A topic that should get more attention in science outreach is the weirdness of the small. And no – I do not mean the ad nauseam covered ‘quantum weirdness’, which is not* about small stuff anyway. The classical (non-quantum) behavior of the small is counterintuitive enough. Many misconceptions could be avoided with some awareness about how the surfaces of objects, even smooth looking metal surfaces, look like at small scales (think mountainous battle fields).


Perhaps the best way to introduce the surprising world of nanometer** sized objects like molecules, is by talking about water. Whatever you are looking at, you are looking at water! The water molecule is not only small and thus likes to get stuck in the tiny crevices in between, for example, a metal’s crystals. The water molecule is also an electrical dipole, its oxygen being negative, its hydrogen positive. This induces fields near the molecule, thus water molecules stick well to almost any surface.



When you succumb to thirst in the desert, rest assured that you actually rest on water. Every grain of sand is wrapped in water. That hot towel you take out of the dryer? Completely covered in water! This is a real pain in the behind when you want to achieve a clean vacuum in the laboratory:


“Ultra-high vacuum (UHV) is the vacuum regime characterized by pressures lower than about 10-7 Pascal or 100 nanoPascals (10-9 mbar, ~10-9 torr). UHV requires the use of unusual materials in construction and by heating the entire system to 180°C for several hours ("baking") to remove water and other trace gases which adsorb on the surfaces of the chamber.” Wiki: Ultra-high vacuum


Anybody should have heard this, and if just to undermine the misconception about molecules bumping around like billiard balls. They do not. If they hit against a surface, they mostly get stuck in a layer of water. All those pictures where gas molecules bang against a wall and come off like a light ray from a smooth mirror: Wrong not only because of surface roughness, but because particles get stuck as if in a swamp, then sometime later come loose again due to thermal vibrations.



There are high impact journals publishing nonsense about novel effects that supposedly occur at temperatures around 100 to 200 degrees Celsius in nanosized metal layers. The experiment is often some sort of high voltage on some ultra thin metal layer fastened to a heater, all in a crappy vacuum chamber.


Sure, tin melts at 232 °C and below 13.2 °C, tin becomes brittle, non-metallic alpha-tin, but generally speaking, especially with materials like iron in mind, 100 degree Celsius is not hot. Metals’ characteristic temperatures are around a thousand or even thousands of degrees (say Fermi temperature). There is little difference between room temperature and 200 degrees as far as most metals are concerned. However, something else happens at around 150 to 200 degrees: Adsorbed water starts coming off! (You might expect that those researchers thought about that, having them doctor titles and all. Think again. The ‘beauty’ of peer review is that one is reviewed by one’s peers.) In really dirty vacuum chambers, tempering colors occur due to the oxidation of the surface at these sorts of temperatures.

------------------------

* Photons can have wave and coherence lengths of many kilometers. There is nothing “small” about quantum phenomena, but regurgitating such nonsense distinguishes people who write nonsense (like those Florians on the German ScienceBlogs) from those who understand science.

** 1 nm = 0.001 micrometer = 10-9m (No, I'm not gona translate this in fractions of a hair!)