Transformation of femtoliter metal cups to oxide cups: Chemical mapping by scanning Auger spectroscopy

Cup-like structures of In, Sn and Nb on Si substrates with femtoliter capacity obtained by pulsed laser ablation, have been subjected to different oxidation treatments and examined employing spatially resolved scanning Auger spectroscopy and microscopy (SR-AES and SAM). The as-prepared cups, when exposed to ambient are found to have a native oxide layer on the surface that could be easily removed by Ar ion sputtering to result in clean metal cups, suitable for functionalization. In the case of In cups, the thin metal layer at the bottom of the cups could be removed easily by sputtering to form In rings. The cups subjected to external oxidation have a thicker oxide layer in comparison to in-situ dosing of oxygen. In the case of Nb cups, the high temperature treatment employed during oxidation resulted in segregation of Si to the surface of the cup. There is also evidence for the formation of metal-silicon alloy at the center of the cups, especially of Sn and Nb, during the oxidation treatment at elevated temperatures.