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Surprisingly, scanning electron microscopy (SEM) isn’t as exciting as it might sound. I know, I was shocked too. A lot goes into SEM. First, you have to coat your samples. I’ve been coating mine with gold and palladium (not enough to get rich on though). Then, you have to sit around while the vacuum chamber that your samples will be placed in vents (generally three whole minutes!), put the samples in, and pump it back down (another three minutes!). After that you have to turn on the electron gun (cool) and align everything. Just getting ready takes about twenty frickin minutes!
After all of that, you take pictures of your samples. Here’s one I got yesterday of a silica nanosphere (ok, nanoball) array: Read the rest of this entry »
Yep, that’s the message Gaussian greeted me with today. Looks like my attempt to optimize the DMAC-Ag complex geometry failed. Sort of like this. Anybody out there have any ideas for me? Please?
If you are my faithful reader, then you know that much (all?) of the research that happens here relies on “good” silver colloids. Last week I posted a prep that results in good Ag sols. But what do I mean by good? Well, they have to look good.
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Yesterday we learned how to make silver colloids (well, re-learned for me). I read through the notebooks of several former students, and concocted the following protocol for making 200 mL of Ag colloid via citrate reduction (essentially one of the Lee & Meisel preps):
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We are currently trying to replicate experimental results from a paper by Han, Huang, Zhao and Ozaki (Anal. Chem. 81 3329-3333 (2009)). This seemed like a great place to start trying to understand how to consistently obtain SERS spectra of proteins. Naturally, it isn’t as simple as one might think.
Several weeks ago I thought the laser in our “black box” Raman spectrometer (literally – the DeltaNU 532 is a black box) had stopped working. Yesterday I finally had some time to spend messing around with it and discovered an interesting fact. When you turn the instrument on, the laser actually works. I thought I had left all of this kind of crap behind in grad school. Oh crap, could I be turning into an (shudder) advisor?
This week’s General Chemistry experiment involves the yeast-catalyzed decomposition of hydrogen peroxide:
One of the students asked an excellent question yesterday, “Do we need to collect the waste?” Not only was I happy that the student was aware that proper waste disposal is important, I was also quite happy that it provided a teachable moment. Ultimately we decided that a little yeast and water could go down the drain.
Maybe we should market this as a Green lab.
I don’t know why using significant figures correctly seems to be a problem. The rules are simple, and, as posted at Good Math, Bad Math for those of us who make our livings by measuring things, they are necessary:
The idea of significant figures is that when you’re doing experimental work, you’re taking measurements – and measurements always have a limited precision. The fact that your measurements – the inputs to any calculation or analysis that you do – have limited precision, means that the results of your calculations likewise have limited precision. Significant figures (or significant digits, or just “sigfigs” for short) are a method of tracking measurement precision, in a way that allows you to propagate your precision limits throughout your calculation.
So, just because your calculator or spreadsheet spits 10 digits out at you, it doesn’t mean you get to keep them. Your results can only have as much precision as your measurements.
Now, don’t get me started on units.
This week’s experiments in general chemistry are vapor pressure measurements. Some of us were trying to think up some music to go with the experiments, and we came up with the following pressure, or pressure-related songs:
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