Pang Nganthavee, Week 1&2, Aging Silica Solutions

I began my first day my lab at a group meeting two weeks ago. I still remember that I was extremely nervous, yet excited at the same time. I made sure to arrive a little early at UPenn's Towne building in hopes that I will not get too lost trying to find the room and ultimately arrive late. After a little wondering around the building, trying to find my way to room 336, I finally found where it was and I fortunately got there just five minutes before the presentations began.
During some Mondays, my lab members will all meet to hear two people present about their research. I really enjoyed how the presentations were very interactive and engaging, as other lab members presenting could ask questions or make suggestions to the presenter in order to give constructive criticism. After obtaining this new feedback, they will then proceed to utilize it to improve upon their procedures.

After the meeting, I met with my PI, Dr. Lee, together with my graduate student, Jyo Lyn, to discuss about my project. Like what I was told I would be doing during the emails I had exchanged with Jyo Lyn, I will ultimately be trying to make low filler fraction nanocomposite films by aging the silica solution to induce natural aggregation of the nanoparticles and in turn allow for more porosity and thicker coatings (detailed further in my proposal). However, as various techniques are required in order to allow the success of synthesizing low filler fraction nanocomposite films, Jyo Lyn suggested that I should start my internship by trying to replicate the results of an experiment in one of the primary articles I was sent by her. Before I could start making the nanocomposite films with both the polymer and nanoparticle layer, I would first have to learn how to age silica solutions and also investigate the extent inducing aggregation affects the thickness, porosity and refractive index of the film’s nanoparticle layer.

My first week at the lab was all about trial and error. After I was shown to my desk and given training on the various equipments (i.e. spin coater, vortex mixer, water bath)

Water bath

Spin coater

and techniques (i.e. silicon wafer cutting),

Part of a lab bench is designated for cutting silicon wafers. It is not very clear but the shiny disks in the plastic holders are uncut wafers. 

Jyo Lyn helped me plan the first run of my experiment. For the specific type of nanoparticle solution I used, it was the SM SiO2 at 30 wt %, a commercially available kind of silica. After diluting the concentration to 5 wt % and adding HCl in order to allow the solution to have a pH of 7, I separated my stock solution into vials to be put at 3 different storage places with varying temperatures (fridge - 2°C, my drawer - 23°C/room temperature, water bath - 50°C). Then, for every 3 hour interval, I would use the spin-coater to spin-coat silicon wafers that I would prepare earlier during the three hours I had in between each spin-coating session. I continued to do this for the rest of the week.

Nevertheless, the completion of this overall process was, in fact, filled with a lot more problems than what I had expected. Just to name a few, the following scenarios were some of the difficulties I was faced with during my first week at the lab. Forgetting that water in the water bath would have evaporated overnight if I left it exposed without any coverage, the time for the 50°C silica solutions to be in a heated environment decreased. Due to cutting the silicon wafers too small, the vacuum suction that held the wafer in place during the spin-coating also sucked in the solution that I pipetted onto the silicon wafer and in turn caused a much thinner silica coating than it was supposed to.

After measuring the thickness, refractive index (via values of A, B, and C), roughness and MSE (how well the film fits the ideal model) using the ellipsometer, I gathered the data I wrote in my lab notebook, typed it all into excel and then proceeded to graph it. Unfortunately, due to the various hiccups I had during the first week along with how all the procedures and techniques were extremely new to me, I failed to draw the conclusions that matched up to the results that the primary article I was supposed to replicate reported. However, as this was only the first trial, I would simply have to run it again during the second week, without all the mistakes I made during the first, and try again to replicate the results of one of the primary articles Jyo Lyn sent me.

For every time I noticed some step of a procedure I would accidentally always somehow forget, or encounter a problem that I had to have figured out a solution to during the first week, I would jot it down in my notebook. As a result, when the time came for me to plan a second run of aging the silica solutions, the experience this time was much more smooth-sailing. In order to protect the water from evaporating too much overnight, I covered the bath with some aluminum foil. Meanwhile, to ensure that the vacuum in the spin coater will not suck all of the silica solution away, I made sure to cut my wafers to a much larger size.

As of now, I am still in the process of organizing and analyzing the data that I have collected from the ellipsometer. Therefore, I am still currently unable to fully answer whether or not the second run of my experiment was or was not successful in replicating the results of what the primary article reported. Even so, just from lightly looking at the data tables of ellipsometry results, I could already see a trend that matched what was reported in the primary article - the refractive index decreases whereas the thickness and porosity of the silica layer increases as a function.

Data tables of ellipsometry results from the second run.

Thus, looking ahead, I think what I will be doing for the rest of the weekend and the first few days of next week is to complete the organization and analysis of my data, and proceed to then move on to begin learning how to add a second element to my spin-coating: the polymer - polystyrene. Hopefully it all goes well! Outside the lab, I have also been thoroughly enjoying Philly. As I live together with my dad and Steph, we had gone out to walk along the streets of University City, bought some clothes and ate some really delicious food. For the rest of my time at UPenn, I am really looking forward to explore and travel around to see and take in more of this beautiful place.