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.
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Updated July 30, 2008