It’s Hate Week, and it’s probably time to update everyone on the progress that my beloved and sainted father has made in the laboratory since last we spoke. Let’s dive right in.
In June of 1644, an Italian physicist/mathematician named Evangelista Torricelli wrote a letter to Michelangelo Ricci in Rome about advances Torricelli made in creating a barometer. The letter specifically contained new methods of creating a barometer that involved the creation of a vacuum along with the first working explanation of atmospheric pressure; with that letter (a translation of which can be found here), vacuum science was born. To honor this, the unit of a “Torr” was born and is used even today.
One Torr is defined as exactly 101,325/760 Pascals (see, e.g., the National Institute of Standards and Technology Special Publication 811, Section 5); the “760” part of that number comes from the original (and arbitrary) definition of a “standard” atmosphere, and a Pascal (also named after a famous physicist) is a pressure of one Newton (yep, another famous physicist) per square meter.
All of this is great, but most people think of pressure either in atmospheres (like when people think about SCUBA diving), in inches of mercury (when, e.g., you are watching the local weather, the pressure is generally given in “inHg”), or in pounds per square inch (e.g., when you inflate your car’s tires). To convert, we see that:
- 1 Torr = 1/760 atm (or, perhaps more simply, 1 atmosphere = 760 Torr)
- 1 Torr = 1/25.4 inHg (or, again, 1 inch of mercury is 25.4 Torr)
- 1 Torr = about 1/51.71 psi (or 51.71 Torr is roughly 1 pound per square inch)
Just in case you need reminding, at sea level, you walk around in ~1 atmosphere all the time (~14.7 psi); when you fly in a standard passenger aircraft, the pressure inside the cabin when cruising between 36,00 and 40,000 feet maximizes at 0.76 atmospheres (roughly 11.2 psi).
Why is all of this relevant? You see, one of the things that is important for my beloved and sainted father is getting rid of all that pressure – and creating a vacuum. One of the main goals of his laboratory is the creation of thin films of materials. The materials (and the things on which the materials sit, called substrates) must be clean, and so as my beloved father carefully assembles the films together (sometimes one atomic layer at a time), he cannot have anything else in the way. No air, no water, no alcohol vapors – nothing. Hence, my beloved and sainted father must create a system that holds a vacuum, and we measure the quality of the vacuum by the amount of “stuff” left in the system, which is primarily measured by pressure.
How does one go about this? Well, it depends upon your requirements. Mommy’s vacuum cleaner does a great job of cleaning my sister’s mess off of the floor (I don’t shed — that’s all her fluff, thank you very much), but even the really good vacuum cleaners pull only ~3 psi; if you have a closed system with no leaks, that would take you down from 760 Torr to ~150 Torr. That’s not a very good vacuum.
The massive contraption my beloved and sainted father has managed to create has five (5) different pumps. In order, he has:
- The roughing pump (just upgraded to an Edwards XDS10). This is a dry scroll pump that takes the whole system from 760 Torr (1 atmosphere) down to the sub-milliTorr level (a milliTorr is 0.001 Torr for those who never learned metric prefixes). This pump runs all the time, because it also acts as a back for pump #2. In this range of pressures, the flow is laminar. This is because the distance between molecular collisions is very short (i.e., a gas molecule is likely to hit another gas molecule before it does anything else (like the walls of the chamber).
- The turbomolecular pump (Leybold TurboVac SL 80 DN 63 CF). The turbo pump plows through that range, and takes the whole system down to a few x 10–8 Torr (something like, say, 0.05 microTorr; remember that “micro” means “one millionth” or “one part in one million” – silly metric prefixes). This pressure is achieved within 30 to 45 minutes of closing the main door. At these pressures, the flow is molecular, meaning that a gas molecule is much more likely to run into the chamber walls than to run into another similar gas molecule.
- At this point, my beloved and sainted father would close the valve between the main growth chamber (whence all the goodness happens) and the load lock chamber (think “airlock”) so he can make the pressure in the growth chamber (which is where all the magic happens) continue to drop. With the valve closed, Daddy engages the cryo pump (Oxford Instruments Cryo-Plex 8). This pump uses pressurized liquid helium (at a temperature of 15 Kelvins) to bring the pressure down even more. Remember when Uncle Greg told you to lick that flagpole when it was freezing outside (seriously, that might be the nicest thing he told you to do…)? That’s what happens to most of the molecules that are left — they stick to the unbelievably cold interior of the cryo pump, never to return to my beloved father’s growth chamber.
- Once the cryo pump has been going for a few minutes, Daddy then engages the ion pump (Gamma Vacuum 150T-DI-6P-SC-220-TSPA). The combination of the cryo and ion pumps together bring the system down to a few tenths of a nanoTorr (“nano” meaning “one billionth” or “one part in one billion”). This is the range we call “minus 10” since it is expressed as something like “8.9 x 10–10” Torr, but we aren’t done yet!
- The last pump that is engaged is the titanium sublimation pump that is attached to the ion pump. Titanium is a “getter” material, meaning that it likes bonding to things that the cryo pump and the ion pump don’t like to take out of the system (hydrogen is a good example). The pump doesn’t “pump,” but instead heats up a small filament that lays down a very thin layer of titanium (inside the pump — not inside the system). This fresh titanium acts like a magnet to these last materials and captures them for good. This drops the overall pressure to roughly 0.07 nanoTorr (the “minus 11” range).
At this point, you’d think we’d be done, but we’re not. During operation, to keep the system as clean as possible, my beloved and sainted father uses one last trick — he flows liquid nitrogen into an interior cryo panel. This works just like the cryo pump does, but is the one last way to make sure the deposition process is clean. Once the panel is as cold as we can make it, we can find the “base pressure” of the growth chamber (i.e., the answer to “How low can you go?” but not “How funky is your chicken?”):
This is a photograph of one of my beloved and sainted father’s graduate students kneeling in front of the electronics rack for this system. The blurry (but readable) numbers show 6.4 x 10–11 Torr (that’s 0.064 nanoTorr); this falls nicely into the region scientifically called “ultra-high vacuum” or “UHV.” The “smoke” above the system is really water vapor resulting from Daddy filling the cryo panel. [For reference, daytime pressures on the Moon are roughly 10–7 Torr (see Taylor & Burton 1976, M&PS, 11(3), 225; a pressure that is four orders of magnitude higher than our system); nighttime pressures on the Moon drop down to 2 x 10–12 Torr (only about a factor of 32 less than our chamber).]
It’s not just the pumps that get our pressure this low. It’s a complex combination of:
- The chamber construction. The entire chamber is made up of stainless steel (type 304) that has been thoroughly electropolished. It’s electropolished to make sure that there are as few nooks and crannies as possible. We can’t have random water molecules clinging on for dear life! All of the ports that can be opened (save two) use copper gaskets to close them. By sandwiching a soft copper gasket between two harder stainless steel parts, the copper “flows” into the remaining gaps, creating a really tight seal. The two ports that do not have copper gasket seals are the load lock door (used to move things in and out of the system and not on the growth chamber) and the main door to the growth chamber. Both doors use rubber (Viton) rings as gaskets. The main door to the growth chamber (which should almost never be opened) has a double O-ring seal, and the space between the two rings is differentially pumped using the roughing pump.
- Cleanliness. In vacuum science, cleanliness best be your watchword. Nobody touches this system without a clean lab coat and clean gloves. Even a single fingerprint (probably from some graduate student’s grubby hands) will leave trace oils that are effectively impossible to completely clean off. The remnants of those oils constantly shed particles (in a process we call “outgassing” — again, something similar to a process that Uncle Greg does well) constantly, and would drive the interior pressure up.
- “Bakeout.” After the system has been open to air (even if it is just for a second), water molecules sneak in (yes, even in west Texas — amazing, right?). Those water molecules stick (adsorb) onto every metal surface in the interior of the chamber, and will outgas (similar to the forbidden finger oil). To combat this, we button up the sides of the chamber (see the gray strips of fiberglass blanket with metal twist buckles behind my beloved father’s student?) and force hot air to circulate around the outside of the chamber. Once the chamber reaches 150 degrees Centigrade (well above the boiling point of water), we let the system “bake” for several days. This ensures that everything with a boiling point below 150 degrees C will be forced off of the chamber walls and will (hopefully) find its way down into one of the pumps to be captured. If we did not have any rubber gaskets (i.e., every port used copper gaskets), we could increase the bake temperature to 450 degrees Centigrade and get an even cleaner vacuum. However, some newer information indicates that if you bake at temperatures that high, you might damage the knife edges (the parts of the stainless steel that squish the copper gaskets), thereby ruining them. Further, heating to 450 Centigrade will reduce the hydrogen gas levels in the system, and our sublimation pump takes care of that for us without risking damage to any other part of the system.
- “Look, Mom! No grease!” Since regular bolts can seize when heated (making life very uncomfortable), and since we avoid hydrocarbons (like grease) like Yersinia pestis, all of the assembly hardware (bolts, nuts, and washers) is silver plated.
The next “level” of vacuum (called “extreme high vacuum” or “XHV”) starts at a pressure of 7.5 x 10–13 Torr — about a factor of 100 less than what my beloved father has achieved. XHV is difficult to produce and even more difficult to measure; it is done only in a few laboratories that use very specialized (read: expensive) equipment where the users need to the simulate interstellar space (there are a few other highly specialized applications). Could our system reach XHV pressures? Perhaps, but I’m not sure it’s necessary for the science that we want to do, and it might not be worth the trouble. We should be proud of our base pressure (after we begin depositions next week, we might never see it again!).
At this point, however, my beloved and sainted father got to show his students a condition that shows 13 orders of magnitude difference — they are standing in 1 atmosphere (760 Torr), and they can touch (WITH GLOVES) a chamber with a pressure lower than 0.00000000000012 times less dense.
At this point, you might ask “What does this have to do with Hate Week?” Well, first of all this isn’t the Orwellian version of Hate Week (in his novel Nineteen Eighty-Four); this is serious. See, for example:
What? You don’t like to see little kids cry? Here is some footage from the OU pep rally this week:
There’s really nothing positive about Oklahoma, and even less about OU. From one excellent website, we quote:
First things first – your entire school is built from the ground up on the concept of stealing things. You took the Yale fight song, ravaged it through the least creative rewrite in music history, then made your band beat it into the ground ad nauseam, just like you did to the native population of your state. Yeah I went there. A few scholarships and a statue or two doesn’t erase that kind of history. Especially when your mascot is named for people who illegally stole land (Sooners) and killed Native Americans (Boomers) to get it. That’s only a few degrees of national ignorance away from Washington Redskins territory.
Speaking of territory – Texas Football might be a bit of a dumpster fire at the moment, but your state has been fulfilling the role of national receptacle since it’s inception. People voluntary came to Texas on wagons emblazoned with “GTT.” Some even laid down their lives to preserve the mere idea of Texas (you know the place – we named a bowl game after it). People were FORCED to move to Oklahoma.
The Oklahoma state flag is all kinds of awful. Graphic designers have been killed over less. Protip – if you have to put the state name on your flag you are doing it wrong. I could put the Texas flag here for comparison, but I don’t need to. You know exactly what it looks like. We put it on everything. It is awesome.
(“I dunno JimBob. Just put some stolen Indian stuff on there and a cookie. I like cookies”)
The flag is awful, but surely you guys came up with a better tagline? Nope. For years your official state license plate said “Oklahoma is OK.” Nevermind – I take it back. Most accurate description ever.
Do you know what happens when you make people play that stupid song over and over and over? This:
How about these examples of ultra-classy OU fans:
How about plain old academics? The latest (2015) university rankings from U.S. News and World Report rank the University of Texas at #53, Texas A&M at #68, and OU at #106 (cf. my beloved and sainted father’s alma mater sitting nicely at #16). Mein Gott, mann! OU is tied with the so-called “University” of Tennessee (a true diploma mill).
It’s a common mistake to think that vacuum pumps suck gas from inside the chamber. If the gas molecules in one part of a volume are removed, then the remaining molecules collide and bounce off of the chamber walls until they fill the same volume at a lower pressure. In other words, until a molecule, propelled by random collisions, enters a pump’s pumping mechanism, it cannot be removed from the chamber. The pump does not reach out, grab a molecule, and suck it in (even roughing pumps rely on molecules sticking to each other in laminar flow to work). That means that vacuum doesn’t suck.
At the same time, we know that the only good thing about Oklahoma is that it keeps Texas from falling into the Gulf of Mexico, and no matter what, fuzzier minds everywhere are secure in the knowledge that OU sucks.