Ultrahigh vacuum deposition of CdSe nanocrystals on surfaces by pulse injection

The fabrication of thin films of colloidal semiconductor nanocrystals is attracting much attention due to their exceptional optoelectronic properties. This requires the development of new methods for depositing nanocrystals under well-controlled conditions. Here, we report the use of the pulse injection method to deposit CdSe nanocrystals under ultrahigh vacuum (UHV) on clean and well-ordered surfaces. The deposition of nanocrystals has been tested by x-ray photoelectron spectroscopy (XPS) and near edge x-ray absorption fine structure spectroscopy. Special attention has been paid to the preparation of very pure solutions of CdSe nanocrystals using cadmium stearate, trioctylphosphine oxide (TOPO) and the TOP/Se adduct for the nanocrystals synthesis followed by dissolution in pentane. It has been found that CdSe nanocrystals adsorb with similar sticking coefficients on graphite, hydrogenated silicon (100) and hydrogenated diamond (100) surfaces. Furthermore, the XPS analysis has revealed that the surface of the CdSe nanocrystal is Cd rich, which has important consequences for the optical and chemical properties. This ability to deposit semiconductor nanocrystals under UHV conditions on clean and well-ordered surfaces opens up new perspectives for studying in a reliable manner all their chemical, electronic and optical properties.