Nanostructures or submicrostructures from gas/solid reactions as probed by atomic force microscopy

Abstract

Uniform nanostructures are formed by chemical reaction of gases with the surface regions of crystals. Their size and shape are determined and depicted by atomic force microscopy (AFM). Both depend on the crystal face and this proves that the bulk crystal structure is governing the long-range molecular transports in the range of up to 200 nm. Craters and volcanoes (eggs’ pallets), volcanoes, or valleys and heights are formed without intervening liquid phases upon reaction of a-cinnamic acid 1 and trans-stilbene 3 with gaseous bromine or (benzyl-) thiohydantoin 5 with gaseous methylamine. If chlorine is reacted briefly with a-cinnamic acid a nanoliquid is formed on the surface and this leads to nanostructuring with the AFM tip at low force via transport of liquid and recrystallization effects. Thus holes with flat bottoms are generated which increase steadily upon continuous AFM scanning. In the case of stilbene and bromine, the initial nanostructures undergo a thermal phase transformation which produces uniform flattened plugs of 250 nm height. The chemical generation of nanostructures is very efficient.