| This thesis presents investigations of the surface electronic structures of GaAs(100), porous Si, poly(p-phenylene vinylene) (PPV) and poly(2,3-diphenyl-phenylene vinylene) (DP-PPV) during oxidation or interface formation with metals. Surface characterization was accomplished by X-ray and synchrotron photoelectron spectroscopies (XPS and SPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and visible and infrared photoluminescence (PL) spectroscopy. Chapter IV presents the SPS investigation of methods to passivate GaAs(100) while minimizing surface disruptions. H{dollar}{bsol}sb2{dollar}O is found to photo-oxidize Ga at 90 K without significant changes to As. H{dollar}{bsol}sb2{dollar}O can also be used as a buffer layer to prevent the disruption of GaAs during Cr deposition by reacting with the metal, leading to the formation of a metal-insulator-semiconductor. In Chapter V, surface passivation and its effects on visible PL are investigated in porous Si using XPS and PL spectroscopy. XPS indicates that surface oxidation of a partially oxidized sample increases during aging that induces the loss of PL, yet complete surface oxidation results in stable visible PL. PL spectroscopy reveals the loss of visible PL and the enhancement of IR PL at 350{dollar}{bsol}sp{bsol}circ{dollar}C, implying that surface states participate in visible light emission. In Chapter VI, the interface formation between Ca, Al and Au and PPV and DP-PPV is investigated by XPS and NEXAFS in order to understand the interface electronic structure and its influence on charge injection during electroluminescence. Freshly prepared samples exhibit Schottky barrier formation at the metal/PPV interface during Ca and Al deposition, while sample aging by oxidation prevents band bending at the Al/PPV interface. NEXAFS points to the formation of new intra-gap states following Ca and Au deposition on DP-PPV, while Al does not affect the conduction band significantly. The evolution of the electronic structure of conjugated polymers during metal deposition suggests a band bending modified tunneling model of charge injection at metal/polymer interfaces. This model appears to reconcile the I-V behavior of PPV based light emitting diodes with the results of surface studies of the metal/polymer interface formation. |
