Nucleation and Growth of Gold on MgO Thin Films:  A Combined STM and Luminescence Study

Electroluminescence measurements have been performed with a scanning tunneling microscope (STM) to study the growth of Au particles on thin MgO films prepared on Mo(001). With increasing Au coverage, rapid quenching of the characteristic, defect-related MgO emission is observed, while a new peak emerges in the optical spectra that is attributed to Mie plasmon resonances of the Au particles. The fast decline of the MgO signal with metal exposure indicates that Au nucleation preferentially takes place at the optically active centers in the MgO surface. The nucleation sites have been identified in STM measurements as being located along the step edges of the MgO surface. A sputter-deposition of Au results in a significantly slower decline of the MgO optical signal, manifesting the delayed blocking of optically active MgO centers due to Au nucleation on artificial surface defects.