Growing thin films out of nanoparticles in ordered, crystalline sheets, to make anything from microelectronic components to solar cells, would be a boon for materials researchers, but the physics is tricky because particles of that size don't form crystals the way individual atoms do. Using bigger particles as models, physicists have predicted some unusual properties of nanoparticle crystal growth - in particular, that some particles, due to their sizes and the attractive forces between them, grow crystals that melt when they're cooled. Read more