TOPO capping of InP nanocrystals by hydrogen NMR and to distinguish TOPO molecules free in solution from TOPO molecules

Colloidal semiconductor nanocrystals in the range 1-10 nm are promising building blocks for future nanodevices since they show strong quantum confinement effects even at room temperature [1,2]. Colloidal semiconductor nanocrystals consist of an inorganic core, having the same crystal structure as the corresponding bulk semiconductor, surrounded by a shell of capping molecules. These cappping molecules have several functions. During synthesis, they limit the growth rate of the nanocrystals. This makes it possible to separate nucleation from growth, yielding monodisperse colloidal solutions. In addition, the capping prevents aggregation of the nanocrystal by steric stabilisation. After synthesis, the capping molecules determines the physical and chemical properties of the nanocrystals [2]. For instance, the capping may passivate surface states yielding nanocrystals with a high luminescence quantum yield or the capping molecules may contain functional groups that make it possible to bind nanocrystals to a substrate [3]. Capping engineering, i.e. capping a nanocrystal with molecules that give the nanocrystal a desired property, will be of importance for future work on colloidal semiconductor nanocrystals. This makes direct observation of capping molecules an important challenge.