore has lost some of its ligands.
Week 3: I continued work with my programs. I wrote a program that would calculate the dielectric constants of solutions using the known values of the solvent and the solute. I prepared a PowerPoint for Wednesday for a meeting with Drs. Law and Sorensen, as Dr. Law is leaving for a month in Europe on Friday and I needed to update Dr. Sorensen so that he could guide me in my experiments. I did not go in to work on Thursday, as Dr. Weaver asked that we stay away from the building until some tornado clean-up could be done. On Friday, we had our weekly NIRT meeting, during which the power on half of campus, including Cardwell, went out. The power came back on later that afternoon, and we had our weekly group meeting, during which I gave a brief overview of my project to the other REU students.
Week 4: I realized I had some errors in the theoretical calculations I did with my programs. I had corrected the angle I used as an input to give the same values as my experiment, but the numbers were not correct as I had believed, so I had to re-calculate the angle. I began taking data on a pure tbt solution and added to this some butanone. I also took some measurements for butanone. There was no significant change outside of experimental error. This is important because we were hoping to add some butanone to the nanoparticle solution to try and force a layer to form on the bottom of the glass. If the butanone does not affect the readings, this is a feasible course of action. Dr. Sorensen also suggested trying the same experiment, but replacing the butanone with acetone, as acetone is more hydrophilic. I met with Dr. Weaver and we discussed Fresnel’s equations and how Brewster’s angle can be derived from the expression for rp. On Friday at our NIRT meeting, several suggestions for my next course of action were suggested, ranging from what Dr. Sorensen had suggested on Thursday, to using hydrophilic nanoparticles in lieu of the hydrophobic ones I have been working with. Dr. Sorensen admitted the acetone idea was “lame,” so that has been scrapped. We have determined the best next step would be to use hydrophilic nanoparticles and see if these are more drawn to the bottom surface of the glass. Dr. Aakeröy in the chemistry department will be providing my samples. We had another group meeting Friday afternoon.
Week 5: Dr. Aakeröy gave me a sample of hydrophilic nanoparticles in a DMSO (dimethyl sulfoxide) solution, as well as some extra DMSO so that I could dilute the solution. I took some measurements using pure gold, pure DMSO, and a solution of equal parts of the two. There was a significant drop in the real part of ρ after adding the nanoparticles to the DMSO solution, but the reading for pure gold solution looked very similar to the 50% solution. On Tuesday in the middle of Dr. Weaver’s lecture, we were informed that Cardwell was being evacuated due to possible asbestos contamination. We were out for the rest of Tuesday, Wednesday, and Thursday until 1pm. On Friday, we had our NIRT meeting. Because the drop was so significant between the pure DMSO solution and the equal parts solution, it was decided that I needed to take more data between 0 and 50% concentrations. I returned to the lab after the meeting and looked at the sample I had prepared on Monday. It had been a pink solution with no visible precipitate, but on Friday, all of the nanoparticles had dropped to the bottom of the vial and the solution was completely clear. It seemed bizarre to me that the solute would become less soluble in more solvent, so I took the particles to show Dr. Sorensen. He was also confused by the occurrence. He said there were 2 scenarios he could think of that could cause this effect. 1) The DMSO I added could have been a little wet. The solution, however, was hydrophilic, so water shouldn’t affect it that much. 2) There was an excess of ligands in the original solution, and when the DMSO was added, some of the ligands detached from the nanoparticles to re-establish equilibrium. When the ligands detached from the nanoparticles, they became more inclined to cluster. We called Dr. Aakeröy, who said the second case was more likely, as the DMSO is always wet; the same DMSO was used to make the original sample. He suggested that we sonicate the precipitated solution. After half an hour of sonication, the particles re-dissolved. I will be observing the nanoparticles over the course of the next few days to see if there are any changes in the solution. That afternoon, I took more data on the DMSO system, varying the concentration from 0 to 50% in smaller increments. My measurements here, however, do not appear to agree with my original results from Monday.
Week 6: On Monday, I went into the lab to look at my particles again. The solution I prepared last Monday and sonicated on Friday remains as it looked after sonication. All the particles appear to be in solution. The sample I made Friday afternoon, however, which is also equal parts DMSO and the original nanoparticle solution, appears to be beginning to precipitate. The liquid is still a translucent pink, but there is a small layer of nanoparticles forming. On Tuesday, it appeared the sonicated solution, too, had begun to precipitate, but the un-sonicated solution appeared stable; no more precipitate than what I saw on Monday was observable. I received an email from Dr. Law saying that perhaps the reason my measurements from last Friday do not agree with those from last Monday is that perhaps the cleaning method I have been using is not adequate. I have simply been washing my sample holder in all-purpose cleaner, rinsing it well with ultra-pure Millipore water, and drying it with a heat gun. On Thursday, I met with Sean, who showed me a better cleaning method. First, the sample container is washed in the same manner as before. Then, it is soaked in acetone for about 3 minutes and dried with nitrogen gas. Next, it is soaked in methanol for 3 minutes and dried with nitrogen gas. Finally, it is soaked in toluene for 3 minutes and dried with nitrogen. We didn’t have a NIRT meeting this week, as Friday was Independence Day!
Week 7: On Monday, I took another run of DMSO using the solvent cleaning method and examined my results. The first and third runs match relatively well, but the second run does not fit within experimental error. Sean suggested the problem might be that we used industrial grade nitrogen gas, and the problem might be resolved if we use ultra-high purity (UHP) nitrogen. Erik ordered a tank the week before he left for Europe, but it was to be delivered the day after the tornado hit. He had not received confirmation of its delivery, so I asked Rajesh, who said he had picked it up and put it in Dr. Sorensen’s lab, but he had not attached the regulator. My next task, then, was to find and attach the regulator. Frank, however, sent the regulator in to be cleaned and left for Europe before it was returned. He doesn’t remember the company he sent it to, and I cannot find the purchase order for it. In the meantime, I used the UHP in the basement lab with Sean, who showed me how to use the ozone cleaner between the washing and the solvents, and then again after the solvents. The ozone cleaner is used to break chemical bonds on the surface of the glass, which are then rinsed off by the solvents. On Tuesday afternoon, however, the ozone cleaner sparked and smoked. It is a homemade device and the electrical tape on one of the wires wore out. The metal box that goes on top while it is on welded itself to the machine. Sean was able to pry it off and fix it and it is now usable. The data I took after this, however, did not match well with the other two data sets I took beforehand. I am hoping that this is simply due to the ozone cleaner not working correctly, and it is something that can be easily fixed. One of the bulbs in the cleaner is not glowing, but we do not know if it ever glowed, as it is designed to produce light in the UV, but perhaps it was set up to glow with a gas in the chamber as a safety feature, so that one would know when it was on and could therefore protect one’s skin and eyes from the light. I read through the patent to determine if that might be the case, but was unable to figure it out. We had another NIRT meeting Friday morning. Dr. Sorensen thinks the best cleaning technique might be to prevent air from ever touching the substrate after cleaning, in case this causes a layer to form on the surface. He suggested soaking the container in acid after soap and water wash, then rinsing it again with water, and soaking it in DMSO and water, as DMSO is completely miscible in water, and DMSO is my solvent for the hydrophilic nanoparticles.
Week 8: On Monday, I tested to see whether the DMSO would eat through the UV glue which bonds the glass ring to the microscope slide on my sample cell. Sean put three drops of glue on a microscope slide and cured it for about 20 minutes under the UV lamp. I then put some DMSO on the dots and checked it every few minutes for the first hour, and saw no change. In fact, nothing happened to the glue after 4 hours in DMSO, which is good news; I need not worry about my samples destroying my sample cell. On Tuesday, Dr. Law came back and said I should order a new regulator for the nitrogen tank, since we don’t know where the one Frank sent to be cleaned ended up. I called the company that makes the model we wanted and they were out of stock until mid-August. Then I saw Dr. Sorensen, who suggested that there might be an extra regulator in his lab and I should ask Tehara about it. There was, indeed, an extra regulator and it was the same specifications that I needed. Dr. Law helped me hook up the regulator and hose and now I should be able to use the tank. Sean discovered that the bulb on the ozone cleaner was not the problem, but rather that one of the transformers blew, so he is going to get a new transformer and fix the ozone cleaner. In the meantime, I am going to Chemistry to use the plasma cleaner, which Sean showed me on Tuesday. We also went to see the glass-blower, who is making me some glass rings so that I can make more sample cells; mine might have been contaminated when the ozone cleaner malfunctioned. On Wednesday, I glued the glass rings to some microscope slides. Then I put them under the UV light to cure and baked them over night to cure. On Thursday, I used my new sample containers to try to find consistent results. On Friday, we had our NIRT meeting, Dr. Law’s group meeting, and our REU group meeting.
Week 9: My results from Thursday are not consistent, so I showed them to Dr. Law. He thinks that when Sean and I baked the sample cells, we caused some stress birefringence on the glass, so each slide will give us different results. I need to get more rings made by the glass-blower. In the meantime, I am going to use the sample cell that gave me good results. On Tuesday, I took data using the nanoparticles that Ashley and Sreeram made in June. I started with 0.5 ml of pure tert-butyl toluene, and added 0.5 ml of the nanoparticle solution, 0.1 ml at a time. I took 5 minutes of data for each concentration. On Wednesday, I started with 0.5 ml of the pure nanoparticle solution and added 0.5 ml of tBT in the same manner. My results from those two days appear to be consistent with one another. Now, I have to find a theoretical model which fits my data set.
Week 10: I started working on some contact angle measurements. I looked at the nanoparticle solution on a microscope slide cleaned in the same manner in which I prepared my substrates for the ellipsometer. The solution completely wet the slide and I was unable to get any measurements from the camera. I tried again on Tuesday, this time skipping the plasma cleaning step, as we thought this might have affected the contact angle. Once again, I was unable to get good results, so I have drawn the conclusion that the solution wets the surface regardless of the plasma cleaning. Now, I am finishing my presentation and writing my paper. I will present my report on Thursday, and then I’m gone.
Updated July 30, 2008