Interfacial Electronic Structure and Full Spectral Hamaker Constants of Si3N4 Intergranular Films from VUV and Sr-Veel Spectroscopy

Abstract

AbstractThe interfacial electronic structure, presented as the interband transition strength Jcv(ω) of the interatomic bonds, can be determined by Kramers Kronig (KK) analysis of vacuum ultraviolet (VUV) reflectance or spatially resolved valence electron energy loss (SR-VEEL) spectra. For the wetted interfaces in Si3N4, equilibrium thin glass films are formed whose thickness is determined by a force balance between attractive and repulsive force terms. KK analysis of Jcv(ω) to yield ξ(ξ) for the phases present, permits the direct calculation of the configuration-dependent Hamaker constants for the attractive vdW forces from the interfacial electronic structure.Interband transition strengths and full spectral Hamaker constants for Si3N4 samples containing a SiYA1ON glass have been determined using SR-VEELS from grains and grain boundaries and compared with results from bulk VUV spectroscopy on separate samples of glass and nitride. The At2, Hamaker constant for Si3N4 with glass of the bulk composition is 8 zJ (zJ = 10−21 J) from the more established optical method. The EELS method permits the determination of vdW forces based upon actual local compositions and structure, which may differ noticeably from bulk standards. Current results show that full spectral Hamaker constants determined from VUV and SR-VEEL measurements of uniform bulk samples agree, but care must be taken in the single scattering and zero loss subtraction corrections, and more work is ongoing in this area. Still the results show that for the grain boundary films present in these polycrystalline Si3N4 samples the glass composition is of lower index of refraction. This can arise from increased oxygen content in the intergranular glass and leads to an increased value of the Hamaker constant (24 zJ) determined in situ from the SR-VEELS of a particular grain boundary film.