title: Molecular composition and orientation of interstitial versus surface silicon oxides for Si(111)/SiO2 and Si(100)/SiO2 interfaces using FT-IR and X-ray photoelectron spectroscopies.
abstract: This work represents a characterization study of silicon oxide on Si(111) and Si(100) surfaces intended for use as substrates in organic light-emitting diodes (OLEDs) on chip devices. Samples have been prepared using either native oxide formation or thermal oxidation, and they have also been treated for activation of hydroxyl groups on their surface. Both Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) have been used in order to understand the molecular orientation as well as the chemical composition of the various oxide types formed during these different oxidation processes. These spectroscopic studies reveal the formation of two different types of oxides on these substrates. The first type is a thin oxide layer on the surface, whereas the second type, called interstitial, is found deeper in the substrate. Specifically, it was found that the Si(100) substrate forms a randomly oriented interstitial oxide, whereas the presence of a lower quantity but more oriented interstitial oxide was found for the Si(111) substrate. In addition, we report for the first time the position of the impurity oxygen for Si(111) substrates at 1122 cm(-1). Finally, in both Si(100) and Si(111) substrates, the thin (<15 A) silicon oxide layers are oriented and appear to contain silicon atoms of similar oxidation states. In contrast, both the thicker surface film (100 A) as well as the interstitial oxide produced by the thermal oxidation procedure show random orientation and relative uniformity. Overall these orientation studies clearly show that the formation process of surface oxides in different substrates clearly creates species that are oriented differently with respect to the surface.
authors.affiliation: Institute of Chemical Engineering and High Temperature Processes, Foundation for Research & Technology-Hellas (ICE/HT-FORTH), Patras, 26500 Greece.
authors.forename: Georgia
authors.initials: G
authors.lastname: Kandilioti
authors.forename: Angeliki
authors.initials: A
authors.lastname: Siokou
authors.forename: Vasiliki
authors.initials: V
authors.lastname: Papaefthimiou
authors.forename: Stella
authors.initials: S
authors.lastname: Kennou
authors.forename: Vasilis G
authors.initials: VG
authors.lastname: Gregoriou
mesh_terms: D016880:Anisotropy; D003460:Crystallization / Q000379:methods*; D003461:Crystallography / Q000379:methods*; D046911:Macromolecular Substances; D008422:Materials Testing; D008968:Molecular Conformation; D015394:Molecular Structure; D010084:Oxidation-Reduction; D012825:Silicon / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties
chemical_list: D046911:Macromolecular Substances; D012822:Silicon Dioxide; D012825:Silicon