Now that I have my summer project figured out and the end is approaching, I have started taking a step back and exploring more about what other people in the lab are doing. Last week, I made a sample to be characterized using atomic force microscopy (AFM). The sample I gave him consisted of a 1:1 ratio between butylammonium iodide (BAI) and methyl ammonium lead triiodide (MAPbI3), which is my sample with the highest BAI concentration. I had been inside the AFM room a couple times with Zach (the undergraduate in our lab who does AFM measurements), but this was my first time really sitting down and learning how the software and machine work. Essentially, there is a cantilever with a probe at one end, and there is a laser shining on the top of the cantilever. The probe, which is 1 atom thick at the end, rasters over and interacts with an area of the sample, and the force interaction can be detected by the laser shining into a diode. One of the most physically difficult parts of using the AFM seems to be attaching the probe to the machine, since the probe is so delicate (and expensive!) so it requires practice and steady hands. Unfortunately, there were some issues with getting a good photocurrent image of my sample, but I did end up with an image of the topography. This week, I'll be making another one of my samples with a lower BAI concentration to AFM, and hopefully I'll be able to see a photocurrent image of my sample as well as the topograhy image.
In regards to my experiments, I have been looking at the difference between making my samples in the glovebox versus the fume hood. There does seem to be a significant difference which can be seen even just by eye. Samples that I have made in the fumehood have a rough surface, and can sometimes end up slightly cracked after annealing. The antisolvent drop technique (for me, dropping toluene at ~5 sec during spin coating) does help with creating a smoother surface, but making samples in the glovebox is the best way to get a shiny clear surface. Another significant difference is the time at which the sample's color changes, which indicates the formation of the perovksite. Typically in the glovebox, my sample's change color ~5 seconds, which roughly coincides with the time at which I drop the toluene. By the end of the spin coat, the final perovskite color is already there. In the fumehood, my sample's take longer to change color, and the sample continues to change color while on the hot plate. These differences could be important as future experiments done at the ALS may not be able to be done in a nitrogen atmosphere. If the differences are significant enough, which I will have to determine through characterization (x-ray diffraction, scanning electron microscopy, etc.), then something might need to be done in order to fix this. But we'll cross that bridge when we get to it!
Recently, I worked on synthesizing some more BAI for future use. Unfortunately, something went wrong during the process because the final product was green instead of white! The BAI is currently connected to the Schlenk line under vacumn, so hopefully whatever is causing the green color will evaporate off. If not, I'll probably have to redo the synthesis process. The cause is still unclear, but one of the chemicals used may have been degraded, which may have lead to this different product this time. Regardless, there wasn't much product left after washing with ethanol so many times, so it might be best to just make more anyways. Hopefully things go smoother this time!
Until next time!