Investigation of Measurement Conditions of Metastable De-excitation Spectroscopy of MgO Thin Films Used for Plasma Display Panels

抄録

The measurement conditions of metastable de-excitation spectroscopy (MDS) were investigated in order to apply MDS to the study of the electronic structure of MgO films used for plasma display panels (PDPs). It was demonstrated that positive charging induced on the surface of the MgO film of 50 nm thickness during the MDS measurement can be avoided by employing a low flux of primary metastable He atoms. The positive charges accumulated by successive MDS measurements were found to be completely removed by irradiation of keV electrons, in which the neutralization by the re-distribution of secondary electrons emitted by the keV electron irradiation plays an important role [J. Surf. Anal. 12, 284 (2005)]. The changes in the MDS spectra due to the heating treatment of the MgO film, which is one of the processes employed in the fabrication of PDPs, was investigated, and the ionization potential given as a sum of the band gap and the electron affinity was found to decrease with the increase in the heating temperature. Heating the MgO film at 500 °C in vacuum is effective to clean the surface but not sufficient to completely remove contaminations on the surface, and repeating sputtering and heating at 500 °C is required to clean the MgO film surface. The electronic structure of the clean surface of the MgO film of 50 nm thickness was found to be the same as that of 500 nm thickness, the thickness of which is a typical value for the MgO film used in PDPs. This result revealed that 50 nm thick MgO films, in which effects of charging is much less than those for 500 nm thick films, can be used to evaluate the electronic structure of the MgO film surface. The present results confirmed that MDS is one of the effective techniques to evaluate properties of MgO films used for PDPs.