solid nitrogen

Squeeze nitrogen at 2.4 million atmospheres (240 GPa {GigaPascals}) and you get an opaque solid which is a semiconductor. It remains stable if returned to 1 atmosphere.

"The fact that the major portion of the air has been turned into a semiconducting solid and brought back to be stable at ambient pressure is an important breakthrough for us," said team leader Russell Hemley. Hemley and colleagues Mikhail Eremets, Ho-kwang Mao and Eugene Gregoryanz performed the research at Carnegie's Geophysical Laboratory, a core institution of the NSF's Science and Technology Center for High-Pressure Research.

Source: NSF PR 01-39, 9 May 2001: http://www.nsf.gov/od/lpa/news/press/01/pr0139.htm

It only remains a semiconductor at temperatures below 100 Kelvin: "Novel nitrogen is a semiconductor", PhysicsWeb, 9 May 2001, http://physicsweb.org/article/news/05/5/5.

Some questions:
(1) What is the switching speed of the semiconductor?
(2) What can you dope it with to make transistors?
(3) How stable is it? (Maybe that is why the computers go 'Kablam!' in Star Trek!)

A serious issue in dealing with scientific systems at "ultra-cold" temperatures, solid nitrogen turns out to be a great hindrance when dealing with very cold systems. The majority of high-vacuum and cryogenic laboratory systems are constructed from stainless steel, which, despite having a specific heat far lower than that of water, nonetheless is expensive to cool down by immersion in liquid helium, due to its high cost, as compared with nitrogen. To solve this problem, a lot of such systems are brought down to liquid nitrogen temperatures through being filled/immersed in liquid nitrogen, then further cooled with helium to their final temperature. Because of this, residual nitrogen, which freezes at about 55 Kelvin (at 1 atmospheric pressure) can stick around in these systems, becoming a serious impediment to the smooth operation of low-temperature valves and mechanisms.