Dynamical nuclear polarization by means of shallow donors in ZnO quantum dots

The almost complete dynamic nuclear polarization (DNP) of nuclear spins has been demonstrated can be achieved in ZnO and AgCl single crystals by saturating the EPR transition of the shallow donor (SD) present in this crystals with using high-frequency (275 and 95 GHz) at low temperatures. DNP effects have also been observed in ZnO quantum dots (QD's) where polarization of 67Zn nuclear spins in ZnO core and of 1H nuclear spins in the Zn(OH)2 capping layer have been obtained by saturating the EPR transition of the SD present in the ZnO QD's. DNP manifests itself via a shift of the EPR lines of SD in bulk ZnO and AgCl crystals and the creation of a hole and an antihole in the EPR absorption line of the SD in QD's. The enhancement of the nuclear polarization opens the possibility to study semiconductor nanostructures with NMR techniques.