Molecules: You'd better learn to live with them.
Mica is neat, you might remember it as the really flaky stuff you used during the minerals demo in grade school:
(Public domain wikipedia image)
The coolest thing about mica is that it makes a great substrate for AFM. If you take a sheet of mica and put it between two pieces of scotch tape, and pull them apart carefully, you will cleave the mica. This releases some ancient air that has been ensconced between the sheets for a few billion years (correct me if I'm off by a few orders of magnitude) and gives a perfectly atomically flat surface.
Physical Science
Technology
Comments
That depends on how old the muscovite crystal is, and how long it has been since it has been heated up. Big muscovite crystals are usually found in granite pegmatites - the last bit of magma left before complete crystallization. (Little muscovite crystals are found in most sparkly metamorphic rocks, but they're probably too small to be of much use in AFM.) If you're in an area with really old crust (such as where Chris Rowan is working in South Africa), you could potentially have two-billion-year-old gas trapped. But in most parts of the world, the gas will be much younger - hundreds million years in the Appalachians/Caledonides or the Urals, tens of millions of years in the Alps or the Himalayas.
Posted by: Kim | May 19, 2008 2:19 PM
"Perfectly atomically flat"? That is cool! I used to play with mica every summer since it was fairly common where we vacationed. What's the chemical stucture?
Posted by: Jackal | May 19, 2008 3:10 PM
This may be a stupid question, but... if it is perfectly atomically flat (on both surfaces?), where was the air trapped?
Feel free to use small words; it has been 28 years since I took Inorganic Chem.
Posted by: Anon | May 19, 2008 7:23 PM
That's pretty neat.
Perfectly atomically flat? I would how many applications that has.
I never commented before but I like your blog. Chemistry was one of my favorite courses in college...not that I've graduated yet. Two more years and I'll have a materials engineering degree.
Posted by: Tedi | May 19, 2008 10:46 PM
These nice thin layers with flat surfaces is why Mica has been used for years as an insulator (electrical, but not thermal) between semiconductor packages and heatsinks. Mica washers are still the best available in some applications.
Posted by: MarcB | May 20, 2008 7:05 AM
Large crystal muscovite is not amenable to synthesis. Fluorphlogopite is a a sweetheart!
http://www.hcmat.com/Mica.html
Posted by: Uncle Al | May 20, 2008 11:25 AM
That ain't air, brother.
The K in muscovite (formula unit KAl2AlSi3O10(OH2) ) is loosely bound in between the layers. The minor isotope 40K is radioactive, and decays to either 40Ca or 40Ar. So most of the gas trapped in mica is 40Ar from radioactive decay of potassium.
Of course, most of the Argon in the atmosphere is also from the radioactive decay of 40K. As potassium minerals weather, they release their argon. Heating them also causes Argon loss via diffusion.
Mineral structure here:
http://www.webmineral.com/data/Muscovite.shtml
Posted by: Lab Lemming | May 21, 2008 2:02 AM